Impact of low-level mercury exposure on intelligence quotient in children via rice consumption

Mercury levels in freshwater aquatic products across China: Spatial distribution, species differences, and health risk assessment

Freshwater product consumption is a major source of mercury (Hg) exposure in China. This study analyzed Hg concentrations in 12,560 samples from 29 provinces across China (2010-2021) and conducted probabilistic health risk assessments across various life stages. The average Hg concentration in China's freshwater products was 40.9 ± 32.3 ng/g (wet weight), lower than global averages. However, certain species, Gymnocypris and Schizothoracids from Tibet, exhibited elevated levels (216.2 ± 84.2 ng/g and 156.7 ± 89.9 ng/g, respectively). The estimated dietary intakes (EDIs) of MeHg for all age groups were well below the JECFA threshold of 1.6 μg/kg BW, even at the P95 exposure level. However, long-term exposure assessments revealed elevated risks for children aged 2-12, with Target hazard quotients (THQ) values exceeding 1 at the P95 exposure level, particularly among younger children aged 2-7. Spatially, elevated Hg exposure risks were identified in Hong Kong, Zhejiang, Guizhou, and the Songhua River regions, with contamination in Zhejiang tied to the compact fluorescent lamp industry. Furthermore, prenatal MeHg exposure through freshwater product consumption was estimated to result in Intelligence Quotient (IQ) losses of 0.00548-0.193 points in infants. These findings underscore the need for targeted interventions to mitigate Hg exposure and provides recommendations for safer freshwater fish selection in the Chinese market.

Environmental pollution challenges public health surveillance: the case of mercury exposure and intoxication in Brazil

Pollution, causing millions of deaths annually, disproportionally affects low- and middle-income countries (LMICs). Mercury ranks among the three main chemicals of major public health concern, and even low levels can cause cardiovascular and nervous outcomes, with children and indigenous populations being especially vulnerable. Nearly 80% of all emissions in South America originate from the Amazon. Brazil, the fifth-largest contributor to global mercury emissions, exemplifies the challenges faced by LMICs in effectively monitoring and addressing mercury exposure/intoxication. Despite having powerful tools such as SINAN (a digital platform for compulsory disease reporting), and Community Health Agents, data reveals significant underreporting, especially in the Amazon. Furthermore, SINAN has important delays in its update: for instance, 196 cases of Munduruku Indigenous people in 2019 have only been included in 2023. In this Personal View, we outline insightful recommendations to enhance public health surveillance and implement enduring, effective strategies to monitor, report and address mercury exposure/intoxication, focusing on the Brazilian Amazon. Although these recommendations are tailored to the challenges of this country, they hold potential for adaptation by other Amazonian countries facing similar issues (high mercury emissions and the presence of vulnerable populations, among others).

Economic benefit of ecological remediation of mercury pollution in southwest China 2007-2022

Methylmercury (MeHg) exposure via rice consumption poses health risk to residents in mercury contaminated areas, such as the Wanshan Hg mining area (WSMA) in southwest China. Making use of the published data for WSMA, this study developed a database of rice MeHg concentrations for different villages in this region for the years of 2007, 2012, 2017, and 2019. The temporal changes of human MeHg exposure, health effects, and economic benefits under different ecological remediation measures were then assessed. Results from this study revealed a decrease of 3.88 μg/kg in rice MeHg concentration and a corresponding reduction of 0.039 μg/kg/d in probable daily intake of MeHg in 2019 compared to 2007 on regional average in the WSMA. Ecological remediation measures in this region resulted in the accumulated economic benefits of $38.7 million during 2007-2022, of which 84 % was from pollution source treatment and 16 % from planting structure adjustment. However, a flooding event in 2016 led to an economic loss of $2.43 million (0.38 % of regional total Gross Domestic Product). Planting structure adjustment generates the greatest economic benefits in the short term, whereas pollution source treatment maximizes economic benefits in the long term and prevents the perturbations from flooding event. These findings demonstrate the importance of ecological remediation measures in Hg polluted areas and provide the foundation for risk assessment of human MeHg exposure via rice consumption.

