Biotic reactive oxygen species drive arsenic oxidation in paddy soils

The generation of biotic ROS has increasingly been recognized as a critical process in environmental systems. However, its role in arsenic transformation in paddy soils remains insufficiently elucidated. In this study, the production of biotic ROS and their contribution to As(III) oxidation were systematically investigated using soil microcosm incubations and pure bacterial culture experiments. The results revealed that biotic ROS were broadly involved in As(III) oxidation in paddy soils, with H 2 O 2 playing a more prominent role, contributing up to 37.4% of the total As(III) oxidation. Among environmental factors, manganese was the most immediate driver of biotic ROS activity, while soil total sulfur exerted upstream regulatory effects by influencing both soil pH and Mn. These results provided direct evidence of biotic ROS generation and its role in arsenic oxidation in paddy soil, which offers a novel perspective for improving arsenic mitigation strategies and enhancing rice safety in arsenic-contaminated environments. • As(III) oxidation by biotic ROS is widespread in paddy soils. • H 2 O 2 is the most prominent biotic ROS, exerting a more sustained oxidative effect than •OH and O 2 •- . • Microbially produced ROS can directly oxidize As(III), with microbial respiration playing a key role. • Soil total sulfur regulates biotic ROS-driven As(III) oxidation indirectly by influencing soil pH and manganese content.