Bioaccumulation and elimination of mercury in juvenile seabass (Dicentrarchus labrax) in a warmer environment

Toxicity of methylmercury in aquatic organisms and interaction with environmental factors and coexisting pollutants: A review

Mercury is a hazardous heavy metal that is distributed worldwide in aquatic ecosystems. Methylmercury (MeHg) poses significant toxicity risks to aquatic organisms, primarily through bioaccumulation and biomagnification, due to its strong affinity for protein thiol groups, which results in negative effects even at low concentrations. MeHg exposure can cause various physiological changes, oxidative stress, neurotoxicity, metabolic disorders, genetic damage, and immunotoxicity. To assess the risks of MeHg contamination in actual aquatic ecosystems, it is important to understand how MeHg interacts with environmental factors such as temperature, pH, dissolved organic matter, salinity, and other pollutants such as microplastics and organic compounds. Complex environmental conditions can cause potential toxicity, such as synergistic, antagonistic, and unchanged effects, of MeHg in aquatic organisms. This review focuses on demonstrating the toxic effects of single MeHg exposure and the interactive relationships between MeHg and surrounding environmental factors or pollutants on aquatic organisms. Our review also recommends further research on biological and molecular responses in aquatic organisms to better understand the potential toxicity of combinational exposure.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.

A Meta-analysis Reveals Global Change Stressors Potentially Aggravate Mercury Toxicity in Marine Biota

Growing evidence demonstrates that global change can modulate mercury (Hg) toxicity in marine organisms; however, the consensus on such effect is lacking. Here, we conducted a meta-analysis to evaluate the effects of global change stressors on Hg biotoxicity according to the IPCC projections (RCP 8.5) for 2100, including ocean acidification (-0.4 units), warming (+4 °C), and their combination (acidification-warming). The results indicated an overall aggravating effect (ln RRΔ = -0.219) of global change on Hg toxicity in marine organisms, while the effect varied with different stressors; namely, acidification potentially alleviates Hg biotoxicity (ln RRΔ = 0.117) while warming and acidification-warming have an aggravating effect (ln RRΔ = -0.328 and -0.097, respectively). Moreover, warming increases Hg toxicity in different trophic levels, i.e., primary producers (ln RRΔ = -0.198) < herbivores (ln RRΔ = -0.320) < carnivores (ln RRΔ = -0.379), implying increasing trends of Hg biomagnification through the food web. Notably, ocean hypoxia appears to boost Hg biotoxicity, although it was not considered in our meta-analysis because of the small sample size. Given the persistent global change and combined effects of these stressors in marine environments, multigeneration and multistressor research is urgently needed to fully disclose the impacts of global change on Hg pollution and its risk.

Bioconcentration, bioaccumulation and biomagnification of mercury in plankton of the Mediterranean Sea

Plankton plays a prominent role in the bioaccumulation of mercury (Hg). The MERITE-HIPPOCAMPE campaign was carried out in spring 2019 along a north-south transect including coastal and offshore areas of the Mediterranean Sea. Sampling of sea water and plankton by pumping and nets was carried out in the chlorophyll maximum layer. Two size-fractions of phytoplankton (0.7-2.7 and 2.7-20 μm) and five of zooplankton (between 60 and >2000 μm) were separated, and their total mercury (THg) and monomethylmercury (MMHg) contents were measured. Bioconcentration of THg was significantly higher in the smallest phytoplankton size-fraction dominated by Synechococcus spp. The bioaccumulation and biomagnification of MMHg in zooplankton was influenced by size, food sources, biochemical composition and trophic level. MMHg was biomagnified in the plankton food web, while THg decreased toward higher trophic levels. Higher MMHg concentrations were measured in oligotrophic areas. Plankton communities in the Southern Mediterranean Sea had lower MMHg concentrations than those in the Northern Mediterranean Sea. These results highlighted the influence of environmental conditions and trophodynamics on the transfer of Hg in Mediterranean plankton food webs, with implications for higher trophic level consumers.

Health risk assessment of methyl mercury from fish consumption in a sample of adult Qatari residents

Fish constitutes an essential source of high-quality protein and is, at the same time, the source of exposure to many hazardous contaminants, namely mercury and methyl mercury (MeHg). This study aims at assessing the risk that MeHg poses to the health of adult Qatari residents through fish consumption. Data on fish consumption were collected using a self-administered online survey composed of three sections that collected information about the fish-eating patterns of the participants. The fish species that were reported to be consumed by ≥ 3% of the respondents were sampled and analyzed for their total mercury (T-Hg) content levels. MeHg concentrations were derived from T-Hg content levels using a scenario-based approach. Disaggregated fish consumption and contamination data were combined using the deterministic approach to estimate MeHg intakes. The average, 75th, and 95th percentiles of the MeHg intake estimates were determined and compared to the tolerable weekly intake (TWI) set by the European Food Safety Agency (EFSA) (1.3 μg·kg^-1·w^-1). All fish samples contained T-Hg at levels ˂ 0.3-0.5 µg/g with a mean value of 0.077 µg/g. The study population had an average fish consumption of 736.0 g/week. The average estimated weekly intakes of MeHg exceeded TWI for some fish consumers including females of childbearing age and those following a high-protein diet. Our study highlights the need to establish regulatory guidelines and dietary advice based on risk/benefit ratio.

Warming Affects Bioconcentration and Bioaccumulation of Per- and Polyfluoroalkyl Substances by Pelagic and Benthic Organisms in a Water-Sediment System

Warming and exposure to emerging global pollutants, such as per- and polyfluoroalkyl substances (PFAS), are significant stressors in the aquatic ecosystem. However, little is known about the warming effect on the bioaccumulation of PFAS in aquatic organisms. In this study, the pelagic organisms Daphnia magna and zebrafish, and the benthic organism Chironomus plumosus were exposed to 13 PFAS in a sediment-water system with a known amount of each PFAS at different temperatures (16, 20, and 24 °C). The results showed that the steady-state body burden (C_b-ss) of PFAS in pelagic organisms increased with increasing temperatures, mainly attributed to increased water concentrations. The uptake rate constant (k_u) and elimination rate constant (k_e) in pelagic organisms increased with increasing temperature. In contrast, warming did not significantly change or even mitigate C_b-ss of PFAS in the benthic organism Chironomus plumosus, except for PFPeA and PFHpA, which was consistent with declined sediment concentrations. The mitigation could be explained by the decreased bioaccumulation factor due to a more significant percent increase in k_e than k_u, especially for long-chain PFAS. This study suggests that the warming effect on the PFAS concentration varies among different media, which should be considered for their ecological risk assessment under climate change.

Understanding the role of ecological factors affecting mercury concentrations in the blue shark (Prionace glauca)

Human activities have increased environmental concentrations of pollutants in marine ecosystems, which can cause harmful effects on marine organisms. Top predators are particularly susceptible to bioaccumulation and biomagnification of pollutants through the food webs and are described as good sentinels for monitoring metal accumulation such mercury (Hg) in marine ecosystems. However, to be used as sentinels, it is important to understand the main ecological factors affecting the concentrations of pollutants in these organisms. In the present study, our main objective was to investigate the effect of body size, sex, trophic niche and geographic area on Hg concentrations in a top marine top predator, the blue shark (Prionace glauca). We analysed Hg in muscle samples from male and female blue sharks of different body sizes collected from the waters surrounding the Canary Islands and the South of Portugal, in the Atlantic Ocean, to waters of the north-western Mediterranean Sea. The results revealed that the sampling area was an important factor explaining Hg concentrations, showing higher values in the Mediterranean blue sharks. We also found a positive relationship between Hg concentrations and body size of blue sharks, indicating a bioaccumulation process of this pollutant in relation with body size. Moreover, we observed a relationship between Hg concentrations and δ¹³C values, a proxy of the use of inshore-offshore marine habitats. Individuals with depleted δ¹³C values that potentially foraged in offshore waters showed higher Hg values. Importantly, most of the analysed blue sharks presented Hg concentrations that exceeded the limits established by the European Union for human consumption.

Mercury maternal transfer in two placental sharks and a yolk-sac ray from Baja California Sur, Mexico

Total mercury (THg) concentrations were measured in muscle and liver of two placental viviparous sharks, the Pacific sharpnose shark (Rhizoprionodon longurio) and the brown smooth-hound (Mustelus henlei); as well as in the muscle, liver, and yolk of the yolk-sac viviparous speckled guitarfish (Pseudobatos glaucostigmus) in Baja California Sur. The aim was to determine which factors could be involved in maternal transfer and resultant maternal and embryonic THg concentration. Higher THg concentrations were found in pregnant females compared to embryos paired tissues. THg concentrations of embryo tissues decreased with total length (T_L), except for the muscle of the Pacific sharpnose shark. THg concentrations of embryo muscle was positively related to THg concentration in the muscle of pregnant females. Embryos T_L, muscle THg concentration of pregnant females, percentage of THg concentration in embryos, along with the reproductive strategy are relevant factors required to improve our understanding of THg concentration in embryo tissues.

