Selenium and mercury molar ratios in saltwater fish from New Jersey: individual and species variability complicate use in human health fish consumption advisories

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.

P. Oliveira MB, Prieto MA. Health benefits of bluefin tuna consumption: (Thunnus thynnus) as a case study

Consumers are increasingly interested in food products with high nutritional value and health benefits. For instance, fish consumption is linked with diverse positive health benefits and the prevention of certain widespread disorders, such as obesity, metabolic syndrome, or cardiovascular diseases. These benefits have been attributed to its excellent nutritional value (large amounts of high-quality fatty acids, proteins, vitamins, and minerals) and bioactive compounds, while being relatively low-caloric. Atlantic bluefin tuna (Thunnus tynnus) is one of the most consumed species worldwide, motivated by its good nutritional and organoleptic characteristics. Recently, some organizations have proposed limitations on its consumption due to the presence of contaminants, mainly heavy metals such as mercury. However, several studies have reported that most specimens hold lower levels of contaminants than the established limits and that their richness in selenium effectively limits the contaminants' bioaccessibility in the human body. Considering this situation, this study aims to provide baseline data about the nutritional composition and the latest evidence regarding the beneficial effects of Atlantic bluefin tuna consumption. A review of the risk-benefit ratio was also conducted to evaluate the safety of its consumption, considering the current suggested limitations to this species' consumption.

Biomonitoring of mercury and selenium in commercially important shellfish: Distribution pattern, health benefit assessment and consumption advisories

This study aims to explore the concentrations of Se and Hg in shellfish along the Gulf of Mannar (GoM) coast (Southeast India) and to estimate related risks and risk-based consumption limits for children, pregnant women, and adults. Se concentrations in shrimp, crab, and cephalopods ranged from 0.256 to 0.275 mg kg-1, 0.182 to 0.553 mg kg-1, and 0.176 to 0.255 mg kg-1, respectively, whereas Hg concentrations differed from 0.009 to 0.014 mg kg-1, 0.022 to 0.042 mg kg-1 and 0.011 to 0.024 mg kg-1, respectively. Se and Hg content in bamboo shark (C. griseum) was 0.242 mg kg-1 and 0.082 mg kg-1, respectively. The lowest and highest Se concentrations were found in C. indicus (0.176 mg kg-1) and C. natator (0.553 mg kg-1), while Hg was found high in C. griseum (0.082 mg kg-1) and low in P. vannamei (0.009 mg kg-1). Se shellfishes were found in the following order: crabs > shrimp > shark > cephalopods, while that of Hg were shark > crabs > cephalopods > shrimp. Se in shellfish was negatively correlated with trophic level (TL) and size (length and weight), whereas Hg was positively correlated with TL and size. Hg concentrations in shellfish were below the maximum residual limits (MRL) of 0.5 mg kg-1 for crustaceans and cephalopods set by FSSAI, 0.5 mg kg-1 for crustaceans and 1.0 mg kg-1 for cephalopods and sharks prescribed by the European Commission (EC/1881/2006). Se risk-benefit analysis, the AI (actual intake):RDI (recommended daily intake) ratio was > 100%, and the AI:UL (upper limit) ratio was < 100%, indicating that all shellfish have sufficient level of Se to meet daily requirements without exceeding the upper limit (UL). The target hazard quotient (THQ < 1) and hazard index (HI < 1) imply that the consumption of shellfish has no non-carcinogenic health impacts for all age groups. However, despite variations among the examined shellfish, it was consistently observed that they all exhibited a Se:Hg molar ratio > 1. This finding implies that the consumption of shellfish is generally safe in terms of Hg content. The health benefit indexes, Se-HBV and HBVse, consistently showed high positive values across all shellfish, further supporting the protective influence of Se against Hg toxicity and reinforcing the overall safety of shellfish consumption. Enhancing comprehension of food safety analysis, it is crucial to recognize that the elevated Se:Hg ratio in shellfish may be attributed to regular selenoprotein synthesis and the mitigation of Hg toxicity by substituting Se bound to Hg.

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.

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.

Factors determining bioaccumulation of neurotoxicant Hg in the zebra mussels (Dreissena polymorpha): Influence of biometric parameters, sex and storage of shell

One of benthic organisms exposed to contact with mercury in the southern Baltic is alien species of clam: Dreissena polymorpha. As this organism is increasingly dynamic in various regions of the world including the southern Baltic region, it is reasonable to ask whether it tolerates elevated concentrations of xenobiotics? Does it effectively eliminate Hg? The study determined the effects of biometric parameters and water temperature on the rate of accumulation and efficiency of eliminating Hg from body. Investigations focused on the shell which represents poorly-recognized role in the process of Hg distribution in clams. The results showed that especially during warm season, clams effectively reduced the levels of Hg in their body by the biodilution of Hg and reproduction. Important factor influencing detoxification was Hg transfer from the soft tissue to the shell. This protects the soft tissue against the toxic effect of Hg.

Simultaneous speciation analysis of Hg and Se in fish by high-performance liquid chromatography and inductively coupled plasma-mass spectrometry following microwave-assisted enzymatic hydrolysis

This study reports the development and validation of a new analytical method for simultaneous speciation analysis of Se and Hg in fish muscle. For this purpose, four Se species (selenite/Se(IV), selenate/Se(VI), selenomethionine/SeMet, and selenocysteine/SeCys) and two Hg species (inorganic mercury/iHg and methylmercury/MeHg) were extracted simultaneously by microwave-assisted enzymatic hydrolysis and then separated by HPLC in less than 15 min by using a column with both anion and cation exchange mechanisms and a mobile phase consisting of a mixture of methanol 5% (v/v), 45 mM HNO3, 0.015% 2-mercaptoethanol, and 1.5 mM sodium 3-mercapto-1-propanesulfonate. The separated species of Hg and Se were detected online by inductively coupled plasma-mass spectrometry (ICP-MS). The speciation analysis method was validated by means of the accuracy profile approach by carrying out three series of measurements in duplicate on three different days over a time-span of 3 weeks. The limits of quantification (LOQ) are in the range of 0.010-0.013 mg/kg wet weight (ww) for all selenium species, except for Se(IV) (0.15 mg/kg ww), while the coefficient of variation in terms of intermediate reproducibility (CVR) was < 7%. The LOQ for MeHg was 0.006 mg/kg ww, while the CVR was 3%. The method was successfully applied to the analysis of muscle samples from four different fish species: rainbow trout, tuna, swordfish, and dogfish.

Ecotoxicology applied to conservation: Potential negative metal and metalloid contamination effects on the homeostatic balance of the critically endangered Brazilian guitarfish, Pseudobatos horkelii (Elasmobranchii: Rhinobatidae)

Metal contamination poses a significant threat to elasmobranchs, underscoring the need for targeted conservation approaches. The critically endangered Brazilian guitarfish, Pseudobatos horkelii, confronts an array of challenges, notably overexploitation, putting its survival at risk. Our study investigated the potential toxicity arising from arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) contamination across various adult guitarfish tissues from southeastern Brazil. Serological stress indicators, nutritional metabolites, and creatinine, an organ function marker, were also assessed, and Selenium (Se) levels were also investigated for possible protective effects. Our investigation unveiled significant correlations between metal concentrations and the determined physiological markers, shedding light on potential adverse effects. Remarkably, six correlations were indicative of how Hg and Pb negatively impact hepatic metabolite assimilation, while As was shown to influence renal phosphorus dynamics, Cd to affect rectal gland phosphorus regulation, and Pb to influence creatinine production in muscle tissue. Furthermore, Se demonstrated protective properties against Cd, Hg, and Pb, suggesting a role in alleviating the toxicity of these elements. Despite probable protective Se influences, the detected elemental interactions still suggest potential for organ impairment. These findings gain heightened significance within the context of the cumulative stressors faced by the Brazilian guitarfish, with metal contamination exhibiting the capacity to erode this species resilience against both anthropogenic and environmental pressures, thereby disrupting systemic equilibrium and jeopardizing wild populations. By investigating the intricate balance between metal accumulation and physiological consequences, our study contributes with crucial insights into potential conservation strategy formulations towards pollution for this critically endangered elasmobranch species.

