Mercury transport and human exposure from global marine fisheries

Historical and seasonal patterns of Hg accumulation: A comparative study of 210Pb-dated sediment cores and sediment trap records in a large coastal lagoon, southern Gulf of Mexico

Sedimentary processes, ecological risks, and historical trends of mercury (Hg) contamination were assessed through 210Pb-dated sediment cores and sediment traps (period 2017-2019) in Términos Lagoon (TL), a critical coastal ecosystem in the southern Gulf of Mexico. Hg natural background levels in TL cores widely varied (7-153 ng g-1), and Hg concentrations were higher in the cores (median 32 ng g-1, range 6-4240 ng g-1) than in the sediment traps (median 54 ng g-1, range 44-1311 ng g-1). In most cores, enrichment factors ranged from null to moderate, except for very severe levels found in core LT01, indicating the presence of an Hg hotspot. Enrichments (minor to severe) were confined to river discharge areas in the sediment traps. Low to very high ecological risks were observed across the sampling areas. Factor analysis, including the core and trap samples, indicated fine-grained terrigenous sediments and high organic matter content as major drivers of Hg accumulation, with river discharges playing a central role. The sediment records displayed increasing Hg fluxes after the 1970s, coinciding with the local urban-industrial boom, while peak values in recent decades corresponded with population growth around the lagoon. Sediment trap data suggested that Hg fluxes are somewhat independent of rainfall, as peak values were observed during dry and winter storm seasons. These findings highlight the interplay of natural and anthropogenic factors promoting Hg accumulation in TL, offering insights to mitigate the effects of global change in one of Mesoamerica's most important coastal ecosystems.

Global seafood production practices and trade patterns contribute to disparities in exposure to methylmercury

Seafood consumption is a major pathway for exposure to methylmercury (MeHg), a globally pervasive neurotoxin. Yet, how upstream processes in the seafood value chain influence MeHg exposure remains poorly understood. Here we quantified MeHg in seafood production, trade and consumption in 2019 around the world. We found that countries with seafood-MeHg exposures beyond the recommended threshold by the World Health Organization were predominately high-income countries. These countries experienced a tenfold increase in exposure levels compared with low-income countries, due to greater consumption and long-overlooked higher MeHg concentrations in seafood inherited from production. Notably, 43% of seafood MeHg in production was redistributed through seafood trade, marked by inequality, as exports from high-income to lower-income countries contained higher seafood-MeHg concentrations. These exposures may have resulted in 61,800 global premature deaths and economic losses of around US$2.87 trillion, underscoring the need to change seafood production practices and trade patterns.

Hydroxyl radicals produced from oxidation of ferrous sulfides promote mobilization of mercuric sulfide in soil-water system

Mercuric sulfide nanoparticles (HgS-NPs) are recognized as a significant source of bioavailable mercury in paddy fields. The factors influencing the mobilization and bioavailability of HgS-NPs formed in flooded or drained paddy field-like systems are complicated and remain unexplored to date. Here, we show that ferrous sulfide (FeS) as an important mineral substance plays a crucial role in the dissolution and transformation of HgS-NPs in overlying water or during the drainage stage, as well as their bioavailability toward rice. Specifically, we found that oxidation of FeS significantly enhances the dissolution of HgS-NPs, with the degree of activation intensified with increasing FeS concentrations. This activation was further evidenced to be driven by the generation of hydroxyl radicals (•OH) during FeS oxidation, leading to the release of Hg(Ⅱ). The enhanced dissolution of HgS-NPs increases its bioavailability, as verified by the augmented accumulation of Hg in rice upon FeS oxidation. This study underscores the overlooked yet important role of FeS in affecting the fate of HgS-NPs and offers valuable insights for pollution control of Hg-contaminated paddy fields and wetlands.

China's municipal wastewater policies enhanced seafood safety and offset health risks from atmospheric mercury emissions in the past four decades

The neurotoxin methylmercury in seafood threatens food safety worldwide. China has implemented stringent wastewater policies, established numerous treatment facilities and enforced rigorous water quality standards to address pollution in its waterways. However, the impact of these policies on seafood safety and methylmercury exposure remains unknown. Here we developed a process-based model showing that, although mercury reductions from municipal wastewater policies accounted for only 9% of atmospheric mercury emissions during 1980-2022, these measures unexpectedly prevented102,000 - 6,600 + 11,000 mercury-related deaths and counteracted nearly two thirds of potential deaths from those emissions. Furthermore, these policies ensured that146 - 9 + 8 megatonnes of freshwater seafood met the World Health Organization and China's mercury-safety standards, preventing US $ 498 - 29 + 32 billion in economic losses. Finally, we explore how China, as the primary global seafood producer and exporter, could develop municipal wastewater policies at the regional level to reduce aquatic pollutants and unlock the health benefits of seafood consumption.

Declines in anthropogenic mercury emissions in the Global North and China offset by the Global South

Human activities have emitted substantial mercury into the atmosphere, significantly impacting ecosystems and human health worldwide. Currently, consistent methodologies to evaluate long-term mercury emissions across countries and industries are scant, hindering efforts to prioritize emission controls. Here, we develop a high-spatiotemporal-resolution dataset to comprehensively analyze global anthropogenic mercury emission patterns. We show that global emissions increased 330% during 1960-2021, with declines in developed Global North countries since the 1990s and China since the 2010s completely offset by rapid growth in Global South countries (excluding China). Consequently, global emissions have continued to rise slightly since the 2013 Minamata Convention. In 2021, Global South countries produced two-thirds of global emissions, despite comprising only one-fifth of the global economy. We predict that, although large uncertainties exist, continued emission growth in Global South countries under a business-as-usual scenario could increase 10%-50% global mercury emissions by 2030. Our findings demonstrate that global control of anthropogenic mercury emissions has reached a critical juncture, highlighting the urgent need to target reductions in Global South countries to prevent worsening health and environmental impacts.

Forest cover influences fish mercury concentrations in national parks of the western U.S

The global prevalence of mercury (Hg) contamination and its complex biogeochemical cycling has resulted in elevated Hg concentrations in biota in remote and pristine environments. However, there is uncertainty in the relative importance of Hg deposition and landscape factors that control Hg cycling and bioaccumulation. To address this, we measured total mercury (THg) concentrations in 1344 fish across 60 subalpine lakes from 12 national parks (NPs). These parks represent three distinct high-elevation regions across the western U.S.: Cascades and Olympic Peninsula, Sierra Nevada and Great Basin, and Rocky Mountains. Within these regions, three NPs (Mount Rainier, Yosemite, and Rocky Mountain) were intensively studied representatives of each region. This study aimed to (1) assess the magnitude of mercury contamination in a collection of remote, small catchment lakes; (2) quantify the variability of fish THg concentrations among and within parks; and (3) test the relative importance of Hg inputs in comparison to landscape characteristics on lake-specific fish THg concentrations. The spatial variability in fish THg concentrations was 2.6-fold higher than variation in deposition to watersheds, suggesting that factors other than Hg delivery are important determinants of Hg accumulation in these environments. Spatially, fish THg concentrations (ng/g ww ± standard error) were lower in the Rockies (46.2 ± 5.0) and Sierra (56.5 ± 5.8) compared to the Cascades (67.8 ± 6.1). Additionally, fish THg concentrations increased with increasing conifer forest cover (Intensive parks: P < 0.0001, R2 = 0.43; All parks: P = 0.0001, R2 = 0.23) but were not correlated with wet Hg deposition across the catchment. These findings suggest that forest composition is likely an important aspect of Hg delivery to lake food webs, and although the mechanisms are unclear, could be tied to some combination of forest influences on catchment organic carbon and increased surface area for dry Hg deposition.

