Hg Pollution Research Articles

Two-century sediment records of atmospheric mercury variations in North China and their relations with regional and global emissions.

Sedimentary mercury (Hg) records from remote areas are significant for revealing historical variations of regional Hg and understanding the influence of regional and global Hg emissions. In this study, sediment cores were retrieved from two subalpine lakes in Shanxi Province in North China and employed to reconstruct atmospheric Hg variations over the last two centuries. The two records show similar anthropogenic Hg fluxes and evolution trends, corresponding with that they were affected mainly by regional atmospheric Hg deposition. Before ~1950, the records show negligible Hg pollution signals. Atmospheric Hg in the region had increased rapidly since the 1950s, lagged more than a half-century compared to the global Hg. This indicates that they were seldom affected by Hg emissions dominated by Europe and North America after the industrial revolution. The Hg increases since the 1950s in the two records corresponded well with rapid industrial developments in and around Shanxi Province after the founding of the China, implying the dominant contribution of domestic Hg emissions. By comparing other Hg records, we find that widespread increases in atmospheric Hg in China likely occurred post ~1950. This study rouses to re-examine historical variations in atmospheric Hg at various settings, which is significant to understanding global Hg cycling in the industrial era.

Sequential Capture of Gaseous Hg0 in Flue Gas and Aqueous Hg2+ in Desulfurization Solution by Cu–ZnS: Mechanisms, Kinetics, and Its Application in Hg Recovery as a Supplement of Selective Catalytic Reduction + Wet Flue Gas Desulfurization

The combined technology of selective catalytic reduction and wet flue gas desulfurization (SCR + WFGD) to control Hg0 emissions from coal-fired flue gas is often unsatisfactory due to the undesired Hg0 oxidation efficiency of SCR, the re-emission of Hg0 from WFGD, and the potential secondary pollution. To offset the shortcomings of SCR + WFGD, Cu–ZnS that resulted from Cu2+ activation of natural sphalerite was developed as a difunctional sorbent to sequentially capture gaseous Hg0 in flue gas and aqueous Hg2+ in desulfurization solution. Not only did Cu–ZnS exhibit significant performance in capturing the gaseous Hg0 downstream of an electrostatic precipitator, but it also displayed a superior ability in capturing aqueous Hg2+. Hg0 re-emission from WFGD, which resulted from the reduction of aqueous Hg2+ by SO2, was completely suppressed because Cu–ZnS could adsorb both aqueous Hg2+ and re-emitted Hg0 in desulfurization solution. Spent Cu–ZnS containing Hg can be separated from the desulfurization slurry via flotation for Zn smelting, and adsorbed Hg can be at last recovered as mainly liquid Hg0 in modern smelters for centralized control. Therefore, the sequential capture of gaseous Hg0 and aqueous Hg2+ by Cu–ZnS may be an economically viable and eco-friendly technology to control Hg pollution of coal-fired power plants.

Using multi-technology to characterize transboundary Hg pollution in the largest presently active Hg deposit in China.

ActiveHgmines are primary sources ofHgcontamination in the environment of mining districts and surrounding areas. Alleviation of Hg pollution requires knowledge of pollution sources, migration, and transform pathways across various environmental media. Accordingly, the Xunyang Hg-Sb mine, the largest active Hg deposit in China, presently was selected as the study area. GIS, TIMA, EPMA, μ-XRF, TEM-EDS, and Hg stable isotopes were adopted to investigate the spatial distribution, mineralogical characteristics, in situ microanalysis, and pollution sources of Hg in the environment medium at the macro- and micro-levels. The total Hg concentration in samples showed a regional distribution, with higher levels in areas close to the mining operations. The in situ distribution of Hg in soil was mainly associated with the mineralogical phases of quartz, and Hg was also correlated with Sb and S. Hg was also found to be rich mainly in quartz minerals in the sediment and showed different distributions of Sb. Hg hotspots had S abundances and contained no Sb and O. The contributions from the anthropogenic sources to soil Hg were estimated to be 55.35%, among which 45.97% from unroasted Hg ore and 9.38% from tailing. Natural input of soil Hg due to pedogenic processes accounted for 44.65%. Hg in corn grain was mainly derived from the atmosphere. This study will provide a scientific basis for assessing the current environmental quality in this area and minimizing further impacts that affect the nearby environmental medium.

