Organ-specific toxicokinetics and dose-response of arsenic in tilapia Oreochromis mossambicus

Innovative accumulative risk assessment strategy of co-exposure of As and Pb in medical earthworms based on in vivo-in vitro correlation

Recent studies on risks assessment of heavy metal(loid) are usually based on their total concentrations. Nevertheless, such an analysis does not assess their real amounts absorbed by human body. To scientifically assess the health risks, in this study medical earthworms were analyzed for relative bioavailability (RBA) of arsenic (As) and lead (Pb) using a multiple gavage mouse model with liver, kidneys, brain, and leg bones as biomarkers for the first time. Metal(loid) bioaccessibility was determined using in vitro physiologically based extraction (PBET) assay. We are the first to develop a novel accumulative health risk assessment strategy by combinational analyzing bioavailability of heavy metal(loid) levels to calculate target organ toxicity dose (TTD) modification of the HI and total cancer risk (TCR), which has capacity to evaluate the health risks of co-exposure of Pb and As in medical earthworms. As a result, As-RBA ranged from 7.2% to 45.1%, and Pb-RBA ranged from 16.1% to 49.8%. Additionally, As and Pb bioaccessibility varied from 6.7% to 48.3% and 7.8% to 52.5%, respectively. Moreover, strong in vivo-in vitro correlations (IVIVCs) were observed between metal-RBA and bioaccessibility, indicating the robustness of the in vitro PBET assay to predict metal-RBA in medical earthworms. The refined accumulative assessment strategy revealed that when adjusted by heavy metal(loid) bioavailability, the TTD modification of HI method typically exhibited an acceptable health risk caused by the co-exposure of Pb and As for cardiovascular, hematological, neurological, and renal system. The TCR levels associated with exposure to Pb and As due to the ingestion of medical earthworms were also acceptable after adjustment by bioavailability. Collectively, our innovation on accumulative risk assessment based on in vivo-in vitro correlation provides a novel approach engaging in assessing the risks due to co-exposure of As and Pb in medical earthworms.

Inorganic arsenic causes apoptosis cell death and immunotoxicity on European sea bass (Dicentrarchus labrax)

Inorganic arsenic (As) is one of the most toxic pollutants in the water. We have studied their effects on the marine teleost European sea bass (Dicentrarchus labrax) at 2 and 10 days of 5 μM of As₂O₃ (sub-lethal doses) waterborne exposure. Arsenic accumulates in liver and gill tissues. The expression profile of five genes (bax, blc2, casp3, casp8 and casp9) involved in apoptosis cell death confirmed apoptotic effects in liver, slight changes in gill and no effects in skin according with the histopathology findings. Total IgM level and peroxidase activities were increased at 2 and 10 days, respectively. The bactericidal activity was decreased at 2 days after As exposure. A general decrease of cellular immune activities with significant differences in the case of respiratory burst activity was observed after 2 and 10 days of exposure. This work describes for the first time the effects of As exposure on European sea bass.

Mitochondrial dysfunction, oxidative stress and apoptotic induction in microglial BV-2 cells treated with sodium arsenate

The treatment of microglial BV-2 cells with sodium arsenate (As(V): 0.1-400μmol/L - 48hr) induces a dose-dependent response. The neurotoxic effects of high concentrations of As(V) (100, 200 and 400μmol/L) are characterized by increased levels of mitochondrial complexes I, II, and IV followed by increased superoxide anion generation. Moreover, As(V) triggers an apoptotic mode of cell death, demonstrated by an apoptotic SubG1 peak, associated with an alteration of plasma membrane integrity. There is also a decrease in transmembrane mitochondrial potential and mitochondrial adenosine triphosphate ATP. It is therefore tempting to speculate that As(V) triggers mitochondrial dysfunction, which may lead to defective oxidative phosphorylation subsequently causing mitochondrial oxidative damage, which in turn induces an apoptotic mode of cell death.

