Mercury's neurotoxicity is characterized by its disruption of selenium biochemistry

Total mercury and methylmercury (MeHg) in braised and crude Boletus edulis carpophores during various developmental stages

We collected and processed Boletus edulis (King Bolete) carpophores grouped in four batches based on their developmental stage (button stage, young-white, large-white, and large-yellow). The study aimed, for the first time, to examine the B. edulis content and effect of braising and to estimate the intake of total mercury (THg) and methylmercury (MeHg) from a single meal based on whole (wet) weight (ww) and dry weight (dw). In braised carpophores, THg concentrations ranged from 0.2668 ± 0.0090 to 0.5434 ± 0.0071 mg kg-1 ww at different developmental stages, whereas crude products concentrations ranged from 0.1880 ± 0.0247 to 0.2929 ± 0.0030 mg kg-1 ww. The button stage crude carpophores were more highly contaminated with THg than at later stages of maturity, but MeHg levels were lower (p < 0.0001). On the other hand, braised button stage carpophores showed more MeHg than at later maturity stages. MeHg contributed at 1.9 ± 0.7% in THg in crude mushrooms and at 1.4 ± 0.3% in braised meals. The effect of braising was to increase the average THg and MeHg contents in fresh mushroom meals by 52 ± 31% and 53 ± 122% respectively, but a reduction of 40 ±14% and 40 ± 49% respectively was seen on a dw basis. The potential intakes of THg and MeHg from braised meals of B. edulis studied were small and considered safe.

Non-invasive electrochemistry-driven metals tracing in human biofluids

Wearable analytical devices represent the future for fast, de-centralized, and human-centered health monitoring. Electrochemistry-based platforms have been highlighted as the role model for future developments amid diverse strategies and transduction technologies. Among the various relevant analytes to be real-time and non-invasively monitored in bodily fluids, we review the latest wearable achievements towards determining essential and toxic metals. On-skin measurements represent an excellent possibility for humankind: real-time monitoring, digital/fast communication with specialists, quick interventions, removing barriers in developing countries. In this review, we discuss the achievements over the last 5 years in non-invasive electrochemical platforms, providing a comprehensive table for quick visualizing the diverse sensing/technological advances. In the final section, challenges and future perspectives about wearables are deeply discussed.

Tissue Distribution of Mercury and Its Relationship with Selenium in Atlantic Bluefin Tuna (Thunnus thynnus L.)

Mercury (Hg) is an important heavy metal to consider in marine predators, while selenium (Se) has a natural antagonistic effect on this metal in fish. The Atlantic bluefin tuna (ABFT, Thunnus thynnus) is a pelagic top-level predator of the trophic web and their Hg muscular content is an object of concern in food safety. Nevertheless, little is known about levels of this metal in remaining tissues, which may be important as by-product source, and its relationship with Se. Thus, concentration of both elements in liver, kidney, brain, gill and bone, in addition to muscle, of ABFT were determined. The kidney was the tissue with the highest concentration of Hg (Total-Hg, THg) and Se, and the Se/THg concentration ratio was similar in all tissues, except bone and muscle. The Selenium Health Benefit Value (HBV_Se) was positive in each specimen and tissue, indicating that the Se plays an important role against Hg not only in the muscle.

Mercury and selenium in developing and mature fruiting bodies of Amanita muscaria

Both mercury (Hg) and selenium (Se) occur in many mushroom species, but the morphological distribution of these elements during different developmental stages of the fruiting bodies is not known. Although Amanita muscaria can be consumed after suitable processing, they are often ignored by mushroom foragers, leaving an abundance for investigative study. Multiple specimens in each of six developmental stages (button to fully mature) were collected in excellent condition during a single morning from the same forested location and composited. With an average of 30 specimens per composite, and low temporal, spatial, and measurement uncertainty, the data are likely to be representative of the typical concentrations of Hg and Se for each developmental stage. Hg (range 0.58-0.74 mg kg-1 dry weight cap; 0.33 to 0.44 mg kg-1 dw stipe) and Se (range 8.3-11 mg kg-1 dw cap; 2.2 to 4.3 mg kg-1 dw stipe) levels were observed to vary during the developmental stages, and the variability may relate to the demands in growth. In common with some other species, the lower stipe concentrations may be consistent with nutrient/contant transport and support functions. Both Hg and Se levels were lowest during periods of maximum sporocarp growth. Selenium occurs at almost an order of magnitude greater levels than Hg. Due to its role in mitigating the effects of Hg toxicity, this property is of significance to those who consume the species either for nutritional, medicinal, or recreational purposes, although the losses of both these elements during processing are not known.

Methylmercury Can Facilitate the Formation of Dehydroalanine in Selenoenzymes: Insight from DFT Molecular Modeling

Experimental studies have indicated that electrophilic mercury forms (e.g., methylmercury, MeHg⁺) can accelerate the breakage of selenocysteine in vitro. Particularly, in 2009, Khan et al. (Environ. Toxicol. Chem. 2009, 28, 1567-1577) proposed a mechanism for the degradation of a free methylmercury selenocysteinate complex that was theoretically supported by Asaduzzaman et al. (Inorg. Chem. 2010, 50, 2366-2372). However, little is known about the fate of methylmercury selenocysteinate complexes embedded in an enzyme, especially in conditions of oxidative stress in which methylmercury target enzymes operate. Here, an accurate computational study on molecular models (level of theory: COSMO-ZORA-BLYP-D3(BJ)/TZ2P) was carried out to investigate the formation of dehydroalanine (Dha) in selenoenzymes, which irreversibly impairs their function. Methylselenocysteine as well as methylcysteine and methyltellurocysteine were included to gain insight on the peculiar behavior of selenium. Dha forms in a two-step process, i.e., the oxidation of the chalcogen nucleus followed by a syn-elimination leading to the alkene and the chalcogenic acid. The effect of an excess of hydrogen peroxide, which may lead to the formation of chalcogenones before the elimination, and of MeHg⁺, a severe toxicant targeting selenoproteins, which leads to the formation of methylmercury selenocysteinate, are also studied with the aim of assessing whether these pathological conditions facilitate the formation of Dha. Indeed, elimination occurs after chalcogen oxidation and MeHg⁺ facilitates the process. These results indicate a possible mechanism of toxicity of MeHg⁺ in selenoproteins.

Evaluation of dietary selenium, vitamin C and E as the multi-antioxidants on the methylmercury intoxicated mice based on mercury bioaccumulation, antioxidant enzyme activity, lipid peroxidation and mitochondrial oxidative stress

Mercury (Hg) in high exposures can be a potent life threatening heavy metal that bioaccumulate in aquatic food-chain mainly as organic methylmercury (MeHg). In this regard, fish and seafood consumptions could be the primary sources of MeHg exposure for human and fish-eating animals. The objective of the present study was to elucidate the effects of dietary supplementation of some antioxidants on induced mercury toxicity in mice model. In this study, a 30-day long investigation has been conducted to evaluate the dietary effect of selenium (Se) in combination with vitamin C and vitamin E on methylmercury induced toxicity in mice. Total 54 mice fed the diets with three levels of Hg (0, 50 or 500 μg kg^-1) and two levels of Se in combination with vitamin C and E (Se: 0, 2 mg kg^-1; vitamin C: 0, 400 mg kg^-1; vitamin E: 0, 200 mg kg^-1) in triplicates. The results show that Hg accumulated in blood and different tissues such as muscle, liver and kidney tissues of mice on dose dependent manner. The bioaccumulation pattern of dietary Hg, in decreasing order, kidney > liver > muscle > blood. Superoxide dismutase levels in blood serum showed no significant differences in mice fed the diets. However, dietary antioxidants significantly reduced the levels of thiobarbituric acid reactive substances in mice fed the mercury containing diets. Cytochrome c oxidase enzyme activities showed no significant differences as the mercury level increases in liver and kidney tissues of mice. Kaplan-Meier curve showed a dose- and time-dependent survivability of mice. Cumulative survival rate of Hg intoxicated mice fed the antioxidant supplemented diets were increased during the experimental period. Overall, the results showed that dietary Se, vitamin C and vitamin E had no effect on reducing the mercury bioaccumulation in tissues but reduced the serum lipid peroxidation as well as prolonged the cumulative survival rate in terms of high Hg exposures in mice.

