Chronic toxicity of ZnO nanoparticles, non-nano ZnO and ZnCl2 to Folsomia candida (Collembola) in relation to bioavailability in soil

The chronic toxicity of zinc oxide nanoparticles (ZnO-NP) to Folsomia candida was determined in natural soil. To unravel the contribution of particle size and free zinc to NP toxicity, non-nano ZnO and ZnCl2 were also tested. Zinc concentrations in pore water increased with increasing soil concentrations, with Freundlich sorption constants K-f of 61.7, 106 and 96.41/kg (n = 1.50, 1.34 and 0.42) for ZnO-NP, non-nano ZnO and ZnCl2 respectively. Survival of E candida was not affected by ZnO-NP and non-nano ZnO at concentrations up to 6400 mg Zn/kg d.w. Reproduction was dose-dependently reduced with 28-d EC50s of 1964,1591 and 298 mg Zn/kg d.w. for ZnO-NP, non-nano ZnO and ZnCl2, respectively. The difference in EC50s based on measured pore water concentrations was small (7.94-16.8 mg Zn/I). We conclude that zinc ions released from NP determine the observed toxic effects rather than ZnO particle size. (C) 2011 Elsevier Ltd. All rights reserved.