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The biotic ligand model: A historical overview
Abstract
During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has gained widespread interest amongst the scientific, regulated and regulatory communities because of its potential for use in developing water quality criteria (WQC) and in performing aquatic risk assessments for metals. Specifically, the BLM does this in a way that considers the important influences of site-specific water quality. This journal issue includes papers that describe recent advances with regard to the development of the BLM approach. Here, the current status of the BLM development effort is described in the context of the longer-term history of advances in the understanding of metal interactions in the environment upon which the BLM is based. Early developments in the aquatic chemistry of metals, the physiology of aquatic organisms and aquatic toxicology are reviewed first, and the degree to which each of these disciplines influenced the development of water quality regulations is discussed. The early scientific advances that took place in each of these fields were not well coordinated, making it difficult for regulatory authorities to take full advantage of the potential utility of what had been learned. However, this has now changed, with the BLM serving as a useful interface amongst these scientific disciplines, and within the regulatory arena as well. The more recent events that have led to the present situation are reviewed, and consideration is given to some of the future needs and developments related to the BLM that are envisioned. The research results that are described in the papers found in this journal issue represent a distinct milestone in the ongoing evolution of the BLM approach and, more generally, of approaches to performing ecological assessments for metals in aquatic systems. These papers also establish a benchmark to which future scientific and regulatory developments can be compared. Finally, they demonstrate the importance and usefulness of the concept of bioavailability and of evaluative tools such as the BLM.
... Several mathematical modelling tools have been developed focusing on ecosystem protection in the ecotoxicology field [5][6][7]. One of these, in particular, has been widely investigated as a risk assessment predictor, termed the Biotic Ligand Model (BLM) [8][9][10][11][12][13]. The BLM is a mathematical model developed to measure, assess, and understand how the chemical properties of a waterbody can affect metallic contaminant speciation, bioavailability, and consequent toxicity, comprising an important tool in understanding and predicting metal toxicity in different waterbodies [8,10]. ...
... One of these, in particular, has been widely investigated as a risk assessment predictor, termed the Biotic Ligand Model (BLM) [8][9][10][11][12][13]. The BLM is a mathematical model developed to measure, assess, and understand how the chemical properties of a waterbody can affect metallic contaminant speciation, bioavailability, and consequent toxicity, comprising an important tool in understanding and predicting metal toxicity in different waterbodies [8,10]. ...
... The BLM is based on three processes, as follows: (i) the interaction between water and dissolved chemical species, forming organic and inorganic compounds (2) competition between the bioavailable portion of dissolved chemical species with major cations and anions binding to gill surfaces (the main metal action site, commonly referred to as the biotic ligand), and (iii) metal uptake into the organism, resulting in mimetic processes, inhibiting enzymes responsible for sodium export, namely Na + /K + -ATPase and Ca +2 -ATPase, leading to toxic effects in case the exposed organism is not able to compensate for the ionic disturbance [10,14]. ...
Brazil boasts of large hydrographic basins, numerous lentic environments, and an extensive coastal region. These aquatic environments are susceptible to the presence of metals originated from both natural and anthropic activities, so methods to assess the ecological risk to these environments, such as the Biotic Ligand Model (BLM), are of immense value. This study comprises a systematic review of selected articles published from 2008 to 2020 to answer the following question: Why is BLM so scarcely applied in Brazil? Data was compiled to identify the origin, tests, methods, journal impact factor, and year of publication of all included papers retrieved from the Scopus database. The BLM was shown as efficient in predicting metal toxicity in both seawater and freshwater considering both organisms and environmental factors (speciation in water). Copper, cadmium, nickel, zinc, lead, and silver were the most reported throughout the years, with copper ranking first, reported in 133 publications. Other metals were also reported, but in a lower number of published papers. Daphnia magna was the most evaluated test organism. Several BLM papers were published in relatively high impact factor journals (4,93 on average), reinforcing the importance of the subject. Brazil ranked 7th in BLM publishing, participating with 4% of the published articles from the retrieved total, with most studies published by research groups in the South region. Some recommendations are raised in this review, such as the need for more interactions between research groups in Brazil, deeper connectivity between legislation and BLM studies and further BLM applications in the country, as each waterbody displays its own specific particularities.
... It has been long established that the form or "speciation" of many trace elements (e.g. copper, nickel, zinc, lead, aluminium, cadmium) controls their toxicity (Paquin et al., 2002). Specifically, it is the most chemically reactive forms of metals that are likely to be of the greatest concern from an ecotoxicological point of view. ...
... Combining the metal speciation with a better understanding of the fate of metals in the natural environment (Dwane and Tipping, 1998;Van Veen et al., 2002) coupled with ecotoxicology data, resulted in the production of biotic ligand models (BLM) for many metals (e.g. Paquin et al., 2002;De Schamphelaere and Janssen, 2004;Santore et al., 2006). These initial models have evolved into simplified versions (wca, 2015), including BioMET (Peters et al., 2019), MBAT (Rüdel et al., 2015) and PNEC-pro (Verschoor et al., 2017). ...
... For copper there were 63 and 71 sites over the calcium application range for upstream and downstream respectively (BioMet, 2019). Given higher concentrations of calcium are likely to only reduce the bioavailability of the metal (Paquin et al., 2002), and that the simplified BLM tools are conservative in free metal ion estimation (BioMet, 2019), then it is justified to retain these samples in the compliance assessment. ...
The impact of wastewater treatment works (WwTW) effluent on downstream river water quality is of increasing concern, particularly owing to the presence in effluents of a range of trace substances. In the case of contamination by metals the question of bioavailability has recently been accounted for in setting water quality standards for several metals. In the UK over the past decade the Chemical Investigations Programme (CIP) has generated upstream and downstream river quality data as well as associated WwTW effluent monitoring for over 600 sites, for the main contaminants of regulatory interest under the Water Framework Directive. Data presented here show that at a local level WwTW discharges have little impact for many contaminants. Soluble reactive phosphorus, hexabromocyclododecane (HBCDD), cypermethrin, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) have been shown to be the principal substances where downstream concentrations were at least 10 % larger than the upstream value. Otherwise, poor compliance with riverine water quality standards tends to be associated with contamination at the river catchment scale, with corresponding implications for the nature of remedial actions that are likely to be successful. Compliance with water quality criteria for metals, taking account of bioavailability, is high overall.
... Scientists around the world have developed a series of models for the prediction of Cu bioavailability, such as the biotic ligand model (BLM), generalized bioavailability model (gBAM) ( DiToro et al., 2001 ;De Schamphelaere et al., 2003 ). The BLM, which is fundamentally a chemical equilibrium-based model, has gained widespread interest amongst in some developed countries and regions DiToro et al., 2001 ;Paquin et al., 2002 ). However, at present the precise mechanisms of Cu to aquatic organisms remains elusive in a complex water body. ...
... Homeostatic systems may become dysfunctional when intracellular Cu levels rise to the point at which protein functions become impaired following exposure to elevated Cu levels in the water. Acute toxicity of Cu to aquatic organisms mainly involves respiratory depression and interference with ion regulation ( Paquin et al., 2002 ;Grosell, 2012 ). Some places that have been exposed to Cu pollutants will reach a concentration level of acute toxicity of aquatic organisms, resulting in the death of aquatic organisms ( Fu et al., 2016 ;Johnson et al., 2017 ). ...
... Regardless of the target organ, Cu toxicity is not merely a function of the environmental Cu concentration. Factors such as complexation with organic and inorganic negatively charged molecules, and competition between Cu and cations for uptake exert a strong influence on toxicity, which are important means by which water quality parameters affect the biological toxicity of Cu Paquin et al., 2002 ;Taylor et al., 2000 ). ...
Copper (Cu) exists in a variety of forms in different aquatic environments, and affects their bioavailability. In this study we provide a systematic review on toxicity of Cu which focuses on identifying evidence in the mechanisms of Cu toxicity, and apply an adverse outcome pathway (AOP) analysis to identify multiple potential mechanisms and their interactions of Cu toxicity to fish. This analysis process included the mechanisms of behavior toxicant, oxidative toxicant, ion regulation disruption toxicity, as well as endocrine disruption toxicity. It was found that at low levels of Cu exposure, swimming, avoid predators, locating prey and other sensory functions will be impaired, and the organism will suffer from metabolic alkalosis and respiratory acidosis following the inhibition of the carbonic anhydrase active. The main pathway of acute toxicity of Cu to fish is the inhibition of the Na⁺/K⁺-ATPase enzyme, and lead to reduced intracellular sodium absorption, as well as Cu-induced increased cell permeability, in turn resulting in increased sodium ion loss, leading to cardiovascular collapse and respiratory insufficiency. The endocrine disruption toxicity of Cu to fish caused growth inhibition and reproductive reduction. In addition, there are several key pathways of Cu toxicity that are affected by hardness (e.g., Ca²⁺) and intracellular DOC concentrations, including inhibition Cu-induced, improved branchial gas exchange, alteration in membrane transport functions, decreased Na⁺ loss, and increased Na⁺ uptake. The results of the AOP analysis will provide a robust framework for future directed research on the mechanisms of Cu toxicity.
... It has been long established that the form or "speciation" of many trace elements (e.g. copper, nickel, zinc, lead, aluminium, cadmium) controls their toxicity (Paquin et al., 2002). Specifically, it is the most chemically reactive forms of metals that are likely to be of the greatest concern from an ecotoxicological point of view. ...
... Combining the metal speciation with a better understanding of the fate of metals in the natural environment (Dwane and Tipping, 1998;Van Veen et al., 2002) coupled with ecotoxicology data, resulted in the production of biotic ligand models (BLM) for many metals (e.g. Paquin et al., 2002;De Schamphelaere and Janssen, 2004;Santore et al., 2006). These initial models have evolved into simplified versions (wca, 2015), including BioMET (Peters et al., 2019), MBAT (Rüdel et al., 2015) and PNEC-pro (Verschoor et al., 2017). ...
... For copper there were 63 and 71 sites over the calcium application range for upstream and downstream respectively (BioMet, 2019). Given higher concentrations of calcium are likely to only reduce the bioavailability of the metal (Paquin et al., 2002), and that the simplified BLM tools are conservative in free metal ion estimation (BioMet, 2019), then it is justified to retain these samples in the compliance assessment. ...
... There is extensive peer-reviewed literature demonstrating that metal toxicity in waters is poorly correlated with total metal concentrations (e.g. Erickson et al., 1996;Paquin et al., 2002;Peijnenburg et al., 2002;Vink, 2002;Erickson, 2013) and it has been recognized that only a portion of the total amount of metal in the environment can actually be taken up by organisms and subsequently induce adverse effects. The main idea behind this "bio-availability concept" is that the toxic effect of a metal does not only depend on the total (dissolved) concentration of that metal in the surrounding environment but also on the complex interactions between physicochemical and biological factors. ...
... BLMs are metal and organism specific, requiring the incorporation of empirically determined metal-binding constants and intrinsic metal sensitivity of different biological species. These concepts (SCHER, 2010; Rüdel et al., 2015) and the practical application (Paquin et al., 2002;Vijver et al., 2008;EU, 2019) are well reviewed and documented. To calculate water-type specific effect concentrations, a stepby-step approach is used to combine experimental laboratory-based effect concentrations (from bioassays) with water type specific characteristics. ...
Since the soil quality Tool for Risk Identification, Assessment and Display (TRIAD) approach introduced the "three lines of evidence" accounting for chemical, toxicological and ecological stressors to explain adverse effects in biota, the assessment of contaminant risks in the environment has significantly evolved. The concept of chemical speciation, related to water characteristics, boosted the understanding of the role of free-ion activities in the overall accumulation of pollutants in biota. New modeling concepts (e.g. biotic ligand models) and measuring techniques were developed. This in turn triggered widespread research addressing the quantitative role of sediment in the overall water quality, focusing on redox interfaces. For contaminant mixtures in river catchments, complex relations between (bio)availability of compounds, including nutrients, help to explain aquatic toxicity. Variation in ecological patterns and processes across environmental or spatiotemporal gradients occur, which may identify ecological factors that influence contaminant fate and effects. Empirical evidence by meta-analysis and theoretical underpinning by modelling showed relationships between population growth rates and carrying capacities, across chemicals and across species. The potentially affected fraction (PAF) of species may be related to the mean species abundance, an often-used indicator in global change studies. Knowledge gaps remain on how pollutants travel through ecological communities and which species and species-relationships are affected. Outdoor experimental systems that examine the natural environment under controlled conditions may be useful at the higher biological level to investigate the impact of stressors on a variety of species, including mutual interactions.
... The biotic ligand model (BLM) describes the influence of site-specific water quality on metal ion bioavailability and toxicity Niyogi and Wood, 2004a;Paquin et al., 2002). In brief, the BLM assumes that the bioavailable form is the equilibrium concentration of free metal ion in the bulk exposure medium. ...
... The free metal ion is assumed to bind to gill surface transporters (biotic ligands). Biotic ligands are envisaged to be ionoregulatory proteins Paquin et al., 2002) with a fixed concentration and a single (conditional) affinity constant for the target metal ion (Playle et al., 1993). In reality, metal ion binding sites will have a distributed affinity, the average value of which will depend on the metal-to-binding site ratio, and their concentration may be up/down regulated in response to changing external and/or internal conditions. ...
