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Sonke JE, Angot H, Zhang Y, Poulain A, Björn E, Schartup A. Global change effects on biogeochemical mercury cycling. AMBIO 2023; 52:853-876. [PMID: 36988895 PMCID: PMC10073400 DOI: 10.1007/s13280-023-01855-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 02/07/2023] [Accepted: 03/03/2023] [Indexed: 06/18/2023]
Abstract
Past and present anthropogenic mercury (Hg) release to ecosystems causes neurotoxicity and cardiovascular disease in humans with an estimated economic cost of $117 billion USD annually. Humans are primarily exposed to Hg via the consumption of contaminated freshwater and marine fish. The UNEP Minamata Convention on Hg aims to curb Hg release to the environment and is accompanied by global Hg monitoring efforts to track its success. The biogeochemical Hg cycle is a complex cascade of release, dispersal, transformation and bio-uptake processes that link Hg sources to Hg exposure. Global change interacts with the Hg cycle by impacting the physical, biogeochemical and ecological factors that control these processes. In this review we examine how global change such as biome shifts, deforestation, permafrost thaw or ocean stratification will alter Hg cycling and exposure. Based on past declines in Hg release and environmental levels, we expect that future policy impacts should be distinguishable from global change effects at the regional and global scales.
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Affiliation(s)
- Jeroen E. Sonke
- Géosciences Environnement Toulouse, CNRS/IRD, Université Paul Sabatier Toulouse 3, 14 ave Edouard Belin, 31400 Toulouse, France
| | - Hélène Angot
- Univ. Grenoble Alpes, CNRS, INRAE, IRD, Grenoble INP, IGE, 1025 rue de la piscine, 38000 Grenoble, France
| | - Yanxu Zhang
- School of Atmospheric Sciences, Nanjing University, 163 Xianlin Road, Nanjing, 210023 Jiangsu China
| | - Alexandre Poulain
- Department of Biology, University of Ottawa, Ottawa, ON K1N6N5 Canada
| | - Erik Björn
- Department of Chemistry, Umeå University, 90187 Umeå, Sweden
| | - Amina Schartup
- Geosciences Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093 USA
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Desai AR, Murphy BA, Wiesner S, Thom J, Butterworth BJ, Koupaei‐Abyazani N, Muttaqin A, Paleri S, Talib A, Turner J, Mineau J, Merrelli A, Stoy P, Davis K. Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems. JOURNAL OF GEOPHYSICAL RESEARCH. BIOGEOSCIENCES 2022; 127:e2022JG007014. [PMID: 37502709 PMCID: PMC10369927 DOI: 10.1029/2022jg007014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 11/18/2022] [Accepted: 11/21/2022] [Indexed: 07/29/2023]
Abstract
Long-running eddy covariance flux towers provide insights into how the terrestrial carbon cycle operates over multiple timescales. Here, we evaluated variation in net ecosystem exchange (NEE) of carbon dioxide (CO2) across the Chequamegon Ecosystem-Atmosphere Study AmeriFlux core site cluster in the upper Great Lakes region of the USA from 1997 to 2020. The tower network included two mature hardwood forests with differing management regimes (US-WCr and US-Syv), two fen wetlands with varying levels of canopy sheltering and vegetation (US-Los and US-ALQ), and a very tall (400 m) landscape-level tower (US-PFa). Together, they provided over 70 site-years of observations. The 19-tower Chequamegon Heterogenous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 campaign centered around US-PFa provided additional information on the spatial variation of NEE. Decadal variability was present in all long-term sites, but cross-site coherence in interannual NEE in the earlier part of the record became weaker with time as non-climatic factors such as local disturbances likely dominated flux time series. Average decadal NEE at the tall tower transitioned from carbon source to sink to near neutral over 24 years. Respiration had a greater effect than photosynthesis on driving variations in NEE at all sites. Declining snowfall offset potential increases in assimilation from warmer springs, as less-insulated soils delayed start of spring green-up. Higher CO2 increased maximum net assimilation parameters but not total gross primary productivity. Stand-scale sites were larger net sinks than the landscape tower. Clustered, long-term carbon flux observations provide value for understanding the diverse links between carbon and climate and the challenges of upscaling these responses across space.