Molecular crosstalk and putative mechanisms underlying mitochondrial quality control: The hidden link with methylmercury-induced cognitive impairment

Methylmercury (MeHg) is a neurotoxin associated with foetal neurodevelopmental and adult cognitive deficits. Neurons are highly dependent on the tricarboxylic acid cycle and oxidative phosphorylation to produce ATP and meet their high energy demands. Therefore, mitochondrial quality control (MQC) is critical for neuronal homeostasis. While existing studies have generated a wealth of data on the toxicity of MeHg, the complex cascades and molecular pathways governing the mitochondrial network remain to be elucidated. Here, 0.6, 1.2 and 2.4 mg/kg body weight of MeHg were administered intragastrically to pregnant Sprague Dawley rats to model maternal MeHg exposure. The results of the in vivo study revealed that MeHg-treated rats tended to perform more directionless repetitive strategies in the Morris Water Maze and fewer target-orientation strategies than control offspring. Moreover, pathological injury and synaptic toxicity were observed in the hippocampus. Transmission electron microscopy (TEM) demonstrated that the autophagosomes encapsulated damaged mitochondria, while showing a typical mitochondrial fission phenotype, which was supported by the activation of PINK1-dependent key regulators of mitophagy. Moreover, there was upregulation of DRP1 and FIS1. Additionally, MeHg compensation promoted mitochondrial biogenesis, as evidenced by the activation of the mitochondrial PGC1-α-NRF1-TFAM signalling pathway. Notably, SIRT3/AMPK was activated by MeHg, and the expression and activity of p-AMPK, p-LKB1 and SIRT3 were consistently coordinated. Collectively, these findings provide new insights into the potential molecular mechanisms regulating MeHg-induced cognitive deficits through SIRT3/AMPK MQC network coordination.

Isotope Data Constrains Redox Chemistry of Atmospheric Mercury

The redox chemistry of mercury (Hg) in the atmosphere exerts a significant influence on its global cycle. However, our understanding of this important process remains shrouded in uncertainty. In this study, we utilize three-dimensional atmospheric Hg isotope modeling to evaluate the isotopic composition of particle-bound mercury [HgII(P)] in the global atmosphere. We investigate various chemistry mechanisms and find that they induce remarkably disparate odd-number mass-independent fractionation (odd-MIF) in HgII(P) on a global scale. The observed odd-MIF data identify the essential role of sea salt aerosol debromination in the redox chemistry of atmospheric Hg and underscore the predominant influence of Br oxidation in the marine boundary layer. The odd-MIF signatures significantly narrow the uncertainty range of redox chemistry rates and constrain the photoreduction of HgII(P) at a magnitude of 10-3 JNO2 (local photolysis frequency of NO2) in the global atmosphere. This study advances our understanding of atmospheric Hg chemistry processes and provides insights into the potential impacts of climate change on Hg cycling.

Mercury abatement in the environment: Insights from industrial emissions and fates in the environment

Mercury's neurotoxic effects have prompted the development of advanced control and remediation methods to meet stringent measures for industries with high-mercury feedstocks. Industries with significant Hg emissions, including artisanal and small-scale gold mining (ASGM)-789.2 Mg year-1, coal combustion-564.1 Mg year-1, waste combustion-316.1 Mg year-1, cement production-224.5 Mg year-1, and non-ferrous metals smelting-204.1 Mg year-1, use oxidants and adsorbents capture Hg from waste streams. Oxidizing agents such as O3, Cl2, HCl, CaBr2, CaCl2, and NH4Cl oxidize Hg0 to Hg2+ for easier adsorption. To functionalize adsorbents, carbonaceous ones use S, SO2, and Na2S, metal-based adsorbents use dimercaprol, and polymer-based adsorbents are grafted with acrylonitrile and hydroxylamine hydrochloride. Adsorption capacities span 0.2-85.6 mg g-1 for carbonaceous, 0.5-14.8 mg g-1 for metal-based, and 168.1-1216 mg g-1 for polymer-based adsorbents. Assessing Hg contamination in soils and sediments uses bioindicators and stable isotopes. Remediation approaches include heat treatment, chemical stabilization and immobilization, and phytoremediation techniques when contamination exceeds thresholds. Achieving a substantially Hg-free ecosystem remains a formidable challenge, chiefly due to the ASGM industry, policy gaps, and Hg persistence. Nevertheless, improvements in adsorbent technologies hold potential.

