Responses of conventional and molecular biomarkers in turbot Scophthalmus maximus exposed to heavy fuel oil no. 6 and styrene

Hypothesis-driven weight of evidence evaluation indicates styrene lacks endocrine disruption potential

Styrene is among the U.S. EPA's List 2 chemicals for Tier 1 endocrine screening subject to the agency's two-tiered Endocrine Disruptor Screening Program (EDSP). Both U.S. EPA and OECD guidelines require a Weight of Evidence (WoE) to evaluate a chemical's potential for disrupting the endocrine system. Styrene was evaluated for its potential to disrupt estrogen, androgen, thyroid, and steroidogenic (EATS) pathways using a rigorous WoE methodology that included problem formulation, systematic literature search and selection, data quality evaluation, relevance weighting of endpoint data, and application of specific interpretive criteria. Sufficient data were available to assess the endocrine disruptive potential of styrene based on endpoints that would respond to EATS modes of action in some Tier 1-type and many Tier 2-type reproductive, developmental, and repeat dose toxicity studies. Responses to styrene were inconsistent with patterns of responses expected for chemicals and hormones known to operate via EATS MoAs, and thus, styrene cannot be deemed an endocrine disruptor, a potential endocrine disruptor, or to exhibit endocrine disruptive properties. Because Tier 1 EDSP screening results would trigger Tier 2 studies, like those evaluated here, subjecting styrene to further endocrine screening would produce no additional useful information and would be unjustified from animal welfare perspectives.

Biological responses and toxicopathic effects elicited in Solea senegalensis juveniles by waterborne exposure to benzo[a]pyrene

Polycyclic aromatic hydrocarbons (PAHs) are priority contaminants in coastal and estuarine ecosystems under anthropogenic pressure. Although PAHs tend to accumulate in the sediment, toxicity for benthic flat fish such as soles may be caused by PAHs released from the sediment to the water column. Within this context, the present investigation aims at recognizing toxicopathic effects elicited after waterborne exposure to benzo[a]pyrene B[a]P, a model individual PAH compound, in juvenile Solea senegalensis. Sole juveniles were exposed to various concentrations of waterborne B[a]P for 3 and 7 days. Brain, liver, gills and gonad were the target tissues selected to determine biochemical and lysosomal biomarkers, and histopathology. Biological responses and toxicopathic effects were consistent with B[a]P concentration and exposure time. From day 3, hepatic catalase inhibition indicated potential oxidative effects of B[a]P. At day 7, contaminant exposure produced hepatic glutathione-S-transferase induction at low concentrations and inhibition at higher levels, evidencing a bell-shaped response. A clear gradient in lysosomal membrane destabilisation was observed in relation with B[a]P concentrations. Histopathological lesions were more frequent at day 7 and at higher contaminant levels. It seems that environmentally relevant waterborne concentrations of B[a]P (1000 ng/l) would suffice to cause toxicopathic effects on sole juveniles in relatively short exposure times. In agreement, the Integrative Biological Response index (IBR/n) indicated a dose-dependent decline in health condition upon exposure to B[a]P (IBR/n_HighB[a]P > IBR/n_MidB[a]P > IBR/n_LowB[a]P > IBR/n_DMSO > IBR/n_Control). Overall, changes in antioxidant enzymes activity, lysosomal biomarkers and gill and liver histopathology are responsive early-warning signs of health disturbance in sole juveniles exposed to waterborne PAHs.

Global distribution of two polystyrene-derived contaminants in the marine environment: A review

Plastic pollution is one of the major issues impacting on the marine environment. Plastic polymers are known to leach industrial chemicals and associated contaminants. In this review, we focused on assessing the global distribution and concentration of two polystyrene-derived contaminants, hexabromocyclododecanes (HBCDs) and styrene oligomers (SOs), in marine sediments and seawater. Overall, most of the studies were carried out in Asia, North America, and Europe. Relatively high concentrations of these contaminants are generally attributed to the proximity of urban cities, plastic industries, polystyrene pollution, and aquaculture. Moreover, the concentrations in sediments are many times higher than in seawater. HBCDs were found to be a negligible risk to marine biota when compared to the ecotoxicological endpoints. However, realistic concentrations of SOs could compromise the wellbeing of certain species in highly polluted sites. The future perspectives and research were discussed.