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Affiliation(s)
- Ankur R. Desai
- Department of Atmospheric and Oceanic SciencesUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Bailey A. Murphy
- Department of Atmospheric and Oceanic SciencesUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Susanne Wiesner
- Department of Plant and Earth ScienceUniversity of Wisconsin–River FallsRiver FallsWIUSA
| | - Jonathan Thom
- Space Science and Engineering CenterUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Brian J. Butterworth
- Cooperative Institute for Research in Environmental SciencesCU BoulderBoulderCOUSA
- NOAA Physical Sciences LaboratoryBoulderCOUSA
| | | | - Andi Muttaqin
- Department of Atmospheric and Oceanic SciencesUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Sreenath Paleri
- Department of Atmospheric and Oceanic SciencesUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Ammara Talib
- Department of Civil and Environmental EngineeringUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Jess Turner
- Freshwater & Marine SciencesUniversity of Wisconsin–MadisonMadisonWIUSA
| | - James Mineau
- Department of Atmospheric and Oceanic SciencesUniversity of Wisconsin–MadisonMadisonWIUSA
| | - Aronne Merrelli
- Department of Climate and Space Sciences and EngineeringUniversity of MichiganAnn ArborMIUSA
| | - Paul Stoy
- Department of Plant and Earth ScienceUniversity of Wisconsin–River FallsRiver FallsWIUSA
| | - Ken Davis
- Department of MeteorologyPennsylvania State UniversityUniversity ParkPAUSA
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Zhao L, Wang R, Zhang C, Yin D, Yang S, Huang X. Geochemical controls on the distribution of mercury and methylmercury in sediments of the coastal East China Sea. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 667:133-141. [PMID: 30826674 DOI: 10.1016/j.scitotenv.2019.02.334] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 02/20/2019] [Accepted: 02/21/2019] [Indexed: 06/09/2023]
Abstract
We examined the spatial and vertical distribution of total mercury (THg) in 119 surface sediment samples and 4 sediment cores from the coastal East China Sea. The THg concentrations (3.6-69.2 μg kg-1, average 34.7 μg kg-1) in surface sediments exhibited a decreasing trend from the inner shelf towards the outer shelf. The THg levels in sediment cores showed a significant increasing trend from the bottom to the top layer. Both the spatial and vertical distribution of THg indicates the impacts of anthropogenic inputs. The THg concentrations in the surface sediments of Yangtze River estuary were strongly correlated with sediment particle size and organic matter, governing by the Yangtze River inputs. The relatively higher THg levels in the surface sediments of southern inner shelf were attributed to the stronger binding affinity of the finer-grained sediments, the nature of organic matter, as well as local inputs. The spatial distribution of toxic methylmercury (MeHg) was distinct from THg, controlled by direct terrigenous MeHg inputs and in situ MeHg formation. The net Hg methylation potential (indicated by MeHg/THg ratio) in surface sediments were significantly influenced by both geochemical factors (DO, temperature and water depth) and the physicochemical properties of sediments (grain size, TOC, S, Fe2O3 and MnO), and exhibited the highest correlation with TOC, suggesting the key role of organic matter in governing net MeHg production. Moreover, sites with high MeHg/THg ratios mainly occurred within the summer hypoxia zones adjacent to the Yangtze River estuary, suggesting special attention on Hg ecological risks should be paid in this region.
