Publications by authors named "Xinbin Feng"

214 Publications

Occurrence of total mercury and methylmercury in rice: Exposure and health implications in Nepal.

Ecotoxicol Environ Saf 2021 Nov 22;228:113019. Epub 2021 Nov 22.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

Emerging studies have indicated that the consumption of rice could be the major methylmercury (MeHg) contributor to human mercury (Hg) exposure. Nonetheless, few studies are available on Hg in rice around the world, especially in countries with heavy rice diet. In this study, total Hg (THg) and MeHg levels in rice samples (n = 172) across Nepal were first investigated. The geometric mean THg was 7.05 ± 7.71 µg/kg with a range of 0.622 µg/kg to 158 µg/kg, and the maximum THg level was up to 791% of the Chinese National Standard Limit for THg in rice (20 µg/kg). The geometric mean MeHg was 0.820 ± 0.660 µg/kg with a range of 0.189 µg/kg to 8.59 µg/kg. Overall, the mean MeHg exposure (0.00445 ± 0.00477 µg/kg bw/day) and inorganic Hg (IHg) exposure (0.0360 ± 0.0739 µg/kg bw/day) were lower than the reference dose (RfD) of 0.1 µg/kg bw/day for MeHg and the provisional tolerable weekly intake (PTWI) of 0.571 µg/kg bw/day for IHg, respectively. Concerning different groups of vulnerable populations, the highest MeHg exposure (0.126 µg/kg bw/day) and IHg exposure (1.57 µg/kg bw/day) of preschoolers (37-50 months old) were approximately 126% of the RfD for MeHg and 275% of the PTWI for IHg. When the pregnant mothers eat the rice without awareness of the Hg content in rice, the mean and highest intelligence quotients (IQs) losses were 9554 and 118659 points, respectively, and the corresponding economic costs due to IQ loss could be 15.1 million USD and 188 million USD in Nepal. The results of rice THg and MeHg levels and corresponding exposure in populations highlighted the occurrence of rice THg and MeHg pollution issues in Nepal. More efforts should be made to protect younger groups in Nepal from high rice Hg exposure. CAPSULE: Owing to the high rice consumption rates relative to body mass, preschoolers (37-50 months) may meet the 126% reference dose (0.1 µg/kg bw/day) for MeHg and 275% provisional tolerable weekly intake (0.571 µg/kg bw/day) for IHg exposure in Nepal.
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http://dx.doi.org/10.1016/j.ecoenv.2021.113019DOI Listing
November 2021

The underappreciated role of natural organic matter bond Hg(II) and nanoparticulate HgS as substrates for methylation in paddy soils across a Hg concentration gradient.

Environ Pollut 2022 Jan 8;292(Pt A):118321. Epub 2021 Oct 8.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China. Electronic address:

Rice consumption is the major pathway for human methylmercury (MeHg) exposure in inland China, especially in mercury (Hg) contaminated regions. MeHg production, a microbially driven process, depends on both the chemical speciation of inorganic divalent mercury, Hg(II), that determines Hg bioavailability for methylation. Studies have shown that Hg(II) speciation in contaminated paddy soils is mostly controlled by natural organic matter and sulfide levels, which are typically thought to limit Hg mobility and bioavailability. Yet, high levels of MeHg are found in rice, calling for reconsideration of the nature of Hg species bioavailable to methylators in paddy soils. Here, we conducted incubation experiments using a multi-isotope tracer technique including Hg(NO), natural organic matter bond Hg(II) (NOM-Hg(II)), ferrous sulfide sorbed Hg(II) (≡FeS-Hg(II)), and nanoparticulate mercuric sulfide (nano-HgS), to investigate the relative importance of geochemically diverse yet relevant Hg(II) species on Hg methylation in paddy soils across a Hg concentration gradient. We show that methylation rates for all Hg(II) species tested decreased with increasing Hg concentrations, and that methylation rates using NOM-Hg(II) and nano-HgS as substrates were similar or greater than rates obtained using the labile Hg(NO) substrate. ≡FeS-Hg(II) yielded the lowest methylation rate in all sites, and thus the formation of FeS is likely a sink for labile Hg(NO) in sulfide-rich paddy soils. Moreover, the variability in the methylation data for a given site (1 to 5-fold variation depending on the Hg species) was smaller than what was observed across the Hg concentration gradient (10-10 fold variation between sites). These findings emphasize that at broad spatial scales, site-specific characteristics, such as microbial community structure, need to be taken into consideration, alongside the nature of the Hg substrate available for methylation, to determine net MeHg production. This study highlights the importance of developing site-specific strategies for remediating Hg pollution.
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http://dx.doi.org/10.1016/j.envpol.2021.118321DOI Listing
January 2022

Selenium-amended biochar mitigates inorganic mercury and methylmercury accumulation in rice (Oryza sativa L.).

Environ Pollut 2021 Dec 29;291:118259. Epub 2021 Sep 29.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China. Electronic address:

Rice, as a dominant crop in China and Asia, can be a major route of methylmercury (MeHg) exposure for humans in inland China, especially in those living in mercury (Hg) polluted areas. Soil is the most prominent MeHg accumulation source for rice grains. The development of management practices to reduce MeHg in rice grains is crucial. This study explored the mitigation effect of biochar (BC) and sodium selenite-amended biochar (BC + Se) on MeHg production in paddy soil and accumulation in rice. Mercury-contaminated soil was treated with 1% and 5% of both BC and BC + Se. Soil MeHg concentration slightly increased under 1% BC/BC + Se compared to control soil but decreased at the rate of 5%. Moreover, soil phytoavailable MeHg (P-MeHg) diminished as the amount of Se-amended BC increased. BC + Se effectively mitigated MeHg accumulation in rice grains. The highest average contents of MeHg and inorganic Hg (IHg) in rice seeds were found in the control samples, followed by the 1%-BC, 5%-BC, 1%-BC + Se, and 5%-BC + Se samples. Under the 5%-BC + Se treatment, rice MeHg levels were reduced significantly (94%) compared to the control, and P-MeHg concentrations in soil were lower than all the other experimental groups throughout the rice-growing season. These results demonstrate the effectiveness of BC + Se in reducing MeHg and IHg accumulation in rice and could be employed for remediation of Hg polluted paddies.
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http://dx.doi.org/10.1016/j.envpol.2021.118259DOI Listing
December 2021

Chemistry and Isotope Fractionation of Divalent Mercury during Aqueous Reduction Mediated by Selected Oxygenated Organic Ligands.