Two cetacean species reveal different long-term trends for toxic trace elements in European Atlantic French waters

Cetaceans have been naturally exposed to toxic trace elements (TEs) on an evolutionary time scale. Hence, they have developed mechanisms to control and/or mitigate their toxic effects. These long-lived species located at high trophic positions and bioaccumulating toxic elements are assumed to be good biomonitoring organisms. However, anthropogenic emissions have strongly increased environmental levels of toxic TEs in the last decades, questioning the efficiency of the detoxication mechanisms in cetaceans. In this context, temporal trends of mercury (Hg), cadmium (Cd) and lead (Pb) concentrations were studied through the analysis of 264 individuals from two cetacean species the common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) and belonging to two different Management Units (MUs) for the latter. These individuals stranded along the French Atlantic coasts from 2000s to 2017. All the trends presented were age- and sex-corrected and stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were measured as proxies of their feeding ecology. Results showed that Pb concentrations clearly decreased over time in both species and MUs. This decrease agrees with the lead petrol regulation after 2000s, supporting the use of these species as valuable bioindicators of changes for TE levels in the marine environment. A significant long-term increase of total Hg concentrations was only observed in common dolphins. Cadmium concentrations also revealed different trends over the period in both species. The different Hg and Cd trends observed in the two species, probably reflected a contrasted contamination of habitat and prey species than a global increase of the contamination in the environment. These results highlight the necessity and gain of using different species to monitor changes in marine environments, each of them informing on the contamination of its own ecological niche. Lastly, the Se:Hg molar ratios of species suggested a low risk for Hg toxicity over time.

Predicted Near-Future Oceanic Warming Enhances Mercury Toxicity in Marine Copepods

The effects of acute mercury exposure (118 µg/L) on the marine copepod Tigriopus japonicus were examined at 22 and 25 °C for 24 h and compared with controls. Mercury accumulation and seven genes related to antioxidant/stress responses were analyzed after exposure. The 24-h LC₅₀ value decreased in the warmer environment and mercury accumulation was elevated. Under both temperatures, mercury significantly affected the expression of all analyzed genes and probably caused oxidative stress. Intriguingly, at the same mercury concentration, most genes were upregulated at the higher relative to the lower temperature, and the copepods likely initiated more compensatory reactions to counteract increased mercury toxicity associated with the warmer temperature. Overall, this study suggests a molecular mechanism by which marine copepods could respond to future oceanic warming and mercury pollution.

Mediterranean Mercury Assessment 2022: An Updated Budget, Health Consequences, and Research Perspectives

Mercury (Hg) and especially its methylated species (MeHg) are toxic chemicals that contaminate humans via the consumption of seafood. The most recent UNEP Global Mercury Assessment stressed that Mediterranean populations have higher Hg levels than people elsewhere in Europe. The present Critical Review updates current knowledge on the sources, biogeochemical cycling, and mass balance of Hg in the Mediterranean and identifies perspectives for future research especially in the context of global change. Concentrations of Hg in the Western Mediterranean average 0.86 ± 0.27 pmol L^-1 in the upper water layer and 1.02 ± 0.12 pmol L^-1 in intermediate and deep waters. In the Eastern Mediterranean, Hg measurements are in the same range but are too few to determine any consistent oceanographical pattern. The Mediterranean waters have a high methylation capacity, with MeHg representing up to 86% of the total Hg, and constitute a source of MeHg for the adjacent North Atlantic Ocean. The highest MeHg concentrations are associated with low oxygen water masses, suggesting a microbiological control on Hg methylation, consistent with the identification of hgcA-like genes in Mediterranean waters. MeHg concentrations are twice as high in the waters of the Western Basin compared to the ultra-oligotrophic Eastern Basin waters. This difference appears to be transferred through the food webs and the Hg content in predators to be ultimately controlled by MeHg concentrations of the waters of their foraging zones. Many Mediterranean top-predatory fish still exceed European Union regulatory Hg thresholds. This emphasizes the necessity of monitoring the exposure of Mediterranean populations, to formulate adequate mitigation strategies and recommendations, without advising against seafood consumption. This review also points out other insufficiencies of knowledge of Hg cycling in the Mediterranean Sea, including temporal variations in air-sea exchange, hydrothermal and cold seep inputs, point sources, submarine groundwater discharge, and exchanges between margins and the open sea. Future assessment of global change impacts under the Minamata Convention Hg policy requires long-term observations and dedicated high-resolution Earth System Models for the Mediterranean region.

The nutritional and sensory quality of seafood in a changing climate

Climate change is impacting living marine resources, whilst concomitantly, global reliance on seafood as a source of nutrition is increasing. Here we review an emerging research frontier, identifying significant impacts of climate-driven environmental change on the nutritional and sensory quality of seafood, and implications for human health. We highlight that changing ocean temperature, pH and salinity can lead to reductions in seafood macro and micronutrients, including essential nutrients such as protein and lipids. However, the nutritional quality of seafood appears to be more resilient in taxa that inhabit naturally variable environments such as estuaries and shallow near-coastal habitats. We develop criteria for assessing confidence in categorising the nutritional quality of seafood as vulnerable or resilient to climate change. The application of this criteria to a subset of seafood nutritional studies demonstrates confidence levels are generally low and could be improved by more realistic experimental designs and research collaboration. We highlight knowledge gaps to guide future research in this emerging field.

Selecting the best non-invasive matrix to measure mercury exposure in human biomonitoring surveys

Exposure to mercury, even at low doses, can affect human health, well-being and life quality at a broad scale. Human biomonitoring is the most straightforward approach to measure and quantify mercury exposure in humans. The objective of the present study is to compare and discuss the relationships between Hg levels in the most used matrices, hair, urine and blood, with the aim to ascertain to what extent mercury exposure and internal mercury levels could be predicted by monitoring non-invasive matrices. The study population (n = 527) is a subsample from Spanish BIOAMBIENT. ES study (18-65 y, both sexes), with data of Hg levels in blood, hair, and urine from the same individuals. We found strong inter-matrix Spearman correlations between blood and hair mercury (r² = 0.84), while the correlations for urine and blood mercury (r²⁼0.64) and urine and hair mercury (r²⁼0.65) were weaker. The geometric mean of the ratios between matrices were (GM, 95%CI): Hair/Blood 280 (271-290), Urine/Blood 0.174 (0.163-0.186) and Hair/Urine 2070 (1953-2194) and Urine/Blood 0.135 (0.128-0.144) for urine corrected by creatinine. High individual variation was observed particularly in those ratios involving urine. Considering the wide range of values observed in the ratios, we do not recommend applying them at individual level. The predictive models indicate that hair Hg was a more accurate predictor than urine. The inclusion of urine values did not increase the predictive accuracy, so, we recommend a cautious interpretation of urine mercury levels. Our study presents clear evidence that in a population highly exposed to food-borne mercury, a large portion of urinary mercury primarily emanates from methylmercury demethylation. We conclude that urine, as a non-invasive matrix, can be used as a reliable qualitative biomarker for Hg exposure when hair measurements not are available. For quantitative individual assessments, still blood measurements are to be preferred.

Biochemical, physiological (haematological, oxygen-consumption rate) and behavioural effects of mercury exposures on the freshwater snail, Bellamya bengalensis

The widespread occurrence of Mercury (Hg) and its derivatives in the aquatic environment and risks to the health of local populations has necessitated investigations into its toxic effects on sessile species. The toxicity of Mercury was observed sequentially from 96 h acute exposure regime (behavioural endpoints) to chronic durations (haematological and biochemical toxicity endpoints) in Bellamya bengalensis. Time-dependent lethal endpoints for acute toxicity (LC50) of mercury i.e., 24,48,72 and 96 h were estimated as 0.94, 0.88, 0.69 and 0.40 mg/l respectively. Threshold effect values i.e., LOEC (Lowest Observed Effect Concentration), NOEC (No Observed Effect Concentration) and MATC (Maximum Acceptable Toxicant Concentration) at 96 h were found to be 0.10, 0.05, 0.039 mg/l respectively. The study of oxygen consumption rate and behavioural changes during acute toxicity and haematological and biochemical responses during chronic toxicity to sublethal concentrations (10% and 20% of 96 h LC50) of mercury to the snail were also conducted. The organisms showed initial elevation at 24 h but later gradual decrease in oxygen consumption rate with the increase of concentration of mercury and time of exposure. For behavioural studies, variable test concentrations from 0.00 to 1.00 mg/l were used for 24, 48, 72 and 96 h. The crawling activity and clumping tendency decreased with the progress of time at all treatment periods and stopped ultimately at 96 h of exposure from 0.7 mg/l onwards whereas touch reflex was not observed at 96 h exposure at all treatments except at 0.09 mg/l. In haemocyte count, no significant variation was observed among control values between various exposure periods (p > 0.05) though variations were observed in sub-lethal concentrations versus control at all treatment duration (7, 14, 21, 28d, p < 0.05). In biochemical response study, the protein content in hepatopancreas of the snails treated at sublethal concentrations of mercury (10% and 20% of 96 h LC50) reduced significantly versus control after 21d of exposure (p < 0.05). In gonads, the protein content of the treated snails significantly reduced at all treatment concentrations versus control at all exposure times (p < 0.05). Based on the safe levels indicated above, the concentration of 0.01 to 0.04 ppm of mercury can be considered safe for Bellamya bengalensis and any less-hardy aquatic species. These responses elicited by our molluscan model will not only help in biomonitoring of environmental mercury contamination in water bodies but will also provide support to ecological health and risk assessment.