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Affiliation(s)
- Lu Zhao
- Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China
| | - Rui Wang
- Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China.
| | - Chi Zhang
- Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China
| | - Daqiang Yin
- Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China
| | - Shouye Yang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, PR China
| | - Xiangtong Huang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, PR China
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Regnell O, Watras CJ. Microbial Mercury Methylation in Aquatic Environments: A Critical Review of Published Field and Laboratory Studies. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:4-19. [PMID: 30525497 DOI: 10.1021/acs.est.8b02709] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Methylmercury (MeHg) is an environmental contaminant of concern because it biomagnifies in aquatic food webs and poses a health hazard to aquatic biota, piscivorous wildlife and humans. The dominant source of MeHg to freshwater systems is the methylation of inorganic Hg (IHg) by anaerobic microorganisms; and it is widely agreed that in situ rates of Hg methylation depend on two general factors: the activity of Hg methylators and their uptake of IHg. A large body of research has focused on the biogeochemical processes that regulate these two factors in nature; and studies conducted within the past ten years have made substantial progress in identifying the genetic basis for intracellular methylation and defining the processes that govern the cellular uptake of IHg. Current evidence indicates that all Hg methylating anaerobes possess the gene pair hgcAB that encodes proteins essential for Hg methylation. These genes are found in a large variety of anaerobes, including iron reducers and methanogens; but sulfate reduction is the metabolic process most often reported to show strong links to MeHg production. The uptake of Hg substrate prior to methylation may occur by passive or active transport, or by a combination of both. Competitive inhibition of Hg uptake by Zn speaks in favor of active transport and suggests that essential metal transporters are involved. Shortly after its formation, MeHg is typically released from cells, but the efflux mechanisms are unknown. Although methylation facilitates Hg depuration from the cell, evidence suggests that the hgcAB genes are not induced or favored by Hg contamination. Instead, high MeHg production can be linked to high Hg bioavailability as a result of the formation of Hg(SH)2, HgS nanoparticles, and Hg-thiol complexes. It is also possible that sulfidic conditions require strong essential metal uptake systems that inadvertently bring Hg into the cytoplasm of Hg methylating microbes. In comparison with freshwaters, Hg methylation in open ocean waters appears less restricted to anoxic environments. It does seem to occur mainly in oxygen deficient zones (ODZs), and possibly within anaerobic microzones of settling organic matter, but MeHg (CH3Hg+) and Me2Hg ((CH3)2Hg) have been shown to form also in surface water samples from the euphotic zone. Future studies may disclose whether several different pathways lead to Hg methylation in marine waters and explain why Me2Hg is a significant Hg species in oceans but seemingly not in most freshwaters.
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Affiliation(s)
- Olof Regnell
- Department of Biology/Aquatic Ecology , Lund University , SE-223 62 Lund , Sweden
| | - Carl J Watras
- Bureau of Water Quality , Wisconsin Department of Natural Resources , Madison , Wisconsin 53703 , United States
- Center for Limnology , University of Wisconsin-Madison , 3110 Trout Lake Station Drive , Boulder Junction , Wisconsin 54512 , United States
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5
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Creswell JE, Shafer MM, Babiarz CL, Tan SZ, Musinsky AL, Schott TH, Roden EE, Armstrong DE. Biogeochemical controls on mercury methylation in the Allequash Creek wetland. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2017; 24:15325-15339. [PMID: 28502050 DOI: 10.1007/s11356-017-9094-2] [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: 10/11/2016] [Accepted: 04/24/2017] [Indexed: 06/07/2023]
Abstract
We measured mercury methylation potentials and a suite of related biogeochemical parameters in sediment cores and porewater from two geochemically distinct sites in the Allequash Creek wetland, northern Wisconsin, USA. We found a high degree of spatial variability in the methylation rate potentials but no significant differences between the two sites. We identified the primary geochemical factors controlling net methylmercury production at this site to be acid-volatile sulfide, dissolved organic carbon, total dissolved iron, and porewater iron(II). Season and demethylation rates also appear to regulate net methylmercury production. Our equilibrium speciation modeling demonstrated that sulfide likely regulated methylation rates by controlling the speciation of inorganic mercury and therefore its bioavailability to methylating bacteria. We found that no individual geochemical parameter could explain a significant amount of the observed variability in mercury methylation rates, but we found significant multivariate relationships, supporting the widely held understanding that net methylmercury production is balance of several simultaneously occurring processes.
