Toxic concentrations in fish early life stages peak at a critical moment

The Impact of Polychlorinated Biphenyls on the Development of Zebrafish (Danio rerio)

Polychlorinated biphenyls (PCBs) are a group of 209 highly stable molecules that were used extensively in industry. Although their commercial use ceased in 1979, they are still present in many aquatic ecosystems due to improper disposal, oceanic currents, atmospheric deposition, and hydrophobic nature. PCBs pose a significant and ongoing threat to the development and sustainability of aquatic organisms. In areas with PCB exposure high mortality rates of organisms inhabiting them are still seen today, posing a significant threat to local species. Zebrafish were exposed to a standard PCB mixture (Aroclor 1254) for the first 5 days post fertilization, as there is a gap in knowledge during this important developmental period for fish (i.e., organization of the body). This PCB mixture was formally available commercially and has a high prevalence in PCB-contaminated sites. We tested for the effects of PCB dosage (control (embryo water only; 0 mg/L), methanol (solvent control; 0 mg/L); PCB 1 (0.125 mg/L), PCB 2 (0.25 mg/L), PCB 3 (0.35 mg/L), and PCB 4 (0.40 mg/L)) on zebrafish survival, rate of metamorphosis, feeding efficiency, and growth. We found significant, dose-dependent effects of PCB exposure on mortality, feeding efficiency, and growth, but no clear effect of PCBs on the rate of zebrafish metamorphosis. We identified a concentration in which there were no observable effects (NOEC), PCB concentration above the NOEC had a significant impact on life-critical processes. This can further inform local management decisions in environments experiencing PCB contamination.

The brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO), causes multigenerational effects on reproductive capacity of Japanese medaka (Oryzias latipes)

Exposure of fishes to endocrine disrupting chemicals (EDCs) during early development can induce multigenerational and transgenerational effects on reproduction. Both in vivo and in vitro studies have demonstrated that the brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO), is an EDC. The present study investigated whether TBCO has mutigenerational and/or transgenerational effects on the reproductive performance of Japanese medaka (Oryzias latipes). Sexually mature fish (F0 generation) were fed either a control diet or a low (40.6 μg/g) or high (1034.4 μg/g) diet containing TBCO, and three generations of embryos were reared to determine reproductive performance using a standard 21-day reproduction assay. Concentrations of TBCO in eggs (F1 generation) from F0 fish given the low and high diets were 711.3 and 2535.5 ng/g wet weight, respectively. Cumulative fecundity of the F1 generation in the low and high treatment were reduced by 33.9% and 33.3%, respectively, compared to the control. In the F2 generation, cumulative fecundity of the low treatment returned to the level of the controls, but the high treatment was decreased by 29.8%. There was no decrease in cumulative fecundity in the F3 generation compared to the controls. Mechanistically, mRNA abundances of cholesterol side chain cleavage enzyme (cyp11a), aromatase (cyp19a), and luteinizing hormone receptor (lhr) were differentially expressed in gonads from F1 females, suggesting that TBCO might cause developmental reprogramming that disrupts steroidogenesis leading to decreased fecundity. However, concentrations of E2 in plasma and mRNA abundance of vitellogenin in liver were not significantly different compared to controls suggesting a mechanism other than disruption of steroidogenesis or vitellogenesis. Mechanistically, no effects were observed in the F2 or F3 generation. Overall, results suggest that TBCO has multigenerational effects on the reproductive performance of Japanese medaka. However, no transgenerational effects were observed as the F3 generation fully recovered. The mechanism by which multigenerational effects were induced is not known.

Environmental microplastics disrupt swimming activity in acute exposure in Danio rerio larvae and reduce growth and reproduction success in chronic exposure in D. rerio and Oryzias melastigma

