The use of soil enzymes activity, microbial biomass, and basal respiration to assess the effects of cobalt oxide nanomaterial in soil microbiota

Abstract Despite the high array of potential applications of cobalt oxide nanomaterial (nano-Co3O4), data regarding its toxicity to soil biota is limited, compromising the capability of predicting the risks of this metal oxide nanomaterial (MO-NM). In a previous study the predicted no effect concentration of nano-Co3O4 to soil (PNECsoil) was estimated to be 5.3 mg kg−1 soildw. Given limitations in available data, this threshold was obtained through the application of assessment factors, which are known to overestimate the risks, by being a deterministic and highly protective approach. Thus, this PNECsoil value could be refined if there were more ecotoxicological data. Aiming to contribute to fill this lack of data, this work intended to assess the impact of nano-Co3O4 on soil microorganisms, by measuring soil enzymes activity (dehydrogenase, acid phosphatases, arylsulphatase, CM-cellulase, urease), the nitrogen mineralization, the soil microbial biomass carbon and the soil basal respiration at a range of concentrations up to 1000 mg of nano-Co3O4 kg−1 soildw. The results showed that the arylsulphatase (87.8–296.3 mg kg−1soildw), the acid phosphatase (87.8–1000 mg kg−1soildw) and the soil basal respiration at the lowest concentration tested (87.8 mg kg−1) were significantly affected by the nano-Co3O4 exposure. Conversely, significant stimulatory effects were observed in enzymes activity related to carbon (296.3–666.7 mg kg−1soildw) and nitrogen cycling (87.8–296.3 and 1000 mg kg−1soildw) and basal respiration (131.7–197.5 and 666.7–1000 mg kg−1soildw). Microbial biomass carbon was not significantly affected in any test treatment but showed a tendency to increase with increasing nano-Co3O4 concentration. Multiple mechanisms may be involved in the interaction of this NM with soil enzymes and soil microbial cells. The data obtained did not allow any adjustment to the previous PNECsoil value by taking into account the soil microbial community, because the results obtained point for effects at concentrations lower than the range tested in this study (87.8 mg nano-Co3O4 kg−1soildw) in terrestrial environment.