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Affiliation(s)
- Joel E Creswell
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA.
- U.S. House of Representatives, 2346 Rayburn House Office Building, Washington DC, 20515, USA.
| | - Martin M Shafer
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
- Wisconsin State Laboratory of Hygiene, 2601 Agriculture Dr, Madison, WI, 53718, USA
| | - Christopher L Babiarz
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
- Wisconsin Water Science Center,U.S. Geological Survey, 8505 Research Way, Middleton, WI, 53562, USA
| | - Sue-Zanne Tan
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
| | - Abbey L Musinsky
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
| | - Trevor H Schott
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
| | - Eric E Roden
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
- Department of Geoscience, University of Wisconsin - Madison, 1215 W. Dayton St, Madison, WI, 53706, USA
| | - David E Armstrong
- Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N. Park St, Madison, WI, 53706, USA
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Singer MB, Harrison LR, Donovan PM, Blum JD, Marvin-DiPasquale M. Hydrologic indicators of hot spots and hot moments of mercury methylation potential along river corridors. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 568:697-711. [PMID: 26994752 DOI: 10.1016/j.scitotenv.2016.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 03/01/2016] [Accepted: 03/02/2016] [Indexed: 06/05/2023]
Abstract
The biogeochemical cycling of metals and other contaminants in river-floodplain corridors is controlled by microbial activity responding to dynamic redox conditions. Riverine flooding thus has the potential to affect speciation of redox-sensitive metals such as mercury (Hg). Therefore, inundation history over a period of decades potentially holds information on past production of bioavailable Hg. We investigate this within a Northern California river system with a legacy of landscape-scale 19th century hydraulic gold mining. We combine hydraulic modeling, Hg measurements in sediment and biota, and first-order calculations of mercury transformation to assess the potential role of river floodplains in producing monomethylmercury (MMHg), a neurotoxin which accumulates in local and migratory food webs. We identify frequently inundated floodplain areas, as well as floodplain areas inundated for long periods. We quantify the probability of MMHg production potential (MPP) associated with hydrology in each sector of the river system as a function of the spatial patterns of overbank inundation and drainage, which affect long-term redox history of contaminated sediments. Our findings identify river floodplains as periodic, temporary, yet potentially important, loci of biogeochemical transformation in which contaminants may undergo change during limited periods of the hydrologic record. We suggest that inundation is an important driver of MPP in river corridors and that the entire flow history must be analyzed retrospectively in terms of inundation magnitude and frequency in order to accurately assess biogeochemical risks, rather than merely highlighting the largest floods or low-flow periods. MMHg bioaccumulation within the aquatic food web in this system may pose a major risk to humans and waterfowl that eat migratory salmonids, which are being encouraged to come up these rivers to spawn. There is a long-term pattern of MPP under the current flow regime that is likely to be accentuated by increasingly common large floods with extended duration.
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Affiliation(s)
- Michael Bliss Singer
- Department of Earth & Environmental Sciences, University of St Andrews, St Andrews, UK; Earth Research Institute, University of California Santa Barbara, Santa Barbara, CA, USA.
