Compositional alterations in soil bacterial communities exposed to TiO2 nanoparticles are not reflected in functional impacts

Yujia Zhai,Ellard R Hunting,Gang Liu,Elise Baas,Willie J.G.M Peijnenburg,Martina G Vijver

doi:10.1016/j.envres.2019.108713

Abstract

Titanium dioxide nanoparticles (TiO2NP) are increasingly released in soil ecosystems, while there is limited understanding of the impacts of TiO2NP on soil bacterial communities. Here we investigated the effects of TiO2NP on the taxonomic composition and functional profile of a soil bacterial community over a 60-day exposure period. In short-term exposure (1-day), contradictory effects on the taxonomic composition of soil bacterial communities were found after exposure to a low realistic environmental concentration of TiO2NP at 1 mg/kg as compared to the effects induced by medium and high concentrations of TiO2NP at 500 and 2000 mg/kg. After long-term exposure (60-day), the negative effects of TiO2NP at the low concentration disappeared, and the inhibition by TiO2NP of the abundance of core taxa was enhanced along with increasing exposure concentrations. However, although significant alterations were observed in the taxonomic composition over time and exposure concentrations, no significant change was observed in the community functional profile as well as enzyme activity after 60-day exposure, indicating that functional redundancy likely contributed to the bacterial community tolerance after the exposure to TiO2NP. Our study highlighted the importance of assessing bacterial community compositional and functional responses in assessing the environmental risk of nanoparticles on soil ecosystems.

Highlights

Titanium-dioxide nanoparticles (TiO2NP) are among the metal NPs that are produced in the highest volumes
After 60 days, there was no significance difference found between the control and the 1 and 500 mg/kg treatments, while the bacterial abundance in the 2000 mg/ kg treatment was significantly lowered compared with the control
This study investigated the effect of different TiO2NP concentrations at different time-points considering the taxonomic composition and catabolic potential of a soil bacterial community

Summary

Introduction

Titanium-dioxide nanoparticles (TiO2NP) are among the metal NPs that are produced in the highest volumes. They are, amongst others, nowadays applied in agriculture as biosolids, nano-agrochemicals, and additives for crops (Liu et al, 2019). The release of TiO2NP into soil as induced by anthropogenic activities could result in elevated concentrations. This raises concerns about their potential impact on the soil bacterial community as well as on the soil ecosystems (McKee and Filser, 2016). When TiO2NP enter the environment, the natural aging processes such as aggregation/agglomeration and sorption could change the effect of TiO2NP on natural bacterial communities, resulting in different toxicity from what has observed on single cultures (Fang et al, 2009; Hotze et al, 2010). Simonin et al found no TiO2NP toxicity on the C-mineralization and microbial community abundance except for soils with a high organic matter content (Simonin et al, 2015), while Ge et al observed a decline in microbial biomass and community diversity in forest soil exposed to

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