1
|
Wu Z, Li Z, Shao B, Chen J, Cui X, Cui X, Liu X, Zhao YX, Pu Q, Liu J, He W, Liu Y, Liu Y, Wang X, Meng B, Tong Y. Differential response of Hg-methylating and MeHg-demethylating microbiomes to dissolved organic matter components in eutrophic lake water. JOURNAL OF HAZARDOUS MATERIALS 2024; 465:133298. [PMID: 38141310 DOI: 10.1016/j.jhazmat.2023.133298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 12/01/2023] [Accepted: 12/15/2023] [Indexed: 12/25/2023]
Abstract
Methylmercury (MeHg) production in aquatic ecosystems is a global concern because of its neurotoxic effect. Dissolved organic matter (DOM) plays a crucial role in biogeochemical cycling of Hg. However, owing to its complex composition, the effects of DOM on net MeHg production have not been fully understood. Here, the Hg isotope tracer technique combined with different DOM treatments was employed to explore the influences of DOM with divergent compositions on Hg methylation/demethylation and its microbial mechanisms in eutrophic lake waters. Our results showed that algae-derived DOM treatments enhanced MeHg concentrations by 1.42-1.53 times compared with terrestrial-derived DOM. Algae-derived DOM had largely increased the methylation rate constants by approximately 1-2 orders of magnitude compared to terrestrial-derived DOM, but its effects on demethylation rate constants were less pronounced, resulting in the enhancement of net MeHg formation. The abundance of hgcA and merB genes suggested that Hg-methylating and MeHg-demethylating microbiomes responded differently to DOM treatments. Specific DOM components (e.g., aromatic proteins and soluble microbial byproducts) were positively correlated with both methylation rate constants and the abundance of Hg-methylating microbiomes. Our results highlight that the DOM composition influences the Hg methylation and MeHg demethylation differently and should be incorporated into future Hg risk assessments in aquatic ecosystems.
Collapse
Affiliation(s)
- Zhengyu Wu
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Zhike Li
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Bo Shao
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Ji Chen
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
| | - Xiaomei Cui
- School of Ecology and Environment, Tibet University, Lhasa 850000, China
| | - Xiaoyu Cui
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Xianhua Liu
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Ying Xin Zhao
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Qiang Pu
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
| | - Jiang Liu
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
| | - Wei He
- School of Water Resource and Environment, China University of Geoscience (Beijing), Beijing 100083, China
| | - Yiwen Liu
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
| | - Yurong Liu
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China
| | - Xuejun Wang
- College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
| | - Bo Meng
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
| | - Yindong Tong
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China; School of Ecology and Environment, Tibet University, Lhasa 850000, China.
| |
Collapse
|
2
|
Li D, Han X, Li Y. Mechanism of methylmercury photodegradation in the yellow sea and East China Sea: Dominant pathways, and role of sunlight spectrum and dissolved organic matter. WATER RESEARCH 2024; 251:121112. [PMID: 38198975 DOI: 10.1016/j.watres.2024.121112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 12/31/2023] [Accepted: 01/05/2024] [Indexed: 01/12/2024]
Abstract
Mercury (Hg) is among the most concerned contaminants in the world due to its high toxicity, prevalent existence in the environments, and bioaccumulation via food chain. Methylmercury (MeHg) is the major form of Hg that accumulates along the food chain and poses threat to humans and wild life. Photodegradation is the dominant process that MeHg is eliminated from freshwater system and upper ocean. The formation of MeHg-dissolved organic matter (DOM) complexes and a variety of free radicals (FR)/reactive oxygen species (ROS) have been previously proposed to be involved in MeHg photodegradation. However, most of these studies were conducted in freshwater, and the mechanism of MeHg photodegradation in seawater remains unclear. In this study, the main pathways of MeHg photodegradation in the seawater of Yellow Sea (YS) and East China Sea (ECS) were investigated using FR/ ROS scavenger addition and DOM competing-ligand addition techniques. The results showed that direct photodegradation of MeHg-DOM complexes is the major pathway of MeHg photodegradation in the YS and ECS, while indirect photolysis of MeHg by hydroxyl radical (·OH) also plays a certain role at some sites. MeHg photodegradation was found to be mainly induced by ultraviolet (UV) light rather than visible light in YS and ECS seawater, and the contribution of UV-B was higher than UV-A which was opposite to that previously reported in freshwater. The energy for breaking the bond of CHg in MeHg-Cl complexes formed in seawater is higher than that in MeHg-DOM complexes and this may cause the relatively greater contribution of UV-B with higher energy to MeHg photodegradation in seawater. In addition, MeHg photodegradation in various fractions of natural DOM with different molecular weights, hydrophilicity/hydrophobicity and acid-base was tested. MeHg photodegradation rates (kd) varied in these fractions and kd in high molecular weight DOM and hydrophobic Acid (HOA) fractions were faster than that in the other fractions. A significantly positive correlation was observed between kd and thiol concentrations while there was no significant correlation between kd and other measured parameters representing the composition of DOM (specific UV absorbance at 254 nm (SUVA254), spectral slope (SR), chromophoric dissolved organic matter (CDOM), humification index (HIX), biological index (BIX) and fluorescent components). These results indicate that thiol may be the key functional group in DOM affecting the photodegradation of MeHg in the YS and ECS.
