Dietary and tissue selenium in relation to methylmercury toxicity

Distribution and trophic transfer of mercury and selenium in European hake (Merluccius merluccius) from the Northeast Atlantic Ocean: A stable isotope approach

European hake (EH - Merluccius merluccius) are a commercially valuable, high trophic position marine fish species inhabiting the Northeast Atlantic Ocean (NEAO). Here, we investigated total mercury (Hg) bioaccumulation and trophic transfer dynamics, and selenium (Se) Hg interactions in EH fillets at a historic waste disposal site with a known Hg point source (n = 25) and at reference sites (n = 763) throughout Norway. Fillet concentrations of Hg (> 91 % methylmercury - MeHg) and Se, were elevated in samples from the polluted site (Hgpolluted = 0.271 ± 0.153, Hgreference = 0.114 ± 0.096, Sepolluted = 0.425 ± 0.033, and Sereference = 0.321 ± 0.044 mg/kg wet weight). The opposite was found for Se:Hg molar ratios (Se:Hgreference = 12.1 ± 7.91, Se:Hgpolluted = 6.39 ± 4.96), however when controlling for Hg concentrations, the EH Se:Hg ratio from the polluted site was higher compared to reference conditions. We further investigated trophic niches using stable carbon, nitrogen, and Hg isotopes and found different isotopic niches between reference and polluted sites. EH from both site types had different Hg isotopic signatures and were enriched in heavier isotopes at reference sites (e.g., δ202Hgreference = 0.964 ± 0.177, δ202Hgpolluted = 0.714 ± 0.115 ‰). Hg enriched in fillet tissue primarily underwent MeHg photodegradation at both sites. However, due to the local Hg point source, lower MDF isotope values and odd MIF isotope values (e.g., ∆199Hgreference = 0.981 ± 0.105, and ∆199Hgpolluted = 0.829 ± 0.110 ‰) were observed at the polluted site. Overall, our findings indicate good discriminability regarding Hg source apportionment and highlight the role of point source pollution as an important modulator of the EH Hg bioaccumulation regime in the NEAO study system.

Assessment of mercury and selenium concentrations in Sepia pharaonis and Uroteuthis duvauceli from the Persian Gulf, Iran: Implications for human health and seafood safety

This study investigates the concentrations of mercury and selenium in Sepia pharaonis and Uroteuthis duvauceli from the Persian Gulf. Based on 30 sample from these species our results showed that the concentration of mercury and selenium metals in the hepatopancreas of both species was significantly higher than in the muscle, with Uroteuthis duvauceli exhibiting higher overall mercury concentrations than Sepia pharaonis. Selenium concentrations were lower than mercury concentrations. The correlation of mercury and selenium in muscle and hepatopancreas of Sepia pharaonis and Uroteuthis duvauceli was negative; the correlations was clearer for the hepatopancreas. Furthermore, the daily intake values and hazard indices calculated for both metals indicated that selenium poses minimal risk, while the consumption of these cephalopods warrants caution due to elevated mercury levels. The study emphasizes the importance of continued vigilance and species-specific assessments to ensure safe seafood consumption and protect public health.

Size- and month-dependent bioaccumulation of trace elements and toxic metals in atlantic bonito (Sarda sarda, Bloch, 1793): Implications for nutritional security and environmental health

BACKGROUND

Trace elements play dual roles in marine ecosystems and human health, acting as trace elements (e.g., Cu, Fe, Se, Zn) or toxic contaminants (e.g., Hg, As). This study investigates the bioaccumulation of 14 trace elements in Sarda sarda, a commercially and ecologically important species, to evaluate size- and season-dependent trends and their implications for environmental health and nutritional security.

METHODS

This study investigated the bioaccumulation of heavy metals (mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni)) and trace elements (arsenic (As), zinc (Zn), iron (Fe), selenium (Se), copper (Cu), manganese (Mn), aluminum (Al), boron (B), lithium (Li)) in Sarda sarda individuals categorized by size classes (small, medium, large, based on body length and weight) sampled monthly from the Sinop fishery, Turkey, in September, October, and November 2023. Metal concentrations were quantified in muscle tissue using inductively coupled plasma mass spectrometry (ICP-MS) with strict quality assurance protocols. Health risk indices (EDI, THQ, TTHQ, CRR, ADC, CDR, HBVSe) were calculated to assess dietary exposure risks.

RESULTS SIZE-DEPENDENT TRENDS

Hg and As levels increased significantly with fish size (p < 0.05), reflecting trophic magnification, while Li exhibited an inverse relationship, with higher concentrations in smaller fish.

SEASONAL DYNAMICS

Cu, Mn, and Se peaked in September. Pb and Cd were undetectable (<0.005 mg/kg), indicating low anthropogenic contamination.

HEALTH RISKS

All metals fell below international safety thresholds.

CONCLUSION

This study highlights the dual influence of biological (fish size, trophic position) and environmental (seasonal pollutant fluxes) factors on trace element bioaccumulation in Sarda sarda. While current levels pose minimal health risks, proactive monitoring is essential to address emerging contaminants and ensure sustainable fisheries management. These findings provide a template for adaptive monitoring frameworks in transitional marine ecosystems.

Re-thinking the link between exposure to mercury and blood pressure

Hypertension or high blood pressure (BP) is a prevalent and manageable chronic condition which is a significant contributor to the total global disease burden. Environmental chemicals, including mercury (Hg), may contribute to hypertension onset and development. Hg is a global health concern, listed by the World Health Organization (WHO) as a top ten chemical of public health concern. Most people are exposed to some level of Hg, with vulnerable groups, including Indigenous peoples and small-scale gold miners, at a higher risk for exposure. We published a systematic review and meta-analysis in 2018 showing a dose-response relationship between Hg exposure and hypertension. This critical review summarizes the biological effects of Hg (both organic and inorganic form) on the underlying mechanisms that may facilitate the onset and development of hypertension and related health outcomes and updates the association between Hg exposure (total Hg concentrations in hair) and BP outcomes. We also evaluated the weight of evidence using the Bradford Hill criteria. There is a strong dose-response relationship between Hg (both organic and inorganic) exposure and BP in animal studies and convincing evidence that Hg contributes to hypertension by causing structural and functional changes, vascular reactivity, vasoconstriction, atherosclerosis, dyslipidemia, and thrombosis. The underlying mechanisms are vast and include impairments in antioxidant defense mechanisms, increased ROS production, endothelial dysfunction, and alteration of the renin-angiotensin system. We found additional 16 recent epidemiological studies that have reported the relationship between Hg exposure and hypertension in the last 5 years. Strong evidence from epidemiological studies shows a positive association between Hg exposure and the risk of hypertension and elevated BP. The association is mixed at lower exposure levels but suggests that Hg can affect BP even at low doses when co-exposed with other metals. Further research is needed to develop robust conversion factors among different biomarkers and standardized measures of Hg exposure. Regulatory agencies should consider adopting a 2 µg/g hair Hg level as a cut-off for public health regulation, especially for adults older than child-bearing age.

Chemical mixtures of mercury, PCBs, PFAS, and pesticides in freshwater fish in the US and the risks they pose for fish consumption

BACKGROUND

Freshwater fish are important food sources that also pose risks to human and wildlife health because of the bioaccumulation of environmental chemicals in their tissues. Although most studies, fish consumption advisories, and regulations focus on individual contaminants, fish consumers are exposed to mixtures of chemicals, including legacy contaminants and contaminants of emerging concern, that can have combined effects. Chemicals of emerging concern represent one source of hazard, but legacy contaminants can still pose threats to fish consumers due to their persistence in the environment.

OBJECTIVES

We investigate the following questions: 1) Do different chemicals correlate with one another in fish tissue, and if so, how? 2) How do levels of different chemicals in fish tissue vary by time and location? and 3) How do observed chemical levels compare with risk-based screening levels?

METHODS

Using several national data sources established and maintained by the US Environmental Protection Agency (NRSA, NCCA-GL, GLENDA, and NLFTS), this study examines the co-occurrence of chemicals in freshwater fish in lakes, ponds, streams, and rivers in the US.

RESULTS

We determine that organic contaminants correlate with one another, but generally not with mercury; organic chemicals have declined over time, but mercury has not; and fish concentrations of legacy contaminants-even those banned for decades-continue to exceed risk-based screening levels.

