Effects of metal oxide nanoparticles on soil enzyme activities and bacterial communities in two different soil types

With the increased availability of nanoparticle-based products, their releases to soil are undoubtedly inevitable. Among the nanoparticle-based products, potential risks of metal oxide nanoparticles (MO-ENPs) have attracted increasing concerns. However, their effects on soil and soil microorganisms remain largely unknown. In this study, four metal oxide nanoparticles, i.e., zinc oxide nanoparticles (nZnO), titanium dioxide nanoparticles (nTiO(2)), cerium dioxide nanoparticles (nCeO(2)), and magnetite nanoparticles (nFe(3)O(4)), were enrolled to evaluate their impact on soil enzyme activities (invertase, urease, catalase, and phosphatase) and bacterial communities in two typical soils from northeast China (black soil and saline-alkali soil). The community structure and size were analyzed using pyrosequencing and real-time polymerase chain reaction (RT-PCR). The soils were exposed to metal oxide nanoparticles at 0.5, 1.0, and 2.0 mg g(-1) for 15 and 30 days. In general, nZnO had a stronger effect on soil enzymatic activities than nTiO(2), nCeO(2), and nFe(3)O(4), and saline-alkali soil was more susceptible to metal oxide nanoparticles than black soil. In RT-PCR analysis, a significant decrease (41.66, 36.34, and 47.99%, respectively) on total bacteria population was only observed in saline-alkali soil treated by 0.5, 1.0, and 2.0 mg g(-1) nZnO. Meanwhile, pyrosequencing analysis revealed that the samples of saline-alkali soil treated with nZnO showed high variance in their bacterial community composition, e.g., Bacilli, Alphaproteobacteria, and Gammaproteobacteria class. The results suggested that metal oxide nanoparticle incubation could influence soil enzyme activities and change soil bacterial community. Moreover, the soil type was a key component dictating the effect of metal oxide nanoparticles on the bacterial community composition and size. These findings are of great help towards building a comprehensive understanding of the potential environmental risks of metal oxide nanoparticles.