Microplastics (MPs), widely present in aquatic ecosystems, can be ingested by numerous organisms, but their toxicity remains poorly understood. Toxicity of environmental MPs from 2 beaches located on the Guadeloupe archipelago, Marie Galante (MG) and Petit-Bourg (PB) located near the North Atlantic gyre, was evaluated. A first experiment consisted in exposing early life stages of zebrafish (Danio rerio) to MPs at 1 or 10 mg/L. The exposure of early life stages to particles in water induced no toxic effects except a decrease in larval swimming activity for both MPs exposures (MG or PB). Then, a second experiment was performed as a chronic feeding exposure over 4 months, using a freshwater fish species, zebrafish, and a marine fish species, marine medaka (Oryzias melastigma). Fish were fed with food supplemented with environmentally relevant concentrations (1% wet weight of MPs in food) of environmental MPs from both sites. Chronic feeding exposure led to growth alterations in both species exposed to either MG or PB MPs but were more pronounced in marine medaka. Ethoxyresorufin-O-deethylase (EROD) and acetylcholinesterase (AChE) activities were only altered for marine medaka. Reproductive outputs were modified following PB exposure with a 70 and 42% decrease for zebrafish and marine medaka, respectively. Offspring of both species (F1 generation) were reared to evaluate toxicity following parental exposure on unexposed larvae. For zebrafish offspring, it revealed premature mortality after parental MG exposure and parental PB exposure produced behavioural disruptions with hyperactivity of F1 unexposed larvae. This was not observed in marine medaka offspring. This study highlights the ecotoxicological consequences of short and long-term exposures to environmental microplastics relevant to coastal marine areas, which represent essential habitats for a wide range of aquatic organisms.

Toxicokinetic Models for Bioconcentration of Organic Contaminants in Two Life Stages of White Sturgeon (Acipenser transmontanus)

The white sturgeon (Acipenser transmontanus) is an endangered ancient fish species that is known to be particularly sensitive to certain environmental contaminants, partly because of the uptake and subsequent toxicity of lipophilic pollutants prone to bioconcentration as a result of their high lipid content. To better understand the bioconcentration of organic contaminants in this species, toxicokinetic (TK) models were developed for the embryo-larval and subadult life stages. The embryo-larval model was designed as a one-compartment model and validated using whole-body measurements of benzo[a]pyrene (B[a]P) metabolites from a waterborne exposure to B[a]P. A physiologically based TK (PBTK) model was used for the subadult model. The predictive power of the subadult model was validated with an experimental data set of four chemicals. Results showed that the TK models could accurately predict the bioconcentration of organic contaminants for both life stages of white sturgeon within 1 order of magnitude of measured values. These models provide a tool to better understand the impact of environmental contaminants on the health and the survival of endangered white sturgeon populations.

In vitro-in vivo and cross-life stage extrapolation of uptake and biotransformation of benzo[a]pyrene in the fathead minnow (Pimephales promelas)

Understanding internal dose metrics is integral to adequately assess effects environmental contaminants might have on aquatic wildlife, including fish. In silico toxicokinetic (TK) models are a leading approach for quantifying internal exposure metrics for fishes; however, they often do not adequately consider chemicals that are actively biotransformed and have not been validated against early-life stages (ELS) that are often considered the most sensitive to the exposure to contaminants. To address these uncertainties, TK models were parameterized for the rapidly biotransformed chemical benzo[a]pyrene (B[a]P) in embryo-larval and adult life stages of fathead minnows. Biotransformation of B[a]P was determined through measurements of in vitro clearance. Using in vitro-in vivo extrapolation, in vitro clearance was integrated into a multi-compartment TK model for adult fish and a one-compartment model for ELS. Model predictions were validated using measurements of B[a]P metabolites from in vivo flow-through exposures to graded concentrations of water-borne B[a]P. Significantly greater amounts of B[a]P metabolites were observed with exposure to greater concentrations of parent compound in both life stages. However, when assessing biotransformation capacity, no differences in phase I or phase II biotransformation were observed with greater exposures to B[a]P. Results of modelling suggested that biotransformation of B[a]P can be successfully implemented into in silico models to accurately predict life stage-specific abundances of B[a]P metabolites in either whole-body larvae or the bile of adult fish. Models developed increase the scope of applications in which TK models can be used to support environmental risk assessments.

Multigenerational Impacts of Benzo[a]pyrene on Bone Modeling and Remodeling in Medaka (Oryzias latipes)

