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ABSTRACT: Copper toxicity and accumulation in plants are affected by physicochemical characteristics of soil solutions such as the concentrations of coexistent cations (e.g., Ca(2+), Mg(2+), K(+), Na(+), and H(+)). The biotic ligand model (BLM) approach has been proposed to predict metal phyto-toxicity and -accumulation by taking into account the effects of coexistent cations, given the assumption of the partition equilibrium of metal ions between soil solution and solid phase. The alleviation effects of Mg on Cu toxicity and accumulation in grapevine roots were the main concerns in this study and were investigated by using a hydroponic experiment of grapevine cuttings. The BLM approach, which incorporated competition of Mg(2+) with Cu(2+) to occupy the biotic ligands on root surfaces, was developed to predict Cu rhizotoxicity and accumulation by grapevine roots. In the results, the effective activity of Cu, {Cu (2+)}, resulting in a 50 % reduction of root elongation (EA (50)), linearly increased with increments of Mg activity, {Mg (2+)}. In addition, the Cu concentration in root, Cu ( root ), was retarded by an increase of {Mg (2+)}. The linear model was significantly fitted to the relationship between {Cu (2+)}/Cu ( root ) and {Mg (2+)}. According to the concept of BLM, the present results revealed that the amelioration effects of Mg on Cu toxicity and accumulation in roots could arise from competition between Mg(2+) and Cu(2+) on the binding sites (i.e., the biotic ligands). Then, the developed Cu-BLMs incorporating the Mg(2+) competition effectiveness were validated provide accurate predictions of Cu toxicity and accumulation in grapevine roots. To our knowledge this is the first report of the successful development of BLMs for a woody plant. This BLM approach shows promise of being widely applicable for various terrestrial plants.
Ecotoxicology 11/2012; · 2.36 Impact Factor
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ABSTRACT: To better understand the ability of switchgrass (Panicum virgatum L.), a perennial grass often relegated to marginal agricultural areas with minimal inputs, to remove cadmium, chromium, and zinc by phytoextraction from contaminated sites, the relationship between plant metal content and biomass yield is expressed in different models to predict the amount of metals switchgrass can extract. These models are reliable in assessing the use of switchgrass for phytoremediation of heavy-metal-contaminated sites. In the present study, linear and exponential decay models are more suitable for presenting the relationship between plant cadmium and dry weight. The maximum extractions of cadmium using switchgrass, as predicted by the linear and exponential decay models, approached 40 and 34 μg pot(-1), respectively. The log normal model was superior in predicting the relationship between plant chromium and dry weight. The predicted maximum extraction of chromium by switchgrass was about 56 μg pot(-1). In addition, the exponential decay and log normal models were better than the linear model in predicting the relationship between plant zinc and dry weight. The maximum extractions of zinc by switchgrass, as predicted by the exponential decay and log normal models, were about 358 and 254 μg pot(-1), respectively. To meet the maximum removal of Cd, Cr, and Zn, one can adopt the optimal timing of harvest as plant Cd, Cr, and Zn approach 450 and 526 mg kg(-1), 266 mg kg(-1), and 3022 and 5000 mg kg(-1), respectively. Due to the well-known agronomic characteristics of cultivation and the high biomass production of switchgrass, it is practicable to use switchgrass for the phytoextraction of heavy metals in situ.
Ecotoxicology and Environmental Safety 04/2012; 80:393-400. · 2.29 Impact Factor
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ABSTRACT: Although the ecotoxicological effects of copper (Cu) on grapevine are of global concern due to the intensive and long-term application of Cu-based fungicides in vineyards, comparatively little is known about the phytotoxicity, accumulation, and translocation of Cu in grapevines. Therefore, this study was to conduct a hydroponic experiment to determine the influence of solution Cu concentration not only on bioaccumulation and the translocation of Cu in grapevine roots, stems, and leaves, but also on the subsequent growth inhibition of the roots.