Collapse
Affiliation(s)
- Dan Li
- Weifang University, Weifang 261061, China
| | - Xiaoxiao Han
- Shandong Institute for Food and Drug Control, Jinan 250000, China
| | - Yanbin Li
- Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, and College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China.
| |
Collapse
|
3
|
Yu C, Peng M, Wang X, Pan X. Photochemical demethylation of methylmercury (MeHg) in aquatic systems: A review of MeHg species, mechanisms, and influencing factors. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 344:123297. [PMID: 38195023 DOI: 10.1016/j.envpol.2024.123297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Revised: 12/01/2023] [Accepted: 01/02/2024] [Indexed: 01/11/2024]
Abstract
Photodemethylation is the major pathway of methylmercury (MeHg) demethylation in surface water before uptake by the food chain, whose mechanisms and influence factors are still not completely understood. Here, we review the current knowledge on photodemethylation of MeHg and divide MeHg photolysis into three pathways: (1) direct photodemethylation, (2) free radical attack, and (3) intramolecular electron or energy transfer. In aquatic environments, dissolved organic matter is involved into all above pathways, and due to its complex compositions, properties and concentrations, DOM poses multiple functions during the PD of MeHg. DOM-MeHg complex (mainly by sulfur-containing molecules) might weaken the C-Hg bond and enhance PD through both direct and indirect pathways. In special, synergistic effects of both strong binding sites and chromophoric moieties in DOM might lead to intramolecular electron or energy transfer. Moreover, DOM might play a role of radical scavenger; while triplet state DOM, which is generated by chromophoric DOM under light, might become a source of free radicals. Apart from DOMs, transition metals, halides, NO3-, NO2-, and carbonates also act as radical initialaters or scavengers, and significantly pose effects on radical demethylation, which is generally mediated by hydroxyl radicals and singlet oxygen. Environmental factors such as pH, light wavelength, light intensity, dissolved oxygen, salinity, and suspended particles also affect the PD of MeHg. This study assessed previously published works on three major mechanisms, with the goal of providing general estimates for photodemethylation under various environment factors according to know effects, and highlighting the current uncertainties for future research directions.
Collapse
Affiliation(s)
- Chenghao Yu
- Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China
| | - Mao Peng
- Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China
| | - Xiaonan Wang
- Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China
| | - Xiangliang Pan
- Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China.
| |
Collapse
|
4
|
Lin H, Wei Y, Li S, Mao X, Qin J, Su S, He T. Changes in transcriptome regulations of a marine rotifer Brachionus plicatilis under methylmercury stress. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART D, GENOMICS & PROTEOMICS 2024; 49:101177. [PMID: 38104474 DOI: 10.1016/j.cbd.2023.101177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 12/04/2023] [Accepted: 12/07/2023] [Indexed: 12/19/2023]
Abstract
Mercury (Hg), a heavy metal pollutant worldwide, can be transformed into methylmercury (MeHg) by various aquatic microorganisms in water, thus accumulating along the aquatic food chain and posing a particular challenge to human health. Zooplankton plays a crucial role in aquatic ecosystems and serves as a major component of the food chain. To evaluate the effects of MeHg on the rotifer Brachionus plicatilis and reveal the underlying mechanism of these effects, we exposed B. plicatilis to MeHg by either direct immersion or by feeding with MeHg-poisoned Chlorella pyrenoidesa, respectively, and conducted a transcriptomic analysis. The results showed that B. plicatilis directly exposed to MeHg by immersion showed significant enrichment of the glutathione metabolism pathway for detoxification of MeHg. In addition, the exposure to MeHg by feeding induced a significant enrichment of lysosome and notch signaling pathways of rotifers, supporting the hypothesis that MeHg can induce autophagy dysfunction in cells and disturb the nervous system of rotifers. In two different routes of MeHg exposure, the pathway of cytochrome P450 in rotifers showed significant enrichment for resisting MeHg toxicity. Our results suggest further studies on the potential mechanism and biological responses of MeHg toxicity in other links of the aquatic food chain.