An endless list of new chemicals are entering nature, which makes it an impossible task to assess all possible mixture combinations at all possible concentrations and conditions that are leading to the ubiquitous anthropogenic impacts on the aquatic environment resulting from deteriorating water quality. Therefore, ecotoxicology is moving more toward a mechanistic understanding of toxicological processes, using trait-based approaches and sublethal molecular and physiological endpoints to understand the mode of action of pollutants and the adverse outcomes at the organismal and population level. These molecular and physiological endpoints can be used as biomarkers, applicable in the field. This brings ecotoxicological research much closer to conservation physiology. Understanding the relationships between chemical reactivity in the water and in organisms, and assessing the consequences at higher levels, allows conservation physiologists and managers to take the right restoration measures for an optimal improvement of the aquatic habitats of concern. In this chapter we discuss the role which the promising approach of mechanistic-based Adverse Outcome Pathways (AOPs) can play in ecotoxicological research. It studies a pathway of events, from the direct interaction of a chemical with a molecular target, through subsequent intermediate events at cellular, tissue, organ and individual organism levels which then result in an Adverse Outcome (AO) relevant to ecotoxicological risk assessment and regulatory decision-making. In this context, we also discuss the importance of modeling, including bioavailability based and effect based models. Finally, we reflect on the possibilities that meta-analysis has to offer to detect unifying physiological processes, as well as interesting outliers.
... The toxicity of other divalent metals (e.g., Ag, Al, Cd, Co, Cu, Ni, and Zn) is decreased by calcium and magnesium (Paquin et al., 2002). ...
... A more sophisticated example of an ecotoxicological model is the biotic ligand model (BLM) (Paquin et al., 2002;Niyogi and Wood, 2004). BLM combines an aqueous metal speciation model with a model of competitive binding of nutrient and toxic cations to ligands on the respiratory surfaces of fish and aquatic invertebrates. ...
Causal thinking is an everyday activity. We all are confronted with questions of causation, whether to figure out why the car is making a funny noise or why a toddler is running a fever. Our fascination with investigating causes is reflected in the enduring popularity of detective stories and in the frequency of investigative reports in the news.
Because causal inference is commonplace, a book on ecological causal assessment may seem unnecessary. However, causes are not always easy to determine. Ecosystems are complex; the factors we can influence interact with natural factors, random processes, and initial conditions to produce the effects that are observed. Taking corrective action to remedy an environmental problem before knowing its cause could target the wrong thing, depleting scarce resources and missing an opportunity to improve environmental quality.
Formal processes for causal assessment, as described in this book, are particularly helpful when the situation is complex or contentious. A wellarticulated process guides the analysis of available data and optimizes further collection efforts. A transparent process helps others replicate results and is more likely to convince skeptics that the true cause has been identified. A consistent process helps meet legal and regulatory standards for reasonableness and ensures that scientific information contributes to these decisions. Perhaps most importantly, formal methods help to eliminate biases that arise because of the all-too-human tendency to make and defend causal judgments too readily. As aptly articulated by the physicist Richard Feynman, “The first rule of science is not to fool yourself—and you are the easiest person to fool.”
We began this project with a practical purpose—to share useful methods and strategies for identifying causes of undesirable biological effects in specific places. Causal assessment is a challenging, often humbling, but endlessly fascinating endeavor. It begins with the intrigue of a good mystery— why did this effect happen? Success requires the persistence to figure things out and solid strategies for using the information that you have and getting more of the right kind of information that you need. We feel fortunate to have been involved with adapting existing methods and testing new approaches. It has led us to renewed study of our intellectual heritage of science and philosophy, the strengths and foibles of human cognition, and the underlying assumptions of different sampling designs and analytical methods. It has also allowed us to provide scientific assessments and advice on some of the more complex ecological problems of our times.
We have drawn on our personal experiences and those of our colleagues to provide examples and to describe approaches for assessing causes of undesirable biological effects in ecological systems. Some of these effects have captured the public’s attention and concern: collapsing fisheries and bee colonies; bleaching coral reefs; endangered species; dwindling stream life; and kills of fish, birds, and bats. Behind these reports are scientists who monitor our ecological systems and carefully document when something is amiss. In the past 20 years, biological monitoring has become an essential part of the environmental management tool kit. Causal assessment is the next essential tool. When we wonder why a condition has worsened, causal assessment finds the explanation.
We believe that this book provides sound advice for the near term. We hope that it will lead the way to future improvements in methods and applicable scientific knowledge. We also hope that our study of causal assessment in the context of environmental management advances the larger field of causal assessment and provides insights into how we all can improve our causal reasoning.
... The toxicity of other divalent metals (e.g., Ag, Al, Cd, Co, Cu, Ni, and Zn) is decreased by calcium and magnesium (Paquin et al., 2002). ...
... A more sophisticated example of an ecotoxicological model is the biotic ligand model (BLM) (Paquin et al., 2002;Niyogi and Wood, 2004). BLM combines an aqueous metal speciation model with a model of competitive binding of nutrient and toxic cations to ligands on the respiratory surfaces of fish and aquatic invertebrates. ...
... The toxicity of other divalent metals (e.g., Ag, Al, Cd, Co, Cu, Ni, and Zn) is decreased by calcium and magnesium (Paquin et al., 2002). ...
... A more sophisticated example of an ecotoxicological model is the biotic ligand model (BLM) (Paquin et al., 2002;Niyogi and Wood, 2004). BLM combines an aqueous metal speciation model with a model of competitive binding of nutrient and toxic cations to ligands on the respiratory surfaces of fish and aquatic invertebrates. ...
... The Biotic Ligand Model (BLM) was then developed on the basis of the fish gill surface interaction model, allowing for the application of that principle to other organisms. The BLM is based on the assumption that the onset of metal toxicity originates from the binding of free metal ions or other reactive species to physiologically active sites or transport sites at biotic ligands on the organism-water interface (De Schamphelaere & Janssen, 2002;Di Toro et al., 2001;Paquin et al., 2002). This assumption is supported by a correlation between metal accumulation at the fish gill and metal toxicity reported by MacRae et al. (1999). ...
... Na þ , Ca 2þ , Mg 2þ , and K þ ) (Playle, 1998;Playle et al., 1993aPlayle et al., , 1993b, are assumed to determine metal toxicity. This chemical equilibrium-based model links metal accumulation at sites of action of toxicity at biotic ligands to toxicological responses Paquin et al., 2002). The biotic ligands are specific proteins regulating the uptake of essential elements (Niyogi & Wood, 2003. ...
... The Biotic Ligand Model (BLM) was then developed on the basis of the fish gill surface interaction model, allowing for the application of that principle to other organisms. The BLM is based on the assumption that the onset of metal toxicity originates from the binding of free metal ions or other reactive species to physiologically active sites or transport sites at biotic ligands on the organism-water interface (De Schamphelaere & Janssen, 2002;Di Toro et al., 2001;Paquin et al., 2002). This assumption is supported by a correlation between metal accumulation at the fish gill and metal toxicity reported by MacRae et al. (1999). ...
... Na þ , Ca 2þ , Mg 2þ , and K þ ) (Playle, 1998;Playle et al., 1993aPlayle et al., , 1993b, are assumed to determine metal toxicity. This chemical equilibrium-based model links metal accumulation at sites of action of toxicity at biotic ligands to toxicological responses Paquin et al., 2002). The biotic ligands are specific proteins regulating the uptake of essential elements (Niyogi & Wood, 2003. ...
A general concept in risk assessment is that a threshold of exposure exists above which adverse effects are initiated. Toxicity is related to the target-site concentration or the biologically active dose. Although it is often a huge challenge to measure the specific dose metric of metal toxicity, significant progress has been obtained to approach closer to the target-site concentration. Such developments are reviewed in the present study. In addition, a general framework to simulate the subcellular metal partitioning, which is supposed to account for the internal metal sequestration, is developed and applied to various metals. The framework allows for delineating mechanisms of internal metal sequestration. Moreover, the specificity in these mechanisms, which varies among metals, species, and exposure conditions, might explain the complicated relationship between the internal concentration and metal toxicity. Attention should be paid to the data requirements as the high number of unknown parameters might be accompanied by potential uncertainties. In addition, future efforts should focus on linking the concentration of metals in sensitive fractions and toxicological effects.
... Al(III)-fluoride (Wilkinson et al., 1990). In any case, equilibrium-based approaches do not take into account the rate at which free metal ions are released from their complexed forms in the exposure medium (Paquin et al., 2002). Such assumptions are only valid if certain kinetic criteria are met, i.e. the unsupported diffusive flux of the free metal ion from the bulk solution to the biointerface is much greater than the biouptake flux and there is no bulk depletion. ...
... The BLM literature generally does not mention, let alone verify, compliance with these criteria. For predictions of toxicity, BLMs correlate the amount of metal ions bound to the so-called "biotic ligands" with toxicological endpoints (Paquin et al., 2002). Various empirical correction factors are used as fitting parameters in BLMs to account for the effects of pH, hardness, and dissolved organic carbon (DOC) on toxicological endpoints (Peters et al., 2018;Santore et al., 2021), and typically their applicability is limited to the range of conditions over which they have been developed (Nys et al., 2016). ...
A robust description of the bioavailability of Ni(II) in freshwaters is fundamental for the setting of environmental quality standards. Current approaches assume that bioavailability is governed by the equilibrium concentration of the free metal ion in the bulk aqueous medium. Such strategies generally have limited predictive value: a suite of empirical fitting parameters is required to deal with variations in water chemistry. Herein we compile data on Ni(II) speciation under typical freshwater conditions and compute the lability of Ni(II) complexes with typical molecular and nanoparticulate components of dissolved organic carbon. In combination with an analysis of the kinetic setting of Ni(II) biouptake by freshwater organisms, we assess the potential contribution from dissociation of Ni(II) complexes to the diffusive supply flux of free Ni²⁺. The strategy takes into account the absolute and relative magnitudes of the Michaelis-Menten bioaffinity and bioconversion parameters for a range of freshwater organisms, together with dynamic chemical speciation descriptors under environmentally relevant conditions. The results show that the dissociation kinetics of Ni(II) complexes play a crucial role in buffering the free metal ion concentration at the biointerface. Our results highlight the need to couple the timescales of chemical reactivity with those of biouptake to properly identify the bioavailable fraction of Ni(II) in freshwaters.
... A few methods have developed to measure bioavailable metal ions. A well-known biological method is a biotic ligand model [6,7]. It treats the bonding between the metal ions and the biological receptor as a metal-ligand system. ...
A novel copper(II) ion indicator based on polymer conformational change is designed and its chemo-response to the target analyte is tested in this paper. The word ‘telechelic’ in the title means that a polymer has two different fluorophores on either end. If one of them is a fluorescent donor and the other is a fluorescent acceptor, then the extent of Foerster resonance energy transfer (FRET) will depend on polymer conformation. The sensitivity of these sensors is tunable based on the chain length and the amount of the receptor on the polymer. This is revealed by the fluorescence response of 30mer, 50mer, and 100mer of poly(N-isopropyl)acrylamide with different amounts of metal chelation monomers. We also address the change in fluorescence over time due to the untangling of poly(N-isopropylacrylamide) in water. The fluorescent signal can maintain stability after metal binding. The photoluminescence results agree with the length calculation of polyelectrolytes. A fluorescent standard curve is created for the measurement of different concentrations of copper ions. The sensing limit can reach 10−10 M analytes, which is suitable for the measurement of chemicals in trace amounts in the environment.
... Toxicity of Cu to aquatic organisms is dependent on various accessory, physicochemical characteristics of surface water, especially chemical speciation related to water quality parameters, such as pH, hardness and dissolved organic carbon (DOC) [11][12][13][14][15]. Hardness-dependent corrections of toxic potency of Cu was the earliest and most widely used criterion in water quality criteria studies regarding metals [14]. ...
Background
Risks of adverse ecological effects of copper (Cu) consider of water quality parameters were not fully understood in China. Here, a national-scale exposure of Cu in Chinese surface water was investigated, and the first report using multiple linear regression approach to predict and correct toxicity data based on water chemistries in China. Risk of Cu was overestimated without considering water quality parameters in the previous studies.
Results
Under prevalent water quality conditions of hardness = 150.0 mg/L, pH = 7.8, and dissolved organic carbon (DOC) = 3.0 mg/L, across China, the predicted no effect concentration for total, dissolved Cu was 9.71 μg/L. Based on results of the preliminary risk quotients method, 1.19% (a total of 43 in 3610 sites) were classified as “high risk”, only one sixth of the percentage of sites with “high risk” than the proportion predicted when not considering water quality parameters, which was 7.51%. Similar results were obtained by application of both the margin of safety method (0.71% compared to 2.81%) and joint probability curve method (3.34% compared to 16.29%), both of which overestimated risks posed by Cu to aquatic organisms in China.
Conclusion
After correcting for bioavailability based on water quality parameters, consider both concentrations and frequencies during ecological risk assessment, regions of China at greatest risk from adverse effects of Cu were the Hai River ( Haihe ), Huai Rivers ( Huaihe ) and Chao Lake. These findings provide a comprehensive method for a more accurate assessment of risks of adverse effects of Cu to aquatic life in surface waters.
