Evaluation of the combined toxicity of multi-walled carbon nanotubes and sodium pentachlorophenate on the earthworm Eisenia fetida using avoidance bioassay and comet assay

In this study, the adsorption kinetics of sodium pentachlorophenate (PCP-Na) onto multi-walled carbon nanotubes (MWCNTs) was determined and acute toxicity tests were performed to evaluate the toxicity of MWCNTs and PCP-Na on the earthworm Eisenia fetida in artificial soil samples, and then the toxicities of their mixture were investigated using soil avoidance test and comet assay. The results of the acute toxicity test showed that no mortality was observed for MWCNTs concentration up to 1000 mg kg−1. The earthworms suffered DNA damage in soils amended with MWCNTs at 50 mg kg−1 in a natural soil, despite of the fact that no significant (p > 0.05) avoidance had occurred at this level of MWCNTs in artificial soil. The LC50 values of PCP-Na for the 7-d and 14-d were 176.0 and 71.1 mg kg−1, respectively. PCP-Na at the concentration of 35.6 mg kg−1 in soil induced behavior toxicity in avoidance test, and genetic toxicity could be determined at a relatively low concentration (1.4 mg kg−1). The avoidance assay revealed a synergetic effect of the two chemicals on E. fetida, regardless of whether these compounds were both added separately or after the adsorption of PCP-Na to the MWCNTs. The two exposure methods showed no differences on the combined toxicity of MWCNTs and PCP-Na when low concentrations of the chemicals were used. Comet assay is not a suitable method for evaluation of combined toxicity of the two chemicals in this study, because exposure to PCP-Na at high dosages could induce lower values of the parameters compared with the lower dosages. [Display omitted] •Combined toxicity of multi-walled carbon nanotubes and sodium pentachlorophenate to Eisenia fetida was investigated.•The data from avoidance assay revealed a synergetic effect of the two chemicals on E. fetida.•MWCNTs enhanced toxicity of PCP-Na to E. fetida.•Comet assay was not suitable for evaluation of combined toxicity of the two chemicals.