Seafood and health: What you need to know?

Seafood, including fish and shellfish, provides an ideal package of nutrients and is an important part of a healthy diet. Strong evidence has shown that eating fish and other seafoods improve brain, eye, and heart health. The new 2020-2025 Dietary Guidelines for Americans (DGA) recommend that Americans of all ages should eat more seafood-at least twice a week-particularly pregnant women and young children. However, less than one in five Americans heed that advice. About one-third of Americans eat seafood once a week, while nearly half eat fish only occasionally or not at all. This calls for a drastic shift in the American diet to vary protein sources and include more seafood products in order to receive the most health benefits. This chapter covers (1) seafood nutrition and health benefits, (2) seafood's protective effects against mercury toxicity, (3) selenium health benefit values (HBVs), and (4) challenges and opportunities for seafood production, demand and sustainability. This chapter aims to convey recent advances in science-based information to increase public awareness of seafood safety, nutrition and health benefits of seafood as part of a healthy diet, and to advocate healthy eating with smart food choices by promoting two servings of seafood per week. This will support the healthy eating patterns and promotes a minimum two to three servings of seafood recommended by the current DGA.

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.

The Prevalence of Inorganic Mercury in Human Kidneys Suggests a Role for Toxic Metals in Essential Hypertension

The kidney plays a dominant role in the pathogenesis of essential hypertension, but the initial pathogenic events in the kidney leading to hypertension are not known. Exposure to mercury has been linked to many diseases including hypertension in epidemiological and experimental studies, so we studied the distribution and prevalence of mercury in the human kidney. Paraffin sections of kidneys were available from 129 people ranging in age from 1 to 104 years who had forensic/coronial autopsies. One individual had injected himself with metallic mercury, the other 128 were from varied clinicopathological backgrounds without known exposure to mercury. Sections were stained for inorganic mercury using autometallography. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used on six samples to confirm the presence of autometallography-detected mercury and to look for other toxic metals. In the 128 people without known mercury exposure, mercury was found in: (1) proximal tubules of the cortex and Henle thin loops of the medulla, in 25% of kidneys (and also in the man who injected himself with mercury), (2) proximal tubules only in 16% of kidneys, and (3) Henle thin loops only in 23% of kidneys. The age-related proportion of people who had any mercury in their kidney was 0% at 1-20 years, 66% at 21-40 years, 77% at 41-60 years, 84% at 61-80 years, and 64% at 81-104 years. LA-ICP-MS confirmed the presence of mercury in samples staining with autometallography and showed cadmium, lead, iron, nickel, and silver in some kidneys. In conclusion, mercury is found commonly in the adult human kidney, where it appears to accumulate in proximal tubules and Henle thin loops until an advanced age. Dysfunctions of both these cortical and medullary regions have been implicated in the pathogenesis of essential hypertension, so these findings suggest that further studies of the effects of mercury on blood pressure are warranted.

Development and evaluation of a DGT sampler using functionalised cross-linked polyethyleimine for the monitoring of arsenic and selenium in mine impacted wetlands

Arsenic and selenium are both carcinogenic and their presence in fresh water has attracted the development of robust and accurate monitoring techniques. A new diffusive gradients in thin-films (DGT) sampler was developed and evaluated for the in situ measurements of arsenic and selenium. The binding layer was made from a mixture of sulphonated and phosphonated cross-linked polyethylenimine (SCPEI and PCPEI, respectively). The optimum ratio of a SCPEI and PCPEI resin mixture was determined. The DGT sampler was calibrated under laboratory conditions to determine the influence of sample turbulence, concentration and pH. The optimised DGT passive sampler was field deployed in a mine impacted dam for 12 days. Binding layer optimisation shows that the polymers had to be mixed in a specific ratio of 80% sulphonated and 20% phosphonated per 0.8 g of the resin mixture, in the loose polymer form. Embedding the resin mixture in agarose gel reduced the uptake of both arsenic and selenium dramatically. At sample pH 3.0 and 5.0, the DGT sampler did not show significant differences in uptake of the two elements during the 15 day deployment. The passive sampler had limited adsorption capacity and was found better suited for dilute solutions, with concentrations below 0.5 mg L^-1 of the target metals. This effect was more pronounced when exposed to dam water which had competing cations. Cations may have reduced the capacity by binding to the PEI backbone via the large number of amine groups. Nonetheless, these cations did not show linear uptake.

In Vivo Formation of HgSe Nanoparticles and Hg-Tetraselenolate Complex from Methylmercury in Seabirds-Implications for the Hg-Se Antagonism

In vivo and in vitro evidence for detoxification of methylmercury (MeHg) as insoluble mercury selenide (HgSe) underlies the central paradigm that mercury exposure is not or little hazardous when tissue Se is in molar excess (Se:Hg > 1). However, this hypothesis overlooks the binding of Hg to selenoproteins, which lowers the amount of bioavailable Se that acts as a detoxification reservoir for MeHg, thereby underestimating the toxicity of mercury. This question was addressed by determining the chemical forms of Hg in various tissues of giant petrels Macronectes spp. using a combination of high energy-resolution X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy coupled to elemental mapping. Three main Hg species were identified, a MeHg-cysteinate complex, a four-coordinate selenocysteinate complex (Hg(Sec)₄), and a HgSe precipitate, together with a minor dicysteinate complex Hg(Cys)₂. The amount of HgSe decreases in the order liver > kidneys > brain = muscle, and the amount of Hg(Sec)₄ in the order muscle > kidneys > brain > liver. On the basis of biochemical considerations and structural modeling, we hypothesize that Hg(Sec)₄ is bound to the carboxy-terminus domain of selenoprotein P (SelP) which contains 12 Sec residues. Structural flexibility allows SelP to form multinuclear Hg_x(Se,Sec)_y complexes, which can be biomineralized to HgSe by protein self-assembly. Because Hg(Sec)₄ has a Se:Hg molar ratio of 4:1, this species severely depletes the stock of bioavailable Se for selenoprotein synthesis and activity to one μg Se/g dry wet in the muscle of several birds. This concentration is still relatively high because selenium is naturally abundant in seawater, therefore it probably does not fall below the metabolic need for essential selenium. However, this study shows that this may not be the case for terrestrial animals, and that muscle may be the first tissue potentially injured by Hg toxicity.

Demethylation of Methylmercury in Bird, Fish, and Earthworm

Toxicity of methylmercury (MeHg) to wildlife and humans results from its binding to cysteine residues of proteins, forming MeHg-cysteinate (MeHgCys) complexes that hinder biological functions. MeHgCys complexes can be detoxified in vivo, yet how this occurs is unknown. We report that MeHgCys complexes are transformed into selenocysteinate [Hg(Sec)₄] complexes in multiple animals from two phyla (a waterbird, freshwater fish, and earthworms) sampled in different geographical areas and contaminated by different Hg sources. In addition, high energy-resolution X-ray absorption spectroscopy (HR-XANES) and chromatography-inductively coupled plasma mass spectrometry of the waterbird liver support the binding of Hg(Sec)₄ to selenoprotein P and biomineralization of Hg(Sec)₄ to chemically inert nanoparticulate mercury selenide (HgSe). The results provide a foundation for understanding mercury detoxification in higher organisms and suggest that the identified MeHgCys to Hg(Sec)₄ demethylation pathway is common in nature.