Collapse
Affiliation(s)
- Hangyu Lin
- College of Fisheries, Southwest University, Chongqing 400715, China; Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, 400715, China
| | - Yanlin Wei
- College of Fisheries, Southwest University, Chongqing 400715, China; Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, 400715, China
| | - Songzhang Li
- College of Fisheries, Southwest University, Chongqing 400715, China
| | - Xiaodong Mao
- College of Fisheries, Southwest University, Chongqing 400715, China; Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, 400715, China
| | - Jianguang Qin
- College of Science and Engineering, Flinders University, South Australia 5001, Australia
| | - Shengqi Su
- College of Fisheries, Southwest University, Chongqing 400715, China; Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, 400715, China.
| | - Tao He
- College of Fisheries, Southwest University, Chongqing 400715, China; Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, 400715, China.
| |
Collapse
|
5
|
Willacker J, Eagles-Smith CA, Chandler JA, Naymik J, Myers R, Krabbenhoft DP. Reservoir Stratification Modulates the Influence of Impoundments on Fish Mercury Concentrations along an Arid Land River System. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:21313-21326. [PMID: 38051342 PMCID: PMC10734268 DOI: 10.1021/acs.est.3c04646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 10/20/2023] [Accepted: 10/25/2023] [Indexed: 12/07/2023]
Abstract
Impoundment is among the most common hydrologic alterations with impacts on aquatic ecosystems that can include effects on mercury (Hg) cycling. However, landscape-scale differences in Hg bioaccumulation between reservoirs and other habitats are not well characterized nor are the processes driving these differences. We examined total Hg (THg) concentrations of Smallmouth Bass (Micropterus dolomieu) collected from reservoir, tailrace, and free-flowing reaches along an 863 km segment of the Snake River, USA, a semiarid river with 22 impoundments along its course. Across three size-classes (putative 1-year-old, first reproductive, and harvestable sized fish), THg concentrations in reservoirs and tailraces averaged 76% higher than those in free-flowing segments. Among reservoirs, THg concentrations were highest in reservoirs with inconsistent stratification patterns, 47% higher than annually stratified, and 144% higher than unstratified reservoirs. Fish THg concentrations in tailraces immediately downstream of stratified reservoirs were higher than those below unstratified (38-130%) or inconsistently stratified (32-79%) reservoirs. Stratification regimes influenced the exceedance of fish and human health benchmarks, with 52-80% of fish from stratifying reservoirs and downstream tailraces exceeding a human consumption benchmark, compared to 6-17% where stratification did not occur. These findings suggest that impoundment and stratification play important roles in determining the patterns of Hg exposure risk across the landscape.
Collapse
Affiliation(s)
- James
J. Willacker
- U.S.
Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, Oregon 97331, United States
| | - Collin A. Eagles-Smith
- U.S.
Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, Oregon 97331, United States
| | - James A. Chandler
- Idaho
Power Company, 1221 West Idaho Street, Boise, Idaho 83702, United States
| | - Jesse Naymik
- Idaho
Power Company, 1221 West Idaho Street, Boise, Idaho 83702, United States
| | - Ralph Myers
- Idaho
Power Company, 1221 West Idaho Street, Boise, Idaho 83702, United States
| | - David P. Krabbenhoft
- U.S.