Home-produced eggs: An important pathway of methylmercury exposure for residents in mercury mining areas, southwest China

In light of the documented elevated concentrations of total mercury (Hg) and methylmercury (MeHg) in poultry originating from Hg-contaminated sites, a knowledge gap persists regarding the levels of Hg found in home-produced eggs (HPEs) and the associated dietary exposure risks in regions affected by Hg mining. To address this knowledge gap, a comprehensive investigation was undertaken with the primary objectives of ascertaining the concentrations of THg and MeHg in HPEs and evaluating the potential hazards associated with the consumption of eggs from the Wanshan Hg mining area in Southwest China. The results showed that THg concentrations in HPEs varied within a range of 10.5-809 ng/g (with a geometric mean (GM) of 64.1 ± 2.7 ng/g), whereas MeHg levels spanned from 1.3 to 291 ng/g (GM, 23.1 ± 3.4 ng/g). Remarkably, in half of all eggs, as well as those collected from regions significantly impacted by mining activities, THg concentrations exceeded the permissible maximum allowable value for fresh eggs (50 ng/g). Consumption of these eggs resulted in increased exposure risks associated with THg and MeHg, with GM values ranging from 0.024 to 0.17 µg/kg BW/day and 0.0089-0.066 µg/kg BW/day, respectively. Notably, the most substantial daily dosage was observed among children aged 2-3 years. The study found that consuming HPEs could result in a significant IQ reduction of 34.0 points for the whole mining area in a year. These findings highlight the potential exposure risk, particularly concerning MeHg, stemming from the consumption of local HPEs by residents in mining areas, thereby warranting serious consideration within the framework of Hg exposure risk assessment in mining locales.

Association between mercury exposure and lung function in young adults: A prospective cohort study in Shandong, China

BACKGROUND

Mercury has been associated with many adverse health outcomes. However, limited studies have explored the association between blood mercury concentrations and lung function.

OBJECTIVE

To examine the association between blood mercury concentrations and lung function among young adults.

METHODS

We conducted a prospective cohort study among 1800 college students based on the Chinese Undergraduates Cohort in Shandong, China during August 2019 and September 2020. Lung function indicators including forced vital capacity (FVC, ml), forced expiratory volume in 1 s (FEV₁, ml) and peak expiratory flow (PEF, ml) were collected with a spirometers (Chestgraph Jr. HI-101, Chest M.I., Tokyo, Japan). The blood mercury concentration was measured using inductively coupled plasma mass spectrometry. We divided participants into low (≤25 percentiles), intermediate (25-75 percentiles), and high (≥75 percentile) subgroups according to blood mercury concentrations. The multiple linear regression model was used to examine the associations between blood mercury concentrations and lung function changes. Stratification analyses by sex and fish consumption frequency were also conducted.

RESULTS

The results showed that each 2-fold increase in blood mercury concentrations was significantly associated with -70.75 ml [95 % confidence interval (CI): -122.35, -19.15] change in FVC, -72.68 ml (95%CI: -120.36, -25.00) in FEV₁, and -158.06 ml (95%CI: -283.77, -32.35) in PEF. The effect was more pronounced among participants with high blood mercury and male participants. Participants who consumed fish more than once a week more likely to be affected by mercury.

CONCLUSION

Our study indicated that blood mercury was significantly associated with decreased lung function in young adults. It is necessary to implement corresponding measures to reduce the effect of mercury on the respiratory system, especially for men and people who consumed fish more than once a week.

Embryonic mercury exposure in zebrafish: Alteration of metabolites and gene expression, related to visual and behavioral impairments

