Heavy metal toxicity and genotoxicity in water and sewage determined by microbiological methods

Acute toxicity and genotoxicity of cadmium, copper, chromium, mercury, nick el, and zinc dissolved in deionized water and in sewage were established by comparing the EC50 and EC20 values obtained by different microbial assays. For acute toxicity determination, The Netherlands Standard NEN6509 test, t he spectrophotometric assays of respiratory inhibition using Saccharomyces cerevisiae and Pseudomonas fluorescens, and the Microtox(TM) test were empl oyed. To determine metal genotoxicity, the Salmonella typhimurium and Esche richia coli mutagenicity tests, the SOS-beta-galactosidase genotoxicity tes t, and the Mutatox(TM) assay were used. The toxicity of the different assay ed metals varied from the most toxic, mercury, to the least toxic, nicker a nd zinc. Two different rankings of toxicity and genotoxicity, very similar to each other, were established. The toxicity ranking was Hg > Cr > Cd simi lar to Cu similar to Zn > Ni, and the genotoxicity ranking was Hg > Cr > Cu similar to Cd similar to Ni > Zn. The association between the toxicity and genotoxicity of copper and chromium in the dissolved and suspended fractio ns of sewage was also determined. Copper was mainly associated with the sus pended fractions and chromium with the dissolved fractions of sewage.