Importance of salinity on regulating the environmental fate and bioaccumulation of lithium in the Yangtze River Estuary

The demand of lithium (Li) has increased rapidly in recent decades under carbon neutrality strategies, but the environmental fate and potential risks of Li in aquatic ecosystem are barely known. This study conducted a comprehensive field survey in the Yangtze River Estuary (YRE) and the adjacent East China Sea (ECS), to investigate the spatial distribution of dissolved Li and bioaccumulation of Li in the coastal food web. The dissolved Li increased with salinity (from 7.39 to 189 μg L-1), controlled by the conservative mixing of Li-enriched seawater and Li-poor riverine water. Negative correlation was observed between Li content and stable nitrogen isotope in the coastal biota, indicating bio-diminish of Li in the food web. Furthermore, the Li contents in muscle tissues were significantly higher in bivalves (as filter-feeders; mean: 0.75 ± 0.41 μg g-1) than in fish (as predator; mean: 0.10 ± 0.05 μg g-1) and other biota species, indicating that dissolved uptake might be the major exposure pathway for Li. Importantly, it was noticed that the bioaccumulation factors (BAFs) in fish muscle varied greatly (from 0.17 to 5.82), showing lower BAFs for fish inhabiting in marine and benthic regions (with higher salinity and higher dissolved Li concentration). Such inhibition effects of salinity on Li bioaccumulation could not be explained by the modulation of salinity on Li speciation, but highly attributed to the inhibition of high salinity on the dissolved uptake of Li, which was associated with the co-transportation of Li and Na. Our results illuminate the importance of salinity on regulation the spatial variations of dissolved Li and Li bioaccumulation in the YRE and the adjacent ECS, which could help the understanding of Li biogeochemical cycling and potential risks in estuarine and coastal regions.

Application of time series and multivariate statistical models for water quality assessment and pollution source apportionment in an Urban River, New Jersey, USA

Water quality monitoring reveals changing trends in the environmental condition of aquatic systems, elucidates the prevailing factors impacting a water body, and facilitates science-backed policymaking. A 2020 hiatus in water quality data tracking in the Lower Passaic River (LPR), New Jersey, has created a 5-year information gap. To gain insight into the LPR water quality status during this lag period and ahead, water quality indices computed with 16-year historical data available for 12 physical, chemical, nutrient, and microbiological parameters were used to predict water quality between 2020 and 2025 using seasonal autoregressive moving average (ARIMA) models. Average water quality ranged from good to very poor (34 ≤ µWQI ≤ 95), with noticeable spatial and seasonal variations detected in the historical and predicted data. Pollution source tracking with the positive matrix factorization (PMF) model yielded significant R2 values (0.9 < R2 ≤ 1) for the input parameters and revealed four major LPR pollution factors, i.e., combined sewer systems, surface runoff, tide-influenced sediment resuspension, and industrial wastewater with pollution contribution rates of 23-30.2% in the upstream and downstream study areas. Significant correlation of toxic metals, nutrients, and sewage indicators suggest similarities in their sources.

Global fishing patterns amplify human exposures to methylmercury

Global pollution has exacerbated accumulation of toxicants like methylmercury (MeHg) in seafood. Human exposure to MeHg has been associated with long-term neurodevelopmental delays and impaired cardiovascular health, while many micronutrients in seafood are beneficial to health. The largest MeHg exposure source for many general populations originates from marine fish that are harvested from the global ocean and sold in the commercial seafood market. Here, we use high-resolution catch data for global fisheries and an empirically constrained spatial model for seafood MeHg to examine the spatial origins and magnitudes of MeHg extracted from the ocean. Results suggest that tropical and subtropical fisheries account for >70% of the MeHg extracted from the ocean because they are the major fishing grounds for large pelagic fishes and the natural biogeochemistry in this region facilitates seawater MeHg production. Compounding this issue, micronutrients (selenium and omega-3 fatty acids) are lowest in seafood harvested from warm, low-latitude regions and may be further depleted by future ocean warming. Our results imply that extensive harvests of large pelagic species by industrial fisheries, particularly in the tropics, drive global public health concerns related to MeHg exposure. We estimate that 84 to 99% of subsistence fishing entities globally likely exceed MeHg exposure thresholds based on typical rates of subsistence fish consumption. Results highlight the need for both stringent controls on global pollution and better accounting for human nutrition in fishing choices.

Warming-Induced Vegetation Greening May Aggravate Soil Mercury Levels Worldwide

Mercury, a neurotoxic substance, circulates globally, significantly stored in soils through atmospheric deposition and plant decay. Despite being deposited, mercury can be remobilized and released into the atmosphere and water, enhancing its global cycle. Recent research suggests that climate warming may amplify the remobilization of soil mercury, facilitating its incorporation into food webs that humans exploit. However, the potential geospatial feedback of soil mercury levels in response to warming remains unclear. By leveraging up-to-date soil measurements and observation-driven models, we determined the amount of mercury stored in global 0-100 cm soils to be 4.3 Tg (interquartile range: 2.5-6.3 Tg). Furthermore, our analysis indicates that warming likely aggravates global soil mercury levels, particularly in many temperate areas in East Asia, North Europe, and North America (>20 ng g-1 increase by 2100) due to warming-induced vegetation greening. Critically, observation-driven models raise the possibility that implementing ambitious mercury-emission-control schemes alone may be insufficient to counterbalance the positive feedback of soil mercury concentration, while process-based biogeochemical modeling demonstrates consistent patterns that reinforce this concern. These findings hold broad implications; for example, such feedback may catalyze mercury remobilization in land-ocean continuums and exacerbate human risks, stressing the necessity for continued reductions in greenhouse gas and mercury emissions.

Modelling the anthropogenic Hg pollution fingerprint on the marine fishery production worldwide: A preliminary exposure assessment for people living in countries having different income levels

Mercury is a toxic pollutant that poses risks for the human population, mainly by eating contaminated fish. Mercury is released into the atmosphere from a variety of anthropogenic activities, with levels of emissions and under policy controls that largely vary across the world, leading thus to different relative contributions to the environmental matrices. Establishing the exact sources of this contaminant in the environment is crucial to optimising the policies aimed at mitigating the exposure risks for specific populations or ecosystems. In this study, we modelled, for the first time, the fingerprint of mercury anthropogenic emissions, jointly released by source-sectors (11) and source-regions (13), on the deposition over (19) FAO fishery zones, and on the FAO official fishery productions worldwide over the 2012-2021 decade. Using mercury anthropogenic emissions for 2012 from EDGAR, East Asia and "Artisanal and Small scale Gold Mining" result the source-region and the source-sector, respectively, that contribute the most to the mercury deposition over all the FAO fishery zones. The only exception applies for the FAO fishery zone 37, the Mediterranean Sea, where the "Industrial Combustion" from the closest Europe is the pair region-sector whose joint contribution is the greatest. When normalised to the overall fishery production worldwide, representing the global fish consumption, the anthropogenic mercury fingerprint showed a similar general pattern, however with notable differences, amplifying the relative contributions of all source-sectors from East Asia and attenuating the relative contributions of the regions in the Southern Hemisphere. This fingerprint further changes when the fish consumption in countries, classified by the World Bank as having different incomes, is considered. These results demonstrate that the same anthropogenic mercury deposited on any fishery zone actually affects in a different way the different population segments worldwide. This study aims to urge the science community as well as the policy makers to use a measure that better represents the mercury hazard for human health. Further, we hope that this study, using nomenclatures that are largely used on final shelf-product, could increase the people's awareness regarding the products they consume.

