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Abstract: The fish acute toxicity test method is foundational to aquatic toxicity testing strategies, yet the literature lacks a concise sample size assessment. Although various sources address sample size, historical precedent seems to play a larger role than objective measures. We present a novel and comprehensive quantification of the effect of sample size on estimation of the median lethal concentration (LC50), covering a wide range of scenarios. The results put into perspective the practical differences across a range of sample sizes, from n = 5/concentration up to n = 23/concentration. We also provide a framework for setting sample size guidance illustrating ways to quantify the performance of LC50 estimation, which can be used to set sample size guidance given reasonably difficult (or worst‐case) scenarios. There is a clear benefit to larger sample size studies: they reduce error in the determination of LC50s, and lead to more robust safe environmental concentration determinations, particularly in cases likely to be called worst‐case (shallow slope and true LC50 near the edges of the concentration range). Given that the use of well‐justified sample sizes is crucial to reducing uncertainty in toxicity estimates, these results lead us to recommend a reconsideration of the current de minimis 7/concentration sample size for critical studies (e.g., studies needed for a chemical registration, which are being tested for the first time, or involving difficult test substances). Environ Toxicol Chem 2018;37:1565–1578. © 2018 SETAC [ABSTRACT FROM AUTHOR]

Abstract: Offspring of wild adult brown trout exposed to a range of Se concentrations were reared in a laboratory setting to primarily assess effects on survival and deformities. Maternal whole‐body Se concentrations ranged from 4.7 to 22.6 mg/kg dry weight for wild fish. Corresponding Se concentrations in embryos ranged from 6.2 to 40.3 mg/kg dry weight. Significant relationships were found between embryo and whole‐body tissue concentrations. Increasing egg Se concentrations were correlated with decreasing survival; however, hatch success was not significantly correlated with increasing embryo Se. The best fit effect concentration, 10% (EC10) for survival in the hatch to swim‐up period was 20.6 mg/kg dry weight, and the EC10 for hatch to test termination at 88 d was 20.5 mg/kg dry weight egg Se. The best fit model for deformities was based on a baseline‐adjusted severity index and resulted in an EC10 of 21.8 mg/kg dry weight egg Se. Both the best fit model EC10s represent more sensitive values than the published range of trout species EC10s. An egg to whole‐body tissue conversion factor derived from the paired data resulted in a conversion factor for brown trout of 1.46, which resulted in a whole‐body tissue EC10 of 14.04 mg/kg dry weight at an egg tissue EC10 of 20.5 mg/kg dry weight. Environ Toxicol Chem 2018;37:1396–1408. © 2018 SETAC [ABSTRACT FROM AUTHOR]

Abstract: In 2013 the Organisation for Economic Co‐operation and Development (OECD) test guideline (236) for fish embryo acute toxicity (FET) was adopted. It determines the acute toxicity of chemicals to embryonic fish. Previous studies show a good correlation of FET with the standard acute fish toxicity (AFT) test; however, the potential of the FET test to predict AFT, which is required by the Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) regulation (EC 1907/2006) and the Classification, Labelling and Packaging (CLP) Regulation (EC 1272/2008), has not yet been fully clarified. In 2015 the European Chemicals Agency (ECHA) requested that a consultant perform a scientific analysis of the applicability of FET to predict AFT. The purpose was to compare the toxicity of substances to fish embryos and to adult fish, and to investigate whether certain factors (e.g., physicochemical properties, modes of action, or chemical structures) could be used to define the applicability boundaries of the FET test. Given the limited data availability, the analysis focused on organic substances. The present critical review summarizes the main findings and discusses regulatory application of the FET test under REACH. Given some limitations (e.g., neurotoxic mode of action) and/or remaining uncertainties (e.g., deviation of some narcotic substances), it has been found that the FET test alone is currently not sufficient to meet the essential information on AFT as required by the REACH regulation. However, the test may be used within weight‐of‐evidence approaches together with other independent, relevant, and reliable sources of information. The present review also discusses further research needs that may overcome the remaining uncertainties and help to increase acceptance of FET as a replacement for AFT in the future. For example, an increase in the availability of data generated according to OECD test guideline 236 may provide evidence of a higher predictive power of the test. Environ Toxicol Chem 2018;37:657–670. © 2017 SETAC [ABSTRACT FROM AUTHOR]

