Mercury methylation in rice paddies and its possible controlling factors in the Hg mining area, Guizhou province, Southwest China

Zhao, Lei; Qiu, Guangle; Anderson, Christopher; Meng, Bo; Wang, Dingyong; Shang, Lihai; Yan, Haiyu

doi:10.1016/j.envpol.2016.05.001

Cited by 120 publications

(85 citation statements)

References 48 publications

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“…1b). Other authors have reported a pulse of MeHg after soils are flooded (Marvin-DiPasquale et al, 2009;Rothenberg and Feng, 2012;Zhao et al, 2016) but peaks in concentration occurred sooner than observed here. Samples collected at 40 DAP and 64 DAP showed no hint of elevated concentrations, so studies with higher sampling frequency are needed to understand the elevated concentrations at 57 DAP.…”

Section: Soil Hg and Mehg Dynamicscontrasting

confidence: 49%

Alternate Wetting and Drying Decreases Methylmercury in Flooded Rice (Oryza sativa) Systems

Tanner

Windham‐Myers

Marvin-DiPasquale

et al. 2018

Soil Science Soc of Amer J

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In flooded soils, including those found in rice (Oryza sativa L.) fields, microbes convert inorganic Hg to more toxic methylmercury (MeHg). Methylmercury is accumulated in rice grain, potentially affecting health. Methylmercury in rice field surface water can bioaccumulate in wildlife. We evaluated how introducing aerobic periods into an otherwise continuously flooded rice growing season affects MeHg dynamics. Conventional continuously flooded (CF) rice field water management was compared with alternate wetting and drying, where irrigation was stopped twice during the growing season, allowing soil to dry to 35% volumetric moisture content, at which point plots were reflooded ( Abbreviations: %Fe(II), ferrous iron as a percent of total citrate-dithionite extractable Fe; %MeHg, the percentage of total Hg that is methylmercury; AWD, alternate wetting and drying; AWD-35, alternate wetting and drying to 35% volumetric moisture content; CF, continuous flooding; DAP, day after planting; Fe(II) AE , acid-extractable ferrous Fe; (Fe(III) a, amorphous ferric iron; Fe T , total citrate-dithionite extractable Fe; FeRB, Fe-reducing bacteria; MeHg, methylmercury; SRB, sulfate-reducing bacteria; THg, total Mg. R ice is grown on 161 million ha worldwide and is the staple crop for 3.5 billion people globally (Muthayya et al., 2014). Rice is a semiaquatic plant and is usually grown under flooded conditions to help control weeds, increase nutrient availability, and ensure water supply during drought (Kendig et al., 2003). Flooded conditions also allow rice fields to serve as important wildlife habitat (Czech and Parsons, 2002); however, rice production is also associated with several negative impacts. First, rice requires higher water inputs than other cereal crops (Pimentel et al., 2004). Increasing food demand from a growing population and decreasing water availability (Mekonnen and Hoekstra, 2016) are placing pressure on rice growers to reduce the amount of water used for rice production. Second, the global warming potential of rice is elevated compared with other crops, caused in large part by high methane emissions (Linquist et al., 2012;Wassmann et al., 2010). Finally, flooded conditions can also change the speciation and increase the bioavailability of As and k. Christy Tanner* Core Ideas• We studied how alternate wetting and drying (AWd) water management effects methylmercury (MeHg) dynamics in rice fields.• Alternate wetting and drying reduced MeHg concentrations in soil, water, and rice grain.• Iron speciation indicated that AWd oxidized the soil and regenerated electron acceptors.• Rice yield did not differ between AWd and the control over 4 yr.

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Section: Soil Hg and Mehg Dynamicscontrasting

confidence: 49%

Alternate Wetting and Drying Decreases Methylmercury in Flooded Rice (Oryza sativa) Systems

Tanner

Windham‐Myers

Marvin-DiPasquale

et al. 2018

Soil Science Soc of Amer J

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“…Gouxi 24 ± 1.7 8.3 ± 0.24 7.4 ± 0.43 28 ± 4.4 7.2 ± 0.24 3.0 ± 0.95 (23-26) (8.1-8.6) (6.9-8.0) (24-33) (6.9-7.4) (1.8-3.9) Wukeng 25 ± 2.1 11 ± 0.45 7.4 ± 0.56 25 ± 2.7 8.6 ± 1.3 4.4 ± 0.73 (23-27) (11-12) (6.8-8.1) (23-29) (7.3-9.8) (3.6-5.2) in soil across the two sampling sites, indicating that absolute pH and organic matter might not be the most important factors regulating Hg methylation activity (Zhao et al, 2016). Changing redox parameters over the rice growing season may affect the process of Hg methylation.…”

Section: Samplingmentioning

confidence: 99%

“…Methylation can be affected by the pH and organic matter content of soil, and an analysis of soil physicochemical parameters in the soil cores of this study is reported in a related paper (Zhao et al, 2016). Briefly, the mean organic matter in soil cores was 4.8 ± 0.75 and 3.5 ± 0.59 % at Gouxi and Wukeng, respectively.…”

