Detrimental Effects of Metal Nanoparticles on Microorganisms and ‎Biochemical Activities through Soil Quality Index Analysis ‎

The expanding use of nanoparticles broachs their environmental impacts, but their effects on ecosystem functions ‎and the organisms remain largely unknown. Few studies have targeted soil biochemical activities which are ‎regarded as sensitive soil health indicators. Thus, present study designed to estimate the ecotoxicological effects ‎of Al2O3 and ZnO NPs at various concentrations (30, 60, 90, 120, 150 and 180 mg/l) in a 60-day microcosm ‎incubation experiment under 25±3°C. Microbial count, enzyme activity, basal respiration rate and microbial ‎biomass were estimated, besides the inhibition rate, toxicity index, potential soil fertility index and soil quality ‎index (SQI). Significant differences in pH, EC, TDS and SOM were observed after application of NPs. Microbial ‎activity was generally increased in response to both NPs, whereas Azotobacter was not affected by Al2O3 NPs. ‎Various results were observed in biochemical activities. Dehydrogenase, catalase, nitrate reductase and biomass C ‎were generally decreased, while urease and respiration rate were increased in comparing with control. The greatest ‎inhibition rates shown by both Al2O3 and ZnO NPs were in dehydrogenase activity by 159.5% and in free-living ‎nitrogen-fixing bacteria by 213.7% respectively. Referring to toxicity index, both NPs showed toxicity on free-‎living nitrogen-fixing bacteria, dehydrogenase, catalase and nitrate reductase. The highest SQI recognized as 0.792 ‎in 90 mg/l treated soils with Al2O3 NPs, while the highest SQI recognized as 0.978 in 150 mg/l treated soils with ‎ZnO NPs. Consequently, NPs may measurably impact soil microbiological and biochemical properties and all the ‎used bioindicators be advantageous in monitoring soil contamination by NPs through analysis of soil quality ‎index