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 nTiO 2 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 nTiO 2 were selected to investigate the effects of size and crystal structure on the toxicity, bioconcentration, and trophic transfer of nTiO 2 to algae and daphnia. In the exposed daphnids, metabolic pathways affected by nTiO 2 and nTiO 2 -exposed algae (nTiO 2 -algae) were also explored. The 96 h IC 50 values of algae and the 48 h LC 50 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 nTiO 2 -5A, nTiO 2 -10A, nTiO 2 -100A, nTiO 2 -P25, and nTiO 2 -25R, respectively. The bioconcentration factors (BCFs) for 0.1, 1, and 10 mg/L nTiO 2 in daphnia ranged from 21,220 L/kg to 145,350 L/kg. The nTiO 2 biomagnification factors (BMFs) of daphnia fed with 1 and 10 mg/L nTiO 2 -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 nTiO 2 . All types of nTiO 2 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 nTiO 2 and nTiO 2 -algae treatments, including glutathione metabolism, aminoacyl-tRNA biosynthesis, among others. Six and four KEGG metabolic pathways were significantly disturbed in daphnids exposed to nTiO 2 and nTiO 2 -algae, respectively, indicating the presence of algae partially alleviated the negative impact of nTiO 2 on metabolism. These findings increase understanding of the impacts of physicochemical properties of nTiO 2 on the food chain from molecular scale to that of the whole organism, and provide new insight into the ecological effect of nanomaterials .