Toxic effects of mercury in humans and mammals

The clinical manifestations of methylmercury toxicity do not differ greatly according to the acute and/or chronic methylmercury overexposure.

Regional variations and drivers of mercury and selenium concentrations in Steller sea lions

Mercury (Hg) can be neurotoxic to mammals and impact reproduction, whereas selenium (Se) is an important antioxidant known to ameliorate some adverse effects of Hg. Total Hg concentrations ([THg]) were measured in lanugo (pelage grown in utero) of 812 Steller sea lion (Eumetopias jubatus) pups across Alaska and Russia to assess fetal exposure during late gestation. The molar ratio of total Se to THg (TSe:THg) was determined in whole blood collected from 291 pups. Stable isotope ratios of carbon and nitrogen were measured in sections of vibrissae (whiskers, n = 498) and in lanugo (n = 480) of pups grown during late gestation to track diet variations among adult females that can drive Hg and Se exposure during this critical fetal development period. Lanugo [THg] ranged from 1.4 to 73.7 μg/g dry weight with the lowest median [THg] in Southeast Alaska. Pups from the Western Aleutian Islands had higher median lanugo [THg] than pups from other metapopulations in Alaska. Over 25% of pups in the Western Aleutian Islands had [THg] above published risk thresholds (20 μg/g) for other mammals. Whole blood molar TSe:THg was significantly lower in the Western Aleutian Islands and in some parts of the Central Aleutian Islands with higher molar ratios found in the Eastern Aleutian Islands and Central Gulf of Alaska. This suggests a limitation on potential protective functions of Se in the western regions with the highest relative [THg]. The Central Aleutian Island pups with [THg] over 20 μg/g had higher δ¹⁵N ratios than pups with lower [THg] suggesting dams consuming higher trophic level prey is a key driver for Hg exposure. However, regional differences likely reflect variability in diet of the dam during gestation and in Hg food web dynamics between oceanic regimes east and west of key passes in the Aleutian Islands.

Mercury in traditionally foraged species of fungi (macromycetes) from the karst area across Yunnan province in China

The objective of this study is to better quantify the occurrence, intake, and potential risk from Hg in fungi traditionally foraged in SW China. The concentrations and intakes of Hg were measured from 42 species including a "hard" flesh type polypore fungi and a" soft" flesh type edible species that are used in traditional herbal medicine, collected during the period 2011-2017. Three profiles of forest topsoil from the Zhenyuan site in 2015 and Changning and Dulong sites in 2016 were also investigated. The concentrations of Hg in composite samples of polypore fungi were usually below 0.1 mg kg-1 dry weight (dw) but higher levels, 0.11 ± 0.01 and 0.24 ± 0.00 mg kg-1 dw, were noted in Ganoderma applanatum and Amauroderma niger respectively, both from the Nujiang site near the town of Lanping in NW Yunnan. Hg concentrations in Boletaceae species were usually well above 1.0 mg kg-1 dw and as high as 10 mg kg-1 dw. The quality of the mushrooms in this study in view of contamination with Hg showed a complex picture. The "worst case" estimations showed probable intake of Hg from 0.006 μg kg-1 body mass (bm) ("hard" type flesh) to 0.25 μg kg-1 bm ("soft" flesh) on a daily basis for capsulated products, from 17 to 83 μg kg-1 bm ("soft" flesh) in a meal ("hard" type flesh mushrooms are not cooked while used in traditional herbal medicine after processing), and from 0.042 to 1.7 and 120 to 580 μg kg-1 bm on a weekly basis, respectively. KEY POINTS: • Polypore species were slightly contaminated with Hg. • Hg maximal content in the polypore was < 0.25 mg kg-1 dry weight. • Many species from Boletaceae family in Yunnan showed elevated Hg. • Locals who often eat Boletus may take Hg at a dose above the daily reference dose.

Effects of early and recent mercury and lead exposure on the neurodevelopment of children with elevated mercury and/or developmental delays during lactation: A follow-up study

This follow-up study of 82 children investigated the potential impact of early and recent exposure to mercury and lead on their neurodevelopmental performance at 5-8 years of age (2017-2018). Early exposure of these children to mercury, methylmercury, and lead was assessed during lactation at 3-12 months old, as well as their mother's exposure using measurements from a cross-sectional study (2011-2013). Only infants who failed to pass the neurodevelopment screening tools and/or had elevated mercury were included in this study. Urine and hair were sampled during the follow-up study to assess the children's recent exposure to mercury, methylmercury, and lead. Their cognitive performance and visual-motor integration were also measured using the Test of Non-Verbal Intelligence (TONI) and the Beery-Visual-Motor Integration (Beery VMI), respectively. The association between alterations in urinary porphyrins excretion and exposure to metals was analyzed and their influence on the children's neurodevelopment was explored. Linear regression models revealed a significant negative association between the infants' mercury exposure during lactation and the TONI Quotient (β = -0.298, 95%CI = -4.677, -0.414) and Beery VMI Age Equivalent scores at age 5-8 (β = -0.437, 95%CI = -6.383, -1.844). The mothers' blood methylmercury was inversely and significantly associated with their children's TONI Quotient (β = -0.231, 95%CI = -8.184, -0.331). In contrast, the children's Beery VMI Age Equivalent scores were positively and significantly associated with the hair methylmercury of the mothers (β = 0.214, 95%CI = 0.088, 3.899) and their infants (β = 0.256, 95%CI = 0.396, 4.488). These relationships suggest the presence of negative confounding that we did not take into account. Unlike mercury, there was some evidence that lead in breast milk had an inverse relationship with the children's visual-motor coordination skills. Our study did not show a clear association between children's recent exposure to metals and neurodevelopment. However, a significant inverse association was observed between the TONI Quotient and the interaction of hair methylmercury × ∑porphyrins (ß = -0.224, 95%CI = -0.86, -0.049), implying that porphyrins are a sensitive measure of low body-mercury burden. Although lead induced higher ∑porphyrins excretion in urine (β = 0.347, 95%CI = 0.107, 0.525), their interaction did not influence children's neurodevelopmental scores. The interactions between metals and porphyrins might provide insights into their potential contributory role in the pathogenesis associated with neurological disorders or other diseases. Despite the small sample size of the present study, its findings about the association between toxic metal exposure and the high risk of poor neurodevelopmental performance are worrying, particularly at an early age, and additional research is needed using larger sample sizes.

Response of selenoproteins gene expression profile to mercuric chloride exposure in chicken kidney

Kidney is a primary target organ for mercuric chloride (HgCl₂) toxicity. Selenium (Se) can exert antagonistic effect on heavy metals-induced organ toxicity by regulating the expression of selenoproteins. The objective of this study was to investigate the effect of HgCl₂ on the gene expression of selenoproteins in chicken kidney. Sixty male Hyline brown chickens were randomly and evenly divided into two groups. After acclimatization for one week, chickens were provided with the standard diet as well as non-treated water (CON group), and standard diet as well as HgCl₂-treated water (250 ppm, HgCl₂ group). After seven weeks, kidney tissues were collected to examine the mRNA expression levels of 25 selenoproteins genes and protein expression levels of 4 selenoproteins. Moreover, correlation analysis and principal component analysis (PCA) were used to analyze the expression patterns of 25 selenoproteins. The results showed that HgCl₂ exposure significantly decreased the mRNA expression of Glutathione peroxidase 1 (GPX1), GPX4, Thioredoxin reductase 2 (TXNRD2), Iodothyronine deiodinase 1 (DIO1), Methionine-Rsulfoxide reductase 1 (SELR), 15-kDa selenoprotein (SEP15), selenoprotein I (SELI), SELK, SELM, SELN, SELP, SELS, SELT, SELW, and SEPHS2. Meanwhile, HgCl₂ exposure significantly increased the mRNA expression of GPX3, TXNRD1, and SELU. Western blot analysis showed that the expression levels of GPX3, TXNRD1, SELK, and SELN were concordant with these mRNA expression levels. Analysis results of selenoproteins expression patterns showed that HgCl₂-induced the main disorder expression of selenoproteins with antioxidant activity and endoplasmic reticulum resident selenoproteins. In conclusion, selenoproteins respond to HgCl₂ exposure in a characteristic manner in chicken kidney.