Hepatic gene transcription profiles in turbot (Scophthalmus maximus) experimentally exposed to heavy fuel oil nº 6 and to styrene

Oil and chemical spills in the marine environment, although sporadic, are highly dangerous to biota inhabiting coastal and estuarine areas. Effects of spilled compounds in exposed organisms occur at different biological organization levels: from molecular, cellular or tissue levels to the physiological one. The present study aims to determine the specific hepatic gene transcription profiles observed in turbot juveniles under exposure to fuel oil n °6 and styrene vs controls using an immune enriched turbot (Scophthalmus maximus) oligo-microarray containing 2716 specific gene probes. After 3 days of exposure, fuel oil specifically induced aryl hydrocarbon receptor mediated transcriptional response through up-regulation of genes, such as ahrr and cyp1a1. More gene transcripts were regulated after 14 days of exposure involved in ribosomal biosynthesis, immune modulation, and oxidative response among the most significantly regulated functional pathways. On the contrary, gene transcription alterations caused by styrene did not highlight any significantly regulated molecular or metabolic pathway. This was also previously reported at cell and tissue level where no apparent responses were distinguishable. For the fuel oil experiment, obtained specific gene profiles could be related to changes in cell-tissue organization in the same individuals, such as increased hepatocyte vacuolization, decrease in melano-macrophage centers and the regulation of leukocyte numbers. In conclusion, the mode of action reflected by gene transcription profiles analyzed hereby in turbot livers could be linked with the responses previously reported at higher biological organization levels. Molecular alterations described hereby could be preceding observed alterations at cell and tissue levels.

Exposure of marine mussels Mytilus spp. to polystyrene microplastics: Toxicity and influence on fluoranthene bioaccumulation

The effects of polystyrene microbeads (micro-PS; mix of 2 and 6 μm; final concentration: 32 μg L(-1)) alone or in combination with fluoranthene (30 μg L(-1)) on marine mussels Mytilus spp. were investigated after 7 days of exposure and 7 days of depuration under controlled laboratory conditions. Overall, fluoranthene was mostly associated to algae Chaetoceros muelleri (partition coefficient Log Kp = 4.8) used as a food source for mussels during the experiment. When micro-PS were added in the system, a fraction of FLU transferred from the algae to the microbeads as suggested by the higher partition coefficient of micro-PS (Log Kp = 6.6), which confirmed a high affinity of fluoranthene for polystyrene microparticles. However, this did not lead to a modification of fluoranthene bioaccumulation in exposed individuals, suggesting that micro-PS had a minor role in transferring fluoranthene to mussels tissues in comparison with waterborne and foodborne exposures. After depuration, a higher fluoranthene concentration was detected in mussels exposed to micro-PS and fluoranthene, as compared to mussels exposed to fluoranthene alone. This may be related to direct effect of micro-PS on detoxification mechanisms, as suggested by a down regulation of a P-glycoprotein involved in pollutant excretion, but other factors such as an impairment of the filtration activity or presence of remaining beads in the gut cannot be excluded. Micro-PS alone led to an increase in hemocyte mortality and triggered substantial modulation of cellular oxidative balance: increase in reactive oxygen species production in hemocytes and enhancement of anti-oxidant and glutathione-related enzymes in mussel tissues. Highest histopathological damages and levels of anti-oxidant markers were observed in mussels exposed to micro-PS together with fluoranthene. Overall these results suggest that under the experimental conditions of our study micro-PS led to direct toxic effects at tissue, cellular and molecular levels, and modulated fluoranthene kinetics and toxicity in marine mussels.

A critical review finds styrene lacks direct endocrine disruptor activity

The European Commission lists styrene (S) as an endocrine disruptor based primarily on reports of increased prolactin (PRL) levels in S-exposed workers. The US Environmental Protection Agency included S in its list of chemicals to be tested for endocrine activity. Therefore, the database of S for potential endocrine activity is assessed. In vitro and in vivo screening studies, as well as non-guideline and guideline investigations in experimental animals indicate that S is not associated with (anti)estrogenic, (anti)androgenic, or thyroid-modulating activity or with an endocrine activity that may be relevant for the environment. Studies in exposed workers have suggested elevated PRL levels that have been further examined in a series of human and animal investigations. While there is only one definitively known physiological function of PRL, namely stimulation of milk production, many normal stress situations may lead to elevations without any chemical exposure. Animal studies on various aspects of dopamine (DA), the PRL-regulating neurotransmitter, in the central nervous system did not give mechanistic explanations on how S may affect PRL levels. Overall, a neuroendocrine disruption of PRL regulation cannot be deduced from a large experimental database. The effects in workers could not consistently be reproduced in experimental animals and the findings in humans represented acute reversible effects clearly below clinical and pathological levels. Therefore, unspecific acute workplace-related stress is proposed as an alternative mode of action for elevated PRL levels in workers.