| | - Lee R Harrison
- Earth Research Institute, University of California Santa Barbara, Santa Barbara, CA, USA; NOAA Fisheries, Santa Cruz, CA, USA
| | - Patrick M Donovan
- Department of Earth & Environmental Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Joel D Blum
- Department of Earth & Environmental Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Mark Marvin-DiPasquale
- National Research Program, Water Resources Division, US Geological Survey, Menlo Park, CA, USA
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7
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Zeng L, Luo G, He T, Guo Y, Qian X. Effects of sulfate-reducing bacteria on methylmercury at the sediment-water interface. J Environ Sci (China) 2016; 46:214-219. [PMID: 27521953 DOI: 10.1016/j.jes.2016.05.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 05/15/2016] [Accepted: 05/31/2016] [Indexed: 06/06/2023]
Abstract
Sediment cores (containing sediment and overlying water) from Baihua Reservoir (SW China) were cultured under different redox conditions with different microbial activities, to understand the effects of sulfate-reducing bacteria (SRB) on mercury (Hg) methylation at sediment-water interfaces. Concentrations of dissolved methyl mercury (DMeHg) in the overlying water of the control cores with bioactivity maintained (BAC) and cores with only sulfate-reducing bacteria inhibited (SRBI) and bacteria fully inhibited (BACI) were measured at the anaerobic stage followed by the aerobic stage. For the BAC and SRBI cores, DMeHg concentrations in waters were much higher at the anaerobic stage than those at the aerobic stage, and they were negatively correlated to the dissolved oxygen concentrations (r=-0.5311 and r=-0.4977 for BAC and SRBI, respectively). The water DMeHg concentrations of the SRBI cores were 50% lower than those of the BAC cores, indicating that the SRB is of great importance in Hg methylation in sediment-water systems, but there should be other microbes such as iron-reducing bacteria and those containing specific gene cluster (hgcAB), besides SRB, causing Hg methylation in the sediment-water system.
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Affiliation(s)
- Lingxia Zeng
- Key Laboratory of Karst Environment and Geohazard Prevention, Guizhou University, Guiyang 550003, China.
| | - Guangjun Luo
- Key Laboratory of Karst Environment and Geohazard Prevention, Guizhou University, Guiyang 550003, China
| | - Tianrong He
- Key Laboratory of Karst Environment and Geohazard Prevention, Guizhou University, Guiyang 550003, China.
| | - Yanna Guo
- Power China Guiyang Engineering Corporation Limited, Guiyang 550081, China
| | - Xiaoli Qian
- The School of Resources and Environment Engineering, Guizhou University, Guiyang 550003, China
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8
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Lewis AS, Huntington TG, Marvin-DiPasquale MC, Amirbahman A. Mercury remediation in wetland sediment using zero-valent iron and granular activated carbon. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2016; 212:366-373. [PMID: 26874318 DOI: 10.1016/j.envpol.2015.11.047] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Revised: 11/25/2015] [Accepted: 11/26/2015] [Indexed: 06/05/2023]
Abstract
Wetlands are hotspots for production of toxic methylmercury (MeHg) that can bioaccumulate in the food web. The objective of this study was to determine whether the application of zero-valent iron (ZVI) or granular activated carbon (GAC) to wetland sediment could reduce MeHg production and bioavailability to benthic organisms. Field mesocosms were installed in a wetland fringing Hodgdon Pond (Maine, USA), and ZVI and GAC were applied. Pore-water MeHg concentrations were lower in treated compared with untreated mesocosms; however, sediment MeHg, as well as total Hg (THg), concentrations were not significantly different between treated and untreated mesocosms, suggesting that smaller pore-water MeHg concentrations in treated sediment were likely due to adsorption to ZVI and GAC, rather than inhibition of MeHg production. In laboratory experiments with intact vegetated sediment clumps, amendments did not significantly change sediment THg and MeHg concentrations; however, the mean pore-water MeHg and MeHg:THg ratios were lower in the amended sediment than the control. In the laboratory microcosms, snails (Lymnaea stagnalis) accumulated less MeHg in sediment treated with ZVI or GAC. The study results suggest that both GAC and ZVI have potential for reducing MeHg bioaccumulation in wetland sediment.
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Affiliation(s)
- Ariel S Lewis
- Department of Civil and Environmental Engineering, University of Maine, Orono, ME, USA
| | | | | | - Aria Amirbahman
- Department of Civil and Environmental Engineering, University of Maine, Orono, ME, USA.
