水稻根际土壤中汞的微生物循环过程

甲基汞(MeHg)是一种具有神经毒性的环境污染物。稻田土壤中在微生物作用下由无机汞转化产生的甲基汞,经水稻根系吸收后最终会富集于稻米中,由此造成人体的甲基汞暴露风险。水稻根际土壤在此过程中可能扮演着至关重要的作用。受水稻根系分泌的有机碳及氧气等的影响,根际土壤被视为稻田环境中的特殊生境,其间的微生物群落结构与丰度以及若干关键元素的循环过程与非根际土壤相比存在巨大差异。这一特殊生境会对无机汞(IHg)以及甲基汞在稻田环境中的命运产生重要影响。本文首先简要综述了稻田土壤环境中甲基汞产生与降解的微生物学过程研究进展,并进一步着重分析了水稻根际土壤中Fe、S、C、N和P等关键元素对汞的微生物循环过程的影响。深刻认识这些过程,有助于研究者准确评估汞污染区稻田土壤甲基汞的产生及向水稻体内的转移效率,这对未来选择适当的农业手段降低人体甲基汞暴露风险具有重要意义。文章最后提出了若干值得探索的研究方向,期望能为相关研究提供新思考。

Microbial Cycle Processes of Mercury in Rice Rhizosphere Soil

As a neurotoxic environmental pollutant, methylmercury (MeHg) could be produced from mercury-containing compounds in paddy soil with the participation of microorganisms, and then be assimilated by rice root and finally be enriched in rice grain, which could cause human health exposure risk to MeHg. Rice rhizosphere soil could play an essential role in this process. Influenced by the organic carbon and oxygen secreted by rice roots, rhizosphere soil is regarded as a special habitat for microorganisms in paddy environment, and the microbial community structure and abundance as well as the cycling process of some key elements in the rhizosphere soil are significantly different from those in bulk soil. This special habitat will have an important impact on the fate of IHg and MeHg in the paddy environment. In this review, the microbiological processes of the production and degradation of MeHg in paddy soil were briefly reviewed, and the effects of key elements such as Fe, S, C, N and P in rice rhizosphere soil on the microbial cycle of mercury were further discussed. A deep understanding of these processes will favor us to accurately assess the production capacity of MeHg in mercury-contaminated paddy soils and the transfer efficiency to different parts of rice plant, which are of great significance for choosing appropriate agricultural methods to reduce the risk of MeHg exposure in humans in the future. Finally, some research directions worth of exploring are put forward, hoping to provide new thinking for related researches.