Titanium dioxide nanoparticles negatively affect microbes but not algae in stream ecosystems
Titanium dioxide is a novel nano-particulate contaminant found in surface waters. It is commonly used in numerous pharmaceutical and personal care products ranging from make-up to pill casings, and is a common additive in food and paint. Despite the rapid rise in the number of products using TiO2, and increased presence in surface waters, little information exists on how TiO2 affects ecosystem processes. We examined the effect of two environmentally relevant concentrations (0.5 mg/L , 3mg/L) of TiO2 on stream ecosystems by measuring algal and microbial community metabolism after a chronic 22 day in-situ exposure. We also measured responses to acute exposure (12hr) in laboratory chamber studies. We expected decreased metabolic function in both algal and microbial components of the benthic biofilm due to sensitivities to metal oxides.
We found that biofilm heterotrophs were more strongly affected by TiO2 nanoparticles than autotrophs. Exposure to either concentration of TiO2 caused community respiration to decrease compared to controls. Gross primary production either increased or stayed the same as control. Interestingly, algal chl a concentrations increased in the higher treatment. We hypothesize that the positive effect of TiO2 on algae may be a result of reduced competitive pressure from microbes for resources, including nutrients and space. In addition, TiO2 is opaque, and may have coated algal cells causing shading of chlorophyll cells. Algae could increase chl a concentrations to compensate for this loss of light.
Although the effects of TiO2 on algae and microbes in this study were apparent, the extent to which such changes in metabolism will affect whole ecosystem function at this dosage is unclear. Future studies aim to examine higher concentrations would be necessary to gain a greater insight into the relationship of TiO2 and algal and microbial growth and respiration.