DISCUSSION

Despite some successes in curtailing release of pollutants, some contaminants in fish tissue have not declined and legacy and emerging pollutants continue to pose risks to fish consumers in the US. Correlations between chemicals in fish tissue suggest that exposures to mixtures is prevalent in the US but that organic contaminants do not generally correlate with mercury-noteworthy particularly since fish consumption advisories in the US are frequently driven by the level of mercury, and do not account for exposure to multiple contaminants. While programs such as the National Aquatic Resource Surveys (NARS) Program seek to systematically monitor contaminants in fish tissue and other environmental indicators, continuous support from the US federal government is required to sustain this monitoring. Moreover, greater legislative and regulatory efforts are required at both the state and federal levels to reduce continuing sources and ongoing contamination.

Mercury and selenium in biological pump under upwelling-downwelling influence in Cabo Frio shelf, South Atlantic Ocean, Brazil

The knowledge of metals concentration in upwelling areas are a concern due the higher productivity of these areas In Cabo Frio Upwelling-Downwelling System (CFUS) is high primary productivity area and has been identified as an Hg hotspot to biota in SE Brazil that has been susceptible to Hg inputs, due to growing industrialization in the region. To investigate the concentration of Hg and Se metals, as well as the trophic transfer of these metals, the present study investigated Hg and Se concentrations in 64 samples collected in net mesh of >20, >64, >150 and >300 μm, in 2012, in the region's water masses. Higher mean Hg concentrations were found in zooplankton, 0.15 ± 0.09 μg g-1 (>300 μm) and 0.18 ± 0.1 μg g-1 (>150 μm), compared to phytoplankton, 0.11 ± 0.11 μg g-1 (>64 μm) and 0.06 ± 0.07 μg g-1 (>20 μm), and the calculation of the biomagnification factor (BMF) indicated that there was a process of magnification and trophic transfer. An opposite trend was found for Se in phytoplankton: higher average Se concentrations were observed in phytoplankton, 93.0 ± 65.2 μg g-1 (>64 μm), 93.8 ± 96.4 μg g-1 (>20 μm), compared to zooplankton, 91.1 ± 67.3 μg g-1 (>300 μm), 97.3 ± 71.3 μg g-1 (>150 μm). A positive linear relationship for the Hg:Al vs P:Al ratios was identified and indicated intracellular incorporation of Hg according to plankton size. Anthropogenic Hg sources were identified in the plankton samples by comparison with the sediment background values for the CFUS. Upwelling waters probably increased the availability of Hg and Se, these elements tend to bioaccumulate 10 to 100 times more than in areas with the influence of upwelling, due to fertilization and the increase in primary production.

Assessing the role of selenium in Minamata disease through reanalysis of historical samples

Minamata disease, a severe neurological disorder identified in Japan in 1956, results from methylmercury (MeHg) intoxication in humans due to environmental contamination. Before MeHg was recognized as the cause, selenium (Se) was suspected of being the potential cause owing to elevated Se levels in patients' organs. Subsequent animal studies indicated that Se mitigates MeHg toxicity; however, its role in Minamata disease remains unexplored. We analyzed Hg and Se in historical samples of the industrial wastes (n = 4) on the factory site, sediments (n = 9), and fish/shellfish (n = 16) in Minamata Bay, and organs of patients with Minamata disease (n = 12). All samples showed elevated levels of both Hg and Se, providing the first evidence that Se was also discharged into Minamata Bay, entering the food chain and accumulating at high levels in patient organs. The Hg/Se molar ratio in contaminated shellfish (median > 3.0) indicated exceptionally high MeHg exposure, far exceeding the ordinary level (< 1.0). Patients exhibited significantly increased Se levels in the liver and kidney but lower amounts in the brain. Notably, median Hg/Se molar ratios exceeding 4.0 were observed, particularly in the cerebrum and cerebellum in acute cases, closely mirroring the molar ratios found in seafood. The elevated Hg/Se molar ratio in the brain helps explain the severe neurological damage in patients' central nervous systems, despite higher Hg levels in the liver and kidney compared to the brain. These findings provide important insight into the mechanism of MeHg intoxication and highlight the risks associated with MeHg-contaminated seafood, aiding efforts to protect consumers.

Selenium-mercury interactions and relationship to aquatic toxicity: a review

A review of the literature pertaining to selenium-mercury (Se/Hg) interactions in aquatic species was performed to provide insight into the mechanisms allowing for the reported changes in bioaccumulation and toxicity that have been observed when the two elements occur at elevated concentrations. Selenium (Se) has been shown to protect against mercury (Hg) toxicity in all animal models evaluated (fish, birds, mammals, and plants). To explore the interaction between the two elements, data are presented on concentrations of both elements in wild-caught fish at numerous locations. The data show that most fish have Se/Hg ratios >1.0. The importance of this ratio has been reported, with suggestions that the protective interaction is due in large part to the formation of HgSe. Data show that when the Se/Hg molar ratio is <1.0 in the diet of fish and animals, Hg toxicity will be expressed, provided that the Hg concentration is sufficiently high. This toxicity is likely the result of Se deficiency leading to an excess of reactive oxygen species. Laboratory fish toxicity studies reviewed show that Se toxicity can be reduced or eliminated when Hg is added to the diet in moderate amounts. Field studies have shown reduced accumulation of Hg when Se concentrations are increased. When Hg in the diet is significantly elevated (usually >10 µg/g), toxicity is expressed regardless of the Se present. Likewise, amelioration of Se toxicity by Hg occurs over a limited range. Tissue thresholds for Se toxicity have been derived primarily from studies where fish eggs were extracted from wild fish and embryo deformities were observed; however, the amount of Hg in the fish or ovaries was not considered, which could lead to uncertainty in the toxicity threshold. It is recommended that both elements be measured and evaluated when performing risk assessments and setting water quality criteria.

A preliminary assessment of mercury, methylmercury and other potentially toxic elements in largemouth bass (Micropterus salmoides) from the Almadén mining district

The food chain of the Valdezogues River system is at considerable risk due to the presence of mercury in the environment and to intense bioaccumulation and biomagnification processes in some fish species, particularly in piscivorous. Moreover, the presence of mercury in fish is a reliable indicator of the presence of its most toxic form, methylmercury. Of interest is that selenium, when present together with mercury in food, represents a significant decrease in the risks related to the ingestion of methylmercury. This study presents the concentrations of total mercury, methylmercury, selenium, and other elements in Micropterus salmoides from a transect of the Valdeazogues River. This water course cuts across the Almadén mining district, which has been the most important producer of this element for over 2000 years. Results highlight the highest total- and methylmercury concentrations ranging between 0.47 and 7.61 mg kg-1 ww for total mercury, and with methylmercury representing between 79.7 and 92.1% of total mercury. These are the highest concentrations in the element ever found in this species. Seven sampling sites were examined along a 34 km long transect of the river, starting at an open pit lake corresponding to a decommissioned Hg mine (El Entredicho open pit, isolated from the river course), with the rest of the sites located downstream. Concentrations of mercury are the highest in this open pit lake and decrease steadily downstream. Concentrations of selenium are also high to very high, ranging between < 2.5 and 11.4 mg kg-1 ww. The Se/Hg molar ratio, as well as the HBVSe index, show values indicating low risk, except for specimens of low size/age from the most highly Hg contaminated site considered in this study. The rest of the potentially toxic elements (Se, As, Pb, Zn, Sb and Cu) show no concerning values even though the area is heavily populated with decommissioned polymetallic mines.

Levels of trace elements in the blood of chick gulls from the English Channel: Spatial and trophic implications

Anthropogenic activity has disturbed the natural distribution and circulation of trace elements in the environment. This has led to increased background levels of numerous elements, causing global pollution. In this context, seabirds are relevant bioindicators of environmental contamination. This study focuses on the ecological factors that influence the concentrations of 14 trace elements in the blood of the chicks of three sympatric gull species from the French coast of the English Channel. Between 2015 and 2017, 174 birds were sampled in the industrialised Seine Estuary (in the city of Le Havre and on Ratier Island) and in the remote Chausey Islands, 200 km to the west. We also considered the Se:Hg molar ratio using Hg concentrations in those birds. Ag and V concentrations were below the quantification limit in all cases, while the fraction of non-quantified samples was higher than 30 % for Cd, Cr and Ni. Among the elements quantified in the samples, the lowest concentrations were noted for Co and the highest for Fe, building the following order: Co < Cd < Ni < Mn ≤ Pb < Cr < Hg < Cu < Se < As < Zn < Fe. No unanimous scheme of concentrations among elements, species and sites existed. Similarly, different models were fitted and different factors were significant for different species and elements. We observed the biomagnification of As and the biodilution of Pb. Pb concentrations were also highest in the industrial site in the city of Le Havre. Despite the high proportion of non-quantified samples for Cd, Cr and Ni, we continued to notice higher concentrations in the marine environment of the Chausey Islands. Concentrations of some elements clearly revealed habitat dependence. In some cases the Se:Hg molar ratio was lower than 4, a threshold for diminishing Hg toxicity by Se.