Methylmercury cycling in the Bohai Sea and Yellow Sea: Reasons for the low system efficiency of methylmercury production

Coastal seas contribute the majority of human methylmercury (MeHg) exposure via marine fisheries. The terrestrial area surrounding the Bohai Sea and Yellow Sea (BS and YS) is one of the mercury (Hg) emission "hot spots" in the world, resulting in high concentrations of Hg in BS and YS seawater in comparison to other marine systems. However, comparable or even lower Hg levels were detected in seafood from the BS and YS than other coastal regions around the word, suggesting a low system bioaccumulation of Hg. Reasoning a low system efficiency of MeHg production (represented by MeHg/THg (total Hg) in seawater) may be present in these two systems, seven cruises were conducted in the BS and YS to test this hypothesis. MeHg/THg ratios in BS and YS seawater were found to be lower than that in most coastal systems, indicating that the system efficiency of MeHg production is relatively lower in the BS and YS. The low system efficiency of MeHg production reduces the risk of Hg in the BS and YS with high Hg discharge intensity. By measuring in situ production and degradation of MeHg using double stable isotope addition method, and MeHg discharge flux from various sources and its exchange at various interfaces, the budgets of MeHg in the BS and YS were estimated. The results indicate that in situ methylation and demethylation are the major source and sink of MeHg in the BS and YS. By comparing the potential controlling processes and environmental parameters for MeHg/THg in the BS and YS with the other coastal seas, estuaries and bays, lower transport efficiency of inorganic Hg from water column to the sediment, slower methylation of Hg, and rapid demethylation of MeHg were identified to be major reasons for the low system efficiency of MeHg production in the BS and YS. This study highlights the necessity of monitoring the system efficiency of MeHg production, associated processes, and controlling parameters to evaluate the efficiency of reducing Hg emissions in China as well as the other countries.

Review: myogenic and muscle toxicity targets of environmental methylmercury exposure

A number of environmental toxicants are noted for their activity that leads to declined motor function. However, the role of muscle as a proximal toxicity target organ for environmental agents has received considerably less attention than the toxicity targets in the nervous system. Nonetheless, the effects of conventional neurotoxicants on processes of myogenesis and muscle maintenance are beginning to resolve a concerted role of muscle as a susceptible toxicity target. A large body of evidence from epidemiological, animal, and in vitro studies has established that methylmercury (MeHg) is a potent developmental toxicant, with the nervous system being a preferred target. Despite its well-recognized status as a neurotoxicant, there is accumulating evidence that MeHg also targets muscle and neuromuscular development as well as contributes to the etiology of motor defects with prenatal MeHg exposure. Here, we summarize evidence for targets of MeHg in the morphogenesis and maintenance of skeletal muscle that reveal effects on MeHg distribution, myogenesis, myotube formation, myotendinous junction formation, neuromuscular junction formation, and satellite cell-mediated muscle repair. We briefly recapitulate the molecular and cellular mechanisms of skeletal muscle development and highlight the pragmatic role of alternative model organisms, Drosophila and zebrafish, in delineating the molecular underpinnings of muscle development and MeHg-mediated myotoxicity. Finally, we discuss how toxicity targets in muscle development may inform the developmental origins of health and disease theory to explain the etiology of environmentally induced adult motor deficits and accelerated decline in muscle fitness with aging.

Intestinal microbiota protects against methylmercury-induced neurotoxicity

Methylmercury (MeHg) remains a global public health issue because of its frequent presence in human food sources obtained from the water. The excretion of MeHg in humans occurs slowly with a biological half-time of 32-47 days. Short-term MeHg exposure may cause long-lasting neurotoxicity. The excretion through feces is a major route in the demethylation of MeHg. Accumulating evidence suggests that the intestinal microbiota plays an important role in the demethylation of MeHg, thereby protecting the host from neurotoxic effects. Here, we discuss recent developments on the role of intestinal microbiota in MeHg metabolism, based on in vitro cell culture experiments, experimental animal studies and human investigations. Demethylation by intestinal bacteria is the rate-limiting step in MeHg metabolism and elimination. The identity of bacteria strains responsible for this biotransformation is currently unknown; however, the non-homogenous distribution of intestinal microbiota may lead to different demethylation rates in the intestinal tract. The maintenance of intestinal barrier function by intestinal microbiota may afford protection against MeHg-induced neurotoxicity, which warrant future investigations. We also discuss studies investigating the effects of MeHg exposure on the population structural stability of intestinal microbiota in several host species. Although this is an emerging area in metal toxicity, current research suggests that a change in certain phyla in the intestinal microbiota may indicate MeHg overexposure.

World war munitions as a source of mercury in the southwest Baltic Sea

Mercury (Hg) fulminate was used as a primary fuse in World War (WW) munitions, and may consequently be a Hg source for impacted environments. Mercury is a conspicuous and persistent pollutant, with methylmercury (MeHg) acting as a notorious neurotoxin. Considerable amounts of munitions were intentionally dumped in the North Sea and Baltic Sea following the First and Second WWs. After more than 70 years on the seafloor many munitions have corroded and likely release explosive compounds, including Hg fulminate. The Germany coastal city of Kiel was a manufacturing centre for submarines, and accordingly a prominent target for bombing and post-war disarmament. We collected water and sediment samples around Kiel Bay to assess regional levels and quantify any Hg contamination. The munition dump site Kolberger Heide (KH) and a former anti-aircraft training center Dänisch-Nienhof are situated in Kiel Bay, and were targeted for sampling. Sediment Hg concentrations around KH were notably elevated. Average Hg concentrations in KH sediments were 125 ± 76 ng/g, compared to 14 ± 18 ng/g at background (control) sites. In contrast, dissolved Hg in the water column exhibited no site variations, all ranging between 0.8 and 2.1 pM. Methylmercury in sediments and waters did not have enhanced concentrations amongst sites (<30 pg/g and <50 fM, respectively). Sediment-water exchange experiments showed elevated Hg and MeHg fluxes (i.e. >400 pmol m-2 d-1 MeHg) at one KH location, however remaining cores had low to no Hg and MeHg output (<0-27 pmol m-2 d-1 MeHg). Thus, sediments in Kiel Bay proximate to WW munitions could harbor and form a source of Hg, however water column mixing and removal processes attenuate any discharge from the seafloor to overlying waters.

Large-Scale Observations Support Aboveground Vegetation as an Important Biological Mercury Sink in the Tibetan Plateau

Mercury, a pervasive global pollutant, primarily enters the atmosphere through human activities and legacy emissions from the land and oceans. A significant portion of this mercury subsequently settles on land through vegetation uptake. Characterizing mercury storage and distribution within vegetation is essential for comprehending regional and global mercury cycles. We conducted an unprecedented large-scale aboveground vegetation mercury survey across the expansive Tibetan Plateau. We find that mosses (31.1 ± 0.5 ng/g) and cushion plants (15.2 ± 0.7 ng/g) outstood high mercury concentrations. Despite exceptionally low anthropogenic mercury emissions, mercury concentrations of all biomes exceeded at least one-third of their respective global averages. While acknowledging the role of plant physiological factors, statistical models emphasize the predominant impact of atmospheric mercury on driving variations in mercury concentrations. Our estimations indicate that aboveground vegetation on the plateau accumulates 32-12+21 Mg (interquartile range) mercury. Forests occupy the highest biomass and store 82% of mercury, while mosses, representing only 3% of the biomass, disproportionally contribute 13% to mercury storage and account for 43% (2.5-1.4+3.0 Mg/year) of annual mercury assimilation by vegetation. Additionally, our study underscores that extrapolating aboveground vegetation mercury storage from lower-altitude regions to the Tibetan Plateau can lead to substantial overestimation, inspiring further exploration in alpine ecosystems worldwide.

Food Web Structures and Mercury Exposure Pathway to Fish in Minamata Bay

We analyzed total mercury content (THg) and carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in fish, subtidal macrobenthos, and particulate organic matter (POM) as a proxy for pelagic phytoplankton and attached microalgae as a proxy for microphytobenthos to investigate the mercury exposure pathway in fish. For four seasons, samples of the above-mentioned organisms were collected on five occasions (July and October 2018 and January, April, and July 2019) in Minamata Bay. Isotope analysis showed that Minamata Bay food web structures were almost entirely fueled by microphytobenthos. The THg values of the fish and macrobenthos species were positively correlated with their δ13C. This indicates that their diets, which were highly fueled by microphytobenthos, led to high THg bioaccumulation in both macrobenthos and fish. The feeding habits of fishes differ depending on the species, and they prey on organisms of many taxa, including fish (mainly Japanese anchovy), crabs, shrimp, copepods, annelids, and algae. Fish species that preyed on benthic crustaceans had high THg. These results suggest that the main pathway of Hg bioaccumulation in fish from Minamata Bay is the benthic food chain, which is primarily linked to benthic crustaceans fueled by microphytobenthos.