... Inhibition of Na + uptake upon exposure to acidic pH (Maetz, 1973;Shaw, 1960) led to the realization of the potential damaging effects of acid release from coal mining and of acid rain on IOAB regulation (see Ultsch et al., 1981). A few years later, another link between anthropogenic pollution and aquatic IOAB regulation would be established, as scientists discovered the effects of metals on gill apical transporters involved in Na + and Ca 2+ uptake, paracellular NaCl efflux and NKA activity (reviewed in Paquin et al., 2002). ...
The regulation of ionic, osmotic and acid-base (IOAB) conditions in biological fluids is among the most fundamental functions in all organisms; being surrounded by water uniquely shapes the IOAB regulatory strategies of water-breathing animals. Throughout its centennial history, Journal of Experimental Biology has established itself as a premier venue for publication of comparative, environmental and evolutionary studies on IOAB regulation. This Review provides a synopsis of IOAB regulation in aquatic animals, some of the most significant research milestones in the field, and evolving views about the underlying cellular mechanisms and their evolutionary implications. It also identifies promising areas for future research and proposes ideas for enhancing the impact of aquatic IOAB research.
... Although all the projects we reviewed had measured some aspect of water or environmental conditions, not all measured the metrics necessary for developing an adaptive treatment regime (see Table 4). For example, toxicities of copper-based products are affected by competing ion concentrations in the water, as well as by environmental characteristics like dissolved organic carbon and water temperature 26,42,[58][59][60][61] . If these water chemistry variables are measured, they can be used in bioavailability models (e.g., the Biotic Ligand Model, Visual MINTEQ, and others) to predict the appropriate concentration of copper needed to achieve a desired toxicity response [e.g., a concentration that kills 50% of a species (LC50)]. ...
Dreissenid mussels are one of the most problematic aquatic invasive species (AIS) in North America, causing substantial ecological and economic effects. To date, dreissenid mussel control efforts in open water have included physical, biological, and chemical methods. The feasibility of successful dreissenid mussel management or eradication in lakes is relatively undocumented in the freshwater management literature. This review presents information on 33 open water dreissenid mussel control projects in 23 North America lakes. We reviewed data from past dreissenid mussel control projects and identified patterns and knowledge gaps to help inform adaptive management strategies. The three key lessons learned include (1) pre- and post-treatment survey methods that are designed to meet management objectives are beneficial, e.g., by sampling for all life stages and taking into account that no survey method is completely comprehensive; (2) defining the treatment area—particularly ensuring it is sufficiently large to capture all life stages present—is critical to meeting management objectives; and (3) control projects provide an opportunity to collect water chemistry, effects on non-target organisms, and other efficacy-related data that can inform safe and effective adaptive management.
... For living organisms, trace elements are particularly important, especially zinc. They have been studied in various research concerning fish feeding and toxicity since they are abundant in the environment and engaged in crucial physiological processes in organisms (Paquin et al. 2002;Niyogi and Wood 2004;Erickson et al. 2008;Celik et al., 2013;Soaudy et al. 2021). As an essential element for fish, zinc can be found in a variety of forms, including elemental, inorganic, and organic forms. ...
Fish use zinc for various vital physiological processes throughout their life cycle. It is necessary for the typical development, growth, and upkeep of fish. Many metalloenzymes and their involvement as a cofactor in several enzyme systems are the foundations of the major functions of zinc. Fish can absorb zinc from both the water environment and dietary sources. As zinc is involved in many processes of cellular metabolism, adding zinc to the diet increases the growth rate of fish. Nano-zinc oxide (nano-ZnO) has been shown to promote fish growth more than other traditional inorganic zinc forms. Although exposure to nano-ZnO resulted in histological abnormalities in several different tissues and organs, changes in the small intestinal tissues may have facilitated the transit of feed to the site of absorption, increased the capacity to absorb various nutrients, and provided protection from pathogens. In general, fish hematological and blood biochemical profiles improved with dietary zinc incorporation. When fed in small amounts, zinc can also function as an antioxidant. Although dietary nano-ZnO are thought to be nontoxic and healthy for fish, there is more bioaccumulation of zinc nanoparticles than zinc bulk particles in several tissues. There is a need for more research on the use of dietary zinc as a supplement in the diets of various aquatic species since there are a few variables that could affect the levels of dietary zinc and make it more difficult to estimate its required levels. The actual bioavailability of ZnO nanoparticles to animals also needs to be determined. In this review, we have tried to evaluate and draw conclusions about the advantages of zinc in various forms and its potential application as a mineral supplement to various aquatic animals species.
... From the 159 articles, 31 were reviews focusing on several approaches to model metal effects on aquatic organisms (Jørgensen, 1979;Reinfelder et al., 1998;Wang and Fisher, 1999;Brown and Markich, 2000;Bell et al., 2002;Bianchini and Bowles, 2002;Paquin et al., 2002a;Wang, 2002;Janssen et al., 2003;Wood, 2003, 2004;Playle, 2004;Luoma and Rainbow, 2005;Slaveykova and Wilkinson, 2005;Rainbow, 2007;Chapman et al., 1998;Chapman, 2008;Wang andRainbow, 2006, 2008;Zhou et al., 2008;Ardestani et al., 2014;Smith et al., 2015;Rüdel et al., 2015;DeForest et al., 2018;Philipps et al., 2018;Wang and Tan, 2019;Sánchez-Marín, 2020;Santore et al., 2021;Pontoni et al., 2022;Peters et al., 2023). The remaining 128 articles concerned either mechanistic or statistical models, or both. ...
Industrial deep-sea mining will release plumes containing metals that may disperse over long distances; however, there is no general understanding of metal effects on marine ecosystems. Thus, we conducted a systematic review in search of models of metal effects on aquatic biota with the future perspective to support Environmental Risk Assessment (ERA) of deep-sea mining. According to results, the use of models to study metal effects is strongly biased towards freshwater species (83% freshwater versus 14% marine); Cu, Hg, Al, Ni, Pb, Cd and Zn are the best-studied metals, and most studies target few species rather than entire food webs. We argue that these limitations restrain ERA on marine ecosystems. To overcome this gap of knowledge, we suggest future research directions and propose a modelling framework to predict the effects of metals on marine food webs, which in our view is relevant for ERA of deep-sea mining.
... ex., Cubatão -SP), mas influenciaram os resultados basais de genotoxicidade nessas espécies de caranguejo. Assim, uma maior genotoxicidade foi registrada nas espécies de manguezal que interagem com mais compartimentos, em especial com o sedimento, que nos manguezais apresenta elevado teor de matéria orgânica e, por isso, mais metais associados (Paquin et al., 2002). Os dados obtidos confirmam o elevado potencial destas espécies endêmicas como sentinelas de manguezal, conforme sugerido por Pinheiro et al. (2017). ...
O crescimento demográfico humano tem promovido extrema elevação dos impactos antrópicos, acarretando declínio da biodiversidade mundial em vários ecossistemas, tornando imprescindível a aplicação de monitoramentos eficazes e ações efetivas de conservação. Atualmente, existe uma tendência de que os monitoramentos sejam de menor custo operacional e financeiro, bem como que possam ser desenvolvidos por longa duração. Os biomarcadores de efeito (p. ex., ensaios cometa, micronúcleo e vermelho neutro), têm sido empregados com sucesso em espécies emblemáticas, que têm se mostrado um ótimo reflexo da qualidade de um ambiente. Tais espécies, nomeadas “sentinelas ambientais”, evidenciam impactos antrópicos danosos ainda nos momentos iniciais, antecipando ações de gestão que evitem danos persistentes (às vezes irreversíveis) nas espécies, populações e comunidades locais, que somente seriam constatados futuramente. Espécies sentinelas precisam ser resistentes o suficiente, residentes do ambiente em avaliação, possuir reduzida vagilidade e mostrar interação com o maior número de componentes ambientais, sejam eles abióticos ou bióticos. Os trabalhos desenvolvidos com espécies de invertebrados (p. ex., bivalves e crustáceos) e vertebrados (p. ex., peixes e mamíferos) têm mostrado a excelência e eficácia dos biomarcadores, com avaliações no nível celular e molecular. O presente estudo visa apresentar os procedimentos que devem ser adotados durante a avaliação da qualidade ambiental pelo uso de biomarcadores de efeito (genotoxicidade e citotoxicidade), desde a escolha das espécies sentinelas, os cuidados na condução dos protocolos e a eficácia dos métodos em casos reais.
... ex., Cubatão -SP), mas influenciaram os resultados basais de genotoxicidade nessas espécies de caranguejo. Assim, uma maior genotoxicidade foi registrada nas espécies de manguezal que interagem com mais compartimentos, em especial com o sedimento, que nos manguezais apresenta elevado teor de matéria orgânica e, por isso, mais metais associados (Paquin et al., 2002). Os dados obtidos confirmam o elevado potencial destas espécies endêmicas como sentinelas de manguezal, conforme sugerido por Pinheiro et al. (2017). ...
O crescimento demográfico humano tem promovido extrema elevação dos impac-tos antrópicos, acarretando declínio da biodiversidade mundial em vários ecossistemas, tornando imprescindível a aplicação de monitoramentos eficazes e ações efetivas de conservação. Atualmente, existe uma tendência de que os monitoramentos sejam de menor custo operacional e financeiro, bem como que possam ser desenvolvidos por longa duração. Os biomarcadores de efeito (p. ex., ensaios cometa, micronúcleo e vermelho neutro), têm sido empregados com sucesso em espécies emblemáticas, que têm se mostrado um ótimo reflexo da qualidade de um ambiente. Tais espécies, nomeadas "sentinelas ambientais", evidenciam impactos antrópicos danosos ainda nos momentos iniciais, antecipando ações de gestão que evitem danos persistentes (às vezes irreversíveis) nas espécies, populações e comunidades locais, que somente seriam constatados futuramente. Espécies sentinelas precisam ser resis-tentes o suficiente, residentes do ambiente em avaliação, possuir reduzida vagilidade e mos-trar interação com o maior número de componentes ambientais, sejam eles abióticos ou bió-ticos. Os trabalhos desenvolvidos com espécies de invertebrados (p. ex., bivalves e crustá-ceos) e vertebrados (p. ex., peixes e mamíferos) têm mostrado a excelência e eficácia dos biomarcadores, com avaliações no nível celular e molecular. O presente estudo visa apresentar os procedimentos que devem ser adotados durante a avaliação da qualidade ambiental pelo uso de biomarcadores de efeito (genotoxicidade e citotoxicidade), desde a escolha das espécies sentinelas, os cuidados na condução dos protocolos e a eficácia dos métodos em casos reais.
... Due to this process, the organism's exposure routes may also vary. The sediment biotic ligand model approach (sBLM) is used to predict the bioavailability of metals in overlying water in such cases [10]. ...
Bioaccumulation can be used as a measurement tool for analyses of sediment and soil toxicity. Heavy metal toxicity in sediments can be measured with bioaccumulation tests. Metal bioaccumulation has recently achieved more concentration from researchers due to its feasibility to conduct both field and laboratory experiments with indicative organisms. Bioaccumulation can be measured directly or using models. For this study, the concentrations of trace metals (Zn, Pb and Cu) in earthworm tissues were analyzed and compared with the total contents of heavy metals in contaminated parts of soils of Pallikaranai marshland. Samples were taken from different parts of the marshland, which have been reported to have heavy metal presence decades ago. Mostly predominant species found in the marshland L. mauritii and P. excavatus were used for the experiment. Soil samples were collected at six points along a gradient of increasing pollution. A regression model was applied to the results, and the order of accumulation of heavy metals BAF in the present study is Zn > Cu > Pb, indicating that zinc is a potentially high accumulating metal compared to Cu and Pb.
... Nevertheless, delineating an AOP can be less than straightforward for the CMs under variable conditions such as ambient water quality, yet they may be postulated. Predicting potential health outcomes for humans and fish could be advanced with a better understanding of factors that influence speciation and bioavailability and incorporating some constructs of the biotic ligand model (BLM) to better understand metal interactions in site-specific environments-such as predictions of the degree of metal binding at the site of action-being in turn related to a toxicological response [160]. The BLM has contributed to the understanding of physiological mechanisms for acute toxicities, assisting in setting water quality standards [55]. ...
Emerging and low-carbon technologies and innovations are driving a need for domestic sources, sustainable use, and availability of critical minerals (CMs)—those vital to the national and economic security of the United States. Understanding the known and potential health effects of exposures to such mineral commodities can inform prudent and environmentally responsible handling and harvesting. We review the occurrence, use, predominant exposure pathways, and adverse outcome pathways (AOP) for human and fish receptors of those CMs that are nutritionally essential trace metals (specifically, cobalt, chromium, manganese, nickel, and zinc), as well as the rare earth elements. Biological responses to some elements having comparable biogeochemistry can sometimes be similar. Candidate quantifiable biomarkers for assessing potential AOP are conveyed.
... Grab water samples were filtered through a hydrophilic PTFE filter (0.45-μm pore size), and measurements were carried out on the filtrates for dissolved trace metals and major ions (Na + , K + , Ca 2+ , Mg 2+ , Cl -, and SO 4 2-). The filtrates were also analyzed for dissolved organic carbon (DOC), which can affect metal bioavailability and toxicity (Paquin et al., 2002;Adams et al., 2020). All the water samples were refrigerated in the field. ...
