Historical and future trends of cadmium in rice soils deduced from long-term regional investigation and probabilistic modeling

Highlights: • Changes in traditional management of rice straw and irrigation channel are necessary. • The combined measures might take 50 years to ensure the safety of rice practice in local soils. • The fate and transport of Cd in soils can be better estimated with proper defined parameters. • Proposed mass balance model may be extended to cover other contaminants and scenarios. When rice soils are contaminated by cadmium (Cd), the sources and timing of such contaminations need to be identified. In this study, we aimed to quantify the sources, history, and fate of Cd in the rice soils of southern China, by combining a near 10-year regional investigation, by developing a normalized positive matrix factorization algorithm, a Cd mass balance model, and probabilistic simulation. We simulated the historical contamination process of Cd in rice soils from 1991 to 2019 and the future changes from 2019 to 2069 under varying input parameters, as affected by different environmental management measures. Over the period of 1991–2019, the input flux of Cd through atmospheric deposition was estimated at 421 g ha⁻¹, which contributed 52.1% of the total increments in soil Cd concentration. Over the next decade, a 25.6% probability is predicted that the Cd concentration of local rice soils would increase from the baseline to the upper level of soil threshold, despite the efforts of environmental regulators. Removing the rice straw from production fields, cleaning up the irrigation channels, and strengthening environmental regulations would take approximately 50 years (2019–2069) to ensure that 90% of soils were safe for rice cultivation.