Relationship between trace element concentrations and body length in dolphinfish (Coryphaena hippurus) in the northwest Atlantic Ocean

Dolphinfish (Coryphaena hippurus) is a popular seafood choice worldwide, however, except for mercury (Hg) and selenium (Se), little is known about the concentration of other trace elements in dolphinfish muscle tissue, especially in the northwest Atlantic Ocean. This study investigated the relationship between body length (61 to 94 cm fork length) and trace element [silver (Ag), arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), Hg, manganese (Mn), nickel (Ni), lead (Pb), Se, and zinc (Zn)] concentrations in muscle tissue of dolphinfish caught off Long Island, New York (n = 16). There was a positive relationship with body length for As and Hg, a negative relationship with body length for Cu and Zn, and no relationship with body length for Cd, Fe, Mn, Pb, and Se. A negative relationship between the Se:Hg molar ratio and body length and Se:Hg molar ratio and Hg concentration was observed. Dolphinfish were low in Hg with only 18.9% (n = 3) of individuals exceeding the U.S. EPA human health criterion of 0.3 µg/g wet weight, making this species a suitable seafood choice to reduce dietary intake of Hg at the investigated body length. All fish had a Se:Hg molar ratio > 1:1 indicating that Se may have a protective effect against Hg toxicity. The selenium health benefit value (HBVSe) for all individuals was > 1, indicating there may be health benefits from consuming dolphinfish.

Mercury and selenium co-ingestion assessment via rice consumption using an in-vitro method: Bioaccessibility and interactions

Mercury (Hg) was reported to accumulate in rice grains, and, together with the selenium (Se) was found in rice, the co-exposure of Hg-Se via rice consumption may present significant health effects to human. This research collected rice samples containing high Hg:high Se and high Se:low Hg concentrations from high Hg and high Se background areas. The physiologically based extraction test (PBET) in vitro digestion model was utilized to obtain bioaccessibility data from samples. The results showed relatively low bioaccessible for Hg (<60%) and Se (<25%) in both rice sample groups, and no statistically significant antagonism was identified. However, the correlations of Hg and Se bioaccessibility showed an inverse pattern for the two sample groups. A negative correlation was detected in the high Se background rice group and a positive correlation in the high Hg background group, suggesting various micro forms of Hg and Se in rice from different planting locations. In addition, when the benefit-risk value (BRV) was calculated, some "fake" positive results showed while Hg and Se concentrations were directly used, which indicated that bioaccessibility should not be neglected in benefit-risk assessment.

Selenium in the liver facilitates the biodilution of mercury in the muscle of Planiliza haematocheilus in the Jiaozhou Bay, China

There are increasing evidences that the biodilution effect can significantly reduce the biomagnification of mercury (Hg) in fish. The significant antagonism of selenium (Se) -Hg may have a potential diluting effect on Hg in fish; however, there is still lack of knowledge on such effect. To reveal the Se-Hg interaction and its role in controlling the biodilution effect of Hg, we investigated levels of Hg and Se in the muscle and liver of redlip mullet from Jiaozhou Bay, China, an urbanized semi-enclosed bay highly impacted by human activities. In general, Hg levels in fish muscle were significantly negatively correlated to the levels of Se in the liver and fish size for fish with a size of < 200 mm, indicating that the antagonistic effect of Se on Hg increased with fish growth. This relationship was not significant for fish with a size of > 200 mm, possibly because the normal metabolism of Hg in muscle was hindered by homeostatic regulation or physiological activities such as gonadal development in vivo. Furthermore, the molar ratio of Se in the liver/Hg in the muscle was significantly increasing with Se/Hg in the liver, suggesting that the liver may be the key organ involved in Se-Hg antagonism. Moreover, both ratios continued to decrease with increasing fish size, implying that the antagonistic effect weakens with fish growth. These results indicate that Hg sequestration by liver may be a key mechanism of Se-Hg antagonism in fish and function as a driver for the biodilution effect of Hg, especially at a size of < 200 mm. These findings are further supported by the established linear model of Se-Hg antagonism at different developmental stages.

Total mercury, methylmercury, and selenium concentrations in blue marlin Makaira nigricans from a long-term dataset in the western north Atlantic

Mercury in seafood is a neurotoxicant that threatens human health. Dynamic rates of mercury emission, re-emission, and atmospheric deposition warrant studies into mercury concentrations in fish because many are consumed by humans and can serve as sentinels of mercury levels in the environment. We modeled trends in total mercury content in an apex marine fish predator, Atlantic blue marlin Makaira nigricans, whose muscle tissues were opportunistically sampled from North Carolina (USA) sportfishing tournaments over a discontinuous time period: between 1975 and 77 and 1998-2021 (n = 148). The model-estimated influence of marlin weight on total mercury concentration was constant across years (shared slope) allowing for comparisons of weight-corrected mercury concentrations among years. Weight-corrected total mercury concentrations revealed an inter-decadal decline of approximately 45 % between the 1970s and late 1990s and then variable but relatively stable concentrations through 2021. The mean (SD) wet weight concentration of total mercury was 9.47 (4.11) from 1975 to 77 and 4.17 (2.61) from 2020 to 2021. Methylmercury and selenium were measured on a subset of fish to address questions related to human health and consumption. Methylmercury levels (mean = 0.72 μg/g) were much lower than total mercury (mean = 4.69 μg/g) indicating that total mercury is not a good proxy for methylmercury in Atlantic blue marlin. Selenium, examined as a Se:Hg molar ratio and as a selenium health benefit value (HBV_Se), showed high protective value against mercury toxicity. Long-term trends in the concentration of mercury in blue marlin should continue to be monitored to determine whether policies to mitigate anthropogenic contributions to global mercury are achieving their intended goals and to provide information to inform safe human consumption.

Risk and Benefit Analysis of Fish Consumption in NW Mexico: Mercury, Selenium, and Fatty Acids

To balance the risks and benefits of fish consumption, selenium, fatty acids (DHA + EPA), and mercury in fishery products were determined. Analyzed products were canned tuna, frozen tuna (Thunnus albacares), smoked striped marlin (Tetrapturus audax), fresh Pacific sierra (Scomberomorus sierra), fresh dolphinfish (Coryphaena hippurus), fresh tilapia (Gerres cinereus), and fresh bullseye puffer (Sphoeroides annulatus). Mercury (μg g^-1 wet weight) ranged from 0.01 (dolphinfish) to 0.23 (bullseye puffer); Se ranged from 0.12 to 0.25. EPA + DHA ranged from 1.16 to 10.72 mg g^-1. Intake of EPA + DHA was comparable or above the recommended daily intake; Hg intake was below the reference dose but Se intake was below than recommended values for the different population groups. Considering the HBV_Se, fishery products had positive values; i.e., they are healthy food items. According to the interaction of Hg and Se and the rate of fishery product consumption, the risk for consumers is below one percent.