Integration of multi-level biomarker responses to cadmium and benzo[k]fluoranthene in the pale chub (Zacco platypus)

The Cd exposure for 14 days significantly increased both the molecular (DNA single-strand breaks) and biochemical (metallothionein concentrations) biomarkers in the freshwater pale chub, Zacco platypus, whereas changes in the histological and physiological biomarker responses were negligible. The BkF exposure for 14 days led to significant increases in the mRNA expression of catalase and superoxide dismutase, 7-ethoxyresorufin-O-deethylase enzymatic activity and DNA single-strand breakage at the molecular and biochemical levels. In addition, exposure to 50μg/L of BkF induced histological alteration in the liver, with significant changes to the liver somatic index and condition factor at the physiological level. The integration of multi-level biomarker responses at the molecular, biochemical and physiological levels was highly correlated with the concentrations of Cd and BkF.

Short- and long-term responses and recovery of mussels Mytilus edulis exposed to heavy fuel oil no. 6 and styrene

Biomarkers have the potential to be used to assess the impact of anthropogenic discharges in marine waters. We have used a suite of biomarkers spanning from enzymatic to histopathological alterations and general stress responses to assess the short- and long-term impact on mussels Mytilus edulis of heavy fuel oil no. 6 and styrene. Mussels were exposed for 5 months, with a refilling of the exposure system, to a water soluble fraction of heavy fuel and, then, kept for a month in clean water for recovery. In a second experiment, mussels were exposed to styrene for 19 days and maintained in clean water for up to 4 months. Chemical body tissue levels reflected the weathering processes of these compounds. Acyl-CoA oxidase activity was induced in oil-exposed mussels after refilling, whereas styrene inhibited it after 19 days of exposure and after 2 weeks in clean water. Gamete development and alkali-labile phosphate levels suggest that neither oil nor styrene behaved as endocrine disruptors. Neutral red retention time was lower in treated groups than in controls. Lysosomal membrane stability was significantly reduced in exposed groups and recovered after withdrawal of oil but not after removal of styrene. Neither oil nor styrene exposure affected the condition index except for the reduction seen in mussels exposed to oil for 1 month. Biomarker response index discriminated exposed mussels, which showed higher values, and returned to control levels after recovery. Results obtained from these pilot experiments can help to identify relevant monitoring tools to assess the impact of oil and chemicals in marine spill scenarios.

Comparative study of different exposure routes on the biotransformation and genotoxicity of PAHs in the flatfish species, Scophthalmus maximus

In this study, laboratory experiments were carried out in order to come to a better understanding of the fate of polycyclic aromatic hydrocarbons (PAHs) in the marine environment and especially on their bioaccumulation, biotransformation and genotoxic effects in fish. Juveniles of turbot (Scophthalmus maximus) were exposed to PAHs through different routes via (1) a mixture of dissolved PAHs, (2) a PAH-polluted sediment and (3) an oil fuel elutriate. Fish were exposed 4 days followed by a 6-day depuration period. In each experiment, PAH concentrations in the seawater of the tanks were analysed regularly by gas chromatography coupled with mass spectrometry. Muscle and liver samples were also analysed for parent PAH levels and PAH bioconcentration factors were calculated. Biotransformation was evaluated by measuring the levels of PAH metabolites in fish bile. Genotoxicity was assessed by the alkaline comet assay. Regardless of exposure route, the parent PAH concentrations in the liver and muscle showed a peak level 1 day after the beginning of the exposure, followed by a decrease up to the background level towards the end of the experiment, except for the exposure to dissolved PAHs for which levels were relatively low throughout the study. As a consequence, no bioaccumulation was observed in fish tissues at the end of the experiment. In contrast, regardless of exposure routes, a rapid production of biliary metabolites was observed throughout the whole exposure experiment. This was especially true for 1-hydroxypyrene, the major metabolite of pyrene. After 6 days of recovery in clean water, a significant decrease in the total metabolite concentrations occurred in bile. Fish exposed through either route displayed a significant increase in DNA strand breaks after 4 days of exposure, and significant correlations were observed between the level of biliary PAH metabolites and the level of DNA lesions in fish erythrocytes. Overall results indicate that exposure to either a mixture of dissolved PAHs, a PAH-contaminated sediment or a dispersed oil fuel elutriate leads to biotransformation and increase in DNA damage in fish. The quantification of PAH metabolites in bile and DNA damage in erythrocytes appear to be suitable for environmental monitoring of marine pollution either in the case of accidental oil spills or sediment contamination.