Abstract

In 2010, 50 indica rice varieties were cultivated in three sites in southwestern China along a contamination gradient (background, moderately-contaminated and highly-contaminated sites) to determine environment and genotype controls on MeHg accumulation in polished white rice and bran. Rice grain MeHg concentrations were significantly higher in the moderately-contaminated site compared to the other two sites (ANOVA, p<0.0001). Lower rice grain MeHg concentrations in the highly-contaminated site possibly reflected differences in surface water pH (highly-contaminated site: pH 11, other two sites: pH 7.6-8.0). More alkaline conditions at the highly-contaminated site possibly decreased the bioavailability of MeHg and/or other trace elements, thus lowering the uptake of MeHg from paddy soil to rice grain. Polished white rice MeHg concentrations were significantly associated with rice genotype (p<0001), indicating there may be genetic markers associated with the translocation of MeHg from the maternal tissue to the filial tissue (i.e., from the bran to the polished grain). Additionally, low MeHg-accumulating rice varieties were identified, which decreased MeHg exposure up to 69%, and may be recommended to farmers to mitigate MeHg accumulation in rice grain.

Highlights

  • Mercury (Hg) is a global pollutant and potent neurotoxin

  • Polished white rice MeHg concentrations were significantly associated with rice genotype (p

  • Both environment and genotype controls contributed to MeHg accumulation in polished white rice

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Summary

Introduction

Mercury (Hg) is a global pollutant and potent neurotoxin. China is the largest producer of rice, generating 29% of the global rice supply in 2009 (IRRI, 2012). In Guizhou province, southwestern China, a 600-year legacy of Hg mining contaminated the soil, water and air (Feng et al, 2008). Hg mining officially ended in 2002, mine tailings are routinely smelted in the surrounding countryside, releasing fugitive Hg emissions to nearby rice paddies (Li et al, 2009). Fish ingestion is the primary human exposure pathway for methylmercury (MeHg); in some villages in the Hg mining region of Guizhou province, rice ingestion is an important MeHg exposure pathway (Feng et al, 2008; Horvat et al, 2003; Rothenberg et al, 2011; Zhang et al, 2010)

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