Environ Sci Technol 2021 10 14;55(19):13376-13386. Epub 2021 Sep 14.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

We have investigated the chemistry and Hg isotope fractionation during the aqueous reduction of Hg by oxalic acid, -quinone, quinol, and anthraquinone-2,6-disulfonate (AQDS), a derivate of anthraquinone (AQ) that is found in secondary organic aerosols (SOA) and building blocks of natural organic matter (NOM). Each reaction was examined for the effects of light, pH, and dissolved O. Using an excess of ligand, UVB photolysis of Hg was seen to follow pseudo-first-order kinetics, with the highest rate of ∼10 s observed for AQDS and oxalic acid. Mass-dependent fractionation (MDF) occurs by the normal kinetic isotope effect (KIE). Only the oxalate ion, rather than oxalic acid, is photoreactive when present in HgCO, which decomposes via two separate pathways distinguishable by isotope anomalies. Upon UVB photolysis, only the reduction mediated by AQDS results in a large odd number mass-independent fractionation (odd-MIF) signified by enrichment of odd isotopes in the reactant. Consistent with the rate, MDF, and odd-MIF reported for fulvic acid, our AQDS result confirms previous assumptions that quinones control Hg reduction in NOM-rich waters. Given the magnitude of odd-MIF triggered via a radical pair mechanism and the significant rate in the presence of air, reduction of Hg by photoproducts of AQDS may help explain the positive odd-MIF observed in ambient aerosols depleted of Hg.
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http://dx.doi.org/10.1021/acs.est.1c03171DOI Listing
October 2021

Unravelling the interactive effect of soil and atmospheric mercury influencing mercury distribution and accumulation in the soil-rice system.

Sci Total Environ 2022 Jan 28;803:149967. Epub 2021 Aug 28.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, PR China; Center for Excellence in Quaternary Science and Global Change, Chinese Academy of Sciences, Xian 710061, PR China. Electronic address:

Mercury (Hg) accumulation in rice is an emerging health concern worldwide. However, sources and interactions responsible for Hg species accumulation in different rice tissues are still uncertain. Four experimental plots were carefully designed at an artisanal Hg mining site and a control site to evaluate the effect of atmospheric and soil Hg contents on Hg accumulation in rice. We showed that inorganic Hg (IHg) contents in rice tissues grown either in contaminated or control site soil (non-contaminated soil) were higher at Hg artisanal mining site than those at the control site. Elevated total gaseous mercury (TGM) levels in ambient air were the predominant source of IHg to rice at the Hg mining area. Methylmercury (MeHg) concentrations in rice plant tissues increased in proportionality with MeHg contents in paddy soil. Our results suggest that both atmosphere and soil Hg sources have been impacted the IHg accumulation in rice. Above ground rice tissues, grains, leaves, and stalk accumulated IHg from both atmosphere and soil to varying degrees. Nonetheless, the study also provides the first direct evidence that atmospheric Hg accumulated by above-ground rice tissues could be translocated to below-ground tissues (roots). However, the extent to which atmosphere or soil Hg contributes to IHg in rice tissues may vary with each source's concentration gradient at the given site. No evidence of in planta Hg methylation was found during the current study. Hence, paddy fields are potential MeHg production sites, whereas paddy soil is a unique MeHg accumulation source in rice plants. This study expands and clarifies the contribution of various sources involved in Hg accumulation in the soil rice system. The findings here provide the basis for future research strategies to deal with the global issue of Hg contaminated rice.
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http://dx.doi.org/10.1016/j.scitotenv.2021.149967DOI Listing
January 2022

Compound-Specific Stable Isotope Analysis Provides New Insights for Tracking Human Monomethylmercury Exposure Sources.

Environ Sci Technol 2021 09 1;55(18):12493-12503. Epub 2021 Sep 1.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

Monomethylmercury (MMHg) exposure can induce adverse neurodevelopmental effects in humans and is a global environmental health concern. Human exposure to MMHg occurs predominately through the consumption of fishery foods and rice in Asia, but it is challenging to quantify these two exposure sources. Here, we innovatively utilized MMHg compound-specific stable isotope analyses (MMHg-CSIA) of the hair to quantify the human MMHg sources in coastal and inland areas, where fishery foods and rice are routinely consumed. Our data showed that the fishery foods and rice end members had distinct ΔHg values in both coastal and inland areas. The ΔHg values of the human hair were comparable to those of fishery foods but not those of rice. Positive shifts in the δHg values of the hair from diet were observed in the study areas. Additionally, significant differences in δHg versus ΔHg were detected between MMHg and inorganic Hg (IHg) in the human hair but not in fishery foods and rice. A binary mixing model was developed to estimate the human MMHg exposures from fishery foods and rice using ΔHg data. The model results suggested that human MMHg exposures were dominated (>80%) by fishery food consumption and were less affected by rice consumption in both the coastal and inland areas. This study demonstrated that the MMHg-CSIA method can provide unique information for tracking human MMHg exposure sources by excluding the deviations from dietary surveys, individual MMHg absorption/demethylation efficiencies, and the confounding effects of IHg.
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http://dx.doi.org/10.1021/acs.est.1c01771DOI Listing
September 2021

Quantification of Atmospheric Mercury Deposition to and Legacy Re-emission from a Subtropical Forest Floor by Mercury Isotopes.

Environ Sci Technol 2021 09 27;55(18):12352-12361. Epub 2021 Aug 27.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

Air-soil exchange of elemental mercury vapor (Hg) is an important component in the budget of the global mercury cycle. However, its mechanistic detail is poorly understood. In this study, stable Hg isotopes in air, soil, and pore gases are characterized in a subtropical evergreen forest to understand the mechanical features of the air-soil Hg exchange. Strong Hg reduction in soil releases Hg to pore gas during spring-autumn but diminishes in winter, limiting the evasion in cold seasons. ΔHg in air modified by the Hg efflux during flux chamber measurement exhibit seasonality, from -0.33 ± 0.05‰ in summer to -0.08 ± 0.05‰ in winter. The observed seasonal variation is caused by a strong pore-gas driven soil efflux caused by photoreduction in summer, which weakens significantly in winter. The annual Hg gross deposition is 42 ± 33 μg m yr, and the corresponding Hg evasion from the forest floor is 50 ± 41 μg m yr. The results of this study, although still with uncertainty, offer new insights into the complexity of the air-surface exchange of Hg over the forest land for model implementation in future global assessments.
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http://dx.doi.org/10.1021/acs.est.1c02744DOI Listing
September 2021

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.

Environ Pollut 2021 Nov 5;288:117727. Epub 2021 Jul 5.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China. Electronic address:

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.
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http://dx.doi.org/10.1016/j.envpol.2021.117727DOI Listing
November 2021

Mobilization, Methylation, and Demethylation of Mercury in a Paddy Soil Under Systematic Redox Changes.

