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

TiO2 nanoparticles exert an adverse effect on aquatic microbial communities

Titanium dioxide nanoparticle (n-TiO₂) is a widely used nanomaterial, which is inevitably released as a residue into aquatic ecosystems during material production and usage. However, the effects of n-TiO₂ on aquatic microbial communities have not been completely elucidated. This study examined the toxic effects of n-TiO₂ on eukaryotic and prokaryotic microbial communities in freshwater environments. We determined that n-TiO₂ had a greater inhibitory effect on the growth of eukaryotic algae than cyanobacteria in monocultures. A similar phenomenon was observed in a microcosm experiment, revealing that n-TiO₂ slightly reduced the content of chlorophyll-a but evidently increased the phycocyanin content. Moreover, the alpha diversity of the eukaryotic community was not affected, whereas its beta diversity increased with exposure to n-TiO₂. Although n-TiO₂ altered the composition of freshwater microbial communities, it did not change the functions of the prokaryotic community, which might be attributed to the functional redundancy of microbiota. Co-occurrence network analysis indicated that n-TiO₂ destabilized the freshwater community, especially the eukaryotic community, and potentially disturbed the aquatic ecosystem. Our study revealed that the ecological risk of n-TiO₂ on aquatic microbial communities is complex; hence, rational utilization of n-TiO₂ should be emphasized.

Combined effects of nano-TiO2 and hexavalent chromium towards marine crustacean Artemia salina

There has been a significant increased concern of the impact of the toxicity of multiple contaminants in the marine environment. Thus, this study was aimed at determining whether the interaction between nano-TiO₂ and Cr(VI) would modulate their toxic effects with the marine crustacean, Artemia salina. Nano-TiO₂ agglomerated in artificial sea water (ASW) and readily formed micron-sized particles that settled down in the medium. The addition of Cr(VI) to nano-TiO₂ aggravated their agglomeration through sorption of Cr(VI) onto nano-TiO₂. This was reflected by a decrease in the residual concentration of Cr in the suspension. Acute toxicity tests performed using pristine nano-TiO₂ (0.25, 0.5, 1, 2, and 4 mg/L) and Cr(VI) (0.125, 0.25, 0.5, and 1 mg/L) displayed a concentration dependent rise in the mortality of Artemia salina. To examine the effects of mixtures of nano-TiO₂ and Cr(VI) on Artemia salina, two groups of experiments were designed. The former group studied the toxic effect of nano-TiO₂ (0.5, 1, 2, and 4 mg/L) with a fixed concentration (0.125 mg/L) of Cr(VI). While the latter group studied the toxicity of Cr(VI) (0.25, 0.5, and 1 mg/L) with a fixed concentration (0.25 mg/L) of nano-TiO₂. The toxic effects of nano-TiO₂ was not significantly reduced at a fixed concentration of Cr(VI) but in contrast, a significant reduction in the Cr(VI) toxicity by fixed concentration of nano-TiO₂ was observed. Toxicity data was well supported by an independent action model that proved the mode of action between nano-TiO₂ and Cr(VI) to be antagonistic. Furthermore, ROS generation and measurement of antioxidant enzyme activities were also in line with toxicity results. From this study, the modification of Cr(VI) toxicity at fixed concentration of nano-TiO₂ could have a huge impact on the reduction in Cr(VI) toxicity across trophic levels.