ENSO Climate Forcing of the Marine Mercury Cycle in the Peruvian Upwelling Zone Does Not Affect Methylmercury Levels of Marine Avian Top Predators

Climate change is expected to affect marine mercury (Hg) biogeochemistry and biomagnification. Recent modeling work suggested that ocean warming increases methylmercury (MeHg) levels in fish. Here, we studied the influence of El Niño Southern Oscillations (ENSO) on Hg concentrations and stable isotopes in time series of seabird blood from the Peruvian upwelling and oxygen minimum zone. Between 2009 and 2016, La Niña (2011) and El Niño conditions (2015-2016) were accompanied by sea surface temperature anomalies up to 3 °C, oxycline depth change (20-100 m), and strong primary production gradients. Seabird Hg levels were stable and did not co-vary significantly with oceanographic parameters, nor with anchovy biomass, the primary dietary source to seabirds (90%). In contrast, seabird Δ¹⁹⁹Hg, proxy for marine photochemical MeHg breakdown, and δ¹⁵N showed strong interannual variability (up to 0.8 and 3‰, respectively) and sharply decreased during El Niño. We suggest that lower Δ¹⁹⁹Hg during El Niño represents reduced MeHg photodegradation due to the deepening of the oxycline. This process was balanced by equally reduced Hg methylation due to reduced productivity, carbon export, and remineralization. The non-dependence of seabird MeHg levels on strong ENSO variability suggests that marine predator MeHg levels may not be as sensitive to climate change as is currently thought.

Co-occurrence of contaminants in marine fish from the North East Atlantic Ocean: Implications for human risk assessment

Marine fish from the North East Atlantic Ocean (NEAO) are nutrient rich and considered a valuable economic resource. However, marine fish are also a major dietary source of several contaminants, including persistent organic pollutants (POPs) and heavy metals. Using one of the world's largest seafood datasets (n > 25,000 individuals), comprising 12 commercially important fish species collected during 2006-2019 in the NEAO, we assessed the co-occurrence of elements and POPs, and evaluated potential risks to human consumers. Several positive correlations between concentrations of mercury (Hg), dioxins, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were observed. Concentrations of Hg, dioxins, PCBs and PBDEs increased from North to South and associations between marine sediment contamination, sea temperature, and fish Hg and POPs concentrations were identified using multi-linear regression (MLR) models. In general, Hg concentrations in fillet and liver of fish were positively associated with increases in both sediment contamination and sea temperature. POPs concentrations in both fillet and liver were positively associated with increases in sediment contamination, and only POPs concentrations in the liver of benthopelagic and demersal species were found to be positively correlated with sea temperature. Using a probabilistic approach to estimate human contaminant exposure from seafood, we showed that intake of pelagic species posed the highest risk of dioxins and dioxin-like PCBs (DL-PCBs) exposure, while intake of benthopelagic and demersal species posed the highest risk of Hg exposure. This study can serve as a model to further understand the distribution, co-occurrence, and trends of contaminants in seafood harvested from the NEAO and their potential risks to human consumers.

Monitoring of Environmental Hg Occurrence in Tunisian Coastal Areas

Total mercury (Hg) was determined in 450 environmental samples (seawater, sediment plant and fish) from five Mahdia coastal areas (Tunisia). Tolerable Weekly Intake% (TWI) values, according to the European Food Safety Authority (EFSA), were calculated based on the average metal concentration in fish and the average weekly fish consumption rate. Hg was accumulated mainly in fish and in Posidonia oceanica leaves. Hg in sediment ranged from 1.88 μg/kg dry weight (d.w.) to 7.48 μg/kg d.w., while it was between 0.32 μg/kg and 0.19 μg/kg in seawaters. Our study showed high concentration in Posidonia oceanica in S3 (plant = 16.76 ± 4.48 μg/kg d.w.) as compared to those in S4 sites (plant = 5.33 ± 0.05 μg/kg d.w.). Concentrations for S. aurata and S. salpa in the Rejiche area exceeded the EC 1881/2006 legislation with values of 1.9 mg/kg and 2.5 mg/kg, respectively, and consumers may be exposed to high concentrations of Hg that exceeds the EFSA. The results showed that the fish species should be constantly monitored due to their TWI% of 154.5% for S. aurata and 209.8% S. salpa respectively.

Distribution of mercury species in different tissues and trophic levels of commonly consumed fish species from the south Bay of Biscay (France)

Mercury (Hg) is a contaminant of global concern in marine ecosystems, notably due to its ability to accumulate and concentrate in food webs. Concentrations of total mercury (THg), methylmercury (MeHg) and inorganic mercury (IHg) were assessed and compared in different tissues (liver, muscle, and gonads) of three common fish species (hake Merluccius merluccius, red mullet Mullus surmuletus, and sole Solea solea) from the continental shelf from the southern part of the Bay of Biscay. Several studies investigated Hg concentration in fish muscle, but few assessed concentrations in other organs, despite the importance of such data to understand contaminant organotropism and metabolization. Results showed that trophic position and feeding habitat are required to understand the variability of Hg concentration in muscle between fish species. In addition, high MeHg/THg ratio in muscle could be explained by the predatory behavior of the studied fish species and the biomagnification of this Hg species within the food web, MeHg. Despite differences between species, Hg concentration was always higher in muscle (from 118 ± 64 to 338 ± 101 ng g^-1 w.w.) and liver (from 122 ± 108 to 271 ± 95 ng g^-1 w.w.). These results can be related to physiological processes especially the MeHg detoxification strategies.

Acquiring an evolutionary perspective in marine ecotoxicology to tackle emerging concerns in a rapidly changing ocean

Tens of thousands of anthropogenic chemicals and wastes enter the marine environment each year as a consequence of the ever-increasing anthropogenic activities and demographic growth of the human population, which is majorly concentrated along coastal areas. Marine ecotoxicology has had a crucial role in helping shed light on the fate of chemicals in the environment, and improving our understanding of how they can affect natural ecosystems. However, chemical contamination is not occurring in isolation, but rather against a rapidly changing environmental horizon. Most environmental studies have been focusing on short-term within-generation responses of single life stages of single species to single stressors. As a consequence, one-dimensional ecotoxicology cannot enable us to appreciate the degree and magnitude of future impacts of chemicals on marine ecosystems. Current approaches that lack an evolutionary perspective within the context of ongoing and future local and global stressors will likely lead us to under or over estimations of the impacts that chemicals will exert on marine organisms. It is therefore urgent to define whether marine organisms can acclimate, i.e. adjust their phenotypes through transgenerational plasticity, or rapidly adapt, i.e. realign the population phenotypic performances to maximize fitness, to the new chemical environment within a selective horizon defined by global changes. To foster a significant advancement in this research area, we review briefly the history of ecotoxicology, synthesis our current understanding of the fate and impact of contaminants under global changes, and critically discuss the benefits and challenges of integrative approaches toward developing an evolutionary perspective in marine ecotoxicology: particularly through a multigenerational approach. The inclusion of multigenerational studies in Ecological Risk Assessment framework (ERA) would provide significant and more accurately information to help predict the risks of pollution in a rapidly changing ocean.

An upwelling area as a hot spot for mercury biomonitoring in a climate change scenario: A case study with large demersal fishes from Southeast Atlantic (SE-Brazil)

Data concerning the monomethylmercury (MeHg) bioaccumulation in marine biota from Southeast Atlantic Ocean are scarce. This study purchased large specimens of demersal fishes from an upwelling region: Warsaw grouper (Epinephelus nigritus), Dusky grouper (Epinephelus marginatus) and Namorado sandperch (Pseudopercis numida). The authors addressed the bioaccumulation and toxicokinetic of mercury in fish organs, and the toxicological risk for human consumption of this metal in the muscle tissues accessed. Additionally, the present study discussed the possible implications of shifts in key variables of the environment related to a climate-changing predicted scenario, to the mercury biomagnification in a tropical upwelling system. The muscle was the main stock of MeHg, although the highest THg concentrations have been found in liver tissue. Regarding the acceptable maximum level (ML = 1 mg kg^-1), E. nigritus and E. marginatus showed 22% of the samples above this limit. Concerning P. numida, 77% were above 0.5 mg kg^-1, but below the ML. The %MeHg in liver and muscle showed no significative correlations, which suggest independent biochemical pathways to the toxicokinetic of MeHg, and constrains the indirect assessment of the mercury contamination in the edible tissue by the liver analyses. The present study highlights the food web features of a tropical upwelling ecosystem that promote mercury biomagnification. Additionally, recent studies endorse the enhancement of upwelling phenomenon due to the climate global changes which boost the pumping of mercury enriched water to the oceanic upper layer. Therefore, the upwelling areas might be hot spots for MeHg monitoring in marine biota.