Abstract: Testing for acute fish toxicity is an integral part of the environmental safety assessment of chemicals. A true replacement of primary fish tissue was recently proposed using cell viability in a fish gill cell line (RTgill‐W1) as a means of predicting acute toxicity, showing good predictivity on 35 chemicals. To promote regulatory acceptance, the predictivity and applicability domain of novel tests need to be carefully evaluated on chemicals with existing high‐quality in vivo data. We applied the RTgill‐W1 cell assay to 38 fragrance chemicals with a wide range of both physicochemical properties and median lethal concentration (LC50) values and representing a diverse range of chemistries. A strong correlation (R2 = 0.90–0.94) between the logarithmic in vivo LC50 values, based on fish mortality, and the logarithmic in vitro median effect concentration (EC50) values based on cell viability was observed. A leave‐one‐out analysis illustrates a median under‐/overprediction from in vitro EC50 values to in vivo LC50 values by a factor of 1.5. This assay offers a simple, accurate, and reliable alternative to in vivo acute fish toxicity testing for chemicals, presumably acting mainly by a narcotic mode of action. Furthermore, the present study provides validation of the predictivity of the RTgill‐W1 assay on a completely independent set of chemicals that had not been previously tested and indicates that fragrance chemicals are clearly within the applicability domain. Environ Toxicol Chem 2018;37:931–941. © 2017 SETAC [ABSTRACT FROM AUTHOR]

Long-term effect assessments in ecotoxicological investigations are important, yet there is a lack of suitable exposure systems for these experiments that can be used for riverine species. A cost-efficient miniature circulatory system was developed that was evaluated for its applicability in long-term exposures in 2 stream-dwelling species: brown trout ( Salmo trutta) and an amphipod ( Gammarus roeseli). In an egg-to-fry exposure of S. trutta, the toxicity of 2 reverse osmosis concentrates was investigated as examples. Control hatching rate of yolk sac fry was 75 ± 7% and thus complies with the Organisation for Economic Co-operation and Development validity criterion (≥66%). The reverse osmosis concentrates did not impair the hatching rate in any tested concentration. In G. roeseli, mortality rates remained below 20% during a 21-d cultivation, fulfilling the common validity criterion in ecotoxicological testing. Mortality was significantly lower when the species was fed with conditioned alder leaves instead of an artificial shrimp food. Finally, a toxicity test on G. roeseli using copper as the test substance revealed median lethal concentration (LC50) values of 156 μg/L after 96 h and 99 μg/L after 264 h, which is in line with literature findings using other accepted exposure units. In conclusion, the miniature circulatory system provides a novel and cost-efficient exposure system for long-term investigations on riverine species that may also be applicable for other species of fishes and macroinvertebrates. Environ Toxicol Chem 2016;35:2827-2833. © 2016 SETAC [ABSTRACT FROM AUTHOR]

The need for alternative approaches to the use of vertebrate animals for hazard assessment of chemicals and pollutants has become of increasing importance. It is now the first consideration when initiating a vertebrate ecotoxicity test, to ensure that unnecessary use of vertebrate organisms is minimized wherever possible. For some regulatory purposes, the use of vertebrate organisms for environmental risk assessments has been banned; in other situations, the number of organisms tested has been dramatically reduced or the severity of the procedure refined. However, there is still a long way to go to achieve a complete replacement of vertebrate organisms to generate environmental hazard data. The development of animal alternatives is based not just on ethical considerations but also on reducing the cost of performing vertebrate ecotoxicity tests and in some cases on providing better information aimed at improving environmental risk assessments. The present Focus article provides an overview of the considerable advances that have been made toward alternative approaches for ecotoxicity assessments over the last few decades. Environ Toxicol Chem 2016;35:2637-2646. © 2016 SETAC [ABSTRACT FROM AUTHOR]