Geological Survey, Upper Midwest Water Science Center, 8505 Research Way, Middleton, Wisconsin 53562, United States
| |
Collapse
|
6
|
Peterson BD, Poulin BA, Krabbenhoft DP, Tate MT, Baldwin AK, Naymik J, Gastelecutto N, McMahon KD. Metabolically diverse microorganisms mediate methylmercury formation under nitrate-reducing conditions in a dynamic hydroelectric reservoir. THE ISME JOURNAL 2023; 17:1705-1718. [PMID: 37495676 PMCID: PMC10504345 DOI: 10.1038/s41396-023-01482-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 07/13/2023] [Accepted: 07/14/2023] [Indexed: 07/28/2023]
Abstract
Brownlee Reservoir is a mercury (Hg)-impaired hydroelectric reservoir that exhibits dynamic hydrological and geochemical conditions and is located within the Hells Canyon Complex in Idaho, USA. Methylmercury (MeHg) contamination in fish is a concern in the reservoir. While MeHg production has historically been attributed to sulfate-reducing bacteria and methanogenic archaea, microorganisms carrying the hgcA gene are taxonomically and metabolically diverse and the major biogeochemical cycles driving mercury (Hg) methylation are not well understood. In this study, Hg speciation and redox-active compounds were measured throughout Brownlee Reservoir across the stratified period in four consecutive years (2016-2019) to identify the location where and redox conditions under which MeHg is produced. Metagenomic sequencing was performed on a subset of samples to characterize the microbial community with hgcA and identify possible links between biogeochemical cycles and MeHg production. Biogeochemical profiles suggested in situ water column Hg methylation was the major source of MeHg. These profiles, combined with genome-resolved metagenomics focused on hgcA-carrying microbes, indicated that MeHg production occurs in this system under nitrate- or manganese-reducing conditions, which were previously thought to preclude Hg-methylation. Using this multidisciplinary approach, we identified the cascading effects of interannual variability in hydrology on the redox status, microbial metabolic strategies, abundance and metabolic diversity of Hg methylators, and ultimately MeHg concentrations throughout the reservoir. This work expands the known conditions conducive to producing MeHg and suggests that the Hg-methylation mitigation efforts by nitrate or manganese amendment may be unsuccessful in some locations.
Collapse
Affiliation(s)
- Benjamin D Peterson
- Department of Civil and Environmental Engineering, University of Wisconsin - Madison, Madison, WI, 53706, USA.
- Department of Bacteriology, University of Wisconsin - Madison, Madison, WI, 53706, USA.
- Department of Environmental Toxicology, University of California - Davis, Davis, CA, 95616, USA.
| | - Brett A Poulin
- Department of Environmental Toxicology, University of California - Davis, Davis, CA, 95616, USA
| | - David P Krabbenhoft
- U.S. Geological Survey, Upper Midwest Water Science Center, Mercury Research Laboratory, Madison, WI, 53726, USA
| | - Michael T Tate
- U.S. Geological Survey, Upper Midwest Water Science Center, Mercury Research Laboratory, Madison, WI, 53726, USA
| | - Austin K Baldwin
- U.S. Geological Survey, Idaho Water Science Center, Boise, ID, 83702, USA
| | | | | | - Katherine D McMahon
- Department of Civil and Environmental Engineering, University of Wisconsin - Madison, Madison, WI, 53706, USA
- Department of Bacteriology, University of Wisconsin - Madison, Madison, WI, 53706, USA
| |
Collapse
|
7
|
Poulin BA, Tate MT, Ogorek J, Breitmeyer SE, Baldwin AK, Yoder AM, Harris R, Naymik J, Gastelecutto N, Hoovestol C, Larsen C, Myers R, Aiken GR, Krabbenhoft DP. Biogeochemical and hydrologic synergy control mercury fate in an arid land river-reservoir system. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2023; 25:912-928. [PMID: 37186129 DOI: 10.1039/d3em00032j] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Reservoirs in arid landscapes provide critical water storage and hydroelectric power but influence the transport and biogeochemical cycling of mercury (Hg). Improved management of reservoirs to mitigate the supply and uptake of bioavailable methylmercury (MeHg) in aquatic food webs will benefit from a mechanistic understanding of inorganic divalent Hg (Hg(II)) and MeHg fate within and downstream of reservoirs. Here, we quantified Hg(II), MeHg, and other pertinent biogeochemical constituents in water (filtered and associated with particles) at high temporal resolution from 2016-2020. This was done (1) at inflow and outflow locations of three successive hydroelectric reservoirs (Snake River, Idaho, Oregon) and (2) vertically and longitudinally within the first reservoir (Brownlee Reservoir). Under spring high flow, upstream inputs of particulate Hg (Hg(II) and MeHg) and filter-passing Hg(II) to Brownlee Reservoir were governed by total suspended solids and dissolved organic matter, respectively. Under redox stratified conditions in summer, net MeHg formation in the meta- and hypolimnion of Brownlee reservoir yielded elevated filter-passing and particulate MeHg concentrations, the latter exceeding 500 ng g-1 on particles. Simultaneously, the organic matter content of particulates increased longitudinally in the reservoir (from 9-29%) and temporally with stratified duration. In late summer and fall, destratification mobilized MeHg from the upgradient metalimnion and the downgradient hypolimnion of Brownlee Reservoir, respectively, resulting in downstream export of elevated filter-passing MeHg and organic-rich particles enriched in MeHg (up to 43% MeHg). We document coupled biogeochemical and hydrologic processes that yield in-reservoir MeHg accumulation and MeHg export in water and particles, which impacts MeHg uptake in aquatic food webs within and downstream of reservoirs.