Regulation of glutathione-dependent antioxidant defense system of grass carp Ctenopharyngodon idella under the combined stress of mercury and temperature

In this study, we investigated the combined effects of temperatures fluencies and mercury (Hg) on glutathione-dependent antioxidant system in fish, by measuring the oxidative stress indicator (LPO, lipid peroxidation) and the parameters involved in the glutathione-related antioxidant defense system (GPx, glutathione peroxidase; GR, glutathione reductase; GST, glutathione S-transferase; GSH, reduced glutathione), as well as the expression of related genes in grass carp, Ctenopharyngodon idella. Fish (45.37 ± 3.58 g) were exposed to 10 test groups, e.g., 15 °C with/without Hg, 20 °C with/without Hg, 25 °C with/without Hg, 30 °C with/without Hg, 35 °C with/without Hg for 4 weeks. Three-way ANOVA was used to analyze the correlation between the measured parameters and experimental conditions (water temperature, Hg exposure, exposure time, and their interactions.). Our results show that there is no interaction between mercury and low temperature, but the combined effect at high temperature has been confirmed, which indicated the glutathione-dependent enzyme system in grass carp has a complex regulatory mechanism with temperature fluctuations. In the actual field monitoring, it is necessary to consider the impact of extreme temperature on the toxicity of pollutants in the aquatic ecosystem.

Stable mercury concentrations of tropical tuna in the south western Pacific ocean: An 18-year monitoring study

Global anthropogenic mercury (Hg) emissions to the atmosphere since industrialization are widely considered to be responsible for a significant increase in surface ocean Hg concentrations. Still unclear is how those inputs are converted into toxic methylmercury (MeHg) then transferred and biomagnified in oceanic food webs. We used a unique long-term and continuous dataset to explore the temporal Hg trend and variability of three tropical tuna species (yellowfin, bigeye, and skipjack) from the southwestern Pacific Ocean between 2001 and 2018 (n = 590). Temporal trends of muscle nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope ratios, amino acid (AA) δ¹⁵N values and oceanographic variables were also investigated to examine the potential influence of trophic, biogeochemical and physical processes on the temporal variability of tuna Hg concentrations. For the three species, we detected significant inter-annual variability but no significant long-term trend for Hg concentrations. Inter-annual variability was related to the variability in tuna sampled lengths among years and to tuna muscle δ¹⁵N and δ¹³C values. Complementary AA- and model-estimated phytoplankton δ¹⁵N values suggested the influence of baseline processes with enhanced tuna Hg concentrations observed when dinitrogen fixers prevail, possibly fuelling baseline Hg methylation and/or MeHg bioavailability at the base of the food web. Our results show that MeHg trends in top predators do not necessary capture the increasing Hg concentrations in surface waters suspected at the global oceanic scale due to the complex and variable processes governing Hg deposition, methylation, bioavailability and biomagnification. This illustrates the need for long-term standardized monitoring programs of marine biota worldwide.

Warming enhances lanthanum accumulation and toxicity promoting cellular damage in glass eels (Anguilla anguilla)

Cumulative and continuing human emissions of greenhouse gases to the atmosphere are causing ocean warming. Rising temperature is a major threat to aquatic organisms and may affect physiological responses, such as acid-base balance, often compromising species fitness and survival. It is also expected that warming may influence the availability and toxicological effects of pollutants, including Rare Earth Elements. These are contaminants of environmental emerging concern with great economic interest. This group comprises yttrium, scandium and lanthanides, being Lanthanum (La) one of the most common. The European eel (Anguilla anguilla) is critically endangered and constitutes a delicacy in South East Asia and Europe, being subject to an increasing demand on a global scale. Considering the vulnerability of early life stages to contaminants, we exposed glass eels to 1.5 μg L^-1 of La for five days, plus five days of depuration, under a present-day temperature and warming scenarios (△T = +4 °C). The aim of this study was to assess the bioaccumulation, elimination and specific biochemical enzymatic endpoints in glass eels (Anguilla anguilla) tissues, under warming and La. Overall, our results showed that the accumulation and toxicity of La were enhanced with increasing temperature. The accumulation was higher in the viscera, followed by the head, and ultimately the body. Elimination was less effective under warming. Exposure to La did not impact acetylcholinesterase activity. Moreover, lipid peroxidation peaked after five days under the combined exposure of La and warming. The expression of heat shock proteins was majorly suppressed in glass eels exposed to La, at both tested temperatures. This result suggests that, when exposed to La, glass eels were unable to efficiently prevent cellular damage, with a particularly dramatic setup in a near-future scenario. Further studies are needed towards a better understanding of the effects of lanthanum in a changing world.

Elevated temperature enhances the bioavailability of pyrene to Daphnia magna in the presence of dissolved organic matter: Implications for the effect of climate warming

Dissolved organic matter (DOM) is an essential factor in natural waters to affect the bioavailability of hydrophobic organic compounds (HOCs). Climate warming may influence the partition of HOCs between DOM and water as well as the physiology of organisms. Thus, we hypothesized that elevated temperature might affect the bioavailability of HOCs in the presence of DOM. To test this hypothesis, the effect of temperature on the bioavailability of pyrene to Daphnia magna (D. magna) in water-DOM (fulvic acid) system was investigated. The results showed that, although the concentration of freely dissolved pyrene increased slightly with temperature in the presence of DOM when the level of total dissolved pyrene was kept constant, D. magna immobilization (increased by 50.0-167%) and internal body burden of pyrene (increased by 18.4-41.5%) increased significantly with every 4 °C increase in temperature (16, 20, 24 °C). The main reasonable explanation for this result is that elevated temperature promoted pyrene uptake by D. magna. It was found that the increase percentage of 1-hydroxypyrene (main metabolite of pyrene) concentrations with temperature was higher than that of pyrene concentrations in the body except gut of D. magna. This result indicated that increased temperature might enhance the metabolic rates of D. magna, thus leading to increased uptake rate of freely dissolved and DOM-associated pyrene. This study suggests that elevated temperature might enhance the bioavailability of HOCs in natural waters through influencing both the bioavailable fraction of HOCs and their uptake rates in aquatic organisms, and this should be considered for evaluating their eco-environmental risks under the context of climate warming.

Tissue-Specific Accumulation and Antioxidant Defenses in Flounder (Paralichthys olivaceus) Juveniles Experimentally Exposed to Methylmercury

Methylmercury (MeHg) is the most toxic form of mercury and can accumulate in the cells of marine organisms, such as fish, causing adverse effects on various physiological functions. This study examined MeHg accumulation and its toxicological role in antioxidant defenses in tissues, including the liver, gills, and muscle of flounder (Paralichthys olivaceus) juveniles. After 30 d of MeHg exposure (0, 0.1, 1.0, 10.0, and 20.0 µg L^-1), the accumulation of MeHg in the three tissues correlated positively with the concentration of MeHg and exhibited tissue specificity in the order of liver > gills > muscle. Among the antioxidant markers, the activities of SOD (superoxide dismutase) and GST (glutathione S-transferase) as well as the content of glutathione (GSH) in the liver and gills were induced at 0.1-10.0 µg L^-1 but repressed at 20.0 µg L^-1. The activities of SOD and GST and the content of GSH in the muscle significantly increased with increasing MeHg concentration. Catalase (CAT) activity in the liver was induced at 0.1-1.0 µg L^-1 but inhibited at 10.0-20.0 µg L^-1, whereas exposure to MeHg did not remarkably affect CAT activity in the gills and muscle. The levels of lipid peroxidation (LPO) increased dose dependently, showing tissue specificity with the highest level in the liver, then the gills, followed by muscles. Overall, higher sensitivity to oxidative stress induced by MeHg was detected in the liver than the gills and muscle. These findings improve our understanding of the tissue-specific accumulation of heavy metals and their roles in antioxidant responses in marine fish subjected to MeHg exposure.

Differential susceptibility of PC12 and BRL cells and the regulatory role of HIF-1α signaling pathway in response to acute methylmercury exposure under normoxia

Hypoxia-inducible factor 1 (HIF-1) is a critical nuclear transcription factor for adaptation to hypoxia; its regulatable subunit, HIF-1α, is a cytoprotective regulatory factor. We examined the effects of methylmercury (MeHg) in rat adrenal pheochromocytoma (PC12) cells and the rat hepatocyte cell line BRL. MeHg treatment led to time- and concentration-dependent toxicity in both lines with statistically significant cytotoxic effects at 5 μM and 10 μM in PC12 and BRL, respectively, at 0.5 h. HIF-1α protein levels were significantly decreased at 2.5 (PC12) and 5 (BRL) μM MeHg. Furthermore, MeHg reduced the protein levels of HIF-1α and its target genes (glucose transporter-1, vascular endothelial growth factor-A and erythropoietin). Overexpression of HIF-1α significantly attenuated MeHg-induced toxicity in both cell types. Notably, cobalt chloride, a pharmacological inducer of HIF-1α, significantly attenuated MeHg-induced toxicity in BRL but not PC12. In both cell lines, an inhibitor of prolyl hydroxylase, 3, 4-dihydroxybenzoic acid, and the proteasome inhibitor carbobenzoxy-L-leucyl-L-leucyl-L-leucinal(MG132), antagonized MeHg toxicity, while 2-methoxyestradiol, a HIF-1α inhibitor, significantly increased it. These data establish that: (a) neuron-like PC12 cells are more sensitive to MeHg than non-neuronal BRL cells; (b) HIF-1α plays a similar role in MeHg-induced toxicity in both cell lines; and (c) upregulation of HIF-1α offers general cytoprotection against MeHg toxicity in PC12 and BRL cell lines.

