Main content area

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.