Collapse
Affiliation(s)
- Brett A Poulin
- Department of Environmental Toxicology, University of California, Davis, USA.
| | - Michael T Tate
- U.S. Geological Survey, Upper Midwest Water Science Center, USA
| | - Jacob Ogorek
- U.S. Geological Survey, Upper Midwest Water Science Center, USA
| | | | | | - Alysa M Yoder
- U.S. Geological Survey, Idaho Water Science Center, USA
| | - Reed Harris
- Reed Harris Environmental Ltd, Toronto, Canada
| | | | | | | | | | | | | | | |
Collapse
|
8
|
Chen T, Li Y, Liu J, Wang Y, Wei S. The burden of mild intellectual disability attributed to prenatal exposure to methylmercury in China, 2017. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2023; 254:114748. [PMID: 36921496 DOI: 10.1016/j.ecoenv.2023.114748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 03/05/2023] [Accepted: 03/06/2023] [Indexed: 06/18/2023]
Abstract
Methylmercury (MeHg) is a neurodevelopmental toxicant that is widespread in the environment and food. Considering the presence of multiple sources of MeHg exposure in the environment, the burden attributable to different exposure sources needs to be determined. This study aimed to estimate the burden of mild intellectual disability (MID) caused by in-utero exposure to MeHg and identify the attributable burden related to MeHg exposure from different sources in China. We applied the hair mercury concentrations from studies to evaluate the burden of MID associated with maternal MeHg exposure and quantify it by disability-adjusted life years (DALYs). The DALYs attributable to MeHg exposure sources were calculated by combining the total DALYs and the contribution rates of various sources of MeHg exposure. The maternal MeHg exposure resulted in 6504 MID cases and a loss of 63,354 DALYs in China in 2017. The contribution rates of aquatic products and rice were 52.2% and 27.1%, respectively, leading to health losses of 28,115 and 18,011 DALYs. The burden of MeHg-induced MID associated with aquatic products was high in coastal areas. Several sites such as Zhejiang, Hunan, and Guangxi had high DALYs caused by rice MeHg exposure. Regions with high DALYs of MID related to MeHg exposure require more attention. Local governments should establish targeted measures to reduce MeHg exposure, thus preventing health loss.
Collapse
Affiliation(s)
- Tingting Chen
- Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Yiling Li
- Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Jialin Liu
- Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Yibaina Wang
- Risk Assessment Division I, China National Center for Food Safety Risk Assessment, Building 2, 37 Guangqu Road, Beijing 100020, China.
| | - Sheng Wei
- Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; School of Public Health and Emergency Management, Southern University of Science and Technology, Shenzhen, 518000, China.
