Effects of sodium dodecyl benzene sulfonate on the combined toxicity of multi-walled carbon nanotubes and cadmium to Escherichia coli

Abstract

The combined biological toxicity of carbon nanotubes (CNTs) and the coexisting pollutants have attracted increasing attention. As a common used surfactant, sodium dodecyl benzenesulfonate (SDBS) could interact with both CNTs and heavy metals. Escherichia coli ( E.coli ) was chosen as a model microorganism, and the effects of SDBS on the combined toxicity of three types of multi-walled carbon nanotubes (MWCNTs) and Cd 2+ were studied. The three types of MWCNTs with the concentration below 200 mg∙L -1 didn’t show obvious growth inhibition to E.coli , and they reduced the toxicity of Cd 2+ to different degrees with the order of carboxylated MWCNTs > hydroxylated MWCNTs > MWCNTs without surface functional groups. The combined toxicity of all the three types of MWCNTs and 10 mg∙L -1 of Cd 2+ increased with the increasing SDBS concentration. The free Cd 2+ and Cd 2+ complexing with SDBS (SDBS-Cd + ) were the main toxicity sources for the mixture of MWCNTs, Cd 2+ , and SDBS. SDBS-Cd + increased the bacterial outer membrane permeability, and thus enhanced the combined toxicity of Cd 2+ and MWCNTs. The results could provide a scientific basis for the ecological risk assessment of water polluted by surfactants, carbon nanotubes and heavy metals.