Ancestral benzo[a]pyrene (BaP) (1 μg/L, 21 days) exposure has previously been shown to cause skeletal deformities in medaka (Oryzias latipes) larvae in the F1-F3 generation. However, when and how this deformity is induced during bone development remain to be elucidated. The col10a1:nlGFP/osx:mCherry double transgenic medaka model was employed to determine the temporal and spatial changes of col10a1:nlGFP- positive osteochondral progenitor cells (OPCs) and osx:mCherry-positive premature osteoblasts (POBs) [8 days postfertilization (dpf)-31 dpf] in combination with changes in bone mineralization at the tissue level. Ancestral BaP exposure delayed the development of col10a1:nlGFP- and osx:mCherry-positive osteoblasts and reduced the abundance of col10a1:nlGFP-positive osteoblast progenitors and col10a1:nlGFP/osx:mCherry double-positive premature osteoblasts during critical windows of early vertebral bone formation, associated with reduced bone mineralization in embryos (14 dpf) and larvae (31 dpf), compressed vertebral segments in larvae (31 dpf), and reduced bone thickness in adult male medaka (6 months old) of the F1-F3 generations. Both Col10a1:nlGFP and osx:mCherry were identified as potential targets of epigenetic modifications underlying the transgenerational inheritance of BaP bone toxicity. The present study provides novel knowledge of the underlying mechanisms of transgenerational toxicity of BaP at the cellular level.

Spatiotemporal variation in occurrence and co-occurrence of pesticides, hormones, and other organic contaminants in rivers in the Chesapeake Bay Watershed, United States

Investigating the spatiotemporal dynamics of contaminants in surface water is crucial to better understand how introduced chemicals are interacting with and potentially influencing aquatic organisms and environments. Within the Chesapeake Bay Watershed, United States, there are concerns about the potential role of contaminant exposure on fish health. Evidence suggests that exposure to contaminants in surface water is causing immunosuppression and intersex in freshwater fish species. Despite these concerns, there is a paucity of information regarding the complex dynamics of contaminant occurrence and co-occurrence in surface water across both space and time. To address these concerns, we applied a Bayesian hierarchical joint-contaminant model to describe the occurrence and co-occurrence patterns of 28 contaminants and total estrogenicity across six river sites and over three years. We found that seasonal occurrence patterns varied by contaminant, with the highest occurrence probabilities during the spring and summer months. Additionally, we found that the proportion of agricultural landcover in the immediate catchment, as well as stream discharge, did not have a significant effect on the occurrence probabilities of most compounds. Four pesticides (atrazine, metolachlor, fipronil and simazine) co-occurred across sites after accounting for environmental covariates. These results provide baseline information on the contaminant occurrence patterns of several classes of compounds within the Chesapeake Bay Watershed. Understanding the spatiotemporal dynamics of contaminants in surface water is the first step in investigating the effects of contaminant exposure on fisheries and aquatic environments.

Environmental occurrences, fate, and impacts of microplastics

Microplastics (MPs) are small plastic pieces with size less than 5 mm that have entered and polluted the environment. While many investigations including several critical reviews on MPs in the environment have been conducted, most of them are focused on their occurrences in marine environment. Current understanding on the occurrences, behaviors, and impacts of MPs in the terrestrial environment is far from complete. A systematic review of the literature was thus conducted to promote the research on MPs in the environment. This work is designed to provide a comprehensive overview that summarizes current knowledge and research findings on environmental occurrences, fate and transport, and impacts of MPs. In addition to discussing the occurrences, characteristics, and sources of MPs in the ocean, freshwater, sediments, soils, and atmosphere, the review also summarizes both the experimental and modeling data of the environmental fate and transport of MPs. Research findings on the toxic effects, bioaccumulation, and bioavailability of MPs in the environment are also covered in this critical review. Future perspectives are discussed as well.

Integrating physiological data with the conservation and management of fishes: a meta-analytical review using the threatened green sturgeon (Acipenser medirostris)

Reversing global declines in the abundance and diversity of fishes is dependent on science-based conservation solutions. A wealth of data exist on the ecophysiological constraints of many fishes, but much of this information is underutilized in recovery plans due to a lack of synthesis. Here, we used the imperiled green sturgeon (Acipenser medirostris) as an example of how a quantitative synthesis of physiological data can inform conservation plans, identify knowledge gaps and direct future research actions. We reviewed and extracted metadata from peer-reviewed papers on green sturgeon. A total of 105 publications were identified, spanning multiple disciplines, with the primary focus being conservation physiology (23.8%). A meta-analytical approach was chosen to summarize the mean effects of prominent stressors (elevated temperatures, salinity, low food availability and contaminants) on several physiological traits (growth, thermal tolerance, swimming performance and heat shock protein expression). All examined stressors significantly impaired green sturgeon growth, and additional stressor-specific costs were documented. These findings were then used to suggest several management actions, such as mitigating salt intrusion in nursery habitats and maintaining water temperatures within optimal ranges during peak spawning periods. Key data gaps were also identified; research efforts have been biased towards juvenile (38.1%) and adult (35.2%) life-history stages, and less data are available for early life-history stages (embryonic, 11.4%; yolk-sac larvae, 12.4%; and post yolk-sac larvae, 16.2%). Similarly, most data were collected from single-stressor studies (91.4%) and there is an urgent need to understand interactions among stressors as anthropogenic change is multi-variate and dynamic. Collectively, these findings provide an example of how meta-analytic reviews are a powerful tool to inform management actions, with the end goal of maximizing conservation gains from research efforts.