Evaluation and Source Analysis of Soil Heavy Metal Pollution in a Planting Area in Wanquan District, Zhangjiakou City

Taking the soil of a vegetable planting area in Wanquan District of Zhangjiakou City as the research object, 132 surface and 80 deep soil samples were collected to test and analyze the contents of eight heavy metals such as As, Cd, Cr, Hg, Cu, Ni, Pb, and Zn and the occurrence forms of Cr and Ni. By applying geostatistical analysis and the PMF receptor model and combining three heavy metal pollution evaluation methods, the spatial distribution characteristics of soil heavy metals in the study area, the degree of heavy metal pollution, and the distribution of Cr and Ni fugitive forms in the vertical layer were clarified, and the sources and contribution rates of soil heavy metal pollution were analyzed. The results showed that the average contents of Cd and Pb in surface soils were higher than the background values of soils in Hebei Province, and the spatial distribution characteristics of Cr, Ni, Cu, Cd, Pb, and Zn in surface soils were similar. The ground accumulation index method showed that the study area was mainly free of pollution, with a small number of lightly polluted sites, and most of them were polluted with Cd. The enrichment factor method showed that the study area was mainly free-weakly polluted, with medium pollution of all elements; the significantly polluted elements in the background area were As, Pb, and Hg, and the significantly polluted element in the key area was Cd. The potential ecological risk index method showed that the study area was mainly lightly polluted, with local distribution. The potential ecological risk index method showed that the study area was mainly lightly polluted, with a local distribution of "medium" and "strong" risk points, with "very strong" risk points for Hg in the background area and "very strong" risk points for Cd in the focus area. These three evaluation results indicated that the background area was dominated by Cd and Hg pollution, whereas the focus area was dominated by Cd pollution. The study on the fugitive morphology of vertical soil showed that Cr was dominated by the residue state (F4) and supplemented by the oxidizable state (F3), and the vertical direction was dominated by the surface aggregation type and supplemented by the weak migration type. Ni was dominated by the residue state (F4) and supplemented by the reducible state (F2), and the vertical direction was dominated by the strong migration type and supplemented by the weak migration type. The sources of heavy metals in the surface soil were divided into three categories; Cr, Cu, and Ni were mainly from natural geological background sources. The contributions of Cr, Cu, and Ni were 66.9%, 66.9%, and 76.1%, respectively. As, Cd, Pb, and Zn were mainly from anthropogenic sources, with contributions of 77.38%, 59.2%, 83.5%, and 59.5%, respectively. Hg was mainly from dry and wet atmospheric deposition, with a contribution of 87.8%.

Pollution Characteristics and Risk Assessment of Heavy Metals in Surface Dusts and Surrounding Green Land Soils from Yellow River Custom Tourist Line in Lanzhou

In order to investigate the contamination levels of dust and its surrounding green land soil heavy metal pollution and potential ecological and health risks in the scenic areas of urban waterfront parks, the gardens, squares, and theme parks of the Yellow River Custom Tourist Line in Lanzhou were selected as the research area, using 27 dust samples and 26 soil samples from its surrounding green lands. The contamination characteristics and potential ecological risks of eight heavy metals (Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb) were evaluated using the geo-accumulation index (Igeo), single-factor pollution index (Pi), Nemerow integrated pollution index (PN), and improved potential ecological risk index (RI). The human health risk assessment was also evaluated using the exposure risk model. The results showed that the average concentrations of the other heavy metals in the surface dusts were higher than the background values of Gansu Province and Lanzhou City, except that the As mean concentrations in the surface dusts and the surrounding green land soils were slightly lower than the Gansu Province background values. For its surrounding green land soils, the mean concentrations of the other heavy metals (Cu, Zn, Cd, Hg, and Pb) exceeded the soil background values of Gansu Province and Lanzhou City, whereas the Cr and Ni mean concentrations were lower than their corresponding soil background values of Gansu Province and Lanzhou City. The geo-accumulation and single-factor pollution indices demonstrated that a slight to moderate pollution of Cr, Cu, Zn, Cd, Hg, and Pb occurred in surface dusts, and Cu, Zn, Cd, Hg, and Pb appeared in varying degrees of contamination levels in its surrounding green land soils. The Nemerow integrated pollution index analysis manifested that the overall contamination status of the study areas was between slightly and heavily polluted. The potential ecological risk index suggested that Cd and Hg were recognized as significant pollutant elements and that the RI of the other heavy metals were all below 40, presenting slight ecological risk. The health risk assessment indicated that ingestion was the dominant exposure pathway for heavy metals from the surface dusts and the surrounding green land soils, and no carcinogenic and noncarcinogenic risks posed threats to adults and children.