Ecological impacts of chemicals such as metal mixtures in the field are predicted by one of two approaches: component-based and whole-mixture approaches. Knowledge about how to relate results of these approaches to field effect levels is limited. We aimed to examine the ability of two methods to discriminate field effect levels: (1) a component-based approach that calculates a cumulative criterion unit (CCU) equal to the sum of the ratios of four trace-metal concentrations (Cd, Cu, Zn, and Pb) to the corresponding US EPA hardness-adjusted water quality criterion, and (2) a whole-mixture approach that employs three ambient toxicity levels based on acute and chronic toxicity tests with cladocerans. To assess field effect levels, we used data from benthic macroinvertebrate surveys conducted at 26 sites, including 13 metal-contaminated sites, in four river basins across Japan. Based on decreases in mayfly richness and abundances of two metal-sensitive mayfly families, we defined four field effect levels 0–3: (0) no significant effect; (1) a significant decrease in ephemerellid and/or heptageniid mayfly abundance; (2) a significant decrease in mayfly richness; and (3) no mayflies or a few baetid mayfly species present. Sites with CCU values of ∼5–10 were assigned to either field effect level 1 or 2, while a site with a CCU value of 27 was assigned to field effect level 3. Sites with significant chronic toxicity to cladocerans (ambient toxicity level 1) were assigned to field effect level 1 or 2, whereas those with significant acute and chronic toxicity (ambient toxicity level 2) were assigned to field effect level 2 or 3. CCU values and ambient toxicity levels were both significantly correlated with field effect levels. These results provide encouraging evidence that field effect levels such as losses of species richness can be approximately discriminated by CCU values and ambient toxicity levels.
... Consideration of all the involved timescales is therefore fundamental for a proper interpretation of the dynamics of ongoing interfacial processes. For example, in the domain of metal bioavailability to organisms, the widely used biotic ligand model (BLM) and free ion activity model (FIAM) assume a priori that the equilibrium concentration of free M in the bulk solution is the only relevant parameter irrespective of timescales of all possibly contributing processes [2]. However, such assumptions correspond to a limiting scenario of the overall dynamic speciation/biouptake framework. ...
The electric charge at a reactive interface influences the diffusion rate of ionic species towards the interface as well as their local concentration profiles. For metal ions (M) and their complexes (ML) formed with ligands (L), the interfacial electric field at a metal-consuming interface will lead to coupling between reaction layer and electric Debye layer, interfacial polarization of species concentrations and, thereby, so-far unexplored changes in ML contribution (lability) to sustain or not metal accumulation fluxes. A formalism and computational approach -based on coupled steady-state Nernst-Planck equations corrected for interfacial electrostatics and chemical kinetics- are here elaborated to obtain relevant metal surface flux and spatial distributions of M, L and ML. ML lability is subsequently derived and evaluated for practical settings of ML chemodynamics and macrosurface electrostatics under metal sink boundary condition. The extent to which the interfacial electric field affects lability of metal complexes depends on the charges of the reactive species and macrosurface. For example, repulsive M/ML-macrosurface interactions lead to significant loss of lability. Mass transfer features of ligands, even when present in large excess in bulk solution, are also found to impact on lability, even for moderately charged reactive surfaces. Predictions are in qualitative agreement with the available experimental data.
... • Hazard characterisation such as Persistence, Bioaccumulation and Toxicity (PBT) for organic chemicals, along with longrange transport potential (LRTP) (Stockholm Convention 2019) • Ecotoxicological paradigms such as the free ion activity model (FIAM) (Campbell 1995) and biotic ligand model (BLM) (Paquin et al. 2002) for understanding metal bioavailability in aquatic systems • Toxicological groupings such as Carcinogenic, Mutagenic, Reproductive (CMR) toxins (eurostat 2020) and endocrine active/disruptive chemicals (EACs/EDCs/EDs) (e.g. EC 2022). ...
Environmental context In previous instances of global impacts from chemicals, there were significant gaps between the onset of use and observations that triggered management. The lessons of the past have informed the development of strong paradigms for chemical management, but at some point, major impacts will again emerge, not covered by these paradigms. Holistic observation of the environment and collaborative reporting are needed to identify signals of future major issues. Abstract Increasing concern over per- and polyfluoroalkyl substances (PFAS) in the environment, in the last decade, has sparked an interest in emerging chemicals more broadly, leading to the development or strengthening of many useful programs for understanding and prioritising environmental hazards and risks for chemicals. While important and useful, such efforts mostly rely on comparing chemical properties with paradigms generated from previous environmental issues. The lessons of the past demonstrate that, at some point, major challenges to our existing paradigms will eventuate. Key to addressing these challenges is our ability for early identification of ‘blind spots’ not covered by our existing paradigms. Furthermore, if we only look for gross observable changes in the environment, we will only ever be able to respond with reactive measures. We suggest that while various relevant monitoring programs are in place and have been proposed, encouraging those processes to look beyond existing hazard paradigms and look for more subtle environmental signals will improve the ability to respond proactively when harm is still limited.
... Through passive diffusion over the gills or ingested and absorbed via endocytosis, metal ions enter chloride cells in the gills through calcium channels (Olsson et al., 1998) and interact with different cytoplasmatic components such as MTs (Perera et al., 2015). In fish, naturally occurring waterborne cations and trace metals interact with gill surfaces and other exchange structures resulting in competitive/non-competitive inhibition of the uptake and accumulation processes, hence, modifying metal toxicity (Paquin et al., 2002). In female fathead minnow Cu exposure had no effect on the expression of ERß and VTG; while ERα expression was slightly decreased (Driessnack et al., 2017). ...
The increasing efflux on a large scale of organic contaminants holding endocrine disrupting activity from sewage treatment plants produces detrimental biological effects to various fish species. However, the impact of small-scale sewage treatment plant-efflux in small river streams and narrow creeks is largely unknown. Extensive pesticide output especially in vineyards and orchards also causes adverse effects on the endocrine system of wildlife fish species inhabiting nearby rivers. To elaborate whether fish species and populations in the areas of interest were at risk of experiencing endocrine disruption, we identified different biomarkers related to endocrine disruption in Cottus gobio and Salmo trutta fario and applied this approach to selected Austrian freshwater streams pre and post sewage treatment plants and permanent cultures with extensive pesticide output in South Tyrol. Overall, mRNA expression levels of vitellogenin, estrogen receptor α and zona pellucida genes in wildlife fish, compared to a control population reared under constant conditions in the laboratory were significantly increased. Sewage-treatment plant efflux did not significantly affect the mRNA expression levels while extensive use of pesticides altered mRNA expression significantly in C. gobio . C. gobio and S. trutta fario display different levels of mRNA expression. Cadmium and copper concentrations in liver tissues varied but did not indicate significant levels of contamination. Our results demonstrate the presence of endocrine disrupting chemicals in the tested freshwater streams. We anticipate our study to be a starting point for further studies focusing on the effects of endocrine disrupting chemicals on individuals and populations. Especially the fact that the two selected species reveal highly different levels of mRNA expression levels is of interest when applying biomarker approaches which can be a useful tool for monitoring projects and risk-assessment associated studies.
... The influence of pH, hardness and alkalinity, on metal toxicity may have been studied (see reviews by Sheppard et al. 2005 for U studies, and Gensemer & Playle 1999 for Al studies), but of the few studies that have addressed the influence of DOC on metal toxicity, the majority of them are temperate studies. The development of the Biotic Ligand Model (Paquin et al., 2002) for metals such as copper, indicates the importance of knowledge of how these variables affect metal toxicity. However, additional research involving the influence of DOC, in particular, on the toxicity of other metals, is required in order to enable appropriate revision of current water quality guidelines. ...
The influence of DOC on the toxicity of U and Al to three Australian tropical freshwater species (for U: the northern trout gudgeon, Mogurnda mogurnda, the green alga, Chlorella sp. and the green hydra, Hydra viridissima and Al: the cladoceran Moinodaphnia macleayi, Chlorella sp. and Hydra viridissima) was investigated. Two DOC sources were assessed: (i) Suwannee River fulvic acid standard (SRFA) and (ii) local DOC sourced from Sandy Billabong water, Northern Territory, Australia. The influence of SRFA on U toxicity was studied at 0, 1, 5, 10 and 20 mg/L DOC in synthetic Magela Creek water (SMCW). Uranium toxicity to M. mogurnda (96-h survival) was approximately four times lower in SMCW containing 20 mg/L DOC than SMCW devoid of DOC (the concentration that results in 50% survival relative to the control response (LC 50), increased from 1550 to 7200 µg/L). Chlorella sp. (72-h population growth rate) was the most sensitive of the organisms to U, with toxicity being reduced 16 fold in the presence of 20 mg/L DOC compared with 0 mg/L DOC (an increase in IC 50 from 40 to 650 µg/L). For H. viridissima (96-h population growth), U toxicity was reduced seven fold with the addition of 20 mg/L DOC (the IC 50 increased from 65 to 470 µg/L). For E. gracilis an additional 20 mg/L DOC in the form of SRFA, reduced U toxicity by three to five-fold (an increase in IC 50 from 57 to 254 µg/L. Uranium toxicity in Sandy Billabong water (SBW) assessed at 0, 1, 5 and 10 mg/L DOC showed U toxicity was halved for M. mogurnda and H. viridissima at 10 mg/L DOC compared to DOC-free water (M. mogurnda IC 50 increased from 1730 to 3100 µg/L and the IC 50 for H. viridissima increased from 50 to 113 µg/L). For Chlorella sp. in SBW containing 10 mg/L DOC there was a 12-fold reduction in U toxicity IV compared to toxicity in DOC-free test waters (the IC 50 increased from 13 to 150 µg/L). Mechanistic studies exposing the unicellular eukaryote Euglena gracilis to U at background DOC in the presence of a reactive oxygen stress (ROS) probe, indicated
... The toxicity of metals (e.g., Zn, Cu, Ni) in aquatic environments is dependent on water quality characteristics (e.g., hardness, pH, dissolved organic carbon (DOC), etc.). Recently, a Biotic Ligand Model (BLM) was developed to evaluate the toxic effects of metals to aquatic organisms Santore et al., 2001;Paquin et al., 2002;. As such, environmental quality guidelines that incorporate site-specific water quality characteristics using various BLMs are currently being used in the United States and Europe. ...
The present study investigated copper (Cu) toxicity and the influence of water quality characteristics of Dongnai River and Mekong River (Vietnam) surface waters to three tropical species; Daphnia lumholtzi, Ceriodaphnia cornuta, and Danio rerio. The river waters had a range of water quality parameters that modify Cu bioavailability and toxicity. The range of total hardness, alkalinity, pH and dissolved organic carbon were 15e64 mg/L as CaCO3, 18e58 mg/L as CaCO3, 6.62e7.88, and 6.9e14.7 mg/l, respectively. The
US EPA acute toxicity test method with a modification to the light photoperiod and temperature for tropical organisms was used to investigate Cu toxicity. Result of the present study found that Cu produced toxic effect to the studied organisms at low concentrations. The 48-h LC50 ranged from 3.92 to 8.61 mg/l, 2.92e9.56 mg/l, and 15.71e68.69 mg/l dissolved Cu for D. lumholtzi, C. cornuta, and D. rerio, respectively. In general, water quality had an influence on Cu bioavailability and toxicity to the studied
organisms. The toxicity of Cu was higher in water with lower hardness, DOC, and/or pH. The present study indicates a contribution of Cu hydroxide and carbonate to Cu bioavailability to Mekong organisms. Results of the present study will be used for calibrating the US Cu Biotic Ligand Model (BLM) to Mekong River water and organisms in support of application of the BLM for setting site-specific Cu water quality guidelines in the ecosystem of the Lower Mekong River Basin.
... Dissolved organic matter (DOM) decreases metal bioavailability and thus toxicity to aquatic organisms, by complexing free metal ions in natural waters (Campbell, 1995;Playle et al., 1993;Tipping, 2002). Thus, DOM concentration is a critical input parameter in bioavailability-based models used to assess the environmental risk of metals under local water chemistry conditions (e.g. the Biotic Ligand Model, BLM) (Di Toro et al., 2001;Niyogi and Wood, 2004;Paquin et al., 2002). Notably, a copper (Cu) BLM is currently used to generate site-specific water quality guidelines in various jurisdictions (e.g. ...
We investigated how natural dissolved organic matter (DOM) of the Rio Negro (Amazon) affects acute copper (Cu) toxicity to local fish: the cardinal tetra (Paracheirodon axelrodi) and the dwarf cichlid (Apistogramma agassizii). It is established that Cu2+ complexation with DOM decreases Cu bioavailability (and thus toxicity) to aquatic organisms, as conceptualized by the Biotic Ligand Model (BLM). However, we also know that Rio Negro's DOM can interact with fish gills and have a beneficial effect on Na + homeostasis, the main target of acute Cu toxicity in freshwater animals. We aimed to tease apart these potential protective effects of DOM against Cu-induced Na + imbalances in fish. In the laboratory, we acclimated fish to Rio Negro water (10 mg L-1 DOC) and to a low-DOM water (1.4 mg L-1 DOC) with similar ion composition and pH (5.9). We measured 3-h Cu uptake in gills and unidirectional and net Na + physiological fluxes across a range of Cu concentrations in both waters. Various DOM pre-acclimation times (0, 1 and 5 days) were evaluated in experiments with P. axelrodi. Copper exposure led to similar levels of net Na + loss in the two fish, but with distinct effects on Na + influx and efflux rates reflecting their different ionoregulation strategies. Rio Negro DOM protected against Cu uptake and toxicity in the two fish species. Both Cu uptake in fish gills and Na + regulation disturbances were relatively well predicted by the modelled aqueous free Cu2+ ion concentration. These findings suggest that protection by DOM occurs mainly from Cu complexation under the tested conditions. The prevalence of this geochemical-type protection over a physiological-type protection agrees with the BLM conceptual framework, supporting the use of the BLM to assess the risk of Cu in these Amazonian waters.
