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Investigating the Toxicity of Cu, CuO and ZnO Nanoparticles on Earthworms in Urban Soils

Mwaanga P*, Mbulwe S, Shumbula P and NyirendaJ

Even though some studies have shown that copper (Cu), copper oxide (CuO) and zinc oxide (ZnO) nanoparticles (NPs) are toxic to a number of organisms, fewer studies have investigated toxicity of these NPs in actual soils. This study investigated the effect of Cu, CuO and ZnO NPs in both urban and artificial soils. The aim was to examine the differences on these NPs’ ability to cause oxidative stress to organisms in urban and artificial soils. Earthworms, Eisenia fetida, (2 months old) were exposed to varying concentrations of NPs and bulk materials (used for comparison purposes) of Cu, CuO and ZnO ranging from 100-500 mg/kg, 100-4000 mg/kg and 100-4000 mg/kg, respectively, for 14 days, for each soil type. Superoxide dismutase (SOD), reduced glutathione (GSH) and hydrogen peroxide (H₂O₂) were measured at the end of exposure period. The accumulation of Cu and Zn in the earthworm tissues was measured using AAS. In urban soils, SOD, GSH and H₂O₂ all showed an initial increase as the concentration of NPs increased and but decreased at higher concentrations. Similar results for bulk materials were observed, though with less intensity. Cu and Zn accumulation in earthworm tissues increased as a function of NPs/bulk materials concentrations in both soils. Interestingly however, SOD, GSH and H₂O₂ from artificial soils for both NPs and bulk materials did not show significant differences from the controls, except at higher NPs/bulk materials concentrations.