Effect of ZnO and CuO Nanoparticles on Culturable Bacterial Population, Microbial Biomass, and Enzyme Activities in Two Soil Types

Metal oxide nanoparticles are widely used in many agricultural, medical, and electronic products. This study was conducted to assess the effects of metal oxide nanoparticles on the total culturable soil bacterial population and enzymatic activities – namely, dehydrogenase (DHA), urease (UA), and microbial biomass (MCB) – using Philippine soils. The factors included the two soil types – Lipa clay loam (LCL) and Sariaya sandy loam (SSL) – and five treatments – namely, copper oxide bulk particles (bCuO), zinc oxide bulk particles (bZnO), copper oxide nanoparticles (CuONPs), zinc oxide nanoparticles (ZnONPs), and untreated control. The experiment was laid out in a split-plot completely randomized design over a 28- day incubation period under laboratory conditions. Results showed no significant effect on the culturable bacterial population. The DHA of ZnONPs-, bCuO-, and CuONPs-treated LCL was significantly reduced up to 7, 14, and 28 days after amendment (DAA), respectively. This result was probably due to the strongly acidic property, high level of organic matter (OM), low permeability due to particle size distribution, and low phosphate concentration of LCL. For UA, it was significantly reduced in LCL by CuONPs up to 28 DAA, perhaps due to the inactivation of soil UA. UA, however, was significantly increased by ZnONPs up to 28 DAA, presumably due to the release of intracellular urease from dead cells due to the toxic level of Zn2+. Soil MCB was significantly reduced at 7 DAA in CuONP-amended LCL and ZnONPs- amended SSL, whereas bCuO- and bZnO-amended LCL had a significant increase in MCB. The effect of CuONPs and ZnONPs on the parameters measured was influenced by soil type. In conclusion, CuONPs could pose a threat to soil microorganisms, especially in clayey soils.