Risk assessment for seafood consumers exposed to mercury and other trace elements in fish from Long Island, New York, USA

We determined concentrations of Hg, Pb, Cd, Cr, As, Ni, Ag, Se, Cu, and Zn in muscle tissue of six commonly consumed Long Island fish species (black seabass, bluefish, striped bass, summer flounder, tautog, and weakfish, total sample size = 1211) caught off Long Island, New York in 2018 and 2019. Long-term consumption of these coastal fish could pose health risks largely due to Hg exposure; concentrations of the other trace elements were well below levels considered toxic for humans. By combining the measured Hg concentrations in the fish (means ranging from 0.11 to 0.27 mg/kg among the fish species), the average seafood consumption rate, and the current US EPA Hg reference dose (0.0001 mg/kg/d), it was concluded that seafood consumption should be limited to four fish meals per month for adults for some fish (bluefish, tautog) and half that for young children. Molar ratios of Hg:Se exceeded 1 for some black seabass, bluefish, tautog, and weakfish.

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.

Metal accumulation varies with life history, size, and development of larval amphibians

Amphibian larvae are commonly used as indicators of aquatic ecosystem health because they are susceptible to contaminants. However, there is limited information on how species characteristics and trophic position influence contaminant loads in larval amphibians. Importantly, there remains a need to understand whether grazers (frogs and toads [anurans]) and predators (salamanders) provide comparable information on contaminant accumulation or if they are each indicative of unique environmental processes and risks. To better understand the role of trophic position in contaminant accumulation, we analyzed composite tissues for 10 metals from larvae of multiple co-occurring anuran and salamander species from 20 wetlands across the United States. We examined how metal concentrations varied with body size (anurans and salamanders) and developmental stage (anurans) and how the digestive tract (gut) influenced observed metal concentrations. Across all wetlands, metal concentrations were greater in anurans than salamanders for all metals tested except mercury (Hg), selenium (Se), and zinc (Zn). Concentrations of individual metals in anurans decreased with increasing weight and developmental stage. In salamanders, metal concentrations were less correlated with weight, indicating diet played a role in contaminant accumulation. Based on batches of similarly sized whole-body larvae compared to larvae with their digestive tracts removed, our results indicated that tissue type strongly affected perceived concentrations, especially for anurans (gut represented an estimated 46-97% of all metals except Se and Zn). This suggests the reliability of results based on whole-body sampling could be biased by metal, larval size, and development. Overall, our data shows that metal concentrations differs between anurans and salamanders, which suggests that metal accumulation is unique to feeding behavior and potentially trophic position. To truly characterize exposure risk in wetlands, species of different life histories, sizes and developmental stages should be included in biomonitoring efforts.

Biomonitoring selenium, mercury, and selenium:mercury molar ratios in selected species in Northeastern US estuaries: risk to biota and humans

The mutual mitigation of selenium and mercury toxicity is particularly interesting, especially for humans. Mercury is widely recognized as a pantoxic element; all forms are toxic to all organisms. Less well known is that selenium in excess is toxic as well. The high affinity between these elements influences their bioavailability and toxicity. In this paper, we use selected species from Barnegat and Delaware Bays in New Jersey to examine variations in levels of selenium and mercury, and selenium:mercury molar ratios between and within species. We report on species ranging from horseshoe crab eggs (Limulus polyphemus), a keystone species of the food chain, to several fish species, to fish-eating birds. Sampling began in the 1970s for some species and in the 1990s for others. We found no clear time trends in mercury levels in horseshoe crab eggs, but selenium levels declined at first, then remained steady after the mid1990s. Concentrations of mercury and selenium in blood of migrant shorebirds directly reflected levels in horseshoe crab eggs (their food at stopover). Levels of mercury in eggs of common terns (Sterna hirundo) varied over time, and may have declined slightly since the mid2000s; selenium levels also varied temporally, and declined somewhat. There were variations in mercury and selenium levels in commercial, recreational, and subsistence fish as a function of species, season, and size (a surrogate for age). Selenium:mercury molar ratios also varied as a function of species, year, season, and size in fish. While mercury levels increased with size within individual fish species, selenium levels remained the same or declined. Thus selenium:mercury molar ratios declined with size in fish, reducing the potential of selenium to ameliorate mercury toxicity in consumers. Mercury levels in fish examined were higher in early summer and late fall, and lower in the summer, while selenium stayed relatively similar; thus selenium:mercury molar ratios were lower in early summer and late fall than in midsummer. We discuss the importance of temporal trends in biomonitoring projects, variations in levels of mercury, selenium, and the molar ratios as a function of several variables, and the influence of these on risks to predators and humans eating the fish, and the eggs of gulls, terns. Our data suggests that variability limits the utility of the selenium:mercury molar ratio for fish consumption advisories and for risk management.

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.

Composition of nutrients, heavy metals, polycyclic aromatic hydrocarbons and microbiological quality in processed small indigenous fish species from Ghana: Implications for food security

The triple burden of malnutrition is an incessant issue in low- and middle-income countries, and fish has the potential to mitigate this burden. In Ghana fish is a central part of the diet, but data on nutrients and contaminants in processed indigenous fish species, that are often eaten whole, are missing. Samples of smoked, dried or salted Engraulis encrasicolus (European anchovy), Brachydeuterus auritus (bigeye grunt), Sardinella aurita (round sardinella), Selene dorsalis (African moonfish), Sierrathrissa leonensis (West African (WA) pygmy herring) and Tilapia spp. (tilapia) were collected from five different regions in Ghana. Samples were analyzed for nutrients (crude protein, fat, fatty acids, several vitamins, minerals, and trace elements), microbiological quality (microbial loads of total colony counts, E. coli, coliforms, and Salmonella), and contaminants (PAH4 and heavy metals). Except for tilapia, the processed small fish species had the potential to significantly contribute to the nutrient intakes of vitamins, minerals, and essential fatty acids. High levels of iron, mercury and lead were detected in certain fish samples, which calls for further research and identification of anthropogenic sources along the value chains. The total cell counts in all samples were acceptable; Salmonella was not detected in any sample and E. coli only in one sample. However, high numbers of coliform bacteria were found. PAH4 in smoked samples reached high concentrations up to 1,300 μg/kg, but in contrast salted tilapia samples had a range of PAH4 concentration of 1 μg/kg to 24 μg/kg. This endpoint oriented study provides data for the nutritional value of small processed fish as food in Ghana and also provides information about potential food safety hazards. Future research is needed to determine potential sources of contamination along the value chains in different regions, identify critical points, and develop applicable mitigation strategies to improve the quality and safety of processed small fish in Ghana.

Subsistence fish consumption in rural Alaska: Using regional monitoring data to evaluate risk and bioavailability of dietary methylmercury

On average, Alaskans in rural communities consume over three times the Federally recommended maximum weekly fish ingestion rate (IR), the overwhelming majority of which is Pacific salmon. Results of statewide monitoring efforts consistently show that Pacific salmon from Alaska have low concentrations of mercury, yet concerns regarding dietary exposure to methylmercury (MeHg) and other aquatic contaminants continue to contribute to declining subsistence fish consumption rates in rural communities. Therefore, the goal of the present study was to use statewide biomonitoring datasets and regional fish IRs to quantitatively evaluate potential risk from dietary MeHg exposure via subsistence consumption of salmon from Alaska. Hazard Indices (HIs) did not exceed 1 for any of the groups evaluated, indicating negligible risk for the average Alaskan subsistence consumer. Selenium health benefit values (HBV_Se) of various fish species from AK were also calculated, with positive results for all commonly consumed subsistence species. Additionally, mercury concentrations in the hair of Alaskan women were evaluated as a proxy for dietary MeHg exposure. Results reveal that Alaskan women of childbearing age have substantially lower hair Hg concentrations than their counterparts in other large-scale biomonitoring studies, despite similar fish IRs. Collectively, results of the present study suggest that MeHg in Pacific salmon does not pose an unacceptable hazard for the average subsistence consumer in Alaska.