A review of toxicity and mechanisms of individual and mixtures of heavy metals in the environment

The rational for the study was to review the literature on the toxicity and corresponding mechanisms associated with lead (Pb), mercury (Hg), cadmium (Cd), and arsenic (As), individually and as mixtures, in the environment. Heavy metals are ubiquitous and generally persist in the environment, enabling them to biomagnify in the food chain. Living systems most often interact with a cocktail of heavy metals in the environment. Heavy metal exposure to biological systems may lead to oxidation stress which may induce DNA damage, protein modification, lipid peroxidation, and others. In this review, the major mechanism associated with toxicities of individual metals was the generation of reactive oxygen species (ROS). Additionally, toxicities were expressed through depletion of glutathione and bonding to sulfhydryl groups of proteins. Interestingly, a metal like Pb becomes toxic to organisms through the depletion of antioxidants while Cd indirectly generates ROS by its ability to replace iron and copper. ROS generated through exposure to arsenic were associated with many modes of action, and heavy metal mixtures were found to have varied effects on organisms. Many models based on concentration addition (CA) and independent action (IA) have been introduced to help predict toxicities and mechanisms associated with metal mixtures. An integrated model which combines CA and IA was further proposed for evaluating toxicities of non-interactive mixtures. In cases where there are molecular interactions, the toxicogenomic approach was used to predict toxicities. The high-throughput toxicogenomics combines studies in genetics, genome-scale expression, cell and tissue expression, metabolite profiling, and bioinformatics.

Citrate coated silver nanoparticles change heavy metal toxicities and bioaccumulation of Daphnia magna

Citrate-coated AgNPs (c-AgNPs) have negatively charged surfaces and their surface interactions with heavy metals can affect metal toxicity in aquatic environments. This study used Daphnia magna to compare the acute toxicities and bioaccumulation of As(V), Cd, and Cu when they interact with c-AgNPs. The 24-h acute toxicities of As(V) and Cu were not affected by the addition of c-AgNPs, while bioaccumulation significantly decreased in the presence of c-AgNPs. In contrast, both the 24-h acute toxicity and bioaccumulation of Cd increased in the presence of c-AgNPs. These toxicity and bioaccumulation trends can be attributed to the interactions between the AgNP surface and the heavy metals. As(V) and c-AgNPs compete by negative charge, decreasing As(V) toxicity. Copper adheres readily to c-AgNP citrate, decreasing Cu bioavailability, and thus reducing Cu toxicity and bioaccumulation. Citrate complexes with divalent cations such as Ca and Mg reduce the competition between divalent cations and Cd on biotic ligand, increasing toxicity and bioaccumulation of Cd. This study shows that surface properties determine the effect of c-AgNPs on heavy metal toxicities and bioaccumulations; hence, further studies on the effect of nanoparticle by it surface properties are warranted.

The arsenic accumulation and its effect on oxidative stress responses in juvenile rockfish, Sebastes schlegelii, exposed to waterborne arsenic (As3+)

Juvenile rockfish (mean length 16.4 ± 1.9 cm, and mean weight 71.6 ± 6.4 g) were exposed for 20 days with the different levels of waterborne arsenic concentration (0, 50, 100, 200 and 400 μg/L). The profile of As accumulation among tissue of rockfish is dependent on the exposure periods and As concentration. After 4 weeks, the highest accumulation of As was observed in the kidney, and the order of As accumulation in tissues was liver > kidney > spleen > gill > intestine > muscle. Generally, significant As accumulation increase in most tissues was observed at the higher concentration of 200 μg/L waterborne As exposure, whereas there was no considerable increase in muscle except the concentration of 400 μg/L at 20 days. In oxidative stress indicators, liver and gill superoxide dismutase (SOD) activity and glutathione-S-transferase (GST) activity were considerably increased after the 20 days exposure. Glutathione (GSH) level in liver and gill was also notably increased in response to the waterborne As exposure after 20 days. The results demonstrated that waterborne As exposure can induce considerable As accumulation in major tissues and alterations in antioxidant enzyme parameters of experimental fish, rockfish.

Immunotoxicological effects of inorganic arsenic on gilthead seabream (Sparus aurata L.)

