FRACTIONATION AND TOXICITY OF METALS IN SEWAGE-SLUDGE

Single extractions of metal fractions in sewage sludge are compared with toxicity to the marine bacterium Photobacterium phosphoreum. Copper, and to a lesser extent Pb and Zn, were in concentrations sufficiently high to account for extracted toxicity. The results point to ammonium acetate and EDTA (ethylenediaminetetraacetic acid) as the most suitable single extractants for extracting the toxic fraction, ammonium acetate for limed sludge and EDTA for the raw and digested sludges. Zinc was found to have antagonistic effects on Cu toxicity at low Zn/Cu ratios. This may be an important mechanism in alleviating Cu toxicity in sludge-amended soils.