Warmer temperature increases mercury toxicity in a marine copepod

Marine biota have been co-challenged with ocean warming and mercury (Hg) pollution over many generations because of human activities; however, the molecular mechanisms to explain their combined effects are not well understood. In this study, a marine planktonic copepod Pseudodiaptomus annandalei was acutely exposed to different temperature (22 and 25 °C) and Hg (0 and 118 μg/L) treatments in a 24-h cross-factored experiment. Hg accumulation and its subcellular fractions were determined in the copepods after exposure. The expression of the genes of superoxide dismutase (SOD), glutathione peroxidase (GPx), metallothionein1 (mt1), heat shock protein 70 (hsp70), hsp90, hexokinase (hk), and pyruvate kinase (pk) was also analyzed. Both the Hg treatment alone and the combined exposure of warmer temperature plus Hg pollution remarkably facilitated Hg bioaccumulation in the exposed copepods. Compared with the Hg treatment alone, the combined exposure increased total Hg accumulation and also the amount of Hg stored in the metal-sensitive fractions (MSF), suggesting elevated Hg toxicity in P. annandalei under a warmer environment, given that the MSF is directly related to metal toxicity. The warmer temperature significantly up-regulated the mRNA levels of mt1, hsp70, hsp90, and hk, indicating the copepods suffered from thermal stress. With exposure to Hg, the mRNA level of SOD increased strikingly but the transcript levels of hsp90, hk, and pk decreased significantly, indicating that Hg induced toxic events (e.g., oxidative damage and energy depletion). Particularly, in contrast to the Hg treatment alone, the combined exposure significantly down-regulated the mRNA levels of SOD and GPx but up-regulated the mRNA levels of mt1, hsp70, hsp90, hk, and pk. Collectively, the results of this study indicate that ocean warming will potentially boost Hg toxicity in the marine copepod P. annandalei, which is information that will increase the accuracy of the projections of marine ecosystem responses to the joint effects of climate change stressors and metal pollution on the future ocean.

Imaging Differential Mercury Species Bioaccumulation in Glass Eels Using Isotopic Tracers and Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Dramatic increases in global mercury pollution require a deeper understanding of specific toxicity mechanisms for mercury compounds in organisms. Despite numerous studies addressing mercury toxicity, the detailed mechanisms underlying its transport and accumulation in fish remain unclear. The aim of this study was to unravel differential uptake pathways for mercury compounds, metabolisation, and sequestration mechanisms in glass eels using techniques able to localize at the tissue and organ levels. A multi isotope image mapping procedure was developed to simultaneously study the uptake and distribution of both mercury compounds MeHg and Hg(II) within the organs of the whole organism. The use of isotopically labelled Hg species (methylmercury Me201Hg and inorganic mercury 199Hg(II)) and image based on isotope ratio instead of elemental signals allowed to visualize spatially and with time the differential Hg species uptake, transport, and sequestration routes. The results showed a preferential uptake of the MeHg counterpart and a dynamic transport of MeHg within different organs. The gills were the main target organs for MeHg uptake, whereas the skeletal muscle was the final MeHg storage tissue. Hg(II) was found to mainly transit by the gills and the olfactory bulbs with a very low transfer and storage in the other organs and a rapid depuration. No significant internal demethylation and methylation was observed during this experimentation.

Mercury in Juvenile Solea senegalensis: Linking Bioaccumulation, Seafood Safety, and Neuro-Oxidative Responses under Climate Change-Related Stressors

Mercury (Hg) is globally recognized as a persistent chemical contaminant that accumulates in marine biota, thus constituting an ecological hazard, as well as a health risk to seafood consumers. Climate change-related stressors may influence the bioaccumulation, detoxification, and toxicity of chemical contaminants, such as Hg. Yet, the potential interactions between environmental stressors and contaminants, as well as their impacts on marine organisms and seafood safety, are still unclear. Hence, the aim of this work was to assess the bioaccumulation of Hg and neuro-oxidative responses on the commercial flat fish species Solea senegalensis (muscle, liver, and brain) co-exposed to dietary Hg in its most toxic form (i.e., MeHg), seawater warming (ΔT°C = +4 °C), and acidification (pCO2 = +1000 µatm, equivalent to ΔpH = −0.4 units). In general, fish liver exhibited the highest Hg concentration, followed by brain and muscle. Warming enhanced Hg bioaccumulation, whereas acidification decreased this element’s levels. Neuro-oxidative responses to stressors were affected by both climate change-related stressors and Hg dietary exposure. Hazard quotient (HQ) estimations evidenced that human exposure to Hg through the consumption of fish species may be aggravated in tomorrow’s ocean, thus raising concerns from the seafood safety perspective.

Evaluation of Dietary Organic and Inorganic Mercury Threshold Levels on Induced Mercury Toxicity in a Marine Fish Model

Simple Summary

This investigation was executed to establish the threshold level of inorganic and organic mercury incorporated in the diet of juvenile olive flounder in relation to the broken-line regression model for the percentage of weight gain of fish. Organic mercury incorporated diet resulted in more toxic behavior than its counterpart inorganic mercury in olive flounder. Mercury was found to be more biomagnified in kidney tissue than liver and gill tissues of fish. The study has importance in terms of knowledge on mercury toxicity in marine fish.

Abstract

Mercury as one of the most toxic elements can be present in organic or inorganic form in marine fishes, which may cause a potential threat to public health. In this study, we investigated to determine the dietary organic (O-Hg) and inorganic (I-Hg) mercury threshold levels on induced mercury toxicity in juvenile olive flounder, Paralichthys olivaceus as a marine fish model. Twenty-eight fish averaging 3.1 ± 0.05 g (mean ± SD) were arbitrarily assigned to each of 27 tanks. Each tank was arbitrarily restricted to triplicates of nine experimental diets for eight weeks. The experimental diets were manufactured to contain 0 (Control), 10 (I-Hg10, O-Hg10), 20 (I-Hg20, O-Hg20), 40 (I-Hg40, O-Hg40) and 160 (I-Hg160, O-Hg160) mg/kg diet in organic form as methylmercury (MeHg) or in inorganic form as mercuric chloride (HgCl₂). At the termination of the experimental trial, weight gains (WGs) of fish fed the control and 10 (I-Hg10, O-Hg10) diets were remarkably higher than those of fish fed the 20 (I-Hg20, O-Hg20), 40 (I-Hg40, O-Hg40) and 160 (I-Hg160, O-Hg160) (p < 0.05). Specific growth rate and feed efficiency of fish fed control and 10 (I-Hg10, O-Hg10) diets were significantly higher than those of fish fed 40 (I-Hg40, O-Hg40) and 160 (I-Hg160, O-Hg160) diets. In comparison to the dietary inorganic mercury, dietary MeHg bioaccumulation rates were significantly higher in the tissue levels according to the dietary inclusion levels. MeHg accumulated mostly in kidney, followed by liver and gill tissues. HgCl₂ accumulated in tissues, in decreasing order, liver > kidney > gills. A broken-line regression model for percentage of WG indicated that the threshold toxicity level for an Hg-incorporated diet of juvenile olive flounder could be 13.5 mg Hg/kg in the form of HgCl₂ and 8.7 mg Hg/kg in the form of MeHg.

Effects of temperature, salinity, and sediment organic carbon on methylmercury bioaccumulation in an estuarine amphipod

Mercury (Hg) is a global contaminant that poses a human health risk in its organic form, methylmercury (MeHg), through consumption of fish and fishery products. Bioaccumulation of Hg in the aquatic environment is controlled by a number of factors expected to be altered by climate change. We examined the individual and combined effects of temperature, sediment organic carbon, and salinity on the bioaccumulation of MeHg in an estuarine amphipod, Leptocheirus plumulosus, when exposed to sediment from two locations in the Gulf of Maine (Kittery and Bass Harbor) that contained different levels of MeHg and organic carbon. Higher temperatures and lower organic carbon levels individually increased uptake of MeHg by L. plumulosus as measured by the biota-sediment accumulation factor (BSAF), while the effect of salinity on BSAF differed by sediment source. Multi-factor statistical modeling using all data revealed a significant interaction between temperature and organic carbon for both sediments, in which increased temperature had a negative effect on BSAF at the lowest carbon levels and a positive effect at higher levels. Our results suggest that increased temperature and carbon loading, of a magnitude expected as a result from climate change, could be associated with a net decrease in amphipod BSAF of 50 to 71%, depending on sediment characteristics. While these are only first-order projections, our results indicate that the future fate of MeHg in marine food webs is likely to depend on a number of factors beyond Hg loading.

Patterns of trace metal bioaccumulation and trophic transfer in a phytoplankton-zooplankton-small pelagic fish marine food web

Trace metal contamination in the European sardine and anchovy food web was investigated in the Gulf of Lions, NW Mediterranean Sea, including seawater and size fractions of plankton. The results highlighted: i) higher and more variable concentrations in the smaller plankton size classes for all metals except cadmium; ii) higher concentrations in anchovy versus sardine for all elements except lead; iii) different patterns of metal bioaccumulation through the food web: cobalt, nickel, copper, silver, lead and zinc displayed continuously decreasing concentrations (with the exception of increased zinc in fish only), while mercury concentrations dropped considerably in larger plankton size classes and rose significantly in fish. Lastly, cadmium concentrations were found to be highest in intermediate plankton size classes, with very low levels in fish. The need to efficiently characterize the biological composition of plankton in order to fully identify its role in the mobilization and transfer of metals was highlighted.

