Total mercury and methylmercury in the soil and vegetation of a riparian zone along a mercury-impacted reservoir

Factors controlling methylmercury concentration in soils of Northern Poland

Soil acts as storage for many toxic substances, including mercury and its compounds. However, in addition to its storage function, soil can also be a source of many substances to the aquatic environment. Methylmercury (MeHg) is one of the most toxic form of mercury (Hg) present in the environment. Some studies consider Poland to be one of the major emitters of Hg into both the atmosphere and the Baltic Sea. The purpose of the study was to identify factors affecting the formation and retention of MeHg in the soil as well as it remobilization to the river. Fifteen soil core samples with a length of 200 cm were collected during the fall/winter of 2021-2022. The factors responsible for the inflow and formation of MeHg were precipitation, distance from the riverbank, soil moisture and age of organic matter. MeHg can be transported to topsoil with precipitation. An increase in MeHg concentration was also observed in moist soils located in the vicinity of riverbank. MeHg concentration was lower in soils with degraded organic matter than with fresh organic matter.

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.

A high-throughput, straightforward procedure for biomonitoring organomercury species in human hair

Mercury is a pervasive and concerning pollutant due to its toxicity, mobility, and tendency to biomagnify in aquatic and terrestrial ecosystems. Speciation analysis is crucial to assess exposure and risks associated with mercury, as different mercury species exhibit varying properties and toxicities. This study aimed at developing a selective detection method for organic mercury species in a non-invasive biomonitoring matrix like human hair. The method is based on frontal chromatography (FC) in combination with inductively coupled plasma mass spectrometry (ICP-MS), using a low pressure, homemade, anion exchange column inserted in a standard ICP-MS introduction system, without requiring high-performance liquid chromatography (HPLC) hyphenation. In addition to the extreme simplification and cost reduction of the chromatographic equipment, the proposed protocol involves a fast, streamlined and fully integrated sample preparation process (in contrast to existing methods): the optimized procedure features a 15-min ultrasonic assisted extraction procedure and 5 min analysis time. Consequently, up to 100 samples could be analyzed daily, making the method highly productive and suitable for large-scale screening programs in public and environmental health. Moreover, the optimized procedure enables a limit of detection (LOD) of 5.5 μg/kg for a 10 mg hair microsample. All these features undeniably demonstrate a significant advancement in routine biomonitoring practices. To provide additional evidence, the method was applied to forty-nine human hair samples from individuals with varying dietary habits successfully finding a clear correlation between methylmercury levels (ranging from 0.02 to 3.2 mg/kg) in hair and fish consumption, in line with previous literature data.

Multimedia fate simulation of mercury in a coastal urban area based on the fugacity/aquivalence method

Due to intensive industrial production and living activities, urban areas are the main anthropogenic mercury (Hg) emission sources. After entering the environment through exhaust gases, wastewater or waste residues, Hg can migrate and transform among different environmental compartments in various species, such as elemental mercury (Hg0), divalent mercury (Hg2+) and methylmercury (MeHg). Studies have yet to report on the multimedia behaviors of Hg in urban areas due to the complexity of the processes involved. In this study, the atmospheric Hg emission in Dalian, a coastal city in Northeast China, was estimated by an anthropogenic emission inventory, and a Level III multimedia model was constructed based on the fugacity/aquivalence method to simulate the fate of Hg in air, water, soil, sediment, vegetation and film. The total annual atmospheric emission was 9.91 t, of which coal combustion and non-coal sources accounted for 70.1 % and 29.9 %, respectively. Atmospheric emission and advection were dominated by Hg0, and aquatic emission and advection were dominated by Hg2+. The migration of air-vegetation, vegetation-soil and soil-air were three important pathways of Hg in urban areas. The model was validated by collecting local soil and vegetation samples and regional air, seawater and sediment monitoring data. The scenario simulation indicated that the local load would decrease to different extents with a 21.0 % reduction in atmospheric Hg emission by implementing the "coal-to-gas" measures. Our developed model can characterize the fate of Hg in coastal urban areas and provide a reference for control strategies.

Mercury transformations in algae, plants, and animals: The occurrence, mechanisms, and gaps

Mercury (Hg) is a global pollutant showing potent toxicity to living organisms. The transformations of Hg are critical to global Hg cycling and Hg exposure risks, considering Hg mobilities and toxicities vary depending on Hg speciation. Though currently well understood in ambient environments, Hg transformations are inadequately explored in non-microbial organisms. The primary drivers of in vivo Hg transformations are far from clear, and the impacts of these processes on global Hg cycling and Hg associated health risks are not well understood. This hinders a comprehensive understanding of global Hg cycling and the effective mitigation of Hg exposure risks. Here, we focused on Hg transformations in non-microbial organisms, particularly algae, plants, and animals. The process of Hg oxidation/reduction and methylation/demethylation in organisms were reviewed since these processes are the key transformations between the dominant Hg species, i.e., elemental Hg (Hg0), divalent inorganic Hg (IHgII), and methylmercury (MeHg). By summarizing the current knowledge of Hg transformations in organisms, we proposed the potential yet overlooked drivers of these processes, along with potential challenges that hinder a full understanding of in vivo Hg transformations. Knowledge summarized in this review would help achieve a comprehensive understanding of the fate and toxicity of Hg in organisms, providing a basis for predicting Hg cycles and mitigating human exposure.