Arsenic (As) has been associated with multitude of animal and human health problems; however, its impact on host immune system has not been extensively investigated. In fish, there are very few works on the potential risks or problems associated to the presence of arsenic. In the present study we have evaluated the effects of exposure (30 days) to sub-lethal concentrations of arsenic (5 μM As₂O₃) in the teleost fish gilthead seabream (Sparus aurata), with special emphasis in the innate immune response. The arsenic concentration was determined using atomic fluorescence spectrometry (AFS) in liver and muscle of exposed fish showing As accumulation in the liver after 30 days of exposure. The hepatosomatic index was increased at significant extent after 10 days but returned to control values after 30 days of exposure. Histological alterations in the liver were observed including hypertrophy, vacuolization and cell-death processes. Focusing on the immunological response, the humoral immune parameters (seric IgM, complement and peroxidase activities) were no affected to a statistically significant extent. Regarding the cellular innate parameters, head-kidney leucocyte peroxidase, respiratory burst and phagocytic activities were significantly increased after 10 days of exposition compared to the control fish. Overall, As-exposure in the seabream affects the immune system. How this might interfere with fish biology, aquaculture management or human consumers warrants further investigations. This paper describes, for the first time, the immunotoxicological effects of arsenic exposure in the gilthead seabream, which is a species with the largest production in Mediterranean aquaculture.

Assessment of heavy metals in water samples and tissues of edible fish species from Awassa and Koka Rift Valley Lakes, Ethiopia

The Ethiopian Rift Valley Lakes host populations of edible fish species including Oreochromis niloticus, Labeobarbus intermedius and Clarias gariepinus, which are harvested also in other tropical countries. We investigated the occurrence of six heavy metals in tissues of these fish species as well as in the waters of Lake Koka and Lake Awassa. Both lakes are affected by industrial effluents in their catchments, making them ideal study sites. Mercury concentrations were very low in the water samples, but concentrations in the fish samples were relatively high, suggesting a particularly high bioaccumulation tendency as compared with the other investigated metals. Mercury was preferentially accumulated in the fish liver or muscle. It was the only metal with species-specific accumulation with highest levels found in the predatory species L. intermedius. Lower mercury concentrations in O. niloticus could be attributed to the lower trophic level, whereas mercury values in the predatory C. gariepinus were unexpectedly low. This probably relates to the high growth rate of this species resulting in biodilution of mercury. Accumulation of lead, selenium, chromium, arsenic and cadmium did not differ between species, indicating that these elements are not biomagnified in the food chain. Values of cadmium, selenium and arsenic were highest in fish livers, while lead and chromium levels were highest in the gills, which could be related to the uptake pathway. A significant impact of the industrial discharges on the occurrence of metals in the lakes could not be detected, and the respective concentrations in fish do not pose a public health hazard.

Arsenic induced toxicity and histopathological changes in gill and liver tissue of freshwater fish, tilapia (Oreochromis mossambicus)

Acute toxicity of arsenic to tilapia (Oreochromis mossambicus) and its histopathological impacts on gill and liver tissue were evaluated. The median lethal concentration (96 h; LC50) of arsenic (NaAsO₂) was calculated as 28.22 ppm in repeated semi static test method. Fish were exposed to 3 ppm, 28 ppm and 56 ppm concentrations of NaAsO₂ and gill and liver samples were collected after 48 h, 96 h and 192 h of exposure. The changes in gill were characterized by epithelial hyperplasia, epithelial lifting and oedema, lamellar fusion, aneurism, desquamation and necrosis, whereas, the liver tissue showed focal lymphocytic and macrophage infiltration, congestion, vacuolization and shrinkage of hepatocytes, dilation of sinusoids, cloudy swelling, vacuolar degeneration, focal necrosis and nuclear hypertrophy. The result showed that acute arsenic toxicity severely affects the normal behavior and vital organs which is deleterious for the exposed fish.