Risk-Benefit Assessment for Total Mercury, Arsenic, Selenium, and Omega-3 Fatty Acids Exposure from Fish Consumption in Jamaica

Fish is important in the traditional diet of Jamaicans, and the fishing industry contributes to social and economic development, as well as food security in Jamaica. However, there are associated health risks from contaminant exposure. The aim of this paper was to use risk-benefit analysis methods to determine the best fish species for consumption. Composite samples consisting of 14 fish species were collected from major fishing villages in 2016 and measured for total mercury, arsenic, selenium, and omega-3 fatty acids (EPA and DHA). Food frequency questionnaires were randomly distributed to 400 participants from different locations on the island. Participants were asked to identify the types of fish, portion size, and the frequency of consumption. An estimate of their weight was also recorded. Total mercury concentrations in fish samples ranged from 0.003 to 0.215 μg/g. The range of arsenic concentrations was 0.11 to 7.8 μg/g. The range of selenium concentrations was 0.302 μg/g to 1.08 μg/g. The mean omega-3 fatty acid concentration was 123.1 ± 93.6 mg/100 g. The fish consumption rates range from 3.2 to 1132.8 g/day. Cod fish was the most consumed species at 23.2 g/day. Four risk-benefit analysis methods were able to recommend four fish species that were best for consumption based on the levels of mercury, arsenic, selenium, and omega-3 fatty acids. They were doctorfish, parrotfish, snappers, and cod fish. The results of this study concluded that there was a low risk of mercury exposure from fish consumed in Jamaica.

Assessing oxidative stress in Steller sea lions (Eumetopias jubatus): Associations with mercury and selenium concentrations

Selenium (Se) bioavailability is required for synthesis and function of essential Se-dependent antioxidants, including the enzyme glutathione peroxidase (GPx). Strong interactions between monomethyl mercury and Se impair the critical antioxidant role of Se. Approximately 20% of Steller sea lion (Eumetopias jubatus, SSL) pups sampled in the western Aleutian Islands, Alaska, had total Hg concentrations ([THg]) measured in hair and whole blood above thresholds of concern for adverse physiologic effects in pinnipeds. Importantly, low molar ratios of TSe:THg, in some cases < 1 in several tissues (hair, liver, pelt, muscle, spleen, intestine, heart, lungs, brain) were documented for one SSL pup with [THg] above threshold of concern, which may lead to antioxidant deficiency. Our aim with this study was to evaluate the relationship between circulating [THg], [MeHg⁺], [TSe] and TSe:THg molar ratio status relative to oxidative stress and antioxidants measured during general anesthesia in free-ranging SSL. We captured, anesthetized and sampled newborn SSL pups at rookeries located in the Aleutian Islands or Gulf of Alaska. Biomarkers analyzed for oxidative stress included 4-hydroxynenonal and thiobarbituric acid reactive substances (4-HNE and TBARS, respectively, lipid peroxidation), protein carbonyl content (PCC, protein oxidation), and GPx activity as a key indicator for Se-dependent antioxidant defense levels. We found a negative association between TBARS and [TSe], and SSL with low [TSe] had higher concentrations of 4-HNE than those with intermediate [TSe]. These results suggest that SSL with lower [TSe] experience increased lipid peroxidation potentially associated with [THg] status.

Toxic heavy metals: impact on the environment and human health, and treatment with conducting organic polymers, a review

Water pollution by heavy metals has many human origins, such as the burning of fossil fuels, exhaust gases of vehicles, mining, agriculture, and incineration of solid and liquid wastes. Heavy metals also occur naturally, due to volcanoes, thermal springs activity, erosion, infiltration, etc. This water contamination is a threat for living beings because most heavy metals are toxic to humans and to aquatic life. Hence, it is important to find effective techniques for removing these contaminants in order to reduce the level of pollution of the natural waters. In this work, we have reviewed the toxicity of several heavy metals (mercury, lead, cadmium, chromium, nickel), their impact on the environment and human health, and the synthesis and characterization methods of conducting organic polymers (COPs) utilized for the removal of heavy metals from the environment. Therefore, this review was essentially aimed to present recent works and methods (2000-2020) on the environmental impact and toxicity of heavy metals and on the removal of toxic heavy metals, using chemically and/or electrochemically synthesized COPs. We have also stressed the great interest of COPs for the removal of toxic heavy metals from waters.

Mercury exposure in relation to foraging ecology and its impact on the oxidative status of an endangered seabird

Mercury is a natural element extensively found in the Earth's crust, released to the atmosphere and waters by natural processes. Since the industrial revolution, atmospheric deposition of Hg showed a three-to-five-fold enrichment due to human activities. Marine top predators such as seabirds are recognized valuable bioindicators of ocean health and sensitive victims of Hg toxic effects. Hg negatively affects almost any aspect of avian physiology; thus, birds prove valuable to study the effect of Hg exposure in vertebrates. The Black-vented Shearwater is endemic to the North-Eastern Pacific Ocean, where it forages along the Baja California Peninsula during the breeding period. The area has no industrial settlement and is in the southern portion of the California Current System (CCS). After observing possible contamination effects in eggshells, we decided to quantify the exposure of breeding birds to Hg and test for possible effects on oxidative status of the species. The concentration of Hg in erythrocytes averaged 1.84 μg/g dw and varied from 1.41 to 2.40 μg/g dw. Males and females had similar Hg concentrations. The individual trophic level (reflected by δ¹⁵N) did not explain Hg exposure. In contrast, individuals foraging inshore had higher Hg concentrations than those foraging more offshore (reflected by δ¹³C). Shearwaters having higher concentrations of Hg had lower activity of the antioxidant enzyme glutathione peroxidase and showed lower non-enzymatic antioxidant capacity. Levels of plasma oxidative damage, superoxide dismutase and catalase were not associated with Hg. Our results indicate that (i) the foraging habitat is the factor explaining Hg exposure and (ii) there is some evidence for potential harmful effects of Hg exposure to this seabird species of conservation concern. CAPSULE: The foraging habitat is the factor explaining Hg exposure in seabirds and we observed potential harmful effects of Hg exposure in a seabird species of conservation concern.

Concentrations of toxic metals and essential trace elements vary among individual neurons in the human locus ceruleus

Objective

Damage to locus ceruleus neurons could play a part in the pathogenesis of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis because of impairment of the blood-brain barrier and enhanced neuroinflammation. The locus ceruleus has connections throughout the brain and spinal cord, so the characteristic widespread multifocal pathology in these disorders could be due to damage to different subsets of locus ceruleus neurons. Previous studies have shown that only certain locus ceruleus neurons accumulate the neurotoxic metal mercury. To find out if concentrations of other toxic metals or of essential trace elements also vary between individual locus ceruleus neurons, we used synchrotron X-ray fluorescence microscopy on frozen sections of locus ceruleus neurons taken from people with multiple sclerosis, in whom the locus ceruleus is structurally intact.

