A Review of Mercury Bioavailability in Humans and Fish

Aquatic food animals in the United States: Status quo and challenges

This review summarizes (1) the U.S. status quo for aquatic food animal production and marketing; (2) major food safety and quality issues/concerns for aquatic food animals in the United States, including fish misbranding, finfish/shellfish allergies, pathogens, toxins and harmful residues, microplastics, and genetically engineered salmon; and (3) various U.S. regulations, guidances, and detection methods for the surveillance of fishery products. Overall, fish misbranding is the biggest challenge in the United States due to the relatively low inspection rate. In addition, due to the regulatory differences among countries, illegal animal drugs and/or pesticide residues might also be identified in imported aquatic food animals. Future regulatory and research directions could focus on further strengthening international cooperation, enhancing aquatic food animal inspection, and developing reliable, sensitive, and highly efficient detection methods.

Prenatal Mercury Exposure and Neurodevelopment up to the Age of 5 Years: A Systematic Review

Neurodevelopmental delays can interfere with children’s engagement with the world and further development, and may have negative consequences into adulthood. Mercury is highly toxic and may negatively influence neurodevelopment because it can freely cross the placenta and accumulate in the fetal brain. We searched four publication databases (Embase, PsycINFO, PubMed/MEDLINE, Scopus) for studies examining the relationship between early life mercury exposure and scores on neurodevelopmental performance measures in children aged 0 to 5 years old. Study quality was assessed using the National Institutes of Health (NIH) Quality Assessment Tool. Thirty-two prospective studies were included in the review. Neurodevelopmental performance was measured using 23 different scales, most commonly the Bayley Scales of Infant and Toddler Development (BSID). In most cases, the evidence for an association between mercury and neurodevelopment was weak. There did not appear to be exceptions for particular childhood ages, outcome scales, or mercury levels. The small number of results to the contrary were more likely to be studies which did not meet our high-quality criteria, and could be a consequence of multiple testing, selection bias, or incomplete confounder adjustment. Based on current evidence, dietary mercury exposure during pregnancy is unlikely to be a risk factor for low neurodevelopmental functioning in early childhood.

Mercury accumulation in muscle and liver tissue and human health risk assessment of two resident freshwater fish species in Flanders (Belgium): a multilocation approach

Detrimental effects of chemical pollution-primarily caused by human activities-on aquatic ecosystems have increasingly gained attention. Because of its hydrophobic qualities, mercury is prone to easily bioaccumulate and biomagnify through the food chain, decreasing biodiversity and eventually also affecting humans. In the present study, accumulated mercury concentrations were measured in muscle and liver tissue of perch (Perca fluviatilis) and European eel (Anguilla anguilla) collected at 26 sampling locations in Flemish (Belgian) waterbodies, allowing a comparison of these species within a variety of environmental situations. Furthermore, effects of size and weight have been assessed, expected to influence accumulation and storage of pollutants. Mercury concentrations in perch ranged up to 1.7 μg g^-1 dw (median: 0.29 μg g^-1 dw) in muscle and from 0.02 to 0.77 μg g^-1 dw (median: 0.11 μg g^-1 dw) in liver tissue. For eel, these concentrations were between 0.07 and 1.3 μg g^-1 dw (median: 0.39 μg g^-1 dw) and between 0.08 and 1.4 μg g^-1 dw (median: 0.55 μg g^-1 dw) respectively. We found a correlation of accumulated mercury with length in perch, independent of location. Furthermore, a significant difference in accumulated mercury concentrations between the targeted species was measured, with the highest mean concentrations per dry weight in eel liver and muscle tissue. In perch, higher concentrations were found in muscle compared to liver tissue, while in eel, liver tissue showed the highest concentrations. These findings were further considered with concentrations corrected for lipid content, excluding the fat compartment, which is known to a hold negligible portion of the total and methyl mercury concentrations. This confirmed our previous conclusions, except for mercury concentrations in eel. Here there was no longer a significant difference between muscle and liver concentrations. Finally, health risk analyses revealed that only frequent consumption of local eel (> 71 g day^-1) could pose risks to humans.

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.

Effect of abiotic factors and environmental concentrations on the bioaccumulation of persistent organic and inorganic compounds to freshwater fish and mussels

Many aquatic ecosystems are under persistent stress due to influxes of anthropogenic chemical pollutants. High concentrations can harm entire ecosystems and be toxic to humans. However, in case of highly hydrophobic compounds, their low water solubility precludes direct measurement in water, and thus alternative monitoring strategies are needed. In the present study, we investigated the extent to which bioaccumulated concentrations of persistent compounds can be predicted by concentrations in environmental compartments (water and sediment). Due to their high biomagnification potential, Hg and PFOS were included in this analysis as well. At 44 field locations in Flanders (Belgium), we monitored the concentrations of 11 priority compounds and their derivatives, included in the Water Framework Directive, in both sediment and water (where feasible) and biota (European perch, European eel and freshwater mussels). Besides, some sediment (i.e. total organic carbon (TOC) and clay content) and water characteristics were measured (i.e. pH, oxygen level, conductivity, nitrate, nitrite and dissolved organic carbon (DOC)). Measurements of HCB, HCBD, cis-heptachlorepoxide, HBCD and PFOS in sediment and ∑PCB in water showed a lower detection frequency than in fish samples. While PCB profiles were comparable between all matrices, for PBDE clear differences were detected between sediment and fish profiles, with BDE99 contributing the most for sediment (34%) and BDE47 for fish (≥44%), followed by BDE99 for perch (28%) and BDE100 for eel (25%). Water concentrations for PFOS and benzo(a)pyrene were predictive of respective bioaccumulated concentrations. HCB, ∑PCB and ∑PBDE, concentrations in fish were dependent on sediment concentrations and negatively related to organic compound levels (p < 0.05). Furthermore, pH and nitrite were negatively associated with accumulated concentrations in eel for HCB and PFOS, respectively (p < 0.05). Strong relationships between bioaccumulation and sediment and/or water concentrations strengthened the basis for surrogate monitoring methods. Finally, the extrapolation potential of Hg, ∑PBDE, PFOS, HBCD and ∑PCB between both fish species offered new opportunities in extrapolating different European monitoring frameworks.

Dietary Exposure of the Taiwan Population to Mercury Content in Various Seafood Assessed by a Total Diet Study

This paper examines the health risks of exposure to methylmercury (MeHg) through the consumption of mercury-contaminated seafood in Taiwan, based on the total diet study (TDS) method. Samples of seafood (n = 140) were purchased at fishing harbors or supermarkets and classified into seven categories (pelagic fish, inshore fish, farmed fish, shellfish, cephalopods, crustaceans, and algae). For each sample, we analyzed raw and cooked versions and compared the concentration difference. Total mercury (THg) was detected at the highest rate and in the highest concentrations in pelagic fish, followed by inshore fish and other farmed fish. The average concentration of THg was higher after cooking. In a 75th percentile scenario, the hazard indices for children aged 1 to 3 years and children aged 4 to 6 years were higher than 100% of the provisional tolerable weekly intake. Taking into consideration the risk assessment results, MeHg concentrations, and the nutritional composition of fish, we have provided weekly consumption advisories for children aged 1 to 3 years, children aged 4 to 6 years, and childbearing women aged 19 to 49 years. The weekly consumption advisories for childbearing women are 35 g/week of pelagic fish and 245 g/week of inshore fish based on the risk results from MeHg and the potential benefits from eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) intake.