Toxicokinetics/toxicodynamics links bioavailability for assessing arsenic uptake and toxicity in three aquaculture species

The purpose of this study was to link toxicokinetics/toxicodynamics (TK/TD) and bioavailability-based metal uptake kinetics to assess arsenic (As) uptake and bioaccumulation in three common farmed species of tilapia (Oreochromis mossambicus), milkfish (Chanos chanos), and freshwater clam (Corbicula fluminea). We developed a mechanistic framework by linking damage assessment model (DAM) and bioavailability-based Michaelis-Menten model for describing TK/TD and As uptake mechanisms. The proposed model was verified with published acute toxicity data. The estimated TK/TD parameters were used to simulate the relationship between bioavailable As uptake and susceptibility probability. The As toxicity was also evaluated based on a constructed elimination-recovery scheme. Absorption rate constants were estimated to be 0.025, 0.016, and 0.175 mL g(-1) h(-1) and As uptake rate constant estimates were 22.875, 63.125, and 788.318 ng g(-1) h(-1) for tilapia, milkfish, and freshwater clam, respectively. Here we showed that a potential trade-off between capacities of As elimination and damage recovery was found among three farmed species. Moreover, the susceptibility probability can also be estimated by the elimination-recovery relations. This study suggested that bioavailability-based uptake kinetics and TK/TD-based DAM could be integrated for assessing metal uptake and toxicity in aquatic organisms. This study is useful to quantitatively assess the complex environmental behavior of metal uptake and implicate to risk assessment of metals in aquaculture systems.

Detoxification and bioregulation are critical for long-term waterborne arsenic exposure risk assessment for tilapia

Long-term metal exposure risk assessment for aquatic organism is a challenge because the chronic toxicity of chemical is not only determined by the amount of accumulated chemical but also affected by the ability of biological regulation or detoxification of biota. We quantified the arsenic (As) detoxification ability of tilapia and developed a biologically based growth toxicity modeling algorithm by integrating the process of detoxification and active regulations (i.e., the balance between accumulated dose, tissue damage and recovery, and the extent of induced toxic effect) for a life span ecological risk prediction. Results showed that detoxification rate (k (dex)) increased with increasing of waterborne As when the accumulated metal exceeded the internal threshold level of 19.1 μg g( - 1). The k (dex) values were comparable to or even higher than the rates of physiological loss and growth dilution in higher exposure conditions. Model predictions obtained from the proposed growth toxicity model were consistent with the measured growth data. The growth toxicity model was also used to illustrate the health condition and growth trajectories of tilapia from birth to natural death under different exposure scenarios. Results showed that temporal trends of health rates and growth trajectories of exposed fish in different treatments decreased with increasing time and waterborne As, revealing concentration-specific patterns. We suggested that the detoxification rate is critical and should be involved in the risk assessments framework. Our proposed modeling algorithm well characterizes the internal regulation activities and biological response of tilapia under long-term metal stresses.

Hematological, biochemical and ionoregulatory responses of Indian major carp Catla catla during chronic sublethal exposure to inorganic arsenic

In the present study the acute toxicity of arsenic trioxide in fingerlings of Catla catla an Indian major carp was evaluated with renewal bioassay method. The median lethal concentration of arsenic trioxide to the fish C. catla for 96 h was found to be 20.41 ppm (with 95% confidence limits). From this a non-lethal dose of (2.041 ppm; 1/10th of LC 50 96 value) was selected and fingerlings were exposed to 35 d and hematological, biochemical and ionoregulatory responses were studied at days 7, 14, 21, 28 and 35. Arsenic trioxide produced a significant increase in hemoglobin, hematocrit, WBC count, plasma GPT levels and reduction in RBC count, plasma sodium, chloride, potassium, glucose, protein, GOT, LDH levels as compared to the control group. Gill Na(+)/K(+)-ATPase activity was influenced by arsenic trioxide exposure. A biphasic response was noted in the value of MCH and MCV. However the MCHC level was not altered in arsenic trioxide treated fish throughout the study period. Results of the present investigation suggest that arsenic trioxide affects the hematological, biochemical and ionoregulatory parameters of fish and alterations of these parameters can be useful in environmental biomonitoring of arsenic contamination.

Systems-level modeling the effects of arsenic exposure with sequential pulsed and fluctuating patterns for tilapia and freshwater clam

The purpose of this paper was to use quantitative systems-level approach employing biotic ligand model based threshold damage model to examine physiological responses of tilapia and freshwater clam to sequential pulsed and fluctuating arsenic concentrations. We tested present model and triggering mechanisms by carrying out a series of modeling experiments where we used periodic pulses and sine-wave as featured exposures. Our results indicate that changes in the dominant frequencies and pulse timing can shift the safe rate distributions for tilapia, but not for that of freshwater clam. We found that tilapia increase bioenergetic costs to maintain the acclimation during pulsed and sine-wave exposures. Our ability to predict the consequences of physiological variation under time-varying exposure patterns has also implications for optimizing species growing, cultivation strategies, and risk assessment in realistic situations.

