Effects of Titanium Dioxide Nanoparticles on Red Clover and Its Rhizobial Symbiont

Titanium dioxide nanoparticles (TiO(2) NPs) are in consideration to be used in plant protection products. Before these products can be placed on the market, ecotoxicological tests have to be performed. In this study, the nitrogen fixing bacterium Rhizobium trifolii and red clover were exposed to two TiO(2) NPs, i.e., P25, E171 and a non-nanomaterial TiO(2). Growth of both organisms individually and their symbiotic root nodulation were investigated in liquid and hydroponic systems. While 23 and 18 mg l(-1) of E171 and non-nanomaterial TiO(2) decreased the growth rate of R. trifolii by 43 and 23% respectively, P25 did not cause effects. Shoot length of red clover decreased between 41 and 62% for all tested TiO(2) NPs. In 21% of the TiO(2) NP treated plants, no nodules were found. At high concentrations certain TiO(2) NPs impaired R. trifolii as well as red clover growth and their symbiosis in the hydroponic systems.