Toxicity of coal fly ash and coal gangue leachate to Daphnia magna: Focusing on typical heavy metals

Abstract To identify potential toxicity of heavy metals (HMs) in coal fly ash (FA) and coal gangue (CG), this study measured Cd, Cr, Cu, Zn, Pb and Ni in two FAs and two CGs, and assessed their leachates' toxicity to Daphnia magna (D. magna). The results showed that the selected HMs in material and their leachates were low. However, under simplified Elendt M7 medium exposure system, the added leachates inhibited the survival and reproduction of D. magna. The HMs in D. magna increased as leachate increased, and D. magna mortality increased as the HMs in D. magna increased overall. The Cr and Ni in D. magna both showed significant linear positive correlation with the mortality. These indicated that HMs in leachate dilutions were important reason to inhibit D. magna. Moreover, the HMs in leachate also changed the biomarkers and caused oxidative stress in D. magna. Antioxidant system and cell structure of D. magna were further destroyed as leachates increased. The leachates’ inhabitation (mortality and living offspring) to D. magna depended on the properties of FA and CG, and the chemical composition of their leachates. Element level (e.g., C, S and N) and their chemical speciation (e.g., S2− and NH4+) likely impacted the leaching rate and toxicity of HMs.