Grapevine cuttings were grown for 30 days and then exposed to various Cu concentrations (0.1-50 μM) for 15 days. The dose-response profile was described by a sigmoid Hill equation. Optical microscopy was used to examine the cytotoxicity of Cu on the roots. In addition, bioaccumulation factors (BAFs) and translocation factors (TFs) were calculated from the results of the hydroponic experiment.
Copper was tolerated by grapevines at a concentration ≤1 μM. The median inhibition concentration (IC(50)) obtained from the Hill model was 3.94 μM (95% confidence interval, 3.65-4.24). From the light micrographs of root tip cells, signs of toxicity including increased vacuolization and plasmolysis were observed at solution Cu concentrations ≥10 μM. In addition, a higher Cu concentration was found in the roots (25-12,000 mg kg(-1)) than in the stems (5-540 mg kg(-1)) and leaves (7-46 mg kg(-1)), indicating a very limited translocation of Cu from the roots to the aboveground parts.
This study investigated not only the macroscopic root growth and Cu accumulation by grapevine, but also the microscopic changes in root tissue at the cell level after the exposure experiment. Based on the BAFs and TFs, the grapevine could be considered a Cu-exclusive plant. For toxic effects on the exposure of roots to Cu, this study also revealed that root growth, as well as the histological changes in rhizodermal cells, can be used as phytotoxic indicators of grapevine under Cu stress.
Environmental Science and Pollution Research 11/2011; 19(4):1315-22. · 2.65 Impact Factor
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ABSTRACT: It has been proposed that irreversible responses of organisms exposed to contaminants are due to a systems-level feedback. Here we tested this hypothesis by reanalyzing the published data on toxicokinetics and survival probability based on a systems-level threshold damage model (TDM) incorporating with a positive damage feedback to explore the steady-state response and dynamic behavior of damage for tilapia and freshwater clam exposed to waterborne arsenic (As). We found that ultrasensitivity appeared in As-tilapia and freshwater clam systems with Hill coefficient n ≥ 4, indicating that the positive damage feedback mechanism has been triggered. We confirmed that damage can trigger a positive feedback loop that together with As stressor increases irreversibility. This study also showed that TDM with positive feedback gave a much better predictability than that of TDM at As concentrations ranging from 100 to 500 mg l(-1) for freshwater clam, whereas for tilapia, two models had nearly same performance on predictability. We suggested that mortality-time profile derived Hill coefficient could be used as a new risk indicator to assess the survival probability for species exposed to waterborne metals. We anticipated that the proposed toxicokinetics/toxicodynamics with a positive damage feedback may facilitate our understanding and manipulation of complex mechanisms of metal susceptibility among species and improve current risk assessment strategies.
Ecotoxicology 11/2011; 21(2):485-95. · 2.36 Impact Factor
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ABSTRACT: The purpose of this study is to conduct a long-term site-specific risk assessment for zinc (Zn) susceptibility of bivalves, green mussel Perna viridis and hard clam Ruditapes philippinarum, based on published experimental data by linking the biologically-based damage assessment model with the subcellular partitioning concept. A comprehensive risk modeling framework was developed to predict susceptibility probability of two bivalve species exposed to waterborne Zn. The results indicated that P. viridis accumulates more Zn toxicity, whereas both toxic potency and the recovery rate of Zn are higher for R. philippinarum. We found that negative linear correlations exist in elimination-recovery and elimination-detoxification relationships, whereas a positive linear correlation was observed in recovery-detoxification relationships for bivalves exposed to waterborne Zn. Simulation results showed that the spatial differences of susceptibility primarily resulted from the variation of waterborne Zn concentration under field conditions. We found that R. philippinarum is more susceptible of Zn than P. viridis under the same exposure condition. Results also suggested that Zn posed no significant susceptibility risk to two bivalve species in Taiwan. We suggested that these two species can be used to biomonitor the water quality on Taiwan coastal areas.
