The effects of phosphorus on the fate and transformation of sediment-associated cadmium from river sediments

The coexistence of phosphorus (P) and cadmium (Cd) in river sediments poses a significant challenge for remediating these contaminants in aquatic environments, given the ongoing debates regarding their interactions. This study aimed to elucidate the impact of water-soluble phosphorus (PO43-) on the fate and transformation of sediment-associated Cd under varying conditions. The findings revealed that the impact of PO43- on the release of sediment-associated Cd depends on the presence or absence of cations such as Ca2+ and Mg2+, with Ca2+ exerting a more pronounced effect than Mg2+. In the absence of Ca2+ and Mg2+, PO43- effectively inhibits the release of sediment-associated Cd by facilitating the formation of more stable precipitates, including (Cd)3(PO4)2. Conversely, when Ca2+ and Mg2+ are present, they compete with Cd for PO43- binding sites, reducing the formation of (Cd)3(PO4)2 and indirectly enhancing the release of sediment-associated Cd. Furthermore, redox conditions play a significant role in Cd release from sediments depending on its fractions. However, this influence may be less prominent compared to that caused by PO43-. Notably, increasing sediment ageing time diminishes the enhancing effect exerted by PO43-, likely attributed to the conversion of Cd into a more stable residual fraction. This study offers further insights into the impact of PO43- on the fate and transformation of sediment-associated Cd within river sediments, necessitating simultaneous consideration of multiple variables such as cations, redox conditions, and sediment ageing.