The silver linings of mercury: Reconsideration of its impacts on living organisms from a multi-timescale perspective

Research on mercury (Hg), a naturally occurring element in Earth's lithosphere, has been extremely hot in the past few decades due to the outbreak of a series of disastrous poisoning incidents. However, such studies might provide us a biased view towards Hg if no thorough review about its long-term effects on living organisms from a multi-timescale perspective was performed. Hg might have played a mysterious role in critical intervals (e.g., mass extinction and oceanic anoxia events) in several geologic periods due to the elevated Hg levels induced by volcanism whereas it has long been used for various purposes in human history. Therefore, it is necessary to go through previous studies and historical records of different timescales (10⁰ to 10⁶ yr). In this work, we conducted a thorough review of Hg knowledge at three different timescales, i.e., geologic periods (10⁶ yr), human history (10³ yr), and contemporary history (10⁰ yr), summarizing recent advances and indicated potential research gaps. By doing so, we demonstrated that it is possible to achieve safe and sustainable Hg applications despite the current Hg crisis. However, such silver linings depend on a better understanding of ecosystem dynamics. Besides, considering the possible dire consequences of erupted Hg levels as suggested in geological periods, swift actions to mitigate the impacts of anthropogenic activities on the Hg cycle will be another key point. Overall, this review presented a unique perspective of Hg combining different timescales, shedding light on the importance of a better understanding of the global ecosystem as a whole and maintaining the sustainability of planet Earth in the future.

Imaging Microstructural Damage and Alveolar Bone Loss in Rats Systemically Exposed to Methylmercury: First Experimental Evidence

The alveolar bone is an important mineralized structure of the periodontal support apparatus, and information about the methylmercury (MeHg) effects on the structural integrity is scarce. Therefore, this study aimed to investigate whether systemic, chronic, and low-dose exposure to MeHg can change the alveolar bone microstructure of rats. Adult Wistar rats (n = 30) were exposed to 0.04 mg/kg/day of MeHg or vehicle through intragastric gavage. The animals were euthanized after 60 days, and blood samples were collected for trolox equivalent antioxidant capacity (TEAC), glutathione (GSH), lipid peroxidation (LPO), and comet assays. The mandible of each animal was collected and separated into hemimandibles that were used to determine the total Hg level in the bone and to analyze microstructural damage and alveolar bone loss in terms of trabecular number (Tb.N), trabecular thickness (Tb.Th), bone volume fraction (BV/TV), and exposed root area of the second molars. MeHg exposure triggered oxidative stress in blood represented by lower levels of GSH and TEAC and the increase in LPO and DNA damage of the blood cells. High total Hg levels were found in the alveolar bone, and the microstructural analyses showed a reduction in Tb.N, Tb.Th, and BV/TV, which resulted in an increase in the exposed root area and a decrease in bone height. Long-term MeHg exposure promotes a systemic redox imbalance associated with microstructural changes and alveolar bone loss and may indicate a potential risk indicator for periodontal diseases.

Association between Chromosome 4 and mercury accumulation in muscle of the three-spined stickleback (Gasterosteus aculeatus)

Anthropogenic stressors, such as pollutants, act as selective factors that can leave measurable changes in allele frequencies in the genome. Metals are of particular concern among pollutants, because of interference with vital biological pathways. We use the three-spined stickleback as a model for adaptation to mercury pollution in natural populations. We collected sticklebacks from 21 locations in Flanders (Belgium), measured the accumulated levels of mercury in the skeletal muscle tissue, and genotyped the fish by sequencing (GBS). The spread of muscle mercury content across locations was considerable, ranging from 21.5 to 327 ng/g dry weight (DW). We then conducted a genome-wide association study (GWAS) between 28,450 single nucleotide polymorphisms (SNPs) and the accumulated levels of mercury, using different approaches. Based on a linear mixed model analysis, the GWAS yielded multiple hits with a single top hit on Chromosome 4, with eight more SNPs suggestive of association. A second approach, a latent factor mixed model analysis, highlighted one single SNP on Chromosome 11. Finally, an outlier test identified one additional SNP on Chromosome 4 that appeared under selection. Out of all ten SNPs we identified as associated with mercury in muscle, three SNPs all located on Chromosome 4 and positioned within a 2.5 kb distance of an annotated gene. Based on these results and the genome coverage of our SNPs, we conclude that the selective effect of mercury pollution in Flanders causes a significant association with at least one locus on Chromosome 4 in three-spined stickleback.

Bioaccumulation of mercury is equal between sexes but different by age in seabird (Sula leucogaster) population from southeast coast of Brazil

Since several seabird species have sexual size dimorphism, in which one sex is larger than the other, and may consume bigger prey, this size difference may affect the contamination concentration in the seabird's tissues depending on their sex and age. In this study, mercury contamination was investigated in brown booby (Sula leucogaster) adults and juveniles during their breeding season at the Santana Archipelago, on the southeast coast of Brazil. Two hypotheses were evaluated: 1. As females consume larger prey than males due to the reverse sexual dimorphism, higher total mercury (THg) and methylmercury (MeHg) concentrations are expected in females tissues than in males; 2. Adult seabirds have more time to accumulate mercury than juveniles, so it is expected that adults will show higher THg and MeHg concentrations than juveniles in their feathers, but none in blood since the last indicates the exposure of short time (30-60 days), as it is a constantly synthesized tissue. Feathers and blood were sampled from 20 individuals of each group (males, females and juveniles). Also, 10 eggs of the brown booby and muscle tissue samples of their main prey were collected, from February to October 2018. Females and males had similar THg concentrations in the tissues with no statistical differences between sexes. Thus, the sexual size dimorphism did not influence mercury concentrations among the tissues and both genders can be used as a biomonitor. Brown booby juveniles had low THg and MeHg concentrations compared to adults due to a shorter time of exposure for mercury to bioaccumulate in their tissues. This is the first study, to the best of our knowledge, analyzing methylmercury in feathers, blood and eggs of a tropical seabird, which can be a useful baseline for future studies on the effects of contaminants on this species in tropical regions.

Human Methylmercury Exposure and Potential Impacts in Central Tibet: Food and Traditional Tibetan Medicine

Methylmercury presents potent neurotoxicity to humans. Fish consumption is the leading source of human exposure to methylmercury worldwide. However, the exposure source in Tibet remains poorly understood because of the scarcity of observational data on most Tibetan foods, although high mercury levels were recently detected in some traditional Tibetan medicines. Here, the results of field investigations show that the joint consumption of traditional Tibetan medicines (TTMs), fish, and rice constitutes a primary exposure pathway to methylmercury in Tibetans and that the probable daily intake of methylmercury is close to that for many coastal regions. People who are young and high-income may have higher methylmercury exposure levels mainly because of economic development and cultural exchanges among regions. Our analysis indicates that a large proportion of the Tibetan population are likely to face a high methylmercury exposure risk and that mercury-susceptible populations in Tibet should be attentive to consuming TTMs with fish.