Chemosphere 04/2011; 84(5):707-15. · 3.21 Impact Factor
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ABSTRACT: The purpose of this study is to evaluate the phytoextraction of cadmium (Cd) from contaminated soils by switchgrass (Panicum virgatum L.), which is a promising energy crop with high biomass. Two ecotypes of switchgrass cultivars, Alamo and Blackwell, were investigated in a pot experiment. Dry weight and plant Cd concentration of the switchgrass plants growing on Cd-spiked soils (0, 20, and 60 mg Cd kg(-1) soil) with chelating agent amendments (1 g kg(-1) citric acid [CA] and 0.1 g kg(-1) ethylene diaminetetraacetic acid [EDTA]) were measured to examine the phytotoxicity and accumulation of Cd in the switchgrass. Fractions of Cd (F1, exchangeable; F2, carbonate; F3, Fe-Mn oxide; F4, organic matter; F5, residual) for the soils sampled at the time of harvesting were also determined using chemically sequential extractions. In the results, the dry weight of the switchgrass decreased with increasing Cd, with a significant dry weight reduction when Cd exceeded 20 mg kg(-1). However, the high Cd spike of 60 mg kg(-1) was not lethal to Alamo and Blackwell, which suggests that switchgrass plants can tolerate Cd and grow in contaminated soils. Compared with the control, the CA and EDTA amendments had no adverse effect on the growth of switchgrass plants. With regard to Cd accumulation, higher plant Cd concentrations were frequently found after CA amendment in Alamo; however, the Cd concentrations of Blackwell plants may increase when amended with EDTA. On the basis of the fractionation of soil Cd, dry weight and plant Cd concentration could be expressed as a function of Cd fractionation to predict the phytoextraction of Cd. Thus, the fractionation of Cd is a useful approach for evaluating the phytoextraction of Cd by switchgrass in contaminated soils. According to the comparison of phytoextractions of Cd between Alamo and Blackwell, Alamo plants removed substantially more Cd from Cd-spiked soils than Blackwell. Therefore, Alamo is better suited for the phytoextraction of Cd from contaminated soils.
Ecotoxicology 03/2011; 20(2):409-18. · 2.36 Impact Factor
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ABSTRACT: The purpose of this study was to link toxicokinetics/toxicodynamics and subcellular partitioning for assessing the susceptibility and the growth inhibition risks of abalone Haliotis diversicolor supertexta exposed to waterborne and foodborne cadmium (Cd) and silver (Ag). We reanalyzed published data on growth inhibition and subcellular partitioning associated with the present mechanistic model to explore the correlations among elimination (k (e)), detoxification (k (d)), and recovery (k (r)) rate constants and to assess the growth inhibition risk. We found a positive correlation among k (e), k (d), and k (r) in abalone exposed to Ag. We also employed a life-stage based probabilistic assessment model to estimate the growth inhibition risk of abalone to environmentally relevant Cd (5-995 μg l(-1)) and Ag (0.05-9.95 μg l(-1)) concentrations in Taiwan. The results showed that abalone had a minimum 20% probability of the growth inhibition risk exposed to Cd, whereas Ag exposure was not likely to pose the risk. The maximum biomasses were estimated to be 0.0039 and 0.0038, 61.61 and 43.87, and 98.88 and 62.97 g for larvae, juveniles, and adults of abalone exposed to the same levels of Cd and Ag, respectively. Our study provides a useful tool to detect potential growth biomass of abalone populations subjected to Cd and Ag stresses and mechanistic implications for a long-term ecotoxicological risk assessment in realistic situations.
Ecotoxicology 03/2011; 20(4):912-24. · 2.36 Impact Factor
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ABSTRACT: A major challenge in phytoextraction is to increase plants' removal rates of metals from contaminated soils. In this study, we developed a phytoextraction model, by coupling a saturable Michaelis-Menten type accumulation model and an energy-based toxicity model, to predict copper (Cu) removal by switchgrass (Panicum virgatum L.) grown hydroponically under various exposure concentrations. Results of the present study indicated that the phytotoxicity of Cu to switchgrass is relatively low, whereas a certain accumulation capacity exists in the plant for Cu. In addition, the simulation results suggested that, under a lower dissolved concentration, Cu removal is increased more efficiently as the exposure duration increases. Although it is difficult to extrapolate the results from greenhouse-based hydroponic experiments to field conditions, we believe that the current methodology can offer a first approximation in predicting the phytoextraction duration needed for plant species to remove a specific metal from contaminated sites, which is crucial in evaluating the economic costs for remediation purposes.
