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°C) under flooding. In the soil solution (pore water), only As^III(arsenite), As^V(arsenate), and DMA^V(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 As^V, with the proportion of 35%, and DMA^V, with the least proportion of 1%. Soil sterilization or non-sterilization had less effect on the concentrations of As^IIIand DMA^V in the soil solution, but remarkably affected the reduction of As^V and the methylation of As^III. The promotion effect of soil sterilization decreased gradually with the increasing time of flooding and incubation. At 50°C and after flooded for 23 days, the DMA^V 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 As^III. In sum, the total arsenic concentration in non-sterilized soil at incubation temperature 27°C 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.