The widespread presence of mercury, a heavy metal found in the environment and used in numerous industries and domestic, raises concerns about its potential impact on human health. Nevertheless, the adverse effects of this environmental toxicant at low concentrations are often underestimated. There are emerging studies showing that accumulation of mercury in the eye may contribute to visual impairment and a comorbidity between autism spectrum disorders (ASD) trait and visual impairment. However, the underlying mechanism of visual impairment in humans and rodents is challenging. In response to this issue, zebrafish larvae with a cone-dominated retinal visual system were exposed to 100 nM mercury chloride (HgCl₂), according to our previous study, followed by light-dark stimulation, a social assay, and color preference to examine the functionality of the visual system in relation to ASD-like behavior. Exposure of embryos to HgCl₂ from gastrulation to hatching increased locomotor activity in the dark, reduced shoaling and exploratory behavior, and impaired color preference. Defects in microridges as the first barrier may serve as primary tools for HgCl₂ toxicity affecting vision. Depletion of polyunsaturated fatty acids (PUFAs), linoleic acid, arachidonic acid (ARA), alpha-linoleic acid, docosahexaenoic acid (DHA), stearic acid, L-phenylalanine, isoleucine, L-lysine, and N-acetylputrescine, along with the increase of gamma-aminobutyric acid (GABA), sphingosine-1-phosphate, and citrulline assayed by liquid chromatography-mass spectrometry (LC-MS) suggest that these metabolites serve as biomarkers of retinal impairments that affect vision and behavior. Although suppression of adsl, shank3a, tsc1b, and nrxn1a gene expression was observed, among these tsc1b showed more positive correlation with ASD. Collectively, these results contribute new insights into the possible mechanism of mercury toxicity give rise to visual, cognitive, and social deficits in zebrafish.

Heavy Metals Content in Selected Medicinal Plants Produced and Consumed in Serbia and Their Daily Intake in Herbal Infusions

The heavy metals content (HMs) was investigated in 14 different medicinal plants collected from the three regions in Central Serbia, Zlatar, Sokobanja, and Kopaonik. The concentrations of Cd, Cr, Ni, Hg and Pb were determined: Cd (<0.03-2.72 mg/kg); Cr (<0.08-12.1 mg/kg); Ni (<0.08-12.2 mg/kg); Pb (0.6-49.0 mg/kg); the Hg concentration was below the detection limit of 0.06 mg/kg in all samples. The daily intake of HMs due to ingestion of 200 mL of herbal infusion was in all cases below the recommended limit prescribed by the World Health Organization. The estimated daily intake values were below the values for the oral reference dose regulated by the U.S. Environmental Protection Agency (USA EPA). The target hazard quotient and hazard index for Cd, Cr Ni, and Pb were below 1. Nevertheless, due to the tendency of heavy metals to accumulate in the organism, attention should be paid to the daily intake of herbal infusion during long-term usage. Specifically, it is recommended to consume not more than one cup (200 mL) of infusion per day made from thyme (Mt. Zlatar) and blueberry (Mt. Kopaonik), and not more than two cups per day for other herbs.

Impacts of Mercury Exposure Levels and Sources on the Demethylation of Methylmercury Through Human Gut Microbiota

This study aims to investigate methylmercury (MeHg) demethylation processes in human gut. Here, we determined the compositions and MeHg demethylation rates of gut microbiota in residents from different Hg exposure levels (Wanshan (WS) town and Yangtou (YT) town) and different Hg exposure sources (Zhuchang (ZC) town and YT town) regions. MeHg and inorganic Hg exposure levels in residents of WS town were significantly higher than those of YT and ZC town. Desulfovibrio and Methanogens, which related to Hg methylation/demethylation, showed significantly higher abundance in WS and ZC, comparing with YT. In vitro experiments demonstrated that human intestinal microbiota could degrade MeHg directly. Besides, gut microbiota in WS and ZC exhibited significantly higher demethylation rates than YT, suggesting Desulfovibrio and Methanogens may play important roles in intestinal MeHg demethylation. This study highlights Hg exposure levels and sources may affect demethylation efficiency of gut microbiota, which provides new insights for MeHg demethylation processes in human body.

