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Increased Methylmercury Accumulation in Rice after Straw Amendment
- Tang, Wenli, Hintelmann, Holger, Gu, Baohua, Feng, Xinbin, Liu, Yurong, Gao, Yuxi, Zhao, Jiating, Zhu, Huike, Lei, Pei, Zhong, Huan
- Environmental science & technology 2019 v.53 no.11 pp. 6144-6153
- Asians, Oryza sativa, bioaccumulation, crop production, diet, dietary exposure, farming systems, fish, issues and policy, mercury, methylation, methylmercury compounds, neurotoxins, paddy soils, rice, risk, roots, sand, seedlings, straw, surveys, tissues, China
- Consumption of rice has been shown to be an important route of dietary exposure to methylmercury (MeHg, a neurotoxin) for Asians having a low fish but high rice diet. Therefore, factors that increase MeHg production and bioaccumulation in soil–rice systems, could enhance the risk of MeHg exposure. On the basis of a national-scale survey in China (64 sites in 12 provinces) and rice cultivation experiments, we report that straw amendment, a globally prevalent farming practice, could increase MeHg concentrations in paddy soils (11–1043%) and rice grains (95%). By carrying out a series of batch incubation, seedling uptake and sand culture experiments, we demonstrate that these increases could be attributed to (1) enhanced abundances/activities of microbial methylators and the transformation of refractory HgS to organic matter-complexed Hg, facilitating microbial Hg methylation in soils; (2) enhanced MeHg mobility, and increased root lengths (35–41%) and tip numbers (60–105%), increasing MeHg uptake by rice roots; and (3) enhanced MeHg translocation to rice grains from other tissues. Results of this study emphasize fresh organic matter-enhanced MeHg production and bioaccumulation, and highlight the increased risk of MeHg after straw amendment and thus the need for new policies concerning straw management.