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

► ZnO nanoparticles and non-nano ZnO were equally toxic to Folsomia candida in soil. ► Pore water from soil spiked with ZnO nanoparticles showed saturation with zinc suggesting aggregation. ► Pore water based EC50 values for ZnO nanoparticles and ZnCl2 were similar. ► ZnO nanoparticle toxicity in soil was most probably due to Zn dissolution from the nanoparticles.