Se and Hg in processed fish-derived products and their fish raw materials: Occurrence, Se:Hg molar ratio, HBVSe index, bioaccessibility and Caco-2 cells toxicity

Processing conditions applied during food production could affect food component contents and bioaccessibility. Here, possible changes in Hg and Se total and species contents and bioaccessibility have been tracked in each stage of the production chain of processed fish-derived products. Therefore, Se:Hg molar ratio and Selenium Health Benefit Value (HBVSe) were calculated for final products and raw materials, resulting favorable in all cases, suggesting the safety of surimi-based products regarding mercury. Speciation studies revealed the presence of SeMeSeCys and SeMet in all samples. Thus, the integrity of the selenium species seems to be maintained. Moreover, in vitro gastrointestinal digestion model evidenced that Se bioaccessibility ranged between 20-39 % for all samples, while in case of Hg was between 8-37 %. Additionaly, SeMeSeCys and SeMet were also identified in the gastrointestinal extracts. Finally, no cytotoxicity was observed after exposure of Caco-2 cells to the gastrointestinal extracts.

Trace Elements in Stenella coeruleoalba: Assessment of Marine Environmental Pollution and Dolphin Health Status

Heavy metals are environmental contaminants and can easily accumulate and biomagnify in various marine species (fishes and mammalians) at the top of the aquatic food chain. Among marine mammalians, the striped dolphin (Stenella coeruleoalba) is the most abundant cetacean in the Mediterranean Sea and is considered to be a sentinel species to monitor the environmental marine pollution. In this study, the contents of toxic metals and metalloids (Cd, Pb, Hg, and As), micro-elements (Ni, Cr, Cu, Fe, Co, Mn, Se and Zn) and macro-elements (Na, Ca, K, Mg and P) were evaluated by ICP-MS analysis in several organs/tissues (lung, skin, muscle and liver) of Stenella coeruleoalba. The assessment of marine environmental pollution and dolphins health status was carried out through further analysis of the same specific parameters such as the metal pollution index (MPI) and coefficient of condition (K). Finally, the correlation between toxic metals and metalloids and essential micro-elements, expressed as molar ratios, was analyzed to evaluate the detoxifying ability (effectiveness) of Zn, Se and Cu. Data obtained showed the presence of toxic metals and metalloids analyzed in the Stenella coeruleoalba samples but the MPI values suggested a low environmental contamination of the Mediterranean Sea where dolphins lived. The content of micro- and macro-elements was found to be in a normal range for this species and predictive of dolphins good health status, as confirmed by the coefficient of condition K. However, the correlation between toxic and essential metals, expressed as molar ratios, showed that the following toxic metals cannot be detoxified by the essential metals: 66Zn/201Hg, 82Se/201Hg, 63Cu/201Hg and 66Zn/52Cr, 82Se/52Cr, 63Cu/52Cr. Therefore, this study highlights the key role of dolphin Stenella coeruleoalba to assess marine pollution and the importance of analyzing the complete mineral profile to evaluate the animal health status.

Potentially toxic trace elements in the muscle of coastal South American fish: Implications for human consumption and health risk assessment

Micropogonias furnieri and Urophycis brasiliensis are two coastal demersal fish species distributed in the southwestern Atlantic Ocean. Considering that many coastal areas in the southwestern Atlantic Ocean suffer from anthropogenic pressure, the aim of this study was to assess the level of potentially toxic trace elements (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, Sr, V and Zn) in the muscle of coastal species, and evaluated the human health risk related to the consumption of muscle. Mercury, inorganic As (Asi), V, and Se showed a higher contribution to the total THQ. Considering two possible scenarios, Asi represents 1 % or 5 % of the total As, the total THQ was <1 for general population and of some health concerns for fishermen population (Total THQ > 1; 5 % Asi). Consequently these results show the importance of quantifying As species in muscle to generate more reliable risk estimates for human health.

Mercury bioaccumulation and its relationship with trophic biomarkers in a Mediterranean elasmobranch mesopredator

Human activity has led to increased concentrations of mercury (Hg) in the world's oceans. Mercury can bioaccumulate and biomagnify in animal tissues via trophic transfer, thus, becoming most pronounced in larger and older predators. Here, we measured Hg concentrations and their relationship with stable isotopes-based proxies of trophic level (δ13C and δ15N values) in multiple tissues of Mustelus spp. from the Mediterranean Sea. We found higher Hg concentrations in muscle than in liver and fin tissues. The relationship between Hg concentrations and δ15N values in muscle suggested repeated foraging for low trophic level and Hg-poor prey, and biomagnification of Hg at higher trophic levels. Seasonal variations in δ13C values could indicate shifts in primary production sources and/or in local prey availability. The HBVSe index suggested no risk to human health, however the safe meal limit recommendations are 4.5 and 2.2 portions per month for adults and children, respectively.

Evaluation of Metal Partitioning across Humboldt Penguin (Spheniscus humboldti) Egg Components

Humboldt Penguin (Spheniscus humboldti) population declines are attributable to several multifaceted anthropogenic impacts. At present, the exposure of Humboldt Penguins to high concentrations of heavy metals in the marine environment is a preeminent concern, due to mining along the Peruvian coast near key rookery sites. Metal and selenium concentrations were determined in eggs collected from September 2020 to April 2021 from a managed-care penguin population at the Brookfield Zoo to establish reference values for health indices conducted on wild populations. Concentrations of 16 elements, with emphasis on those found in mine efflux-arsenic, cadmium, copper, lead, mercury, selenium, and zinc-were assessed via inductively coupled plasma mass spectrometry in yolk, albumen, and eggshell. Data analyses indicate a clear delineation between egg constituents, with lipid-rich yolk displaying notably higher concentrations (μg/g) of arsenic (0.20 ± 0.064), chromium (0.086 ± 0.03), cobalt (0.01 ± 0.003), iron (238.65 ± 54.72), lead (0.32 ± 0.97), manganese (2.71 ± 0.66), molybdenum (0.57 ± 0.14), tin (3.29 ± 0.99), and zinc (64.03 ± 13.01) than other components (albumen and eggshell). These data confirm that heavy metals are partitioned differently across Humboldt Penguin egg components, which provides insight into the potential connection between embryonic nutrient source contamination and subsequent chick viability.

Selenium and mercury concentration, Se/Hg molar ratio and risk-benefit assessment of marine fish consumption: Human health risks and protective role of Se against Hg toxicity

This study aimed to explore the concentrations of Se and Hg in marine fish along the Gulf of Mannar (southeast coast of India) and to assess related risks and risk-based consumption limits for children, pregnant women, and adults. Se concentrations in pelagic and benthic fish ranged from 0.278 to 0.470 mg/kg and 0.203 to 0.294 mg/kg, respectively, whereas Hg concentrations ranged from 0.028 to 0.106 mg/kg and 0.026 to 0.097 mg/kg, respectively. Se and Hg contents in demersal fish (Nemipterus japonicus) were 0.282 and 0.039 mg/kg, respectively. The lowest and highest Hg concentrations in pelagic fish were found in Scomberomorus commersoni and Euthynnus affinis whereas the lowest and highest Se concentrations in benthic fish were found in Scarus ghobban and Siganus javus. Se concentrations in marine fishes were found in the following order: pelagic > demersal > benthic whereas Hg concentrations were found in the following order: pelagic > benthic > demersal. The presence of Se in fish was positively correlated with trophic level (TL) and size whereas that of Hg was weakly correlated with TL and habitat and negatively correlated with size. Se risk-benefit analysis, the AI/RDI (actual intake/recommended daily intake) ratio was > 100 % and the AI/UL (upper limit) ratio was < 100 %, indicating that all fish have sufficient levels of Se to meet daily requirements without exceeding the UL. Hg level was below the maximum residual limit (MRL) of 0.5 mg/kg for most fish but it was 1 mg/kg in E. affinis and Lethrinus lentjan. The target hazard quotient (THQ < 1) and hazard index (HI < 1) imply that the consumption of fish poses no noncarcinogenic health risks. However, all examined fish had a mean Se/Hg molar ratio > 1, indicating that human intake of fishwas rather safe relative to Hg content. Health benefit indexes (Se-HBV and HBVse) with high positive values in all fish supported the protective effect of Se against Hg toxicity, suggesting the overall safety of fish consumption. The high Se/Hg ratio in fish could be attributed to the replacement of Se bound to Hg, thereby suppressing Hg toxicity and maintaining normal selenoprotein synthesis. This insight is useful for a better understanding of food safety analysis.