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Rothenberg SE, Windham-Myers L, Creswell JE. Rice methylmercury exposure and mitigation: a comprehensive review. ENVIRONMENTAL RESEARCH 2014; 133:407-23. [PMID: 24972509 PMCID: PMC4119557 DOI: 10.1016/j.envres.2014.03.001] [Citation(s) in RCA: 119] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 01/25/2014] [Accepted: 03/01/2014] [Indexed: 05/20/2023]
Abstract
Rice cultivation practices from field preparation to post-harvest transform rice paddies into hot spots for microbial mercury methylation, converting less-toxic inorganic mercury to more-toxic methylmercury, which is likely translocated to rice grain. This review includes 51 studies reporting rice total mercury and/or methylmercury concentrations, based on rice (Orzya sativa) cultivated or purchased in 15 countries. Not surprisingly, both rice total mercury and methylmercury levels were significantly higher in polluted sites compared to non-polluted sites (Wilcoxon rank sum, p<0.001). However, rice percent methylmercury (of total mercury) did not differ statistically between polluted and non-polluted sites (Wilcoxon rank sum, p=0.35), suggesting comparable mercury methylation rates in paddy soil across these sites and/or similar accumulation of mercury species for these rice cultivars. Studies characterizing the effects of rice cultivation under more aerobic conditions were reviewed to determine the mitigation potential of this practice. Rice management practices utilizing alternating wetting and drying (instead of continuous flooding) caused soil methylmercury levels to spike, resulting in a strong methylmercury pulse after fields were dried and reflooded; however, it is uncertain whether this led to increased translocation of methylmercury from paddy soil to rice grain. Due to the potential health risks, it is advisable to investigate this issue further, and to develop separate water management strategies for mercury polluted and non-polluted sites, in order to minimize methylmercury exposure through rice ingestion.
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Affiliation(s)
- Sarah E Rothenberg
- University of South Carolina, Arnold School of Public Health, Department of Environmental Health Sciences, 921 Assembly Street, Room 401, Columbia, SC 29208, USA.
| | | | - Joel E Creswell
- Brooks Rand Instruments, 4415 6th Ave NW, Seattle, WA 98107, USA.
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Sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 as a model for understanding bacterial mercury methylation. Appl Environ Microbiol 2011; 77:3938-51. [PMID: 21515733 DOI: 10.1128/aem.02993-10] [Citation(s) in RCA: 172] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
We propose the use of Desulfovibrio desulfuricans ND132 as a model species for understanding the mechanism of microbial Hg methylation. Strain ND132 is an anaerobic dissimilatory sulfate-reducing bacterium (DSRB), isolated from estuarine mid-Chesapeake Bay sediments. It was chosen for study because of its exceptionally high rates of Hg methylation in culture and its metabolic similarity to the lost strain D. desulfuricans LS, the only organism for which methylation pathways have been partially defined. Strain ND132 is an incomplete oxidizer of short-chain fatty acids. It is capable of respiratory growth using fumarate as an electron acceptor, supporting growth without sulfide production. We used enriched stable Hg isotopes to show that ND132 simultaneously produces and degrades methylmercury (MeHg) during growth but does not produce elemental Hg. MeHg produced by cells is mainly excreted, and no MeHg is produced in spent medium. Mass balances for Hg and MeHg during the growth of cultures, including the distribution between filterable and particulate phases, illustrate how medium chemistry and growth phase dramatically affect Hg solubility and availability for methylation. The available information on Hg methylation among strains in the genus Desulfovibrio is summarized, and we present methylation rates for several previously untested species. About 50% of Desulfovibrio strains tested to date have the ability to produce MeHg. Importantly, the ability to produce MeHg is constitutive and does not confer Hg resistance. A 16S rRNA-based alignment of the genus Desulfovibrio allows the very preliminary assessment that there may be some evolutionary basis for the ability to produce MeHg within this genus.
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