Examining multi- and transgenerational behavioral and molecular alterations resulting from parental exposure to an environmental PCB and PBDE mixture

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants extensively used during the 20^th century and still present in aquatic environments despite their ban. Effects of exposure to these compounds over generations are poorly documented. Therefore, our aims were to characterize behavioral responses and underlying molecular mechanisms in zebrafish exposed to an environmentally relevant mixture of PCBs and PBDEs as well as in four unexposed offspring generations. Zebrafish (F0) were chronically exposed from the first meal onward to a diet spiked with a mixture containing 22 PCB and 7 PBDE congeners in proportions and concentrations reflecting environmental situations (ΣPCBs = 1991 and ΣPBDEs = 411 ng/g). Four offspring generations (F1 to F4) were obtained from this F0 and were not further exposed. Behavior was assessed at both larval and adult stages. Mechanisms related to behavioral defects (habenula maturation and c-fos transcription) and methylation (dnmts transcription) were monitored in larvae. Exposed adult F0 as well as F1 and F3 adults displayed no behavioral change while F2 expressed anxiety-like behavior. Larval behavior was also disrupted, i.e. hyperactive after light to dark transition in F1 or hypoactive in F2, F3 and F4. Behavioral disruptions may be related to defect in habenula maturation (observed in F1) and change in c-fos transcription (observed in F1 and F2). Transcription of the gene encoding DNA methyltransferase (dnmt3ba) was also modified in all generations. Our results lead us to hypothesize that chronic dietary exposure to an environmentally relevant mixture of PCB and PBDE triggers multigenerational and transgenerational molecular and behavioral disruptions in a vertebrate model.

Fish life-history traits are affected after chronic dietary exposure to an environmentally realistic marine mixture of PCBs and PBDEs

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that have been shown to affect fish life-history traits such as reproductive success, growth and survival. At the individual level, their toxicity and underlying mechanisms of action have been studied through experimental exposure. However, the number of experimental studies approaching marine environmental situations is scarce, i.e., in most cases, individuals are exposed to either single congeners, or single types of molecules, or high concentrations, so that results can hardly be transposed to natural populations. In the present study, we evaluated the effect of chronic dietary exposure to an environmentally realistic marine mixture of PCB and PBDE congeners on zebrafish life-history traits from larval to adult stage. Exposure was conducted through diet from the first meal and throughout the life cycle of the fish. The mixture was composed so as to approach environmentally relevant marine conditions in terms of both congener composition and concentrations. Life-history traits of exposed fish were compared to those of control individuals using several replicate populations in each treatment. We found evidence of slower body growth, but to a larger asymptotic length, and delayed spawning probability in exposed fish. In addition, offspring issued from early spawning events of exposed fish exhibited a lower larval survival under starvation condition. Given their strong dependency on life-history traits, marine fish population dynamics and associated fisheries productivity for commercial species could be affected by such individual-level effects of PCBs and PBDEs on somatic growth, spawning probability and larval survival.

Effect of sublethal α-cypermethrin exposure on main macromolecules concentration, energy content, and malondialdehyde concentration in free-feeding Danio rerio larvae