Ecotoxicology 03/2011; 20(4):827-35. · 2.36 Impact Factor
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ABSTRACT: The purpose of this study was to use a risk-based integrated-scale toxicological model to examine the impact of waterborne and dietborne cadmium (Cd) toxicity on rainbow trout (Oncorhynchus mykiss) susceptibility appraised with recent published data. A probabilistic assessment model was performed to estimate Cd susceptibility risk. The dose-response models were constructed based on two endpoints of % Cd in metabolically active pool (MAP) and susceptibility time that causes 50% effect (ST50). We further constructed an elimination-detoxification-recovery scheme to enhance the model predictive ability. We found a 95% probability of % Cd in gill and liver MAP exceeding 47-49% and it was likely (70% probability) to have exceeded 52-55%, but it was unlikely (30% probability) to have exceeded 56-60%. In contrast to gill and liver, gut had a relative lower Cd susceptibility risk (15-17% Cd in MAP) with a longer ST50. We suggested that the proposed probabilistic risk assessment framework can incorporate the elimination-detoxification-recovery scheme to help government based biomonitoring and bioassessment programs to prevent potential aquatic ecosystems and human health consequences.
Science of The Total Environment 01/2011; 409(3):503-13. · 3.29 Impact Factor
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ABSTRACT: Risk-based assessment is a way to evaluate the potential hazards of contaminated sites and is based on considering linkages between pollution sources, pathways, and receptors. These linkages can be broken by source reduction, pathway management, and modifying exposure of the receptors. In Taiwan, the Soil and Groundwater Pollution Remediation Act (SGWPR Act) uses one target regulation to evaluate the contamination status of soil and groundwater pollution. More than 600 sites contaminated with heavy metals (HMs) have been remediated and the costs of this process are always high. Besides using soil remediation techniques to remove contaminants from these sites, the selection of possible remediation methods to obtain rapid risk reduction is permissible and of increasing interest. This paper discusses previous soil remediation techniques applied to different sites in Taiwan and also clarified the differences of risk assessment before and after soil remediation obtained by applying different risk assessment models. This paper also includes many case studies on: (1) food safety risk assessment for brown rice growing in a HMs-contaminated site; (2) a tiered approach to health risk assessment for a contaminated site; (3) risk assessment for phytoremediation techniques applied in HMs-contaminated sites; and (4) soil remediation cost analysis for contaminated sites in Taiwan.
International Journal of Environmental Research and Public Health 10/2010; 7(10):3595-614. · 1.61 Impact Factor
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ABSTRACT: Tens of millions of people worldwide ingest excessive amounts of arsenic (As) through drinking water and food. The dietary intake of seafood is the major As exposure route in humans and can cause As-related adverse health effects including cancers. The aim of this study was to quantify potential cancer risks of As exposure for children and adults through seafood consumption. By coupling the age-specific physiologically based pharmacokinetic (PBPK) model and a Weibull-based dose-response function, a more accurate estimate of urinary arsenic metabolites could be achieved to better characterize potential cancer risks. The simulation results show that the proportion of inorganic As, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in human urine are estimated to total 6.7, 26.9, and 66.4% for children, and 6.2, 27.4, and 66.4% for adults, respectively. The estimated median cumulative cancer incidence ratios were respectively 2.67x10(-6) and 3.83x10(-6) for children and adults, indicating a low cancer risk for local residents exposed to As through the consumption of seafood. However, it is necessary to incorporate other exposure routes into the model to make it more realistic. The methodology proposed here can not only be applied to calculate the concentrations of As metabolites in urine, but also to provide a direct estimation of adverse health effects caused by the calculated internal concentrations.