... The DGT technique measures a time-weighted average during the deployment time of usually several days (Altier et al., 2019;Cindrić et al., 2020;Layglon et al., 2020). The BLM speciation codes requires the input of the water quality parameters pH, alkalinity, major hardness cations and anions, dissolved organic matter in addition to total trace-metal concentration Paquin et al., 2002). With the exception of pH, which may be monitored in situ, all parameters must be determined by laboratory analysis after discrete sampling. ...
The water column of harbors contains significant amounts of (priority) hazardous trace metals that may be released into coastal areas of high societal and economic interests where they may disturb their fragile equilibria. To deepen our understanding of the processes that influence the transport of the various metal fractions and allow for a more rigorous environmental risk assessment, it is important to spatially monitor the relevant chemical speciation of these metals. It is of particular interest to assess their so-called dynamic fraction, which comprises the dissolved chemical forms that are potentially bioavailable to living organisms. In this study this was achieved in the Genoa Harbor (NW Italy) for copper (Cu), lead (Pb), cadmium (Cd) and zinc (Zn) by applying a multi-method approach. For the first time in this system the dynamic fractions of the target metals (Cu Dyn , Cd Dyn , Pb Dyn , Zn Dyn) were observed in real-time on-board by voltammetry using innovative electrochemical sensing devices. Trace metals in the operationally defined dissolved <0.2 μm and <0.02 μm fractions were equally quantified through sampling/laboratory-based techniques. The obtained results showed a clear spatial trend for all studied metals from the enclosed contaminated part of the harbor towards the open part. The highest Cu Dyn and Cd Dyn fractions were found in the inner part of the harbor while the highest Pb Dyn fraction was found in the open part. The proportion of Zn Dyn was negligible in the sampled area. Small and coarse colloids were involved in Cu, Cd and Zn partitioning while only coarse colloids played an important role in Pb partitioning. The determined concentrations were compared to the Environmental Quality Standards (EQS) established by the EU and those determined by the Australia and New Zealand to trigger for 99 and 95% species protection values. The results of this work allow us to highlight gaps in the EQS for which metal concentration thresholds are excessively high or non-existent and should urgently be revised. They also reflect the need to quantify the potentially bioavailable fraction of hazardous trace metals instead of just their total dissolved concentrations. The data support the establishment of environmental quality standards and guidelines based on realistic risk assessment to protect aquatic life and resources and ultimately human health.
Efforts to incorporate bioavailability adjustments into regulatory water quality criteria in the United States have included four major procedures: hardness-based single-linear regression equations, water-effect ratios (WERs), biotic ligand models (BLMs), and multiple-linear regression models (MLRs) that use dissolved organic carbon, hardness, and pH. The performance of each with copper (Cu) is evaluated, emphasizing the relative performance of hardness-based versus MLR-based criteria equations. The WER approach was shown to be inherently highly biased. The hardness-based model is in widest use, and the MLR approach is the US Environmental Protection Agency's (USEPA's) present recommended approach for developing aquatic life criteria for metals. The performance of criteria versions was evaluated with numerous toxicity datasets that were independent of those used to develop the MLR models, including olfactory and behavioral toxicity, and field and ecosystem studies. Within the range of water conditions used to develop the Cu MLR criteria equations, the MLR performed well in terms of predicting toxicity and protecting sensitive species and ecosystems. In soft waters, the MLR outperformed both the BLM and hardness models. In atypical waters with pH <5.5 or >9, neither the MLR nor BLM predictions were reliable, suggesting that site-specific testing would be needed to determine reliable Cu criteria for such settings. The hardness-based criteria performed poorly with all toxicity datasets, showing no or weak ability to predict observed toxicity. In natural waters, MLR and BLM criteria versions were strongly correlated. In contrast, the hardness-criteria version was often out of phase with the MLR and, depending on waterbody and season, could be either strongly overprotective or underprotective. The MLR-based USEPA-style chronic criterion appears to be more generally protective of ecosystems than other models. Environ Toxicol Chem 2023;00:1-35. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Cobalt distribution and speciation were quantified in space and time in the water column of a small, stratified, eutrophic lake, Linsley Pond, North Branford, CT. While scrupulously employing clean techniques, we used ligand exchange with dimethylglyoxime and cathodic stripping voltammetry to evaluate free and complexed forms of Co. Free aquo Co ion concentrations [Co2+] were found in the range from 0.014 to 0.28 nM from June to October 2018. Despite the orthograde distribution for total dissolved Co (0.42–3.34 nM), free Co2+ was higher in the epilimnion, decreasing with depth. Natural organic ligand concentrations [L] were in the span from 0.7 to 8.1 nM, with conditional stability constants (as logK) in the range from 9.43 to 11.13. Nearly all of the Co was complexed with highly selective ligands, and patterns suggest three controlling processes: (1) Co release from dissolving Mn (and perhaps Fe) oxides, (2) possible limitation by solubility of CoS(s), and (3) stabilization in solution via complexation by strong ligands. No correlation was observed between dissolved organic carbon and [L] in this study, suggesting that the ligands are not a simple subset of total dissolved organic matter, but may be specific compounds, perhaps S based. The hypothesis that the biological activity of plankton in Linsley Pond might be limited by micronutrient Co is only weakly supported. Cobalamin (VB12) measured via enzyme-linked immunosorbent assays ranged from 0.033 to 0.048 nM in this lake and does not follow a simple pattern with either total dissolved Co or Co2+, or with biological activity as indicated by chlorophyll levels.
Five metal mixture dose‐response models are used to predict toxicity of porewater to young sturgeon at areas of interest in the Upper Columbia River and to evaluate these models as tools for risk assessments. Dose components of metal mixture models include exposure to free metal ion activities or metal accumulation by biotic ligands or humic acid, whereas links of dose to response use logistic equations, independent joint action equations, or additive toxicity functions. Laboratory bioassay studies of single metal exposures to juvenile sturgeon, porewater collected in‐situ in the fast‐flowing Upper Columbia River, and metal mixture models are used to evaluate toxicity.
The five metal mixture models are very similar in their predictions of adverse response of juvenile sturgeon and in identifying copper (Cu) as the metal responsible for the most toxic conditions. Although the modes of toxic action and EC20 values are different among the dose models, predictions of adverse response are consistent among models because all doses are tied to the same biological responses. All models indicate that 56 + 5% of 122 porewater samples are predicted to have <20% adverse response, 25 + 5% of samples are predicted to have 20‐80% adverse response, and 20 + 4% are predicted to have >80% adverse response of juvenile sturgeon.
The approach of combining bioassay toxicity data, compositions of field porewater, and metal mixture models to predict lack of growth and survival of aquatic organisms due to metal toxicity is an important tool that can be integrated with other information (e.g., survey studies of organism populations, lifecycle and behavior characteristics, sediment geochemistry, and food sources) to assess risks to aquatic organisms in metal‐enriched ecosystems.
In 2007, the US Environmental Protection Agency issued its "Framework for Metals Risk Assessment." The framework provides technical guidance to risk assessors and regulators when performing human health and environmental risk assessments of metals. This paper focuses on advances in the science including assessing bioavailability in aquatic ecosystems, short- and long-term fate of metals in aquatic ecosystems and advances in risk assessment of metals in sediments. Notable advances have occurred in the development of bioavailability models for assessing toxicity as a function of water chemistry in freshwater ecosystems. The Biotic Ligand Model (BLM), Multiple Linear Regression model (MLR) and Multi-Metal BLM (mBLM) now exist for most of the common mono- and di-valent metals. Species sensitivity distributions (SSDs) for many metals exist making it possible for many jurisdictions to develop or update their water quality criteria or guidelines. The understanding of the fate of metals in the environment has undergone significant scrutiny over the past 20 years. Transport and toxicity models have evolved including the Unit World Model (UWM) allowing for estimation of concentrations of metals in various compartments as a function of loading and time. There has been significant focus on the transformation of metals in sediments to forms that are less bioavailable and on understanding conditions that result in re-solubilization or redistribution of metals in and from sediments. Methods for spiking sediments have advanced such that the resulting chemistry in the laboratory mimics that in natural systems. Sediment bioavailability models are emerging including models that allow for prediction of toxicity in sediments for copper and nickel. Biodynamic models have been developed for several organisms and many metals. The models allow for estimates of transport of metals from sediments to organisms via their diet as well as their water exposure. All these advances expand the tool set available to risk assessors.
Background
Risks of adverse ecological effects of copper (Cu) conditions of water quality parameters were not fully understood in China. Here, a multiple linear regression approach was employed to assess risks posed by Cu under various conditions of water quality. Results of the approach were compared to assessments in Chinese surface waters that did not consider water quality parameters that might affect availability of Cu.
Results
Under prevalent water quality conditions of hardness = 150.0 mg/L, pH = 7.8, and DOC = 3.0 mg/L, across China, the predicted no effect concentration for total, dissolved Cu was 9.71 µg/L. Based on results of the preliminary risk quotients method, 1.19% of sites were classified as “high risk”, only one sixth of the percentage of sites with “high risk” than the proportion predicted when not considering water quality parameters, which was 7.51%. Similar results were obtained by application of both the margin of safety and joint probability curve methods, both of which overestimated risks posed by Cu to aquatic organisms in China.
Conclusion
After correcting for bioavailability based on water quality parameters, based on both concentrations and frequencies, regions of China at greatest risk from adverse effects of Cu were the Hai River (Haihe), Huai Rivers (Huaihe) and Chao Lake. These findings provide a comprehensive method for a more accurate assessment of risks of adverse effects of Cu to aquatic life in surface waters.
Proposed development of a mine within Alaska's Bristol Bay watershed has raised concerns about the potential impact of copper (Cu) on Pacific salmon (Oncorhynchus spp.). We conducted 96-hour flow-through bioassays using low-hardness and low-dissolved organic carbon water to determine the acute lethal toxicity of Cu to sockeye (O. nerka), Chinook (O. tshawytscha), and coho salmon (O. kisutch) fry. We aimed to determine Cu toxicity under field-relevant water quality conditions and to assess three methods of calculating ambient Cu criteria: the USEPA-endorsed biotic ligand model (BLM), a multiple linear regression model, and the hardness-based model currently used by the State of Alaska. The criteria generated by all models were below 20% lethal Cu concentrations by factors ranging from 2.2 to 54.3, indicating that all criteria would be protective against mortality. The multiple linear regression-based criteria were the most conservative and comparable to BLM-based criteria. The median lethal concentrations (LC50s) for sockeye, Chinook, and coho, were 35.2, 23.9, and 6.3 µg Cu/L, respectively. We also used the BLM to predict LC50s for each species. Model-predictions differed from empirical LC50s by factors of 0.7 for sockeye and Chinook salmon, and 1.1 for coho salmon. These differences fell within the acceptable range of ± 2, indicating the model's accuracy. We calculated critical lethal Cu accumulation values for each species to account for differing water chemistry in each bioassay, revealing that coho salmon were most sensitive to Cu, followed by sockeye, and Chinook salmon. Our findings underscore the importance of considering site- and species-specific factors when modeling Cu toxicity. The empirical data presented in this study may enhance Cu risk assessments for Pacific salmon.
This study reviews the concept, classifications, and techniques involved in the synthesis of nanocomposites. The environmental and health implications of nanoparticles and composite materials were detailed, as well as the applications of nanocomposites in water remediation, antibacterial application, and printed circuit boards. The study gave insights into the challenges of water pollution treatment and provided a broad list of nanocomposites that have been explored for water remediation. Moreover, the emergence of multi-drug resistance to many antibiotics has made current antibiotics inadequate in the treatment of disease. This has engineered the development of alternative strategies in the drug industries for the production of effective therapeutic agents, comprising nanocomposites with antibacterial agents. The new therapeutic agents known as nanoantibiotics are more efficient and have paved the way to handle the challenges of antibiotic resistance. In printed circuit boards, nanocomposites have shown promising applications because of their distinct mechanical, thermal, and electrical characteristics. The uniqueness of the write-up is that it provides a broad explanation of the concept, synthesis, application, toxicity, and harmful effects of nanocomposites. Thus, it will provide all-inclusive awareness to readers to identify research gaps and motivate researchers to synthesize novel nanocomposites for use in various fields.
HIGHLIGHTS
The size of nanocomposites makes them ideal for different applications.;
The applications of nanocomposites in water treatment, antibacterial activity, and printed circuit boards are detailed.;
There are concerns about the environmental and health implications of nanomaterials.;
The review gave insights into the challenges, research gaps, future considerations, and health implications of nanocomposites.;
Chemicals are at the top of public health concerns and metals have received much attention in terms of toxicological studies. Cadmium (Cd) and mercury (Hg) are among the most toxic heavy metals and are widely distributed in the environment. They are considered important factors involved in several organ disturbances. Heart and brain tissues are not among the first exposure sites to Cd and Hg but they are directly affected and may manifest intoxication reactions leading to death. Many cases of human intoxication with Cd and Hg showed that these metals have potential cardiotoxic and neurotoxic effects. Human exposure to heavy metals is through fish consumption which is considered as an excellent source of human nutrients. In the current review, we will summarize the most known cases of human intoxication with Cd and Hg, highlight their toxic effects on fish, and investigate the common signal pathways of both Cd and Hg to affect heart and brain tissues. Also, we will present the most common biomarkers used in the assessment of cardiotoxicity and neurotoxicity using Zebrafish model.