Characteristics of total gaseous mercury at a tropical megacity in Vietnam and influence of tropical cyclones

Southeast Asia (SEA) has been suggested as a hotspot of mercury (Hg) emission worldwide but research on atmospheric Hg remains scarce in this region. This study reported monitoring data of total gaseous mercury (TGM) at Ho Chi Minh City (HCMC), a tropical megacity in SEA. TGM was measured over a 6-month period (June–November) in 2022 during two distinct monsoon seasons in HCMC. The average TGM concentration at HCMC was 1.89 ± 0.55 ng m−3 being comparatively lower than other sites in East Asia. For seasonal variation, changes in air mass origins resulted in a nearly 50% more elevated TGM concentration during October–November (2.47 ± 0.56 ng m−3) as compared to June–September (1.71 ± 0.40 ng m−3). Meanwhile, planetary boundary height and anthropogenic activities were responsible for TGM diurnal variation. Both backward trajectory and PSCF analysis revealed East Asian outflow as an important factor contributing to higher TGM levels at the sampling site. This study identified two instances of tropical cyclones affecting HCMC. For the event in July, TGM concentrations decreased due to the increases in atmospheric disturbances and the contribution of marine air masses. On the other hand, for the event in October, the increase in TGM concentration was possibly due to the enhancement export of polluted air mass from continental East Asia, induced by the tropical cyclone. This study provided valuable atmospheric Hg data in SEA, propose further insight into regional Hg understanding and suggest the impact of monsoon influence on local and regional Hg pollution.

Reduced Antibiotic Resistance in the Rhizosphere of Lupinus albus in Mercury-Contaminated Soil Mediated by the Addition of PGPB.

The emergence of antibiotic resistance (AR) poses a threat to the "One Health" approach. Likewise, mercury (Hg) pollution is a serious environmental and public health problem. Its ability to biomagnify through trophic levels induces numerous pathologies in humans. As well, it is known that Hg-resistance genes and AR genes are co-selected. The use of plant-growth-promoting bacteria (PGPB) can improve plant adaptation, decontamination of toxic compounds and control of AR dispersal. The cenoantibiogram, a technique that allows estimating the minimum inhibitory concentration (MIC) of a microbial community, has been postulated as a tool to effectively evaluate the evolution of a soil. The present study uses the metagenomics of 16S rRNA gene amplicons to understand the distribution of the microbial soil community prior to bacterial inoculation, and the cenoantibiogram technique to evaluate the ability of four PGPB and their consortia to minimize antibiotic resistance in the rhizosphere of Lupinus albus var. Orden Dorado grown in Hg-contaminated soils. Results showed that the addition of A1 strain (Brevibacterium frigoritolerans) and its consortia with A2, B1 and B2 strains reduced the edaphic community´s MIC against cephalosporins, ertapenem and tigecycline. The metagenomic study revealed that the high MIC of non-inoculated soils could be explained by the bacteria which belong to the detected taxa,. showing a high prevalence of Proteobacteria, Cyanobacteria and Actinobacteria.

Polyethyleneimine (PEI) and Chitosan (CS) grafted with L-cysteine were used as effective materials for Hg(II) adsorption

Naturally derived polymer materials have attracted extensive attention due to their abundant and environmentally friendly characteristics, and have been modified by more and more scholars to meet specific properties. As a global pollutant that seriously affects human health and ecosystems, Hg(II) is posing a great threat to human and environmental safety. Therefore, it is of great practical significance and commercial value to develop cheap, easily available and excellent Hg(II) adsorbent materials. In this paper, two kinds of effective porous materials for Hg(II) adsorption were successfully prepared by using the water-soluble polymer polyethyleneimine(PEI) and chitosan(CS) as raw materials and modified with L-cysteine(L-Cys), which is simple in structure and environmentally friendly. The maximum Hg(II) adsorption capacities of PEI-Cys and CS-Cys were 231.2 mg/g and 407.4 mg/g. This work provides a new and reliable idea for the practical application of Hg(II) pollution removal.

