大气中汞的浓度水平对农作物中甲基汞富集的影响

The concentration of mercury in crops are certain to increase under the double pressures of high levels of mercury in soil and ambient air in china,and subseqently enhance the risk exposure for humans and ecosysytem. So it is very important to do intensive researches to comprehend the characteristics, formation mechanisms and sources of mercury and methylmercury in crop tissues. This is greatly significant to futher promote understanding of mercury biogeochemistry and provide references for the mercury pollution prevention and control in our country.However,it has not yet been studied and reported on the potential sources of methylmercury from the atmosphere in rice and other crops tissues. In this project rice and wheat are used for experiment, and the field in-situ experiments will perform using open top chambers (OTCs), which can be adjusted the concentrations of gaseous elemental mercury(Hg0) and gaseous methylmercury(GMeHg) in air. The objectives of this project is main focus on the characteristic and response of methylmercury in crop tissues to the variation of Hg0 and GMeHg concentration in OTCs, and explore the new ways for the sources of methylmercury in rice and other crops. Combing the results from the field experiments of cultivation for rice and wheat under different levels of mercuey in soil, the relative contributions of methylmercury in crop tissues from air and soil will be recognite and assess.These will benefit for understanding the health effects from mercury and effectively avoiding or reducing the Hg exposure for humans and ecosystem.

在高水平大气汞污染和土壤汞污染的双重压力下，我国农作物中汞污染物含量势必上升，导致健康和生态风险增加，因此，有必要开展深入研究，以认识农作物中汞和甲基汞的富集特征、形成机制和不同来源，增进对汞生物地球化学循环过程的理解，为我国汞污染防治提供参考。目前，尚未见有关水稻等植物体中甲基汞直接大气来源的研究报道。本项目拟以水稻和小麦为典型作物，利用开顶气室进行田间原位实验研究，通过控制气室中气态单质汞和甲基汞的浓度，研究农作物各部位甲基汞含量的变化特征和对不同形态大气汞浓度变化的响应，分析和探讨其特征和规律；同时，通过土壤汞添加实验，分析土壤汞含量变化对作物中甲基汞的影响。结合以上研究，评估大气和土壤汞对水稻等农作物中甲基汞的相对贡献；探索水稻等农作物中甲基汞来源的新途径。

本项目针对当前高水平大气汞污染和土壤汞污染双重压力下我国农作物中甲基汞污染含量上升这一关键问题，通过建立高效稳定的气态二甲基汞发生系统和开展在线田间开顶气室汞同位素示踪实验，率先证实了典型农作物水稻在生长的不同时期均能吸收大气中气态有机汞，确立了水稻植株各组织甲基汞富集与大气气态二甲基汞浓度响应二次函数关系，且吸收的大气甲基汞主要富集在水稻植株地上部分极少被转运至根部；但田间开顶气室实验表明大气中气态单质汞对水稻植株及籽粒甲基汞富集影响可以忽略。.另外，调查发现除了在海洋上升流和深层海水中，我国环渤海海水和贵州地区稻田覆水中同样存在可检出的溶解性气态二甲基汞，且万山汞矿区竖井尾矿堆稻田覆水中溶解性气态二甲基汞浓度可高达15.55±24.14pg L-1，与已报告的海洋上升流和深层海水中二甲基汞浓度一致；更重要的是，竖井稻田冠层下空气中气态二甲基汞的浓度也高达10.7±3.4 pg m-3（1.27 到 20.57 pg m-3），且由于光解作用导致稻田冠层下覆水和空气中二甲基汞浓度呈现凌晨最高午间最低的日变化趋势；进一步培育实验表明二甲基汞是稻田土水系统气态有机汞产生的主体，且土壤可利用汞、硫酸盐、Fe3+和醋酸盐均可促进稻田土壤气态有机汞的排放。.由此，本项目利用在线田间开顶气室汞同位素示踪实验建立的水稻植株对气态二甲基汞的响应关系函数，结合万山汞矿区竖井尾矿堆稻田冠层内气态二甲基汞浓度和测定水稻植株甲基汞实际浓度，估算水稻糙米、叶和上部茎中约有11.8% ,14.3% 和13.4% 的甲基汞来自大气，而稻根中的甲基汞99.5%来自稻田土-水系统。本项目对典型汞矿区水稻甲基汞大气来源的量化成果完善和更新了水稻甲基汞来源的新认识，为汞污染和健康风险防止以及汞的生物地球化学循环提供了科技支撑。