Formation of copper complexes in landfill leachate and their toxicity to zebrafish embryos

Toxic metal organic complexes have not been found in natural waters, althou gh some organic acids form bioavailable lipophilic and metabolite-type meta l complexes. Landfill leachates usually contain organic acids and in the ur ban environment these leachates, when mixed with storm waters containing Cu , could be a source of toxic Cu organic complexes in streams and estuaries. We investigated the formation of Cu complexes in the leachate from an acti ve urban landfill and found that some of the complexes formed were toxic to zebrafish embryos. High and low nominal molecular weight (NMWT) fractions; >5,000 Da and <700 Da, of leachate both formed Cu complexes with almost id entical Cu complexing characteristics but the toxicity was due solely to th e low NMWT complexes formed in the <700 Da fraction. Chemical equilibrium m odelling with MINTEQA2 and H and Cu complex conditional association constan ts and ligand concentrations obtained from pH and Cu titrations with a Cu i on-selective electrode and van dcn Berg-Ruzic analyses of the titration dat a was used to calculate the copper speciation in the embryo test solutions. This calculated speciation, which was confirmed by measurements of Cu2+ in the test solutions, enabled the toxicity due to the free Cu ion and to the Cu complexes to be distinguished.