Biotic ligand modeling to predict the toxicity of HWO4- and WO42- on wheat root elongation in solution cultures: Effects of pH and accompanying anions.

ABSTRACT

Increasing evidence demonstrates that hexavalent tungsten (W(VI)) can affect the survival of various organisms. This study explored the influences of pH and common anions on W(VI) toxicity on wheat and established a biotic ligand model (BLM) for predicting W(VI) toxicity. It was found that as the pH value increased from 6.0 to 8.5, the EC50[W(VI)]T values increased greatly from 24.7 to 46.6 µM, indicating that increasing pH values can alleviate W(VI) toxicity. A linear relationship between the ratio of HWO4- to WO42- and EC50{WO42-} indicated that WO42- and HWO4- were two toxic species of W(VI). The toxicity of W(VI) decreased as the H2PO4- and SO42- activities increased but not when the activities of Cl- and NO3- increased, demonstrating that the competition from H2PO4- and SO42- significantly influenced W(VI) toxicity. By applying BLM theory, the stability constants for HWO4-, WO42-, H2PO4-, and SO42- were obtained logKWO4BL = 4.08, logKHWO4BL = 6.44, logKH2PO4BL = 2.09, and logKSO4BL = 1.87, fWBL50% = 0.300, ß = 1.99. Results demonstrated that BLM outperformed the free metal activity model(FIAM) in predicting W(VI) toxicity when considering the influences of pH, W(VI) species, and H2PO4- and SO42- competition for active ligand sites.