A Quantitative Assessment and Biomagnification of Mercury and Its Associated Health Risks from Fish Consumption in Freshwater Lakes of Azad Kashmir, Pakistan

Issues regarding biomagnification of mercury (Hg) due to its persistence, bioaccumulation, and toxicity in freshwater lakes have gained much attention in the last two decades especially in remote regions of the world where anthropogenic inputs are considered as negligible. In this study, spatial distribution of total mercury (THg), interspecific accumulation patterns, trophic transfer, and associated health risks in fish of freshwater lakes (357-3107 masl) in Azad Kashmir, Pakistan, were investigated. THg concentrations in the regions were 0.20 ± 0.08 μg g^-1 in glacial, 0.54 ± 0.21 μg g^-1 in rural, and 1.35 ± 0.46 μg g^-1 in urban region. Omnivorous, herbivorous, and carnivorous fish showed THg concentrations of 0.94, 0.85, and 0.49 μg g^-1. Regional, lake, trophic level, and specie-specific differences of THg accumulation were found significant in the study. Among growth parameters, length and age varied significantly among species, trophic levels, and lakes, whereas weight showed significant variation among lakes as well. Condition factor (K) showed significant differences within species, lakes, and trophic levels. Biomagnification was observed in all lakes with the trophic magnification slopes (TMS) ranging from 0.03 to 0.20 with an average of 0.094 ± 0.07. Isotopic values of nitrogen (δ¹⁵N) and condition factor were found to dominate THg accumulation trends; however, no significant health risks were found in the study.

Impacts of water level fluctuations on mercury concentrations in hydropower reservoirs: A microcosm experiment

Hydropower generation, a renewable source of electricity, has been linked to elevated methylmercury (MeHg) concentrations in impoundments and aquatic biota. This study investigates the impact of water level fluctuations (WLF) on MeHg concentrations in water, sediment, and fish. Using a set of controlled microcosm experiments emulating the drawdown/refill dynamics and subsequent sediment exposure to air experienced in reservoirs, we demonstrate that less frequent WLFs, and/or increased exposure of sediment to air, can lead to elevated MeHg concentrations in sediment, and total mercury (THg) and MeHg concentrations in water. In examining the effects of WLF frequency (two-day, weekly, and monthly), the monthly treatment displayed the highest THg and MeHg water levels, while the weekly treatment was characterized by the highest MeHg levels in the sediment. Our work supports emerging evidence that longer duration between WLF creates a larger surface area of sediment exposed to air leading to conditions conducive to higher MeHg concentrations in sediments and water. In contrast, THg, MeHg, and fatty acid trends in fish were largely inconclusive characterized by similar among-treatment effects and minimal temporal variability over the course of our experiment. This result could partly be attributed to overall low mercury levels and simple "worm-forage fish" food web in our experiment. To elucidate the broader impacts of water fluctuations on aquatic chemistry and biota, other factors (e.g., longer WLF cycles, dissolved organic matter, temperature, more complex food webs) which modulate both methylation rates and food web dynamics must be considered.

Biotransport of mercury and human methylmercury exposure through crabs in China - A life cycle-based analysis

Exposure to methylmercury (MeHg) has various toxic effects on humans. The evaluation of human MeHg exposure has previously focused on fish consumption. However, in this study, we found that MeHg levels in domestic crabs in China were also relatively high (range: 50-1400 ng/g, dry weight). The high MeHg levels in crabs and their high consumption do not match the risk assessment of MeHg, indicating an underestimated exposure risk, especially in MeHg-sensitive groups such as pregnant women. The annual crab MeHg content output in China was estimated to be 30 ± 27 kg. A total of 6.8% of the country's land area contributes 71% of the MeHg output. However, 66% of the output is redistributed to non-crab-producing regions via interregional food trade, posing risks to the population on a national scale. The daily intake of MeHg from crabs could easily exceed the reference dose (0.1 µg/kg of body weight per day) suggested by the United States Environmental Protection Agency with consideration of coexposure from fish, rice, and other food sources. We suggest that future MeHg exposure analysis includes crab MeHg as a coexposure pathway to estimate the dietary MeHg limit accurately and emphasize the influence of interregional food trade on MeHg exposure.

Trophic ecology of sympatric batoid species (Chondrichthyes: Batoidea) assessed by multiple biogeochemical tracers (δ13C, δ15N and total Hg)

Aquatic pollution is known to reduce biodiversity and disrupt wildlife populations. Mercury (Hg) pollution is pervasive worldwide, contributing to the degradation of ecosystems, and causing deleterious effects to exposed organisms and populations. Batoids have a life history linked to the benthic substrate of coastal areas and occupy upper trophic levels. These combined with large bodies, long lifespan, and slow growth rates contributes to increased uptake and accumulation of Hg. However, mechanisms governing these associations are not well understood. Using multiple biogeochemical tracers (δ¹³C, δ¹⁵N and total Hg), we describe trophic interactions of three sympatric batoid species inhabiting an urbanized estuary and identify diet sources that contribute to Hg accumulation and trophic position among these mesopredators. We also use the Bat-ray (Myliobatis californica) as a model species, to compare diet composition, trophic position, and isotopic niche between two populations in two Californian bays. Trophic plasticity in M. californica was characterized by isotopic niche, diet proportions, and trophic position estimates using Bayesian statistics. We found diet and local contamination background strongly associated with Hg accumulation, and Hg levels that exceed EPA water quality criterion (<0.3 μg.g^-1 w.w.) in all studied species.

From Past Use to Present Effects: Total Mercury in Crustaceans and Fish in the Inner Estuary of Paraíba do Sul River, Southeast Brazil

Total mercury (Hg) concentration and stable isotope ratios (δ¹³C and δ¹⁵N) were used as chemical tracers in two crustaceans and four fish species that are targets of subsistence fishery in the inner estuary of the Paraíba do Sul River. This fluvial environment in southeast Brazil has a large historical utilization of Hg. δ¹⁵N was a better predictor of Hg concentration in the muscle (edible part) than δ¹³C; i.e., the Hg concentration was more closely related to the trophic position of species than species' trophic habitat. Consumers at higher trophic levels had higher Hg concentrations. The Hg concentration was below the maximum permissible limits established by the Brazilian Government in fishery products, and there are no human risks related to its consumption.

Selected Instrumental Techniques Applied in Food and Feed: Quality, Safety and Adulteration Analysis

This review presents an overall glance at selected instrumental analytical techniques and methods used in food analysis, focusing on their primary food science research applications. The methods described represent approaches that have already been developed or are currently being implemented in our laboratories. Some techniques are widespread and well known and hence we will focus only in very specific examples, whilst the relatively less common techniques applied in food science are covered in a wider fashion. We made a particular emphasis on the works published on this topic in the last five years. When appropriate, we referred the reader to specialized reports highlighting each technique's principle and focused on said technologies' applications in the food analysis field. Each example forwarded will consider the advantages and limitations of the application. Certain study cases will typify that several of the techniques mentioned are used simultaneously to resolve an issue, support novel data, or gather further information from the food sample.

Sustainable Diets for Cardiovascular Disease Prevention and Management

PURPOSE OF REVIEW

Healthy dietary patterns are recommended for prevention of cardiovascular disease, which remains the leading cause of morbidity and mortality globally. In this review, we discuss dietary patterns that are not only optimal for CVD prevention and management but also sustainable in maximizing health, environmental, and economic benefits.

RECENT FINDINGS

The growing literature on sustainable diets in the context of environmental sustainability includes subtopics of climate change, land use, biodiversity loss, freshwater use, and reactive nitrogen emissions. Similarly, economic sustainability, beyond the retail cost of food, extends to healthcare costs and the economic costs of environmental destruction related to current agricultural practices and food choices. Dietary patterns that are high in plant foods and low in animal foods could maximize health, environmental, and economic benefits; however, questions remain about how to best promote these patterns to achieve wider adoption in an environmentally and economically sustainable way.