Environmental management decisions at mercury-contaminated sediment sites are predicated on the understanding of risks to various receptors, including fish. Toxicity reference values (TRVs) for interpreting risks to fish have been developed to assess mercury concentrations in fish or fish prey. These TRVs were systematically evaluated based on several lines of evidence. First, their conceptual basis and specific derivation were evaluated, including a close review of underlying toxicity studies. Second, case studies were reviewed to investigate whether TRVs are predictive of effects on fish populations in the field. Third, TRVs were compared with available information regarding preindustrial and present-day background concentrations of mercury in fish. The findings show that existing TRVs are highly uncertain, because they were developed using limited data from studies not designed for TRV derivation. Although field studies also entail uncertainty, several case studies indicate no evidence of adverse effects despite mercury exposures that exceed the available TRVs. Some TRVs also fall within the range of background mercury concentrations in predatory or prey fish. Lack of information on the selenium status of mercury-exposed fish is a critical confounding factor, and the form of methylmercury used in toxicity testing may also contribute to differences between TRV-based predictions and field observations of mercury effects on fish. On balance, the available information indicates that several of the TRVs reviewed are lower than necessary to protect fish populations. The 20% effect concentration from a previously published dose-response analysis appears closer to an effect threshold, based on available laboratory data. Additional research is needed to provide a stronger basis to establish dose-response relationships for mercury effects on fish. Environ Toxicol Chem 2016;35:529-549. © 2016 SETAC [ABSTRACT FROM AUTHOR]

The present study determined concentrations of estrogenic bisphenol A (BPA), nonylphenol, octylphenol (4-tert-octylphenol), butylphenol (4-tert-butylphenol), and progestogenic norethindrone by liquid chromatography-tandem mass spectrometry in bile extracts from field fish from the Xin'an River and market fish in Shanghai, China. Compared with the field fish, endocrine disrupting chemical (EDC) concentrations in market fish bile were at relatively high levels with high detectable rates. The average concentrations of BPA, nonylphenol, 4-tert-octylphenol, 4-tert-butylphenol, and norethindrone in field fish bile were 30.1 µg/L, 203 µg/L, 4.69 µg/L, 7.84 µg/L, and 0.514 µg/L, respectively; in market fish bile they were 240 µg/L, 528 µg/L, 76.5 µg/L, 12.8 µg/L, and 5.26 µg/L, respectively; and in the surface water of Xin'an River they were 38.8 ng/L, 7.91 ng/L, 1.98 ng/L, 2.66 ng/L, and 0.116 ng/L, respectively. The average of total estrogenic activity of river water was 3.32 ng/L estradiol equivalents. High bioconcentration factors (BCFs) were discovered for all 5 EDCs (998-fold) in field fish bile. Furthermore, the authors analyzed the BCF value of BPA in fish bile after 30-d exposure to environmentally relevant concentrations of BPA in the laboratory, and the analysis revealed that BCF in fish bile (BCFFish bile) changed in an inverse concentration-dependent manner based on the log10-transformed BPA concentration in water. Strikingly, the data from the field study were well fitted within this trend. The data together suggested that analysis of fish bile extracts could be an efficient method for assessing waterborne EDCs exposure for aquatic biota. [ABSTRACT FROM AUTHOR]

Pyrethroid insecticides can affect salmonids either indirectly through toxicity to their prey or directly by toxicity to the fish themselves. In support of a study on pyrethroid impacts to Chinook salmon and steelhead trout in the American River (Sacramento, California, USA), 96-h median effective concentration (EC50) and median lethal concentration (LC50) values for the pyrethroid bifenthrin were determined for taxa not traditionally used for toxicity testing but of interest as salmonid prey, including a chironomid, caddisflies, mayflies, and stoneflies. A laboratory was constructed on the banks of the American River to expose macroinvertebrates, Chinook salmon, and steelhead trout to flow-through river water containing urban runoff during storm events. Bifenthrin from urban runoff was found in river water following 5 rain events, reaching 14.6 ng/L. Mortality to the exposed salmonids was not observed, and sublethal effects were not seen in vitellogenin or sex steroid levels. Indirect effects via toxicity to salmonid prey are possible. Mortality to Hyalella azteca, a potential prey, was observed in every event tested, and peak bifenthrin concentrations were comparable to the 96-h EC50 of the caddisfly, Hydropsyche sp., the most important prey species on a biomass basis for American River Chinook salmon. The other invertebrates tested had EC50s exceeding bifenthrin concentrations seen in the American River, though could potentially be at risk at concentrations previously reported in smaller urban tributaries. Environ Toxicol Chem 2015;34:649-657. © 2014 SETAC [ABSTRACT FROM AUTHOR]

