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-TiO2) 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-TiO2. Direct evidence of TEM and EDX image showed that nano-TiO2 (anatase) entered the exposed algae. Thus, nano-TiO2 as carriers boosted arsenic accumulation and methylation in these two algae species, which varied with both inorganic As speciation and algae species. Specifically, nano-TiO2 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-TiO2 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-TiO2 than M. aeruginosa. Due to changes in pH levels inside these exposed algae, the As dissociation from nano-TiO2 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-TiO2 entry is assumed to promote As accumulation into exposed algae.•Nano-TiO2 had different carrying capacities for different forms of As and algae.•As dissociation from nano-TiO2 is assumed to enhance As methylation in algae.