Nanoparticle TiO2 size and rutile content impact bioconcentration and biomagnification from algae to daphnia.

Little information is available about effect of particle size and crystal structure of nTiO2 on their trophic transfer. In this study, 5 nm anatase, 10 nm anatase, 100 nm anatase, 20 nm P25 (80% anatase and 20% rutile), and 25 nm rutile nTiO2 were selected to investigate the effects of size and crystal structure on the toxicity, bioconcentration, and trophic transfer of nTiO2 to algae and daphnia. In the exposed daphnids, metabolic pathways affected by nTiO2 and nTiO2-exposed algae (nTiO2-algae) were also explored. The 96 h IC50 values of algae and the 48 h LC50 values of daphnia were 10.3, 18.9, 43.9, 33.6, 65.4 mg/L and 10.5, 13.2, 37.0, 28.4, 60.7 mg/L, respectively, after exposed to nTiO2-5A, nTiO2-10A, nTiO2-100A, nTiO2-P25, and nTiO2-25R, respectively. The bioconcentration factors (BCFs) for 0.1, 1, and 10 mg/L nTiO2 in daphnia ranged from 21,220 L/kg to 145,350 L/kg. The nTiO2 biomagnification factors (BMFs) of daphnia fed with 1 and 10 mg/L nTiO2-exposed algae were consistently greater than 1.0 (5.7-122). The results show that the acute toxicity, BCF, and BMF all decreased with increasing size or rutile content of nTiO2. All types of nTiO2 were largely accumulated in the daphnia gut and were not completely depurated within 24 h. At the molecular level, 22 Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways of daphnia were impacted by the nTiO2 and nTiO2-algae treatments, including glutathione metabolism, aminoacyl-tRNA biosynthesis, among others. Six and four KEGG metabolic pathways were significantly disturbed in daphnids exposed to nTiO2 and nTiO2-algae, respectively, indicating the presence of algae partially alleviated the negative impact of nTiO2 on metabolism. These findings increase understanding of the impacts of physicochemical properties of nTiO2 on the food chain from molecular scale to that of the whole organism, and provide new insight into the ecological effect of nanomaterials.