Maternal seafood consumption is associated with improved selenium status: Implications for child health

Selenium (Se) is required for synthesis of selenocysteine (Sec), an amino acid expressed in the active sites of Se-dependent enzymes (selenoenzymes), including forms with essential functions in fetal development, brain activities, thyroid hormone metabolism, calcium regulation, and to prevent or reverse oxidative damage. Homeostatic mechanisms normally ensure the brain is preferentially supplied with Se to maintain selenoenzymes, but high methylmercury (CH3Hg) exposures irreversibly inhibit their activities and impair Sec synthesis. Due to Hg's high affinity for sulfur, CH3Hg initially binds with the cysteine (Cys) moieties of thiomolecules which are selenoenzyme substrates. These CH3Hg-Cys adducts enter selenoenzyme active sites and transfer CH3Hg to Sec, thus irreversibly inhibiting their activities. High CH3Hg exposures are uniquely able to induce a conditioned Se-deficiency that impairs synthesis of brain selenoenzymes. Since the fetal brain lacks Se reserves, it is far more vulnerable to CH3Hg exposures than adult brains. This prompted concerns that maternal exposures to CH3Hg present in seafood might impair child neurodevelopment. However, typical varieties of ocean fish contain far more Se than CH3Hg. Therefore, eating them should augment Se-status and thus prevent Hg-dependent loss of fetal selenoenzyme activities. To assess this hypothesis, umbilical cord blood and placental tissue samples were collected following delivery of a cohort of 100 babies born on Oahu, Hawaii. Dietary food frequency surveys of the mother's last month of pregnancy identified groups with no (0 g/wk), low (0-12 g/wk), or high (12 + g/wk) levels of ocean fish consumption. Maternal seafood consumption increased Hg contents in fetal tissues and resulted in ∼34% of cord blood samples exceeding the EPA Hg reference level of 5.8 ppb (0.029 µM). However, Se concentrations in these tissues were orders of magnitude higher and ocean fish consumption caused cord blood Se to increase ∼9.4 times faster than Hg. Therefore, this study supports the hypothesis that maternal consumption of typical varieties of ocean fish provides substantial amounts of Se that protect against Hg-dependent losses in Se bioavailability. Recognizing the pivotal nature of the Hg:Se relationship provides a consilient perspective of seafood benefits vs. risks and clarifies the reasons for the contrasting findings of certain early studies.

Selenium Health Benefit Values and Hg and Se speciation studies for elucidating the quality and safety of highly consumed fish species and fish-derived products

Nowadays, there has been an increase in the consumption of fish-derived products that constitute alternative ways of introducing fish into the diet, such as fish roe and products made from fish (crab sticks andsurimi-derived products). However, there is no data available considering selenium and mercury total contents along with speciation studies in these kinds of samples, which are mandatory for a proper safety and quality assessment. In this study,Selenium Health Benefit Values (HBVSe) in fish and fish-derived products were evaluated, resulting inpositivein all cases. Selenium speciation studies performed by HPLC-ICP-MS and confirmed by HPLC-ESI-MS/MS revealed that SeMet and SeMeSeCys are present in fish and fish-derived products. Finally, Hg speciation studiesshow that the percentage of Hg2+ increases in fishes lower in the food chain as well as in fish-derived products.

The Impact of Various Types of Cooking on the Fate of Hg and Se in Predatory Fish Species

This study addresses the effect of various cooking approaches on total Hg (HgT) and total Se (SeT) contents in three predatory fish species. For this purpose, samples of swordfish, dogfish, and tuna from regular French (fish) markets were cooked by boiling, steaming, grilling, and frying, respectively. The levels of HgT and SeT in raw and cooked samples were determined by inductively coupled plasma-mass spectrometry. The data showed a significant increase in HgT and SeT levels between raw and cooked samples (33% of the samples for SeT and 67% for HgT) due to the water loss during the cooking. High intra-species variation related to HgT and SeT levels was found. Considering the level of exposure to HgT through fish consumption and taking also into account the possible protective effect of Se (expressed here via the Se/Hg molar ratio), the safest cooking approach corresponds to grilled swordfish, fried tuna, and steamed dogfish, which show Se/Hg molar ratios of (1.0 ± 0.5), (4.3 ± 4.2), and (1.0 ± 0.6), respectively.

Relationship of mercury and selenium in ocean fish frequently consumed in the Seychelles: A comparison to levels in ocean fish consumed in the US

We characterized mercury and selenium in the fish consumed in the Seychelles Islands to determine if their levels are similar to fish consumed in the US. A secondary aim was to examine whether fish weight and species predict mercury and selenium in fish consumed in the Seychelles. We measured total mercury (THg) and selenium (Se) content of 10 samples from each of the 19 most frequently consumed fish species in Seychelles and for each calculated the Se:Hg molar ratios and the Selenium Health Benefit Value Index (HBV Se). Linear regression models examined associations with weight and species. Average MeHg levels in fish ranged from less than 0.01 ppm (streamlined spinefoot) to 0.7 ppm (bludger trevally) with an overall mean of 0.21 ± 0.23 ppm. Average Se levels ranged from 0.34 ppm (blue-barred parrot fish) to 0.93 ppm (blue-lined large-eye bream) with a mean of 0.54 ± 0.23 ppm. All fish species had a mean Se:Hg molar ratio > 1 and positive mean HBV Se index values. Weight was strongly predictive of MeHg and Se:Hg molar ratio, both across and within most species, but was less predictive of Se and HBV Se. Our study demonstrated that fish consumed in Seychelles have mercury and selenium content similar to that of fish consumed in the US. Fish in both countries have favorable positive values for Se:Hg molar ratios and HBV Se indexes. Because mercury and selenium concentrations in fish are similar to those in the US but fish consumption is substantially higher in Seychelles, the Seychellois make an ideal population in which to determine if there are adverse effects of prenatal, postnatal, and lifetime low dose MeHg exposure from fish consumption.

Mercury accumulation and biomarkers of exposure in two popular recreational fishes in Hawaiian waters

Mercury (Hg) exposure has not been examined in many recreational nearshore fish species that are commonly consumed around the Hawaiian Islands. Specific gene transcripts, such as metallothionein (MET) and thioredoxin reductase (TrxR), can be used to examine Hg exposure responses in aquatic organisms. This study measured total mercury (THg) in four species from two groups of Hawaiian nearshore fishes: giant trevally (Caranx ignobilis, n = 13), bluefin trevally (C. melampygus, n = 4), sharp jaw bonefish (Albula virgata, n = 2), and round jaw bonefish (A. glossodonta, n = 19). Total Hg accumulation and abundance profiles of MET and TrxR were evaluated for muscle, liver, and kidney tissues. Total Hg in round jaw bonefish and giant trevally tissues accumulated with length and calculated age. In round jaw bonefish tissues, mean THg was greater in kidney (1156 ng/g wet mass (wm)) than liver (339 ng/g wm) and muscle (330 ng/g wm). Giant trevally muscle (187 ng/g wm) and liver (277 ng/g wm) mean THg did not differ significantly. Fish species in this study were compared to commercial and local fish species with state and federal muscle tissue consumption advisories based on THg benchmarks developed by the U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA). Both bonefishes had mean muscle THg that exceeded benchmarks suggesting consumption advisories should be considered. MET transcript in round jaw bonefish kidney tissue and kidney THg exhibited a marginally significant positive correlation, while TrxR transcript in liver tissue negatively correlated with increasing liver THg. These results contribute to our understanding of Hg exposure associated health effects in fish.

Effects of floods resulting from climate change on metal concentrations in whiting (Merlangius merlangus euxinus) and red mullet (Mullus barbatus) and health risk assessment

In this research, the effect of flooding caused by heavy precipitation, postulated to be one of the consequences of climate change, on toxic metal concentrations in two demersal fish species, whiting (Merlangius merlangus euxinus) and red mullet (Mullus barbatus), was investigated. For both demersal fish species, concentrations of Hg, Fe, Cd, Pb, Se, Al, Zn, Cu, Sr, B, Cr, Mn, Ni, Ba, and Li were compared between samples taken from Türkeli, Sinop, Black Sea, before and after the flood event in August 2021. Hg, Mn, Se, Li, B, and Sr metal concentrations increased in whiting and in red mullet in the post-flood samples. Estimated daily intake, target hazard quotient, cancer risk, the maximum allowable daily consumption rate and minimum daily requirements, and health risk analyses indicated that daily consumption of whiting and red mullet was risky due to the heavy metal Hg level after the flood. In addition, it was found that the samples had higher levels of Se than Hg, Se/Hg ratios were above 1, and Se-HBV were positive. Therefore, whiting and red mullet fishing should be restricted for a limited time period in the region.