Bioavailability links mode of action can improve the long-term field risk assessment for tilapia exposed to arsenic

The objective of this paper was to develop a mechanistic-based framework to explicitly incorporate the factors controlling the bioavailability, toxicodynamics and mode of action to enhance predictive ability of arsenic (As) toxicity to protect the health of farmed tilapia Oreochromis mossambicus. We linked the biotic ligand model and damage assessment model to develop a toxicokinetic model for elucidating the site-specific temporal changes of As bioavailability and to characterize how the fish regulate the metal toxicity. We built a bioavailability-mode of action-based growth toxicity model by linking a bioenergetic growth model and damage assessment model to predict how the As affects on the tilapia growth in the entire life span in site-specific field ecosystems. Here we show that the proposed model well describes the water-chemistry-dependent toxicokinetics and toxicodynamics variations of As to tilapia. We selected two local tilapia farms with different water chemistries located at southwestern Taiwan coast region to implement the proposed algorithm to predict the risk of As exposure. Results indicate that the growth toxicity of O. mossambicus in Taihsi is more sensitive than that in Peimen. We found that the effect of ion competition on the As bioavailability and their ecotoxicological effects on tilapia are more obvious in Taihsi comparing with that in Peimen. We suggested that the proposed bioavailability- and mode of action-based framework can be used to capture the biological response and regulation of tilapia to As exposures. It is applicable for a site-specific and long-term ecotoxicological risk assessment.

Chronic exposure to low concentration of arsenic is immunotoxic to fish: role of head kidney macrophages as biomarkers of arsenic toxicity to Clarias batrachus

The present study was aimed at elucidating the effect of chronic low-level arsenic exposure on the head kidney (HK) of Clarias batrachus and at determining the changes in head kidney macrophage (HKM) activity in response to arsenic exposure. Chronic exposure (30 days) to arsenic (As(2)O(3), 0.50 microM) led to significant increase in arsenic content in the HK accompanied by reduction in both HKM number and head kidney somatic index (HKSI). Arsenic induced HK hypertrophy, reduction in melano-macrophage population and increased hemosiderin accumulation. Transmission electron microscopy of 30 days exposed HKM revealed prominent endoplasmic reticulum, chromatin condensation and loss in structural integrity of nuclear membrane. Head kidney macrophages from exposed fish demonstrated significant levels of superoxide anions but on infection with Aeromonas hydrophila were unable to clear the intracellular bacteria and died. Exposure-challenge experiments with A. hydrophila revealed that chronic exposure to micromolar concentration of arsenic interfered with the phagocytic potential of HKM, helped in intracellular survival of the ingested bacteria inside the HKM inducing significant HKM cytotoxicity. The immunosuppressive effect of arsenic was further evident from the ability of A. hydrophila to colonize and disseminate efficiently in exposed fish. Enzyme linked immunosorbent assay indicated that chronic exposure to arsenic suppressed the production of pro-inflammatory 'IL-1beta like' factors from HKM. It is concluded that arsenic even at very low concentration is immunotoxic to fish and the changes observed in HKM may provide a useful early biomarker of low-level xenobiotic exposure.

A biotic ligand model-based toxicodynamic approach to predict arsenic toxicity to tilapia gills in cultural ponds

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.