Speciation of Inorganic Compounds in Aquatic Systems Using Diffusive Gradients in Thin-Films: A Review

The speciation of trace metals in an aquatic system involves the determination of free ions, complexes (labile and non-labile), colloids, and the total dissolved concentration. In this paper, we review the integrated assessment of free ions and labile metal complexes using Diffusive Gradients in Thin-films (DGT), a dynamic speciation technique. The device consists of a diffusive hydrogel layer made of polyacrylamide, backed by a layer of resin (usually Chelex-100) for all trace metals except for Hg. The best results for Hg speciation are obtained with agarose as hydrogel and a thiol-based resin. The diffusive domain controls the diffusion flux of the metal ions and complexes to the resin, which strongly binds all free ions. By using DGT devices with different thicknesses of the diffusive or resin gels and exploiting expressions derived from kinetic models, one can determine the labile concentrations, mobilities, and labilities of different species of an element in an aquatic system. This procedure has been applied to the determination of the organic pool of trace metals in freshwaters or to the characterization of organic and inorganic complexes in sea waters. The concentrations that are obtained represent time-weighted averages (TWA) over the deployment period.

Effects of Speciation, Cooking and Changes in Bioaccessibility on Methylmercury Exposure Assessment for Contrasting Diets of Fish and Marine Mammals

Uptake of the neurotoxicant monomethylmercury (MeHg) from fish and marine mammals continues to present a public health concern in Canada and elsewhere. However, fish and marine mammals are key diet items contributing to food security for some Indigenous populations in Canada. Mercury (Hg) exposure is estimated assuming that 100% of Hg is methylated, that 100% will be absorbed by the consumer and that cooking does not affect MeHg concentrations. Some of these assumptions do not correspond to our current state of knowledge. The aim of this study was to assess the impact of additional variables on Hg exposure equation using probabilistic risk analysis. New variables tested were (1) the proportion of methylated Hg compared to total Hg (pMeHg, %), (2) the relative absorption factor (RAF, %) expressed as bioaccessibility and (3) the mass loss factor (MLF, unitless) that represents the loss of moisture during cooking, known to increase MeHg concentration in fish and mammals. For the new variables, data from literature were used in order to set point estimate values that were further used in the probabilistic risk analysis. Modelling results for both fish and marine mammals indicate that adding these new variables significantly influenced estimates of MeHg exposure (Mood's median test, p < 0.05). This study highlights that the evaluation of exposure to MeHg is sensitive to pMeHg, RAF and MLF, and the inclusion of these variables in risk assessment should be considered with care. Further research is needed to provide better food-dependent, population-specific estimates of RAF and MLF before formal inclusion in exposure estimates.

Concentration and potential health risks of trace metals in warty crab (Eriphia verrucosa Forskal, 1775) from Southern Coasts of the Black Sea, Turkey

The drastic increase of human population and industrial wastes mostly affects coastal areas. Crabs with limited mobility, especially in benthic regions of the coasts, are more affected by metal pollution. Monitoring of trace metals in terms of food safety and potential health risks is important for consumers. Warty crab (Eriphia verrucosa) samples were collected with trammel nets between July 2015 and June 2016. The crab extracts were analyzed by an ICP-MS optical emission spectrophotometer. Trace metal densities of crab meats in the present study were determined in the order of Zn > Cu > Fe > As > Al > Mn > Hg > Pb ≥ Cd. These levels were below the acceptable values reported by the Turkish Food Codex and the EU Commission. The target hazard quotient (THQ) was above 1 in terms of As, Cu, and Hg trace metals in both groups. This study showed that although the level of trace metal was below allowable values, consumption of warty crab more than once a month may cause metal toxicity according to potential health risk analyses.

Dried blood spots to characterize mercury speciation and exposure in a Colombian artisanal and small-scale gold mining community

The artisanal and small-scale gold mining (ASGM) sector uses the most mercury (Hg) worldwide. Despite health concerns associated with high Hg exposures in these communities, ASGM sites are often situated in resource limited and remote regions which challenge traditional human biomonitoring approaches. To help overcome such challenges, here we report on the development of a high-quality method to characterize chemical speciation of Hg in dried blood spots (DBS), and then apply this method to assess Hg exposures in people sampled from an ASGM community (Pueblito Mejia) and a nearby town (Barranco de Loba) in Colombia. We collected DBS and urine samples from 35 individuals in 2018, and used these to assess occupational (DBS inorganic Hg (InHg) and urine total Hg (THg) measures) and environmental (DBS methylmercury (MeHg) measures) exposure of participants to different forms of Hg. The accuracy and precision of the DBS-based measures generally met assay performance guideline. In study participants, the mean concentrations of DBS MeHg, InHg, and THg, and urine THg were 1.9, 4.1, 6.0, and 3.1 μg/L, respectively. For 37% of the participants, DBS THg values exceeded the 5 μg/L 'alert level' proposed by the German HBM Commission. About 60% of the blood Hg was in the InHg form thus exemplifying a need to speciate Hg in blood sampled from ASGM sites to better understand the contributions of environmental and occupational exposure sources. This study demonstrates the feasibility of using DBS for Hg speciation exposure assessments in remote and resource-limited areas such as ASGM communities.

Mapping metal (Hg, As, Se), lipid and protein levels within fish muscular system in two fish species (Striped Bass and Northern Pike)

Current guidelines tend to limit fish consumption based on mercury (Hg) or monomethylmercury (MeHg) content in fish flesh, without considering the presence of antagonist chemical elements that could modulate Hg toxicity. However, it is difficult to assess the potential for antagonistic interactions of these elements since their covariation within muscle tissues is poorly known. Here we present the first study simultaneously mapping multiple metal(oid)s (Hg, As and Se), lipids and proteins in fish fillets in order to assess the magnitude of intra-organ variability of metals and the potential for antagonistic interactions. We mapped two fish species (Striped Bass and Northern Pike) with contrasting muscular structure with respect to the presence of white, intermediate and red muscles. In individual Striped Bass muscle tissues, metals varied on average by 2.2-fold. Methylmercury and selenium covaried strongly and were related to protein content as assessed by % N; arsenic was inversely related to these elements and was associated with the lipid fraction of the muscle. In Pike, no such relationship was found because the contents in proteins and lipids were less variable. Arsenic speciation revealed that arsenobetaine and arsenolipids were the only As species in those fish species, whereas the toxic inorganic As species (As³⁺) was under the detection limit. Arsenobetaine was related to % N, whereas arsenolipids covaried with % lipids. Elemental associations found with muscle lipids and proteins could help explain changes in bioaccumulation patterns within and between individuals with potential implications on fish toxicology, biomonitoring and human consumption guidelines.