Metal concentrations, selenium-mercury balance, and potential health risk assessment for consumer of whiting (Merlangius merlangus euxinus L., 1758) from different regions of the southern Black Sea

The significant increase in the human population and the associated industrial wastes have a widespread impact on coastal areas. It is important to monitor trace elements that affect food safety and pose a potential consumer health threat. All over the Black Sea coast, people enjoy consuming whiting as both meat and roe. In February 2021, whitings were caught by bottom trawling from four different locations on the coasts of Kastamonu, Sinop (Sarıkum, Adabaşı), and Samsun in the southern Black Sea region. The meat and roe extracts obtained from whiting samples were analyzed through an optical emission spectrophotometer (ICP-MS). Trace element concentrations of whiting meat and roe in this study were Zn > Fe > Sr > As > Al > Se > B > Mn > Cu > Hg > Li > Ni > Ba > Pb > Cr > Cd and Zn > Fe > Al > As > Cu > Sr > Mn > Se > B > Ba > Li > Ni > Hg > Cr > Pb > Cd, respectively. These amounts were lower than the acceptable values accepted by the EU Commission. In case of whiting and roe consumption of a maximum of three portions (860.33 g) for Adabaşı, six portions for Kastamonu (1432.37 g), three portions for Samsun (828.55 g), and five portions (1253.04 g) for Sarıkum per month do not pose a health risk.

Relation among Mercury, Selenium, and Biomarkers of Oxidative Stress in Northern Pike (Esox lucius)

Mercury (Hg) is a toxic environmental contaminant associated with oxidative stress in freshwater fish. A known antagonist to Hg, selenium (Se), may reduce the toxic effects of Hg. In this study, the relation among Se, methylmercury (MeHg), inorganic mercury (IHg), total mercury (THg), and the expression of biomarkers of oxidative stress and metal regulation in livers of northern pike were examined. Livers from northern pike were collected from 12 lakes in Isle Royale National Park, Pictured Rocks National Lakeshore, Sleeping Bear Dunes National Lakeshore, and Voyageurs National Park. The concentrations of MeHg, THg, and Se were measured in liver tissue, and the expression of superoxide dismutase (sod), catalase (cat), glutathione s-transferase (gst), and metallothionein (mt) was assessed. There was a positive relationship between the concentrations of THg and Se, with a Hg:Se molar ratio less than one in all livers examined. There was no significant relation between sod, cat, gst, or mt expression and Hg:Se molar ratios. cat and sod expression were significantly related to increases in percent MeHg, relative to THg; however, gst and mt expression were not significantly altered. This suggests that incorporating biomarkers containing Se may be a better indicator than non-selenium-containing proteins of assessing the long-term effect of Hg and the interactions between Hg and Se in the livers of fish, such as northern pike, especially when molar concentrations of Se are greater than Hg.

Metal(loid)s and persistent organic pollutants in yellow European eel from the Raša River, Croatia

The anthropogenic impact on the aquatic environment of the Raša River (Croatia) was investigated through the analysis of seven polybrominated diphenyl ethers (PBDEs), seven polychlorinated biphenyls (PCBs), three DDT isomers, and 22 major and trace elements using yellow European eel (Anguilla anguilla L.) as a biological indicator of contamination. The obtained data indicated generally low contamination status in the surrounding area. Levels of all organic contaminants in muscle significantly increased with lipid content, length, weight and body condition. In both muscle and liver, most metal(loid)s decreased or remained unchanged with increasing size, while at downstream location only several elements (Cd, Cu, Fe, Na, Se, U, V, Zn) accumulated in the liver with fish growth. Spatial analysis revealed higher pressure of Ag, Cd, Cr, Mo, Tl, U, and V at the downstream location, revealing the potentially limited impact of historical coal mining industry on the lower reaches of the Raša River.

Bioaccumulation of Cd and comparative transcriptome analysis after the antagonism of Se in the hepatopancreas of estuary mud crab (Scylla paramamosain)

Cadmium (Cd) is a heavy metal contaminant and can be toxic to environment. What's more, Selenium (Se) protects organism as heavy metal antagonist. The present study aimed to investigate whether inorganic (Na₂SeO₃) or organic (L-SeMc) Se have an effect on the Cd bioaccumulation, antioxidant and immunity of the mud crab (Scylla paramamosain) under Cd exposure. The study showed that the concentration of Cd in hepatopancreas under Cd exposure was higher than the inorganic or organic Se group (P < 0.05), notably, Cd concentration of hepatopancreas in organic Se treatment is less than that in inorganic Se treatment (P < 0.05). Furthermore, this study analyzed 28 gene expression about antioxidant and immune from transcriptome, the result indicated that L-SeMc (organic Se) can reduced intracellular ROS production and oxidative damage. Furthermore, apoptosis was enhanced after Cd exposure, but Se could protect against apoptosis via expression of cathepsin B. Consequently, Organic Se may have a better effect than inorganic Se on reducing Cd toxicity. This study could provide the molecular basis that Se might alleviate Cd toxicity and increases the understanding of the environmental contaminant on crustaceans.

Potentially Toxic Elements in Water, Sediments and Fish from the Karstic River (Raša River, Croatia) Located in the Former Coal-Mining Area

The assessment of the environmental quality of a sensitive karst aquatic system under the centuries-long anthropogenic influence of the coal mining industry is important for both improving the quality of water resources and protecting aquatic wildlife and human health. In this study, we investigated the anthropogenic impact on the aquatic environment of the upper and middle course of the Raša River through the analysis of a suite of metal(loid)s in three aquatic compartments (water, sediment, fish) using inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of inorganic constituents in water were low, while the chemical composition of stream sediments mainly reflected the geological background of the area, indicating the origin of metal(loid)s from predominantly natural sources. Although comparison with PEC-Q values indicated that existing sediment quality conditions could pose a threat to benthic organisms with regard to Cr and Ni, the constant vertical profiles of these elements suggested their natural origin from the weathering of flysch. Element levels in the muscle of targeted fish species were in accordance with the values typical for low-contaminated freshwater systems, while levels of Cd, Pb and Hg were mostly below the European regulatory limits for toxic elements in foods, indicating that the low concentrations of most contaminants in muscles of fish from the Raša River do not present a risk to humans or other consumers. The obtained data indicated a generally low contamination status of the western part of the Raša River basin with regard to the analyzed inorganic elements.

Selenium Status: Its Interactions with Dietary Mercury Exposure and Implications in Human Health

Selenium is an essential trace element in humans and animals and its role in selenoprotein and enzyme antioxidant activity is well documented. Food is the principal source of selenium, and it is important that selenium status in the body is adequately maintained for physiological functions. There has been increasing attention on the role of selenium in mitigating the toxic effects of mercury exposure from dietary intake in humans. In contrast, mercury is a neurotoxin, and its continuous exposure can cause adverse health effects in humans. The interactions of selenium and mercury are multi-factorial and involve complex binding mechanisms between these elements at a molecular level. Further insights and understanding in this area may help to evaluate the health implications of dietary mercury exposure and selenium status. This review aims to summarise current information on the interplay of the interactions between selenium and mercury in the body and the protective effect of selenium on at-risk groups in a population who may experience long-term mercury exposure.

Metals in Ten Commercial Demersal Fish from the East China Sea: Contribution to Aquatic Products Nutrition and Toxic Risk Assessment

Metal accumulation in the marine environment can increase the metal content of fish living in it. For this reason, it is essential to evaluate the nutrition from fish consumption and assess metal toxicity risk. Ten species of demersal fish, which are part of the daily diet of coastal residents, were sampled using trammel net in the East China Sea. Levels of the microelements, the constant elements, and the toxic elements of muscle tissue were analyzed. Spiny red gurnard had the highest concentrations of calcium, copper, and iron, whereas pufferfish and threadfin porgy were good sources of zinc and magnesium. The levels of lead, cadmium, and inorganic arsenic in all samples were below the limit values according to Chinese national standards. Although some concerns were raised about the concentration of mercury (Hg) in threadfin porgy, silver croaker, and fivespot flounder, molar ratios (selenium, Se:Hg) and the Se health benefit values (HBV_Se) indicated that they were safe for human consumption. Additionally, the estimated weekly intake and % weekly contribution of 10 fish species with different elements were provided, giving a reference for the people's healthy consumption.