Journal of hazardous materials 09/2010; 181(1-3):161-9. · 4.14 Impact Factor
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ABSTRACT: The main purpose of the present study was to conduct a field investigation to map copper (Cu) vertical distribution in vineyard soils and to investigate the Cu contents in shoots, leaves, and grapes of grapevines in the studied plots in central Taiwan. The mean total Cu concentrations in vineyard soils of the present study ranged from 9.1 to 100 mg kg−1, which were lower than those reported in other vine-growing areas in Brazil and parts of Europe, yet well within the range of those in Canada, Australia, and New Zealand. The Cu concentration in grapevine organs was found to be highest in the leaves, followed by the perennial wood parts, annual shoots, and grapes. The bioaccumulation factors in various organs of the grapevines were mostly greater than unity, indicating that a process of bioaccumulation of Cu occurred in the soil-grapevine system. Results of the present study can be used as one of the risk management factors in making the final decision in examining and refining the existing trigger level of Cu at vine-growing areas.
Soil Science and Plant Nutrition 09/2010; 56(4):601 - 606. · 1.02 Impact Factor
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ABSTRACT: Farming of tilapia Oreochromis mossambicus is an important aquacultural activity in Taiwan. Due to the elevated arsenic (As) concentration in pond water, it is important to assess the bioavailability and toxicity of As to tilapia for protection of aquatic life and human health. In the present study, we developed a biotic ligand model (BLM)-based toxicodynamic approach to dynamically predict both acute and chronic effective concentrations of As to tilapia in two tilapia farms located at Pudai and Chiangchun counties in southwestern Taiwan. Parameters revealed in the mechanistic model were obtained by fitting this model to the toxicokinetic and toxicodynamic data from our previous laboratory experiments. Based on our extended BLM concepts, the site-specific water effect ratios and ambient water quality criteria can be determined with known water chemistry. The proposed methodology was capable of bridging the gap between laboratory toxicity bioassays and field investigations. With respect to risk assessments, our research may also provide an useful means of generating and adjusting the site-specific ambient water quality criteria.
Ecotoxicology 01/2009; 18(3):377-83. · 2.36 Impact Factor
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ABSTRACT: A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models were developed for arsenic (As) in tilapia Oreochromis mossambicus from blackfoot disease area in Taiwan. The PBPK/PD model structure consisted of muscle, gill, gut wall, alimentary canal, and liver, which were interconnected by blood circulation. We integrate the target organ concentrations and dynamic response describing uptake, metabolism, and disposition of As and the associated area-under-curve (AUC)-based toxicological dynamics following an acute exposure. The model validations were compared against the field observations from real tilapia farms and previously published uptake/depuration experimental data, indicating that predicted and measured As concentrations in major organs of tilapia were in good agreement. The model was utilized to reasonably simulate and construct a dose-dependent dynamic response between mortality effect and equilibrium target organ concentrations. Model simulations suggest that tilapia gills may serve as a surrogate sensitive biomarker of short-term exposure to As. This integrated As PBPK/PD/AUC model quantitatively estimates target organ concentration and dynamic response in tilapia and is a strong framework for future waterborne metal model development and for refining a biologically-based risk assessment for exposure of aquatic species to waterborne metals under a variety of scenarios.
Environmental Pollution 06/2005; 135(2):221-33. · 3.75 Impact Factor
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ABSTRACT: We developed a risk-based approach to assess how the valve closure behavior of Asiatic clam Corbicula fluminea responds to waterborne copper (Cu) and cadmium (Cd). We reanalyzed the valve closure response data from published literature to reconstruct the response time-dependent dose-response profiles based on an empirical three-parameter Hill equation model. We integrated probabilistic exposure profiles of measured environmental Cu and Cd concentrations in the western coastal areas of Taiwan with the reconstructed dose-response relationships at different integration times of response to quantitatively estimate the valve response risk. The risk assessment results implicate exposure to waterborne Cu and Cd may pose no significant risk to clam valve activity in the short-time response periods (e.g., <30 min), yet a relative high risk for valve closure response to waterborne Cu at response times greater than 120 min is alarming. We successfully linked reconstructed dose-response profiles and EC50-time relationships associated with the fitted daily valve opening/closing rhythm characterized by a three-parameter lognormal function to predict the time-varying bivalve closure rhythm response to waterborne metals. We parameterized the proposed predictive model that should encourage a risk-management framework for discussion of future design of biological monitoring systems.