Materials and methods

Paraffin embedded sections containing the locus ceruleus from seven people with multiple sclerosis were stained with autometallography that demonstrates accumulations of mercury, silver and bismuth. These were compared to maps of multiple elements obtained from frozen sections of locus ceruleus neurons from the same people using X-ray fluorescence microscopy. Neurons in the anterior pons from three of these donors were used as internal controls.

Results

Autometallography staining was observed in scattered locus ceruleus neurons from three of the seven donors. X-ray fluorescence microscopy showed variations among individual locus ceruleus neurons in levels of mercury, selenium, iron, copper, lead, bromine, and rubidium. Variations between donors of locus ceruleus neuronal average levels of mercury, iron, copper, and bromine were also detected. Anterior pons neurons contained no mercury, had varied levels of iron, and had lower copper levels than locus ceruleus neurons.

Conclusions

Individual human locus ceruleus neurons contain varying levels of toxic metals and essential trace elements. In contrast, most toxic metals are absent or at low levels in nearby anterior pons neurons. The locus ceruleus plays a role in numerous central nervous system functions, including maintaining the blood-brain-barrier and limiting neuroinflammation. Toxic metals, or alterations in essential trace metals within individual locus ceruleus neurons, could be one factor determining the non-random destruction of locus ceruleus neurons in normal aging and neurodegenerative diseases, and subsequently the sites of the widespread multifocal central nervous system pathology in these disorders.

Transcriptomic and Proteomic Tools in the Study of Hg Toxicity: What Is Missing?

Mercury is a hazardous substance that has unique neurodevelopmental toxic effects in humans. However, the precise sequence of molecular events that culminate in Hg-induced neuropathology is still unknown. Though the omics studies have been generating an enormous amount of new data about Hg toxicity, our ability to interpret such a large quantity of information is still limited. In this opinion article, we will reinforce the necessity of new high throughput and accurate analytical proteomic methodologies, especially, thiol and selenol-proteome. Overall, we posit that improvements in thiol- and selenol-proteomic analyses will be pivotal in identifying the primary cellular targets of Hg. However, a better understanding of the complex cascades and molecular pathways involved in its toxicity will require extensive complementary studies in more complex systems.

Occurrence, distribution and estimated intake of mercury and selenium from sclerotia of the medicinal fungus Wolfiporia cocos from China

The contamination and distribution of mercury and selenium in the Chinese medicinal fungus Wolfiporia cocos was investigated. The sclerotial mercury concentrations ranged from 0.0043 to 0.027 mg kg¹ dry biomass (db) in the inner white part and 0.019-0.074 mg kg^-1 db in the shell (outer part), while selenium concentrations ranged from < 0.00048 to 0.0040 mg kg^-1 db (white) and 0.0034-0.038 mg kg^-1 db (shell). Positive correlations were found for mercury, as well as for mercury and selenium but they were not consistent for both morphological parts. Mercury concentrations exceeded selenium in 16 of 17 white part pools (molar quotient 0.53 to > 10) and in 11 of 17 shell pools (quotient 0.37 to 3.2). The estimated maximal exposure to mercury contained in sclerotial products based on 45 g per capita daily intake for a 60 kg individual over one week, was 0.000020 mg kg^-1 body mass (bm; white) and 0.000055 mg kg^-1 bm (shell) on a daily basis, and 0.00014 mg kg^-1 bm (white) and 0.00039 mg kg^-1 bm (shell) on a weekly basis. Relative to mercury, the corresponding intake rates of selenium were considered very low, i.e., they averaged on a daily basis at 0.00075 μg kg^-1 bm (white) and 0.0097 μg kg^-1 bm (shell) with maximum intake at 0.0030 μg kg^-1 bm (white) and 0.028 μg kg^-1 bm (shell).

Toxicity of thimerosal in biological systems: Conformational changes in human hemoglobin, decrease of oxygen binding capacity, increase of protein glycation and amyloid's formation

Thimerosal (TH), an organomercurial compound, is used as a preservative in vaccines and cosmetics. Its interaction with human hemoglobin (Hb) was investigated under physiological conditions using biophysical and biological assays, aiming to evaluate hazardous effects. TH interacts spontaneously with Hb (stoichiometry 2:1, ligand-protein), preferably by electrostatic forces, with a binding constant of 1.41 × 10⁶ M^-1. Spectroscopic data allows to proposing that TH induces structural changes in Hg, through ethylmercury transfer to human Hb-Cys93 residues, forming thiosalicylic acid, which, in turn, interacts with the positive side of the amino acid in the Hb-HgEt adduct chain. As a consequence, inhibition of Hb-O₂ binding capacity up to 72% (human Hb), and 50% (human erythrocytes), was verified. Dose-dependent induction of TH forming advanced glycation end products (AGE) and protein aggregates (amyloids) was additionally observed. Finally, these results highlight the toxic potential of the use of TH in biological systems, with a consequent risk to human health.

Neuropathology associated with exposure to different concentrations and species of mercury: A review of autopsy cases and the literature

BACKGROUND

Human exposure to mercury (Hg) is widespread and both organic and inorganic Hg are routinely found in the human brain. Millions of people are exposed to methyl Hg (MeHg) due to the consumption of fish and to inorganic Hg from dental amalgams, small scale gold mining operations, use of Hg containing products, or their occupations. Neuropathology information associated with exposures to different species of Hg is primarily based on case reports of single individuals or collections of case studies involving a single species of Hg at toxic exposure levels such as occurred in Japan and Iraq.

METHODS/RESULTS

This study brings together information on the neuropathological findings and deposition of Hg in the central nervous system of people exposed to different species of Hg at varying concentrations. The low dose exposures were lifetime exposures while the high dose exposures were generally acute or short term by different exposure routes with survival lasting various lengths of time. Total and inorganic Hg deposits were identified in formalin-fixed, paraffin embedded tissues from both low and high exposure Hg cases. Low concentration exposures were studied in adult brains from Rochester, New York (n = 4) and the Republic of Seychelles (n = 17). Rochester specimens had mean total Hg concentrations of 16-18 ppb in the calcarine, rolandic, and cerebellar cortices. Inorganic Hg averaged between 5-6 ppb or 30-37% for the cerebral and cerebellar cortices of the Rochester subjects. Total Hg was approximately 10-fold higher in specimens from Seychelles, where consumption of ocean fish is high and consequently results in exposure to MeHg. The predominant Hg species was MeHg in both the Rochester and Seychelles brain specimens. Histologically, cerebral and cerebellar cortices from Rochester and Seychelles specimens were indistinguishable. High concentration exposures were studied in brains from four adults who were autopsied at variable time periods after exposure to organic Hg (methyl or dimethyl) or inorganic Hg (inhaled vapor or intravenous injection of metallic Hg). In contrast to the Seychellois adults, these individuals had acute or subacute exposures to lethal or significantly higher concentrations. The pattern of Hg deposition differed between subjects with high organic Hg exposure and high inorganic Hg exposure. In the organic Hg cases, glia (astrocytes and microglia) and endothelial cells accumulated more Hg than neurons and there were minimal Hg deposits in cerebellar granule and Purkinje cells, anterior horn motor neurons, and neocortical pyramidal neurons. In the inorganic Hg cases, Hg was seen predominantly in neurons, vascular walls, brainstem, and cerebellar and cerebral deep gray nuclei. The presence of inorganic Hg in neural and neural supporting cells in the four high exposure Hg cases was not closely correlated with cellular pathology; particularly in the inorganic Hg cases.

CONCLUSIONS

Different Hg species are associated with differing neuropathological patterns. No neuropathological abnormalities were present in the brains of either Rochester or Seychelles residents despite substantial differences in dietary MeHg exposure. Increasing concentrations of inorganic Hg were present in the brain of relatively low exposure subjects with increasing age.