Mobility and bioavailability of mercury in sediments of the southern Baltic sea in relation to the chemical fractions of iron: Spatial and temporal patterns

Marine sediments play a significant role as reservoirs for mercury (Hg), a bioaccumulative toxic pollutant that poses risks to human and ecosystem health. Iron (Fe) has been recognized as an influential factor in the complexation and bioavailability of Hg in sediments. However, limited studies have investigated the interactions between the chemical fractions of these elements in natural settings. This study aims to examine the fractions of Hg and Fe in sediments of the Baltic Sea, a region historically impacted by Hg pollution. The Hg fractions were determined using the thermodesorption technique, while sequential extraction was employed to identify the Fe fractions. The findings confirm the crucial role of Fe in the formation, as well as the horizontal and vertical distribution of labile and stable Hg in marine sediments. Factors such as the contribution of organic matter, the presence of reactive Fe, and Fe associated with sheet silicates emerged as significant drivers that positively influenced the content of the most labile Hg fractions, potentially affecting the mobility and bioavailability of Hg in the marine environment.

Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Estuaries are an important food source for the world's growing population, yet human health is at risk from elevated exposure to methylmercury (MeHg) via the consumption of estuarine fish. Moreover, the sources and cycling of MeHg in temperate estuarine ecosystems are poorly understood. Here, we investigated the seasonal and tidal patterns of mercury (Hg) forms in Long Island Sound (LIS), in a location where North Atlantic Ocean waters mix with the Connecticut River. We found that seasonal variations in Hg and MeHg in LIS followed the extent of riverine Hg delivery, while tides further exacerbated the remobilization of earlier deposited riverine Hg. The net production of MeHg near the river plume was significant compared to that in other locations and enhanced during high tide, possibly resulting from the enhanced microbial activity and organic carbon remineralization in the river plume. Statistical models, driven by our novel data, further support the hypothesis that the river-delivered organic matter and inorganic Hg drive net MeHg production in the estuarine water column. Our study sheds light on the significance of water column biogeochemical processes in temperate tidal estuaries in regulating MeHg levels and inspires new questions in our quest to understand MeHg sources and dynamics in coastal oceans.

Global change effects on biogeochemical mercury cycling

Past and present anthropogenic mercury (Hg) release to ecosystems causes neurotoxicity and cardiovascular disease in humans with an estimated economic cost of $117 billion USD annually. Humans are primarily exposed to Hg via the consumption of contaminated freshwater and marine fish. The UNEP Minamata Convention on Hg aims to curb Hg release to the environment and is accompanied by global Hg monitoring efforts to track its success. The biogeochemical Hg cycle is a complex cascade of release, dispersal, transformation and bio-uptake processes that link Hg sources to Hg exposure. Global change interacts with the Hg cycle by impacting the physical, biogeochemical and ecological factors that control these processes. In this review we examine how global change such as biome shifts, deforestation, permafrost thaw or ocean stratification will alter Hg cycling and exposure. Based on past declines in Hg release and environmental levels, we expect that future policy impacts should be distinguishable from global change effects at the regional and global scales.

Our evolved understanding of the human health risks of mercury

Mercury (Hg) is a chemical of health concern worldwide that is now being acted upon through the Minamata Convention. Operationalizing the Convention and tracking its effectiveness requires empathy of the diversity and variation of mercury exposure and risk in populations worldwide. As part of the health plenary for the 15th International Conference on Mercury as a Global Pollutant (ICMGP), this review paper details how scientific understandings have evolved over time, from tragic poisoning events in the mid-twentieth century to important epidemiological studies in the late-twentieth century in the Seychelles and Faroe Islands, the Arctic and Amazon. Entering the twenty-first century, studies on diverse source-exposure scenarios (e.g., ASGM, amalgams, contaminated sites, cosmetics, electronic waste) from across global regions have expanded understandings and exemplified the need to consider socio-environmental variables and local contexts when conducting health studies. We conclude with perspectives on next steps for mercury health research in the post-Minamata Convention era.

Toward a Global Model of Methylmercury Biomagnification in Marine Food Webs: Trophic Dynamics and Implications for Human Exposure

Marine fish is an excellent source of nutrition but also contributes the most to human exposure to methylmercury (MMHg), a neurotoxicant that poses significant risks to human health on a global scale and is regulated by the Minamata Convention. To better predict human exposure to MMHg, it is important to understand the trophic transfer of MMHg in the global marine food webs, which remains largely unknown, especially in the upper trophic level (TL) biota that is more directly relevant to human exposure. In this study, we couple a fish ecological model and an ocean methylmercury model to explore the influencing factors and mechanisms of MMHg transfer in marine fish food webs. Our results show that available MMHg in the zooplankton strongly determines the MMHg in fish. Medium-sized fish are critical intermediaries that transfer more than 70% of the MMHg circulating in food webs. Grazing is the main factor to control MMHg concentrations in different size categories of fish. Feeding interactions affected by ecosystem structures determine the degree of MMHg biomagnification. We estimate a total of 6.1 metric tons of MMHg potentially digested by the global population per year through marine fish consumption. The model provides a useful tool to quantify human exposure to MMHg through marine fish consumption and thus fills a critical gap in the effectiveness evaluation of the convention.

Aptamer-based NanoBioSensors for seafood safety

Chemical and biological contaminants are of primary concern in ensuring seafood safety. Rapid detection of such contaminants is needed to keep us safe from being affected. For over three decades, immunoassay (IA) technology has been used for the detection of contaminants in seafood products. However, limitations inherent to antibody generation against small molecular targets that cannot elicit an immune response, along with the instability of antibodies under ambient conditions greatly limit their wider application for developing robust detection and monitoring tools, particularly for non-biomedical applications. As an alternative, aptamer-based biosensors (aptasensors) have emerged as a powerful yet robust analytical tool for the detection of a wide range of analytes. Due to the high specificity of aptamers in recognising targets ranging from small molecules to large proteins and even whole cells, these have been suggested to be viable molecular recognition elements (MREs) in the development of new diagnostic and biosensing tools for detecting a wide range of contaminants including heavy metals, antibiotics, pesticides, pathogens and biotoxins. In this review, we discuss the recent progress made in the field of aptasensors for detection of contaminants in seafood products with a view of effectively managing their potential human health hazards. A critical outlook is also provided to facilitate translation of aptasensors from academic laboratories to the mainstream seafood industry and consumer applications.

Development and validation of the DGT technique using the novel cryogel for measuring dissolved Hg(II) in the estuary

The complex seawater matrix has significantly influenced the determination of estuarine dissolved Hg(II), hindering its monitoring and risk assessment in maricultural areas. In this work, SiO2-SH-DGT assembled by the sulfhydryl-modified silica cryogel (SiO2-SH cryogel) as the novel binding phase was developed to tackle this problem. The uniform dispersion of the cryogel into binding gel was advantageous for achieving remarkable and comparable capacity, which endowed the estimated diffusion coefficient (D) to be 1.39-3.08 times of the existing research. The SiO2-SH-DGT performance was independent of pH (3-9), ionic strength (10-800 mM), fulvic acid at low content, and seawater matrix (Na+, K+, Ca2+, Cl-), but the high content of Mg2+ did interfere with the Hg(II) accumulation, which manifested as competitive adsorption and diffusion. Therefore, the calibrated model was established by calibrating accumulated mass (M') and diffusion coefficient (D') based on the Mg2+ concentration, its high accuracy was further verified in the lab. Finally, SiO2-SH-DGT was deployed in the three typical aquaculture areas in Beibu Gulf, field trials achieved the actual Hg(II) level to be 1.52-5.38 ng/L with consideration of the diffusion boundary layer. The finding could provide new thought and technical support for metal pollution monitoring in estuary maricultural areas.