Environmental Pollution 05/2005; 135(1):41-52. · 3.75 Impact Factor
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ABSTRACT: A biologically based risk-assessment model of arsenic (As) exposure evaluated farmed tilapia (Orechromis mossambicus) and human health during tilapia consumption in an area of southwestern Taiwan where blackfoot disease (BFD) occurs. The risk assessment addressed exposures to city residents who lived in Taipei, Taichung, and Kaohsiung, as well as subsistence fishers living in the BFD area who consumed tilapia. The models implemented included a physiologically based toxicokinetic and toxicodynamic (PBTK/TD) model to account for As exposure and dose-response profiles in tilapia and a human health exposure/risk model that accounts for target lifetime risk (TR) and hazard quotient (HQ) for humans consuming farmed tilapia. Results demonstrated that 90th percentiles of TR ranged from 1.53 x 10(-8) to 1.62 x 10(-6) for city residents with farmed tilapia consumption rates of 0.41 to 1.37 g/d. The 90th percentiles ranged from 2.07 x 10(-6) to 7.89 x 10(-5) for subsistence fishers in the BFD area with farmed tilapia consumption rates of 16.80 to 59.15 g/d. All predicted 90th percentiles of HQ were less than 1 for city residents and subsistence fishers in the BFD area, indicating small contributions from farmed tilapia consumption. Critical variables included whole-fish body weight, water As content, and As level in tilapia muscle. Although bioaccumulation of As seems unlikely to result in toxicity to farmed tilapia and humans consuming tilapia, the theoretical human health risks in the BFD area are alarming, using a probabilistic risk-assessment model based on conservative assumptions.
Integrated Environmental Assessment and Management 02/2005; 1(1):40-54.
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ABSTRACT: Dietary and nondietary accumulation of waterborne zinc (Zn) by shell of abalone Haliotis diversicolor supertexta was studied to determine if abalone shell can accumulate and eliminate Zn biokinetically. Shell of H. diversicolor supertexta rapidly accumulated Zn at microgram per gram concentrations during a 7-d uptake period for dietary and nondietary exposure to 1 microgml(-1) Zn seawater. Depuration half-lives were 7.22 and 15.40 d for dietary and nondietary exposure, respectively. The uptake rate constants were 5.12 and 4.84 ml g(-1)d(-1), respectively, for dietary and nondietary exposure. The depuration rate constants were 0.048 and 0.10 d(-1), respectively for dietary and nondietary exposure. Results from this study showed that the shell of H. diversicolor supertexta accumulated Zn and that it reflected the composition of the seawater in which the abalone lived. This suggested that the shell of H. diversicolor supertexta can be used as a bioindicator or can act as a receptor to biokinetically eliminate heavy metals from aquatic food webs.