Human Health Risk Assessment from Mercury-Contaminated Soil and Water in Abu Hamad Mining Market, Sudan

Artisanal and small-scale gold mining (ASGM) poses a significant global threat due to mercury emissions and resulting health hazards. This study focuses on assessing these risks in the Abu Hamad ASGM community in Sudan. Utilizing the Mercury Analyzer 3000 (NIC), analyses of twelve soil samples (including one tailings sample) and seven water samples revealed the highest concentrations near amalgam burning locations: 34.8 mg/kg in soil (S06) and 3.26 µg/L in water (W03). Concentrations decrease with distance, with soil near burning exceeding tailings (S05 = 19.0 mg/kg). Hazard quotients indicate mercury vapor inhalation as the primary exposure route from soil, with the Hazard Index reaching 5.34 for adults and 33.4 for children close to amalgam burning sites. Water samples generally pose little risk except for W03, where children face potential danger via ingestion (HI = 1.74). These findings emphasize the urgent need for adopting retorts and eco-friendly practices to reduce mercury emissions and protect ASGM communities.

Differentially-expressed genes related to glutathione metabolism and heavy metal transport reveals an adaptive, genotype-specific mechanism to Hg2+ exposure in rice (Oryza sativa L.)

Rice consumption is an essential cause of mercury (Hg) exposure for humans in Asia. However, the mechanism of Hg transport and accumulation in rice plants (Oryza sativa L.) remains unclear. Here, rice genotypes with contrasting Hg uptake and translocation abilities, i.e. H655 (high Hg-accumulator) and H767 (low Hg-accumulator), were selected from 261 genotypes. Through comparative physiological and transcriptome analyses, we investigated the processes responsible for the relationship between Hg accumulation, transport and tolerance. The results showed significant stimulation of antioxidative metabolism, particularly glutathione (GSH) accumulation, and up-regulated expression of regulatory genes of glutathione metabolism for H655, but not for H767. In addition, up-regulated expression of GSH S-transferase (GST) and OsPCS1 in H655 that catalyzes the binding of Hg and GSH, enhances the Hg detoxification capacity, while high-level expression of YSL2 in H655 enhances the transport ability for Hg. Conclusively, Hg accumulation in rice is a consequence of enhanced expression of genes related to Hg binding with GSH and Hg transport. With these results, the present study contributes to the selection of rice genotypes with limited Hg accumulation and to the mitigation of Hg migration in food chains thereby enhancing nutritional safety of Hg-polluted rice fields.

Effect of peat and thiol-modified peat application on mercury (im)mobilization in mercury-polluted paddy soil

Mercury (Hg) pollution in paddy soil has gained special attention because methylmercury (MeHg) can accumulate in rice grains. Therefore, there is an urgent need to explore the remediation materials of mercury-polluted paddy soil. In this study, herbaceous peat (HP), peat moss (PM), and thiol-modified HP/PM (MHP/MPM) were selected to investigate the effects and probable mechanism of their application on Hg (im)mobilization in mercury-polluted paddy soil through pot experiments. The results showed that HP, PM, MHP and MPM addition increased MeHg concentrations in the soil, indicating that the addition of peat and thiol-modified peat might increase the exposure risk of MeHg in soil. The addition of HP could significantly decrease the total mercury (THg) and MeHg concentrations in rice, with average reduction efficiencies of 27.44% and 45.97%, respectively, while adding PM slightly increased the THg and MeHg concentrations in rice. In addition, the addition of MHP and MPM significantly decreased the bioavailable Hg concentrations in the soil and THg and MeHg concentrations in rice, with reduction efficiencies of rice THg and MeHg of 79.14∼93.14% and 82.72∼93.87%, respectively, indicating that thiol-modified peat had good remediation potential. The possible mechanism is that Hg can bind with thiols in MHP/MPM and form steady compounds in the soil, reducing Hg mobility in the soil and inhibiting its uptake by rice. Our study showed the potential value of HP, MHP and MPM addition for Hg remediation. Additionally, we must weigh the pros and cons when adding organic materials as remediation agents to mercury-polluted paddy soil.

Extremely Elevated Total Mercury and Methylmercury in Forage Plants in a Large-Scale Abandoned Hg Mining Site: A Potential Risk of Exposure to Grazing Animals

Ninety-five wild forage plants (belonging to 22 species of 18 families) and their corresponding rhizosphere soil samples were collected from wastelands of a large-scale abandoned Hg mining region for total Hg (THg) and methylmercury (MeHg) analysis. The forage plant communities on the wastelands were dominated by the Asteraceae, Crassulaceae, and Polygonaceae families. The THg and MeHg concentrations in the forage plants varied widely and were in the range of 0.10 to 13 mg/kg and 0.19 to 23 μg/kg, respectively. Shoots of Aster ageratoides showed the highest average THg concentration of 12 ± 1.1 mg/kg, while those of Aster subulatus had the highest average MeHg concentrations of 7.4 ± 6.1 μg/kg. Both the THg and MeHg concentrations in the aboveground plant parts exhibited positive correlations with the THg (r = 0.70, P < 0.01) and MeHg (r = 0.68, P < 0.01) concentrations in the roots; however, these were not correlated with the THg and MeHg concentrations in their rhizosphere soils. The species A. ageratoides, A. subulatus, and S. brachyotus showed strong accumulation of Hg and are of concern for herbivorous/omnivorous wildlife and feeding livestock. Taking the provisional tolerable weekly intake (PTWI) values for IHg recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA in Summary and conclusions of the seventy-second meeting of the joint FAO/WHO expert committee on food additives Rome, Italy, 2010) for human dietary exposure of 4 ng/g into account, the daily intake of IHg by a 65 kg animal grazing on 1.0 kg of forage (dry weight) would be between 190 and 13,200 μg, three to five orders of magnitude higher than the permitted limit, suggesting a potential risk of exposure.