Time to refine mercury mass balance models for fish

Mercury mass balance models (MMBMs) for fish are powerful tools for understanding factors affecting growth and food consumption by free-ranging fish in rivers, lakes, and oceans. Moreover, MMBMs can be used to predict the consequences of global mercury reductions, overfishing, and climate change on mercury (Hg) concentration in commercially and recreationally valuable species of fish. Such predictions are useful in decision-making by resource managers and public health policy makers, because mercury is a neurotoxin and the primary route of exposure of mercury to humans is via consumption of fish. Recent evidence has emerged to indicate that the current-day version of MMBMs overestimates the rate at which fish eliminate mercury from their bodies. Consequently, MMBMs overestimate food consumption by fish and underestimate Hg concentration in fish. In this perspective, we explore underlying reasons for this overestimation of Hg-elimination rate, as well as consequences and implications of this overestimation. We highlight emerging studies that distinguish species and sex as contributing factors, in addition to body weight and water temperature, that can play an important role in how quickly Hg is eliminated from fish. Future research directions for refining MMBMs are discussed.

Risk of Mercury Ingestion from Canned Fish in Poland

In this study, total mercury content was determined in 84 canned fish corresponding to commonly consumed brands (over 14 different producers), which were purchased from local markets in Poland in the years 2019–2020. For comparison purposes, samples of both the matrix in which the fish were kept along with the seafood samples were measured. The analyses were carried out using the cold vapor AAS technique. Statistical analyses were employed to identify significant differences in mercury content in relation to the selected criteria such as fish species, type of fish (predatory, non-predatory) and the producer brand. The obtained results were compared against domestic and international standards as well as with the literature data in order to evaluate the safety of the canned fish consumption. The study revealed that none of canned fish exceeded the acceptable levels set by the FAO/WHO. The highest amount of Hg was recorded for canned tuna (maximum 351.30 µg/kg, mean 74.38 µg/kg). Further, the estimated tolerable dose of weekly mercury intake suggests that the consumption of over 1.8 cans of fish with the highest mean mercury content should not pose a risk to consumers in Poland according to international standards. Among the ten highest mean results for mercury, five of them belonged to canned tuna (Bonito species) kept in different matrices. These consisted of seven domestic and three imported brands of fish products, which is a worrying message for a local community. Mercury content in predatory fish differed significantly from the results gathered for non-predatory fish and the total amount of mercury in studied canned fish corresponded to their status in the aquatic food chain. Moreover, significant differences were stated between various fish species and fishing areas. Fish caught in the Atlantic Ocean (cod and herring) presented higher mercury content than the ones from closed seas.

A representative sampling of tuna muscle for mercury control

The mechanisms of mercury accumulation and distribution in fish tissues are related to its high affinity for sulfhydryl groups in proteins. There is evidence that mercury is distributed unevenly based on the different reactivity of these groups in the various muscle proteins. Tuna fish also shows numerous specialized anatomical features including the structure of the swimming muscles and some form of endothermy, which generates variations in the mercury content between dark and white muscle and between muscle tissues with different lipid content. The aim of the study is to verify, through a suitable sub lot of Thunnus thynnus caught by a static trap in south-western Sardinia, the effective uneven distribution of mercury in the various muscles and also identify the sites representative of the entire carcass. In agreement with other authors, the results show that even in the Bluefin tuna of the Mediterranean, the site "anterior extremity of upper loin (schienale in Italian)" is representative of the mercury average content of muscle tissues as a whole.

A comparative study of effects of dietary mercuric chloride and methylmercury chloride on growth performance, tissue accumulation, stress and immune responses, and plasma measurements in Korean rockfish, Sebastes schlegeli

Mercury (Hg) is known as a highly toxic heavy metal, and its toxicity varies depending on its form due to different toxicokinetics between inorganic and organic Hg. Limited information on comparison of Hg toxicity concerning its chemical form by oral exposure is currently available in cultured fishes. Therefore, we conducted a comparative study to have a better understanding of distinct toxic effects between mercuric chloride (HgCl₂) and methylmercury chloride (CH₃HgCl) in Korean rockfish. The 12-weeks dietary exposure of HgCl₂ and CH₃HgCl with its graded levels (0.4-6.4 ppm) (2 × 5 factorial design) in the young-of-the-year rockfish (initial weight: 82 ± 0.3 g) resulted in neither interactive nor main effects on whole-organism responses, including growth, feed utilization, and survival. However, the distinct pattern of Hg accumulation between the two forms in dorsal muscle, brain, liver and kidney tissues was observed, showing that the rockfish fed the CH₃HgCl-contained diets exhibited the dose-dependent accumulation throughout the sampling points (1, 2, 4, 8, and 12 weeks post feeding), whereas those fed the HgCl₂-contained diets did not show such response. The CH₃HgCl exposure induced higher oxidative stress and immunotoxicity, reflected by the elevated plasma superoxide dismutase and lysozyme activities, respectively. In addition, the CH₃HgCl-induced alteration in plasma measurements, including the plasma aspartate transaminase activity and total protein level was found. Taken together, the dietary exposure of methylmercury chloride had more pronounced toxic effects than mercuric chloride in the young-of-year rockfish, needed to be taken into consideration for regulation of maximum allowed levels for Hg by its chemical form.

Iodine and Mercury Content in Raw, Boiled, Pan-Fried, and Oven-Baked Atlantic Cod (Gadus morhua)

There is a lack of scientific evidence regarding the stability of iodine and mercury during cooking and processing of seafood. In this study, the iodine and mercury content were determined after thawing frozen fillets of Atlantic cod (Cadus morhua), and further in raw compared to boiled, pan-fried, and oven baked fillets. Iodine was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and mercury by atomic absorption spectrophotometry with Direct Mercury Analyzer (DMA-80). Thawing of the cod resulted on average in a 12% loss of iodine to the thawing water. Boiling significantly decreased the total content of iodine per slice of cod fillet corresponding to the concentration of iodine found in the boiling water. Pan-frying and oven-baking did not cause any significant changes of the total iodine content per slice of cod fillet, although iodine content per 100 g increased due to weight reduction of the cod slices from evaporation of water during preparation. For mercury, we found minimal changes of the different cooking methods. In summary, the findings in our study show that boiling had the greatest effect on the iodine content in the cod fillets. Type of cooking method should be specified in food composition databases as this in turn may influence estimation of iodine intake.

Sulfhydryl groups as targets of mercury toxicity

The present study addresses existing data on the affinity and conjugation of sulfhydryl (thiol; -SH) groups of low- and high-molecular-weight biological ligands with mercury (Hg). The consequences of these interactions with special emphasis on pathways of Hg toxicity are highlighted. Cysteine (Cys) is considered the primary target of Hg, and link its sensitivity with thiol groups and cellular damage. In vivo, Hg complexes play a key role in Hg metabolism. Due to the increased affinity of Hg to SH groups in Cys residues, glutathione (GSH) is reactive. The geometry of Hg(II) glutathionates is less understood than that with Cys. Both Cys and GSH Hg-conjugates are important in Hg transport. The binding of Hg to Cys mediates multiple toxic effects of Hg, especially inhibitory effects on enzymes and other proteins that contain free Cys residues. In blood plasma, albumin is the main Hg-binding (Hg2+, CH3Hg+, C2H5Hg+, C6H5Hg+) protein. At the Cys34 residue, Hg2+ binds to albumin, whereas other metals likely are bound at the N-terminal site and multi-metal binding sites. In addition to albumin, Hg binds to multiple Cys-containing enzymes (including manganese-superoxide dismutase (Mn-SOD), arginase I, sorbitol dehydrogenase, and δ-aminolevulinate dehydratase, etc.) involved in multiple processes. The affinity of Hg for thiol groups may also underlie the pathways of Hg toxicity. In particular, Hg-SH may contribute to apoptosis modulation by interfering with Akt/CREB, Keap1/Nrf2, NF-κB, and mitochondrial pathways. Mercury-induced oxidative stress may ensue from Cys-Hg binding and inhibition of Mn-SOD (Cys196), thioredoxin reductase (TrxR) (Cys497) activity, as well as limiting GSH (GS-HgCH3) and Trx (Cys32, 35, 62, 65, 73) availability. Moreover, Hg-thiol interaction also is crucial in the neurotoxicity of Hg by modulating the cytoskeleton and neuronal receptors, to name a few. However, existing data on the role of Hg-SH binding in the Hg toxicity remains poorly defined. Therefore, more research is needed to understand better the role of Hg-thiol binding in the molecular pathways of Hg toxicology and the critical role of thiols to counteract negative effects of Hg overload.