Do Two Wrongs Make a Right? Persistent Uncertainties Regarding Environmental Selenium-Mercury Interactions

Mercury (Hg) is a pervasive environmental pollutant and contaminant of concern for both people and wildlife that has been a focus of environmental remediation efforts for decades. A growing body of literature has motivated calls for revising Hg consumption advisories to co-consider selenium (Se) levels in seafood and implies that remediating aquatic ecosystems with ecosystem-scale Se additions could be a robust solution to Hg contamination. Provided that elevated Se concentrations are also known toxicological threats to aquatic animals, we performed a literature search to evaluate the strength of evidence supporting three assertions underpinning the ameliorating benefits of Se: (1) dietary Se reduces MeHg toxicity in consumers; (2) environmental Se reduces Hg bioaccumulation and biomagnification in aquatic food webs; and (3) Se inhibits Hg bioavailability to, and/or methylmercury production by, microbial communities. Limited or ambiguous support for each criterion indicates that many scientific uncertainties and gaps remain regarding Se mediation of Hg behavior and toxicity in abiotic and biotic compartments. Significantly more information is needed to provide a strong scientific basis for modifying current fish consumption advisories on the basis of Se:Hg ratios or for applying Se amendments to remediate Hg-contaminated ecosystems.

Cadmium, mercury, and selenium in muscle of the scalloped hammerhead Sphyrna lewini from the tropical Eastern Pacific: Variation with age, molar ratios and human health risk

With the aim of assessing health risk to shark consumers, cadmium, mercury, and selenium were measured in muscle of Sphyrna lewini from four coastal states (Baja California Sur, Sinaloa, Nayarit, and Colima) in western Mexico. According to length of specimens, three age modes were found: juveniles and neonates (the majority of the individuals), preadults and adults. Average concentrations (μg g^-1 dry weight) in all the studied individuals followed the order cadmium (0.06), selenium (0.94), and mercury (1.56). The mean concentrations of cadmium and mercury increased significantly (p < 0.001) with mean length of specimens. Overall, hazard quotient and hazard index values were below one so there is no health risk to consumers. According to molar ratios of Hg and Se in the edible portion (muscle) of sharks, and depending on the areas of collection, individuals from Baja California Sur might not be beneficial to consumers.

Determination of Hg in Farmed and Wild Atlantic Bluefin Tuna (Thunnus thynnus L.) Muscle

Mercury (Hg) is a well-known toxic element, diffused in the environment, especially in the Mediterranean Sea which is rich in cinnabar deposits. Mercury bioaccumulation in fish is of great concern, especially for top-level aquatic predators (e.g., shark, tuna, swordfish) and above all for species of large human consumption and high nutritional value. This work aimed to determine Hg concentrations in farmed and wild Atlantic Bluefin tuna (Thunnus thynnus) caught in the Mediterranean area in order to evaluate the level of Hg bioaccumulation. selenium (Se) content was also determined, since this element is an antagonist of mercury toxicity. Mercury and Se were analysed by atomic absorption spectrometry after microwave digestion of the samples. Hg content in farmed tuna was below the legal limit (1 mg/kg, wet weight, w.w.) for all specimens (0.6 ± 0.2 mg/kg), whereas the wild ones had a content over the limit (1.7 ± 0.6 mg/kg); Se concentration was higher in farmed specimens (1.1 ± 0.9 mg/kg) compared to wild ones (0.6 ± 0.3 mg/kg). A safe seafood could show a Se/Hg ratio >1 and a health benefit value (HBV_Se) > 0: farmed tuna had higher values than the wild specimens (Se/Hg 5.48 vs. 1.32; HBV_Se 11.16 vs. 0.29). These results demonstrate that for Hg, there is a better risk/benefit ratio in farmed T. thynnus. making it safer than wild tuna.

Effects of geography and species variation on selenium and mercury molar ratios in Northeast Atlantic marine fish communities

Methylmercury (MeHg) is a potent neurotoxin that bioaccumulates in seafood. Co-occurrence of selenium (Se) may affect the bioavailability and toxicity of MeHg in organisms. Here we report the concentrations of total mercury (Hg) and Se in 17 teleost fish species (n = 8459) sampled during 2006-2015 from the North East Atlantic Ocean (NEAO) and evaluate species variation and effects of geography. Mean Hg concentration ranged from 0.04 mg kg^-1 ww in Atlantic mackerel (Scomber scombrus) and blue whiting (Micromesistius poutassou) to 0.72 mg kg^-1 ww in blue ling (Molva dypterygia). Se concentrations were less variable and ranged from 0.27 mg kg^-1 ww in Atlantic cod (Gadus morhua) to 0.56 mg kg^-1 ww in redfish (Sebastes spp.). The mean Se:Hg molar ratio ranged from 1.9 in blue ling to 43.3 in mackerel. Pelagic species had the lowest Hg concentrations and the highest Se:Hg ratios, whereas demersal species had the highest Hg concentrations and the lowest Se:Hg ratios. Se and Hg concentrations were positively correlated in 13 of the 17 species. Hg concentrations increased from the North to South in contrast to the Se:Hg molar ratio which exhibited the opposite trend. Fish from fjord and coastal areas had higher concentrations of Hg and lower Se:Hg molar ratios compared to fish sampled offshore. All species had average Se:Hg molar ratios >1 and Hg concentrations were largely below the EU maximum level of 0.5 mg kg^-1 ww with few exceptions including the deep water species tusk (Brosme brosme) and blue ling sampled from fjord and coastal habitats. Our results show that two fillet servings of tusk, blue ling or Atlantic halibut (Hippoglossus hippoglossus) exceeded the tolerable weekly intake of MeHg although the surplus Se may possibly ameliorate the toxic effects of MeHg. However, some individuals with selenium deficiencies may exhibit greater sensitivity to MeHg.

Selenium, Mercury, and Their Molar Ratio in Sportfish from Drinking Water Reservoirs

Mercury (Hg) bioaccumulates in aquatic ecosystems and may pose a risk to humans who consume fish. Selenium (Se) has the ability to reduce Hg toxicity, but the current guidance for human consumption of fish is based on Hg concentration alone. The purpose of the present study was to examine the relationship between Se and Hg in freshwater sportfish, for which there is a paucity of existing data. We collected three species of fish from different trophic positions from two drinking water reservoirs in central North Carolina, USA, to assess Hg and Se concentrations in relation to fish total length and to compare two measures of the protective ability of Se, the Se:Hg molar ratio and Se health benefit value (HBV_Se), to current guidance for Hg. According to the Se:Hg molar ratio, all of the low trophic position fish sampled and the middle trophic position fish sampled from one of the reservoirs were safe for consumption. The same number of fish were considered safe using the HBV_Se. More fish were deemed unsafe when using the Se:Hg molar ratio and HBV_Se than were considered unsafe when using the U.S. Environmental Protection Agency (USEPA) Hg threshold. These findings suggest that the measures of Se protection may be unnecessarily conservative or that the USEPA Hg threshold may not be sufficiently protective of human health, especially the health of sensitive populations like pregnant or nursing mothers and young children. Future examination of the Se:Hg molar ratio and HBV_Se from a variety of fish tissue samples would help refine the accuracy of these measures so that they may be appropriately utilized in ecological and human health risk assessment.

Concentrations of mercury (Hg) and selenium (Se) in afterbirth and their relations with various factors

The aim of the study was to evaluate Hg and Se concentrations and Se:Hg molar ratios in the placenta, umbilical cord and fetal membranes, and to examine the relationship between the concentrations of the elements and selected factors. The study material consisted of the placenta, umbilical cord and fetal membranes obtained from 91 healthy women from northwestern and central Poland. In our study mean Hg and Se concentrations in afterbirth were ~ 0.01 mg/kg dry weight (dw) and ≤ 0.5 mg/kg dw, respectively. Correlation analysis showed negative relationships between placenta weight and Se concentration in the placenta and umbilical cord, as well as between placenta length and Se levels in the umbilical cord. We found negative correlations between THg concentration in the placenta and birth weight and between Se concentration in the placenta and umbilical cord and the morphological parameters of the placenta. Furthermore, we noted new types of interactions in specific parts of the afterbirth. In our study, Se:THg molar ratios ranged from 5 to 626; these values indicate protection against Hg toxicity.