Arsenic cancer risk posed to human health from tilapia consumption in Taiwan

Ingested inorganic arsenic is strongly associated with a wide spectrum of adverse health outcomes. We propose a bioaccumulation and the Weibull model-based epidemiological framework to accurately estimate the reference arsenic intake guideline for tilapia consumption and tilapia-cultured water arsenic concentration based on bioaccumulations of tilapia and gender/age/cancer-specific epidemiological data from the arseniasis-endemic area in Taiwan. Our results show a positive relationship between arsenic exposure and age/gender- and cancer-specific cumulative incidence ratio using Weibull dose-response model. Based on male bladder cancer with an excess lifetime cancer risk of 10(-4), we estimate the reference tilapia inorganic arsenic guideline value to be 0.084 microg g(-1) dry wt based on the suggested daily consumption rate of 120 gd(-1). Our findings show that consumption of tilapia in a blackfoot disease (BFD)-endemic area poses no significant cancer risk (excess cancer risks ranging from 3.4 x 10(-5) to 9.3 x 10(-5)), implying that people in BFD-endemic areas are not readily associated with higher fatalities for bladder cancer exposed from tilapia consumption. We are confident that our model can be easily adapted for other aquaculture species, and encourage risk managers to use the model to evaluate the potential population-level long-term low-dose cancer risks. We conclude that, by integrating the bioaccumulation concept and epidemiological investigation of humans exposed to arsenic, we can provide a scientific basis for risk analysis to enhance risk management strategies.

Sub-lethal concentration of arsenic interferes with the proliferation of hepatocytes and induces in vivo apoptosis in Clarias batrachus L

We studied the hepatocellular alterations induced by sub-lethal concentrations (0.50 muM) of arsenic in Indian catfish Clarias batrachus L. Sub-lethal arsenic exposure altered serum aspartate aminotransferase and alkaline phosphatase levels and brought about significant changes in different serum biochemical parameters. Arsenic exposure reduced total hepatocyte protein content and suppressed the proliferation of hepatocytes in a time-dependent manner. Routine histological studies on liver documented arsenic-induced changes characterized by dilated sinusoids, formation of intracellular edema, megalocytosis, vacuolation and appearance of hepatic cells with distorted nuclei. Transmission electron microscopy of hepatocytes further revealed hyperplasia and hypertrophy of mitochondria, development of dilated rough endoplasmic reticulum and changes in peroxisome size with duration of arsenic exposure. Degeneration of mitochondrial cristae and condensation of chromatin was also evident in arsenic-exposed hepatocytes. A significant number of hepatocytes isolated from arsenic-exposed fish stained with annexin V and demonstrated DNA ladder characteristic of apoptosis. Single-cell gel electrophoresis of exposed hepatocytes also revealed the development of comets usually seen in apoptotic cells. Using specific inhibitors it was determined that the arsenic-induced apoptosis of hepatocytes was caspase-mediated, involving the caspase 3 pathway.

Long-term exposure to arsenic affects head kidney and impairs humoral immune responses of Clarias batrachus

The present study was aimed at determining the effects of long-term arsenic exposure on the head kidney (HK) and ensuing humoral immune responses in Clarias batrachus L. Long-term exposure (150 days) to non-lethal concentrations of arsenic (42.42 microM) resulted in significant time-dependent alterations in HK cell number eventually affecting the HK somatic index. Prolonged exposure to arsenic also suppressed HK-B cell proliferation and led to significant reduction in serum immunoglobulin levels and antigen-specific serum bacterial agglutinin titers. A decline in the number of antigen-specific plaque-forming cells with duration of arsenic exposure was noted in the HK. Enzyme linked immunosorbent assays further revealed that arsenic exposure inhibited the release of "IL-4 like factors" from HK-T cells. Histological studies documented time-dependent changes in the structure and cellular composition of HK characterized by extensive lymphocytopenia, decrease in melano-macrophage population and hemosiderin accumulation. From exposure-challenge studies with Aeromonas hydrophila it was evident that pathogens could efficiently disseminate and colonize distant host tissues in the exposed fish. Moreover, the ability to decrease the pathogen load was also significantly reduced in the arsenic-exposed fish. Thus long-term exposure to non-lethal concentrations of arsenic affects HK and interferes with the humoral immune system of C. batrachus rendering them immunocompromised and susceptible to pathogenic challenge.

