Effect of 10 different TiO2 and ZrO2 (nano)materials on the soil invertebrate Enchytraeus crypticus

Nearly 80% of all the nano-powders produced worldwide are metal oxides, and among these materials titanium dioxide (TiO2 ) is one of the most produced. Titanium dioxide's toxicity is estimated as low to soil organisms, but some studies have shown that TiO2 nanoparticles can cause oxidative stress. Additionally, it is known that TiO2 is activated by ultraviolet (UV) radiation, which can promote photocatalytic generation of reactive oxygen species, which is seldom taken into account in toxicity testing. In the present study, the authors investigated the effects of different TiO2 and zirconium materials on the soil oligochaete Enchytraeus crypticus, using exposure via soil, water, and soil:water extracts, and studied the effects combined with UV radiation. The results showed that zirconium dioxide (bulk and nano) was not toxic, whereas zirconium tetrachloride reduced enchytraeid reproduction in soil (50% effect concentration = 502 mg/kg). The TiO2 materials were also not toxic via soil exposure or under UV radiation. However, pre-exposure to TiO2 and UV radiation via aqueous media caused a lower reproductive output post-exposure in clean soil (20-50% less but only observed at the lowest concentration tested, 1 mg/L); that is, the effect of TiO2 in water was potentiated by the UV radiation and measurable as a decrease in reproduction in soil media.