α-Cypermethrin (Cyp) is a synthetic insecticide used to control pests in agricultural crops and to protect human health against noxious insects; this toxic can reach aquatic systems through ground infiltration or by runoff and could affect the aquatic biota. The present study was aimed at evaluating the acute toxicity of Cyp on zebrafish (Danio rerio) exogenous feeding larvae of 10 and 20 days post-fertilization (dpf), and of sublethal concentrations on only 10-dpf larvae. Proteins, lipids, carbohydrates, glycogen concentration, and total energy contents, as well as malondialdehyde (MDA) quantification, through thiobarbituric acid reactive substances, as a lipid peroxidation biomarker, were assessed in free-feeding larvae exposed to sublethal Cyp concentrations. The LC50 for 10-dpf larvae was 1.94 µg L(-1), and these were more sensitive than 20-dpf larvae (3.56 µg L(-1)). The amount of protein, carbohydrates, and glycogen were not significantly affected (p > 0.05), but sublethal Cyp concentrations exposure caused decrement in lipids from 9.05 to 3.74 µg larva(-1), as well as a reduction in MDA and in the total energy content, which affected significantly the development of this fish. Although Cyp is considered an insecticide of reduced residual effect in the environment, the present study revealed that relatively low Cyp concentrations produced significant toxic effects on exogenous feeding fish larvae, a situation that could contribute to increase deaths during this already critical developmental stage in which high mortality is observed frequently.

Early life exposure to PCB126 results in delayed mortality and growth impairment in the zebrafish larvae

The occurrence of chronic or delayed toxicity resulting from the exposure to sublethal chemical concentrations is an increasing concern in environmental risk assessment. The Fish Embryo Toxicity (FET) test with zebrafish provides a reliable prediction of acute toxicity in adult fish, but it cannot yet be applied to predict the occurrence of chronic or delayed toxicity. Identification of sublethal FET endpoints that can assist in predicting the occurrence of chronic or delayed toxicity would be advantageous. The present study characterized the occurrence of delayed toxicity in zebrafish larvae following early exposure to PCB126, previously described to cause delayed effects in the common sole. The first aim was to investigate the occurrence and temporal profiles of delayed toxicity during zebrafish larval development and compare them to those previously described for sole to evaluate the suitability of zebrafish as a model fish species for delayed toxicity assessment. The second aim was to examine the correlation between the sublethal endpoints assessed during embryonal and early larval development and the delayed effects observed during later larval development. After exposure to PCB126 (3-3000ng/L) until 5 days post fertilization (dpf), larvae were reared in clean water until 14 or 28 dpf. Mortality and sublethal morphological and behavioural endpoints were recorded daily, and growth was assessed at 28 dpf. Early life exposure to PCB126 caused delayed mortality (300 ng/L and 3000 ng/L) as well as growth impairment and delayed development (100 ng/L) during the clean water period. Effects on swim bladder inflation and cartilaginous tissues within 5 dpf were the most promising for predicting delayed mortality and sublethal effects, such as decreased standard length, delayed metamorphosis, reduced inflation of swim bladder and column malformations. The EC50 value for swim bladder inflation at 5 dpf (169 ng/L) was similar to the LC50 value at 8 dpf (188 and 202 ng/L in two experiments). Interestingly, the patterns of delayed mortality and delayed effects on growth and development were similar between sole and zebrafish. This indicates the comparability of critical developmental stages across divergent fish species such as a cold water marine flatfish and a tropical freshwater cyprinid. Additionally, sublethal effects in early embryo-larval stages were found promising for predicting delayed lethal and sublethal effects of PCB126. Therefore, the proposed method with zebrafish is expected to provide valuable information on delayed mortality and delayed sublethal effects of chemicals and environmental samples that may be extrapolated to other species.

Differential sensitivity in embryonic stages of the zebrafish (Danio rerio): The role of toxicokinetics for stage-specific susceptibility for azinphos-methyl lethal effects

The occasionally observed differential chemical sensitivity in embryonic life stages of fish is still poorly understood and could represent an important issue for understanding the time course of toxicity and the toxic modes of action of chemicals. In this study we analyzed the toxicity of the acetylcholinesterase inhibitor azinphos-methyl (APM) in different life-stages of zebrafish embryos. To this end, the LC50 of three 48h-exposure windows were determined (12μM for 0-48, no mortality observed for 24-72 and 72-120hpf up to a concentration of 79μM). We hypothesized that the differential sensitivity of the stage-specific embryos may be related to differences in uptake of the compound and/or internal concentrations. Therefore, internal concentrations were determined using HPLC. Similar levels and time courses of internal concentrations for all three exposure windows were observed. Bioconcentration amounted to a factor of about 30. Short-term exposure windows for a concentration 4-fold above the calculated LC50 (47μM) identified the period of 0-4hpf as the most sensitive time window for APM toxicity. Our results indicate that the differential sensitivity of APM in the embryos is not related to differences in internal concentrations but related to a stage specific mechanisms of toxicity.