Environ Sci Technol 2021 07 2;55(14):10133-10141. Epub 2021 Jul 2.

Laboratory of Soil- and Groundwater-Management, Institute of Foundation Engineering, Water- and Waste-Management, School of Architecture and Civil Engineering, University of Wuppertal, Pauluskirchstraße 7, 42285 Wuppertal, Germany.

Methylmercury (MeHg) contamination in paddy fields is a significant environmental issue globally since over half of the population of our planet consumes rice. MeHg is a neurotoxin produced by microorganisms in oxygen-limited environments. Microbial effect on MeHg production is a hotspot of research; however, it has been largely ignored how the oxidation-reduction potential () shapes MeHg formation. Here, we elucidated Hg (de)-methylation in a contaminated soil by increasing stepwise from -300 to +300 mV using a sophisticated biogeochemical microcosm. At the range from -300 to -100 mV, high MeHg concentration and dissolved total Hg (THg) concentration were found due to a high relative abundance of Hg-methylation bacteria (e.g., spp.), acidification, and reductive dissolution of Fe(oxyhydr)oxides. At the range from 0 to +200 mV, the formation of colloids leads to adsorption of Hg and as a result colloidal Hg increased. MeHg reduction with (-300 to +200 mV) increase was mainly attributed to a reduced Hg methylation, as dissolved THg and relative abundance of spp. decreased by 50 and 96%, respectively, at of +200 mV as compared to of -300 mV. Mercury demethylation might be less important since the relative abundance of demethylation bacteria ( spp.) also decreased over 93% at of +200 mV. These new results are crucial for predicting Hg risks in paddy fields.
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http://dx.doi.org/10.1021/acs.est.0c07321DOI Listing
July 2021

Mass balance of nine trace elements in two karst catchments in southwest China.

Sci Total Environ 2021 Sep 4;786:147504. Epub 2021 May 4.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; CAS Centre for Excellence in Quaternary Science and Global Change, Xi'an 710061, China. Electronic address:

High geological background levels of trace elements (TEs) and high population density in the karst areas of southwest China have imposed environmental pressure on the fragile ecosystems in this region. Understanding the mass budget of TEs, especially the toxic ones, is of great importance to sustain future developments. This study investigates the mass balance and fate of nine TEs (cadmium, arsenic, lead, chromium, copper, nickel, zinc, thallium, and antimony) in two karst catchments (Huilong and Chenqi) in southwest China through estimation of their mass budgets in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilization, harvested crops, surface runoff, and underground runoff. The estimated net fluxes are positive, indicating a source region, for four elements (Cu, Cr, Ni, and Tl) and negative, indicating a sink region, for five elements (As, Cd, Pb, Sb, and Zn) in both catchments. The net fluxes for the nine elements in Chenqi catchment are within a relatively small range (2.6, 2.0, 1.6, 0.6, -0.05, -0.5, -0.5, -2.9, and -3.3 mg m yr for Cu, Ni, Cr, Tl, Cd, Zn, Sb, Pb, and As, respectively), but in Huilong catchment in quite a large range (15.5, 6.0, 1.0, 0.8, -0.3, -0.9, -4.5, -7.5, and -8.7 mg m yr for Tl, Cr, Ni, Cu, Cd, Sb, As, Pb, and Zn, respectively). Rainfall (12.3%-66.2%) and litterfall (18.4%-81.3%) are the major input flux pathways, while crops harvest (16%-99%) is the major output flux pathway for the TEs in both catchments, indicating that the fate of TEs is shaped by both natural factors such as precipitation and litterfall and human activities such as fertilization and crop harvesting in these forestland-farmland compound karst catchments. Results from this study suggest that restoring forests from low-yield sloping farmlands will be useful for controlling TEs pollution in these fragile karst regions with high geological background TEs.
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http://dx.doi.org/10.1016/j.scitotenv.2021.147504DOI Listing
September 2021

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

Environ Int 2021 09 23;154:106561. Epub 2021 Apr 23.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an 710061, 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.
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http://dx.doi.org/10.1016/j.envint.2021.106561DOI Listing
September 2021

Characteristics, Accumulation, and Potential Health Risks of Antimony in Atmospheric Particulate Matter.

ACS Omega 2021 Apr 1;6(14):9460-9470. Epub 2021 Apr 1.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

Antimony (Sb), a priority pollutant listed by the U.S. Environmental Protection Agency (USEPA), can cause adverse effects on human health, with particular impacts on skin, eyes, gastrointestinal tract, and respiratory system. In this study, a database of Sb concentrations in the global atmosphere was developed through a survey of measurements published in more than 600 articles, which was then used to assess the health risks of Sb exposure based on a USEPA assessment model. Most measurements showed Sb concentrations of less than ∼10 ng m, but those at several contaminated sites exhibited Sb concentrations of more than 100 ng m. For measurements conducted in urban environments, Sb concentrations in the total suspended particles (TSP) and particles of less than 10 (PM) or 2.5 μm (PM) were the highest in Asia, followed by Europe, South America, and North America. Sb concentrations were generally higher in winter and fall than during other seasons in TSP and PM samples. A significant correlation was observed between Sb and As in TSP and PM on a global scale. Sb was mainly derived from anthropogenic sources, especially traffic emission, industrial emission, and fossil combustion. Hazard quotients (HQ) of Sb in TSP, PM, and PM were higher for children than adults because of their lighter body weight, inferior physical resistance, and higher ingestion probability. The global database for atmospheric Sb concentrations demonstrates a relatively low noncarcinogenic risk in most regions. Long-term monitoring is still required to identify the sources and growth potentials of Sb so that effective control policies can be established.
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http://dx.doi.org/10.1021/acsomega.0c06091DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8047740PMC
April 2021

Diet influence on mercury bioaccumulation as revealed by polyunsaturated fatty acids in zoobenthos from two contrasting environments: Chinese reservoirs and Swedish lakes.

Sci Total Environ 2021 Aug 29;782:146410. Epub 2021 Mar 29.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, PR China.