Effects of seafood consumption on mercury exposure in Norwegian pregnant women: A randomized controlled trial

BACKGROUND

Seafood provides nutrients that are important for optimal development of the unborn child. However, seafood is also a source of contaminants including mercury (Hg) and methylmercury (MeHg) that may have adverse effects on neurodevelopment of the fetus. Humans are predominantly exposed to MeHg through seafood consumption, however, levels of MeHg vary considerably between species.

OBJECTIVES

Investigate, in a randomized controlled trial (RCT) during pregnancy, if an increased intake of Atlantic cod (Gadus morhua), a fish species with relatively low levels of MeHg contamination, influences total hair Hg (THHg) concentrations in humans.

METHODS

Pregnant women (n = 137) were enrolled in the RCT "Mommy's Food" (2016-2017), which was designed to increase iodine status. Participants were randomly assigned to intervention (400 g of cod fillets per week) or control (continued habitual diet) groups for 16 weeks (gestational week 20-36). THHg concentrations were measured at baseline and post-intervention using thermal decomposition, amalgamation, and atomic absorption spectrophotometry (US EPA method 7473). The trial is registered in ClinicalTrials.gov, NCT02610959.

RESULTS

Post-intervention, the intervention group had median (inter-quartile range) THHg concentrations of 554 (392-805) µg/kg, and the control group 485 (341-740) µg/kg (p = 0.186). When adjusting for baseline THHg concentrations, there was a significant difference between the groups in those participants with baseline THHg concentrations below 534 µg/kg. Post-intervention, 8% of the study population exceeded the US EPA reference dose in hair (1,000 µg/kg) (intervention group: n = 6, control group: n = 4).

CONCLUSION

THHg concentrations were generally low in both study groups of pregnant women, despite the relatively high seafood intake. While the intervention with 400 g of cod per week slightly increased THHg concentrations, it did not lead to an increase in number of subjects exceeding the US EPA reference dose; a dose level at which no adverse effects are expected to occur over a period of lifetime exposure.

Patterns of fish and whale consumption in relation to methylmercury in hair among residents of Western Canadian Arctic communities

BACKGROUND

Methylmercury contamination of the environment represents a substantial environmental health concern. Human exposure to methylmercury occurs primarily through consumption of fish and marine mammals. Heavily exposed subgroups include sport or subsistence fishers residing in Arctic communities. We aimed to estimate the association of fish/whale consumption patterns of Canadian Arctic subsistence fishers with the internal dose of methylmercury as measured in hair.

METHODS

This research was conducted within ongoing community projects led by the CANHelp Working Group in Aklavik and Fort McPherson, Northwest Territories and Old Crow, Yukon. We interviewed each participant using a fish-focused food-frequency questionnaire during September-November 2016 and collected hair samples concurrently. Methylmercury was measured in the full-length of each hair sample using gas chromatography inductively-coupled plasma-mass spectrometry. Multivariable linear regression estimated beta-coefficients and 95% confidence intervals (CIs) for the effect of fish/whale consumption on hair-methylmercury concentrations.

RESULTS

Among 101 participants who provided hair samples and diet data, the mean number of fish/whale species eaten was 3.5 (SD:1.9). The mean hair-methylmercury concentration was 0.60 μg/g (SD:0.47). Fish/whale consumption was positively associated with hair-methylmercury concentration, after adjusting for sex, hair length and use of permanent hair treatments. Hair-methylmercury concentrations among participants who consumed the most fish/whale in each season ranged from 0.30-0.50 μg/g higher than those who consumed < 1 meal/week.

CONCLUSIONS

In this population of Canadian Arctic subsistence fishers, hair-methylmercury concentration increased with fish/whale consumption, but the maximum concentrations were below Health Canada's 6.0 μg/g threshold for safe exposure.

Thermal stress accelerates mercury chloride toxicity in Oreochromis niloticus via up-regulation of mercury bioaccumulation and HSP70 mRNA expression

Mercury (Hg) is an environmental pollutant that threatens aquatic life. Many environmental factors, including water temperature, are reported to influence the toxicity of dissolved chemicals in the aquatic ecosystem. Therefore, we investigated the impact of thermal stress on Hg-induced subchronic toxicity in Nile tilapia (Oreochromis niloticus). Fish were randomly allocated into five groups. Group I served as the control and kept at 25 °C. Groups II, III, IV, and V were reared at 25, 28, 31, and 34 °C, respectively, and co-exposed to HgCl₂ (1/10 LC₅₀) for 42 days. Blood and tissue samples were collected after 21 and 42 days. All HgCl₂-exposed groups exhibited significant elevations in serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, and creatinine, along with decreases in the serum total protein and albumin. In addition, marked reductions in antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSPx), were observed. Remarkable increases in Hg tissue concentrations were detected along with increases in heat shock protein (HSP) 70 mRNA expression. Interestingly, the patterns data that were recorded were more coincident with the water temperature than the period of exposure. In conclusion, water temperature and exposure period are two crucial factors modulating HgCl₂-induced toxicity and bioaccumulation in Nile tilapia. Our findings provide new insights concerning the impact of thermal stress as an environmental factor on Hg toxicity and bioaccumulation in Nile tilapia and, in turn, on fish and fish consumer health.

Disruption of selenium transport and function is a major contributor to mercury toxicity in zebrafish larvae

Mercury is one of the most toxic elements threatening the biosphere, with levels steadily rising due to both natural and human activities. Selenium is an essential micronutrient, required for normal development and functioning of many organisms. While selenium is known to counteract mercury's toxicity under some conditions, to date information about the mercury-selenium relationship is fragmented and often controversial. As part of a systematic study of mercury and selenium interactions, zebrafish (Danio rerio) larvae (a model verterbrate) were exposed to methylmercury chloride or mercuric chloride. The influence of pre- and post-treatment of selenomethionine on the level and distribution of mercury and selenium in the brain and eye sections, as well as on toxicity, were examined. Selenomethionine treatment decreased the amount of maternally transfered mercury in the larval brain. Selenomethionine treatment prior to exposure to mercuric chloride increased both mercury and selenium levels in the brain but decreased their toxic effects. Conversely, methylmercury levels were not changed as a result of selenium pre-treatment, while toxicity was increased. Strikingly, both forms of mercury severely disrupted selenium metabolism, not only by depleting selenium levels due to formation of Hg-Se complexes, but also by blocking selenium transport into and out of tissues, suggesting that restoring normal selenium levels by treating the organism with selenium after mercury exposure may not be possible. Disruption of selenium metabolism by mercury may lead to disruption in function of selenoproteins. Indeed, the production of thyroid hormones by selenoprotein deiodinases was found to be severely impaired as a result of mercury exposure, with selenomethionine not always being a suitable source of selenium to restore thyroid hormone levels.