In Antarctica, human activities have been reported to be the major cause of the accumulation of heavy metal contaminants. A comprehensive bibliometric analysis of publications on heavy metal contamination in Antarctica from year 2000 to 2020 was performed to obtain an overview of the current landscape in this line of research. A total of 106 documents were obtained from Scopus, the largest citation database. Extracted data were analysed, and VOSviewer software was used to visualise trends. The result showed an increase in publications and citations in the past 20 years indicating the rising interest on heavy metal contamination in the Antarctic region. Based on the analysis of keywords, the publications largely discuss various types of heavy metals found in the Antarctic water and sediment. The analysis on subject areas detects multiple disciplines involved, wherein the environmental science was well-represented. The top countries and authors producing the most publication in this field were from Australia, China, Brazil and Chile. Numerous efforts have been exercised to investigate heavy metal pollution and its mitigation approaches in the region in the past decades. This paper not only is relevant for scholars to understand the development status and trends in this field but also offers clear insights on the future direction of Antarctic heavy metal contamination and remediation research.
We developed a model that quantifies aquatic cationic toxicity by a combination of the intrinsic toxicities of metals and protons and the intrinsic sensitivities of the test species. It is based on the WHAM-FTOX model, which combines the calculated binding of cations by the organism with toxicity coefficients (αH, αM) to estimate the variable FTOX, a measure of toxic effect; the key parameter αM,max (applying at infinite time) depends upon both the metal and the test species. In our new model, WHAM-FTOXβ, values of αM,max are given by the product αM* × β, where αM* has a single value for each metal, and β a single value for each species. To parameterise WHAM-FTOXβ, we assembled a set of 2182 estimates of αM,max obtained by applying the basic model to laboratory toxicity data for 76 different test species, covering 15 different metals, and including results for metal mixtures. Then we fitted the log10αM,max values with αM* and β values (a total of 91 parameters). The resulting model accounted for 72% of the variance in log10αM,max. The values of αM* increased markedly as the chemical character of the metal changed from hard (average αM* = 4.4) to intermediate (average αM* = 25) to soft (average αM* = 560). The values of log10β were normally distributed, with a 5-95 percentile range of -0.73 to +0.56, corresponding to β values of 0.18 to 3.62. The WHAM-FTOXβ model entails the assumption that test species exhibit common relative sensitivity, i.e. the ratio αM,max / αM* is constant across all metals. This was tested with data from studies in which the toxic responses of a single organism towards two or more metals had been measured (179 examples for the most-tested metals Ni, Cu, Zn, Ag, Cd, Pb), and statistically-significant (p < 0.003) results were obtained.
Over time multiple lines of research have been integrated as important components of evidence for assessing the ecological quality status of water bodies within the framework of Environmental Risk Assessment (ERA) approaches. One of the most used integrative approaches is the triad which combines, based on the weight-of-evidence, three lines of research, the chemical (to identify what is causing the effect), the ecological (to identify the effects at the ecosystem level) and the ecotoxicological (to ascertain the causes of ecological damage), with the agreement between the different lines of risk evidence increasing the confidence in the management decisions. Although the triad approach has proven greatly strategic in ERA processes, new assessment (and monitoring) integrative and effective tools are most welcome. In this regard, the present study is an appraisal on the boost that passive sampling, by allowing to increase information reliability, can give within each of the triad lines of evidence, for more integrative ERA frameworks. In parallel to this appraisal, examples of works that used passive samplers within the triad are presented providing support for the use of these devices in a complementary form to generate holistic information for ERA and ease the process of decision-making.
At the international level, the concept of critical loads developed under the Convention on Long-Range Transboundary Air Pollution directed by the United Nations Economic Commission for Europe is actively used to assess the risks of excessive inputs of pollutants into ecosystems. The review considers the main principles of the concept of critical loads and methods of its application for assessing the current risks of excessive accumulation of heavy metals (HMs) in soil as a component of terrestrial ecosystems from the standpoint of ecotoxicological effects (on plants, soil invertebrates, and microorganisms). Under this concept, the critical concentrations of Cd, Pb, Cu, and Zn for soils are for the first time estimated using the functions of critical concentrations taking into account the properties of soils (primarily, acidity and the contents of organic matter and clay). The main attention is paid to the rationale and development of the models for assessment of the critical concentrations and transfer functions connecting the concentrations of HM compounds in soils and soil solutions. The current environmental risks of excessive HM accumulation are assessed by comparing them with their critical concentrations. Current challenges and future prospects for analyzing the current environmental risks based on the concept of critical loads include the reduction in the uncertainty of estimates, combined effect of different metals in a multicomponent pollution, field validation of processes and modeling results, and the impacts of climate change and land use.
Dreissenid mussels are one of the most problematic aquatic invasive species (AIS) in North America, causing significant ecological and economic impacts. To date, dreissenid mussel control efforts in open water have included physical, biological, and chemical methods. The feasibility of successful dreissenid mussel management or eradication in lakes is relatively undocumented in the freshwater management literature. This review presents information on 33 open water dreissenid mussel control projects in 23 North America lakes. We reviewed data from past dreissenid mussel control projects and identified patterns and knowledge gaps to help inform adaptive management strategies. The three key lessons learned include 1) pre- and post-treatment survey methods should be designed to meet management objectives, e.g., by sampling for all life stages and taking into account that no survey method is completely comprehensive; 2) defining the treatment area – particularly ensuring it is sufficiently large to capture all life stages present – is critical to meeting management objectives; and 3) control projects provide an opportunity to collect mortality, depth, water chemistry, eDNA, effects on non-target organisms, and other efficacy-related data that can inform safe and effective adaptive management.
The expanding applications of lanthanides (Ln) in various aspects have raised concerns about their biosafety. Slight changes in the chemical composition of environmental media can significantly affect the biological effectiveness of poorly water-soluble Ln; however, the knowledge of the effects of environmental factors on Ln toxicity remains limited. Here, the effects of pH, HCO3-, Ca2+, Mg2+, Na+, K+, Cl-, and SO42- on the bioefficacy and biotoxicity of Ln (La, Ce, Gd, and Ho) were comparatively studied using zebrafish (Danio rerio) as the test organism. In the standard water, the toxicity of Ln in zebrafish was significantly correlated with pH, HCO3-, and Ca2+-Mg2+ levels in the medium but not with the levels of Cl-, Na+, K+, and SO42-. At the beginning of the test, the four Ln were complexed with HCO3- in the medium to form precipitates. A decrease in pH or HCO3- concentration can promote the conversion of granular Ln to a soluble state, thus enhancing their bioavailability, biotoxicity, and bioaccumulation. At a pH of 5.0 and 0.2 mmol·L-1 HCO3-, where Ln precipitates were not found, the four Ln showed a consistent trend of 96 h-LC50 in zebrafish. These data indicate that the differences in the toxicities of the four Ln in the standard water may be due to differences in the effective states of the individual elements rather than the different toxicities of the elements. Overall, in biological toxicity assessments, Ln can be regarded as a group of elements with additive patterns of toxicity until the differences in their biological toxicity mechanisms are revealed, and the effects of pH and carbonate should be considered.
The establishment of water quality criteria (WQC) for copper (Cu) was used as the basis for an ecological risk assessment of marine Cu pollution in Liaodong Bay, China. Published ecotoxicity data for Cu were obtained and supplemented with the results of acute Cu toxicity tests. The marine WQC for Cu in Liaodong Bay was developed using a species sensitivity distribution method with a safety factor of 2.0 and the USEPA acute-to-chronic ratio method. The ecological risk of Cu in Liaodong Bay was assessed by comparing the seawater Cu concentrations with the developed WQC. The results of this study showed that the acute and chronic Cu concentrations in Liaodong Bay were 3.31 and 2.18 μg/L, respectively. Comparison of the WQC to Cu concentrations in the bay resulted in risk quotients slightly >1.0 and typically ≤2.0. These data suggest that certain organisms in Liaodong Bay are at risk. These results can assist in the development of a pollution control management approach for the bay.
The basic mechanisms of iono/osmoregulation, acid-base regulation, and homeostasis and excretion of nitrogenous wastes (ammonia and urea) are reviewed for freshwater fish, marine and euryhaline fish, and for special cases (marine hagfish and chondrichthyans). Six different examples are then explored where physiological understanding of environmental impacts on these processes has already informed regulatory and conservation strategies, or should do so in the future. These include: (i) the acid-rain crisis; (ii) survival of fishes in the acidic, ion-poor blackwaters of the Rio Negro; (iii) development of the Biotic Ligand Model for environmental regulation of metals; (iv) survival of fishes in highly alkaline lakes; (v) the commercial hagfish fishery; and (vi) the critical importance of feeding for osmoregulation in chondrichthyans. These lessons argue for a greater awareness of the wide-spread variation in the physical chemistry of natural waters, and the associated physiology of the fish that live there. This knowledge should be incorporated into regulatory strategies for both environmental protection and conservation of resident species at risk.
Currently, the acidification of freshwater ecosystems is an overlooked public concern. In this chapter, a review on the origin, threats, impacts, and recent advances related to the CO2-induced acidification in the freshwater ecosystems is presented and discussed.
Exposure of freshwater trout (Salmo gairdneri) to waterborne Cd2+ results in accumulation of the metal in the branchial epithelial cells and its appearance in the blood. Cd2+ apparently enters the cells via Ca2+ channels in the apical membrane. Transfer of Cd2+ through the basolateral membrane is probably by diffusion. Inhibition by Cd2+ of transepithelial Ca2+ influx is time-and Cd2+-concentration-dependent. The inhibition of transepithelial Ca2+ influx is accompanied by blockage of apical Ca2+ channels. In line with the assumption that cytosolic Cd2+ inhibits Ca2+ uptake by inhibiting the basolateral Ca2+ pump, we hypothesize that the blockage of Ca2+ channels is an indirect effect of Cd2+ and results from a rise in cytosolic Ca2+ level caused by inhibition of the basolateral membrane Ca2+ pump.
Here I quantitatively review the literature on how fish gill morphology is affected by chemical and physical irritants in the surrounding water (e.g. various toxicants, extremes of temperature or pH). I catalogued histopathological gill lesions that were reported, and used statistics to explore how such lesions relate to the irritant-exposure conditions under which they occurred (specifically, to dose and class of irritant, to temperature, and to salinity of the surrounding water). Frequently recorded histopathologic lesions include changes in gill epithelium (lifting, necrosis, hyperplasia, hypertrophy, rupture), bulbing or fusing of gill lamellae, hypersecretion and proliferation of mucocytes, and changes in chloride cells and gill vasculature. I conclude that these lesions are largely nonspecific in nature, as each was detected under many different exposure conditions. The lesions are not entirely independent of exposure conditions, however, as my statistical analysis discerns these trends: (1) Most gill lesion types have been reported more frequently after lethal than after sublethal exposure to irritants. (2) Some lesions were more frequently detected in studies employing heavy metals than in studies using organic toxicants or other irritants; such lesions include necrosis and hypertrophy of gill epithelial cells, plus mucous hypersecretion. (3) Lifting of the branchial epithelium, the most commonly reported lesion, was reported more often in freshwater than in marine fish, suggesting that osmolarity of the ambient water influences this lesion. Little relation was found between recorded lesion frequencies and temperature. Following my statistical analysis, the etiology of irritant-induced gill lesions is considered. The nonspecificity of branchial alterations suggests that they primarily represent stereotyped physiological reactions of gills to stress, and many of them are logically considered defense responses. Some branchial alterations have been considered inflammatory, but I conclude that the literature cannot support that hypothesis. Ultrastructural studies have detected irritant-induced disruptions of branchial epithelial cells, including cytoplasmic vacuolization, autophagosomes and inclusions, loss of microvilli, and abnormal mitochondria and nuclei.
Adult rainbow trout fitted with arterial and bladder catheters were chronically infused with either bicarbonate (as NaHCO3) or NaCl for 19 h at approximately 410μequivkg−1h−1. NaHCO3 infusion produced a pure exogenous metabolic alkalosis of approximately 0.35 pH units accompanied by a decrease in plasma [Cl−] but no change in plasma [Na+]. Alkalosis stimulated Cl− influx and inhibited Na+ influx (measured at 10-16h infusion), resulting in a negative Na+ balance, a positive Cl− balance and a large net basic equivalent excretion (=acidic equivalent uptake) across the gills. The latter was approximately equal to the rate of HCO3−loading. The kidney accounted for approximately 13 % of the acid-base compensation.
Kinetic analysis revealed that reductions in were accomplished by increases in (463μuquivl−1; NaHCO3-infused vs 276μequivl−1; NaCl-infused) and large decreases in (262μequivkg−1h−1 vs 689μequivkg−1 h−1) while stimulation of was accomplished by large increases in only (674 μequiv kg−1 h−1 vs 360μequivkg−1 h−1). Thus, Jmax can be increased or decreased in response to acid-base disturbance, but Km can only be increased; the Na+ and Cl− carriers operate close to maximum affinity under control conditions. Basic equivalent excretion was described by a virtually identical kinetic curve to that of the Cl− uptake. NaHCO3 infusion also induced a differential diffusive efflux of Na+ over Cl− which could account for up to 35 % of the acid-base compensation during alkalosis.