Integrating multiple indices based on heavy metals and macrobenthos to evaluate the benthic ecological quality status of Laoshan Bay, Shandong Peninsula, China

Many different indices have been developed to evaluate habitat quality status (EcoQs) in marine ecosystems; however, few studies have concurrently considered both abiotic and biotic indices in their assessments of benthic EcoQs. Here, we propose and test a framework for integrating heavy metal pollution-related indices and macrobenthos-based indices to assess the benthic EcoQs of Laoshan Bay (Yellow Sea, China). This bay is exposed to urbanization, construction, heavy metal pollution, and land- and marine-based culturing operations for commercially valuable species like fish, scallop, and laver (seaweed). We first assessed the EcoQs of Laoshan Bay using four heavy metal pollution-related indices, i.e., the geo-accumulation index (Igeo), potential ecological risk index (RI), pollution load index (PLI), and Nemerow pollution index (Pn) and four macrobenthos-based indices, i.e., AZTI's Marine Biotic Index (AMBI), the multivariate AMBI (M−AMBI), BENTIX, and the feeding evenness index (jFD). All indices (except Igeo) were then reclassified and combined to assess the overall EcoQs of Laoshan Bay. Our results show that, while some sites in Laoshan Bay have relatively high levels of heavy metal (Hg and Cd) pollution, the benthic EcoQs is acceptable across 88.90% of the bay. Kappa analysis showed that the agreement between any two indices was very low, which suggests that the composite index used here may be more robust for assessing EcoQs and more closely represent the actual status of benthic habitats than assessments based on single indices. In addition, the assessment framework proposed here is relatively flexible and can serve as a useful tool for evaluating the benthic EcoQs of similar marine ecosystems.

Tree Rings Record of Long-Term Atmospheric Hg Pollution in the Monte Amiata Mining District (Central Italy): Lessons from the Past for a Better Future

Trees may represent useful long-term monitors of historical trends of atmospheric pollution due to the trace elements stored along the tree rings caused by modifications in the environment during a tree’s life. Chestnut (Castanea sativa Mill.) tree trunk sections were used to document the yearly evolution of atmospheric Hg in the world-class mining district of Monte Amiata (MAMD; Central Italy) and were exploited until 1982. An additional source of Hg emissions in the area have been the active geothermal power plants. A marked decrease (from >200 µg/kg to <100 µg/kg) in Hg contents in heartwood tree rings is recorded, likely because of mine closure; the average contents (tens of µg/kg) in recent years remain higher than in a reference area ~150 km away from the district (average 4.6 µg/kg). Chestnut barks, recording present-day Hg pollution, systematically show higher Hg concentrations than sapwood (up to 394 µg/kg in the mining area). This study shows that tree rings may be a good record of the atmospheric Hg changes in areas affected by mining activity and geothermal plants and can be used as a low-cost biomonitoring method for impact minimization and optimal resource and land management.

Mercury Biogeochemical Cycle in Yanwuping Hg Mine and Source Apportionment by Hg Isotopes.

Although mercury (Hg) mining activities in the Wanshan area have ceased, mine wastes remain the primary source of Hg pollution in the local environment. To prevent and control Hg pollution, it is crucial to estimate the contribution of Hg contamination from mine wastes. This study aimed to investigate Hg pollution in the mine wastes, river water, air, and paddy fields around the Yanwuping Mine and to quantify the pollution sources using the Hg isotopes approach. The Hg contamination at the study site was still severe, and the total Hg concentrations in the mine wastes ranged from 1.60 to 358 mg/kg. The binary mixing model showed that, concerning the relative contributions of the mine wastes to the river water, dissolved Hg and particulate Hg were 48.6% and 90.5%, respectively. The mine wastes directly contributed 89.3% to the river water Hg contamination, which was the main Hg pollution source in the surface water. The ternary mixing model showed that the contribution was highest from the river water to paddy soil and that the mean contribution was 46.3%. In addition to mine wastes, paddy soil is also impacted by domestic sources, with a boundary of 5.5 km to the river source. This study demonstrated that Hg isotopes can be used as an effective tool for tracing environmental Hg contamination in typical Hg-polluted areas.