Mesocosm validation of the marine No Effect Concentration of dissolved copper derived from a species sensitivity distribution

The Predicted No Effect Concentration (PNEC) for dissolved copper based on the species sensitivity distribution (SSD) of 24 marine single species tests was validated in marine mesocosms. To achieve this, the impact of actively maintained concentrations of dissolved copper on a marine benthic and planktonic community was studied in 18 outdoor 4.6m(3) mesocosms. Five treatment levels, ranging from 2.9 to 31μg dissolved Cu/L, were created in triplicate and maintained for 82days. Clear effects were observed on gastropod and bivalve molluscs, phytoplankton, zooplankton, sponges and sessile algae. The most sensitive biological endpoints; reproduction success of the bivalve Cerastoderma edule, copepod population development and periphyton growth were significantly affected at concentrations of 9.9μg Cu/L and higher. The No Observed Effect Concentration (NOEC) derived from this study was 5.7μg dissolved Cu/L. Taking into account the DOC concentration of the mesocosm water this NOEC is comparable to the PNEC derived from the SSD.

Ecotoxicology of polychlorinated biphenyls in fish--a critical review

Polychlorinated biphenyls (PCBs) are widespread persistent anthropogenic contaminants that can accumulate in tissues of fish. The toxicity of PCBs and their transformation products has been investigated for nearly 50 years, but there is a lack of consensus regarding the effects of these environmental contaminants on wild fish populations. The objective of this review is to critically examine these investigations and evaluate publicly available databases for evidence of effects of PCBs in wild fish. Biological activity of PCBs is limited to a small proportion of PCB congeners [e.g., dioxin-like PCBs (DL-PCBs)] and occurs at concentrations that are typically orders of magnitude higher than PCB levels detected in wild fish. Induction of biomarkers consistent with PCB exposure (e.g., induction of cytochrome P450 monooxygenase system) has been evaluated frequently and shown to be induced in fish from some environments, but there does not appear to be consistent reports of damage (i.e., biomarkers of effect) to biomolecules (i.e., oxidative injury) in these fish. Numerous investigations of endocrine system dysfunction or effects on other organ systems have been conducted in wild fish, but collectively there is no consistent evidence of PCB effects on these systems in wild fish. Early life stage toxicity of DL-PCBs does not appear to occur at concentrations reported in wild fish embryos, and results do not support an association between PCBs and decreased survival of early life stages of wild fish. Overall, there appears to be little evidence that PCBs have had any widespread effect on the health or survival of wild fish.

Chronic dietary exposure to pyrolytic and petrogenic mixtures of PAHs causes physiological disruption in zebrafish--part I: Survival and growth

The release of polycyclic aromatic hydrocarbons (PAHs) into the environment has increased very substantially over the last decades leading to high concentrations in sediments of contaminated areas. To evaluate the consequences of long-term chronic exposure to PAHs, zebrafish were exposed, from their first meal at 5 days post fertilisation until they became reproducing adults, to diets spiked with three PAH fractions at three environmentally relevant concentrations with the medium concentration being in the range of 4.6-6.7 μg g(-1) for total quantified PAHs including the 16 US-EPA indicator PAHs and alkylated derivatives. The fractions used were representative of PAHs of pyrolytic (PY) origin or of two different oils of differing compositions, a heavy fuel (HO) and a light crude oil (LO). Fish growth was inhibited by all PAH fractions and the effects were sex specific: as determined with 9-month-old adults, exposure to the highest PY inhibited growth of females; exposure to the highest HO and LO inhibited growth of males; also, the highest HO dramatically reduced survival. Morphological analysis indicated a disruption of jaw growth in larvae and malformations in adults. Intestinal and pancreatic enzyme activities were abnormal in 2-month-old exposed fish. These effects may contribute to poor growth. Finally, our results indicate that PAH mixtures of different compositions, representative of situations encountered in the wild, can promote lethal and sublethal effects which are likely to be detrimental for fish recruitment.