Bioresource Technology 02/2004; 91(2):117-21. · 4.98 Impact Factor
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ABSTRACT: The general objective of our work was to determine the acute toxicity and bioaccumulation of arsenic (As) in tilapia (Oreochromis mossambicus) from the blackfoot disease (BFD) area in Taiwan. The average concentration of As in pond water ranged from 17.8 to 49 microg L(-1). Acute toxicity tests showed that the As concentration that caused toxicity to tilapia ranged from 69 060 microg As L(-1), in the 24-h toxicity test, to 28 680 microg As L(-1), in the 96-h toxicity test. We measured As concentrations in various tissues of tilapia to identify the affinities of tissues for As. Significant correlations were found among the As concentrations in all tissues. The highest bioconcentration factor (BCF) was found in the intestine (maximum value: 2270). The order of BCFs was: intestine > stomach > liver approximately gill > muscle. Arsenic concentrations in all tissues were allometric, negatively correlating with fish body weight [r(2) = 0.63 +/- 0.045 (mean +/- SE), p < 0.05]. Our results also revealed that As concentrations in muscle tissue were positively correlated with As accumulation in the viscera (r(2) = 0.85, p < 0.05). Significantly higher concentrations of As were obtained in the viscera of tilapia [12.65 +/- 10.17 microg g(-1) dry wt (mean +/- SD)] than in the muscle tissue (3.55 +/- 0.42 microg g(-1) dry wt). Our results suggest that a simple way of reducing the health risk associated with consuming tilapia is to trim and cook the fish properly, that is, removing the viscera of tilapia can greatly reduce the amount of As ingested and consequently reduce the health risks.
Environmental Toxicology 09/2003; 18(4):252-9. · 2.41 Impact Factor
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ABSTRACT: We developed a mortality model, by coupling an acute toxicity model and a pharmacodynamic model, to predict survival of abalone (Haliotis diversicolor supertexta) exposed to waterborne zinc (Zn). We conducted a laboratory 14-day exposure experiment to obtain biokinetic parameters of depuration rate constant (k(2)) and bioconcentration factor (BCF). A one-compartment uptake-depuration model was used to fit the exposure data to estimate BCF and k(2) values. The acute toxicity model was developed based on the receptor theory and was verified with LC(50)(t) data obtained from a 7-day acute toxicity test. A highly significant correlation (r(2) = 0.98) was found between predictions and LC(50)(t) data for the acute toxicity model, indicating a successful description of 7-day LC(50)(t) data of Zn in abalone. The predicted time course of lethal body burden of Zn in abalone was compared with measured data, showing that the average percent error was 14.04 +/- 3.02%. A refined pharmacodynamic model was expressed as the Hill equation, which in terms of waterborne Zn and LC(50)(t) data was used to fit observed mortality percentages to determine the Hill coefficient (r(2) = 0.98). The proposed mortality model in terms of whole body burden and lethal body burden at site of action was then employed to predict the time-varying mortality of abalone exposed to various Zn concentrations in pond water. Our results demonstrate that 96-h LC(50) and incipient LC(50) for H. diversicolor supertexta exposed to Zn are 1.1 and 1.05 mg L(-1), respectively. Our predictions also demonstrate that equilibrium lethal body burden at site of action is about 198 microg g(-1), whereas the mortalities never reach 50% when H. diversicolor supertexta exposed to Zn is < or = 1 mg L(-1).
Environmental Toxicology 11/2002; 17(5):478-86. · 2.41 Impact Factor
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ABSTRACT: The purpose of this paper is to synthesize an optimal trace metal biomonitor control system to efficiently manage aquacultural water quality. A biomonitor organism of gastropod mollusc Haliotis diversicolor supertexta was chosen to estimate zinc (Zn) bioaccumulation. The bioaccumulation dynamics of Zn by H. diversicolor supertexta from an alga Gracilaria tenuistipitata var. liui and ambient water in aquaculture ponds is developed based on a six-compartment pharmacokinetic model. A linear control model based on the dynamic bioaccumulation model is developed to design an optimal feedback biomonitor control system. Linear quadratic regulators (LQRs) with output feedback control of a linear-invariant system are assigned for design algorithm and an optimal proportional plus integral (PI) feedback control strategy is synthesized. Numerical results from the model implementation show that the optimal selection of tuning parameters and the resulting costs vary with desired equilibrium state. The designed optimal feedback biomonitor control system, when suitably tuned, gives a satisfactory monitor of mollusc Zn bioaccumulation. The biomonitor control system developed accounting for bioaccumulation dynamics of Zn in the target tissues of molluscs can be used in the future to evaluate the effects of suspended solid removal devices and biofilters and/or other control scenarios on water quality management in aquacultural ecosystems.
Applied Mathematical Modelling.