| |
Collapse
|
9
|
Millard G, Eckley CS, Luxton TP, Krabbenhoft D, Goetz J, McKernan J, DeWild J. Evaluating the influence of seasonal stratification on mercury methylation rates in the water column and sediment in a contaminated section of a western U.S.A. reservoir. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 316:120485. [PMID: 36279994 PMCID: PMC10259237 DOI: 10.1016/j.envpol.2022.120485] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 10/14/2022] [Accepted: 10/17/2022] [Indexed: 06/14/2023]
Abstract
Mercury methylation frequently occurs at the active oxic/anoxic boundary between the sediment bed and water column of lakes and reservoirs. Previous studies suggest that the predominant mercury methylation zone moves to the water column during periods of stratification and that high potential methylation rates (Km) in sediment require oxygenated overlying water. However, simultaneous measurements of methylmercury (MeHg) production in both the sediment and water column remain limited. Understanding the relative importance of sediment versus water column methylation and the impact of seasonal stratification on these processes has important implications for managing MeHg production. This study measured Km and potential demethylation rates (Kdm) using stable isotope tracers of unfiltered inorganic mercury and MeHg in sediments and water of the littoral and profundal zones of a shallow branch of the Nacimiento Reservoir in California's central coastal range. Field sampling was conducted once during winter (well-mixed/oxygenated conditions) and once during late summer (thermally stratified/anoxic conditions). The results showed very high ambient MeHg concentrations in hypolimnetic waters (up to 7.5 ng L-1; 79% MeHg/total Hg). During late summer, littoral sediments had higher Km (0.024 day-1) compared to profundal sediments (0.013 day-1). Anoxic water column Km were of similar magnitude to Km in the sediment (0.03 day-1). Following turnover, profundal sediment Km did not change significantly, but water column Km became insignificant. Summer and winter sediment Kdm were higher in profundal (2.35, 3.54 day-1, respectively) compared to the littoral sediments (0.52, 2.56 day-1, respectively). When modelled, Km in the water column could account for approximately 40% of the hypolimnetic MeHg. Our modelling results show that the remaining MeHg in the hypolimnion could originate from the profundal sediment. While further study is needed, these results suggest that addressing methylation in the water column and profundal sediment are of equal importance to any remediation strategy.
Collapse
Affiliation(s)
- Geoffrey Millard
- U.S.A. Environmental Protection Agency, Office of Research and Development, 26 W Martin Luther King Dr, Cincinnati, OH, 45220, USA.
| | - Chris S Eckley
- U.S.A. Environmental Protection Agency, Region 10, 1200 Sixth Avenue, Suite 155, Seattle WA, 98101, USA.
| | - Todd P Luxton
- U.S.A. Environmental Protection Agency, Office of Research and Development, 26 W Martin Luther King Dr, Cincinnati, OH, 45220, USA.
| | - David Krabbenhoft
- U.S.A. Geological Survey, Mercury Research Laboratory, 2280 Woodale Drive, Mounds View MN, 55112, USA.
| | - Jennifer Goetz
- U.S.A. Environmental Protection Agency, Office of Research and Development, 26 W Martin Luther King Dr, Cincinnati, OH, 45220, USA.
| | - John McKernan
- U.S.A. Environmental Protection Agency, Office of Research and Development, 26 W Martin Luther King Dr, Cincinnati, OH, 45220, USA.
| | - John DeWild
- U.S.A. Geological Survey, Mercury Research Laboratory, 2280 Woodale Drive, Mounds View MN, 55112, USA.
| |
Collapse
|
10
|
Barkay T, Gu B. Demethylation─The Other Side of the Mercury Methylation Coin: A Critical Review. ACS ENVIRONMENTAL AU 2022; 2:77-97. [PMID: 37101582 PMCID: PMC10114901 DOI: 10.1021/acsenvironau.1c00022] [Citation(s) in RCA: 38] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The public and environmental health consequences of mercury (Hg) methylation have drawn much attention and considerable research to Hg methylation processes and their dynamics in diverse environments and under a multitude of conditions. However, the net methylmercury (MeHg) concentration that accumulates in the environment is equally determined by the rate of MeHg degradation, a complex process mediated by a variety of biotic and abiotic mechanisms, about which our knowledge is limited. Here we review the current knowledge on MeHg degradation and its potential pathways and mechanisms. We describe detoxification by resistant microorganisms that employ the Hg resistance (mer) system to reductively break the carbon-mercury (C-Hg) bond producing methane (CH4) and inorganic mercuric Hg(II), which is then reduced by the mercuric reductase to elemental Hg(0). Very recent research has begun to elucidate a mechanism for the long-recognized mer-independent oxidative demethylation, likely involving some strains of anaerobic bacteria as well as aerobic methane-oxidizing bacteria, i.e., methanotrophs. In addition, photochemical and chemical demethylation processes are described, including the roles of dissolved organic matter (DOM) and free radicals as well as dark abiotic demethylation in the natural environment about which little is currently known. We focus on mechanisms and processes of demethylation and highlight the uncertainties and known effects of environmental factors leading to MeHg degradation. Finally, we suggest future research directions to further elucidate the chemical and biochemical mechanisms of biotic and abiotic demethylation and their significance in controlling net MeHg production in natural ecosystems.
Collapse
Affiliation(s)
- Tamar Barkay
- Department of Biochemistry and Microbiology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey 08901, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| |
Collapse
|