Department of Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany.
Leibniz Center for Agricultural Landscape Research (ZALF), 15374 Müncheberg, Germany.
Environ Sci Technol. 2020 Apr 7;54(7):3940-3950. doi: 10.1021/acs.est.9b05639. Epub 2020 Mar 23.
In flooded paddy soils, inorganic and methylated thioarsenates contribute substantially to arsenic speciation besides the much-better-investigated oxyarsenic species, and thioarsenate uptake into rice plants has recently been shown. To better understand their fate when soil redox conditions change, that is, from flooding to drainage to reflooding, batch incubations and unplanted microcosm experiments were conducted with two paddy soils covering redox potentials from -260 to +200 mV. Further, occurrence of thioarsenates in the oxygenated rice rhizosphere was investigated using planted rhizobox experiments. Soil flooding resulted in rapid formation of inorganic thioarsenates with a dominance of trithioarsenate. Maximum thiolation of inorganic oxyarsenic species was 57% at -130 mV and oxidation caused nearly complete dethiolation. Only monothioarsenate formed again upon reflooding and was the major inorganic thioarsenate detected in the rhizosphere. Maximum thiolation of mono- and dimethylated oxyarsenates was about 70% and 100%, respectively, below 0 mV. Dithiolated species dominated over monothiolated species below -100 mV. Among all thioarsenates, dimethylated monothioarsenate showed the least transformation upon prolonged oxidation. It also was the major thiolated arsenic species in the rhizosphere with concentrations comparable to its precursor dimethylated oxyarsenate, which is especially critical since dimethylated monothioarsenate is highly carcinogenic.
在水淹稻田土壤中，无机和甲基化硫代砷酸盐除了研究得更好的含氧砷物种外，对砷的形态也有很大贡献，并且最近已经证明硫代砷酸盐可以被水稻吸收。为了更好地了解当土壤氧化还原条件发生变化时（即从淹水到排水再到重新淹水）它们的命运，我们进行了批式培养和无植物微宇宙实验，使用了两种稻田土壤，涵盖了从-260 到+200 mV 的氧化还原电位。此外，还使用种植了根箱的实验研究了氧充足的水稻根际中硫代砷酸盐的存在。土壤淹水导致无机硫代砷酸盐的快速形成，其中三硫代砷酸盐占主导地位。在-130 mV 时，无机含氧砷酸盐的最大硫代化程度为 57%，而氧化作用导致几乎完全脱硫。只有在重新淹水时才会再次形成单硫代砷酸盐，并且是根际中检测到的主要无机硫代砷酸盐。在低于 0 mV 时，单甲基化和二甲基化含氧砷酸盐的最大硫代化程度分别约为 70%和 100%。在-100 mV 以下，二硫代物种占主导地位，超过单硫代物种。在所有的硫代砷酸盐中，二甲基单硫代砷酸盐在长时间氧化过程中变化最小。它也是根际中主要的硫代砷酸盐，其浓度与前体二甲基化含氧砷酸盐相当，这尤其重要，因为二甲基单硫代砷酸盐具有高度致癌性。