Age, body size, growth and dietary habits: What are the key factors driving individual variability in mercury of lacustrine fishes in northern temperate lakes?

Fish total mercury concentration ([THg]) has been linked to various fish attributes, but the relative importance of these attributes in accounting for among-individual variation in [THg] has not been thoroughly assessed. We compared the contributions of ontogeny (age, length), growth (growth rate, body condition), and food web position (δ¹³C, δ¹⁵N) to among-individual variability in [THg] within populations of seven common fishes from 141 north temperate lakes. Ontogenetic factors accounted for most variation in [THg]; age was a stronger and less variable predictor than length for most species. Adding both indices of growth and food web position to these models increased explained variation (R²) in [THg] by 6-25% among species. Fish [THg] at age increased with growth rate, while fish [THg] at length decreased with growth rate, and the effect of body condition was consistently negative. Trophic elevation (inferred from δ¹⁵N) was a stronger predictor than primary production source (inferred from δ¹³C) for piscivores but not benthivores. Fish [THg] increased with δ¹⁵N in all species but showed a more variable relationship with δ¹³C. Among-individual variation in [THg] is primarily related to age or size in most temperate freshwater fishes, and effects of growth rate and food web position need to be considered in the context of these ontogenetic drivers.

Development of sensitive and portable immunosensors based on signal amplification probes for monitoring the mercury(II) ions

Mercury ion (Hg²⁺) as a major environmental pollutant threatens human health even at very low concentrations, so it is essential to monitor mercury residues in food. In this study, Hg²⁺ was conjugated with protein carrier using 1-(4-Isothiocyanobenzyl) ethylenediamine N, N, N', N'-tetraacetic acid (ITCBE) as a bifunctional chelator. 7A1 monoclonal antibody (mAb) against Hg²⁺-ITCBE with high affinity (7.3 × 10⁹ L/moL) and good specificity was obtained by cell fusion technology and performed to establish immunosensors. Immunochromatographic test strip using colloidal gold nanoparticles (AuNP with an average diameter of 18 nm) as signal reporter showed low sensitivity. Signal amplification probes including larger multi-branched gold nanoflowers (AuNF) and latex microspheres (LM) were employed to enhance the sensitivity of immunosensors. The visible limit of detection (vLOD) of the AuNF- and LM-based strip were determined to be 50 ng/mL and 25 ng/mL respectively, showing more sensitive than that of AuNP-based strip (200 ng/mL). Quantitative analysis showed that AuNF-based strip exhibited lower quantitative limit of detection (qLOD) (0.44 ng/mL) which was 20-fold lower than that of AuNP-based strip (8.92 ng/mL) for determination of Hg²⁺, and LM-based strip (0.49 ng/mL) was 18 times as sensitive as AuNP-based strip. In summary, the developed immunosensors using AuNF and LM as signal amplification probes exhibited excellent sensitivity and provided portable, on-site detection for Hg²⁺.

An examination of mercury levels in the coastal environment and fish of Cote d'Ivoire

Artisanal and small-scale gold mining (ASGM), energy production and other industrial inputs are a major source of anthropogenic mercury (Hg) to the aquatic environment globally, and these inputs have led to environmental contamination and human exposure. While studies have documented the effects of Hg inputs to rivers and marine waters of the West African region, estuarine waters of Cote d'Ivoire have been understudied, besides the waters surrounding Abidjan. To fill this gap, and to examine the potential for human exposure to methylmercury (MeHg), we measured the concentrations of total Hg, MeHg, and ancillary parameters in water (dissolved and particulate phases), sediment and fish to determine the extent of environmental impact and the potential for MeHg exposure for people consuming these fish. Levels of Hg and MeHg in sediment were elevated in the vicinity of the urban environment (up to 0.3 ng/g dry weight (dw) MeHg and 623 ng/g dw total Hg) and lowest in the more remote estuarine environments. Measurements of Hg in tuna and other larger pelagic coastal species indicated that levels were elevated but comparable to other North Atlantic regions. However, levels of Hg in fish, even smaller estuarine species, were such that the rural and urban populations are potentially being exposed to unsafe levels of MeHg, primarily as a result of the relatively high fish consumption in Cote d'Ivoire compared to other countries. Overall, both local point sources and the transport of Hg used in interior ASGM activities are the sources for Hg contamination to these coastal waters.

The impact of mercury contamination on human health in the Arctic: A state of the science review

The 2021 Arctic Monitoring and Assessment Programme (AMAP) Mercury (Hg) Assessment is motivated by Arctic populations, and most notably Indigenous Peoples in the region, who are particularly vulnerable to Hg pollution. The objective of this review paper is to answer the following AMAP policy-relevant question: what is the human health impact of Hg pollution in the Arctic? In doing so, this state of the science review paper builds on information published 10 years ago in the last AMAP Hg assessment. The synthesized results demonstrate that: a) global influences (e.g., sources and transport pathways, biogeochemical processes, climate change, globalization) drive Hg exposures into human communities; b) Hg exposures are realized through dietary intake of certain country food items, and that new exposure science approaches are helping to deepen understandings; c) the nutritional and cultural benefits of country foods are immense, though a dietary transition is underway raising concerns over metabolic syndrome and broader issues of food security as well as cultural and social well-being; d) blood Hg measures are among the highest worldwide based on the results of human biomonitoring studies; e) Hg exposures are associated with adverse health outcomes across life stages (e.g., neurodevelopmental outcomes in young children to cardiovascular disease in adults); and f) risk communication needs to be balanced, targeted and clear, culturally appropriate, and be done collaboratively. These synthesized findings are particularly timely and policy-relevant given that the Minamata Convention entered into legal force worldwide in 2017 as a regulatory scheme to reduce the use and environmental release of Hg in order to protect human health and the environment. The Convention was influenced by health concerns raised by northern populations as indicated in the preamble text which makes reference to "the particular vulnerabilities of Arctic ecosystems and Indigenous communities".

Molecular Fates of Organometallic Mercury in Human Brain

Mercury is ubiquitous in the environment, with rising levels due to pollution and climate change being a current global concern. Many mercury compounds are notorious for their toxicity, with the potential of organometallic mercury compounds for devastating effects on the structures and functions of the central nervous system being of particular concern. Chronic exposure of human populations to low levels of methylmercury compounds occurs through consumption of fish and other seafood, although the health consequences, if any, from this exposure remain controversial. We have used high energy resolution fluorescence detected X-ray absorption spectroscopy to determine the speciation of mercury and selenium in human brain tissue. We show that the molecular fate of mercury differs dramatically between individuals who suffered acute organometallic mercury exposure (poisoning) and individuals with chronic low-level exposure from a diet rich in marine fish. For long-term low-level methylmercury exposure from fish consumption, mercury speciation in brain tissue shows methylmercury coordinated to an aliphatic thiolate, resembling the coordination environment observed in marine fish. In marked contrast, for short-term high-level exposure, we observe the presence of biologically less available mercuric selenide deposits, confirmed by X-ray fluorescence imaging, as well as mercury(II)-bis-thiolate complexes, which may be signatures of severe poisoning in humans. These differences between low-level and high-level exposures challenge the relevance of studies involving acute exposure as a proxy for low-level chronic exposure.

