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In waterlogged paddy soils, cadmium (Cd) can be precipitated as cadmium sul de (CdS) under reductive environment, thereby limiting the absorption of Cd by plants. Multiple environmental factors (such as water, pH, Eh, etc.) played a role in the control of Cd mobility and bioavailability. In this study, we investigated the in uence of the solar irradiation on the photo-dissolution of synthetic CdSmontmorillonite composites (CdS-M) in solution and the stability of Cdin natural soil. The release kinetic of Cd 2+ showed that after the irradiation of simulated sunlight, CdS-M composites became less stable compared to the dark control. The solar irradiation seemed to enhance the release of Cd 2+ from CdS signi cantly and continuously. Electron paramagnetic resonance (EPR) and quenching experiments con rmed that the photogenerated holes, O 2•and •OH were possibly involved in the photo-induced release of Cd 2+ , while the holes was primarily responsible for the reaction.Irradiation under alkaline solution or the presence of DOM, PO 4 3-, CO 3 2and urea markedly inhibited the photodissolution process of CdS. The photo-mediated activation of Cd was further con rmed in paddy soil under natural sunlight, with a nearly 3-fold increase in concentration of extractable Cd during the 15 days irradiation. This study highlights the importance of photochemical transformation of Cd in the environmental water and soil.

In waterlogged paddy soils, cadmium (Cd) can be precipitated as cadmium sulfide (CdS) under reductive environment, thereby limiting the absorption of Cd by plants. Multiple environmental factors (such as water, pH, Eh, etc.) played a role in the control of Cd mobility and bioavailability. In this study, we investigated the influence of the solar irradiation on the photo-dissolution of synthetic CdS-montmorillonite composites (CdS-M) in solution and the stability of Cdin natural soil. The release kinetic of Cd2+ showed that after the irradiation of simulated sunlight, CdS-M composites became less stable compared to the dark control. The solar irradiation seemed to enhance the release of Cd2+ from CdS significantly and continuously. Electron paramagnetic resonance (EPR) and quenching experiments confirmed that the photogenerated holes, O2·- and •OH were possibly involved in the photo-induced release of Cd2+, while the holes was primarily responsible for the reaction.Irradiation under alkaline solution or the presence of DOM, PO43-, CO32- and urea markedly inhibited the photodissolution process of CdS. The photo-mediated activation of Cd was further confirmed in paddy soil under natural sunlight, with a nearly 3-fold increase in concentration of extractable Cd during the 15 days irradiation. This study highlights the importance of photochemical transformation of Cd in the environmental water and soil.