Selenium and Redox Enzyme Activity in Pregnant Women Exposed to Methylmercury

Selenium (Se) is a micronutrient with essential physiological functions achieved through the production of selenoproteins. Adequate Se intake has health benefits and reduces mercury (Hg) toxicity, which is important due to its neurotoxicity. This study determined the Se status and redox enzyme, including selenoproteins', activity in pregnant women highly exposed to Hg (between 1 to 54 µg Hg/L blood) via fish consumption. A cross-sectional study enrolling 513 women between the first and third trimester of pregnancy from Madeira, Portugal was conducted, encompassing collection of blood and plasma samples. Samples were analyzed for total Se and Hg levels in whole blood and plasma, and plasma activity of redox-active proteins, such as glutathione peroxidase (GPx), thioredoxin reductase (TrxR) and thioredoxin (Trx). Enzyme activities were related to Se and Hg levels in blood. Se levels in whole blood (65.0 ± 13.1 µg/L) indicated this population had a sub-optimal Se status, which translated to low plasma GPx activity (69.7 ± 28.4 U/L). The activity of TrxR (12.3 ± 5.60 ng/mL) was not affected by the low Se levels. On the other hand, the decrease in Trx activity with an increase in Hg might be a good indicator to prevent fetal susceptibility.

The health risk for consumers under heavy metal scenarios: Reduce bioaccumulation of Cd in estuary mud crab (Scylla paramamosain) through the antagonism of Se

Heavy metal pollution has gained increasing attention over past years, and notably, cadmium (Cd) is a non-essential heavy metal that can be toxic to human and wildlife. Furthermore, selenium (Se) is a component of the selenoproteins and influences the toxicity of Cd in different organisms, and protect organisms as a kind of heavy metal antagonist. This study exposed mud crab to 5.0 mg/L Cd for 28 days, and investigated whether different concentrations (0.1, 0.2, 0.3 mg/kg) of selenite (Na₂SeO₃) or selenomethionine (SeMet) affect the bioaccumulation of Cd, serum biochemical index, antioxidant and stress-response genes of S. paramamosain. The results showed that the Cd concentration in Cd group was significantly higher than the organic or inorganic Se group. Serum biochemical index demonstrated that Se might relieve the damage or dysfunction of hepatopancreas caused by both Cd accumulation and toxicity. Furthermore, Se improved CAT, GPx T-AOC and SOD activity, and decreased MDA concentrations and the lipid peroxidation levels, antagonistic to Cd. Then, this study analyzed the expression of 26 stress-related genes, the results indicated that the inorganic and organic Se might reduce the damage of cell and the toxicity of heavy metals in the hepatopancreas after Cd exposure. Therefore, this study indicated that Se might alleviate Cd toxicity via the different antioxidative mechanisms, and increased the understanding of environmental toxins on estuary crustaceans.

Determination of heavy metals from Aloe vera by- product in golden mullet (Liza aurata); A consumer health risk assessment

Heavy metals have become subject of concern in the recent years because of its potency to cause cardiovascular diseases and other toxic health effects. Therefore, this research was assumed to investigate the level of toxicity in terms of heavy metals accumulation in the fish samples and its benefits and risk for human consumers health and also evaluate the partial replacement of plant sources by canarian Aloe vera diets as a pure product or like a by-product on toxicological effects on the golden mullet (Liza aurata) fillet and whole body. In this study risks arising from fish metal content has been measured using various parameters as Estimated Daily Intake (EDI), Maximum Safe Consumption (MSC_A), Target Hazard quotient (THQ), Hazard Index (HI) Carcinogenic risk of As (As- CR), the Value Selenium Health Benefit (Se HBV) and also the Nutritional Values has been evaluated. The results showed that all heavy metal levels in the fish tissue and diets were below the confirmed safe limits for consumption. In case of diets, it is obvious that with the exception of As, Hg, and Se, the presence of heavy or essential metals in both whole fish and raw fillet in golden grey mullet given experimental diets revealed that the whole fish had the highest concentration. Thus, it can be concluded that Aloe vera product and byproduct were in safety limits for fish and also for humans through food chain. Various risk and benefit assessment measures established by national and international authorities concluded that Liza aurata use was mostly safe.

Adolescence as a sensitive period for neurotoxicity: Lifespan developmental effects of methylmercury

Neurotoxicity resulting from the environmental contaminant, methylmercury (MeHg), is a source of concern for many human populations that rely heavily on the consumption of fish and rice as stable ingredients in the diet. The developmental period of exposure is important both to the qualitative effects of MeHg and to the dose required to produce those effects. MeHg exposure during the sensitive prenatal period causes deleterious and long-lasting changes in neurodevelopment at particularly low doses. The effects include a wide host of cognitive and behavioral outcomes expressed in adulthood and sometimes not until aging. However, neurotoxic outcomes of methylmercury when exposure occurs during adolescence are only recently revealing impacts on human populations and animal models. This review examines the current body of work and showcases the sensitivity of adolescence, a period that straddles early development and adulthood, to methylmercury neurotoxicity and the implications such toxicity has in our understanding of methylmercury's effects in human populations and animal models.

Trace elements in seabass, farmed by Turkey, and health risks to the main consumers: Turkish and Dutch populations

Turkey ranked first in sea bass farming in Europe, and almost all extra-EU seabass come from this country. The share of Turkish sea bass in the fish consumption of Europeans has increased significantly, and assessment of potential health risks of trace metals via sea bass, cultured by Turkey, became important. The Netherlands is the main buyer of the Turkish sea bass. Therefore, potential health risks were determined for Turkish and Dutch consumers. In the study, the concentrations of lead (Pb) and mercury (Hg) were below the limits, but the level of cadmium (Cd) was above the guidelines, in spring and winter. Dietary intake and potential health risk were found higher for the Dutch consumer, but all target hazard quotients (THQs) and total THQ (TTHQ) values were well below 1, showing no significant health risk due to the consumption of sea bass, cultured and exported by Turkey. It was determined that these sea basses can be safely consumed in quite high amounts, such as at least 31 meals a month. Se/Hg molar ratios were all above 1 and selenium health benefit values (Se-HBVs) were positive, indicating that selenium (Se) had a protective effect on Hg toxicity and positive health effects. Considering the average annual intake in Turkey and Netherlands, the consumption of sea bass, cultured by Turkey, is safe. Since the risk levels of communities may differ due to their eating habits, it is important to determine the public health impacts of the international fish trade.

Quantitative meta-analysis reveals no association between mercury contamination and body condition in birds

Mercury contamination is a major threat to the global environment, and is still increasing in some regions despite international regulations. The methylated form of mercury is hazardous to biota, yet its sublethal effects are difficult to detect in wildlife. Body condition can vary in response to stressors, but previous studies have shown mixed effects of mercury on body condition in wildlife. Using birds as study organisms, we provide the first quantitative synthesis of the effect of mercury on body condition in animals. In addition, we explored the influence of intrinsic, extrinsic and methodological factors potentially explaining cross-study heterogeneity in results. We considered experimental and correlative studies carried out in adult birds and chicks, and mercury exposure inferred from blood and feathers. Most experimental investigations (90%) showed a significant relationship between mercury concentrations and body condition. Experimental exposure to mercury disrupted nutrient (fat) metabolism, metabolic rates, and food intake, resulting in either positive or negative associations with body condition. Correlative studies also showed either positive or negative associations, of which only 14% were statistically significant. Therefore, the overall effect of mercury concentrations on body condition was null in both experimental (estimate ± SE = 0.262 ± 0.309, 20 effect sizes, five species) and correlative studies (-0.011 ± 0.020, 315 effect sizes, 145 species). The single and interactive effects of age class and tissue type were accounted for in meta-analytic models of the correlative data set, since chicks and adults, as well as blood and feathers, are known to behave differently in terms of mercury accumulation and health effects. Of the 15 moderators tested, only wintering status explained cross-study heterogeneity in the correlative data set: free-ranging wintering birds were more likely to show a negative association between mercury and body condition. However, wintering effect sizes were limited to passerines, further studies should thus confirm this trend in other taxa. Collectively, our results suggest that (i) effects of mercury on body condition are weak and mostly detectable under controlled conditions, and (ii) body condition indices are unreliable indicators of mercury sublethal effects in the wild. Food availability, feeding rates and other sources of variation that are challenging to quantify likely confound the association between mercury and body condition in natura. Future studies could explore the metabolic effects of mercury further using designs that allow for the estimation and/or manipulation of food intake in both wild and captive birds, especially in under-represented life-history stages such as migration and overwintering.