Study Protocol: Interactive Dynamics of Coral Reef Fisheries and the Nutrition Transition in Kiribati

The Kiribati 2019 Integrated Household Income and Expenditure Survey (Integrated HIES) embeds novel ecological and human health research into an ongoing social and economic survey infrastructure implemented by the Pacific Community in partnership with national governments. This study seeks to describe the health status of a large, nationally representative sample of a geographically and socially diverse I-Kiribati population through multiple clinical measurements and detailed socio-economic surveys, while also conducting supporting food systems research on ecological, social, and institutional drivers of change. The specific hypotheses within this research relate to access to seafood and the potential nutritional and health benefits of these foods. We conducted this research in 21 of the 23 inhabited islands of Kiribati, excluding the two inhabited islands-Kanton Islands in the Phoenix Islands group with a population of 41 persons (2020 census) and Banaba Island in the Gilbert Islands group with a population of 333 persons (2020 census)-and focusing exclusively on the remaining islands in the Gilbert and Line Islands groups. Within this sample, we focused our intensive human health and ecological research in 10 of the 21 selected islands to examine the relationship between ecological conditions, resource governance, food system dynamics, and dietary patterns. Ultimately, this research has created a baseline for future Integrated HIES assessments to simultaneously monitor change in ecological, social, economic, and human health conditions and how they co-vary over time.

Mercury Lα1 High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy: A Versatile Speciation Probe for Mercury

Mercury is in some sense an enigmatic element. The element and some of its compounds are a natural part of the biogeochemical cycle; while many of these can be deadly poisons at higher levels, environmental levels in the absence of anthropogenic contributions would generally be below the threshold for concern. However, mercury pollution, particularly from burning fossil fuels such as coal, is providing dramatic and increasing emissions into the environment. Because of this, the environmental chemistry and toxicology of mercury are of growing importance, with the fate of mercury being vitally dependent upon its speciation. X-ray absorption spectroscopy (XAS) provides a powerful tool for in situ chemical speciation, but is severely limited by poor spectroscopic energy resolution. Here, we provide a systematic examination of mercury Lα1 high energy resolution fluorescence detected XAS (HERFD-XAS) as an approach for chemical speciation of mercury, in quantitative comparison with conventional Hg LIII-edge XAS. We show that, unlike some lighter elements, chemical shifts in the Lα1 X-ray fluorescence energy can be safely neglected, so that mercury Lα1 HERFD-XAS can be treated simply as a high-resolution version of conventional XAS. We present spectra of a range of mercury compounds that may be relevant to the environmental and life science research and show that density functional theory can produce adequate simulations of the spectra. We discuss strengths and limitations of the method and quantitatively demonstrate improvements both in speciation for complex mixtures and in background rejection for low concentrations.

Mercury concentrations, biomagnification and isotopic discrimination factors in two seabird species from the Humboldt Current ecosystem

Assessing mercury (Hg) biomagnification requires the description of prey-predator relationships, for each species and ecosystem, usually based on carbon and nitrogen isotope analyses. Here, we analyzed two seabirds from the Humboldt Current ecosystem, the Guanay cormorant (Phalacrocorax bougainvillii) and the Peruvian booby (Sula variegata), as well as their main prey, the Peruvian anchovy (Engraulis ringens). We reported Hg concentrations, Hg biomagnification (BMF) and isotopic discrimination factors (Δ¹³C and Δ¹⁵N) in seabird whole blood. BMFs and Δ¹³C in our study (on wild birds where diet was not controlled) were similar to other piscivorous seabirds previously studied in captive settings, but Δ¹⁵N were lower than most captive experiments. We observed lower Hg concentrations in Humboldt seabirds compared to other oligotrophic ecosystems, possibly due to Hg biodilution in the high biomass of the first trophic levels. This work calls for a better characterization of Hg trophic dynamics in productive upwelling ecosystems.

Observation-Based Mercury Export from Rivers to Coastal Oceans in East Asia

Globally, the consumption of coastal fish is the predominant source of human exposure to methylmercury, a potent neurotoxicant that poses health risks to humans. However, the relative importance of riverine inputs and atmospheric deposition of mercury into coastal oceans remains uncertain owing to a lack of riverine mercury observations. Here, we present comprehensive seasonal observations of riverine mercury and methylmercury loads, including dissolved and particulate phases, to East Asia's coastal oceans, which supply nearly half of the world's seafood products. We found that East Asia's rivers annually exported 95 ± 29 megagrams of mercury to adjacent seas, 3-fold greater than the corresponding atmospheric deposition. Three rivers alone accounted for 71% of East Asia's riverine mercury exports, namely: Yangtze, Yellow, and Pearl rivers. We further conducted a metadata analysis to discuss the mercury burden on seawater and found that riverine export, combined with atmospheric deposition and terrestrial nutrients, quantitatively elevated the levels of total, methylated, and dissolved gaseous mercury in seawater by an order of magnitude. Our observations support that massive amounts of riverine mercury are exported to coastal oceans on a continental scale, intensifying their spread from coastal seawater to the atmosphere, marine sediments, and open oceans. We suggest that the impact of mercury transport along the land-ocean aquatic continuum should be considered in human exposure risk assessments.

Mercury stable isotopes constrain atmospheric sources to the ocean

Human exposure to toxic mercury (Hg) is dominated by the consumption of seafood^1,2. Earth system models suggest that Hg in marine ecosystems is supplied by atmospheric wet and dry Hg(II) deposition, with a three times smaller contribution from gaseous Hg(0) uptake^3,4. Observations of marine Hg(II) deposition and Hg(0) gas exchange are sparse, however⁵, leaving the suggested importance of Hg(II) deposition⁶ ill-constrained. Here we present the first Hg stable isotope measurements of total Hg (tHg) in surface and deep Atlantic and Mediterranean seawater and use them to quantify atmospheric Hg deposition pathways. We observe overall similar tHg isotope compositions, with median Δ²⁰⁰Hg signatures of 0.02‰, lying in between atmospheric Hg(0) and Hg(II) deposition end-members. We use a Δ²⁰⁰Hg isotope mass balance to estimate that seawater tHg can be explained by the mixing of 42% (median; interquartile range, 24-50%) atmospheric Hg(II) gross deposition and 58% (50-76%) Hg(0) gross uptake. We measure and compile additional, global marine Hg isotope data including particulate Hg, sediments and biota and observe a latitudinal Δ²⁰⁰Hg gradient that indicates larger ocean Hg(0) uptake at high latitudes. Our findings suggest that global atmospheric Hg(0) uptake by the oceans is equal to Hg(II) deposition, which has implications for our understanding of atmospheric Hg dispersal and marine ecosystem recovery.

Mitigating the impact of mercury contaminants in fish and other seafood-A review

Mercury (Hg) is a well-known toxicant which enters the marine environment by both natural and anthropogenic sources. Consumption of fish and other seafood that contain methylmercury (MeHg) is a leading source of Hg exposure in humans. Considerable efforts have been made to mitigate the Hg presence and reduce its risks to humans. In this review the acknowledged methods of mitigation are summarized such as regulation and maximum allowable limits, and culinary treatments. In addition, selected industrial level trials are reviewed, and studies on Hg intoxication and the protective effects of the essential trace element, selenium (Se), are discussed. In view of the available literature, Hg reduction in fish and other seafood on a large industrial scale still is largely unsuccessful. Hence, more research and further attempts are necessary in order to better mitigate the Hg problem in fish and other seafood products.

Metal/metalloid levels in hair of Shenzhen residents and the associated influencing factors

129 Shenzhen residents' hair samples were collected and the metal/metalloid concentrations of Hg, As, Pb, Cd, Cr, Cu, Mn, Zn, Fe and Ni were detected. Meanwhile, the relationships between metal/metalloid contents in human hair and gender, age, seafood diet habit, smoking habit, as well as the housing type (dwelling environment) were analyzed. Results showed that the average content of Hg, As, Pb, Cd, Cr, Cu, Mn, Zn, Fe and Ni in human hair of Shenzhen residents was 0.76 ± 0.96, 0.10 ± 0.04, 5.25 ± 4.88, 0.25 ± 0.33, 0.60 ± 0.31, 13.84 ± 3.67, 2.82 ± 2.01, 196.90 ± 145.01, 12.20 ± 5.10 and 0.34 ± 0.32 μg/g, respectively. Compared with other regions at home and abroad, most metal/metalloids in Shenzhen residents were at a moderate level, and the highly toxic elements (i.e. Pb, Cd, As and Hg) didn't exceed the upper limit of normal values in China. Statistical analysis showed that the young male people contained significantly higher (p < 0.05) level of Pb (in age group of 20-30 years old) and Fe (in age group of 20-40 years old) in hair than the female people. Smokers had significantly (p < 0.05) higher level of Cd (0.35 μg/g) but lower level of Zn (101.24 µg/g) than non-smokers (Cd: 0.17 μg/g; Zn: 252.63 µg/g). Hg and Pb contents in hair of Shenzhen people were positively related with the frequencies of seafood consumption and the age, respectively. Moreover, residents lived in private buildings (well decorated house) accumulated significantly higher (p < 0.05) levels of Pb, Cr, Fe and Ni as compared with those lived in public rental house and village house (no decoration or simple decoration), suggesting that decoration material was also an important way for human exposure to heavy metals.

