One-Time Addition of Nano-TiO2 Triggers Short-Term Responses in Benthic Bacterial Communities in Artificial Streams

Abstract

Nano-TiO2 is an engineered nanomaterial whose production and use are increasing rapidly. Hence, aquatic habitats are at risk for nano-TiO2 contamination due to potential inputs from urban and suburban runoff and domestic wastewater. Nano-TiO2 has been shown to be toxic to a wide range of aquatic organisms, but little is known about the effects of nano-TiO2 on benthic microbial communities. This study used artificial stream mesocosms to assess the effects of a single addition of nano-TiO2 (P25 at a final concentration of 1 mg l(-1)) on the abundance, activity, and community composition of sediment-associated bacterial communities. The addition of nano-TiO2 resulted in a rapid (within 1 day) decrease in bacterial abundance in artificial stream sediments, but bacterial abundance returned to control levels within 3 weeks. Pyrosequencing of partial 16S rRNA genes did not indicate any significant changes in the relative abundance of any bacterial taxa with nano-TiO2 treatment, indicating that nano-TiO2 was toxic to a broad range of bacterial taxa and that recovery of the bacterial communities was not driven by changes in community composition. Addition of nano-TiO2 also resulted in short-term increases in respiration rates and denitrification enzyme activity, with both returning to control levels within 3 weeks. The results of this study demonstrate that single-pulse additions of nano-TiO2 to aquatic habitats have the potential to significantly affect the abundance and activity of benthic microbial communities and suggest that interactions of TiO2 nanoparticles with environmental matrices may limit the duration of their toxicity.

Antibacterial properties and toxicity from metallic nanomaterials

“…This study is a good model of the effects nano-TiO 2 could have on bacterial cells in wastewater. 125 Toxicity observations due to nanotitanium have been tested on live animals. Single low doses of nanoanatase TiO 2 particles in ICR mice's abdominal cavity, once a day for 14 days, have shown little differences in comparison to control mice.…”

Chronic addition of a common engineered nanomaterial alters biomass, activity and composition of stream biofilm communities

“…19 Another previous study reported a significant but temporary decrease in abundance of sediment bacteria in artificial streams in response to a single addition of a lower concentration of nano-TiO 2 (1 mg L −1 ). 28 The greater nano-TiO 2 resistance of the bacterial communities in the present study suggests that chronic addition of a low concentration of nano-TiO 2 may give the communities an opportunity to adapt to the stressor, such as through shifts in the relative abundance of sensitive and resistant taxa, whereas a single pulse addition of a high concentration of nano-TiO 2 does not provide the bacterial community with any opportunity to adapt. Results from our experiments support this hypothesis, as the chronic nano-TiO 2 additions resulted in shifts in bacterial community composition but no decrease in bacterial cell numbers at week 18, which corresponds to a total nano-TiO 2 load of 2.7 mg L −1 .…”

“…In contrast, the one-time nano-TiO 2 addition of 1 mg L −1 in the previous study resulted in an almost immediate decrease in sediment bacterial numbers but no shift in the taxonomic composition of bacterial communities. 28 These results provide insight into the potential ecological effects of different nano-TiO 2 exposure scenarios, i.e. chronic low-level inputs from wastewater effluent versus single high concentration inputs from a spill, combined sewer overflow or infrastructure failure event.…”

“…27 More recently our group assessed nano-TiO 2 effects on complex, multi-species bacterial communities in sediments within artificial stream mesocosms, and reported a significant but temporary decrease in bacterial abundance in response to nano-TiO 2 addition. 28 These studies have demonstrated several approaches for assessing potential effects of nano-TiO 2 on aquatic microorganisms under realistic environmental conditions, but both were based on single additions of nano-TiO 2 , whereas inputs of nano-TiO 2 from wastewater are continuous. Furthermore, both of these experiments used a widely studied form of nano-TiO 2 known as Aeroxide P25, which is a model photocatalyst used extensively in research.…”