Organ-specific accumulation of selenium and mercury in Indo-Pacific bottlenose dolphins (Tursiops aduncus)

Delphinids are top ocean predators and accumulate high concentrations of mercury (Hg) through the food chain, particularly in organs such as liver and kidney, although the proportion of methylmercury (MeHg) is relatively low due to the demethylation process. Total mercury (T-Hg) levels in marine mammals have been shown to correlate with selenium (Se) concentrations, and ingested MeHg that is demethylated may be present in tissues as mercury selenide (HgSe). In this study, we determined T-Hg, MeHg and Se concentrations of three Indo-Pacific bottlenose dolphins (Tursiops aduncus), and we used the individual with the highest Hg concentration for electron probe microanalysis to assess the co-localization of Hg and Se in the tissues. By electron probe microanalysis, we found that Hg and Se were co-localized in large granules in hepatic Kupffer cells and in small granules in hepatocytes. The analysis suggested that MeHg was demethylated in hepatocytes and then phagocytosed by Kupffer cells. In the kidney, Hg and Se were co-localized in the glomerular capillary wall and in interstitial blood vessel walls. Hg and Se were also co-localized in the cytoplasm of large neurons and in glial cells in the cerebrum. Divalent Hg and HgSe cannot cross the blood-brain barrier, suggesting that MeHg is demethylated in the dolphin brain and that binding to Se suppresses Hg toxicity.

Advances on the Influence of Methylmercury Exposure during Neurodevelopment

Mercury (Hg) is a toxic heavy-metal element, which can be enriched in fauna and flora and transformed into methylmercury (MeHg). MeHg is a widely distributed environmental pollutant that may be harmful to fish-eating populations through enrichment of aquatic food chains. The central nervous system is a primary target of MeHg. Embryos and infants are more sensitive to MeHg, and exposure to MeHg during gestational feeding can significantly impair the homeostasis of offspring, leading to long-term neurodevelopmental defects. At present, MeHg-induced neurodevelopmental toxicity has become a hotspot in the field of neurotoxicology, but its mechanisms are not fully understood. Some evidence point to oxidative damage, excitotoxicity, calcium ion imbalance, mitochondrial dysfunction, epigenetic changes, and other molecular mechanisms that play important roles in MeHg-induced neurodevelopmental toxicity. In this review, advances in the study of neurodevelopmental toxicity of MeHg exposure during pregnancy and the molecular mechanisms of related pathways are summarized, in order to provide more scientific basis for the study of neurodevelopmental toxicity of MeHg.

Determination of Mercury, Methylmercury and Selenium Concentrations in Elasmobranch Meat: Fish Consumption Safety

This study measures total mercury (THg), methylmercury (MeHg) and selenium (Se) concentrations in elasmobranch fish from an Italian market with the aim of evaluating the risk-benefit associated with their consumption, using estimated weekly intake (EWI), permissible safety level (MeHg_PSL), selenium health benefit value (HBV_Se) and monthly consumption rate limit (CR_mm) for each species. THg and Se were analysed by atomic absorption spectrometry, while MeHg was determined by HrGc/Ms. THg and MeHg concentrations ranged from 0.61 to 1.25 μg g^-1 w.w. and from 0.57 to 0.97 μg g^-1 w.w., respectively, whereas Se levels were 0.49-0.65 μg g^-1 w.w. In most samples European Community limits for THg were surpassed, while for MeHg none of the fish had levels above the limit adopted by FAO/WHO. EWIs for THg and MeHg in many cases were above the provisional tolerable weekly intakes (PTWIs). MeHg_PSL estimate showed that fish should contain approximately 50% of the concentration measured to avoid exceeding the PTWI. Nevertheless, the HBV_Se index indicated that solely skates were safe for human consumption (HBV_Se = 3.57-6.22). Our results highlight the importance of a constant monitoring of THg and MeHg level in fish, especially in apex predators, to avoid the risk of overexposure for consumers.

Assessment of the mercury-selenium antagonism in rainbow trout fish

This study aims at the assessment of mercury (Hg)-selenium (Se) antagonism in fish. For this purpose, rainbow trout fish (Oncorhynchus mykiss) were exposed to methylmercury (MeHg) under controlled conditions, in the presence or absence of selenomethionine (SeMet) using an in-house prepared diet (enriched with MeHg and SeMet at 0.2 μg/g and 5.0 μg/g, respectively). The total duration of the exposure study was 3 months. Fish was sampled and analysed for total Se (Se_T) and total mercury (Hg_T) content after 1, 2 and 3 months of exposure. Six feeding protocols were compared, depending on the exposure type: (i) no MeHg nor SeMet exposure (control group); (ii) exposure to SeMet solely; (iii) exposure to MeHg solely; (iv) exposure to both MeHg and SeMet; (v) exposure first to MeHg during 1 month and then to SeMet during 2 months and (vi), exposure to SeMet during 1 month and then to MeHg for 2 months. The levels of Se_T and Hg_T in the fish (control and supplemented with MeHg/SeMet) were measured by inductively coupled plasma-mass spectrometry (ICPMS). Steadily (linear) bioaccumulation of MeHg in the fish muscle occurred when the fish were exposed individually to this species during the period. The bioaccumulation of MeHg is diminished when the fish are firstly exposed to SeMet and then to MeHg, hence indicating the MeHg detoxification due to SeMet supplementation.

Mercury and selenium levels in archive samples of wild Atlantic bluefin tuna from the Mediterranean Sea

This study examined total mercury (THg) and selenium (Se) levels in archive samples (white and red muscles, liver, gills) of the wild Atlantic bluefin tuna (ABFT) (Thunnus thynnus) (n = 18) captured in the central Adriatic Sea. The influence of fish size, age, and tissue type on element distribution was examined. There were significant differences in THg and Se levels, and Se:THg molar ratios among tissues. THg levels were highest in liver and lowest in gills (liver > red muscle > white muscle > gills), while Se levels were also highest in liver but lowest in white muscle (liver > red muscle > gills > white muscle). Se:THg molar ratios were highest in gills (22-82), intermediate in liver (11-29) and red muscle (7-36), and lowest in white muscle (1.7-7.6). Concentrations of THg in all tissues and Se in liver and caudal muscle were positively correlated with tuna age and size, while the Se:THg molar ratio in gills and all white muscles was negatively correlated with tuna age and size, indicating that the protective role of Se against THg is reduced in older specimens. The selenium health benefit values (HBV_Se) were above zero in all tissues, indicating a small excess of Se after Hg sequestration. However, since the obtained HBV_Se for edible tissues were near zero (0.01-0.04), and more than 70% of white muscle samples and all red muscle samples exceeded the EU regulatory limit for THg in fish muscle, it would be advisable to limit their intake in adults to one meal per month.

Nurse sharks, space rockets and cargo ships: Metals and oxidative stress in a benthic, resident and large-sized mesopredator, Ginglymostoma cirratum

It is widely recognized that apex predators, such as large sharks with highly migratory behavior, are particularly vulnerable to pollution, mainly due to biomagnification processes. However, in highly impacted areas, mesopredator sharks with resident behavior can be as vulnerable as apex sharks. In this context, this study evaluated cadmium (Cd), mercury (Hg), lead (Pb), and rubidium (Rb) concentrations, as well as the potentially protective effects of selenium (Se) and the behavior of two non-enzymatic biomarkers, metallothionein (MT) and reduced glutathione (GSH), employing the Atlantic nurse shark Ginglymostoma cirratum as a study model and compared the results with other resident benthic sharks, as well as highly mobile apex sharks. Muscle tissue samples from 28 nurse sharks opportunistically sampled from the Brazilian Amazon Coast were analyzed. Lower metal concentrations were observed for Pb, Rb and Se in the rainy season, while statistically significant correlations between metals were observed only between Hg and Cd and Pb and Se. Molar ratio calculations indicate potential protective Se effects against Pb, but not against Cd and Hg. No associations between MT and the determined metals were observed, indicating a lack of detoxification processes via the MT detoxification route. The same was noted for GSH, indicating no induction of this primary cellular antioxidant defense. Our results indicate that benthic/mesopredator sharks with resident behavior are, in fact, as impacted as highly mobile apex predators, with the traditional detoxification pathways seemingly inefficient for the investigated species. Moreover, considering the studied population and other literature data, pollution should be listed as a threat to the species in future risk assessments.

