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Short-Term Response of Soil Enzyme Activity and Soil Respiration to Repeated Carbon Nanotubes Exposure

Nanomaterials such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) may repeatedly enter the soil environment with unknown adverse consequences. To provide the information on the effects of repeated exposure of CNTs, we determined the response of soil enzyme activity and soil basal respiration (SBR) through a two-week incubation of farmland soil repeatedly treated with different concentrations of CNTs (100, 200, 500 mg kg−1 for SWCNTs and 100, 500, 1000 mg Kg−1 for MWCNTs). The activities of catalase, alkaline phosphatase, and invertase and SBR were measured after one- and two-time treatments. The repeated contamination of SWCNTs and MWCNTs repressed the activity of alkaline phosphatase and invertase in the 14-day incubation. Alkaline phosphatase and invertase were more sensitive indicators of CNTs’ contamination than catalase and soil basal respiration. High concentration of the SWCNTs stimulated SBR while the lower concentration suppressed SBR. The recurred exposure of SWCNTs and MWCNTs repressed the activity of catalase and invertase. The obtained results indicated that the soil microorganisms were suppressed under repeated pollution, as suggested by the same suppressed response of SBR between SWCNTs and MWCNTs treatment, except for the concentration of 500 mg kg−1.