Mercury and selenium in fishes from the Tapajós River in the Brazilian Amazon: An evaluation of human exposure

This work aimed to evaluate associated risks of fish consumption to human health, concerning mercury (Hg) and selenium (Se) concentrations in fish species largely consumed in the Tapajós River basin in the Brazilian Amazon. Total mercury (THg), methylmercury (MeHg) and Se concentrations were measured in 129 fish specimens from four sites of the Tapajós River basin. Estimated daily intake (EDI) of Hg and Se were reported regarding fish consumption. EDI were compared with the reference value of provisional tolerable daily intake proposed by the World Health Organization (WHO). Se:Hg ratios and selenium health benefit values (Se HBVs) seem to offer a more comprehensive fish safety model. THg concentrations in fishes ranged from 0.03 to 1.51 μg g^-1 of wet weight (w.w.) and MeHg concentrations ranged from 0.02 to 1.44 μg g^-1 (w.w.). 80% of the samples were below the value of Hg recommended by the WHO for human consumption (0.5 μg g^-1 w.w.). However, Hg EDI exceeded the dose suggested by the United States Environmental Protection Agency (0.1 μg kg^-1 day^-1), due to the large level of fish consumption in that area. Se concentrations in fishes ranged from 0.02 to 0.44 μg g^-1 w.w. An inverse pattern was observed between Hg and Se concentrations in the trophic chain (highest levels of Se in the lowest trophic levels). The molar ratio Se:Hg and Se HBVs were higher in iliophagous and herbivorous fishes, which is noteworthy to reduce toxic effects of Hg contamination. For planktivores, the content of Se and Hg was almost equimolar. Carnivorous fishes - with the exception of Hemisorubim platyrhynchos and Pseudoplatystoma fasciatum -, showed Se:Hg ratios <1. Thus, they do not act as a favorable source of Se in the diet. Therefore, reduced intake of carnivorous fishes with preferential consumption of iliophages, herbivores and, to some extent, even planktivores should be promoted as part of a healthier diet.

Mercury Concentrations and Se:Hg Molar Ratios in Flyingfish (Exocoetus volitans) and Squid (Uroteuthis chinensis)

We measured total mercury (Hg) and selenium (Se) concentrations as well as stable nitrogen (N) isotopic composition in flyingfish and squid muscle tissues from the eastern Indian Ocean and western South China Sea. The results showed that the mean Hg concentration in squid muscle from the western South China Sea was lower than that in the eastern Indian Ocean. The Hg concentrations in flyingfish and squid muscle samples were positively correlated with organism size (length and weight) and δ¹⁵N in all the study areas. Furthermore, we found a negative correlation between Se and Hg in molar content of flyingfish and squid muscle from the western South China Sea. The Se:Hg molar ratio was significantly negative correlated with fish weight and δ¹⁵N, suggesting that the Se:Hg molar ratio decreases with the increase of fish size and trophic level in the food web.

Selenium contamination, consequences and remediation techniques in water and soils: A review

Selenium (Se) contamination in surface and ground water in numerous river basins has become a critical problem worldwide in recent years. The exposure to Se, either direct consumption of Se or indirectly may be fatal to the human health because of its toxicity. The review begins with an introduction of Se chemistry, distribution and health threats, which are essential to the remediation techniques. Then, the review provides the recent and common removal techniques for Se, including reduction techniques, phytoremediation, bioremediation, coagulation-flocculation, electrocoagulation (EC), electrochemical methods, adsorption, coprecipitation, electrokinetics, membrance technology, and chemical precipitation. Removal techniques concentrate on the advantages, drawbacks and the recent achievements of each technique. The review also takes an overall consideration of experimental conditions, comparison criteria and economic aspects.

Bioaccumulation of mercury and other metal contaminants in invasive lionfish (Pterois volitans/miles) from Curaçao

A wide range of ecological and environmental factors influence metal bioaccumulation in fish. Studies of mercury and other metal contaminants in invasive Indo-Pacific lionfish are limited, yet consumption of the invasive predator is increasingly utilized as a management strategy. In this study, we examined the effects of body size, body condition, sex, trophic level, carbon source, diet, depth and capture location on mercury concentrations in lionfish collected from Curaçao. In addition, we examined whether or not a local petroleum refinery is the source of metal contamination in lionfish. Mercury concentrations ranged from 0.008 to 0.106 mg/kg and we found no effect of the petroleum refinery on metal bioaccumulation in lionfish. Low concentrations of metal contaminants indicate lionfish from Curaçao are safe for human consumption.

Hair mercury and risk assessment for consumption of contaminated seafood in residents from the coast of the Persian Gulf, Iran

The health risks of mercury exposure due to the high consumption of aquatic were assessed for fishermen and non-fishermen families living on the Bandar Abbas, Bushehr, and Mahshahr cities located in the coast of Persian Gulf (Iran). The mean hair mercury concentration of people in Bandar Abbas, Bushehr, and Mahshahr cities was obtained 1.56 ± 0.17, 1.97 ± 0.22, and 5.12 ± 0.3 μg g^-1, respectively. Hair mercury concentration in 8.8% of people exceeded the no observed adverse effects level (NOAEL) of 10 μg g^-1 declared by the World Health Organization (WHO). The fish and shrimps consumption, place of living, and fisher and non-fisherman family were variables that significantly effected on mercury levels in the hair. The effect of other factors (age, sex, and number of dental amalgam fillings) on hair mercury was not significant. The mean concentrations of mercury in three fish species in Mahshahr exceeded the recommended maximum standard level (0.5 μg g^-1) set by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA). The estimated weekly intake (EWI) for mercury in some fish species in Bandar Abbas, Bushehr, and Mahshahr was higher than the provisional tolerable weekly intake (1.6 μg kg^-1 bw) set by European Food Safety Authority (EFSA) for some groups. The significant positive correlation between daily mercury intake and hair mercury concentration of people (r = 0.64, P < 0.001) reasserts that the hair mercury concentration could be explained by fish consumption. HQ > 1 was obtained for women in child bearing age in fishermen families in Bandar Abbas and Bushehr cities, children in fishermen families in Bushehr, and for all groups of population except adult in non-fishermen families in Mahshahr. So, the limited consumption of some fish species for these groups of people is recommended. The maximum of allowable fish consumption rate was 0.70 meals/month for Pseudorhombus arsius from Mahshahr fish for women of child bearing age. Also, it is necessary to create and monitor and enforce environmental standards, preventing the entry of pollutants released into the marine aquatic environment without proper early treatment.

Total Mercury, Methylmercury, Inorganic Arsenic and Other Elements in Meat from Minke Whale (Balaenoptera acutorostrata) from the North East Atlantic Ocean

Meat samples of 84 minke whales (Balaenoptera acutorostrata) mainly from the Barents Sea, collected between 1 May and 16 August 2011, were analyzed for total mercury, methylmercury, cadmium, lead, total arsenic, inorganic arsenic and selenium. The average total mercury concentration found was 0.15 ± 0.09 mg/kg, with a range from 0.05 to 0.49 mg/kg. The molar ratio of selenium to mercury varied between 1.0 and 10.3. Cadmium content ranged from 0.002 to 0.036 mg/kg, while the content of lead in whale meat ranged from <0.01 to 0.09 mg/kg. None of the whale samples exceeded established EU maximum levels for metals in fish muscle, but 4.8% and 6.8% of the samples exceeded Japanese maximum levels for total mercury and methylmercury, respectively, in whale meat. There was only minor variations in element concentrations between whales from different geographical areas, and cadmium was the only element were the concentration increased with increasing length.

