Methods of determining titanium dioxide nanoparticles enhance inorganic arsenic bioavailability and methylation in two freshwater algae species

Abstract We developed the effect of titanium dioxide nanoparticles (nano-TiO 2 ) on the bioaccumulation and biotransformation of arsenic ( As ), which remain largely unknown. We thus exposed two freshwater algae ( Microcystis aeruginosa and Scenedesmus obliquus ) to inorganic As with the aim of increasing our understanding on As bioaccumulation and methylation in the presence of nano-TiO 2 . Direct evidence of TEM and EDX image showed that nano-TiO 2 (anatase) entered the exposed algae. Thus, nano-TiO 2 as carriers boosted arsenic accumulation and methylation in these two algae species, which varied with both inorganic As speciation and algae species. Specifically, nano-TiO 2 could enhance markedly arsenate accumulation in M. aerugginosa and arsenite accumulation in S. obliquus . Similarly, we found higher content of As methylation in M. aeruginosa of arsenite with 2 mg L −1 of nano-TiO 2 treatment and in S. obliquus of arsenate treatment. Additionally, S. obliquus exhibited higher As methylation compared to M. aeruginosa , being more sensitive to As associated with nano-TiO 2 than M. aeruginosa . Due to changes in pH levels inside these exposed algae, the As dissociation from nano-TiO 2 inside algal cell enhanced As methylation. Accordingly, the potential influence of nanoparticles on the bioaccumulation and biotransformation of their co-contaminants deserves more attention. • Nano-TiO 2 entry is assumed to promote As accumulation into exposed algae. • Nano-TiO 2 had different carrying capacities for different forms of As and algae. • As dissociation from nano-TiO 2 is assumed to enhance As methylation in algae.