Limited information is available on the environmental behavior and associated potential risk of manufactured oxide nanoparticles (NPs). In this research, toxicity of nanoparticulate and bulk ZnO, Al(2)O(3) and TiO(2) were examined to the nematode Caenorhabditis elegans with Escherichia coli as a food source. Parallel experiments with dissolved metal ions from NPs were also conducted. The 24-h median lethal concentration (LC(50)) and sublethal endpoints were assessed. Both NPs and their bulk counterparts were toxic, inhibiting growth and especially the reproductive capability of the nematode. The 24-h LC(50) for ZnO NPs (2.3 mg L(-1)) and bulk ZnO was not significantly different, but significantly different between Al(2)O(3) NPs (82 mg L(-1)) and bulk Al(2)O(3) (153 mg L(-1)), and between TiO(2) NPs (80 mg L(-1)) and bulk TiO(2) (136 mg L(-1)). Oxide solubility influenced the toxicity of ZnO and Al(2)O(3) NPs, but nanoparticle-dependent toxicity was indeed observed for the investigated NPs.