Assessing bioavailable metals in effluent-affected rivers: Effect of iron and chelating agents on the distribution of metal speciation

To assess bioavailability levels and indentify important speciation for trace metals (Ni, Cu, Zn, and Pb), the rivers affected by a waste water treatment plant (WWTP) was studied. Biologically available concentrations were measured by the diffusive gradients in thin films (DGT) method, and DGT results were compared with those predicted by WHAM 7.0. At most sites downstream of the WWTP, bioavailable metals increased. Due to the competitive binding of iron with humic substances, free ions for Cu and Pb increased. High level of ethylenediaminetetraacetic acid (EDTA) was in sampling rivers, EDTA had considerable binding capacity with metals, the fractions of EDTA complexes with metals followed the sequence of Ni > Pb > Cu > Zn, this likely attributed to the result that, measured bioavailable concentrations by DGT were lower than predicted results.