Internal exposure: Linking bioavailability to effects

Swiss Federal Institute for Environmental Science and Technology (EAWAG).
Environmental Science and Technology (Impact Factor: 5.48). 01/2005; 38(23). DOI: 10.1021/es0406740
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    ABSTRACT: Ecotoxicological effect data are generally expressed as effective concentrations in the external exposure medium and do thus not account for differences in chemical uptake, bioavailability, and metabolism, which can introduce substantial data variation. The Critical Body Residue (CBR) concept provides clear advantages, because it links effects directly to the internal exposure. Using CBRs instead of external concentrations should therefore reduce variability. For compounds that act via narcosis even a constant CBR has been proposed. Despite the expected uniformity, CBR values for these compounds still show large variability, possibly due to biased and inconsistent experimental testing. In the present study we tested whether variation in CBR data can be substantially reduced when using an improved experimental design and avoiding confounding factors. The aim was to develop and apply a well-defined test protocol for accurately and precisely measuring CBR data, involving improved (passive) dosing, sampling, and processing of organisms. The chemicals 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 2,3,4-trichloroaniline, 2,3,5,6-tetrachloroaniline, 4-chloro-3-methylphenol, pentylbenzene, pyrene, and bromophos-methyl were tested on Lumbriculus variegatus (California blackworm), Hyalella azteca (scud), and Poecilia reticulata (guppy), which yielded a high-quality database of 348 individual CBR values. Medians of CBR values ranged from 2.1 to 16.1 mmol/kg wet weight (ww) within all combinations of chemicals and species, except for the insecticide bromophos-methyl, for which the median was 1.3 mmol/kg ww. The new database thus covers about one log unit, which is considerably less than in existing databases. Medians differed maximally by a factor of 8.4 between the 7 chemicals but within one species, and by a factor of 2.6 between the three species but for individual chemicals. Accounting for the chemicals' internal distribution to different partitioning domains and relating effects to estimated concentrations in the target compartment (i.e., membrane lipids) was expected to but did not decrease the overall variability, likely because the surrogate partition coefficients for membrane lipid, storage lipid, protein, and carbohydrate that were used as input parameters did not sufficiently represent the actual partitioning processes. The results of this study demonstrate that a well-designed test setup can produce CBR data that are highly uniform beyond chemical and biological diversity.
    Environmental Science & Technology 02/2015; 49:1879-1887. DOI:10.1021/es505078r · 5.48 Impact Factor
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    ABSTRACT: Branchial Na(+)-K(+)-ATPase (NKA) activity has been suggested as a promising biomarker for assessing metal stress in aquatic organisms. However, studies that systematically show the effectiveness of using NKA activity to detect metal exposure and toxicity at the individual level are limited. In this study, we aimed to determine whether branchial NKA activity mechanistically responds to the accumulation of waterborne copper (Cu) and accounts for observed toxicity over time under environmentally-relevant and aquafarming Cu exposure levels (0.2, 1 and 2mgL(-1)). Temporal trends in Cu accumulation and the corresponding responses of branchial NKA activity resulting from Cu exposure were investigated in laboratory experiments conducted on juvenile tilapia (Oreochromis mossambicus), a freshwater teleost that shows potential as a bioindicator of real-time and historical metal pollution. We used the process-based damage assessment model (DAM) to inspect the time course of Cu toxicity by integrating the compensation process between Cu-induced inhibition and repair of branchial NKA activity. NKA activity acted as a sensitive biomarker for Cu exposure and accumulation in tilapia, which showed induced impairment of osmoregulation and lethality when they were exposed to environmentally relevant levels (0.2mgL(-1)), but not to higher exposure levels (1 and 2mgL(-1)) in aquaculture farms or contaminated aquatic ecosystems. This study highlights the benefits and limitations of using branchial NKA activity as a sensitive biomarker to assess the health status of a fish population and its ecosystem. Copyright © 2015 Elsevier B.V. All rights reserved.
    Aquatic toxicology (Amsterdam, Netherlands) 03/2015; 163. DOI:10.1016/j.aquatox.2015.03.016 · 3.51 Impact Factor
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    ABSTRACT: Many factors influence metal speciation in freshwaters. Metal species that are more soluble are considered more bioavailable and toxic. However, evaluation of metal speciation in waters is a complex task. Moreover, the quantification of total and dissolved metals is not sufficient to determine toxic effects on the biota. Here, we review environmental parameters that influence metal bioavailability: mathematical models to predict toxicity, and the biological tools used to evaluate contamination in freshwaters ecosystems. The major points are the following: (1) we discuss many “exceptions” of chemical parameters that are deemed to increase metal bioavailability or to protect against metal uptake, such as pH and water hardness. We provide evidence of organisms and environmental conditions that break these rules and therefore should be considered when predicting impairment by metals. (2) We discuss the advances in mathematical modelling as a proxy to metal toxicity. (3) We discuss advantages and limitations of using multiple biological tools to assess toxicity, such as the use of biomarkers and microorganisms, zooplankton, benthic macroinvertebrates and fish communities. Biomarkers are efficient in detecting low concentrations of metals in a short-term exposition. Changes on biological community structure and composition are good tools to detect high metal concentration or chronic concentration in a long-term exposition. The use of multiple tools including chemical analyses and a set of biological indicators is recommended for a more accurate evaluation of metal impacts on freshwater systems.
    Environmental Chemistry Letters 03/2015; 13(1). DOI:10.1007/s10311-015-0491-9 · 1.91 Impact Factor