Perturbations in the catfish immune responses by arsenic: organ and cell specific effects

The present study was an attempt to elucidate the effect of non-lethal arsenic (As) exposure (1/10 LC50) on different immunologically important organs and cells of a catfish. Clarias batrachus L. were exposed to arsenic trioxide for different time intervals, which resulted in significant, time-dependent changes in total head kidney and splenic leucocyte count (p<0.05) and reduction in the organosomatic indices (p<0.05) of these two important immunocompetent organs. Routine histological studies revealed arsenic induced changes in the cellular composition of head kidney and spleen. Arsenic also induced time-dependent and tissue-specific alterations in T and B cell functioning in catfish. When checked for its effects on macrophages, it was noted that arsenic interfered with bacterial phagocytosis. Furthermore, arsenic affected the general immune status of C. batrachus and rendered the fish immunocompromised and susceptible to pathogens.

Bioenergetics-based matrix population modeling enhances life-cycle toxicity assessment of tilapia Oreochromis mossambicus exposed to arsenic

The objective of this study was to integrate a bioenergetics-based modeling approach into a population stage structure to enhance life-cycle toxicity assessments of the effects of waterborne arsenic (As) on the population dynamics of the tilapia Oreochromis mossambicus. The proposed mathematical model links a Leslie matrix population model and a universal ontogenetic growth model embedding the population-level growth rate and stage-specific modes of toxic action. We present data analyses of key parameters and distributions and discuss the processes of data capture and analysis and the impact of acute/chronic As toxicity responses on population-level effects. We employed a three-parameter Hill equation model to describe the relationship between tilapia whole-body burden and mortality in order to estimate the probability of stage-specific vital rate of survival. Using the DEBtox theory, we distinguished three modes of toxic action (MOA): direct effects on growth and indirect effects via maintenance and food consumption on inhibition by arsenic of the growth of a tilapia population. The asymptotic population growth rate decreased from lambda = 1.0027 for the control group to lambda = 0.9935 for tilapia population exposed to 4 microg mL(-1) As, indicating a potential risk of population intrinsic growth rates for tilapia exposed to higher levels of waterborne As. Our results estimated that an As concentration of 1.02 microg mL(-1) would cause a 50% reduction in the tilapia population. We found that the interplay between external stressors of waterborne As concentration and internally generated modes of action decreasing feeding in the juvenile stage and increasing the maintenance cost in the adult stage had a pronounced influence on the population stage structure of tilapia.

Mode of action and growth toxicity of arsenic to tilapia Oreochromis mossambicus can be determined bioenergetically

We present a bioenergetics-based approach to analyze the chronic effects and growth toxicity mode of action in tilapia Oreochromis mossambicus exposed to waterborne As and to predict fish growth under different exposure scenarios. 7-day exposure bioassays showed that tilapia accumulate As when exposed to waterborne As. We conducted growth bioassays to assess chronic As toxicity to tilapia. We incorporated a universal ontogenetic growth model with the DEB(tox )theory to explore the mode of action of As toxicity. Our results show that the specific growth rates of exposed tilapia are inversely proportional to As concentrations and are calculated as 0.76% d(-1) in 0 microg mL(-1), 0.57% d(-1) in 1 microg mL(-1), 0.2 % d(-1) in 2 microg mL(-1), and 0.04% d(-1) in 4 microg mL(-1) As, respectively. We showed that the internal threshold concentration did not change significantly with time, demonstrating that the critical body residue approach is applicable for As toxicity assessment. We distinguished between three modes of action of As, including direct effects on growth and indirect effects by way of maintenance and food consumption. Our results support that decreased feeding accounts for the growth decrease in the case of feeding ad libitum. The feeding decrease model also illustrates the growth trajectories of tilapia during the entire whole life span, suggesting that the maximum biomass of tilapia are 1038.75 g in uncontaminated water and 872.97 g in 1 microg mL(-1), 403.06 g in 2 microg mL(-1), and 336.65 g in 4 microg mL(-1) As, respectively. We suggest that considering modes of action in ecotoxicology not only improves our understanding of the toxicities of chemicals, it is also useful in setting up models and avoiding pitfalls in species- and site-specific environmental risk assessment. This proposed framework for tilapia gives preliminary information relevant to aquacultural and ecologic management.

Dynamical coupling of PBPK/PD and AUC-based toxicity models for arsenic in tilapia Oreochromis mossambicus from blackfoot disease area in Taiwan

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.