Biotoxicity Assessment of Incinerator Bottom Ash Leachates Using Daphnia magna

Abstract

The Hsinchu City incinerator generated 35.6 kilotons of incinerator bottom ash (IBA) annually. Most of the IBA were landfilled, while part of them was reused as construction materials for public works. Although the toxicity characteristic leaching procedure (TCLP) of IBA met the Taiwan's current environmental regulations, either landfilled or reused applications were still subject to public concerns. This study evaluated the biotoxicity of IBA leachates using Daphnia magna. The IBA samples were collected from the bottom ash storage pit, following a modified leaching procedure to prepare the leachates. The total elemental analysis of IBA leachates showed that contents of Cu and Zn were in the range from 0.35 % and 1.05 %, respectively, and were higher than other heavy metals in IBA leachates. In the TCLP testing, all results indicate the metal ions concentrations are well below toxicity standard of the regulation. Daphnia magna was employed to test the static 24-h acute toxicity, and mortality data obtained were further analyzed using the Probit and Spearman-Karber statistical models. Results in the biotoxicity testing indicated that as dilution ratios in 1:10, the toxicity unit (TU) values were in the range from 66.7 to 71.4, and dilution ratios in 1:500, the TU values were in the range from 2.9 to 3.1. The higher the dilution ratios of the leachates, the lower the TU values, indicating that the dilution ratio has a significant effect on the IBA leachates. Experimental results indicated that though the chemical-based TCLP test results were in compliance with regulatory standards, the biological-based toxicity test may reach a certain level of TU value. Accordingly, it is suggested that a biotoxicity program for IBA should be well established in parallel with current TCLP testing to increase the public acceptance for subsequent applications.