The bioaccumulation of mercury (Hg) and polyunsaturated fatty acids (PUFA) in zoobenthos varies across aquatic food webs. In this field study, contents of total Hg (THg), methylmercury (MeHg) and PUFA were investigated in zoobenthos of Chinese reservoirs and Swedish lakes, with contrasting environmental characteristics and algal diet sources, which can result in difference of Hg and PUFA in zoobenthos from these two habits. Using PUFA as dietary biomarkers of algae in zoobenthos, we evaluated effects of environmental factors and algal diet sources on the accumulation of THg, MeHg, and the highly required PUFA eicosapentaenoic (EPA, 20: 5n-3) and docosahexaenoic acid (DHA, 22:6n-3) in zoobenthos. Average THg and MeHg in zoobenthos were higher in Chinese reservoirs than Swedish lakes (p < 0.05). Average EPA content of zoobenthos was similar in these two habitats (p > 0.05), yet average DHA content of zoobenthos was higher in Chinese reservoirs than Swedish lakes (p < 0.05). Total Hg and MeHg contents of zoobenthos in Swedish lakes were predicted by environmental factors; e.g., negatively with pH and positively with dissolved organic carbon (DOC) concentrations, yet had no significant relationship with the algal dietary. In Chinese reservoirs, however, no environmental factor correlated well with THg contents in zoobenthos, and only DOC concentrations showed positive correlation with MeHg contents in zoobenthos. Besides, the algal dietary was also positively correlated with MeHg contents in zoobenthos. EPA and DHA contents of zoobenthos in Swedish lakes primarily associated with algal diet. By contrast, in Chinese reservoirs, EPA and DHA contents of zoobenthos were affected by both environmental factors and algal diet.
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http://dx.doi.org/10.1016/j.scitotenv.2021.146410DOI Listing
August 2021

Use of biochar to reduce mercury accumulation in Oryza sativa L: A trial for sustainable management of historically polluted farmlands.

Environ Int 2021 08 27;153:106527. Epub 2021 Mar 27.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, PR China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an, 710061, China.

Mitigating the risk of mercury (Hg) contamination in rice soils using environmental friendly amendments is essential to reducing the probable daily intake (PDI) of MeHg via rice consumption. Here, we examined the impacts of different doses (0% (control), 0.6% and 3%) of rice hull-derived biochar (RHB) and mixture of wheat-rice straw-derived biochar (RWB) on the fractionation, phytoavailability, and uptake of total (THg) and methyl Hg (MeHg) by rice in Hg-polluted soil (THg = 78.3 mg kg) collected from Wanshan Hg mining area. Both biochars increased rice biomass up to 119% as compared to control. Application of RHB and RWB significantly (P ≤ 0.05) decreased bioavailable Hg (soluble and exchangeable and specifically-sorbed fractions) concentrations by 55-71% and 67-72%, respectively. The addition of RHB significantly decreased MeHg concentrations in the soil. However, RWB (particularly at 3%) increased significantly MeHg concentrations in the soil as compared to the control and RHB treatments, likely due to the increased abundance of Hg-methylation microorganisms (e.g., Geobacter spp., Nitrospira spp.) in the RWB treatments. Both RHB and RWB significantly decreased MeHg concentrations in the rice grain by 55-85%. We estimated a reduction of the PDI of MeHg from 0.26 μg kg bw dof control to below the reference dose (0.1 μg kg bw d) of two biochar treatments. Our results highlight the potentiality of RWB and RHB for mitigating MeHg accumulation in rice and reducing PDI of MeHg via rice consumption, which offers a sustainable approach for management of Hg-polluted soils.
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http://dx.doi.org/10.1016/j.envint.2021.106527DOI Listing
August 2021

Chemical and bacterial quality monitoring of the Nile River water and associated health risks in Qena-Sohag sector, Egypt.

Environ Geochem Health 2021 Oct 27;43(10):4089-4104. Epub 2021 Mar 27.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China.

The River Nile is the primary source of freshwater for drinking, irrigation, and industrial purposes in Egypt. Thus, the water quality in this river concerns the health of local inhabitants. The present study reveals seasonal variations of various physicochemical and heavy metals parameters and microbial load of water at 15 sites from Qena to Sohag cities, Egypt. The water is fresh with TDS ≤ 270 and 410 mg L in summer and winter, respectively. Fe, Mn, Cd, Cr, Cu, Ni, and Zn concentrations were within drinking water specification in both seasons except Cr and Cd in summer. Viable numbers of total coliform, fecal coliform, and fecal streptococci were recorded in both seasons with fecal streptococci's disappearing in winter. The concentrations of salts and ions in winter were higher than summer due to decreased water quantity and flow rate in this season. On the other hand, heavy metals and bacteria were higher in summer owing to the rain and weathering of upstream rocks and increasing of human activities during the summer. The calculated water quality index (WQI) depicted that the chemical quality of water was poor for drinking and treatment, especially biological treatment, which is required before the water is supplied for drinking. Human health risk assessment factors such as probable daily intake, hazard quotient, and carcinogenic risk indicated high risks of Cr, Cd, and Ni for adults and children in both seasons. The non-carcinogenic and carcinogenic risks are mainly posed by Cr. The WQI values for the other water uses indicated the marginal quality for aquatic life, fair for irrigation, and fair in summer to good in winter for livestock consumption. The irrigation water quality parameters indicated that the water could be used to irrigate all soils and crops except the hazard of biological contamination. The water-rock interaction controls water chemistry besides the contribution of human activities. The agricultural, industrial, and municipal wastewaters were the main contributors to water pollution and should be treated before discharge into the Nile River. Source and drinking water should be monitored continuously to prevent related human waterborne diseases.
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http://dx.doi.org/10.1007/s10653-021-00893-3DOI Listing
October 2021

Stable mercury isotopes stored in Masson Pinus tree rings as atmospheric mercury archives.

J Hazard Mater 2021 08 19;415:125678. Epub 2021 Mar 19.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; Center for Excellence in Quaternary Science and Global Change, Chinese Academy of Sciences, Xian 710061, China. Electronic address:

The accuracy of mercury (Hg) dendrochemistry has been questioned because significant knowledge gaps exist in understanding the Hg translocation and mobility in tree-ring. In this study, we evaluated Hg concentrations and isotopic profiles in the tree-ring at a Hg artisanal mining site and a control site with the documented local Hg production inventory. Results show that the Hg concentration accumulated in tree-ring fails to reconstruct the temporal trend of Hg production due to confounded tree physiological and environmental factors, specifically, the radial translocation and tree age effects occurring during the fast-growing period. The temporal profiles of δHg exhibit pronounced tree-specific variabilities due to the complexity of Hg isotopic mass dependent fractionation during atmospheric Hg uptake and translocation in vegetation. The Hg odd-MIF (mass independent fractionation) profiles in tree-ring can reconstruct a decadal-scale temporal trend of the atmospheric Hg pollution level, and also be used as a tracer to distinguish the emission source shifts of atmospheric Hg. However, the radial translocation would result in uncertainties at the higher resolution because of the mixing of odd-MIF signatures with active rings. Caution should be taken and additional supporting evidence collected from independent methods should be used for verifying the tree-ring records.
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http://dx.doi.org/10.1016/j.jhazmat.2021.125678DOI Listing
August 2021

Soil and ambient air mercury as an indicator of coal-fired power plant emissions: a case study in North China.