Evaluation of blood mercury and serum selenium levels in the pregnant population of the Community of Madrid, Spain

BACKGROUND

The main exposure route to methylmercury (MeHg) is from eating fish and shellfish containing this compound. Since 2004, women of childbearing age in Spain have been urged not to eat some species (eg, tuna, shark, and swordfish), instead choosing low-MeHg seafood as part of a healthy diet.

OBJECTIVE

To describe maternal total blood mercury (THg) and serum selenium (Se) in a cohort of pregnant women living in Spain as it relates to fish intake during the three trimesters and to assess whether or not Spanish women of childbearing age follow the recommendations listed in fish advisories and choose fish species with lower mercury levels.

METHODS

We studied 141 female volunteers of childbearing age (16-45 years), interviewing all participants about their overall eating habits and seafood intake. Hg and Se levels were tested using cold-vapor atomic absorption spectrometry (CVAAS) and electrothermal atomic absorption spectrometry (ETAAS), respectively.

RESULTS

Average THg levels in pregnant women were 2.89 μg/L (standard deviation [SD], 2.75 μg/L, geometric mean [GM], 2.19 μg/L), and THg GM was positively associated with fish intake. Mean Se levels in pregnant women were 73.06 μg/L (SD, 13.38 μg/L), and Se levels were found to increase with tuna intake. In 16 (12%) pregnant women, THg was higher than the level recommended by the U.S. Environmental Protection Agency (EPA) (6.4 μg/L). A positive association was also found between THg and serum Se.

CONCLUSION

Women of childbearing age in Spain had higher THg levels than women in other Western studies. Our study observed that 12% of women had THg levels above the safety limit set by the EPA (6.4 μg/L), and 31% had levels above the relevant benchmark level of 3.5 μg/L suggested by various researchers.

Selenium intake from tuna in Galicia (Spain): Health risk assessment and protective role against exposure to mercury and inorganic arsenic

This study aims to quantify the selenium contribution from tuna to the Spanish diet and evidence the Se protective role against mercury and inorganic arsenic toxicity. Selenium concentrations in tuna were determined by ICP-MS spectrometry (expressed as mg kg^-1), and the risk assessment was evaluated joined to Hg and iAs contrasting criteria of regulatory agencies with those that consider the Se protective role. Differences between Se average concentrations in fresh (1.24) and preserved (1.17) tuna were not statistically significant. In canned tuna species, Se presented higher mean levels in Thunnus albacares (1.28) than Thunnus alalunga (1.01) with statistically significant differences (p = 0.002), and among canned preparations a decreasing sequence was observed in different preparation-packaging media: oil (1.42) > natural (1.01) > pickled (0.92). Statistical study showed Hg-iAs as the only pair significantly correlated in all samples. The HI (sum of individual target hazard quotients -THQs-) on the consumption of tuna in Spain, due to exposure to Se, Hg and iAs, revealed the possibility of risk of adverse chronic effects in the six-year-old children group (1.09). According to the maximum allowable tuna consumption rate in meals/week (CR_mw) and the THQs obtained, tuna intake, especially in children, should be moderated. The health benefit values (HBV_Se) were positive in all samples, 14.53 and 15.65 in fresh and preserved tuna, respectively, which allows tuna to be considered safe. The benefit-risk value (BRV) evidenced the Se molar excess with respect to Hg that reached a surplus of 14.32% on Se AI in adults. Since iAs reduces the Se bioavailability, applying a new BRV criterion, the aforementioned percentage decreased to 13.49% of Se AI. In conclusion, tuna offers high levels of selenium to counteract adverse effects by the presence of Hg and iAs, and to provide consumers an important source of this essential element safely.

Environmental exposure to low-level lead (Pb) co-occurring with other neurotoxicants in early life and neurodevelopment of children

Lead (Pb) is a worldwide environmental contaminant that even at low levels influences brain development and affects neurobehavior later in life; nevertheless it is only a small fraction of the neurotoxicant (NT) exposome. Exposure to environmental Pb concurrent with other NT substances is often the norm, but their joint effects are challenging to study during early life. The aim of this review is to integrate studies of Pb-containing NT mixtures during the early life and neurodevelopment outcomes of children. The Pb-containing NT mixtures that have been most studied involve other metals (Mn, Al, Hg, Cd), metalloids (As), halogen (F), and organo-halogen pollutants. Co-occurring Pb-associated exposures during pregnancy and lactation depend on the environmental sources and the metabolism and half-life of the specific NT contaminant; but offspring neurobehavioral outcomes are also influenced by social stressors. Nevertheless, Pb-associated effects from prenatal exposure portend a continued burden on measurable neurodevelopment; they thus favor increased neurological health issues, decrements in neurobehavioral tests and reductions in the quality of life. Neurobehavioral test outcomes measured in the first 1000 days showed Pb-associated negative outcomes were frequently noticed in infants (<6 months). In older (preschool and school) children studies showed more variations in NT mixtures, children's age, and sensitivity and/or specificity of neurobehavioral tests; these variations and choice of statistical model (individual NT stressor or collective effect of mixture) may explain inconsistencies. Multiple exposures to NT mixtures in children diagnosed with 'autism spectrum disorders' (ASD) and 'attention deficit and hyperactivity disorders' (ADHD), strongly suggest a Pb-associated effect. Mixture potency (number or associated NT components and respective concentrations) and time (duration and developmental stage) of exposure often showed a measurable impact on neurodevelopment; however, net effects, reversibility and/or predictability of delays are insufficiently studied and need urgent attention. Nevertheless, neurodevelopment delays can be prevented and/or attenuated if public health policies are implemented to protect the unborn and the young child.

Risk assessment of methylmercury in pregnant women and newborns in the island of Madeira (Portugal) using exposure biomarkers and food-frequency questionnaires

Methylmercury (MeHg) is a contaminant present in fish which exerts a severe impact on health predominantly exhibiting neurotoxicity that might irreversibly affect fetal neurodevelopment. Fish consumption in Portugal is the third highest in the world, particularly high in regions with fishing tradition such as the Madeira Archipelago. Therefore, this study aimed at assessing the risk of exposure to MeHg in a population of pregnant women residing in Madeira. Blood samples from pregnant women (533) and umbilical cord (194) were collected from volunteer participants collected at primary health services in Madeira (Portugal) and analyzed for total mercury (HgT) level. A food-frequency questionnaire was used to estimate exposure and indices of risk while HgT in blood were correlated with estimated exposure. Analysis of HgT levels in blood indicated that 30% of pregnant women surpassed the maximum safe level of 10 µg/L recommended by the WHO, which was derived from the consumption of predatory fish, rich in MeHg. In addition, HgT levels in cord blood were 1.3 fold higher than in maternal blood, indicating the high risk of exposure to MeHg in this population. It is thus important to provide nutritional advice concerning fish consumption as a food choice in order to reduce fetal exposure and potential neurologic damage.

Selenium health benefit values provide a reliable index of seafood benefits vs. risks

BACKGROUND

Methylmercury (CH₃Hg) toxicity causes irreversible inhibition of selenium (Se)-dependent enzymes, including those that are required to prevent and reverse oxidative damage in the brain. Fish consumption provides numerous essential nutrients required for optimal health, but is also associated with CH₃Hg exposure risks, especially during fetal development. Therefore, it is necessary to assess the amounts of both elements in seafood to evaluate relative risks or benefits. Consumption of ocean fish containing Se in molar excess of CH₃Hg will prevent interruption of selenoenzyme activities, thereby alleviating Hg-exposure risks. Because dietary Se is a pivotal determinant of CH₃Hg's effects, the Selenium Health Benefit Value (HBV) criterion was developed to predict risks or benefits as a result of seafood consumption. A negative HBV indicates Hg is present in molar excess of Se and may impair Se availability while a positive HBV indicates consumption will improve the Se status of the consumer, thus negating risks of Hg toxicity.