As a result of the stringent data requirements of the Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) regulation, a vast amount of ecotoxicological data has become available through the dissemination portal of the European Chemicals Agency (ECHA). As of April 2014, the database contained 12 439 unique substances from 47 909 dossiers. This vast database could be used to refine existing, or to create new, non-testing methods, such as quantitative structure-activity relationships (QSARs). Acute fish toxicity data were mined from the ECHA database using the eChemPortal; after filtering for single organic substances, 1159 experimental data points remained, representing 564 compounds. To evaluate the quality and accessibility of this data, the authors used the data to refine and improve an existing QSAR. The reliability of the data submitted to the ECHA database, as well as the effectiveness of the Klimisch scoring system, were assessed by comparing the refined QSAR with established QSAR benchmarks. The model developed meets all Organisation for Economic Co-operation and Development principles, has strong internal (leave-one-out internally cross-validated correlation coefficient [Q2LOO] = 0.91) and external (external coefficient of determination (predicted vs experimental [test set])) validation statistics, and can provide reliable fish median lethal concentration (LC50) predictions for non-polar narcotics. Although some issues with dossier misinformation were discovered, it was found that the ECHA dissemination portal is a valuable and reliable data source. When queried using the eChemPortal, chemical dossiers containing reliable data could be found quickly. The ECHA dissemination portal holds great potential for future QSAR development and improvement, such as updating QSARs within the Ecological Structure-Activity Relationships (ECOSAR) program. Environ Toxicol Chem 2014;9999:1-10. © 2014 SETAC [ABSTRACT FROM AUTHOR]

Atlantic herring ( Clupea harengus) embryos were exposed to water accommodated fractions (WAFs; oil dissolved in water) and chemically enhanced water accommodated fractions (CEWAFs; oil dispersed in water with Corexit 9500A) of Medium South American (MESA) crude oil. The CEWAF was approximately 100-fold more toxic than WAF based on nominal loadings of test solutions (% v/v). In contrast, the ratio of WAF and CEWAF toxicity expressed as measured oil concentrations approximated 1.0, indicating that the higher toxicity of CEWAFs was caused by an increase in exposure to hydrocarbons with chemical dispersion. In a second experiment, the chronic toxicity of Corexit 9500A and chemically dispersed heavy fuel oil 7102 (HFO 7102) to rainbow trout ( Oncorhynchus mykiss) embryos was compared to chemically dispersed Nujol, a nontoxic mineral oil. Dispersant alone was toxic, but caused different signs of toxicity than HFO 7102. Nujol at a dispersant-to-oil ratio of 1:20 was nontoxic, suggesting that dispersant was sequestered by oil and not present at toxic concentrations. In contrast, the same nominal loadings of dispersed HFO 7102 caused concentration-dependent increases in toxicity. Both experiments suggest that chemically dispersed oil was more toxic to fish embryos than solutions created by mechanical mixing due to the increased exposure of fish to petroleum hydrocarbons and not to changes in hydrocarbon toxicity. The Nujol control discriminated between the toxicity of oil and chemical dispersant and would be a practical addition to programs of dispersant testing. Environ Toxicol Chem 2014;33:107-114. © 2013 SETAC [ABSTRACT FROM AUTHOR]

Diclofenac (DCF) is a widely used nonsteroidal anti-inflammatory drug that is regularly detected in surface waters. To support a robust aquatic risk assessment, two early life stage (ELS) tests, compliant with the Organisation for Economic Co-operation and Development (OECD) test guideline 210, were conducted in rainbow trout and in zebrafish. Population relevant endpoints, such as hatching, growth, and survival, and in the trout study, histopathological effects in potential target organs, were examined. The bioconcentration of DCF in rainbow trout was measured in a separate study according to OECD test guideline 305. The bioconcentration factor (BCF) in rainbow trout remained below 10, demonstrating no relevant bioconcentration of DCF in fish. In the rainbow trout ELS test, the no observed effect concentration (NOEC) including histopathology was 320 µg/L. The effect of DCF on zebrafish growth was less clear, and the NOEC can be interpreted as 10 µg/L. However, for a number of reasons, the authors consider the moderately reduced growth of zebrafish exposed to concentrations of up to 320 µg/L not a repeatable, treatment-related effect of DCF. This leads us to a conclusion that DCF has, with high probability, no adverse effect on both fish species up to 320 µg/L. This NOEC indicates a sufficient safety margin for fish populations, because concentrations of DCF in European rivers are in the range of ng/L to low µg/L. Environ. Toxicol. Chem. 2013;32:442-452. © 2013 SETAC [ABSTRACT FROM AUTHOR]