Selenium: Mercury Molar Ratios in Freshwater Fish in the Columbia River Basin: Potential Applications for Specific Fish Consumption Advisories

Fish provide a valuable source of beneficial nutrients and are an excellent source of low fat protein. However, fish are also the primary source of methylmercury exposure in humans. Selenium often co-occurs with mercury and there is some evidence that selenium can protect against mercury toxicity yet States issue fish consumption advisories based solely on the risks that methylmercury pose to human health. Recently, it has been suggested the selenium: mercury molar ratio be considered in risk management. In order for agencies to utilize the ratio to set consumption guidelines, it is important to evaluate the variability in selenium and mercury in different fish species. We examined 10 different freshwater fish species found within the Columbia River Basin in order to determine the inter- and intra-specific variability in the selenium: mercury molar ratios and the selenium health benefit values. We found significant variation in selenium: mercury molar ratios. The mean molar ratios for each species were all above 1:1, ranging from 3.42:1 in Walleye to 27.2:1 in Chinook salmon. There was a positive correlation between both mercury and selenium with length for each fish species apart from yellow perch and rainbow trout. All species had health benefit values greater than 2. We observed considerable variability in selenium: mercury molar ratios within fish species collected in the Columbia River Basin. Although incorporating selenium: mercury molar ratios into fish consumption holds the potential for refining advisories and assessing the risk of methylmercury exposure, the current understanding of how these ratios apply is insufficient, and further understanding of drivers of variability in the ratios is needed.

Hazardous properties and toxicological update of mercury: From fish food to human health safety perspective

The mercury (Hg) poisoning of Minamata Bay of Japan widely activated a global attention to Hg toxicity and its potential consequences to the aquatic ecosystem and human health. This has resulted to an increased need for a dynamic assembly, contextualization, and quantification of both the current state-of-the-art and approaches for understanding the cause-and-effect relationships of Hg exposure. Thus, the objective of this present review is to provide both hazardous toxic properties and toxicological update of Hg, focusing on how it ultimately affects the aquatic biota to potentially produce human health effects. Primarily, we discussed processes that relate to Hg exposure, including immunological aspects and risk assessment, vulnerability, toxicokinetics, and toxicodynamics, using edible fish, swordfish (Xiphias gladius), as a model. In addition, we summarized available information about Hg concentration limits set by different governmental agencies, as recognized by national and international standardization authorities.

Associations between omega-3 fatty acids, selenium content, and mercury levels in wild-harvested fish from the Dehcho Region, Northwest Territories, Canada

To better understand the risks and benefits of eating wild-harvested fish from the Northwest Territories, Canada, levels of total mercury (HgT) and selenium (Se) and composition of omega-3 fatty acid (n-3 FA) were measured in muscle tissue of fish harvested from lakes in the Dehcho Region, Northwest Territories, Canada. Average HgT levels ranged from 0.057 mg/kg (cisco) to 0.551 mg/kg (northern pike), while average n-3 FA concentrations ranged from 101 mg/100 g (burbot) to 1,689 mg/100 g (lake trout). In contrast to HgT and n-3 FA, mean Se concentrations were relatively similar among species. Consequently, species such as lake whitefish, cisco, and longnose sucker displayed the highest nutrient levels relative to HgT content. Levels of HgT tended to increase with fish size, while Se and n-3 FA levels were typically not associated with fork length or fish weight. Interestingly, HgT concentration was occasionally inversely related to tissue nutrient content. Significant negative correlations were observed between Hg and n-3 FA for lake trout, northern pike, and walleye. There were also significant negative correlations between Hg and Se noted for lake whitefish, cisco, and northern pike. Samples with the highest nutritional content displayed, on occasion, lower levels of HgT. This study provides valuable information for the design of probabilistic models capable of refining public health messaging related to minimizing Hg risks and maximizing nutrient levels in wild-harvested fish in the Canadian subarctic.

Mercury accumulation in marine fish most favoured by Malaysian women, the predictors and the potential health risk

We identified marine fish species most preferred by women at reproductive age in Selangor, Malaysia, mercury concentrations in the fish muscles, factors predicting mercury accumulation and the potential health risk. Nineteen most preferred marine fish species were purchased (n = 175) from selected fisherman's and wholesale market. Length, weight, habitat, feeding habit and trophic level were recognised. Edible muscles were filleted, dried at 80 °C, ground on an agate mortar and digested in Multiwave 3000 using HNO₃ and H₂O₂. Total mercury was quantified using VP90 cold vapour system with N₂ carrier gas. Certified reference material DORM-4 was used to validate the results. Fish species were classified as demersal (7) and pelagic (12) or predators (11), zoo benthos (6) and planktivorous (2). Length, weight and trophic level ranged from 10.5 to 75.0 cm, 0.01 to 2.50 kg and 2.5 to 4.5, respectively. Geometric mean of total mercury ranged from 0.21 to 0.50 mg/kg; maximum in golden snapper (0.90 mg/kg). Only 9 % of the samples exceeded the JECFA recommendation. Multiple linear regression found demersal, high trophic (≥4.0) and heavier fishes to accumulate more mercury in muscles (R ² = 27.3 %), controlling for all other factors. About 47 % of the fish samples contributed to mercury intake above the provisional tolerable level (45 μg/day). While only a small portion exceeded the JECFA fish Hg guideline, the concentration reported may be alarming for heavy consumers. Attention should be given in risk management to avoid demersal and high trophic fish, predominantly heavier ones.

Nutritive values, flavor amino acids, healthcare fatty acids and flesh quality improved by manganese referring to up-regulating the antioxidant capacity and signaling molecules TOR and Nrf2 in the muscle of fish

Flesh quality, amino acid and fatty acid composition, antioxidant status and related molecule expression in fish muscle were estimated by feeding grass carp with diets containing 3.65-27.86mg/kg diet of manganese (Mn) for 8weeks. Results demonstrated that optimal Mn increased toughness, collagen content, and pH, and decreased the cooking loss, and cathepsin B and L activities to enhance the flesh quality of fish. Meanwhile, optimal Mn increased the protein, lipid, the total essential amino acid (AA) (especially umami AA), and healthcare fatty acids, C18: 1c+t, C20: 3n-3, C20: 4 and DHA contents. These might be partially related to the decreased lipid peroxidation and protein oxidation, and the enhanced activities of Mn superoxide dismutase (MnSOD), catalase (CAT) and glutathione peroxidase (GPx) modulated by their gene expression, Nrf2 and TOR signaling. We firstly demonstrated that Mn improved flesh quality, flavor and healthcare function in fish muscle.

Mercury and methyl mercury in fishes from Bacajá River (Brazilian Amazon): evidence for bioaccumulation and biomagnification

This study assessed total mercury (THg) and methyl mercury (MeHg) concentrations, bioaccumulation and biomagnification of THg through the food web in fishes consumed by indigenous communities of Bacajá River, the largest tributary of the right bank of Xingu River. In total, 496 fish (22 species) were sampled. Nine species had THg concentrations above the limit recommended by the World Health Organisation (0·5 µg g(-1) wet mass), and one exceeded the recommended level for Hg in predatory fishes by Brazilian law (1·0 µg g(-1) ). The average concentration of THg increased significantly with trophic guild (herbivorous to piscivorous) and trophic level, with higher accumulation in fishes with greater total length. Ninety-six per cent of all mercury was methylated. These results suggest that feeding habits determine THg concentrations in fishes and that Hg elimination rate is slow during growth, which allows greater accumulation. These findings show that fishes in the Bacajá River contain high concentrations of THg and MeHg.

