Ecotoxicological effect of TiO₂ nano particles on different soil enzymes and microbial community

TiO₂ nano particles (NPs) are one of the most produced nanoparticles in the world which are increasingly being released in to the soil. Soils are exposed to various level of concentration of TiO₂ NPs, which has raised concern over the adverse influence on soil microbial community, in turn on ecosystem functions. Although, increasing number of studies on ecotoxicological effect of TiO₂ NPs are coming up recently, however, a common conscience has yet to be reached regarding the impact of TiO₂ NPs on soil microbial community and processes. Moreover, very few studies have targeted soil enzymes which are being considered as sensitive indicator of soil health. Therefore, the present study has been carried out to estimate the ecotoxicological effect of various doses of TiO₂ NPs (5, 10, 20, 40, 80, 100 mg kg^-1 soil) on different soil enzymes and microbial community structure. Results revealed that soil enzyme activities and microbial biomass had a uniform trend where the value increased up to the dose of 20 mg TiO₂ NPs kg^-1 soil and there onwards reduced drastically up to 100 mg TiO₂ NPs kg^-1 soil dose. On the contrary, soil respiration and metabolic quotient kept increasing up to 100 mg TiO₂ NPs kg^-1 soil dose indicating sub-lethal stress on microbial community. Nevertheless, the structure of microbial community had slightly different trend where the biomass of total phospho lipid fatty acid (PLFA), Gram positive, Gram negative bacteria, fungi, actinomyctetes and anaerobes were found to be increased up to dose of 80 mg TiO₂ NPs kg^-1 soil, but, significantly declined at 100 mg TiO₂ NPs kg^-1 soil dose. Furthermore, temperature effect on TiO₂ NPs toxicity had exhibited a less negative impact at 40 °C rather than at 25 °C. In addition alteration index (AI3), an integrated indicator of C, N, P cycling of soils as well as a well-documented indicator of soil pollution, has been found to be regulated by soil respiration, clay content, anaerobe and eukaryote for AI3-Acid Phos. and by fungi to bacteria ratio, soil respiration, microbial biomass and Gram positive bacteria for AI3-Alk. Phos. Overall, the study provided valuable information regarding ecotoxicological impact of environmentally relevant concentrations of TiO₂ NPs in clay loam soils as well as improved our perception regarding the impact of NPs on soil functioning.