Section: Mercury In Soil Coresmentioning

confidence: 99%

“…In order to better understand the factors controlling Hg methylation in rice paddy soil, the concentration of Fe 2+ , Fe 3+ , S 2− , and SO 2− 4 in soil pore water was determined and this data is described, in detail, in a related paper (Zhao et al, 2016). Briefly, no discernible vertical trend in Fe 3+ distribution was observed in the soil pore water across the two sampling sites during the sampling period.…”

Section: Hg In Soil Pore Watermentioning

confidence: 99%

“…The highest SO 2− 4 concentrations were recorded in the surface soil layer and decreased with depth across the two sampling sites. As described in a related paper (Zhao et al, 2016) Soil depth (cm)…”

Section: Hg In Soil Pore Watermentioning

confidence: 99%

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Mercury methylation in paddy soil: source and distribution of mercury species at a Hg mining area, Guizhou Province, China

et al. 2016

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Abstract. Rice paddy plantation is the dominant agricultural land use throughout Asia. Rice paddy fields have been identified as important sites for methylmercury (MeHg) production in the terrestrial ecosystem and a primary pathway of MeHg exposure to humans in mercury (Hg) mining areas. We compared the source and distribution of Hg species in different compartments of the rice paddy during a complete ricegrowing season at two different typical Hg-contaminated mining sites in Guizhou province, China: an abandoned site with a high Hg concentration in soil but a low concentration in the atmosphere and a current-day artisanal site with a low concentration in soil but a high concentration in the atmosphere. Our results showed that the flux of new Hg to the ecosystem from irrigation and atmospheric deposition was insignificant relative to the pool of old Hg in soil; the dominant source of MeHg to paddy soil is in situ methylation of inorganic Hg (IHg). Elevated MeHg concentrations and the high proportion of Hg as MeHg in paddy water and the surface soil layer at the artisanal site demonstrated active Hg methylation at this site only. We propose that the in situ production of MeHg in paddy water and surface soil is dependent on elevated Hg in the atmosphere and the consequential deposition of new Hg into a low-pH anoxic geochemical system. The absence of depth-dependent variability in the MeHg concentration in soil cores collected from the abandoned Hg mining site, consistent with the low concentration of Hg in the atmosphere and high pH of the paddy water and irrigation water, suggested that net production of MeHg at this site was limited. We propose that the concentration of Hg in ambient air is an indicator for the risk of MeHg accumulation in paddy rice.

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Present and Future Mercury Concentrations in Chinese Rice: Insights From Modeling

Kwon

Selin

Giang

et al. 2018

Global Biogeochemical Cycles

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We construct a rice paddy biogeochemical cycle model to investigate processes governing rice mercury sources and to understand factors influencing spatiotemporal variability in Chinese rice mercury concentrations. The rice paddy model takes atmospheric mercury deposition, simulated from a global atmospheric chemistry transport model (GEOS‐Chem), and soil and irrigable surface water mercury concentrations obtained from literature and calculates rice inorganic (IHg) and methylmercury (MeHg) concentrations. We use ranges of GEOS‐Chem‐simulated future atmospheric mercury deposition—no policy and strict policy to regulate mercury emissions from Chinese coal‐fired power plants under the Minamata Convention on Mercury—to simulate future rice IHg and MeHg concentrations. Sensitivity analyses suggest that rice IHg and MeHg concentrations are more sensitive to the process of soil desorption than infiltration of recently introduced mercury (atmospheric and irrigation source). The rate of internal methylation via microbial activity has the largest modeled influence on rice MeHg concentration. We find that soil mercury, rather than atmospheric deposition, explains observed spatial variability in rice IHg and MeHg concentrations and captures locations of rice mercury hot spots (>20 ng/g; China National Standard Limit). Under our future scenarios, the Chinese median rice IHg and MeHg concentration increases by 13% and decrease by 18% under no policy and strict policy, respectively. Regions with the largest percentage decline in rice IHg and MeHg concentrations under strict policy are in central China, which have high rice mercury concentrations, rice production, and consumption. Our study suggests that addressing Chinese rice mercury contamination requires attention to contaminated soil and regulation of anthropogenic mercury emissions.

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Mercury methylation in rice paddies and its possible controlling factors in the Hg mining area, Guizhou province, Southwest China

Cited by 120 publications

References 48 publications

Alternate Wetting and Drying Decreases Methylmercury in Flooded Rice (Oryza sativa) Systems

Alternate Wetting and Drying Decreases Methylmercury in Flooded Rice (Oryza sativa) Systems

Mercury methylation in paddy soil: source and distribution of mercury species at a Hg mining area, Guizhou Province, China

Present and Future Mercury Concentrations in Chinese Rice: Insights From Modeling

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