Existing standard bioconcentration tests (e.g., the Organization for Economic Cooperation and Development [OECD] test guideline 305) require large numbers of test animals and resources. The minimized aqueous exposure test is a new approach based on the standard bioconcentration test but allows estimation of bioconcentration factor (BCF) by minimized sampling of the test fish. The authors collected BCF data (298 curves from 155 chemicals, using common carp as test species) from Japan's Chemical Substances Control Law database and resampled the data to simulate the calculation of BCF that would be obtained if studies had been designed to obtain kinetic BCF derived from minimized aqueous exposure tests (BCFkm). The correlation was high ( r2 = 0.967) between BCF derived from standard bioconcentration tests (BCFfull) and BCFkm. The average value of the BCFfull to BCFkm ratio (BCFfull:BCFkm) was 1.04 and ranged from 0.54 to 1.93, the 5th and 95th percentiles being 0.74 and 1.45, respectively. The results based on the 5th and 95th percentiles of the BCFfull:BCFkm ratio suggest that BCFfull 2,000 corresponds to BCFkm 1,400 to 2,700, whereas BCFfull 5,000 corresponds to BCFkm 3,400 to 6,800. The authors also emphasize that the standard bioconcentration test should be performed when the resulting BCFkm is in the region of regulatory concern. Environ. Toxicol. Chem. 2013;32:406-409. © 2012 SETAC [ABSTRACT FROM AUTHOR]

The fish toxicity assay most commonly used to establish chronic effects is the Organisation for Economic Co-operation and Development (OECD) 210, fish early-life stage test. However, the authors are not aware of any systematic analysis of the experimental design or statistical characteristics of the test since the test guideline was adopted nearly 20 years ago. Here, the authors report the results of an analysis of data compiled from OECD 210 tests conducted by industry labs. The distribution of responses observed in control treatments was analyzed, with the goal of understanding the implication of this variability on the sensitivity of the OECD 210 test guideline and providing recommendations on revised experimental design requirements of the test. Studies were confined to fathead minnows, rainbow trout, and zebrafish. Dichotomous endpoints (hatching success and posthatch survival) were examined for indications of overdispersion to evaluate whether significant chamber-to-chamber variability was present. Dichotomous and continuous (length, wet wt, dry wt) measurement endpoints were analyzed to determine minimum sample size requirements to detect differences from control responses with specified power. Results of the analysis indicated that sensitivity of the test could be improved by maximizing the number of replicate chambers per treatment concentration, increasing the acceptable level of control hatching success and larval survival compared to current levels, using wet weight measurements rather than dry weight, and focusing test efforts on species that demonstrate less variability in outcome measures. From these analyses, the authors provide evidence of the impact of expected levels of variability on the sensitivity of traditional OECD 210 studies and the implications for defining a target for future animal alternative methods for chronic toxicity testing in fish. Environ. Toxicol. Chem. 2012;31:370-376. © 2011 SETAC [ABSTRACT FROM AUTHOR]

OECD (Organisation for Economic Co-operation and Development) Guideline 203, Fish Acute Toxicity Test, states that the test should be performed using at least five concentrations in a geometric series with a separation factor not exceeding 2.2, with at least seven fish per concentration. However, the efficiency of this design can be questioned, because it often results in only one concentration that causes partial mortality (mortality >0% and <100%). We performed Monte Carlo computer simulations to assess whether more efficient designs could allow reductions in fish use. Simulations indicated that testing with six fish per concentration could yield 50% lethal concentration (LC50) estimates of quality similar to those obtained using seven fish. Experts attending a workshop organized to consider this finding and to identify the best methods for reducing fish use concluded that significant reductions could best be achieved by modifying the test paradigm. They suggested initiating testing using a 96-h fish embryo test instead of juvenile fish to cover the range from the upper threshold concentration (the lowest 50% effective concentration [EC50] in existing algae and daphnia studies) to the highest concentration with no mortality. This would be followed by a confirmatory limit test with juvenile fish at the highest concentration with no mortality or by a full test with juvenile fish, if a point estimate of the LC50 is required. Environ. Toxicol. Chem. 2011; 30:1006-1011. © 2010 SETAC [ABSTRACT FROM AUTHOR]