Endogenous respiratory acidosis and metabolic alkalosis were induced in bladder-catheterized freshwater rainbow trout by exposure to environmental hyperoxia (72 h) and its subsequent removal. Unidirectional and net fluxes of Na+, Cl− and acidic equivalents across the gills were examined over 0.5 h intervals. Hyperoxia resulted in a positive Na+ balance, negative Cl− balance and net acidic equivalent excretion. Return to normoxia caused a negative Na+ balance, a positive Cl− balance and net basic equivalent excretion (=acidic equivalent uptake). Cl−/basic equivalent exchange was more important than Na+/acidic equivalent exchange in the homeostatic responses, and alkalosis was a more potent stimulus than acidosis for change in branchial ion fluxes. Kinetic analysis demonstrated that alterations in ion fluxes were achieved by complex changes in both the Km (inverse of affinity) and the Jmax (maximal transport rate) of the branchial C1−/HCO3− (OH−) and Na+/H+(NH4+) transporters. (control=165μequivl−1) and 114μequivl−1) were increased during hyperoxic acidosis to 250 and 44μ μequivl−1, respectively. (291μequiv kg−1h−1) and (456 μequiv kg−1 h−1) did not change significantly. During post-hyperoxic alkalosis, was further increased to 559μequivl−1, increased to 445μequivkg−1h−1, while and decreased to 137μequivl−1 and 309μequiv kg−1 h−1, respectively. Diffusive efflux was examined using a novel method. There was no significant differential diffusive efflux of Na+ and Cl− during hyperoxia but diffusive Na+ efflux exceeded Cl− efflux during posthyperoxic alkalosis, thereby serving as an additional mechanism for basic equivalent excretion.
Exposure of adult rainbow trout to low pH (pH 4·3) in soft water (Ca2+ = 223 μequiv/1) caused a substantial ionic disturbance which arose primarily because of large net losses at the gills. In contrast, renal ion losses were low initially and declined even further because of a pronounced reduction in urine flow. A net influx of H+ occurred across the gills but this was not sufficient to cause a blood acid-base disturbance or a renal response. Although branchial ion and H+ fluxes declined with time, blood ion levels did not return to normal and many of the fish died. Further reduction in water calcium (Ca2+ = 69 μequiv/1) provoked a higher mortality and a more substantial ionic imbalance. These results contrast sharply with the effects on trout of acid exposure in hard water (Ca2+ ⩾ 1600μequiv/l), where net ion losses and mortality are reduced and H+ uptake increased. A preliminary model for the interaction of low pH and calcium is proposed and evidence for adaptation to acid stress and for the origin of acid lethality is discussed.
Changes in pollutant concentrations in environmental media occur both due to pollutant transport in water or air and due to local processes, such as adsorption, degradation, precipitation, straining, etc. The terms “fate and transport” and “transport and fate” reflect the coupling of moving with the carrier media and biogeochemical processes describing local transformations or interactions. Journal of Environmental Quality (JEQ) was one of the first to publish papers on fate and transport (F&T). This paper is a minireview written to commemorate the 50th anniversary of JEQ and show how the research interests, methodology, and public attention have been reflected in fate and transport publications in JEQ during the last 40 years. We report the statistics showing how the representation of different pollutant groups in papers changed with time. Major focus areas have been the effect of the solution composition on F&T and concurrent F&T, the role of organic matter, and the relative role of different F&T pathways. The role of temporal and spatial heterogeneity was studied at different scales. Value of long‐term F&T studies and developments in modeling as the F&T research approach was amply demonstrated. F&T studies have been an essential part of the conservation measure evaluation and comparison and ecological risk assessment. For 50 years, the JEQ has delivered new insights, methods, and applications related to fate and transport science. The importance of its service to society is recognized, and new generations of F&T researchers will be welcome to present their contributions to JEQ. This article is protected by copyright. All rights reserved
When this book was first published in 1996, the pollution of the earth's freshwater habitats was, as it is now, a topic of major concern. This synthesis considers the effects of pollutants on aquatic animals via a series of research and review articles that present experimental evidence of sublethal and lethal effects of a range of toxicants at the physiological, cellular and subcellular levels, and that explore techniques for detection of pollution damage. Topics covered include routes of uptake of toxicants; the effect of acute and chronic exposure to toxic metal ions, particularly zinc, copper and aluminium, with emphasis on the mechanisms of toxicity and responses to chronic exposure to sublethal levels; the impact on fish biology of two chemicals of current concern, nitrites and polyaromatic hydrocarbons, which may act as oestrogenic substances or potent mutagens; and in vitro studies of the mechanisms of toxicity at the cellular and subcellular level, including damage of DNA, using cultured fish cells.
Contents:
A Short History of Aquatic Toxicology
The Aquatic Environment
Factors that Affect the Environmental Concentration of Chemicals
Basic Toxicological Concepts and Principles
Factors that Influence Toxicity
Toxic Agents and Their Effects
Examination of Concentration-Response Relationships
Toxicity Testing
Interpreting Toxicity Test Data
Biomonitoring
Toxicity Dada and Environmental Regulations
The individual effect of different major cations (Ca(2+), Mg(2+), Na(+), K(+), and H(+)) on the acute toxicity of zinc to the waterflea Daphnia magna was investigated. The 48-h median effective concentration (EC50) in the baseline test medium (i.e., a standard medium with very low ion concentrations) was about 6 muM (Zn(2+)). An increase of Ca(2+) (from 0.25 mM to 3 mM), Mg(2+) (from 0.25 mM to 2 mM), and Na(+) activity (from 0.077 mM to 13 mM) reduced zinc toxicity by a factor of 6.3, 2.1, and 3.1, respectively. No further toxicity reduction was observed when Ca(2+) and Mg(2+) activities exceeded 3.0 and 2.0 mM, respectively. Both K(+) and H(+) did not significantly alter zinc toxicity (expressed as Zn(2+) activity). From these data, conditional stability constants for Ca(2+) (log K = 3.24), Mg(2+) (log K = 2.97), Na(+) (log K = 2.16), and Zn(2+) (log K = 5.31) were derived and incorporated into a biotic ligand model (BLM) predicting acute zinc toxicity to D. magna in surface waters with different water quality characteristics. Validation of the developed BLM using 17 media with different pH, hardness, and dissolved organic carbon (DOC) content resulted in a significant correlation coefficient (R(2) = 0.76) between predicted and observed 48-h EC50. Eighty-eight percent of the predictions were within a factor of 1.3 of the observed 48-h EC50.
Introduction: This report describes the computer program for the computation of chemical equilibria in aqueous systems, MINEQL. The purpose of the report is to present the program in sufficient detail that the reader not only can use the program exactly as it is written, but also can modify it to suit whatever his particular needs may be. The evolution of the program, examples of its use, and general approach to the chemical equilibrium problem are described in Part I of the report. Part II presents a "MINEQL-1 User's Manual". A detailed mathematical description of the solution to the chemical equilibrium problem used in MINEQL appears in Appendix 1. It was felt that the solution could best be presented by an abstract description of the mathematical problem (without any reference to its chemical analog), followed by a very simple example of a chemical problem (which is given in Appendix 2). This avoids the intermingling of chemical and mathematical concepts which is sometimes confusing. Appendix 3 gives a description of the program itself. The three appendices are related in that they present the same concepts - the actual theory and its application in MINEQL - from three different viewpoints: mathematical, chemical, and computational. They should be read in conjunction with one another. First the concepts involved in the basic chemical equilibrium problem, (i.e., where there are no solid phases present) should be mastered, and then the extension to the consideration of solid phases, which is somewhat more complicated, should be undertaken. This report contains a complete description of all of the concepts employed in the program MINEQL. However, a working knowledge of the program is obtainable without attention to all of the details. It is hoped that this roadmap through MINEQL will enable the reader to maximize his use of the program without becoming bogged down in the details of the report.
This chapter presents an overview of the internal morphology of gills. Each gill arch skeleton is jointed with the posterior skull dorsally and with the copula ventrally. The septum contains nerves and blood vessels and bears the filaments. Two rows of filaments are generally inserted on each gill arch. This whole forms the so-called holobranchs. The mode of the insertion of filaments on the gill arch depends on the morphology of the septum and varies with the group of fish. In some groups (Chondrostei and the holostean Lepisosteus), certain arches—the hyoidean and the mandibular only—bear a single row of filaments, called “hemibranchs.” In other groups or species, these arches are completely devoid of filaments or absent, such as in Amia (Holostei), which has a mandibular but no hyoidean arch. The presence of lamellae on gill arches corresponds with the distribution of true aortic arches. The pattern of branchial arch organization is relatively constant among teleosts, but differs significantly in lower groups. In Myxinoidei, the variable number of gill slits correspond to a series of pouches connected by narrower tubes with the gut and body surface.
Whole body, gill, and liver copper uptake, gill Na+-K+-ATPase specific activity, and gill and liver acid-soluble thiols (AST), glutathione, and cysteine of rainbow trout (Salmo gairdneri) were measured during 28 d of exposure to 55 μg copper∙L−1. Na+-K+-ATPase specific activity was inhibited by 33% within 24 h of copper exposure, but this was compensated by a significant increase in microsomal protein so that the total Na+-K+-ATPase activity per milligram of gill tissue returned to normal by day 14. There was no accumulation of copper and no increase in AST, glutathione, or cysteine in the gill. However, after 7 d of exposure, hepatic AST and glutathione had increased by about 2 times, and a sulfhydryl-rich, acid-soluble protein, tentatively identified as metallothionein, increased by 2.8 times. Copper accumulation was highest in the liver, but other tissues also accumulated copper.
This volume aims to review and present research on acid waters and their effects on aquatic animals. Starting initially with the environment in order to assess why the problems have arisen in particular areas, the volume then deals with field and survival studies on invertebrates and vertebrates and examines the extent of the biological problem and the attempts which have been made to relate water quality and the susceptibility of animals. Major advances in this area have included the realization that declining populations are often the result of acid waters and their interactions with traces of other ions and that these situations produce the most severe physiological problems. The natural progression of environmental and field studies, toxicity and survival tests provide the background information for the physiological studies which follow. These form the major component of the book and they seek to analyse the toxic effects of acid waters and trace metals on acid-base balance, respiration, ionic balance together with cardiovascular and endocrinological effects.
This volume aims to review and present research on acid waters and their effects on aquatic animals. Starting initially with the environment in order to assess why the problems have arisen in particular areas, the volume then deals with field and survival studies on invertebrates and vertebrates and examines the extent of the biological problem and the attempts which have been made to relate water quality and the susceptibility of animals. Major advances in this area have included the realization that declining populations are often the result of acid waters and their interactions with traces of other ions and that these situations produce the most severe physiological problems. The natural progression of environmental and field studies, toxicity and survival tests provide the background information for the physiological studies which follow. These form the major component of the book and they seek to analyse the toxic effects of acid waters and trace metals on acid-base balance, respiration, ionic balance together with cardiovascular and endocrinological effects.
A model has been developed to account for the variability in trace-metal toxicity to fishes at different values of alkalinity, hardness, and pH. The model utilizes trace-metal speciation, gill surface interaction, and competitive inhibition to predict effective toxicant concentration (ETC). Copper, cadmium, lead, and zinc bioassay data have been utilized.
Considered the possible effects of environmental acidification (pH 7-4) on 1) metal speciation in solution, 2) metal adsorption at biological surfaces, and 3) metal uptake by and toxicity to aquatic biota. Attention was focused on some 10 metals of potential concern in the context of freshwater acidification (Ag, Al, Cd, Co, Cu, Hg, Mn, Ni, Pb, Zn). For the 4 metals (Al, Cu, Hg, Pb) predicted to manifest speciation changes in the range pH 7-4, confirmatory experimental data are available for Cu and Pb. In the 6 remaining cases predicted to show little sensitivity to pH changes in this range, supporting experimental evidence exists for 4 metals (Ag, Cd, Mn, Zn). A pH-dependent biological response is documented over a realistic range of H + and metal concentrations for 6 of the 10 metals considered (Al, Cd, Cu, Zn, and to a lesser extent, Hg and Pb). These 6 metals fall into 2 groups: those for which a decrease in pH results in a decreased biological response (type I behavior: Cd, Cu, Zn) and those for which the dominant effect of acidification is to increase metal availability (type II behavior: Pb). Data for Al and Hg clearly reveal pH effects, but results are too few and too inconsistent to allow generalizations. -from Authors
In Eriocheir sinensis active uptake of sodium plays a vital role in the maintenance of sodium balance. At external concentrations down to about 6 mM./l. the active uptake mechanism is fully saturated and the uptake rate just balances the rate of loss, which occurs primarily through the body surface. At lower external concentrations balance may be achieved, at least in part, by the activation of the uptake mechanism. A hypothesis is put forward to account for the mechanism of adaptation of the Crustacea to fresh water. Two main factors are involved: (a) a progressive reduction in the permeability of the body surface to salts and, (b) the acquisition of an active uptake mechanism with a high affinity for the ions which it transports. This hypothesis is discussed in relation to previous theories on the adaptation of the Crustacea to fresh water.