Assessment and Monitoring of Fish Quality from a Coastal Ecosystem under High Anthropic Pressure: A Case Study in Southern Italy

Fish is a nutrient-rich food but, at the same time, consumption of fish is a possible source of exposure to heavy metals. Since many coastal Mediterranean areas suffer from great anthropomorphic pressure, the aim of this study was to assess the level of potentially toxic inorganic elements in different fish samples from the coastal zone of Southern Italy (Gela) where there is a high mortality rate linked to cancer disease and congenital malformations. The presence of mercury, cadmium, lead, nickel, arsenic, vanadium, and chromium was measured by inductively coupled plasma-mass spectrometry (ICP-MS). The risk assessment was evaluated in terms of estimated daily intake by calculating the amount of potentially toxic elements that an average individual adult weighing 60 kg would ingest. Moreover the non-carcinogenic risk was estimated by target hazard quotient (THQ). The study evidenced significant contamination by inorganic elements, especially cadmium, which can be linked to industrial pollution. The THQ indexes, as indicators of human health, suggest that the consumption of fish from the study area is not free of risk.

Sensitive determination of methylmercury δ13C compound specific stable isotopic analysis by purge and trap gas chromatography combustion isotope ratio mass spectrometry

Despite several decades of mercury research, answering fundamental questions on where and how methylmercury (CH₃Hg) toxin is naturally produced in aquatic ecosystems, is still highly challenging. Investigating complex and/or coupled processes in the context of global changes requires new high-resolution analytical tools. The purpose of the compound specific carbon stable isotopic analysis (δ¹³C-CSIA) of the methyl group of methylmercury (CH₃Hg), is to explore how the carbon cycle contributes to CH₃Hg sources and formation pathways. The main problem associated with recent CH₃Hg δ¹³C-CSIA methods is the limited sensitivity when using Liquid Injection (LI)-GC-C-IRMS techniques, requiring several micrograms of CH₃Hg (as Hg). In this work, we present the development and application of an original Purge-&-Trap system (PT) coupled to a GC-C-IRMS with the purpose of transferring and analyzing the total amount of CH₃Hg available in a sample vial in the low nanogram range. The new PT-GC-C-IRMS system enhance the sensitivity by a factor better than 200, relative to LI-GC-C-IRMS, by minimizing the sample mass requirements. The δ¹³C_CH3Hg values obtained, following the same sample derivatization approach coupled to PT-GC-C-IRMS (-53.5 ± 1.9 ‰), were in good agreement with the ones obtained in a previous study (-53.8 ± 1.1 ‰). The standard solution was prepared from the same salt, requesting only 25-200 ng of CH₃Hg (as Hg). This new methodology represents a milestone towards the analysis of large array of biological samples displaying CH₃Hg concentrations in the low-mid ng g^-1 range, in order to explore the meaning of the carbon stable isotopic signature of CH₃Hg in the environment.

Mercury forms in the benthic food web of a temperate coastal lagoon (southern Baltic Sea)

The study was conducted in the coastal zone of the southern Baltic. The research material consisted of macrozoobenthos and elements of its diet. The samples were analysed for Hg and its labile and stable forms, using the thermodesorption method. The results showed that the level of total Hg in zoobenthos was associated with dietary preferences and the share of bioavailable Hg in its food. The Hg fractionation in the macrofauna was conditioned by biological features (morphological structure) and environmental parameters (oxygenation, pH) which shape the mobility and assimilation of Hg. The absorption of the most toxic organic Hg in macrofauna was more effective in aerobic conditions, at low primary production and with the limited inflow of organic matter. The trophic transfer of Hg was favoured by the limited biomass of primary producers, and consequently of zoobenthos. An important factor influencing the biomagnification was also the share of labile Hg in macrozoobenthos.

Arsenic, chromium, and other elements of concern in fish from remote boreal lakes and rivers: Drivers of variation and implications for subsistence consumption

Eating fish provides numerous health benefits, but it is also a dominant pathway for human exposure to contaminants. Many studies have examined mercury (Hg) accumulation in fish, but fewer have considered other elements, such as arsenic (As) and chromium (Cr). Recently, freshwater fish from several pristine boreal systems across northern Ontario, Canada, have been reported with elevated concentrations of As and Cr for reasons that are not well understood. Our goal was to investigate the ecological and environmental influences over concentrations of As, Cr, and other elements in these fish to better understand what affects metal uptake and the risk to consumers. We measured 10 elements (including As, Cr, Hg) as well as carbon (δ¹³C), nitrogen (δ¹⁵N), and sulfur (δ³⁴S) stable isotopes in 388 fish from 25 lake and river sites across this remote region. These data were used to determine the effect of: 1) trophic ecology; and 2) watershed geology on piscine elemental content. Overall, most element concentrations were low, often below provincial advisory benchmarks (ABs). However, traces of Hg, As, Cr, and selenium (Se) were detected in most fish. Based on their exceedance of their respective ABs, the most restrictive elements on fish consumption in these boreal systems were Hg > As > Cr. Arsenic and Se, but not Cr concentrations were related to fish size and trophic ecology (inferred from δ¹³C and δ¹⁵N), suggesting bioaccumulation of the former elements. Fish with enriched δ³⁴S values, suggestive of anadromous behaviour, had marginally lower Hg but higher Se concentrations. Modeling results suggested a strong effect of site-specific factors, though we found weak trends between piscine elemental content and geological features (e.g., mafic intrusions), potentially due to the broad spatial scale of this study. Results from this study address gaps in our understanding of As and Cr bioaccumulation and will help to inform fish consumption guidelines.

Methylmercury exposure in wildlife: A review of the ecological and physiological processes affecting contaminant concentrations and their interpretation

Exposure to methylmercury (MeHg) can result in detrimental health effects in wildlife. With advances in ecological indicators and analytical techniques for measurement of MeHg in a variety of tissues, numerous processes have been identified that can influence MeHg concentrations in wildlife. This review presents a synthesis of theoretical principals and applied information for measuring MeHg exposure and interpreting MeHg concentrations in wildlife. Mercury concentrations in wildlife are the net result of ecological processes influencing dietary exposure combined with physiological processes that regulate assimilation, transformation, and elimination. Therefore, consideration of both physiological and ecological processes should be integrated when formulating biomonitoring strategies. Ecological indicators, particularly stable isotopes of carbon, nitrogen, and sulfur, compound-specific stable isotopes, and fatty acids, can be effective tools to evaluate dietary MeHg exposure. Animal species differ in their physiological capacity for MeHg elimination, and animal tissues can be inert or physiologically active, act as sites of storage, transformation, or excretion of MeHg, and vary in the timing of MeHg exposure they represent. Biological influences such as age, sex, maternal transfer, and growth or fasting are also relevant for interpretation of tissue MeHg concentrations. Wildlife tissues that represent current or near-term bioaccumulation and in which MeHg is the predominant mercury species (such as blood and eggs) are most effective for biomonitoring ecosystems and understanding landscape drivers of MeHg exposure. Further research is suggested to critically evaluate the use of keratinized external tissues to measure MeHg bioaccumulation, particularly for less-well studied wildlife such as reptiles and terrestrial mammals. Suggested methods are provided to effectively use wildlife for quantifying patterns and drivers of MeHg bioaccumulation over time and space, as well as for assessing the potential risk and toxicological effects of MeHg on wildlife.