OBJECTIVE

This study examined the Hg and Se contents of varieties of seafood to establish those with positive HBV's offering benefits and those having negative HBVs indicating potential consumption risks.

METHODS

The Hg and Se molar concentrations in samples of meat from pilot whale, mako shark, thresher shark, swordfish, bigeye tuna, and skipjack tuna were used to determine their HBV's in relation to body weight.

RESULTS

The HBVs of pilot whale, mako shark, and swordfish were typically negative and inversely related to body weight, indicating their consumption may impair Se availability. However, the HBV's of thresher shark, bigeye tuna, and skipjack tuna were uniformly positive regardless of body weights, indicating their consumption counteracts Hg-dependent risks of selenoenzyme impairment.

CONCLUSIONS

The HBV criterion provides a reliable basis for differentiating seafoods whose intake should be limited during pregnancy from those that should be consumed to obtain health benefits.

Selenium-Mercury Balance in Commercial Fish Species from the Turkish Waters

The interactions between selenium (Se) and mercury (Hg) were assessed in order to interpret public health risk, associated with dietary mercury exposure due to fish consumption. For this purpose, the mass and molar concentrations of Se and Hg were determined in the edible tissues of six species of fish, collected from the commercial fishing grounds of Turkey. The Se/Hg molar ratios and selenium health benefit values (Se-HBVs) were also calculated. The main fish species exported from Turkey to Europe were studied to determine the risks or benefits for human health. The mean Hg levels (μg g^-1, wet weight) ranged from 0.01 (in turbot) to 0.45 (in Atlantic bluefin tuna). The average selenium concentrations were between 0.96 μg g^-1 (in thornback ray) and 1.86 μg g^-1 (in turbot). The molar ratios of Se/Hg were above 1 for all species and greater than 100 in turbot, red mullet, and whiting. Positive Se-HBVs were determined for all samples, showing health benefits. Since Se is present in molar excess of Hg in the fish muscles, organic Hg exposures from eating these fish is not a public health concern.

Ultra-High Resolution Elemental/Isotopic Mass Spectrometry (m/Δm > 1,000,000): Coupling of the Liquid Sampling-Atmospheric Pressure Glow Discharge with an Orbitrap Mass Spectrometer for Applications in Biological Chemistry and Environmental Analysis

Many fundamental questions of astrophysics, biochemistry, and geology rely on the ability to accurately and precisely measure the mass and abundance of isotopes. Taken a step further, the capacity to perform such measurements on intact molecules provides insights into processes in diverse biological systems. Described here is the coupling of a combined atomic and molecular (CAM) ionization source, the liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma, with a commercially available ThermoScientific Fusion Lumos mass spectrometer. Demonstrated for the first time is the ionization and isotopically resolved fingerprinting of a long-postulated, but never mass-spectrometrically observed, bi-metallic complex Hg:Se-cysteine. Such a complex has been implicated as having a role in observations of Hg detoxification by selenoproteins/amino acids. Demonstrated as well is the ability to mass spectrometrically-resolve the geochronologically important isobaric ⁸⁷Sr and ⁸⁷Rb species (Δm ~ 0.3 mDa, mass resolution m/Δm ≈ 1,700,000). The mass difference in this case reflects the beta-decay of the ⁸⁷Rb to the stable Sr isotope. These two demonstrations highlight what may be a significant change in bioinorganic and atomic mass spectrometry, with impact expected across a broad spectrum of the physical, biological, and geological sciences. Graphical Abstract "".

Heavy Metals in Biota in Delaware Bay, NJ: Developing a Food Web Approach to Contaminants

Understanding the relationship between heavy metal and selenium levels in biota and their foods is important, but often difficult to determine because animals eat a variety of organisms. Yet such information is critical to managing species populations, ecological integrity, and risk to receptors (including humans) from consumption of certain prey. We examine levels of cadmium, lead, mercury, and selenium in biota from Delaware Bay (New Jersey, USA) to begin construction of a “springtime” food web that focuses on shorebirds. Horseshoe crab (Limulus polyphemus) eggs are one of the key components at the base of the food web, and crab spawning in spring provides a food resource supporting a massive stopover of shorebirds. Fish and other biota also forage on the crab eggs, and a complex food web leads directly to top-level predators such as bluefish (Pomatomus saltatrix) and striped bass (Morone saxatilis), both of which are consumed by egrets, eagles, ospreys (Pandion haliaetus), and humans. Metal levels in tissues were generally similar in algae, invertebrates, and small fish, and these were similar to those in blood of shorebirds (but not feathers). There was a significant direct relationship between the levels of metals in eggs of horseshoe crabs and mean metal levels in the blood of four species of shorebirds. Metal levels in shorebird feathers were higher than those in blood (except for selenium), reflecting sequestration of metals in feathers during their formation. Levels in feathers of laughing gulls (Leucophaeus atricilla) were similar to those in feathers of shorebirds (except for selenium). Selenium bears special mention as levels were significantly higher in the blood of all shorebird species than in other species in the food web, and were similar to levels in their feathers. Levels of metals in bluefish and striped bass were similar or higher than those found in the blood of shorebirds (except for selenium). The mean levels of cadmium, lead, and mercury in the blood and feathers of shorebirds were below any effect levels, but selenium levels in the blood and feathers of shorebirds were higher than the sublethal effect levels for birds. This is a cause for concern, and warrants further examination.

Metal and metalloid levels in blood of semipalmated sandpipers (Calidris pusilla) from Brazil, Suriname, and Delaware Bay: Sentinels of exposure to themselves, their prey, and predators that eat them

Identifying animals as sentinels for humans and other animal species is an excellent method for understanding exposure to environmental contamination at different times and places. Shorebirds are useful sentinels because they have a world-wide distribution, eat a range of prey, and are eaten by a range of other species, including humans. We collected blood from semipalmated sandpipers (Calidris pusilla) wintering in northern (Suriname N = 71) and northeastern (Brazil N = 61) South America to examine levels of heavy metals and metalloids (arsenic, selenium), and compare them to blood levels in sandpipers at a heavily used stopover site in New Jersey (N = 30; Delaware Bay, NJ). Since blood represents relatively recent exposure, it can provide information on where and when the birds were exposed. Levels were highest in Brazil for arsenic and particularly selenium; highest in Suriname for cadmium and lead; and highest in New Jersey for chromium. Samples from Brazil and Suriname presented higher levels of mercury than did those from New Jersey. There were no geographic differences for cobalt. Levels of all metals were generally within an order of magnitude. The significant geographic difference for selenium was interesting because it is regulated in the body. Selenium levels in the NJ sample were directly proportional to levels found in their principle food at this migration stopover site (eggs of horseshoe crab, Limulus polyphemus). Mean selenium level was almost an order of magnitude higher in the semipalmated sandpiper blood samples from Brazil (mean of 27,500 µg/L= ppb) compared to the other sampling locations (mean > 5330 µg/L). This is a toxic level and cause for concern and further investigation, alerting us to look for other evidence of excess selenium exposure. Otherwise the levels of other metals are generally not high enough to cause harm to the sandpipers themselves or to predators that eat them. We discuss the implications for these birds and their exposure to contaminants at different stopover sites.