Internal effect concentrations of organic substances for early life development of egg-exposed fish

The present study investigates the likelihood that early life development of marine fish from contaminated areas is affected by maternally transferred persistent organic substances (POPs). The common sole (Solea solea) was used as model species. Fertilized eggs were exposed via the water until hatching, 6 days post fertilization. The newly hatched larvae were allowed to develop further under unexposed conditions until the end of the metamorphosis. Effects on the larvae were determined for the dioxin-like polychlorinated biphenyl PCB 126, the technical PCB-mixture Arochlor 1254, polybrominated diphenylethers (PBDEs), and hexabromocyclododecane (HBCD), for an artificial mixture of PCBs and PBDEs, and for 'field mixtures' extracted from sole from the North Sea and the contaminated Western Scheldt estuary. Effect levels were expressed as tissue concentrations in the newly hatched larvae at the end of the exposure period. Exposure to PCBs, PBDEs, and the artificial and field mixtures caused mortality that started to occur shortly after the larvae became free-feeding (10 days post fertilization) and continued to increase until the onset of metamorphosis, 15 days later. The effects induced by the field mixtures correlated well with the ΣPCB concentrations in the tissue of the exposed larvae. No indications were found for synergistic effects or for substantial contribution of other (unknown) substances in the field mixtures. HBCD did not induce toxic effects. As lipid normalized POP levels in fish eggs are in general comparable to the levels in the tissue of the female fish, fish tissue concentrations are indicative of the internal exposure of the developing larvae as a result maternally transferred POPs will occur in the field. In sole from the Western Scheldt estuary POP levels are about twenty times lower than the larval tissue concentration that produced 50 percent early life stage mortality. Levels in North Sea sole are an order of a magnitude lower. At more heavily contaminated sites negative effect of PCBs, especially of those with dioxin-like toxicity can be expected.

Bioamplification as a bioaccumulation mechanism for persistent organic pollutants (POPs) in wildlife

Persistent organic pollutant bioaccumulation models have generally been formulated to predict bioconcentration and biomagnification. A third bioaccumulation process that can mediate chemical fugacity in an organism is bioamplification.Bioamplification occurs when an organism loses body weight and the chemical partitioning capacity occurs at a rate that is faster than the chemical can be eliminated.Although bioamplification has not been widely recognized as a bioaccumulation process, the potential consequences of this process are significant. Bioamplification causes an increase in chemical fugacity in the animal's tissues and results in there distribution of contaminants from inert storage sites to more toxicologically sensitive tissues. By reviewing laboratory and field studies, we have shown in this paper that bioamplification occurs across taxonomic groups that include, invertebrates,amphibians, fishes, birds, and mammals. Two case studies are presented, and constitute multi-life stage non-steady state bioaccumulation models calibrated for yellow perch and herring gulls. These case studies were used to demonstrate that bioamplification is predicted to occur under realistic scenarios of animal growth and seasonal weight loss. Bioamplification greatly enhances POP concentrations and chemical fugacities during critical physiological and behavioral events in an animal's life history, e.g., embryo development, juvenile stages, metamorphosis, reproduction, migration, overwintering, hibernation, and disease. Consequently,understanding the dynamics of bioamplification, and how different life history scenario scan alter tissue residues, may be helpful and important in assessing wildlife hazards and risks.

Metabolic activation of nonpolar sediment extracts results in enhanced thyroid hormone disrupting potency

Traditional sediment risk assessment predominantly considers the hazard derived from legacy contaminants that are present in nonpolar sediment extracts, such as polychlorinated biphenyls (PCBs), dioxins, furans (PCDD/Fs), and polyaromatic hydrocarbons (PAHs). Although in vivo experiments with these compounds have shown to be thyroid hormone disrupting (THD), in vitro their THD potency is not observed in nonpolar sediment extracts. This is hypothesized to be due to the absence of in vitro biotransformation which will result in bioactivation of the lipophilic compounds into THD hydroxyl metabolites. This study reveals that indeed metabolically activated nonpolar contaminants in sediments can competitively bind to thyroid hormone transport proteins. Sediment fractions were incubated with S9 rat microsomes, and the metabolites were extracted with a newly developed method that excludes most of the lipids to avoid interference in the applied nonradioactive 96-well plate TTR competitive binding assay. Metabolic activation increased the TTR binding potency of nonpolar fractions of POP-polluted sediments up to 100 times, resulting in potencies up to 240 nmol T4 equivalents/g sediment equivalent (nmol T4-Eq/g SEQ). This demonstrates that a more realistic in vitro sediment THD risk characterization should also include testing of both polar and medium polar sediment extracts for THD, as well as bioactivated nonpolar sediment fractions to prevent underestimation of its toxic potency.