Titanium Dioxide (TiO2) nanoparticles more strongly affect bacteria compared to algae in stream ecosystems

Abstract

Titanium dioxide (TiO₂) is a novel nano-particulate contaminant found in surface waters. Nano-TiO₂ is commonly used in numerous pharmaceutical and personal care products ranging from make-up to pill casings, and is an additive in food and household products. Despite the commercialized use of TiO₂, its increased presence in surface waters, and toxic effects on stream organsims, little information exists on how nano-TiO₂ affects stream ecosystems as a whole. We examined the effect of various concentrations (0.5 - 3 mg/L) of nano-TiO₂ on stream ecosystems by measuring the response of algal and microbial communities to acute (12 hr) and chronic (22 day) exposures. We measured gross primary production (GPP), community respiration (CR), and chlorophyll a (chl a) concentrations on intact algae from a local stream.We expected metabolic function of both algal and microbial components of the benthic biofilm to decline with exposure  due to sensitivities to metal oxides. However, we found exposure to any of the concentrations of nano-TiO₂ tested caused CR to decrease compared to controls, but, GPP either increased or stayed the same as our controls. We found algal chl a concentraions to increase in the high exposure treatment. Since nano-TiO₂ had a negative effect on the microbes, we hypothesized that either autotrophs were released from microbial competition and increased chl a production, or that shading from TiO₂ particles may have caused increased chl a production. Additional studies investigating the effects of higher concentrations and longer exposure times to these compounds are warranted.