Mercury accumulation in reef fishes: a comparison among red grouper, scamp, and gag of the Atlantic southeastern US and evaluation of "grouper" consumption guidelines

In fish consumption advisories pertaining to Hg, grouper species in the family Serranidae are often lumped together and labeled generically as Grouper. However, grouper species vary considerably in growth rate, maximum age, and maximum size. This study examined the variability of Hg concentrations and bioaccumulation rates (increase of Hg concentrations in relation to age) for populations of three long-lived, slow-growing, protogynous hermaphrodite grouper species, gag Mycteroperca microlepis, scamp M. phenax, and red grouper Epinephelus morio, which are commercially and recreationally important in the offshore waters of the US southeastern region. A total of 268 samples from the three grouper species were processed for Hg analysis from 2013-2015. Concentrations of Hg ranged from 0.03 to 0.87 ppm wet weight, with a mean of 0.30 ppm. Gag accumulated Hg at a faster rate (as measured by the increase of Hg with fish age) than the other two species. Size, age, and δ¹⁵N were significant predictors for Hg in the two Mycteroperca species, while size and age were significant predictors for Hg in red grouper. Two of the three species had mean Hg concentrations within the one meal per week "Good Choices" consumption category (red grouper and scamp), and one species (gag) had a mean Hg level within the two meals per week "Good Choices" consumption category as advised by the US EPA and US FDA. These results support the separation of grouper species in advisories.

Subcellular Distribution of Dietary Methyl-Mercury in Gammarus fossarum and Its Impact on the Amphipod Proteome

The transfer of methyl-Hg (MeHg) from food is central for its effects in aquatic animals, but we still lack knowledge concerning its impact on invertebrate primary consumers. In aquatic environments, cell walls of plants are particularly recalcitrant to degradation and as such remain available as a food source for long periods. Here, the impact at the proteomic level of dietary MeHg in Gammarus fossarum was established and linked to subcellular distribution of Hg. Individuals of G. fossarum were fed with MeHg in cell wall or intracellular compartments of Elodea nuttallii. Hg concentrations in subcellular fractions were 2 to 6 times higher in animals fed with cell wall than intracellular compartments. At the higher concentrations tested, the proportion of Hg in metal-sensitive fraction increased from 30.0 ± 6.1 to 41.0 ± 5.7% for individuals fed with intracellular compartment, while biologically detoxified metal fraction increased from 30.0 ± 6.1 to 50.0 ± 2.8% when fed with cell wall compartment. Data suggested that several thresholds of proteomic response are triggered by increased bioaccumulation in each subcellular fraction in correlation with Hg exclusively bound to the metal-sensitive fraction, while the increase of biologically detoxified metal likely had a cost for fitness. Proteomics analysis supported that the different binding sites and speciation in shoots subsequently resulted in different fate and cellular toxicity pathways to consumers. Our data confirmed that Hg bound in cell walls of plants can be assimilated by G. fossarum, which is consistent with its feeding strategy, hence pointing cell walls as a significant source for Hg transfers and toxicity in primary consumers. The high accumulation of Hg in macrophytes makes them a risk for food web transfer in shallow ecosystems. The present results allowed gaining new insights into the effects and uptake mechanisms of MeHg in aquatic primary consumers.

Functionalized Nanoplastics (NPs) Increase the Toxicity of Metals in Fish Cell Lines

Nanoplastics (NPs) are one of the most abundant environment-threatening nanomaterials on the market. The objective of this study was to determine in vitro if functionalized NPs are cytotoxic by themselves or increase the toxicity of metals. For that, we used 50 nm polystyrene nanoparticles with distinct surface functionalization (pristine, PS-Plain; carboxylic, PS-COOH; and amino PS-NH₂) alone or combined with the metals arsenic (As) and methylmercury (MeHg), which possess an environmental risk to marine life. As test model, we chose a brain-derived cell line (SaB-1) from gilthead seabream (Sparus aurata), one of the most commercial fish species in the Mediterranean. First, only the PS-NH₂ NPs were toxic to SaB-1 cells. NPs seem to be internalized into the cells but they showed little alteration in the transcription of genes related to oxidative stress (nrf2, cat, gr, gsta), cellular protection against metals (mta) or apoptosis (bcl2, bax). However, NPs, mainly PS-COOH and PS-NH₂, significantly increased the toxicity of both metals. Since the coexistence of NPs and other pollutants in the aquatic environment is inevitable, our results reveal that the combined effect of NPs with the rest of pollutants deserves more attention.

Scalable approach towards specific and ultrasensitive cation sensing under harsh environmental conditions by engineering the analyte-transducer interface

Affordable and high-performing sensing platforms are becoming increasingly critical for sustainable environmental monitoring and medical diagnostics. Such miniaturized and point-of-care sensing platforms need to overcome the fundamental tradeoff between ultrahigh sensitivity and specificity while retaining the dynamic concentration range and robustness of operation. Therefore, designing scalable and robust sensors poses an escalating and immediate demand in a rapidly automated society. Addressing this demand, we demonstrate a cable-type electrochemical sensing platform exhibiting rapid (10 s), extremely reliable (RSD <5%) and ultrahigh sensitivity (ppb levels) towards K⁺, Cd²⁺ and Hg²⁺ found in complex biofluids such as human perspiration and effluent water. The sensor delivers quantifiable performance even with 10 μL of analyte without any requirement of purification or preconcentration and thereby overcomes an important bottleneck for on-field diagnostics. The backbone of the sensor consists of single-walled carbon nanotubes (CNTs) that are conformally coated on affordable cellulose yarns to form ideally non-Faradaic, electrically conductive, capacitive electrodes (CNT-thread). Subsequent coaxial coating of such CNT-threads with an appropriate ionophore membrane (IM) realizes the working electrode exhibiting uniformity in the surface coverage of the ionophore leading to reliable and directly quantifiable signals. Furthermore, we show that the extensive CNT-thread-IM interface is critical to achieve ultrahigh sensitivity and robust operability. Importantly, the design approach adopted is universal and scalable for a range of cations such as K⁺, Hg²⁺ and Cd²⁺. Thus, the sensor delivers ultrasensitive detection of K⁺ from very low volumes (10 μL) of human perspiration that contains a wide range of other ions (Cu²⁺, Zn²⁺, Cd²⁺, Fe²⁺, NO₃ ^-, Cl^-) at 1000-fold higher ionic strength along with bioinorganic suspended matter (dead cells, organelles). This eliminates any sample treatment or preconcentration requirements thereby overcoming a major obstacle for point-of-care applications. Furthermore, both multicomponent and multivariate analyses are demonstrated with the sensing device targeting portable and wearable applications.

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.