High and diurnally fluctuating carbon dioxide exposure produces lower mercury toxicity in a marine copepod

Coastal waters have experienced fluctuations in partial pressure of carbon dioxide (pCO2) and mercury (Hg) pollution, yet little is known concerning how natural pCO2 fluctuations affect Hg biotoxicity. Here, a marine copepod Tigriopus japonicus was interactively exposed to different seawater pCO2 (ambient 400, steady elevated 1000, and fluctuating elevated 1000 ± 600 μatm) scenarios and Hg (control, 2 μg/L) treatments for 7 d. The results showed that elevated pCO2 decreased Hg bioaccumulation, and it was even more under fluctuating elevated pCO2 condition. We found energy depletion and oxidative stress under Hg-treated copepods, while combined exposure initiated compensatory response to alleviate Hg toxicity. Intriguingly, fluctuating acidification presented more immune defense related genes/processes in Hg-treated copepods when compared to steady acidification, probably linking with the greater decrease in Hg bioaccumulation. Collectively, understanding how fluctuating acidification interacts with Hg contaminant will become more crucial in predicting their risks to coastal biota and ecosystems.

Assessment of Hg pollution in stream waters and human health risk in areas impacted by mining activities in the Ecuadorian Amazon.

Illegal gold mining activities have contributed to the release and mobilization of Hg and environmental degradation in many parts of the world. This study aims to determine the concentration of Hg in five provinces of the Amazon Region of Ecuador, in addition to assessing the risk to human health of exposed populations, applying deterministic and probabilistic methods. For this purpose, 147 water samples were collected in rivers and streams crossing and/or located near mining areas. As a result, 100% of the samples analyzed exceeded the maximum permissible limit (MPL) according to the water quality criteria for the preservation of aquatic life of the Ecuadorian regulations, while 7% of the samples exceeded the MPL for drinking water. On the other hand, considering the European Environmental Quality Standard (EQS) for surface water bodies, in our study, 100% of the samples exceed the maximum permissible limit (0.07µg/L), and with respect to the Canadian water quality guidelines, 35% of the samples exceed the permissible limit (0.001mg/l) for drinking water, and 100% of the samples exceed the limit for life in water bodies (0.0001mg/l). The risk assessment revealed that the probability of developing adverse health effects from exposure to Hg is below the recommended limits according to the probabilistic assessment; this is in relation to the criterion of residential and recreational use of water resources. However, it was identified that the child population doubles the acceptable systemic risk level according to the results of the deterministic assessment in the residential scenario. This information can be used by decision-makers to implement strategies to reduce Hg contamination and exposure of the population in Ecuadorian Amazonian rivers.

New insights into sulfur input induced methylmercury production and accumulation in paddy soil and rice

Sulfur has a high affinity for mercury (Hg) and can serve as effective treating agent for Hg pollution. However, conflict effects between reducing Hg mobility and promoting Hg methylation by sulfur were found in recent studies, and there is a gap in understanding the potential mechanism of MeHg production under different sulfur-treated species and doses. Here, we investigated and compared the MeHg production in Hg-contaminated paddy soil and its accumulation in rice under elemental sulfur or sulfate treatment at a relatively low (500 mg·kg−1) or high (1000 mg·kg−1) level. The associated potential molecular mechanisms are also discussed with the help of density functional theory (DFT) calculation. Pot experiments demonstrate that both elemental sulfur and sulfate at high exposure levels increased MeHg production in soil (244.63–571.72 %) and its accumulation in raw rice (268.73–443.50 %). Coupling the reduction of sulfate or elemental sulfur and decrease of soil redox potential leads to the detachment of Hg-polysulfide complexes from the surface of HgS which can be explained by DFT calculations. Enhancement of free Hg and Fe release through reducing Fe(III) oxyhydroxides further promotes soil MeHg production. The results provide clues for understanding the mechanism by which exogenous sulfur promotes MeHg production in paddies and paddy-like environments and give new insights for decreasing Hg mobility by regulating soil conditions.