Analysis of essential and non-essential trace elements in the organs of a mother-fetus pair of spotted seals (Phoca largha) from the Sea of Japan

Concentrations of 22 essential and non-essential trace elements (Be, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, Tl, Pb, Th, U, and Hg) were measured in the organs of a mother-fetus pair (at the last trimester of pregnancy) of spotted seals from the Sea of ​Japan. The concentrations of eleven elements are reported for the first time. Eight organs of the pair were examined: lungs, heart, liver, kidneys, intestines, spleen, muscles, and bones. All trace elements detected in the organs of the mother were found also in the organs of the fetus at various concentrations. Placenta is not an effective barrier to prevent non-essential elements from getting into the fetus, but can control entry of some of them, e.g., aluminum, cadmium, and mercury. In most organs of the fetus, the concentrations of toxic trace elements (beryllium, antimony, thorium, and uranium) were noticeably higher than in the same organs of the mother, which indicates that during pregnancy female removes excess of non-essential trace elements by transferring them to the fetal body through the placental barrier.

Fish tissues for biomonitoring toxic and essential trace elements in the Lower Amazon

Brazilian soils can have high concentrations of toxic elements, mainly mercury (Hg) and arsenic (As), metals also associated with anthropogenic activities (e.g. intensive agriculture, mining, deforestation and hydroelectric plants). This can lead to large amounts of these elements reaching and/or being mobilized in the aquatic ecosystem, which constitutes a serious threat to the environment and to the health of local populations. Thus, we evaluate the feasibility of analyzing the tissues of freshwater fish species for monitoring toxic and trace element accumulation within the aquatic ecosystem in the Lower Amazon, Brazil. Two fish species were considered: Cichla temensis (Tucunaré), a carnivorous species, and Pterygoplichthys pardalis (Acari), a detritivorous species. Samples of liver and muscle from both species were evaluated in relation to their potential use for biomonitoring purposes. The study findings clearly demonstrate the value these fish species and tissues, particularly liver, for biomonitoring toxic and trace element concentrations in the aquatic environment across the study region. While Tucunaré liver proved the best option for biomonitoring elements that accumulate through the food chain (e.g. Hg), Acari liver better reflected elements that typically accumulate in the sediments (e.g. As). Moreover, the trace element profiles, determined using chemometric (multivariate) techniques, differed greatly in specimens from waters in the Andean mountain range (sampling sites located in the main course of the Amazon River) with high sediment concentrations, and in specimens from the Guyana and Brazilian shields (Porto Trombetas on the Trombetas River and Itaituba on the Tapajós River). The findings also indicate that deposition of elements in freshwater fish in this area is mainly associated with the geological origin of the soils and that large amounts of toxic elements can reach the aquatic ecosystem due to anthropogenic activities, thereby posing a serious danger to the environment and the health of the riverside communities.

The Cumulative Risk of Prenatal Exposures to Chemical and Non-Chemical Stressors on Birth Outcomes in Suriname

The cumulative exposure to chemical and non-chemical stressors may have an impact on birth outcomes. The aim of this study is to examine the cumulative exposure of a mixture of chemicals (mercury, lead, selenium and tin) and non-chemical stressors (social support, perceived stress, probable depression and BMI) on birth outcomes (birthweight, gestational age at birth, and Apgar score at 5 min). The study population is a subset (n = 384) of the Caribbean Consortium for Research in Environmental and Occupational Health–MeKiTamara prospective cohort study. Associations between the latent chemical construct, non-chemical stressors and birth outcomes were assessed using path models. The results showed a significant direct relationship between perceived stress and birthweight (β = −0.17), however even though the relationship between perceived stress and depression was significant in all three path models (β = 0.61), the association between depression and birth outcomes was not significant. Perceived stress was significantly associated with community engagement (β = −0.12) and individual resilience (β = −0.12). BMI (β = 0.12) was also significantly directly associated with birthweight. The latent chemical construct did not show an association with the birth outcomes. Our data indicate the need for the development of a support system for pregnant women by involving them in prenatal care programs to reduce maternal stress, which may also influence depression and (in)directly improve the birth outcomes. Interventions regarding weight management for women of childbearing age are necessary to halt obesity and its negative effects on birth outcomes.

Poaching of endangered species in Mediterranean Sea: Alopias vulpinus

A thresher shark poached by fishermen in the stretch of sea between the island of Ponza and the coast of Terracina (Lazio, Central Italy, Mediterranean Sea) and confiscated by the Italian health authorities was evaluated for the presence of chemical contaminants. Hg mean concentration of 2.1 mg kg^-1 was found in muscle; speciation analysis confirmed it was almost in the toxic organic form of MeHg (2.0 mg kg^-1). The Se:Hg molar ratio was <1 not protective against the toxic effect of Hg. ¹³⁷Cs was detected at a mean concentration of 0.53 Bq kg^-1, and ⁴⁰K, radioisotope of natural origin was found at 91 Bq kg^-1. Dioxins and PCBs were found in the common thresher shark at mean concentrations of 0.012 and 0.088 pg TEQ-WHO g^-1 w.w. while NDL PCBs at 4.5 ng g^-1 w.w., lower than limits set by European Regulation. The major concern is constituted by the presence of Hg twice the maximum limit set by EU Regulation, then the consumption of thresher shark flesh should be strongly discouraged.

Trace elements in muscle tissue of three commercial shark species: Prionace glauca, Carcharhinus falciformis, and Alopias pelagicus off the Manzanillo, Colima coast, Mexico

Given their predatory characteristics, long life, and high trophic levels, sharks can have a remarkable ability to bioaccumulate and/or biomagnify trace elements (TE). In the present study, 13 TE (Hg, Pb, Cd, Cu, As, Se, Zn, Cr, V, Fe, Ni, Co, and Mn) were analyzed in the muscle tissue of three shark species (Prionace glauca, Carcharhinus falciformis, and Alopias pelagicus) using high-resolution mass spectrometry inductively coupled to a plasma generator (HR-ICP-MS); 30 shark specimens of each specie were obtained during commercial fish landings in the port of Manzanillo, Mexico. The morphometric characteristics and sex of the sharks were recorded. Shark A. pelagicus accumulated higher concentrations of TE, especially for Hg and Cd, than the other species. Significant differences in the TE levels were detected between sexes in P. glauca and A. pelagicus; in all cases, the highest concentrations were found in female muscle tissue. The ability of sharks to bioaccumulate ETs depends of the metals (essentials higher than non-essential) but is explained mainly by feeding habits associated to sexes (population segregation) and size (ontogeny). The association between TE in shark specimens was related to the essentiality, their antagonistic action, and origin. The Se/Hg ratio was significantly higher than 1, evidence of the protective role of dietary Se against Hg uptake and toxicity in all specimens of the three shark species. Also, the elevate inverse correlation of As and Cd versus Se could indicate a protective action of Se against these toxic metals, but the mechanism must be investigated.

Mercury interactions with selenium and sulfur and the relevance of the Se:Hg molar ratio to fish consumption advice

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for -SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

Levels of Mercury, Methylmercury and Selenium in Fish: Insights into Children Food Safety

Total mercury (THg), methylmercury (MeHg), and selenium (Se) concentrations were measured in various commercially important fish species. The benefit-risk binomial associated with these chemicals was assessed in children through the probability of exceeding the provisional tolerable weekly intakes (PTWIs) of the contaminants and the Se recommended dietary allowance (RDA). The Se:Hg molar ratios, selenium health benefit values (HBVSe), and monthly consumption rate limits (CRmm) for each species were also calculated. THg and Se were analyzed by atomic absorption spectrophotometer (Shimadzu, Milan, Italy), while MeHg was determined by Trace Ultra gas chromatograph connected with a PolarisQ MS (Thermo Fisher Scientific, Waltham, MA, USA). None of the analyzed fish had Hg levels above the European Community regulatory limits, while most large predators had MeHg levels over the threshold concentration set by US EPA. The estimated weekly intakes of THg and MeHg exceeded in many cases the PTWIs and the Se estimated daily intakes were provided from 0.71% to 2.75% of the RDA. Se:Hg molar ratios above 1 and positive HBVSe index suggested that Se in fish could be enough to alleviate the potential toxic effect of Hg. However, high-risk groups as children should consume fish in moderation because a large consumption pattern, especially of swordfish and tunas, might be of concern for health.