Comparative study of raw and cooked farmed sea bass (Lates calcarifer) in relation to metal content and its estimated human health risk

Metallic contamination in seafood, especially fish, has been of increasing concern to human health. Moreover, with increasing dependency on farmed fish for fish resources, the metallic contamination in them is still questionable. This study aimed to investigate the effects of cooking (steaming) on heavy metal concentration in farmed fish and to estimate its potential human health risk. Farmed sea basses (Lates calcarifer) from Setiu Lagoon were used to study the difference in metal uptake through human consumption of raw and cooked (steamed) fish samples. Selected heavy metals, namely copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb), were measured using ICP-MS following Teflon bomb closed digestion of the fish samples. Cooking of the fish muscle by steaming was applied to investigate if cooking changes the concentration of heavy metals. Mercury and As were found accumulated more notably in the fish muscle, though only Hg was found to show significant (p > 0.05) increase when L. calcarifer is cooked. The amount of As in the fish muscle throughout its growth can be potentially harmful to humans, with the highest averaged concentration at 3.29 ± 0.65 mg/kg dw. above the standard set by the Malaysian Food Regulation (1985) of >1 mg/kg. All the other heavy metals were at relatively safe concentrations well below the standard set by both national and international guidelines. The PTWI per individual of L. calcarifer for As was at 0.84 mg/kg bw., which indicated that the amount of this fish safe for consumption without any adverse effect is 170 g/week. Therefore, long-term intake of these fish may pose a risk to human health due to the relatively higher Hg and As concentration found in these fishes.

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

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

Testing the Use of Standardized Laboratory Tests to Infer Hg Bioaccumulation in Indigenous Benthic Organisms of Lake Maggiore (NW Italy)

The chronic toxicity of mercury essentially derives from its strong tendency to biomagnify along food webs. For this reason, the European regulatory framework establishes an environmental quality standard for Hg based on the total Hg concentration in prey fish to protect top predators. A considerable part of the Hg burden of prey fish can come from the ingestion of benthic organisms that, in the presence of contaminated sediments, may remobilize substantial amounts of Hg towards the pelagic food webs. The present study evaluated whether Hg accumulation in assemblages of indigenous chironomids and oligochaetes could be predicted using standardized laboratory bioaccumulation tests with Chironomus riparius and Lumbriculus variegatus. Indigenous chironomids and oligochaetes were recovered at different sites in a lake suffering from legacy Hg pollution and analyzed for total Hg content. Sediment aliquots from the same sites were used to assess Hg bioaccumulation using laboratory-reared C. riparius and L. variegatus. Mercury concentrations in indigenous versus laboratory organisms showed a good correlation (p < 0.05; Spearman correlation test) only in the case of C. riparius versus indigenous chironomids, suggesting the possibility of using linear regressions to predict Hg accumulation by these benthic invertebrates. Further research needs and caveats as to the applicability of the present results to other aquatic systems are identified and discussed.

Mobility of mercury in soil and its transport into the sea

Mercury (Hg) is deposited temporarily in soil and can be remobilised into rivers and seas. Given that rivers are a significant part of the mercury budget in the southern Baltic region (inland sea located in northern Europe) and meteorological changes (e.g. intense rain, drought) are observed more frequently, it is important to recognize the factors affecting the cycling of bioavailable Hg forms. The aim of this study was to identify the processes influencing the changes of labile and stabile mercury proportion in soil and the potential impact on the outflow of labile Hg into fluvial systems. For this purpose, soil samples, river sediments, and river water were collected from the Reda River (southern Baltic Sea catchment area) during the 2015 hydrologic year. The material was analysed for total and particulate mercury content and Hg forms, by a thermo-desorption method. The analysis showed that due to changes of meteorological and hydrological conditions Hg can enter rivers and then be introduced into the marine environment in various forms. On the one hand due to high precipitation events washing out of labile (i.e. bond with halogenides, MeHg, HgSO₄), Hg forms into the river can be enhanced which affects increasing of availability of the most dangerous Hg form in the water systems. On the other hand the same event can cause the limitation of bioavailable mercury forms by a conversion of labile Hg into the most stable one (HgSO₄ ➔ HgS) under anaerobic conditions.

Methylmercury and inorganic mercury in Chinese commercial rice: Implications for overestimated human exposure and health risk

China is the largest rice producer and consumer in the world, and mercury (Hg) levels, particularly methylmercury (MeHg), in rice and health exposure risks are public concerns. Total Hg (THg) and MeHg levels in 767 (domestic = 709 and abroad = 58) Chinese commercial rice were investigated to evaluate Hg pollution level, dietary exposures and risks of IHg and MeHg. The mean rice THg and MeHg levels were 3.97 ± 2.33 μg/kg and 1.37 ± 1.18 μg/kg, respectively. The highest daily intake of MeHg and IHg were obtained in younger groups, accounted for 6% of the reference dose-0.1 μg/kg bw/day for MeHg, 0.3% of the provisional tolerance week intake-0.571 μg/kg bw/day for IHg. Residents in Central China and Southern China meet the highest rice Hg exposure, which were more than 7 times of those in Northwest China. Lower concentrations than earlier studies were observed along the implementations of strict policies since 2007. This may indicate that a declining temporal trend of Hg in Chinese grown rice and associated exposures could be obtained with the implementations of strict policies. Though there exist Hg pollution in commercial rice, Hg levels in Chinese commercial rice is generally safe compared with Hg polluted sites. Populations dwelling in China have relatively a quite low and safe MeHg and IHg exposure via the intake of commercial rice. Strict policies contributed to the decrease in THg and MeHg levels in Chinese-grown rice. More attention should be paid to younger groups.

Human health risk of methylmercury from fish consumption at the largest floodplain in Colombia

Colombia is one of the countries with the highest emissions of mercury (Hg) to the environment, due to its use in gold mining. This study evaluated the human health risk from exposure to Hg through fish consumption in 11 municipalities located in the Mojana region, northern Colombia. The study participants (n = 839) were categorized into three population groups: children (CHD), women of childbearing age (WCHA) and the rest of population (RP). Total Hg (THg) and methylmercury (MeHg) concentrations were evaluated in the top ten most consumed fish species (n = 292). Median concentrations (range: 0.22-0.58 μg/g ww) of the five carnivorous fish species exceeded the reference limit established by FAO/WHO (0.2 μg/g ww) for vulnerable populations. For 6 of the 10 studied fish species, the estimated weekly intake (EWI) in children was above the provisional tolerable weekly intake (PTWI, 1.6 μg/kg bw/week) of MeHg established by JECFA. EWI values for WCHA were above PTWI in 4 fish species, whereas in general, for RP group values were below PTWI (3.2 μg/kg bw/week). Our assessment of potential risks to MeHg exposure indicated that most of the consumed fish could generate negative effects in vulnerable groups, because according to ingestion rate, MeHg permissible is, in some cases, up to 4 times higher than reference limits. Consumption advisories should be a guidance to avoid risk, gain nutritional benefits, and sustain fish populations. Because its high MeHg levels as well as high ingestion, it is recommended that inhabitants of this region should stop eating certain kinds of fish and the whole fish as a single meal. To reduce its harmful intake, we have proposed a didactic strategy based on marbles that control the portion of fish they are eating.