Environ Sci Pollut Res Int 2021 Feb 26. Epub 2021 Feb 26.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China.

Coal-fired power plants (CFPPs) are an important anthropogenic mercury (Hg) source in China, and it is crucial to understand the environmental impacts of this detrimental element emitted from this source. In the present study, field experiments were conducted for measuring Hg in ambient atmosphere and upland agricultural soils within a radius of 10 km surrounding a large scale coal-fired power plant (1550 MW) in Tangshan, Hebei province. Short-term (20 min) average of gaseous elemental mercury (GEM or Hg) in ambient air varying from 1.5 to 9.0 ng/m and total Hg (THg) in surface agricultural soil (0-20 cm) varying from 9.2 to 43.5 μg/kg at different sites were observed. THg in two soil cores decreased with depth, with concentrations being 2-2.5 times higher in the surface layer than that in the deep layer (50-60 cm), indicating the possibility of the atmospheric input of Hg. Based on the information of the total atmospheric Hg emission since this CFPP's operation in 1970s and the increased THg in nearby soils, it was estimated that about 3.9% discharged Hg has accumulated in the nearby agricultural soils. The low retention rate of the total emitted Hg by soils is a result of high proportion of Hg (79.5%) in stack gas emission and potential loss of Hg from soil surface reemission. The positive shifting (~ 0.5‰) of Hg isotopic signature (δHg) from deep soil to surface soil reflected Hg deposition from nearby CFPP emissions that are featured with much heavier Hg isotopic signatures inherited from feed coal (δHg: -0.50‰) and different combustion products (δHg: -0.95 to 3.71‰) compared with that in deep soil layer (δHg: ca -1.50‰). Overall, this study demonstrated that this CFPP has a slight but distinguishable effect on the elevation of ambient GEM and agricultural soil THg in the local environment.
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http://dx.doi.org/10.1007/s11356-021-12842-9DOI Listing
February 2021

Heavy Metal(loid)s Contamination in Ground Dust and Associated Health Risks at a Former Indigenous Zinc Smelting Area.

Int J Environ Res Public Health 2021 01 21;18(3). Epub 2021 Jan 21.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

Indigenous zinc smelting (IZS) is a backward technique that releases a great deal of heavy metal(loid)s into the environment. However, the contamination of heavy metal(loid)s in ground dust and the associated health risks in such areas are poorly known. In this study, a former IZS area in Guizhou, China, was surveyed during 2008-2018 with 15 elements (Ag, As, Bi, Cd, Co, Cr, Cu, Hg, In, Ni, Pb, Sb, Sn, Tl, Zn) being analyzed. The results indicate that most elements (e.g., Ag, As, Cd, Cu, Pb, Sb, Sn, Zn) in ground dust decreased significantly after the cessation of the IZS in 2006; nevertheless, some elements still remained at relatively high levels in 2018, e.g., Pb (average: 762 ± 647 mg/kg), Zn (average: 1287 ± 753 mg/kg), Cd (average: 7.76 ± 5.06 mg/kg), and As (average: 41.9 ± 34.8 mg/kg), indicating they might come from the local contaminated soils, slag residues and smelting potteries. In terms of the impacts on human health, children have both higher non-carcinogenic and carcinogenic risks than that of adults, with the latter subpopulation having a lower risk than the threshold values. Pb and As were the two elements with the highest non-carcinogenic risk for children, the hazard index of local children was still higher than the threshold of 1 (e.g., 1.43 for As, 2.09 for Pb) in 2018. The carcinogenic risk of As exposure to children dropped more than two times to 6.42 × 10 in 2018, which falls below the tolerable range (10-10). This study revealed that although the concentration of heavy metal(loid)s in ground dust and linked health risk in the IZS area has reduced dramatically after the cessation of IZS, continued removal of slag residues and smelting potteries is necessary for further decreasing the human health risk.
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http://dx.doi.org/10.3390/ijerph18030893DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7864351PMC
January 2021

Significant mercury efflux from a Karst region in Southwest China - Results from mass balance studies in two catchments.

Sci Total Environ 2021 May 14;769:144892. Epub 2021 Jan 14.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; CAS Centre for Excellence in Quaternary Science and Global Change, Xi'an 710061, China. Electronic address:

Karst regions have long been recognised as landscapes of ecological vulnerability, however the mass balance and fate of mercury (Hg) in karst regions have not been well documented. This study focused on the largest contiguous karst area in China and investigated Hg mass balance in two catchments, one with high geological Hg (Huilong) and the other representative of regional background Hg (Chenqi). The mass balance of Hg was calculated separately for the two catchments by considering Hg in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilizer, crop harvesting, air-surface Hg exchange, surface runoff and underground runoff. Results show that litterfall Hg deposition is the largest loading (from atmosphere) of Hg in both catchments, accounting for 61.5% and 38.5% of the total Hg input at Huilong and Chenqi, respectively. Air-surface Hg exchange is the largest efflux, accounting for 71.7% and 44.6% of the total Hg output from Huilong and Chenqi, respectively. Because both catchments are subject to farm and forest land use, cultivation plays an important role in shaping Hg fate. Mercury loading through fertilizer was ranked as the second largest input (28.5%) in Chenqi catchment and Hg efflux through crop harvest was ranked as the second largest output pathway in both Huilong (27.0%) and Chenqi (52.9%). The net Hg fluxes from the catchments are estimated to be 1498 ± 1504 μg m yr and 4.8 ± 98.2 μg m yr. The significantly greater magnitude of net Hg source in Huilong is attributed to higher air-surface Hg exchange. The output/input ratio of Hg in this study was much greater than has been reported for other forest or agricultural ecosystems and indicates that the karst region of Southwest China is a significant source of atmospheric Hg. The results of this study should be considered in the development of pollution control policies which seek to conserve fragile karst ecosystems characterised by high geological background of Hg.
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http://dx.doi.org/10.1016/j.scitotenv.2020.144892DOI Listing
May 2021

Mercury accumulation in vegetable Houttuynia cordata Thunb. from two different geological areas in southwest China and implications for human consumption.

Sci Rep 2021 01 8;11(1):52. Epub 2021 Jan 8.

Department of Resources and Environment, Zunyi Normal College, Zunyi, 563006, People's Republic of China.

