Evaluating the mutagenicity of leachates obtained from the bottom ash of a municipal solid waste incinerator by using a Salmonella reverse mutation assay

The mutagenic potential of leachates derived from the bottom ash of a municipal solid waste incinerator in Taiwan were evaluated using an Ames Salmonella mutagenicity assay with three standard tester strains, TA98, TA100, and TA1535. Three types of leachants, leachant A (pH 4.93), leachant B (pH 2.88), and leachant C (deionized water, pH 6.0), were carried out according to toxicity characteristic leaching procedure (TCLP). Moreover, two types of bottom ash, nonsieved and sieved bottom ash (particle size <4.75 mm), were analyzed with the TCLP and the Ames assay. The concentrations of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in the leachates were also estimated with an ICP-OES. The results indicated that the metal concentrations in the TCLP leachates of bottom ash were all below the limits set by Taiwanese regulations. However, leachate A from nonsieved and <4.75-mm-sieved bottom ash showed mutagenicity. Moreover, leachate A from <4.75 mm-sieved bottom ash displayed stronger mutagenicity than that from nonsieved ash. The leachate A from <4.75-mm-sieved bottom ash, that were diluted by 100-fold showed no mutagenicity. In conclusion, our results suggested that the chemical composition and mutagenic potential of leachates should be monitored to evaluate the safety of bottom ash.