University of South Carolina, Arnold School of Public Health, Department of Environmental Health Sciences, 921 Assembly Street, Room 401, Columbia, SC 29208, USA.
United States Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025, USA.
Environ Res. 2014 Aug;133:407-23. doi: 10.1016/j.envres.2014.03.001. Epub 2014 Jun 25.
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.
从田间准备到收获后，水稻种植将稻田变成了微生物汞甲基化的热点，将毒性较低的无机汞转化为毒性更高的甲基汞，甲基汞很可能转移到水稻颗粒中。本综述包括 51 项研究报告，这些研究报告基于在 15 个国家种植或购买的水稻（Orzya sativa），报告了总汞和/或甲基汞浓度。毫不奇怪，受污染地点的水稻总汞和甲基汞水平明显高于未受污染地点（Wilcoxon 秩和检验，p<0.001）。然而，受污染和未受污染地点之间的水稻甲基汞百分比（总汞）在统计学上没有差异（Wilcoxon 秩和检验，p=0.35），这表明这些地点的稻田土壤中汞甲基化率相当，或者这些水稻品种对汞的积累相似。综述了在更有氧条件下种植水稻的研究，以确定这种做法的缓解潜力。利用交替湿润和干燥（而不是连续淹没）的水稻管理实践会导致土壤甲基汞水平飙升，导致田地干燥和重新淹没后出现强烈的甲基汞脉冲；然而，尚不确定这是否导致甲基汞从稻田土壤向水稻颗粒的迁移增加。由于潜在的健康风险，建议进一步调查这个问题，并为汞污染和非污染地点制定单独的水管理策略，以通过摄入水稻来尽量减少甲基汞的暴露。