Climate change and overfishing increase neurotoxicant in marine predators

More than three billion people rely on seafood for nutrition. However, fish are the predominant source of human exposure to methylmercury (MeHg), a potent neurotoxic substance. In the United States, 82% of population-wide exposure to MeHg is from the consumption of marine seafood and almost 40% is from fresh and canned tuna alone¹. Around 80% of the inorganic mercury (Hg) that is emitted to the atmosphere from natural and human sources is deposited in the ocean², where some is converted by microorganisms to MeHg. In predatory fish, environmental MeHg concentrations are amplified by a million times or more. Human exposure to MeHg has been associated with long-term neurocognitive deficits in children that persist into adulthood, with global costs to society that exceed US$20 billion³. The first global treaty on reductions in anthropogenic Hg emissions (the Minamata Convention on Mercury) entered into force in 2017. However, effects of ongoing changes in marine ecosystems on bioaccumulation of MeHg in marine predators that are frequently consumed by humans (for example, tuna, cod and swordfish) have not been considered when setting global policy targets. Here we use more than 30 years of data and ecosystem modelling to show that MeHg concentrations in Atlantic cod (Gadus morhua) increased by up to 23% between the 1970s and 2000s as a result of dietary shifts initiated by overfishing. Our model also predicts an estimated 56% increase in tissue MeHg concentrations in Atlantic bluefin tuna (Thunnus thynnus) due to increases in seawater temperature between a low point in 1969 and recent peak levels-which is consistent with 2017 observations. This estimated increase in tissue MeHg exceeds the modelled 22% reduction that was achieved in the late 1990s and 2000s as a result of decreased seawater MeHg concentrations. The recently reported plateau in global anthropogenic Hg emissions⁴ suggests that ocean warming and fisheries management programmes will be major drivers of future MeHg concentrations in marine predators.

Paralytic Shellfish Toxins and Ocean Warming: Bioaccumulation and Ecotoxicological Responses in Juvenile Gilthead Seabream (Sparus aurata)

Warmer seawater temperatures are expected to increase harmful algal blooms (HABs) occurrence, intensity, and distribution. Yet, the potential interactions between abiotic stressors and HABs are still poorly understood from ecological and seafood safety perspectives. The present study aimed to investigate, for the first time, the bioaccumulation/depuration mechanisms and ecotoxicological responses of juvenile gilthead seabream (Sparus aurata) exposed to paralytic shellfish toxins (PST) under different temperatures (18, 21, 24 °C). PST were detected in fish at the peak of the exposure period (day five, 0.22 µg g^-1 N-sulfocarbamoylGonyautoxin-1-2 (C1 and C2), 0.08 µg g^-1 Decarbamoylsaxitoxin (dcSTX) and 0.18 µg g^-1 Gonyautoxin-5 (B1)), being rapidly eliminated (within the first 24 h of depuration), regardless of exposure temperature. Increased temperatures led to significantly higher PST contamination (275 µg STX eq. kg^-1). During the trial, fish antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; glutathione S-transferase, GST) in both muscle and viscera were affected by temperature, whereas a significant induction of heat shock proteins (HSP70), Ubiquitin (Ub) activity (viscera), and lipid peroxidation (LPO; muscle) was observed under the combination of warming and PST exposure. The differential bioaccumulation and biomarker responses observed highlight the need to further understand the interactive effects between PST and abiotic stressors, to better estimate climate change impacts on HABs events, and to develop mitigation strategies to overcome the potential risks associated with seafood consumption.

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.

Comprehensive study of sulfamethoxazole effects in marine mussels: Bioconcentration, enzymatic activities and metabolomics

Antibiotics accumulation in aquatic organisms may be of great concern from an ecological point of view but also from a human perspective, especially when they are accumulated in edible animals like marine mussels. In this work, mussels (Mytilus galloprovincialis) were exposed to sulfamethoxazole antibiotic (SMX) at 10 µg/L during 96 h, followed by 24 h of depuration. The experiment was carried out at summer and winter conditions. SMX showed a bioconcentration factor in mussel of 1.5 L/kg (dry weight) and 69% of the compound was eliminated from the organism in 24 h. The metabolomics approach revealed alterations in amino acids levels (aspartate, phenylalanine, valine and tryptophan) pinpointing disturbances in osmotic regulation and energy metabolism. Besides, the levels of some nucleotides (guanosine and inosine) and a carboxylic acid were also affected. However, SMX exposed mussels did not show any significant alteration in the enzymatic activities related to the xenobiotic metabolism and oxidative stress. Moreover, some of the changes observed in mussel's metabolites suggested alterations in mussel's organoleptic characteristics that can affect its quality as seafood commodity. Overall, our results showed that SMX exposure to marine mussels may have ecological implications by provoking sub-lethal effects to exposed organisms. Nevertheless, no risk for consumers derived from mussel ingestion is expected due to the low bioconcentration capacity of SMX and fast depuration in this seafood type.

The Toxicological Effects of Mercury Exposure in Marine Fish

Since the Minamata incident in Japan, the public have become increasingly aware of the negative health effects caused by mercury pollution in the ocean. Consequently, there has been significant interest in the health of humans eating fish exposed to mercury (Hg). However, the toxicity of mercury to the marine fish themselves has received far less attention. In this review, we summarize mercury accumulation in marine fish and the toxicological effects of mercury exposure. Results showed that the bioaccumulation of mercury in marine fish was highly variable, and its concentration was affected by the specific physiological and ecological characteristics of different fish species. Mercury exposure can produce teratogenic, neurotoxic effects, and reproductive toxicity. These effects can then cause harm to cells, tissues, proteins and genes, and ultimately, the survival, growth, and behavior of marine fish. Future studies should afford more attention to the toxicological effect of mercury exposure upon marine fish.

Inter-species differences of total mercury and methylmercury in farmed fish in Southern China: Does feed matter?

China is now the largest producer of marine farmed fish and there is a considerable concern of seafood safety due to potential mercury contamination. We analyzed both the total mercury (THg) and methylmercury (MeHg) concentrations in nine species of commercial fish from two marine-cage farms in Southern China. ¹³C and ¹⁵N stable isotopes were concurrently analyzed to identify the artificial feed sources and the trophic levels of farmed fish. Mercury concentrations of all species were much lower than the human health screening values and safety limits established by different countries. Mercury levels in artificial pellets were the main determinants of Hg accumulation in fish between two sites, while somatic growth dilution and size also played an important role. Among the different fish tissues, muscle was a major reservoir for Hg and contained the highest ratio of MeHg/THg, and liver was the second important organ for Hg accumulation in most fish species. Intestine was a critical organ for Hg biotransformation with its %MeHg differing greatly among different fish species. δ¹⁵N analysis could not be used to determine the trophic levels in culturing systems where artificial practices were involved. Based on the δ¹³C signatures, five species of fish were identified to solely feed on the artificial pellets, yet the Hg bioaccumulation differed significantly among these species. We therefore concluded that Hg bioaccumulation in different fish species may be dependent on their internal Hg biotransformation as well as their biokinetics.

A multidimensional concept for mercury neuronal and sensory toxicity in fish - From toxicokinetics and biochemistry to morphometry and behavior

BACKGROUND

Neuronal and sensory toxicity of mercury (Hg) compounds has been largely investigated in humans/mammals with a focus on public health, while research in fish is less prolific and dispersed by different species. Well-established premises for mammals have been governing fish research, but some contradictory findings suggest that knowledge translation between these animal groups needs prudence [e.g. the relative higher neurotoxicity of methylmercury (MeHg) vs. inorganic Hg (iHg)]. Biochemical/physiological differences between the groups (e.g. higher brain regeneration in fish) may determine distinct patterns. This review undertakes the challenge of identifying sensitive cellular targets, Hg-driven biochemical/physiological vulnerabilities in fish, while discriminating specificities for Hg forms.

SCOPE OF REVIEW

A functional neuroanatomical perspective was conceived, comprising: (i) Hg occurrence in the aquatic environment; (ii) toxicokinetics on central nervous system (CNS)/sensory organs; (iii) effects on neurotransmission; (iv) biochemical/physiological effects on CNS/sensory organs; (v) morpho-structural changes on CNS/sensory organs; (vi) behavioral effects. The literature was also analyzed to generate a multidimensional conceptualization translated into a Rubik's Cube where key factors/processes were proposed.

MAJOR CONCLUSIONS

Hg neurosensory toxicity was unequivocally demonstrated. Some correspondence with toxicity mechanisms described for mammals (mainly at biochemical level) was identified. Although the research has been dispersed by numerous fish species, 29 key factors/processes were pinpointed.

GENERAL SIGNIFICANCE

Future trends were identified and translated into 25 factors/processes to be addressed. Unveiling the neurosensory toxicity of Hg in fish has a major motivation of protecting ichtyopopulations and ecosystems, but can also provide fundamental knowledge to the field of human neurodevelopment.

