Behavior of titanium dioxide nanoparticles in Lemna minor growth test conditions.

Titanium dioxide nanoparticles (TiO(2) NPs) have raised concern of environmental risks due to their widespread applications, but little is known about the potential toxicity of TiO(2) NPs to aquatic plants. The aim of this work was to study the effects of TiO(2) NPs on Lemna minor and to study the behavior of TiO(2) NPs under modified ISO 20079 test conditions. TiO(2) NPs had a tendency to aggregate in ISO (Steinberg) growth medium, but modification of the standard growth medium enabled the exposure of L. minor to TiO(2) NPs. By dilution of the growth medium (1:10), and exposure under semi-static conditions with medium renewal every second or third day, the size of TiO(2) particles remained rather stable throughout the test period. TiO(2) NPs showed no adverse effect on the growth rate or chlorophyll a content of L. minor, even at a high exposure concentration of 5 mg L(-1) and extended exposure time of 14 days. TiO(2) NPs attached onto L. minor cell walls, but no cellular uptake was observed. Although TiO(2) NPs were not toxic to L. minor, the potential transfer of TiO(2) NPs in aquatic food chains, e.g. attached to the plant leaves and other biological surfaces may be of importance, causing exposure of other organisms and contributing to the environmental fate of nanoparticles.