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

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

Trends in sensor development toward next-generation point-of-care testing for mercury

Mercury is one of the most common heavy metals and a major environmental pollutant that affects ecosystems. Since mercury and its compounds are toxic to humans, even at low concentrations, it is very important to monitor mercury contamination in water and foods. Although conventional mercury detection methods, including inductively coupled plasma mass spectrometry, atomic absorption spectroscopy, and gas chromatography-mass spectrometry, exhibit excellent sensitivity and accuracy, they require operation by an expert in a sophisticated and fully controlled laboratory environment. To overcome these limitations and realize point-of-care testing, many novel methods for direct sample analysis in the field have recently been developed by improving the speed and simplicity of detection. Commonly, these unconventional sensors rely on colorimetric, fluorescence, or electrochemical mechanisms to transduce signals from mercury. In the case of colorimetric and fluorescent sensors, benchtop methods have gradually evolved through technology convergence to give standalone platforms, such as paper-based assays and lab-on-a-chip systems, and portable measurement devices, such as smartphones. Electrochemical sensors that use screen-printed electrodes with carbon or metal nanomaterials or hybrid materials to improve sensitivity and stability also provide promising detection platforms. This review summarizes the current state of sensor platforms for the on-field detection of mercury with a focus on key features and recent developments. Furthermore, trends for next-generation mercury sensors are suggested based on a paradigm shift to the active integration of cutting-edge technologies, such as drones, systems based on artificial intelligence, machine learning, and three-dimensional printing, and high-quality smartphones.

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

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

Revisiting old lessons from classic literature on persistent global pollutants : This article belongs to Ambio's 50th Anniversary Collection. Theme: Environmental contaminants

Looking back 50 years at classic literature was a reminder of inspiring discoveries and clever theories that were formative to the field of environmental chemistry, but also of the irreparable costs that persistent global pollutants have had on ecosystems and human society. In my view, these three papers have greatly impacted contemporary science and influenced development of policies that have limited the spread of hazardous contaminants. At the same time, a sobering reality is that reversing decades of past pollution has proven impossible in our lifetime, and global trends are dire for both legacy and emerging contaminants. Lessons in these papers are clear to most environmental scientists, but I argue have not resulted in adequate investment in infrastructure or manpower to enable systematic unbiased searching for pollutants as proposed by Sören Jensen in 1972. Acknowledging that the costs of new global contaminants will be too high, we must incentivize safer chemicals and their sustainable use, increase international exchange of lists of chemicals in commerce, and coordinate international efforts in nontarget screening to identify new contaminants before they circulate the world.

Mercury in the human thyroid gland: Potential implications for thyroid cancer, autoimmune thyroiditis, and hypothyroidism

Objective

Mercury and other toxic metals have been suggested to be involved in thyroid disorders, but the distribution and prevalence of mercury in the human thyroid gland is not known. We therefore used two elemental bio-imaging techniques to look at the distribution of mercury and other toxic metals in the thyroid glands of people over a wide range of ages.

Materials and methods

Formalin-fixed paraffin-embedded thyroid tissue blocks were obtained from 115 people aged 1–104 years old, with varied clinicopathological conditions, who had thyroid samples removed during forensic/coronial autopsies. Seven-micron sections from these tissue blocks were used to detect intracellular inorganic mercury using autometallography. The presence of mercury was confirmed using laser ablation-inductively coupled plasma-mass spectrometry which can detect multiple elements.

Results

Mercury was found on autometallography in the thyroid follicular cells of 4% of people aged 1–29 years, 9% aged 30–59 years, and 38% aged 60–104 years. Laser ablation-inductively coupled plasma-mass spectrometry confirmed the presence of mercury in samples staining with autometallography, and detected cadmium, lead, iron, nickel and silver in selected samples.

Conclusions

The proportion of people with mercury in their thyroid follicular cells increases with age, until it is present in over one-third of people aged 60 years and over. Other toxic metals in thyroid cells could enhance mercury toxicity. Mercury can trigger genotoxicity, autoimmune reactions, and oxidative damage, which raises the possibility that mercury could play a role in the pathogenesis of thyroid cancers, autoimmune thyroiditis, and hypothyroidism.

Characterization of the mercury-binding proteins in tuna and salmon sashimi: Implications for health risk of mercury in food

Fish consumption is one of the major ways through which humans receive exposure to mercury (Hg). The existing forms of Hg in food, particularly Hg bound to proteins, may affect the absorption of Hg by humans and subsequently its potentially toxic effects. However, the knowledge regarding Hg-binding proteins in edible fish muscle is scarce. In the present study, salmon and tuna fish muscles, collected from seven different regions and countries, were analyzed using metallomics- and proteomics-based techniques. The concentration of Hg in sashimi samples ranged from 4.4 to 317.4 ng/g. Size exclusion chromatography (SEC) coupled with inductively coupled plasma mass spectrometer (ICP-MS) showed that beta-actin was a novel Hg-binding protein from the fish muscles, and this protein could also bind bismuth (Bi), silver (Ag), and copper (Cu). Hg bound to beta-actin accounted for approximately 30.2-37.6% of the total Hg in the tuna muscles and was significantly correlated to total Hg in the fish muscles (r = 0.98, p < 0.01) and in the fraction of soluble proteins (r = 0.94, p < 0.01). These findings suggest that proteins act as the main Hg accumulation sites in edible fish; thus, increasing human exposure to Hg following gastrointestinal digestion.

Pollutants and nutrition: Are methylmercury effects on blood pressure and lipoprotein profile comparable to high-fat diet in mice?

Human exposure to methylmercury (MeHg) due to contaminated fish intake as part of a high-fat (HFD), high-carbohydrate diets is a reality today for many populations. HFD is associated with hypertension and hyperlipidemia, primary cardiovascular disease (CVD) risk factors. Some studies suggest that MeHg induces those risk factors. We evaluated the effect of MeHg exposure in mice fed with HFD or control diet for eight weeks. In the last experimental 15 days, the half group received a MeHg solution (20 mg/L) replacing water. Blood pressure (BP), heart rate, lipoprotein concentrations, and paraoxonase activity were evaluated. Liver cholesterol, triacylglycerol, and IBA-1+ cells, as well as transcriptional levels of genes related to lipid metabolism and inflammatory response, were also assessed. HFD and both MeHg groups presented increased BP and total cholesterol (TC). In the liver, HFD but not MeHg was related to an increase in TC. Also, MeHg intoxication reduced paraoxonase activity regardless of diet. MeHg intoxication and HFD increased steatosis and the number of IBA-1+ cells and modified some gene transcripts associated with lipid metabolism. In conclusion, we demonstrated that MeHg effects on CVD risk factors resemble those caused by HFD.

Minor effects of dietary methylmercury on growth and reproduction of the sheepshead minnow Cyprinodon variegatus and toxicity to their offspring

Methylmercury (MeHg) is a neurotoxic compound that is found in virtually all fish and biomagnifies in aquatic food webs. Although MeHg concentrations in marine and estuarine fish are often elevated, the impacts of MeHg on marine and estuarine fish have largely been understudied. To evaluate the impact of dietary MeHg on marine fish reproduction and effects on their offspring, female juvenile sheepshead minnows (Cyprinodon variegatus) at three months of age were experimentally exposed to MeHg-contaminated diets for two months and then paired with Hg-free males for spawning. Egg production, hatching success of embryos, time to hatching, survival of larvae, growth of larvae and swimming behavior of larvae were determined. Selenium (Se) was also measured and Se/Hg molar ratios were calculated to assess whether Se reduced MeHg toxicity. MeHg had no significant impact on fish reproduction or on survival and growth of larvae. Larvae produced by MeHg-exposed mothers had concentrations of Hg about 1 ppm (dry wt), or about 12% of that in the muscle of their mothers and consistently displayed 6-15% increased swimming speed relative to controls; the ecological significance of this moderate effect on swimming speed requires further study. The Se/Hg molar ratios in these fish, which were >1 in controls (adults and larvae) and MeHg-exposed larvae but <1 in Hg-exposed adults, did not correlate with MeHg effects. The sheepshead minnow, at a low trophic level, appears to have a high tolerance of MeHg; however, it can pass MeHg to higher trophic levels in marine ecosystems where upper level predators have MeHg concentrations sometimes exceeding US FDA safety limits of 1 ppm wet wt.