The effects of low-dose biochar amendments on arsenic accumulation in rice (Oryza sativa L.)

The accumulation of arsenic (As) in rice is one of the food security-related concerns in As-contaminated areas all over the world. Biochar, a potential green and cost-efficient amendment material, affects As mobility/phytoavailability in soil and As accumulation in rice plants to some extent, which remains unclear. Thus, three different biochars derived from rice straw, corn stalks, and bamboo were used to investigate the impacts of biochar amendments on As mobility/phytoavailability in As-contaminated soil using pot and microcosm experiments. The results showed a limited reduction (by 12-16%) in As accumulation in rice grains under a low-dose (0.5%, w/w) biochar amendment, although the three biochars displayed different physicochemical properties. In addition, the biochar amendments did not significantly decrease the As levels in the straw and roots, potentially because of the small changes in As mobility/phytoavailability in amended soil relative to the control. However, As levels in soil solution in the biochar treatment groups increased substantially, by 2.8-6.6 times, with increasing biochar doses (0.5-5%, w/w) in microcosm-based anaerobic incubation experiments, particularly at higher doses (3-5%, w/w). These results could be attributed to the biochar-enhancing activity of As(V)-/Fe(III)-reducing bacteria at a high biochar application rate. Our results suggested that applying high biochar doses may increase the release of As into the soil, resulting in As accumulation in rice plants. Therefore, to mitigate the health risk of As in As-contaminated paddy soils, the remediation technologies from biochar methods should be subjected to more evaluation.