Mercury Pollution in Dryland Soil and Evaluation of Maize Safety Production in Guizhou Province

Guizhou Province is the province with the largest Hg production and reserves in China, and maize is the second largest grain crop in Guizhou Province. It is necessary to identify the status of soil Hg content in Guizhou Province and evaluate the safety of maize production. A total of 990 soil-maize samples and 270 single soil samples were collected in the main maize-producing areas to determine soil pH, cation exchange capacity (CEC), and organic matter content (SOM), as well as Hg content in soil and maize. The results showed that the pH of dryland soil in Guizhou Province ranged from 3.93 to 9.82, the geometric mean of ω(SOM) was 27.5 g·kg-1, and the geometric mean of CEC was 11.7 cmol·kg-1. Soil ω(Hg) ranged from 0.005 to 686 mg·kg-1, the geometric mean was 0.632 mg·kg-1, and the over-standard rate was 7.22%. Among them, the soil Hg pollution in Tongren was the most prominent, with the exceedance rate of 21.3%. At the county level, Danzhai County, Qiandongnan Miao and Dong Autonomous Prefecture, and Tongren City Wanshan District and Bijiang District had high exceedance rates of Hg. According to the Limit of Pollutants in Food according to National Standards for Food Safety (GB 2762-2017), the exceedance rate of Hg content in maize grains was 1.11%, and the exceedance points were mainly distributed around industrial and mining activity areas such as Wanshan District in Tongren City and Xixiu District in Anshun City. According to the results, there was serious soil Hg pollution in Guizhou Province. On the whole, maize can be safely planted, but it is necessary to pay close attention to the Hg content in grains and the Hg exposure risk of residents around industrial and mining areas.

International trade shapes global mercury-related health impacts.

Mercury (Hg) is a strong neurotoxin with substantial dangers to human health. Hg undergoes active global cycles, and the emission sources there of can also be geographically relocated through economic trade. Through investigation of a longer chain of the global biogeochemical Hg cycle from economic production to human health, international cooperation on Hg control strategies in Minamata Convention can be facilitated. In the present study, four global models are combined to investigate the effect of international trade on the relocation of Hg emissions, pollution, exposure, and related human health impacts across the world. The results show that 47% of global Hg emissions are related to commodities consumed outside of the countries where the emissions are produced, which has largely influenced the environmental Hg levels and human exposure thereto across the world. Consequently, international trade is found to enable the whole world to avoid 5.7 × 105 points for intelligence quotient (IQ) decline and 1,197 deaths from fatal heart attacks, saving a total of $12.5 billion (2020 USD) in economic loss. Regionally, international trade exacerbates Hg challenges in less developed countries, while resulting in an alleviation in developed countries. The change in economic loss therefore varies from the United States (-$4.0 billion) and Japan (-$2.4 billion) to China (+$2.7 billion). The present results reveal that international trade is a critical factor but might be largely overlooked in global Hg pollution mitigation.

Impacts of anthropogenic discharge on distribution, mass budget, and long-term risk of total mercury in coastal region: A case study of the Jiaozhou Bay, China

Mercury (Hg) as a toxic pollutant in marine systems have been paid more attention. The Jiaozhou Bay (JZB) is located at the western coast of the Yellow Sea surrounded by Qingdao city, a developed city in China. >10 rivers and several sewage treatment plants carry lots of Hg input it, increasing the environmental risks JZB facing. However, there is still a lack of knowledge on its cycling in the JZB, limiting sound understanding of Hg fate in coastal regions. To address these needs, four cruises were conducted in different seasons, to investigate distribution, influencing factors, and mass budget of total Hg (THg) in the JZB. Higher THg concentrations were determined in seawater (22.8 ± 13.9 ng L−1) and sediment (148 ± 107 ng g−1), indicating serious Hg pollution in the JZB. Temperature, salinity in water and enrich factor (EF) in sediment were identified to be possible environmental factors influencing THg distribution in the JZB. Mass budget of THg showed that anthropogenic discharge (river, wastewater input, and atmospheric deposition) was dominant source of THg in the JZB. The results of statistical analyses and mass budget of THg also indicated that anthropogenic discharge plays important roles in long-term risk of THg in the JZB. These results suggested that anthropogenic discharge comprehensively affects distribution, mass budget, and long-term risk of THg in coastal systems. The outcomes highlighted that regular investigations of Hg cycling should be conducted to assess Hg pollution in coastal ecosystems. Our study also shed new light on control of long-term risk posed by Hg in marine systems according to investigations of Hg cycling and link between Hg contamination and other pollutant (e.g., nutrient).