Mercury pollution in China: implications on the implementation of the Minamata Convention

Mercury (Hg) is a toxic metal released into the environment through human activities and natural processes. Human activities have profoundly increased the amount of Hg in the atmosphere and altered its global cycling since the Industrial Revolution. Gaseous elemental Hg is the predominant form of Hg in the atmosphere, which can undergo long-range transport and atmospheric deposition into the aquatic systems. Hg deposition elevates the methylmercury (MeHg) level in fish through bioaccumulation and biomagnification, which poses a serious human health risk. Acute poisoning of MeHg can result in Minamata disease, while low-level long-term exposure in pregnant women can reduce the intelligence quotient of infants. After five sessions of intergovernmental negotiation, the Minamata Convention on mercury entered into force in August 2017 to protect human health and the environment from Hg pollution. Currently China contributes the largest quantity of Hg production, consumption, and emission globally. However, the status of Hg pollution in the environment in China and its associated health risk remains relatively unknown, which hinders the development of implementation plans of the Minamata Convention. In this paper, we provide a comprehensive review on the atmospheric release of Hg, distribution of air Hg concentration, human exposure to MeHg and health impacts caused by Hg pollution in China. Ongoing improvement of air pollution control measures is expected to further decrease anthropogenic Hg emissions in China. Air Hg concentrations in China are higher than the background values in the Northern Hemisphere, with spatial distribution largely influenced by anthropogenic emissions. Long-term observations of GEM in China show a decline in recent years. The net Hg transport outflow from China in 2013 is estimated to be 511 t year^-1, and ∼60% of such outflow is caused by natural surface Hg emissions. Hg concentrations in fish and rice in China are relatively low and therefore the associated risks of human Hg exposure are low. Future research needs and recommendations for the implementation of the Minamata Convention are also discussed in this paper.

Concentrations, leachability, and health risks of mercury in green tea from major production areas in China

Green tea has many health benefits and is the most consumed type in China. However, the heavy metals and contaminants in tea can also pose a great risk to human health. In this study, mercury (Hg) concentration in green tea collected from 11 provinces in China was examined. The leaching characteristics of Hg during brewing and the associated exposure to drinkers were also evaluated. Results indicated a low potential of Hg accumulation in green tea. The Hg content of green tea from Wanshan District, Guizhou Province-which has the largest Hg mine in China and is severely contaminated by Hg-could be limited by controlling the harvest time of tea leaves. The average Hg content of green tea from 43 tea production sites in China was only 6.3 ± 6.4 µg/kg dry weight. The brewing experiments of green tea showed that the leaching ratio of Hg was 22.61 ± 7.58% for 40 min of a single brew, and increased to 32.83 ± 12.37% after four rounds (3 min/ round) of brewing. The leaching of Hg from tea leaves was significantly affected by leaching time, temperature, and solid-liquid ratio but not by water hardness. The risk of Hg exposure from green tea intake was found to be very low, with an average hazard quotient (HQ) value of only 1.82 ± 1.85% for a single brew in 40 min and 2.64 ± 2.68% after four rounds of brewing. However, in some highly contaminated areas, with HQ values as high as 43.12 ± 2.41%, green tea intake may still pose a high risk of Hg exposure, and this risk should not be ignored.

Microplastics influence on Hg methylation in diverse paddy soils

Microplastics are widespread in estuarine, coastal, and deep sea sediments. The influence of microplastics on mercury (Hg) methylation in paddy soils with different characteristics, however, has not been well reported. In this research, we conducted a microcosmic experiment using red soil and alkaline soil with 2%, 7% and 10% polyvinyl chloride microplastics (PVC-MPs). Diffusive gradients in thin film (DGT) were used to test bioavailable Hg²⁺ and bioavailable methylmercury (MeHg) in soils. Results showed that PVC-MPs could decrease bioavailable MeHg concentrations both in red soil and alkaline soil. We demonstrated that these decreases could be due to three possible mechanisms: (1) PVC-MPs affected DOM composition, which resulted in a difference in combining capacity for bioavailable Hg²⁺; (2) PVC-MPs decreased MeHg via changing soil properties (including sulfate and dissolved Fe); (3) PVC-MPs affected the abundance of Proteobacteria, Firmicutes, and hgcA gene in soils. Our results emphasized the significance of investigating effects of microplastics on specific contaminants to implement effective environmental remediation strategies in polluted paddy soils.

