盐渍化环境下秸秆还田对稻米汞及甲基汞累积的影响

通过盆栽试验探讨了盐渍化环境下秸秆还田对土壤中总汞（THg）、甲基汞（MeHg）含量和转化以及对水稻吸收汞的影响.试验用土采集自天津典型污灌地区，人为添加不同梯度的盐分（0、0.2%、0.5% NaCl）及外源汞（0、5mg/kg~Hg（NO₃）₂），秸秆还田按照0.1%进行处理.结果显示：1.秸秆还田促进稻田系统中无机汞的甲基化.与未添加秸秆的处理相比，秸秆还田后土壤MeHg含量提高了56.8%~76.8%，水稻MeHg含量增加了127%~171.6%.2.在轻度盐渍化稻田开展秸秆还田，会进一步提高稻田土壤中汞的甲基化水平，进而增加水稻籽粒中甲基汞含量.与不添加盐分处理相比，轻度盐渍化环境中（0.2% NaCl），秸秆还田处理导致土壤MeHg含量提高了92.2%~101.2%，水稻籽粒MeHg含量增长了52.8%~132.1%.更高的盐渍化水平会抑制土壤汞甲基化趋势，水稻籽粒中甲基汞含量降低.在中度盐渍化环境中（0.5% NaCl），秸秆还田导致土壤MeHg含量降低了57.9%~88.6%，水稻籽粒MeHg含量降低了72.9%~86.8%.以上研究结果表明，在盐渍化且汞污染稻田开展秸秆还田可能大幅度增加该地区汞食物链暴露风险，因此在中轻度盐渍化的污灌区，对秸秆还田等农艺措施需要格外慎重.

Influence of rice straw amendment on mercury/methylmercury accumulation in rice grains in the saline soils

A pot experiment was conducted to simulate a mercury-contaminated paddy fields irrigated with wastewater. Soil sample was collected from a typical wastewater-irrigated area of Tianjin, and exogenous salinity (0%, 0.2%, 0.5% NaCl), mercury (0, 5mg/kg Hg(NO₃)₂) and rice straw (0, 0.1%) were added into soil manually to discuss the influence of rice straw amendment on total mercury (THg)/methylmercury (MeHg) accumulation in rice grain. Results showed that, (1) Methylation of inorganic mercury in paddy soil-rice system was promoted by rice straw amendment. After rice straw amendment, MeHg concentration in soil and rice grain increased by 56.8%~76.8% and 127%~171.6% respectively. (2) Stimulation of methylation of inorganic mercury in mild salinized paddy soil by rice straw amendment was even more serious, and which lead to an additional increment of MeHg in rice grain. Compared with un-salinized soil, MeHg in soil and rice grain increased by 92.2%~101.2% and 52.8%~132.1% respectively after rice straw amendment. However, in a more serious salinized soil (0.5% NaCl), methylation of inorganic mercury in soil was suppressed and MeHg accumulation in rice grain decreased. MeHg concentration in soil and rice grain decreased by 57.9%~88.6% and 72.9%~86.8% respectively in moderate salinized soil (0.5% NaCl) after treated with rice straw amendment, compared with in un-salinized soil. These results indicated that the treatment of rice straw amendment in a medium or low level salinized soil with Hg contamination may lead to adverse effect to human health. Therefore, treatment of rice straw amendment in this kind of area should be cautious.