Interaction of zinc oxide nanoparticles with soil: Insights into the chemical and biological properties

Abstract

Widespread use of zinc oxide nanoparticles (ZnO-NPs) threatens soil, plants, terrestrial and aquatic animals. Thus, it is essential to explore the fate and behavior of NPs in soil and also its mechanism of interaction with soil microbial biodiversity to maintain soil health and quality to accomplish essential ecosystem services. With this background, the model experiment was conducted in the greenhouse to study the impact of ZnO-NPs on soil taking maize as a test crop. The X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy and Particles size analysis of engineered NPs confirmed that the material was ZnO-NPs (particle size--65.82 nm). The application of ZnO-NPs resulted in a significant decrease in soil pH. Significantly high EC (0.13 dS m^-1) was recorded where ZnO-NPs were applied at the rate of 2.5 mg Zn kg^-1 soil over control (0.12 dS m^-1). A significant increase in soil available phosphorus was observed on applying ZnO-NPs (15.29 mg kg^-1 of soil) as compared to control (11.84 mg kg^-1 of soil). Maximum soil available Zn (2.09 mg kg^-1) was recorded in ZnO-NPs-amended soil (T₁₁) which was significantly higher than control (0.33 mg kg^-1) as well as treatments containing conventional zincatic fertilizers. The inhibition rates of dehydrogenase enzyme activity in the presence of 0.5 mg, 1.25 mg and 2.5 mg ZnO-NPs per kg soil were 31.3, 46.2 and 49.7%, respectively. Soil microbial biomass carbon was significantly reduced (103.33 µg g^-1 soil) in soils treated with ZnO-NPs over control (111.33 µg g^-1 soil). Soil bacterial count was also significantly lesser (12.33 × 10⁵ CFU) in the case where 2.5 mg kg^-1 ZnO-NPs were applied as compared to control (21.33 × 10⁵ CFU). The corresponding decrease in fungal and actinomycetes colony count was 24.16, 37.35, 46.15% and 14.59, 17.97, 22.45% with the application of 0.5 mg, 1.25 mg and 2.5 mg ZnO-NPs per kg soil, respectively, as compared to control. Thus, the use of ZnO-NPs resulted in an increase in soil available Zn but inhibited soil microbial activity.

Keywords: FTIR; Nanoparticles; PSA; SEM; XRD; Zinc oxide.