Fish embryo toxicology is important because embryos are considered more susceptible than adult fish to the effects of toxic chemicals. Recently, fish embryo bioassay was proposed to replace the conventional fish acute toxicity chemical test of the Organization for Economic Cooperation and Development guidelines because it offers the advantages of fewer reagents, easy handling, and efficient data production. To accelerate the establishment of a chemical toxicity database for the protection of environmental and human health, we need to determine whether the conventional toxicity test can safely be replaced by such fish embryo toxicity tests. For instance, it is unclear how the presence of the chorion moderates the toxic effects of some chemicals. If such chemical toxicities do differ between embryos and, for example, the larval stage, then different toxic effects should appear in later life. We tested the later-life effects of the neurotoxic insecticide carbaryl at sublethal concentrations (0 [control] and 5 and 10 mg/L) in embryos and posthatch larvae of the freshwater fish medaka, Oryzias latipes. Although embryos exposed until hatching showed multiple developmental malformations and reductions in subsequent survival rates over three months, no significant reduction was observed in tolerance to starvation for 7 d and in intrinsic population growth rate (r). Exposure of larvae for 96 h resulted in dose-responsive vertebral fracture, significant reduction in tolerance to starvation for 7 d, and reduced three-month survival rate; r was reduced significantly and consistently. These results suggested that posthatch larvae were more susceptible than embryos to carbaryl exposure and that the toxic cascades may differ between larvae and embryos. The influences of carbaryl exposure on population growth rate differed significantly with developmental stage. [ABSTRACT FROM AUTHOR]

The results of the present study have demonstrated the utility of an estrogen receptor (ER) competitive ligand-binding assay, a hepatocyte vitellogenin (VTG) induction bioassay, and an ER reporter gene bioassay in characterizing the activity of model estrogen agonists (17β-estradiol [E2], ethynylestradiol, and nonylphenol) and antagonists (tamoxifen and ZM 189154) in rainbow trout (Oncorhynchus mykiss). The in vitro results were validated against in vivo trout waterborne exposures to E2 and tamoxifen. The results showed that all three in vitro assays were capable of detecting the hormonal activities of the selected model compounds in a dose-dependent manner, with the exception of nonylphenol in the ER reporter gene bioassay. However, the relative potency rankings of the model compounds were not consistent between these assays, which suggests that the relative potencies obtained within assays may have limited predictive value between assays. Discrepancies in potencies most likely can be attributed to the different levels of cellular organization in each assay. In addition to model compounds, we also evaluated the responses of the ER-binding assay and the hepatocyte VTG induction bioassay to complex mixtures associated with endocrine effects in fish, specifically extracts of pulp mill effluent. Of the 14 pulp mill effluent extracts tested, only six showed activity in both assays, whereas the remaining eight samples showed activity in only one of the two assays. The hepatocyte VTG induction bioassay consistently showed that the pulp mill effluent extracts were antiestrogenic, which to our knowledge has not been reported in previous studies. Collectively, these results suggest that a combination of in vitro assays that depend on differing endpoints is required to identify potential xenoestrogens and to characterize their modes of action. [ABSTRACT FROM AUTHOR]

Despite the fact that marine fish contain relatively high concentrations of the naturally occurring arsenic compound arsenobetaine, little is known about the disposition of arsenobetaine in fish. We investigated the accumulation, distribution, and elimination of dietary arsenobetaine in Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.), with the focus on muscle, liver, and kidney tissues. The fish were exposed to dietary arsenobetaine (24.7 ± 0.6 μg As/g feed) for three months, followed by a three-month depuration period. The two species showed marked differences in the accumulation and elimination of arsenobetaine. Total arsenic concentrations in Atlantic salmon increased significantly in muscle, liver, and kidney, whereas in Atlantic cod, a significant increase in total arsenic concentration was observed only in muscle. Elimination kinetics in muscle were distinct between the two species, with elimination half-lives from muscle tissue estimated at approximately 77 d in Atlantic cod and 37 d in Atlantic salmon, resulting in an absorption efficiency approximately twofold higher in Atlantic cod (15 ± 1%) compared to that in Atlantic salmon (8 ± 1%). The differences in arsenobetaine disposition studied in Atlantic salmon and Atlantic cod contribute to explain the differences in arsenic levels observed among marine fish. [ABSTRACT FROM AUTHOR]