Houttuynia cordata Thunb. (HCT) is a common vegetable native to southwest China, and grown for consumption. The results suggested that THg contents in all parts and MeHg in underground parts of HCT in Hg mining areas were much higher than those in non-Hg mining areas. The highest THg and MeHg content of HCT were found in the roots, followed by the other tissues in the sequence: roots > leaves > rhizomes > aboveground stems (THg), and roots > rhizomes > aboveground stems > leaves (MeHg). The average THg bioaccumulation factor (BCF) of HCT root in the Hg mining area and in non-Hg mining areas could reach 1.02 ± 0.71 and 0.99 ± 0.71 respectively, indicating that HCT is a Hg accumulator. And the THg and MeHg contents in all tissues of HCT, including the leaves, were significantly correlated with THg and MeHg content in the soil. Additionally, preferred dietary habits of HCT consumption could directly affect the Hg exposure risk. Consuming the aboveground parts (CAP) of HCT potentially poses a high THg exposure risk and consuming the underground parts (CUP) may lead to a relatively high MeHg exposure risk. Only consuming the rhizomes (OCR) of the underground parts could significantly reduce the exposure risk of THg and to some extent of MeHg. In summary, HCT should not be cultivated near the Hg contaminated sites, such as Hg tailings, as it is associated with a greater risk of Hg exposure and high root Hg levels, and the roots should be removed before consumption to reduce the Hg risk.
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http://dx.doi.org/10.1038/s41598-020-80183-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7794452PMC
January 2021

Microaerophilic Oxidation of Fe(II) Coupled with Simultaneous Carbon Fixation and As(III) Oxidation and Sequestration in Karstic Paddy Soil.

Environ Sci Technol 2021 03 7;55(6):3634-3644. Epub 2021 Jan 7.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang550081, China.

Microaerophilic Fe(II)-oxidizing bacteria are often chemolithoautotrophs, and the Fe(III) (oxyhydr)oxides they form could immobilize arsenic (As). If such microbes are active in karstic paddy soils, their activity would help increase soil organic carbon and mitigate As contamination. We therefore used gel-stabilized gradient systems to cultivate microaerophilic Fe(II)-oxidizing bacteria from karstic paddy soil to investigate their capacity for Fe(II) oxidation, carbon fixation, and As sequestration. Stable isotope probing demonstrated the assimilation of inorganic carbon at a maximum rate of 8.02 mmol C m d. Sequencing revealed that , , , , , , unclassified , and unclassified were fixing carbon. Fe(II) oxidation produced Fe(III) (oxyhydr)oxides, which can absorb and/or coprecipitate As. Adding As(III) decreased the diversity of functional bacteria involved in carbon fixation, the relative abundance of predicted carbon fixation genes, and the amount of carbon fixed. Although the rate of Fe(II) oxidation was also lower in the presence of As(III), over 90% of the As(III) was sequestered after oxidation. The potential for microbially mediated As(III) oxidation was revealed by the presence of arsenite oxidase gene (), denoting the potential of the Fe(II)-oxidizing and autotrophic microbial community to also oxidize As(III). Thisstudy demonstrates that carbon fixation coupled to Fe(II) oxidation can increase the carbon content in soils by microaerophilic Fe(II)-oxidizing bacteria, as well as accelerate As(III) oxidation and sequester it in association with Fe(III) (oxyhydr)oxides.
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http://dx.doi.org/10.1021/acs.est.0c05791DOI Listing
March 2021

Partitioning behaviors of zinc in eight coal-fired power plants with different fueled coals and air pollution control devices.

Environ Sci Pollut Res Int 2021 May 7;28(17):21599-21609. Epub 2021 Jan 7.

School of Resources and Environment, Zunyi Normal College, Zunyi, 563006, China.

Emissions from coal-fired power plants (CFPPs) have a negative impact on the environment and metals are one of the categories of substances that have received considerable attention. In the present study, atmospheric zinc (Zn) emissions from eight CFPPs with different kinds of boilers and air pollution control devices (APCDs) in Guizhou Province, Southwest China, were investigated as well as the partitioning of this metal among boilers and APCDs. During the investigation of a CFPP, samples were taken of input and output materials during the same period. Our results give a Zn content of 32-165 mg kg for feed coal, 52-237 mg kg for bottom ash, 108-725 mg kg for fly ash, 1.2-6.0 mg kg for limestone, 1.6-7.3 mg kg for gypsum, and 1.39-7.06 μg Nm for stack gas. Most of the zinc content in the feed coal goes with the flue gas after combustion and amounts to 94.2-96.1% and 60.5-78.1% for pulverized coal-fired boilers (PC) and circulating fluidized bed boilers (CFB), respectively. Based on input Zn, a larger share (80.8-96.4%) ends up the captured fly ash of PC boilers than the case of CFB boilers (66.1-73.6%). In turn, a minor portion is captured into the flue gas desulfurization gypsum, while we found a maximum of 0.05‰ is emitted into the atmosphere. The atmospheric emission factors (EMFs) of Zn for the eight CFPPs are 7.55-57.22 mg ton coal, 4.17-22.75 μg (kWh), or 0.39-2.36 g TJ using different benchmarks. Overall, the calculated emission factors here are distinctively low with the upgrading of APCDs in recent years. An estimation of 1276 ± 1047 kg year (range: 498-3777 kg year) of Zn is emitted into the atmosphere from the CFPPs of Guizhou Province in 2017 by coupling the EMFs obtained from this study and the coal consumption by this category of power plants.
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http://dx.doi.org/10.1007/s11356-020-11524-2DOI Listing
May 2021

Use of mercury isotopes to quantify sources of human inorganic mercury exposure and metabolic processes in the human body.

Environ Int 2021 02 23;147:106336. Epub 2020 Dec 23.

Observatoire Midi-Pyrénées, Géosciences Environnement Toulouse (GET), CNRS, IRD, Université Paul Sabatier, Toulouse 31400, France.

The pathways of human mercury (Hg) exposure are complex and accurate understanding of relative contributions from different pathways are crucial for risk assessment and risk control. In this study, we determined total Hg concentration and Hg isotopic composition of human urine, dietary components, and inhaled air in the Wanshan Hg mining area (MA), Guiyang urban area (UA), and Changshun background area (BA) to understand Hg exposure sources and metabolic processes in human body. At the three studied sites, total gaseous mercury (TGM) showed negative δHg (-3.11‰ to + 1.12‰) and near-zero ΔHg (-0.16‰ to + 0.13‰), which were isotopically distinguishable from Hg isotope values of urine (δHg: -4.02‰ to - 0.84‰; ΔHg: -0.14‰ to 0.64‰). We observed an offset of -1.01‰ to -1.6‰ in δHg between TGM and urine samples, and an offset of -1.01‰ to 0.80‰ in δHg between rice and urine samples, suggesting that lighter isotopes are more easily accumulated in the kidneys and excreted by urine. We proposed that the high positive ΔHg in urine samples of UA was derived from fish consumption. The results of a binary mixing model based on ΔHg were compared with those from a classic dietary model. The results from the MIF binary model showed that fish consumption accounted for 22% of urine Hg in the families at UA, whereas fish consumption contributed limited Hg to MA and BA. This study highlighted that Hg isotopes can be a useful tracer in understanding the sources and fates of Hg in human bodies.
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http://dx.doi.org/10.1016/j.envint.2020.106336DOI Listing
February 2021

Determination of trace levels of selenium in natural water, agriculture soil and food samples by vortex assisted liquid-liquid microextraction method: Multivariate techniques.