Living in a multi-stressors environment: An integrated biomarker approach to assess the ecotoxicological response of meagre (Argyrosomus regius) to venlafaxine, warming and acidification

Pharmaceuticals, such as the antidepressant venlafaxine (VFX), have been frequently detected in coastal waters and marine biota, and there is a growing body of evidence that these pollutants can be toxic to non-target marine biota, even at low concentrations. Alongside, climate change effects (e.g. warming and acidification) can also affect marine species' physiological fitness and, consequently, compromising their ability to cope with the presence of pollutants. Yet, information regarding interactive effects between pollutants and climate change-related stressors is still scarce. Within this context, the present study aims to assess the differential ecotoxicological responses (antioxidant activity, heat shock response, protein degradation, endocrine disruption and neurotoxicity) of juvenile fish (Argyrosomus regius) tissues (muscle, gills, liver and brain) exposed to VFX (via water or feed), as well as to the interactive effects of warming (ΔT °C = +5 °C) and acidification (ΔpCO₂ ~ +1000 µatm, equivalent to ΔpH = -0.4 units), using an integrated multi-biomarker response (IBR) approach. Overall, results showed that VFX toxicity was strongly influenced by the uptake pathway, as well as by warming and acidification. More significant changes (e.g. increases surpassing 100% in lipid peroxidation, LPO, heat shock response protein content, HSP70/HSC70, and total ubiquitin content, Ub,) and higher IBR index values were observed when VFX exposure occurred via water (i.e. average IBR = 19, against 17 in VFX-feed treatment). The co-exposure to climate change-related stressors either enhanced (e.g. glutathione S-transferases activity (GST) in fish muscle was further increased by warming) or attenuated the changes elicited by VFX (e.g. vitellogenin, VTG, liver content increased with VFX feed exposure acting alone, but not when co-exposed with acidification). Yet, increased stress severity was observed when the three stressors acted simultaneously, particularly in fish exposed to VFX via water (i.e. average IBR = 21). Hence, the distinct fish tissues responses elicited by the different scenarios emphasized the relevance of performing multi-stressors ecotoxicological studies, as such approach enables a better estimation of the environmental hazards posed by pollutants in a changing ocean and, consequently, the development of strategies to mitigate them.

Bioaccumulation and ecotoxicological responses of juvenile white seabream (Diplodus sargus) exposed to triclosan, warming and acidification

Triclosan (TCS) is a synthetic microbial compound widely used in the formulation of various personal care products. Its frequent detection in marine ecosystems, along with its physical and chemical properties, suggest that TCS can be highly persistent, being easily bioaccumulated by biota and, therefore, eliciting various toxicological responses. Yet, TCS's mechanisms of bioaccumulation and toxicity still deserve further research, particularly focusing on the interactive effects with climate change-related stressors (e.g. warming and acidification), as both TCS chemical behaviour and marine species metabolism/physiology can be strongly influenced by the surrounding abiotic conditions. Hence, the aim of this study was to assess TCS bioaccumulation and ecotoxicological effects (i.e. animal fitness indexes, antioxidant activity, protein chaperoning and degradation, neurotoxicity and endocrine disruption) in three tissues (i.e. brain, liver and muscle) of juvenile Diplodus sargus exposed to the interactive effects of TCS dietary exposure (15.9 μg kg^-1 dw), seawater warming (ΔTºC = +5 °C) and acidification (ΔpCO₂ ∼ +1000 μatm, equivalent to ΔpH = -0.4 units). Muscle was the primary organ of TCS bioaccumulation, and climate change stressors, particularly warming, significantly reduced TCS bioaccumulation in all fish tissues. Furthermore, the negative ecotoxicological responses elicited by TCS were significantly altered by the co-exposure to acidification and/or warming, through either the enhancement (e.g. vitellogenin content) or counteraction/inhibition (e.g. heat shock proteins HSP70/HSC70 content) of molecular biomarker responses, with the combination of TCS plus acidification resulting in more severe alterations. Thus, the distinct patterns of TCS tissue bioaccumulation and ecotoxicological responses induced by the different scenarios emphasized the need to further understand the interactive effects between pollutants and abiotic conditions, as such knowledge enables a better estimation and mitigation of the toxicological impacts of climate change in marine ecosystems.

Antidepressants in a changing ocean: Venlafaxine uptake and elimination in juvenile fish (Argyrosomus regius) exposed to warming and acidification conditions

The presence of antidepressants, such as venlafaxine (VFX), in marine ecosystems is increasing, thus, potentially posing ecological and human health risks. The inherent mechanisms of VFX uptake and elimination still require further understanding, particularly accounting for the impact of climate change-related stressors, such as warming and acidification. Hence, the present work aimed to investigate, for the first time, the effects of increased seawater temperature (ΔT°C = +5 °C) and pCO₂ levels (ΔpCO₂ ∼1000 μatm, equivalent to ΔpH = -0.4 units) on the uptake and elimination of VFX in biological tissues (muscle, liver, brain) and plasma of juvenile meagre (Argyrosomus regius) exposed to VFX through two different exposure pathways (via water, i.e. [VFX ] ∼20 μg L^-1, and via feed, i.e. [VFX] ∼160 μg kg^-1 dry weight, dw). Overall, results showed that VFX can be uptaken by fish through both water and diet. Fish liver exhibited the highest VFX concentration (126.7 ± 86.5 μg kg^-1 and 6786.4 ± 1176.7 μg kg^-1 via feed and water exposures, respectively), as well as the highest tissue:plasma concentration ratio, followed in this order by brain and muscle, regardless of exposure route. Both warming and acidification decreased VFX uptake in liver, although VFX uptake in brain was favoured under warming conditions. Conversely, VFX elimination in liver was impaired by both stressors, particularly when acting simultaneously. The distinct patterns of VFX uptake and elimination observed in the different scenarios calls for a better understanding of the effects of exposure route and abiotic conditions on emerging contaminants' toxicokinetics.

Differential behavioural responses to venlafaxine exposure route, warming and acidification in juvenile fish (Argyrosomus regius)

Antidepressants, such as venlafaxine (VFX), which are considered emerging environmental pollutants, are increasingly more present in the marine environment, and recent evidence suggest that they might have adverse effects on fish behaviour. Furthermore, altered environmental conditions associated to climate change (e.g. warming and acidification) can also have a determinant role on fish behaviour, fitness and survival. Yet, the underlying interactions between these environmental stressors (pharmaceuticals exposure and climate change) are still far from being fully understood. The aim of this study was to assess behavioural responses (in juvenile meagre (Argyrosomus regius) exposed to VFX via water ([VFX] ~20μgL^-1) and via dietary sources ([VFX] ~160μgkg^-1 dry weight), as well as to increased temperature (ΔT°C=+5°C) and high CO₂ levels (ΔpCO₂ ~1000μatm; equivalent to ΔpH=-0.4units). Overall, VFX bioaccumulation in fish plasma was enhanced under the combination of warming and acidification. VFX triggered fish exploration, whereas fish activity and shoal cohesion were reduced. Acidification alone decreased fish exploration and shoal cohesion, and reversed fish preference to turn leftwards compared to control conditions. Such alterations were further enhanced by VFX exposure. The combination of warming and acidification also reduced shoal cohesion and loss of lateralization, regardless of VFX exposure. The distinct behaviour observed when VFX contamination, acidification and warming acted alone or in combination highlighted the need to consider the likely interactive effects of seawater warming and acidification in future research regarding the toxicological aspects of chemical contaminants.

Fish energy budget under ocean warming and flame retardant exposure

Climate change and chemical contamination are global environmental threats of growing concern for the scientific community and regulatory authorities. Yet, the impacts and interactions of both stressors (particularly ocean warming and emerging chemical contaminants) on physiological responses of marine organisms remain unclear and still require further understanding. Within this context, the main goal of this study was to assess, for the first time, the effects of warming (+ 5 °C) and accumulation of a polybrominated diphenyl ether congener (BDE-209, brominated flame retardant) through dietary exposure on energy budget of the juvenile white seabream (Diplodus sargus). Specifically, growth (G), routine metabolism (R), excretion (faecal, F and nitrogenous losses, U) and food consumption (C) were calculated to obtain the energy budget. The results demonstrated that the energy proportion spent for G dominated the mode of the energy allocation of juvenile white seabream (56.0-67.8%), especially under the combined effect of warming plus BDE-209 exposure. Under all treatments, the energy channelled for R varied around 26% and a much smaller percentage was channelled for excretion (F: 4.3-16.0% and U: 2.3-3.3%). An opposite trend to G was observed to F, where the highest percentage (16.0 ± 0.9%) was found under control temperature and BDE-209 exposure via diet. In general, the parameters were significantly affected by increased temperature and flame retardant exposure, where higher levels occurred for: i) wet weight, relative growth rate, protein and ash contents under warming conditions, ii) only for O:N ratio under BDE-209 exposure via diet, and iii) for feed efficiency, ammonia excretion rate, routine metabolic rate and assimilation efficiency under the combination of both stressors. On the other hand, decreased viscerosomatic index was observed under warming and lower fat content was observed under the combined effect of both stressors. Overall, under future warming and chemical contamination conditions, fish energy budget was greatly affected, which may dictate negative cascading impacts at population and community levels. Further research combining other climate change stressors (e.g. acidification and hypoxia) and emerging chemical contaminants are needed to better understand and forecast such biological effects in a changing ocean.

