Effects of exogenous phosphates on speciation and bioavailability of arsenic and cadmium in farmland soils

Purpose Soils contaminated with As and Cd complex pose a serious threat to human health and the ecological environment. Phosphorus is an essential nutrient element in farmland soil, and it is of great significance to study the effects of different types of phosphate on the compound pollution of As and Cd in soil.Methods Four types of phosphates, including aluminum phosphate (AlPO4), ferric phosphate (FePO4), calcium phosphate (Ca-3(PO4)(2)), and potassium dihydrogen phosphate (KH2PO4), were selected to explore the effect of different phosphates on the stability and bioavailability of soil As and Cd by changing soil pH and the concentration of available P. X-ray absorption near edge structure (XANES) spectroscopy was used to determine P speciation in soil samples.Results The results show that all four phosphates can improve the stability of Cd in soil, but the concentration of unstable As in soil increased after applying P because of the competitive effect. Potassium dihydrogen phosphate and ferric phosphate remarkably affected As and Cd. At pH 6.75, both As and Cd in soil can reach a relatively stable state. With the increase in available P in soil, the bioavailability of Cd decreased linearly, while that of As increased exponentially. The fitting curve shows that the available P content of 450 mg/kg can be used as the critical point to control the relative stability of As and Cd in the sampled soil.Conclusion Phosphate can alter the stability of As and Cd by changing soil pH and available P content.

Automated summary

Different phosphates can affect the stability and bioavailability of As and Cd in soil. Aluminum phosphate, ferric phosphate, calcium phosphate, and potassium dihydrogen phosphate can improve the stability of Cd, but increase the concentration of unstable As. Both As and Cd can reach a relatively stable state in soil at pH 6.75. The critical point for controlling the relative stability of As and Cd in the sampled soil is a available P content of 450 mg/kg.