Fathead minnows (Pimephales promelas) were exposed to 17 μg Cu∙L ⁻¹ or 6 μg Cd∙L ⁻¹ in synthetic soft water in the presence of competing ligands. Measured gill metal concentrations correlated with free metal ion concentrations, not with total metal. Langmuir isotherms were used to calculate conditional metal–gill equilibrium constants and the number of binding sites for each metal. Log K Cu-gill was estimated to be 7.4 and the number of Cu binding sites on a set of gills (70 mg, wet weight) was ~2 × 10 ⁻¹⁰ mol (~30 nmol∙g wet weight ⁻¹ ). Log K Cd-gill was ~8.6, and the number of Cd binding sites on minnow gills was ~2 × 10 ⁻¹⁰ mol (~2 nmol∙g wet weight ⁻¹ ). Stability constants for H ⁺ and Ca interactions at metal–gill binding sites and for metal interactions with dissolved organic carbon (DOC) were estimated using these metal–gill constants. All stability constants were entered into the MSNEQL ⁺ aquatic chemistry program, to predict metal accumulation on fish gills using metal, DOC, and Ca concentrations, and water pH. Calculated metal accumulation on gills correlated well with measured gill metal concentrations and with LC 50 values. Our approach of inserting biological data into an aquatic chemistry program is useful for modelling and predicting metal accumulation on gills and therefore toxicity to fish.
Adult fathead minnows (Pimephales promelas) were exposed to 17 g Cu∙L ⁻¹ or 6 g Cd∙L ⁻¹ for 2 to 3 h in synthetic softwater solutions at pH 6.2 containing either naturally-occurring, freeze-dried dissolved organic carbon (DOC) or synthetic ligands such as EDTA. After exposures, gills were assayed for bound Cu or Cd. As a first approximation, lake of origin or molecular size fraction of DOC did not influence Cu binding to gills, while DOC concentration did. DOC concentrations ≥4.8 mg∙L ⁻¹ prevented Cu from accumulating on fathead gills. At the relatively low concentrations used, neither Cu nor Cd interfered with binding of the other metal on gills, suggesting different gill binding sites. Cadmium accumulation on gills was more sensitive to increased concentrations of Ca and H ⁺ than was Cu. Surprisingly, Cd bound to gills to the same or greater extent than did Cu: for synthetic ligands, Cd binds less well than Cu. This result corroborates previously published observations that Cd, unlike Cu, is taken up at gills through high affinity Ca channels. Accumulation of Cd on fish gills was never associated with ¹⁴ C-labelled EDTA or ¹⁴ C-citrate, indicating that free metal interacts with the gill while metal–ligand complexes usually do not.
Static-renewal 7-d toxicity tests for silver nitrate (AgNO{sub 3}) were performed with juvenile rainbow trout (Oncorhynchus mykiss Walbaum). The relative influences of calcium and chloride concentrations on median lethal time (LT50) were assessed. For both calcium salts, a 100-fold elevation in concentration increased the LT50 approximately 10-fold. However, a 100-fold elevation in KCl ameliorated silver (Ag) toxicity at least 100-fold, while NaCl protected against Ag toxicity even more substantially, demonstrating the much greater protective effect of chloride relative to calcium. In a separate series of bioassays, fish were exposed to 0.92 {micro}M Ag with varying amounts of NaCl titrated into each tank to alter the free [Ag{sup +}]. The 7-d LC50 occurred at a [NaCl] of 2,500 {micro}M. Using MINEQL{sup +}, the predicted free [Ag{sup +}] at this LC50 value is 0.0285 {micro}M. Further bioassays were performed in which [chloride] was maintained at either 50 or 225 {micro}M, while total [Ag] was independently varied from 0.0092 to 0.0694 {micro}M (1.0--7.5 {micro}g/L). The 7-d LC50 value was calculated at 0.0294 {micro}M Ag (3.18 {micro}g/L) at a chloride concentration of 50 {micro}M, very similar to the free [Ag{sup +}] value of 0.031 {micro}M calculated from an earlier LC50 test at a fixed [chloride] of 730 {micro}M. Elevating chloride concentrations from 50 to 225 {micro}M did not alter the accumulation of Ag in the liver. In addition, there were no significant differences in hepatic Ag accumulation between any of the Ag-exposed fish, irrespective of the total Ag concentration used during the exposure.
Because of the relationship between water hardness and the toxicity of many metals, total hardness is used as a model parameter to calculate ambient water quality criteria for copper and other metals. However, the relative contribution of the Ca and Mg components of total hardness as modifiers of metals toxicity is not considered in the water quality criteria. Acute Cu toxicity was measured in rainbow trout (Oncorhynchus mykiss) and chinook salmon (O. tshawytscha) swim-up fry in laboratory waters that were formulated to have similar total hardness and alkalinity but different Ca and Mg concentrations. Experiments were performed at nominal total hardness values of 40 and 90 mg/L (as CaCO{sub 3}). In four paired toxicity tests, acute Cu toxicity was significantly lower, i.e., 96-h LC50s were higher, in laboratory waters containing proportionately more Ca (Ca:Mg molar ratios of 1.5--5.2) than in waters containing less Ca (Ca:Mg molar ratios of 0.2--0.8). the relative increase in the 96-h Cu LC50 at higher Ca concentrations, but similar total hardness concentrations, was between 29 and 86% when the low Ca treatment was similar to American Society for Testing and Materials laboratory water. Failure to account for differences in Ca when matching or adjusting for total hardness thus exerts an important influence on the prediction of metal toxicity. These differences must be addressed in water-effect ratio testing in which paired tests with laboratory and site waters are conducted.
Rainbow trout (Oncorhynchus mykiss, 1--3 g) were exposed to {approximately} 1.0 {micro}M silver (Ag) ({approximately} 11 {micro}g {center_dot} L{sup {minus}1} Ag) for 2 to 3 h in synthetic soft water (Ca, Na {approximately} 300 {micro}M, pH 6.5--7.5) to which was added Ca, Na, H{sup +}, dissolved organic carbon (DOC), Cl, or thiosulfate (S{sub 2}O{sub 3}). Gills were extracted and gill Ag concentrations were measured using graphite-furnace atomic absorption spectrophotometry. The concentration of cations (Ca, Na, H{sup +}) and complexing agents (DOC, Cl, S{sub 2}O{sub 3}) needed to keep Ag off the gills were used to calculate conditional equilibrium binding constants (K) at the gills. Log K for Ag-gill binding was 10.0, with approximately 1.3 nmol Ag binding sites per fish. All experimentally determined log K values were entered into an aquatic chemistry equilibrium model, MINEQL{sup +}, to predict Ag binding at trout gills. For a series of natural waters, model-predicted gill Ag concentrations correlated well with observed gill Ag concentrations, with one exception, very hard city of Waterloo tapwater. This exception may indicate a kinetic constraint on the thermodynamic basis of the model.
Juvenile rainbow trout were exposed to zinc in both moderately hard water and soft water for 30 d. Only the 450 {micro}g/L zinc-exposed fish experienced significant mortality. Zinc exposure caused no effect on growth rate, but growth affected tissue zinc levels. Whole body zinc levels were elevated, but gill sand liver showed no consistent increases relative to controls over the 30 d. Therefore, tissue zinc residues were not a good indicator of chronic zinc exposure. After the 30-d exposure, physiological function tests were performed. Zinc was 5.4 times more toxic in soft water. All zinc-exposed trout had acclimated to the metal, as seen by an increase in the LC50 of 2.2 to 3.9 times over that seen in control fish. Physiological costs related to acclimation appeared to be few. Zinc exposure had no effect on whole body Ca{sup 2+} or Na{sup +} levels, on resting or routine metabolic rates, or on fixed velocity sprint performance. However, critical swimming speed (U{sub Crit}) was significantly reduced in zinc-exposed fish, an effect that persisted in zinc-free water. Using radioisotopic techniques to distinguish new zinc incorporation, the gills were found to possess two zinc pools: a fast turnover pool and a slow turnover pool. The fast pool was much larger in soft water than in hard water, but at most it accounted for < 3.5% of the zinc content of the gills. The size of the slow pool was unknown, but its loading rate was faster in soft water. Chronic zinc exposure was found to increase the size of the fast pool and to increase the loading rate of the slow pool.
The rate of reaction of trace metal ions is an important consideration when studying the chemistry of trace metals in natural waters. The application of speciation models to natural water systems requires knowledge of kinetics if reactions are slow. Most bioassay and toxicity tests conducted in static and flow-through systems have not taken reaction kinetics into account. Therefore, results from these studies may overestimate the toxicity in the receiving waters. In the present study, the kinetics of the interaction of Cu(II) with humic acid (HA) and its influence on the toxicity of copper to Ceriodaphnia dubia were investigated by both chemical kinetic studies using a copper ion selective electrode and bioassay tests using a continuous flow-through bioassay system. A two-ligand site, with fist-order rate constants, model gave a very good description of experimental kinetic data of the change of free Cu{sup 2+} concentration. Average k{sub 1} was 1.85/h and average k{sub 2} was 0.094/h. Bioassay tests indicated that different reaction times of copper with HA solution produced different toxic effects to organisms. The authors determined the hydrodynamic characteristics of the bioassay chambers to better describe the exposure of the organisms to free Cu{sup 2+}. The bioassays supported the free ion activity model that the bioavailability and therefore toxicity of copper was directly correlated to the free Cu{sup 2+} concentration rather than to the total copper concentration. It was further shown that conventional chemical kinetics can be used to predict the toxicity of copper in these bioassays. This study supports the importance of considering reaction kinetics when studying the chemistry of trace metals in natural waters.
Based on a biotic-ligand model (BLM), the authors hypothesized that the concentration of a transition metal bound to fish gills ([M{sub gill}]) will be a constant predictor of mortality, whereas a free-ion activity model is generally interpreted to imply that the chemical activity of the aquo (free) ion of the metal will be a constant predictor of mortality. In laboratory tests, measured [Ni{sub gill}] and calculated [Cu{sub gill}] were constant predictors of acute toxicity of Ni and Cu to fathead minnows (Pimephales promelas) when water hardness varied up to 10-fold, whereas total aqueous concentrations and free-ion activities of Ni and Cu were not. Thus, the BLM, which simultaneously accounts for (a) metal speciation in the exposure water and (b) competitive binding of transition-metal ions and other cations to biotic ligands predicts acute toxicity better than does free-ion activity of Ni or Cu. Adopting a biotic-ligand modeling approach could help establish a more defensible, mechanistic basis for regulating aqueous discharges of metals.
Juvenile rainbow trout (Salmo gairdneri) were exposed to 55 μg copper∙L−1 for 28 d and then transferred to uncontaminated water for 7 d. Whole body sodium concentration and sodium uptake (Jin) were measured at weekly intervals; Jin was measured at various Na+ concentrations and kinetic parameters estimated. After 24 h of copper exposure, the maximum rate of sodium uptake (Jmax) was inhibited by 55%, the affinity for sodium (Km) reduced by 49%, and whole body Na+ decreased by about 12.5%. After 7 d of exposure, whole body Na+ had returned to control values, but Jmax was still inhibited by 41%. Recovery of whole body Na+ occurred largely by a reduction of sodium efflux (Jout). Both Jmax and Km continued to recover until day 28, at which time Jin had returned to control values. We conclude that acclimation to sublethal copper depends on changes in both Na+ transport and permeability.
In the foregoing paper on the lymphatic system in a turtle, I have made no mention of the manner of discovering, and demonstrating those vessels; the reason was, there is no difficulty in either the one or the other; for, in that animal the mesentery being very thin and transparent, and the lacteals pretty large, they are more readily discovered than in any other animal; thence it happened that I saw those vessels in a turtle long before I discovered them in birds and fish, and that too by chance, and when I was not intent upon this inquiry.
Water pH in the gill micro-environment of adult fathead minnows (Pimephales promelas Rafinesque) was measured by means of opercular catheters and latex masks. Synthetic soft water of pH 5.7 was made more acidic, so that pH of the gill micro-environment stayed at approximately 5.4 to 5.9 over the inspired pH range 4.8 to 6.3. Copper would therefore be >99% Cu2+ at the gills. To measure Cu accumulation on gills, the target organ for Cu toxicity, adult fathead minnows were exposed for 2 to 3 h to 16 μg/L Cu in synthetic soft water (Ca2+ and Na+ approximately 50 μeq/L) at pH 4.8 and 6.3. Gill Cu concentrations were about 1.7 μg Cu/g wet tissue for the inspired pH 4.8 and 6.3 exposures. Added Ca2+ of 2,100 or 4,000 μeq/L reduced gill Cu accumulation during exposures at pH 4.8 but not at pH 6.3. EDTA eliminated Cu deposition at both pH 4.8 and pH 6.3 when equimolar with Cu, but reduced Cu deposition (by 50%) when half equimolar only in the pH 4.8 exposures. These results can be explained by Ca2+ and H+ competition with Cu for gill binding sites and by complexation of Cu by EDTA. Added CaCO3 did not reduce gill Cu, although both competition by Ca2+ and complexation by CO2−3 were expected. Water chemistry calculations suggested that because little CO2−3 is available at pH < 7, CO2−3 from CaCO3 is less likely to affect Cu deposition on fish gills than is Ca2+ from CaCO3.