Risk source identification and diffusion trends of metal(loid)s in stream sediments from an abandoned arsenic-containing mine

Stream sediments from mine area are a converging source of water and soil pollution. The risk and development trends of metal(loid)s pollution in sediments from an abandoned arsenic-containing mine were studied using modelling techniques. The results showed that the combined techniques of geographic information system (GIS), random forest (RF), and numerical simulation (NS) could identify risk sources and diffusion trends of metal(loid)s in mine sediments. The median values of As, Cd, Hg, and Sb in sediments were 5.01, 3.02, 5.67, and 3.20 times of the background values of stream sediments in China, respectively. As (14.09%) and Hg (18.64%) pollution in mine stream sediments were severe while As is the main potential risk source with a strong spatial correlation. High-risk blocks were concentrated in the landfill area, with the surrounding pollution shows a decreasing trend of “step-type” pollution. The risk correlation between Hg and As (55.37%) in the landfill area is high. As a case of arsenic, the diffusion capacity of As within 500m is strong and stabilizes at 1 km when driven by the flows of 0.05, 0.5, and 5 m3/s, respectively. With the worst-case scenario flow (86 m3/s), it would take only 147 days for the waters within 3 km to become highly polluted. The high pollution levels in a stream under forecast of different distance intervals (500, 1500, 2000 m) within 6.5 km is arrived at approximate 344, 357, and 384 days, respectively. The study suggested the combined technique of GIS, RF, and NS can serve the risk source identification of contaminated sites and risk forecast of toxic element diffusion in emergency situations.

Selenium/sulfur-modified montmorillonite materials mitigate mercury pollution in farmland

Selenium (Se) amendment could reduce mercury (Hg) bioaccumulation in crops, but sometimes it could cause excessive Se accumulation in crops and potential Se exposure risks for humans. In this study, we designed and synthesized selenium and sulfur-modified montmorillonite materials (Se/S-Mont) to effectively reduce mercury levels and avoid excessive Se enrichment in plants. The results of pot experiments (1 g Se/S-Mont/100 g soil) and field microplot trials (0.3 g Se/S-Mont/100 g soil, 8 t/ha) showed that Se/S-Mont amendments significantly reduced the Hg concentrations in water spinach and hybrid Pennisetum by 28–68% and 57%–92% (P < 0.05), respectively, while they did not lead to excessive Se bioaccumulation in the plants. Se/S-Mont was more efficient in mitigating soil Hg pollution than adding raw materials (e.g., NaSeO₃) and their combinations, and they significantly reduced the available Se fraction in the soil and the Se levels in the plants (P < 0.05). The potential mechanisms revealed by X-ray absorption near-edge spectra (XANES) and pot experiments were the adsorption and slow release of Hg, S, and Se by Se/S-Mont, the high affinity between Hg and Se, competition between Se and S, and the formation of stable complexes containing Se–S–Hg. The Se/S-Mont immobilizer was easy to prepare and required the application of small amounts, and the remediation effect was relatively stable and exhibited few negative effects; therefore, the approach showed high environmental and economic potentials.

Mercury biomagnification at higher rates than the global average in aquatic ecosystems of the Qinghai-Tibet Plateau

Mercury biomagnification in aquatic ecosystems is a global issue. Biomagnification patterns and drivers in alpine regions remain poorly understood. Hg biomagnification in the aquatic food web of the Qinghai-Tibetan Plateau (Q-T Plateau) was investigated. A total of 302 fish and macroinvertebrate tissue samples were analysed for total mercury (THg) and nitrogen (δ15N) stable isotope ratios. Overall, 26.75% of fish individuals exceeded the USFWS consumption guidelines. A total of 52.17% of the sampling sites covering different habitats exhibited a significantly positive THg–δ15N relationship, which confirmed the Hg biomagnification potential of Q-T Plateau aquatic ecosystems. The Q-T Plateau Hg biomagnification rates were generally far higher than global averages regardless of the habitat type. Hg in sediments, elevation and population density were positively related to the Hg biomagnification magnitude on the Q-T Plateau, which could be attributed to the disproportionate response of Hg concentrations in macroinvertebrates and fishes along environmental gradients. Our findings offer empirical evidence that fish consumption on the Q-T Plateau poses a substantial Hg exposure risk to people living along river and lake shores. Higher biomagnification rates could further disproportionately accelerate Hg pollution in Q-T Plateau aquatic ecosystems under future anthropogenic activities and climate warming trajectories.