Food Chem 2021 May 23;344:128706. Epub 2020 Nov 23.

National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan.

A green vortex assisted based liquid-liquid microextraction (VA-LLME) method was developed for preconcentration of selenium. Ammonium pyrrolidine dithiocarbamate (APDC) was used to form a hydrophobic complex with selenium in natural water, agricultural soil and food samples by GFAAS. Whereas Triton X-114, a nonionic surfactant and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid were used for Se extraction as a dispersing medium. The conical flasks contents were shack on a vortex mixer to increase the extraction efficiency. Multivariate techniques were used to evaluate extraction parameters; pH, vortex time, APDC amount, volume of ionic liquid and Triton X-114 and centrifugation rate on the recovery of Se. The central composite design (CCD) was used for further optimization of the essential extraction parameters. The enhancement factor and limit of detection were obtained as 98.7 and 0.07 µg L. The certified reference materials was used for accuracy of method and the related standard deviation was found to be 3.51%. The resulted data indicated that concentrations of Se in all types of water samples were below the permissible limit recommended by WHO.
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http://dx.doi.org/10.1016/j.foodchem.2020.128706DOI Listing
May 2021

Mercury, microcystins and Omega-3 polyunsaturated fatty acids in farmed fish in eutrophic reservoir: Risk and benefit assessment.

Environ Pollut 2021 Feb 10;270:116047. Epub 2020 Nov 10.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, PR China.

Fish is an important source of nutritional omega-3 (n-3) polyunsaturated fatty acids, but it also readily accumulates toxic mercury (Hg) and microcystins (MC) in eutrophic aquatic systems. In China, farmed fish was widely consumed, and aquaculture has caused pervasive eutrophication of freshwater lakes, resulting in the increasing accumulation of MC in fish tissue. To assess the risk-benefit of consuming farmed fish, 205 fish samples of 10 primary species were collected from the eutrophic Wujiangdu (WJD) Reservoir, SW China. The contents of Hg, microcystin-RR (MC-RR), microcystin-LR (MC-LR), and polyunsaturated fatty acids (PUFA) in fish were analyzed. The results showed that THg and MeHg concentrations in all fish sampls were well below the safety limit (500 ng/g w.w) established by the Standardization Administration of China, with average values of 22.9 ± 22.8 and 6.0 ± 6.6 ng/g wet weight (w.w.), respectively. Average concentrations of MC-RR and MC-LR were 40 ± 80 and 50 ± 80 ng/g w.w., respectively. MC-RR and MC-LR concentrations in fish were significantly higher in silver carp and black carp than in perch and catfish (p < 0.05). In nutritional terms, average concentrations of n-3 PUFA and the eicosapentaenoic (EPA) + docosahexaenoic acids (DHA) of fish were 2.0 ± 2.5 and 1.4 ± 0.5 mg/g w.w., respectively. The risk-benefit assessment suggests that the n-3 PUFA benefits from consuming all farmed fish species in the WJD Reservoir outweigh the adverse effects of MeHg. However, except for perch, most fish species still pose a high MC-LR exposure risk that created a requirement for fish consumption advisories and monitoring. Consequently, more attention should be paid on the health risk of combined exposure to pollutants by aquatic product consumption.
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http://dx.doi.org/10.1016/j.envpol.2020.116047DOI Listing
February 2021

Behavior of thallium in pulverized coal utility boiler installations in Southwest China.

J Air Waste Manag Assoc 2021 04 13;71(4):488-500. Epub 2021 Jan 13.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, People's Republic of China.

Thallium (Tl) is a toxic element that exists in coal at trace level. Coal-fired power plants (CFPPs) consume large amounts of coal and can potentially release this element into surrounding environment. However, knowledge of fates of Tl inside CFPPs and associated atmospheric emissions is still very limited. In this study, five CFPPs with pulverized coal boilers (PC) in Guizhou province, southwest China, were selected for investigation. All input and output solid materials and the stack flue gas samples were collected simultaneously. Tl concentrations in feed coal (0.10-0.34 mg·kg) of the five CFPPS were only a third to one half of the national average value. Tl concentrations were obviously higher in fly ash (0.39-1.13 mg·kg) than in bottom ash (0.09-0.25 mg·kg), indicating notable redistribution of Tl during coal combustion. Tl concentrations were low in limestone (0.01-0.02 mg·kg), flue gas desulfurization gypsum (0.01-0.03 mg·kg), and the stack flue gas (0.006-0.011 μg·Nm). Most Tl inside these CFPPs was captured by electrostatic precipitator or electrostatic precipitator-fabric filter (ESP/ESP-FF) fly ash (88.66%-97.44%), followed by bottom ash (2.13%-10.73%), gypsum (<3.89%), and stack emissions (0.01%-0.05%). Atmospheric emission factors of Tl from different CFPPs are in the range of 0.04-0.09 mg Tl·t coal, 0.02-0.04 μg·(kW·h), or 0.002-0.004 g Tl·TJ. Using these emission factors, a total of 3.96 ± 1.32 kg (range: 2.64-5.94 kg) Tl is estimated to be released into the atmosphere annually from CFPPs in Guizhou in 2017. To avoid the cross-media contamination from the combustion products, careful treatment of the captured fly ash, bottom ash, and gypsum is needed, considering that a large amount of Tl (average: 728 kg·yr; range: 664-792 kg·yr) is retained in these solid combustion products and the possibility of formation of more toxic Tl during the combustion process.: Thallium (Tl) is a rare but toxic element. Identifying and quantifying its source are high priorities for controling its contamination. Coal-fired power plants (CFPPs) were thought an important source of Tl, but few field studies had been conducted for this area. In this article, we investigated the fate of Tl in five pulverized coal utility power plants in Guizhou province, Southwest China, and found the Tl concentration in stack gas is in low levels of 0.006-0.011 μg·Nm, and less than 0.05% of total input of Tl is escaped into the ambient atmosphere. The majority of Tl (88.7%-97.4% of the total output) is detained by the ESP/ESP-FF fly ashes. Compared to the little amount (~4 kg·yr) of Tl that discharged into the atmosphere from Guizhuo's CFPPs in 2017, more Tl (over 700 kg) ends up in the solid coal combustion products each year, which makes the need of careful disposal of this solid combustion waste to prevent the mobilization of Tl into the environment.
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http://dx.doi.org/10.1080/10962247.2020.1853630DOI Listing
April 2021

Monthly variations in mercury exposure of school children and adults in an industrial area of southwestern China.