A new method of predicting the contribution of TGM to Hg in white rice: Using leaf THg and implications for Hg risk control in Wanshan Hg mine area

Rice plants accumulate Hg from the soil and ambient air, however, evaluating the contribution of Hg from these two sources remains challenging. Here, we proposed a practical method to predict the contribution of total gaseous mercury (TGM) to Hg in white rice in Wanshan Hg mine area (WMM). In this study, rice was planted in the same low-Hg soil at different sites of WMM with varying TGM levels. Comparing to the control sites at IG (Institute of Geochemistry, Guiyang), TGM is the dominant source of Hg in rice leaves and white rice at TB (Tianba) and ZJW (Zhangjiawan) sites of WMM. Subsequently, a good correlation between the Hg concentrations in rice leaves and the concentration contributions of TGM to Hg in white rice was obtained. Such a correlation enabled feasible quantification of the contribution of TGM to Hg in white rice collected from the Wanshan Hg mine. The contribution of TGM to Hg in white rice across the WMM area was also estimated, demonstrating that white rice receives 14-83% of Hg from the air. Considering the high contribution of TGM to Hg in white rice, we compared the relative health risks of Hg via inhalation and rice consumption and found that inhalation, rather than rice consumption, was the major pathway for bioaccessible Hg exposure in adults at high-TGM sites. This study provides new knowledge of Hg biogeochemistry in Hg-mining areas.

High variability of mercury content in the hair of Russia Northwest population: the role of the environment and social factors

PURPOSE

The purpose of this work is to study mercury levels in the hair of different social and demographic groups of the population of the Vologda region in Northwest Russia. This region is selected due to a heterogeneous distribution of rivers and lakes-a resource base for fishing.

METHODS

The mercury content was determined in the hair from the root with a length of about 2 cm. The concentration of total mercury in human hair was determined by the atomic absorption method without preliminary sample preparation using an RA-915M mercury analyzer and a PYRO-915 + pyrolysis unit.

RESULTS

The average level of mercury in the human hair was 0.445 μg/g (median 0.220 μg/g). The concentration of mercury in the hair of people older than 44 years (0.875 μg/g) was three times higher than in the hair of children under 18 years of age (0.270 μg/g). People who eat fish less than once per month had a hair mercury concentration of 0.172 μg/g, for 1-2 times a month 0.409 μg/g, once a week 0.555 μg/g, and several times a week 0.995 μg/g. The concentration of mercury in the hair of smokers (0.514 μg/g) was higher than in the hair of non-smokers (0.426 μg/g).

CONCLUSION

Significantly higher concentrations of mercury were observed in the hair of participants from the western part of the region, where reservoirs are the main commercial sources of fish products. The data showed that the main source of people's mercury intake was fish.

Fish, rice, and human hair mercury concentrations and health risks in typical Hg-contaminated areas and fish-rich areas, China

Human exposure to methylmercury (MeHg) from consuming contaminated fish has been a major concern for decades. Besides, human MeHg exposure through rice consumption has been recently found to be important in some Asian countries. China is the largest country on mercury (Hg) production, consumption, and anthropogenic emission. However, the health risks of human Hg exposure are not fully understood. A total of 624 fish, 299 rice, and 994 human hair samples were collected from typical Hg-contaminated areas and major fish-rich areas to assess the health risks from human Hg exposure in China. Fish and rice samples showed relatively low Hg levels, except the rice in the Wanshan Hg mining area (WMMA). Human hair total Hg (THg) and MeHg concentrations were significantly elevated in WMMA, Zhoushan (ZS), Xiamen (XM), Qingdao (QD), and zinc smelting area (ZSA), and 85% of hair samples in WMMA, 62% in ZS, 40% in XM, 26% in QD, and 17% in ZSA had THg concentrations exceeding the limit set by the USEPA (1 μg/g). Rice consumption was the main pathway (>85%) for human MeHg exposure in the studied Hg-contaminated areas. Meanwhile, fish was the primary human MeHg exposure source (>85%) in coastal cities. Therefore, soil remediation in typical Hg-contaminated areas and scientific guidance for fish consumption in coastal provinces are urgently needed to reduce the health risks from human Hg exposure in China.

