TiO₂ NPs appeared to be more toxic to nematode Caenorhabditis elegans than submicron-sized TiO_2.  At a concentration of 1 mg/l, 7 nm particles affected its fertility and survival rate and were more toxic than 20 nm anatase particles. Similarly, Hu et al. showed that rutile particles (10–20 nm), at concentrations above 1 g/kg soil, can be bio-accumulated in earthworms, where they induce oxidative stress, inhibit the activity of cellulase and induce DNA and mitochondrial damage.