Environ Res 2021 05 22;196:110362. Epub 2020 Oct 22.

Observatoire Midi-Pyrénées, Laboratoire Géosciences Environnement Toulouse, IRD-CNRS-Université Toulouse, 14 Avenue Edouard Belin, Toulouse, 31400, France.

Recent studies have shown that rice consumption can be the major pathway for human methylmercury (MeHg) exposure in inland China. However, few studies have considered the susceptible population of school children's exposure through rice ingestion. In this study, monthly variations in total Hg (THg)/MeHg concentrations in rice, fish, hair, and urine samples were studied to evaluate the Hg (both THg and MeHg) exposure in Guiyang, a typical industrial area with high anthropogenic emission of Hg. A total of 17 primary school (school A) students, 29 middle school (school B) students, and 46 guardians participated in this study for one year. Hair THg, hair MeHg, and urine THg concentrations ranged from 355-413 ng g, 213-236 ng g, and 469-518 ng g Creatinine (ng·g Cr), respectively, and no significant differences were observed between different genders and age groups. Hair and urine Hg concentrations showed slightly higher values in the cold season (October to February) than the hot season (March to September), but without significant difference. High monthly variability of individual hair and urine Hg concentrations suggested that long-term study could effectively decrease the uncertainty. The school students showed significantly higher urine THg concentrations than adults due to children's unique physiological structure and behaviors. Probable daily intake (PDI) of MeHg via rice and fish ingestion averaged at 0.0091, 0.0090, and 0.0079 μg kg d for school A students, school B students, and their guardians, respectively, which means that 86%, 84%, and 87% of the PDI were originated from rice ingestion, respectively. Therefore, more attention should be paid to children as a susceptible population. The results indicated low risk of Hg exposure via rice and fish consumption for urban residents in a Chinese industrial city.
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http://dx.doi.org/10.1016/j.envres.2020.110362DOI Listing
May 2021

Exogenous selenium (cadmium) inhibits the absorption and transportation of cadmium (selenium) in rice.

Environ Pollut 2021 Jan 27;268(Pt A):115829. Epub 2020 Oct 27.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an, 710061, Shanxi Province, China. Electronic address:

Antagonism between selenium (Se) and cadmium (Cd) has been demonstrated in plants. However, a mutual suppression threshold for Se and Cd has not been identified in previous studies using Cd or Se individually. To fill this knowledge gap, we determined the levels of Se and Cd in various tissues of rice under concentration gradients of Se and Cd with different Se application times via hydroponic experiments. The results showed that the application of exogenous Se or Cd reduced the uptake and transport of the other. When the molar ratio of Se/Cd (R (Se/Cd)) was higher than 1, the concentration and transfer factor of Cd (TF-Cd) in all parts of rice simultaneously reached the lowest values. The minimum Se absorption in rice was obtained at R (Cd/Se) greater than 20, while no inhibition threshold was found for Se transport. In addition, approximately 1:1 R (Se/Cd) was observed in roots and the addition of exogenous Cd or Se promoted the enrichment of the other element in roots. These data suggested a mutual inhibition of Se and Cd in their absorption, transportation and accumulation in rice, which might be related to the formation of insoluble Cd-Se complexes in roots. This study provided new insights into a plausible explanation of the interactions between Se and Cd and contributed to the remediation and treatment of combined Se and Cd pollution in farmland systems.
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http://dx.doi.org/10.1016/j.envpol.2020.115829DOI Listing
January 2021

Isotopic Fractionation and Source Appointment of Methylmercury and Inorganic Mercury in a Paddy Ecosystem.

Environ Sci Technol 2020 11 28;54(22):14334-14342. Epub 2020 Oct 28.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.

Bioaccumulation of methylmercury (MeHg) in rice grains has been an emerging issue of human health, but the mechanism of bioaccumulation is still poorly understood. Mercury (Hg) isotope measurements are powerful tools for tracing the sources and biogeochemical cycles of Hg in the environment. In this study, MeHg compound-specific stable isotope analysis (CSIA) was developed in paddy soil and rice plants to trace the biogeochemical cycle of Hg in a paddy ecosystem during the whole rice-growing season. Isotopic fractionation was analyzed separately for MeHg and inorganic Hg (IHg). Results showed distinct isotopic signals between MeHg and IHg in rice plants, indicating different sources. δHg values of MeHg showed no significant differences between roots, stalks, leaves, and grains at each growth stage. The similar ΔHg values of MeHg between rice tissues (0.14 ± 0.08‰, 2SD, = 12), soil (0.13 ± 0.03‰, 2SD, = 4), and irrigation water (0.17 ± 0.09‰, 2SD, = 5) suggested that the soil-water system was the original source of MeHg in rice plants. ΔHg values of IHg in the paddy ecosystem indicated that water, soil, and atmosphere contributed to IHg in grains, leaves, stalks, and roots with varying degree. This study demonstrates that successful application of MeHg CSIA can improve our understanding of the sources and bioaccumulation mechanisms of MeHg and IHg in the paddy ecosystems.
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http://dx.doi.org/10.1021/acs.est.0c03341DOI Listing
November 2020

Methanogenesis Is an Important Process in Controlling MeHg Concentration in Rice Paddy Soils Affected by Mining Activities.

Environ Sci Technol 2020 11 21;54(21):13517-13526. Epub 2020 Oct 21.

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, P. R. China.

Rice paddies are agricultural sites of special concern because the potent toxin methylmercury (MeHg), produced in rice paddy soils, accumulates in rice grains. MeHg cycling is mostly controlled by microbes but their importance in MeHg production and degradation in paddy soils and across a Hg concentration gradient remains unclear. Here we used surface and rhizosphere soil samples in a series of incubation experiments in combination with stable isotope tracers to investigate the relative importance of different microbial groups on MeHg production and degradation across a Hg contamination gradient. We showed that sulfate reduction was the main driver of MeHg formation and concentration at control sites, and that methanogenesis had an important and complex role in MeHg cycling as Hg concentrations increased. The inhibition of methanogenesis at the mining sites led to an increase in MeHg production up to 16.6-fold and a decrease in MeHg degradation by up to 77%, suggesting that methanogenesis is associated with MeHg degradation as Hg concentrations increased. This study broadens our understanding of the roles of microbes in MeHg cycling and highlights methanogenesis as a key control of MeHg concentrations in rice paddies, offering the potential for mitigation of Hg contamination and for the safe production of rice in Hg-contaminated areas.
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http://dx.doi.org/10.1021/acs.est.0c00268DOI Listing
November 2020
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