淹水-控温模式下砷污染水稻土溶液中砷形态的变化

以水稻种植区的砷污染土壤为研究对象，采用高效液相色谱(HPLC)-电感耦合等离子体质谱(ICP-MS)联用分析测试系统，研究了不同培养温度(5、27和50 ℃)对灭菌和不灭菌的土壤淹水后其溶液中砷赋存形态变化的影响.结果表明： 在土壤溶液中检测到的砷形态只有无机三价砷(As^Ⅲ)、无机五价砷(As^V)和有机的二甲基砷(DMA^V)，未检测到单甲基砷(MMA^V)的存在；在不同控温条件下随淹水时间的延长，As^Ⅲ逐渐转变为砷的主要赋存形态，平均比例约为64%；As^V次之，约占35%，DMA^V的含量相对最低，约占1%；土壤灭菌与否对土壤溶液中五价砷的水平没有明显影响，但明显影响了五价砷的还原和促进了无机三价砷的甲基化，并且灭菌的促进效果随着淹水及培养时间的延长而逐渐降低；50 ℃、淹水23 d时，灭菌土壤溶液中DMA^V浓度最高，为23.7 ng·mL^-1，这说明灭菌土壤中残留的某些嗜热微生物成为优势菌群并促进了土壤溶液中砷的甲基化.结合水稻生长的实际环境条件对该研究结果进行分析，培养温度27 ℃淹水23 d后不灭菌的自然土壤溶液中砷浓度处于较低水平，因此在砷污染的水稻种植区建议采用短周期干湿交替的水分管理模式，在保障产量的情况下可尽量降低土壤溶液中砷的水平.

Variations of arsenic species in the solution of arsenic-contaminated paddy soil under flooding and at different temperatures.

Taking arsenic (As)-contaminated paddy soil as test object, and by using high performance liquid chromatography inductively coupled plasma-mass spectrometry (HPLC-ICP MS), this paper studied the variations of As species in soil solution when the soil was sterilized or non sterilized and incubated at different temperatures (5, 27, and 50 ℃) under flooding. In the soil solution (pore water), only AsⅢ(arsenite), AsV (arsenate), and DMAV (dimethylarsinic acid) were detected, but no  MMAV (mono methylarsinic acid) was found. With the increasing time of flooding and at the test temperatures, arsenite became the predominant species, averagely accounting for 64%, followed by  AsV, with the proportion of 35%, and DMAV, with the least proportion of 1%. Soil sterilization or non sterilization had less effect on the concentrations of AsⅢ and DMAV in the soil solution, but remarkably affected the reduction of AsV and the methylation of AsⅢ. The promotion effect of soil sterilization decreased gradually with the increasing time of flooding and incubation. At 50 ℃ and after flooded for 23 days, the DMAV concentration in sterilized soil solution was the highest and up to 23.7 ng·mL-1, indicating that some thermophilic microbes remained in sterilized soil became predominant species, and promoted the methylation of AsⅢ. In sum, the total arsenic concentration in non sterilized soil at incubation temperature 27 ℃ and flooded for 23 days was relatively low (501 ng·mL-1), and thus, in As-contaminated paddy rice planting areas, to adopt the water management mode of short cycle flooding-non flooding could decrease the As level in soil solution as far as possible, and in the same time, save water resources and ensure yielding.