Effects of water warming and acidification on bioconcentration, metabolization and depuration of pharmaceuticals and endocrine disrupting compounds in marine mussels (Mytilus galloprovincialis)

Warming and acidification are expected impacts of climate change to the marine environment. Besides, organisms that live in coastal areas, such as bivalves, can also be exposed to anthropogenic pollutants like pharmaceuticals (PhACs) and endocrine disrupting compounds (EDCs). In this study, the effects of warming and acidification on the bioconcentration, metabolization and depuration of five PhACs (sotalol, sulfamethoxazole, venlafaxine, carbamazepine and citalopram) and two EDCs (methylparaben and triclosan) were investigated in the mussel species (Mytilus galloprovincialis), under controlled conditions. Mussels were exposed to warming and acidification, as well as to the mixture of contaminants up to 15.7 μg L^-1 during 20 days; followed by 20 days of depuration. All contaminants bioconcentrated in mussels with levels ranging from 1.8 μg kg^-1 dry weight (dw) for methylparaben to 12889.4 μg kg^-1 dw for citalopram. Warming increased the bioconcentration factor (BCF) of sulfamethoxazole and sotalol, whereas acidification increased the BCF of sulfamethoxazole, sotalol and methylparaben. In contrast, acidification decreased triclosan levels, while both stressors decreased venlafaxine and citalopram BCFs. Warming and acidification facilitated the elimination of some of the tested compounds (i.e. sotalol from 50% in control to 60% and 68% of elimination in acidification and warming respectively). However, acidification decreased mussels' capacity to metabolize contaminants (i.e. venlafaxine). This work provides a first insight in the understanding of aquatic organisms' response to emerging contaminants pollution under warming and acidification scenarios.

Assessment of mercury contamination in Brycon falcatus (Characiformes: Bryconidae) and human health risk by consumption of this fish from the Teles Pires River, Southern Amazonia

ABSTRACT Brycon falcatus is one of the most highly consumed species of fish within the region in the Teles Pires basin, and has great commercial importance in sport and professional artisanal fishing. The objective of this study was to analyze the presence and concentration of total mercury (THg) in the muscle, liver and gills of B. falcatus, and calculate the risk to human health of THg contamination from ingestion of the fish. THg concentrations were similar in the liver (0.076 mg kg-1) and muscle (0.052 mg kg-1), and higher than in the gills (0.009 mg kg-1). The levels of HgT present in B. falcatus tissues did not influence weight gain and nutritional status. Based on the condition factor, weight and length ratio and hepatosomatic index, it seems that the concentrations of THg did not influence the health and well-being of B. falcatus collected in the Teles Pires River basin. THg concentrations in the muscle of B. falcatus are below the limit recommended by the World Health Organization for people who consume until 250 g of fish per week. The risk of deleterious effects on human health may exist if there is a greater consumption of B. falcatus such as 340 g/day, that is the mean of fish consumption by indigenous and riverine.

Ocean acidification dampens physiological stress response to warming and contamination in a commercially-important fish (Argyrosomus regius)

Increases in carbon dioxide (CO₂) and other greenhouse gases emissions are changing ocean temperature and carbonate chemistry (warming and acidification, respectively). Moreover, the simultaneous occurrence of highly toxic and persistent contaminants, such as methylmercury, will play a key role in further shaping the ecophysiology of marine organisms. Despite recent studies reporting mostly additive interactions between contaminant and climate change effects, the consequences of multi-stressor exposure are still largely unknown. Here we disentangled how Argyrosomus regius physiology will be affected by future stressors, by analysing organ-dependent mercury (Hg) accumulation (gills, liver and muscle) within isolated/combined warming (ΔT=4°C) and acidification (ΔpCO₂=1100μatm) scenarios, as well as direct deleterious effects and phenotypic stress response over multi-stressor contexts. After 30days of exposure, although no mortalities were observed in any treatments, Hg concentration was enhanced under warming conditions, especially in the liver. On the other hand, elevated CO₂ decreased Hg accumulation and consistently elicited a dampening effect on warming and contamination-elicited oxidative stress (catalase, superoxide dismutase and glutathione-S-transferase activities) and heat shock responses. Thus, potentially unpinned on CO₂-promoted protein removal and ionic equilibrium between hydrogen and reactive oxygen species, we found that co-occurring acidification decreased heavy metal accumulation and contributed to physiological homeostasis. Although this indicates that fish can be physiologically capable of withstanding future ocean conditions, additional experiments are needed to fully understand the biochemical repercussions of interactive stressors (additive, synergistic or antagonistic).

Oligotrophy as a major driver of mercury bioaccumulation in medium-to high-trophic level consumers: A marine ecosystem-comparative study

Mercury (Hg) is a global contaminant of environmental concern. Numerous factors influencing its bioaccumulation in marine organisms have already been described at both individual and species levels (e.g., size or age, habitat, trophic level). However, few studies have compared the trophic characteristics of ecosystems to explain underlying mechanisms of differences in Hg bioaccumulation and biomagnification among food webs and systems. The present study aimed at investigating the potential primary role of the trophic status of systems on Hg bioaccumulation and biomagnification in temperate marine food webs, as shown by their medium-to high-trophic level consumers. It used data from samples collected at the shelf-edge (i.e. offshore organisms) in two contrasted ecosystems: the Bay of Biscay in the North-East Atlantic Ocean and the Gulf of Lion in the North-West Mediterranean Sea. Seven species including crustaceans, sharks and teleost fish, previously analysed for their total mercury (T-Hg) concentrations and their stable carbon and nitrogen isotope compositions, were considered for a meta-analysis. In addition, methylated mercury forms (or methyl-mercury, Me-Hg) were analysed. Mediterranean organisms presented systematically lower sizes than Atlantic ones, and lower δ¹³C and δ¹⁵N values, the latter values especially highlighting the more oligotrophic character of Mediterranean waters. Mediterranean individuals also showed significantly higher T-Hg and Me-Hg concentrations. Conversely, Me-Hg/T-Hg ratios were higher than 85% for all species, and quite similar between systems. Finally, the biomagnification power of Hg was different between systems when considering T-Hg, but not when considering Me-Hg, and was not different between the Hg forms within a given system. Overall, the different parameters showed the crucial role of the low primary productivity and its effects rippling through the compared ecosystems in the higher Hg bioaccumulation seen in organisms from oligotrophic Mediterranean waters.

Assessing the effects of seawater temperature and pH on the bioaccumulation of emerging chemical contaminants in marine bivalves

Emerging chemical contaminants [e.g. toxic metals speciation, flame retardants (FRs) and perfluorinated compounds (PFCs), among others], that have not been historically recognized as pollutants nor their toxicological hazards, are increasingly more present in the marine environment. Furthermore, the effects of environmental conditions (e.g. temperature and pH) on bioaccumulation and elimination mechanisms of these emerging contaminants in marine biota have been poorly studied until now. In this context, the aim of this study was to assess, for the first time, the effect of warmer seawater temperatures (Δ = + 4°C) and lower pH levels (Δ = - 0.4 pH units), acting alone or combined, on the bioaccumulation and elimination of emerging FRs (dechloranes 602, 603 and 604, and TBBPA), inorganic arsenic (iAs), and PFCs (PFOA and PFOS) in two estuarine bivalve species (Mytilus galloprovincialis and Ruditapes philippinarum). Overall, results showed that warming alone or combined with acidification promoted the bioaccumulation of some compounds (i.e. dechloranes 602, 604, TBBPA), but also facilitated the elimination of others (i.e. iAs, TBBPA). Similarly, lower pH also resulted in higher levels of dechloranes, as well as enhanced iAs, PFOA and PFOS elimination. Data also suggests that, when both abiotic stressors are combined, bivalves' capacity to accumulate contaminants may be time-dependent, considering significantly drastic increase observed with Dec 602 and TBBPA, during the last 10 days of exposure, when compared to reference conditions. Such changes in contaminants' bioaccumulation/elimination patterns also suggest a potential increase of human health risks of some compounds, if the climate continues changing as forecasted. Therefore, this first study pointed out the urgent need for further research on the effects of abiotic conditions on emerging contaminants kinetics, to adequately estimate the potential toxicological hazards associated to these compounds and develop recommendations/regulations for their presence in seafood, considering the prevailing environmental conditions expected in tomorrow's ocean.

Mercury concentrations in three ray species from the Pacific coast of Baja California Sur, Mexico: Variations by tissue type, sex and length

Total mercury concentrations ([THg]) were determined in muscle and liver of the bat ray (Myliobatis californica), shovelnose guitarfish (Pseudobatos productus) and banded guitarfish (Zapteryx exasperata). Generalized linear models (GLM) were used to determine the effects of size and sex in [THg] and showed that both are determinants of [THg] in these species. The [THg] in both tissues significantly increased with length especially in sexually mature organisms with a steeper slope for mature male than mature female. This may relate to elasmobranchs sexual dimorphism driven variation in growth rates. Median muscle [THg] was significantly greater than liver in each ray species but there were some individuals with higher liver [THg] than muscle. There were individuals with muscle [THg] higher than the advisory thresholds of 0.2 and 0.5mgkg^-1ww (2.4 and 11% of the bat ray; 2.1 and 10% of the shovelnose guitarfish; 12.6 and 45% of the banded guitarfish, respectively).