Neurodevelopment and exposure to neurotoxic metal(loid)s in environments polluted by mining, metal scrapping and smelters, and e-waste recycling in low and middle-income countries

This review covers a wide body of literature to gain an understanding of the impacts of informal activities related to metal extraction (primary mining and recycling) on early life exposure to neurotoxicants and on neurodevelopment. In primary mining, gold extraction with Hg amalgamation is the main environmental cause of Hg pollution in most artisanal small-scale gold mining (ASGM) activities around the world. Nevertheless, in Sub-Saharan Africa (SSA), Pb disrupted from gold-related ores, mining, and artisanal cookware production are an important neurotoxicant that seriously contaminates the affected population, with devastating effects on children. In e-waste recycling settings, the range of neurotoxic substances that contaminate mothers and children is wider than in primary mining environments. Thus, Hg and Pb are major pre- and postnatal neurotoxicants affecting children in the informal metal extraction activities and SSA countries show the highest record of human contamination and of neurotoxic effects on children. There are additional sources of neurotoxic contamination from mining and metal processing activities (cyanide tailing in South America and SSA) and/or co-exposure to Hg-containing products such as cosmetics (soaps and Hg-based skin lightning creams in Africa) and pediatric Thimerosal-containing vaccines (TCVs, that breaks down to ethyl-mercury) in current use in middle and low income countries. However, the action of these neurotoxicants (per se or in combination) on children needs more attention and research. Studies show a negative association between biomarkers of all environmental metal(loid)s (As, Cd, Hg, Mn, and Pb) studied and neurodevelopment in young children. Sadly, in many unregulated activities, child labor is widely employed, thus presenting an additional occupational exposure. Children living in polluted environments related to metal processing are disproportionately exposed to a wide range of co-occurring neurotoxic substances. The review showed compelling evidence from highly representative parts of the world (Africa, Asia, and Latin America) that the studied neurotoxic substances negatively affected areas of the brain associated with language, memory and executive function, as well as psychosocial behavior. Protecting the environment and children from unregulated and highly polluting metal extraction and processing are inextricably intertwined and deserve urgent attention.

Global distribution and environmental drivers of methylmercury production in sediments

Neurotoxic methylmercury (MeHg) in environments poses substantial risks to human health. Saturated sediments are basic sources of MeHg in food chains; however, distribution patterns and environmental drivers of MeHg at a global scale remain largely unexplored. Here, we characterized global patterns of MeHg distribution and environmental drivers of MeHg production based on 495 sediment samples across five typical ecosystems from the literature (1995-2018) and our own field survey. Our results showed the MeHg concentration ranged from 0.009 to 55.7 μg kg^-1 across the different ecosystems, and the highest MeHg concentration and Hg methylation potential were from the sediments of paddy and marine environments, respectively. Further, using combined analysis of random forest and structural equation modeling, we identified temperature and precipitation as important regulators of MeHg production after accounting for the well-known drivers including Hg availability and sediment geochemistry. More importantly, we found increased MeHg production in sediments with elevated mean annual Hg precipitation, and warmer temperature could also accelerate MeHg production by facilitating activities of microbial methylators. Together, this work advances our understanding of global MeHg distribution in sediments and environmental drivers, which are fundamental to the prediction and management of MeHg production and its potential health risk globally.

Phytoremediation and Microorganisms-Assisted Phytoremediation of Mercury-Contaminated Soils: Challenges and Perspectives

Mercury (Hg) pollution is a global threat to human and environmental health because of its toxicity, mobility and long-term persistence. Although costly engineering-based technologies can be used to treat heavily Hg-contaminated areas, they are not suitable for decontaminating agricultural or extensively-polluted soils. Emerging phyto- and bioremediation strategies for decontaminating Hg-polluted soils generally involve low investment, simple operation, and in situ application, and they are less destructive for the ecosystem. Current understanding of the uptake, translocation and sequestration of Hg in plants is reviewed to highlight new avenues for exploration in phytoremediation research, and different phytoremediation strategies (phytostabilization, phytoextraction and phytovolatilization) are discussed. Research aimed at identifying suitable plant species and associated-microorganisms for use in phytoremediation of Hg-contaminated soils is also surveyed. Investigation into the potential use of transgenic plants in Hg-phytoremediation is described. Recent research on exploiting the beneficial interactions between plants and microorganisms (bacteria and fungi) that are Hg-resistant and secrete plant growth promoting compounds is reviewed. We highlight areas where more research is required into the effective use of phytoremediation on Hg-contaminated sites, and conclude that the approaches it offers provide considerable potential for the future.