The levels of mercury, methylmercury and selenium and the selenium health benefit value in grey-eel catfish (Plotosus canius) and giant mudskipper (Periophthalmodon schlosseri) from the Strait of Malacca

The present study examined the concentrations of mercury (Hg), methylmercury (MeHg), and selenium (Se) in the multiple tissues of the Plotosus canius and Periophthalmodon schlosseri collected from the Strait of Malacca. The mean value in mg kg(-1) of Hg (P. canius: 0.34 ± 0.19; P. schlosseri: 0.32 ± 0.18) and MeHg in muscle (P. canius: 0.14 ± 0.11; P. schlosseri: 0.17 ± 0.11) were below the Codex general standard for contaminants and toxins in food and feed (CODEX STAN 193-1995), the Malaysian Food Regulation 1985 and the Japan Food Sanitation Law. For P. canius, the liver contained the highest concentrations of Hg (0.48 ± 0.07 mg kg(-1)) and MeHg (0.21 ± 0.00 mg kg(-1)), whereas for P. schlosseri, the gill contained the highest concentrations of Hg (0.36 ± 0.06 mg kg(-1)) and MeHg (0.21 ± 0.05 mg kg(-1)). The highest concentration of (80)Se (mg kg(-1)) was observed in the liver of P. canius (20.34 ± 5.68) and in the gastrointestinal tract (3.18 ± 0.42) of P. schlosseri. The selenium:mercury (Se:Hg) molar ratios were above 1 and the positive selenium health benefit value (HBVSe) suggesting the possible protective effects of Se against Hg toxicity. The estimate weekly intakes (EWIs) in μg kg(-1) body weight (bw) week(-1) of Hg (P. canius: 0.27; P. schlosseri: 0.15) and MeHg (P. canius: 0.11; P. schlosseri: 0.08) were found to be lower than the provisional tolerable weekly intake established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). Based on the calculated EWIs, P. canius, and P. schlosseri were found to be unlikely to cause mercury toxicity in human consumption.

Mercury, selenium and fish oils in marine food webs and implications for human health

Humans who eat fish are exposed to mixtures of healthful nutrients and harmful contaminants that are influenced by environmental and ecological factors. Marine fisheries are composed of a multitude of species with varying life histories, and harvested in oceans, coastal waters and estuaries where environmental and ecological conditions determine fish exposure to both nutrients and contaminants. Many of these nutrients and contaminants are thought to influence similar health outcomes (i.e., neurological, cardiovascular, immunological systems). Therefore, our understanding of the risks and benefits of consuming seafood require balanced assessments of contaminants and nutrients found in fish and shellfish. In this paper, we review some of the reported benefits of fish consumption with a focus on the potential hazards of mercury exposure, and compare the environmental variability of fish oils, selenium and mercury in fish. A major scientific gap identified is that fish tissue concentrations are rarely measured for both contaminants and nutrients across a range of species and geographic regions. Interpreting the implications of seafood for human health will require a better understanding of these multiple exposures, particularly as environmental conditions in the oceans change.

Mercury and selenium in tissues and stomach contents of the migratory sailfish, Istiophorus platypterus, from the Eastern Pacific: Concentration, biomagnification, and dietary intake

Mercury and selenium were assessed in the sailfish, Istiophorus platypterus, from the Eastern Pacific. Sixty-seven individuals were sampled, muscle, liver, kidney, gonads and the prey found in the stomach contents were isolated during fishing 2011-2013 tournaments. Hg exhibited the following pattern (μg g(-1) wet weight): liver (0.57 ± 0.07)>muscle (0.56 ± 0.04)>kidney (0.44 ± 0.08)>gonad (0.14 ± 0.01). The maximum concentration of Se was found in kidneys (14.1 ± 1.9 μg g(-1)), and the minimum in muscles (0.67 ± 0.03 μg g(-1)). High Se:Hg ratios were found for muscle (4.1 ± 0.3), kidney (132.4 ± 12.1), liver (54.0 ± 4.4) and gonads (88.2 ± 7.9); Hg:Se molar ratios were several orders of magnitude lower (muscle<0.4 and liver, kidney and gonad<0.03). Sailfish feed mainly on fishes and cephalopods with low Hg levels (<0.13 μg g(-1)), these results indicate biomagnification of Hg and Se. The muscle of I. platypterus should be consumed (according the provisional tolerable weekly intake) by people cautiously so as not to exceed the recommended intake of 215 g per week.

Mercury and Selenium in Muscle and Target Organs of Scalloped Hammerhead Sharks Sphyrna lewini of the SE Gulf of California: Dietary Intake, Molar Ratios, Loads, and Human Health Risks

Selenium and mercury were evaluated in muscle, liver, kidney, brain, and the stomach contents of juvenile scalloped hammerhead shark Sphyrna lewini. Se:Hg molar ratios were calculated. The average Hg levels in muscle ranged from 0.12 to 1.17 μg/g (wet weight); Hg was <0.39 μg/g in liver and kidneys and <0.19 μg/g in brain. The lowest value of Se was found in muscle (0.4 μg/g) and the highest in kidney (26.7 μg/g). An excess of Se over Hg was found, with Se:Hg molar ratios >1. Correlations were found for Hg in muscle with size, age, and weight, and also for Hg in liver with size, age, and weight. Hg in muscle was significantly positive correlated to Hg in brain as well as Hg in liver was correlated to Hg in kidney. The highest Hg in preys was for carangid fishes; scombrid and carangid fishes contributed with the highest Se levels. Results suggest that more than 98 % of the total Hg and 62 % of Se end up in muscle and might be affected by factors, such as geographical area, age, size, and feeding habits. The muscle of S. lewini should be consumed by people cautiously so as not to exceed the recommended intake per week.

Effect of Intestinal Tapeworm Clestobothrium crassiceps on Concentrations of Toxic Elements and Selenium in European Hake Merluccius merluccius from the Gulf of Lion (Northwestern Mediterranean Sea)

The capacity for heavy metal bioaccumulation by some fish parasites has been demonstrated, and their contribution to decreasing metal concentrations in tissues of parasitized fish has been hypothesized. The present study evaluated the effect of the cestode Clestobothrium crassiceps on the accumulation of trace elements in 30 European hake, Merluccius merluccius, in Spain (half of them infested by C. crassiceps). Tissue samples from all M. merluccius and specimens of C. crassiceps from the infected hakes were collected and stored until element analysis by inductively coupled plasma mass spectrometry (ICP-MS). Arsenic, mercury, and selenium were generally present in lower levels in the cestode than in all hake tissues. The mean value of the muscular Se:Hg molar ratio in the infested subsample was higher than that in hakes without cestodes. Values indicate that the edible part of infested hakes presents a lower amount of Cd and Pb in relation to noninfested hakes.

Selenium contaminated waters: An overview of analytical methods, treatment options and recent advances in sorption methods

Selenium is an essential trace element for many organisms, including humans, but it is bioaccumulative and toxic at higher than homeostatic levels. Both selenium deficiency and toxicity are problems around the world. Mines, coal-fired power plants, oil refineries and agriculture are important examples of anthropogenic sources, generating contaminated waters and wastewaters. For reasons of human health and ecotoxicity, selenium concentration has to be controlled in drinking-water and in wastewater, as it is a potential pollutant of water bodies. This review article provides firstly a general overview about selenium distribution, sources, chemistry, toxicity and environmental impact. Analytical techniques used for Se determination and speciation and water and wastewater treatment options are reviewed. In particular, published works on adsorption as a treatment method for Se removal from aqueous solutions are critically analyzed. Recent published literature has given particular attention to the development and search for effective adsorbents, including low-cost alternative materials. Published works mostly consist in exploratory findings and laboratory-scale experiments. Binary metal oxides and LDHs (layered double hydroxides) have presented excellent adsorption capacities for selenium species. Unconventional sorbents (algae, agricultural wastes and other biomaterials), in raw or modified forms, have also led to very interesting results with the advantage of their availability and low-cost. Some directions to be considered in future works are also suggested.