Environmental mercury exposure and selenium-associated biomarkers of antioxidant status at molecular and biochemical level. A short-term intervention study

Mercury (Hg) is a potent toxicant. In the field of public health a chronic-low-level environmental Hg exposure resulting from fish consumption in general population is still being discussed. The objective of the study was to assess the influence of real Hg exposure on biomarkers of selenium (Se) status and selected biomarkers of pro-oxidant/anti-oxidant effects in healthy men (n = 67) who participated in the short-term intervention study consisting in daily fish consumption for two weeks. The analysis included Se level, Se-associated antioxidants at molecular (profile of 7 genes encoding selected proteins related to antioxidant defense) and biochemical levels (Se-dependent glutathione peroxidases activities and plasma selenoprotein P concentration). A pro-oxidant/anti-oxidant balance was explored using a biomarker of plasma lipid peroxidation and total antioxidant activity. The study revealed significant correlations (p < 0.05) between the biomarkers of exposure to Hg, Se level and Se-dependent antioxidants. Even though the risk of adverse effects of Hg for volunteers was substantially low, biomarkers of Hg altered levels of circulation selenoproteins and their genes expression. Changes in genes expression during study differed between the main enzymes involved in two systems: downregulation of thioredoxin reductase1 and upregulation of glutathione peroxidases. Hg exposure caused imbalance between the biomarkers of pro-oxidant/anti-oxidant effects.

Selenium Functionalized Metal-Organic Framework MIL-101 for Efficient and Permanent Sequestration of Mercury

Abatement of mercury emission from coal-fired power plants remains a serious task for public health and environmental societies. Selenium functionalized metal-organic framework MIL-101 (Se/MIL-101) was prepared for mercury removal from power plants. The Se/MIL-101 exhibited a remarkable mercury adsorption capacity of 148.19 mg·g^-1, which was about 154 to 705 times larger than that of commercial activated carbons exclusively applied for mercury removal from power plants. The initial mercury adsorption rate for Se/MIL-101 reached up to 44.8 μg·g^-1·min^-1, which was 89- to 1659-fold higher than those of mercury sorbents reported in the literature. The Se/MIL-101 maintained an excellent mercury adsorption stability under simulated flue gas atmosphere containing SO₂, NO, and H₂O. Gaseous elemental mercury (Hg⁰) converted on the Se/MIL-101 to stable and water-insoluble mercury selenide (HgSe), which guaranteed a minimum re-emission even sequestration of mercury. Moreover, the mercury-laden Se/MIL-101 could also immobilize mercury in gypsum and efficiently capture mercury ions from desulfurization effluent to an undetectable level (<0.0035 μg·L^-1). With these advantages, Se/MIL-101 appears to be a promising material for efficient and permanent sequestration of mercury from power plants.

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

BACKGROUND

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

SCOPE OF REVIEW

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

MAJOR CONCLUSIONS

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

GENERAL SIGNIFICANCE

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

Methylmercury's chemistry: From the environment to the mammalian brain

Methylmercury is a neurotoxicant that is found in fish and rice. MeHg's toxicity is mediated by blockage of -SH and -SeH groups of proteins. However, the identification of MeHg's targets is elusive. Here we focus on the chemistry of MeHg in the abiotic and biotic environment. The toxicological chemistry of MeHg is complex in metazoans, but at the atomic level it can be explained by exchange reactions of MeHg bound to -S(e)H with another free -S(e)H group (R¹S(e)-HgMe + R²-S(e)H ↔ R¹S(e)H + R²-S(e)-HgMe). This reaction was first studied by professor Rabenstein and here it is referred as the "Rabenstein's Reaction". The absorption, distribution, and excretion of MeHg in the environment and in the body of animals will be dictated by Rabenstein's reactions. The affinity of MeHg by thiol and selenol groups and the exchange of MeHg by Rabenstein's Reaction (which is a diffusion controlled reaction) dictates MeHg's neurotoxicity. However, it is important to emphasize that the MeHg exchange reaction velocity with different types of thiol- and selenol-containing proteins will also depend on protein-specific structural and thermodynamical factors. New experimental approaches and detailed studies about the Rabenstein's reaction between MeHg with low molecular mass thiol (LMM-SH) molecules (cysteine, GSH, acetyl-CoA, lipoate, homocysteine) with abundant high molecular mass thiol (HMM-SH) molecules (albumin, hemoglobin) and HMM-SeH (GPxs, Selenoprotein P, TrxR1-3) are needed. The study of MeHg migration from -S(e)-Hg- bonds to free -S(e)H groups (Rabenstein's Reaction) in pure chemical systems and neural cells (with special emphasis to the LMM-SH and HMM-S(e)H molecules cited above) will be critical to developing realistic constants to be used in silico models that will predict the distribution of MeHg in humans.

Effects of soft electrophiles on selenium physiology

This review examines the effects of neurotoxic electrophiles on selenium (Se) metabolism. Selenium-dependent enzymes depend on the unique and elite functions of selenocysteine (Sec), the 21st proteinogenic amino acid, to perform their biochemical roles. Humans possess 25 selenoprotein genes, ~ half of which are enzymes (selenoenzymes) required for preventing, controlling, or reversing oxidative damage, while others participate in regulating calcium metabolism, thyroid hormone status, protein folding, cytoskeletal structure, Sec synthesis and Se transport. While selenoproteins are expressed in tissue dependent distributions and levels in all cells of all vertebrates, they are particularly important in brain development, health, and functions. As the most potent intracellular nucleophile, Sec is subject to binding by mercury (Hg) and other electron poor soft neurotoxic electrophiles. Epidemiological and environmental studies of the effects of exposures to methyl-Hg (CH₃Hg⁺), elemental Hg (Hg°), and/or other metallic/organic neurotoxic soft electrophiles need to consider the concomitant effects of all members of this class of toxicants in relation to the Se status of their study populations. The contributions of individual electrophiles' discrete and cooperative rates of Se sequestration need to be evaluated in relation to tissue Se reserves of the exposed populations to identify sensitive subgroups which may be at accentuated risk due to poor Se status. Additional study is required to examine possibilities of inherited, acquired, or degenerative neurological disorders of Se homeostasis that may influence vulnerability to soft electrophile exposures. Investigations of soft electrophile toxicity will be enhanced by considering the concomitant effects of combined exposures on tissue Se-availability in relation to pathological consequences during fetal development or in relation to etiologies of neurological disorders and neurodegenerative diseases. Since selenoenzymes are molecular "targets" of soft electrophiles, concomitant evaluation of aggregate exposures to these toxicants in relation to dietary Se intakes will assist regulatory agencies in their goals of improving and protecting public health.

High-density element concentrations in fish from subtidal to hadal zones of the Pacific Ocean

Anthropogenic use of high density, toxic elements results in marine pollution which is bio-accumulating throughout marine food webs. While there have been several studies in various locations analyzing such elements in fish, few have investigated patterns in these elements and their isotopes in terms of ocean depth, and none have studied the greatest depth zones. We used a flame atomic absorption spectrophotometer-hydride system and an inductively coupled plasma-mass spectrometer to determine concentrations of the high-density elements arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), plus the light-metal barium (Ba), in fish ranging from bathyal (1000 m in Monterey Bay) to upper hadal zones (6500-7626 m in the Kermadec and Mariana Trenches) in the Pacific Ocean. Five species of fish-including the Mariana Trench snailfish, the world's deepest known fish newly discovered-were analyzed for patterns in total element concentration, depth of occurrence, Se:Hg ratio, plus mercury isotopes in the deepest species. Co and As levels decreased with depth. In the Mariana Trench, Pb, Hg, Cd, and Cu were higher than in all other samples, and higher in those plus Ba than in the Kermadec Trench. The latter samples had far higher Ni and Cr levels than all others. Mercury relative isotope analysis showed no depth trends in the deepest species. Se:Hg showed a large molar excess of Se in bathyal flatfish species. These patterns indicate that exposures to pollutants differ greatly between habitats including trenches of similar depths.