Biogeochemical transformation of sulfur and its effects on arsenic mobility in paddy fields polluted by acid mine drainage

This study aimed to study the biogeochemical behaviour of sulfur and its potential impact on arsenic in farmland polluted by acid mine drainage (AMD). Soil samples were collected from paddy fields that were near arsenic-rich coal mines. Different geochemical analysis technologies, combined with the study of microbial populations, were used to analyse the enrichment and transformation characteristics of exogenous sulfur in the soil profile as well as their coupling effect with arsenic transformation. The results showed that sulfur, iron, and arsenic were obviously enriched in the soil, and sulfur easily migrated to deeper layers. The content of arsenic in contaminated soil was about 1.30-3.14 times higher compared to standard Chinese soil quality. Polluted soil had a higher content of bioavailable sulfur and adsorbed sulfur accounted for about 29% of the total sulfur. This promoted an increased microbial population abundance of Desulfosporosinus. The δ34S values of the polluted soil were lower than the background, ranging from -0.69‰ to 11.44‰, but were higher than the theoretical values. There was evidence of dissimilatory sulfur reduction and enrichment in 34S. A significant positive correlation was observed between the contents of adsorbed sulfur and total arsenic. The biogeochemical transformation of sulfur was conducive to the transformation of iron oxide-bound arsenic into sulfide minerals, which enhanced its stability. These results provide theoretical support for understanding the cycling transformation and environmental impact of sulfur in paddy fields polluted by AMD.