Human exposure to mercury in artisanal small-scale gold mining areas of Kedougou region, Senegal, as a function of occupational activity and fish consumption

We investigated mercury (Hg) exposure of food web and humans in the region of Kedougou, Senegal, where Hg is used for gold amalgamation in artisanal small-scale gold mining (ASGM). For this purpose, total mercury (THg) concentration was determined in eight fish species and two shellfish species from Gambia River and in human hair from 111 volunteers of different age and sex, living in urban locations (Kedougou and Samekouta) or in ASGM areas (Tinkoto and Bantako). THg concentrations in fish samples range from 0.03 to 0.51 mg kg(-1) wet weight (ww) and 0.5 to 1.05 mg kg(-1) ww for shellfish. THg concentrations in fish are below the WHO guideline of 0.5 mg kg(-1) ww, whereas 100 % of shellfish are above this safety guideline. In the entire set of fish and shellfish samples, we documented a decrease of THg concentrations with increasing selenium to mercury (Se:Hg) ratio suggesting a protection of Se against Hg. However, local population consuming fish from the Gambia River in the two ASGM areas have higher THg concentrations (median = 1.45 and 1.5 mg kg(-1) at Bantako and Tinkoto) in hair than those from others localities (median = 0.42 and 0.32 mg kg(-1) at Kedougou town and Samekouta) who have diverse diets. At ASGM sites, about 30 % of the local population present Hg concentrations in hair exceeding 1 mg kg(-1), defined as the reference concentration of Hg in hair. We also evidence a higher exposure of women to Hg in the Tinkoto ASGM site due to the traditional distribution of daily tasks where women are more involved in the burning of amalgams. The discrepancy between the calculated moderate exposure through fish consumption and the high Hg concentrations measured in hair suggest that fish consumption is not the only source of Hg exposure and that further studies should focus on direct exposure to elemental Hg of population living at ASGM sites.

Interspecific and locational differences in metal levels in edible fish tissue from Saudi Arabia

Metal levels in fish have been extensively studied, but little data currently exists for the Middle East. We examined the levels of metals and metalloids (aluminum, arsenic, copper, manganese, selenium, zinc, and mercury) in the flesh of 13 fish species collected from three fishing sites and a local fish market in Jeddah, Saudi Arabia. We tested the following null hypotheses: (1) there are no interspecific differences in metal levels, (2) there are no differences in metal levels in fishes between market and fishing sites, (3) there are no size-related differences in metal levels, and (4) there are no differences in selenium:mercury molar ratio among different fish species. There were significant interspecific differences in concentrations for all metals. There was an order of magnitude difference in the levels of aluminum, arsenic, mercury, manganese, and selenium, indicating wide variation in potential effects on the fish themselves and on their predators. Fishes from Area II, close to a large commercial port, had the highest levels of arsenic, mercury, and selenium, followed by market fishes. Mercury was positively correlated with body size in 6 of the 13 fish species examined. Mercury was correlated positively with arsenic and selenium, but negatively with aluminum, cobalt, copper, manganese, and zinc. Selenium:mercury molar ratios varied significantly among species, with Carangoides bajad, Cephalopholis argus, Variola louti, and Ephinephelus tauvina having ratios below 10:1. These findings can be used in risk assessments, design of mercury reduction plans, development of fish advisories to protect public health, and future management decision-making.

Mercury and selenium in tropical marine plankton and their trophic successors

Selenium (Se), mercury (Hg) and methylmercury (MeHg) were determined in microplankton (⩾25μm), crustacean muscle tissue, in the muscle and liver of two fish species and tissues of a dolphin from a bay in the Brazilian Southeast coast. Differences were found between the fish and dolphin muscle and hepatic concentrations. Liver showed the highest concentrations of Se and Hg. Positive biotransference of MeHg from source to consumer was observed for all interactions, demonstrating that MeHg biomagnified along the food web. The pelagic food chain has the highest biomagnification potential when compared to the benthic system. A large excess of Se in relation to Hg was observed in all tissues. The muscle and liver of the predator species, the dolphin and the carnivorous fish, presented similar MeHg. The predator species presented similar MeHg to Hg (% MeHg) ratios in muscle tissues (∼100%), whereas dolphin showed lower hepatic% MeHg (18) than the carnivorous fish (69%). Iliophagous fish presented the lowest % MeHg in tissues. Fish showed a positive relationship between hepatic MeHg and Se, whereas % MeHg did not change with increasing Se:Hg molar ratios in liver. Dolphins showed a significant inverse relationship between hepatic MeHg and Se and the % MeHg and Se:Hg ratios. This suggests a strong antagonistic effect of Se on MeHg assimilation and accumulation in this species. Probably, the differences observed among Hg as MeHg and Se and on the effect of Se on MeHg assimilation and accumulation in all marine species are related to the physiological differences between dolphins and fish.

Protective effects of selenium on mercury induced immunotoxic effects in mice by way of concurrent drinking water exposure

Selenium (Se) has been recognized as one key to understanding mercury (Hg) exposure risks. To explore the effects of Se on Hg-induced immunotoxicity, female Balb/c mice were exposed to HgCl2- or MeHgCl-contaminated drinking water (0.001, 0.01, and 0.1 mM as Hg) with coexisting Na2SeO3 at different Se/Hg molar ratios (0:1, 1/3:1, 1:1 and 3:1). The potential immunotoxicity induced by Na2SeO3 exposure alone (by way of drinking water) was also determined within a wide range of concentrations. After 14 days' exposure, the effects of Hg or Se on the immune system of Balb/c mice were investigated by determining the proliferation of T and B lymphocytes and the activity of natural killer cells. Hg exposure alone induced a dose-dependent suppression effect, whereas Se provided promotion effects at low exposure level (<0.01 mM) and inhibition effects at high exposure level (>0.03 mM). Under Hg and Se coexposure condition, the effects on immunotoxicity depended on the Hg species, Se/Hg ratio, and exposure concentration. At low Hg concentration (0.001 mM), greater Se ingestion exhibited stronger protective effects on Hg-induced suppression effect mainly by way of decreasing Hg concentrations in target organs. At greater Hg concentration (0.01 and 0.1 mM), immunotoxicity induced by Se (>0.03 mM) became evident, and the protective effects appeared more significant at an Se/Hg molar ratio of 1:1. The complex antagonistic effects between Se and Hg suggested that both Se/Hg molar ratio and concentration should be considered when evaluating the potential health risk of Hg-contaminated biota.

Selenium:mercury molar ratios in bullfrog and leopard frog tadpoles from the northeastern United States

Vertebrates experience adverse effects from methylmercury, largely obtained through their food. Selenium has the potential to reduce the toxic effects of methylmercury (and vice versa). In this paper, we examine the selenium:mercury molar ratios in tadpoles (Lithobates sphenocephalus, Lithobates catesbeianus (formerly Rana), and a newly documented leopard frog species currently referred to as R. sp. nov.) and fully formed leopard frog metamorphs. There were no significant differences in metal levels between the two leopard frog species, and data were therefore combined. Selenium:mercury molar ratios varied from 19 to 38 for bullfrog tadpoles, from 16 to 330 for leopard frog tadpoles, and from 7 to 17 for leopard frog metamorphs. Leopard frog tadpoles with less than 45 days exposure to field conditions had significantly higher molar ratios than other tadpoles and leopard frog metamorphs. There were significant locational differences for the molar ratios of bullfrogs, and leopard frog tadpoles with more than 45 days of field exposure. At the sites where we were able to sample both leopard frog tadpoles and leopard frog metamorphs, there were significant differences between the two distinct life stages. Most of the variation in the ratio was accounted for by selenium levels, field sites, and exposure period.