Particle Size and Concentration Dependent Ecotoxicity of Nano- and Microscale TiO2 —Comparative Study by Different Aquatic Test Organisms of Different Trophic Levels

Abstract

A comprehensive ecotoxicity assessment of three different nanosized TiO2 (with 16, 36 and 89 nm particle diameter) and one microscale TiO2 suspension (with 3264 nm particle diameter) was carried out with a special emphasis on the relation between product characteristics and toxic effect. The applied test battery included the combination of modified standardized tests (Aliivibrio fischeri bioluminescence inhibition test, Lemna minor growth inhibition test), and nonstandardized bioassays with unconventional physiological endpoints (Tetrahymena pyriformis phagocytic activity, the Daphnia magna heartbeat rate). Based on the lowest significant effect values, the tested aquatic organisms were the most sensitive to the microscale TiO2 suspension (with 3264 nm particle size). Although the three nanoscale TiO2 particles were aggregated in the A. fischeri and the L. minor growth media, significant inhibition rates were experienced at 0.1 and at 1 μg L─1 concentration of nTiO2 suspensions with 16 and 36 nm primary particle size, respectively. Larger aggregates may have also high impact on biological organisms. In case of the D. magna heartbeat rate test rapid agglomeration was avoided, but lower responses were found compared to other investigated systems. The short term T. pyriformis phagocytic activity test demonstrated outstanding sensitivity; three TiO2 suspensions were significantly toxic even at 0.1 μg L─1. The consequences of our study clearly indicated that nanoscale TiO2 may have an impact on the aquatic ecosystem which is strongly influenced by aggregation. The effect of exposure duration and concentration as contributing factors in nano-titanium dioxide mediated toxicity was also demonstrated.