The nanoparticulate titanium dioxide NM-105 was investigated in two tests with Lumbriculus variegatus in a sediment-water system according to the OECD TG 225 [5]. The nominal test concentrations in the first test were 15; 23; 39; 63 and 100 mg/L NM-105 and 100 mg/L NM-105 in the second test. Chemical analysis of titanium concentrations in test media in the first test showed good agreement with nominal test concentrations.