Effect And Mechanism Of Surfactants On The Combined Toxicity Of MWCNTs And Cd²⁺

The combined toxicity of Multi-walled carbon nanotubes(MWCNTs)and heavy metal has been paid more attention.Surfactants,as a common pollutant in waters,may influence the combined toxicity of MWCNTs and heavy metals.In this study,three types of MWCNTs(Short-MWCNTs(S-MWCNTs),Short-carboxyl-MWCNTs(SC-MWCNTs),Short-hydroxyl-MWCNTs(SO-MWCNTs)),two types of surfactants(SDBS,Tween80)and Cd2+,one representative of heavy metal,were selected.The toxicity tests were conducted to investigate the effect of surfactants on the combined toxicity of MWCNTs and Cd2+.The underlying toxicity influencing mechanism was revealed by multiple experiments such as Zeta potential measurement of MWCNTs,the test of cell outer membrane permeability,the settling of MWCNTs,adsorption tests,and so on.(1)The order of toxicity of three types of MWCNTs was:S-MWCNTs>SC-MWCNTs>SO-MWCNTs.(2)The effect of MWCNTs on the toxicity of Cd2+was:the combined toxicity of S-MWCNTs and Cd2+was higher than the toxicity of Cd2+.When Cd2+>4 mg/L,combined toxicity of SC-MWCNTs and Cd2+was lower than the toxicity of Cd2+.The combined toxicity of SO-MWCNTs and Cd2+was lower than the toxicity of Cd2+.(3)The effect of surfactants on the toxicity of MWCNTs was:the combined toxicity of MWCNTs and SDBS(100 mg/L)was lower than the toxicity of MWCNTs.The combined toxicity of S-MWCNTs and Tween80(100 mg/L)was higher than the toxicity of S-MWCNTs.The combined toxicity of SC-,SO-MWCNTs and Tween80(100 mg/L)was lower than the toxicity of SC-,SO-MWCNTs individually.(4)The effect of surfactants on the toxicity of Cd2+was:The varying concentration of SDBS(0-200 mg/L)didn't^impact the toxicity of Cd2+(1 mg/L).The toxicity of Cd2+(10 mg/L)was enhanced with the increase of concentration of SDBS.The varying concentration of Tween80(0-200 mg/L)hardly impacted the toxicity of Cd2+(1 mg/L,10 mg/L).(5)The effect of surfactants on the combined toxicity of MWCNTs and Cd2+The effect of surfactants on the combined toxicity of S-MWCNTs and Cd2+:When Cd2+<2 mg/L,the combined toxicity of SDBS(100 mg/L),S-MWCNTs and Cd2+was lower than that of S-MWCNTs and Cd2+.When Cd2+>4 mg/L,the combined toxicity of SDBS,S-MWCNTs and Cd2+was the highest.The combined toxicity of Tween80(100 mg/L),S-MWCNTs and Cd2+was slightly higher than that of S-MWCNTs and Cd2+.The combined toxicity of S-MWCNTs and Cd2+(1 mg/L)was hardly impacted by the SDBS with varying concentration(0-200 mg/L).For Cd2+with the concentration of 10 mg/L,when SDBS<50 mg/L,the combined toxicity of the three parts was lower than that of SDBS and Cd2+.When SDBS>50 mg/L,the combined toxicity of the three parts was almost the same as that of SDBS and Cd2+.The effect of surfactants on the combined toxicity of SC-MWCNTs and Cd2+:When Cd2+<4 mg/L,the combined toxicity of SDBS(100 mg/L),SC-MWCNTs and Cd2+was lower than that of SC-MWCNTs and Cd2+.When Cd2+>8 mg/L,the combined toxicity of SDBS,SC-MWCNTs and Cd2+was higher than that of SC-MWCNTs and Cd2+,and lower than SDBS and Cd2+.The combined toxicity of Tween80(100 mg/L),SC-MWCNTs and Cd2+was almost the same as Cd2+.It was higher than the toxicity of SC-MWCNTs and Cd2+,and also lower than Tween80 and Cd2+.When SDBS(0-200 mg/L)<50 mg/L,the combined toxicity of the three parts(Cd2+=1 mg/L)was slightly enhanced with the increase of concentration of SDBS.When SDBS>50 mg/L,the combined toxicity of the three parts was hardly changed.For Cd2+with the concentration of 10 mg/L,the combined toxicity of the three parts was lower than that of SDBS and Cd2+.The effect of surfactants on the combined toxicity of SO-MWCNTs and Cd2+:When Cd2+<2 mg/L,the combined toxicity of three parts was lower than that of SO-MWCNTs and Cd2+.When Cd2+>2 mg/L,the combined toxicity of three parts was higher than that of SO-MWCNTs and Cd2+,and lower than SDBS and Cd2+.When Cd2+<4 mg/L,the combined toxicity of Tween80(100 mg/L),SO-MWCNTs and Cd2+was lower than the toxicity of Cd2+,and was almost the same as that of Tween80 and Cd2+.When Cd2+>4 mg/L,the combined toxicity of Tween80(100 mg/L),SO-MWCNTs and Cd2+was almost the same as Cd2+.For Cd2+ with the concentration of 1 mg/L,when SDBS(0-200 mg/L)<50 mg/L,the combined toxicity of three parts was slightly enhanced with the increase of concentration of the SDBS.When the SDBS>50 mg/L,the combined toxicity of three parts was hardly changed.For Cd2+with the concentration of 10 mg/L,the combined toxicity of three parts was higher than that of SDBS and SO-MWCNTs,and lower than SDBS and Cd2+.The toxicity of MWCNTs and Cd2+with two different concentration was not influenced evidently by the non-ionic surfactant Tween80 with a varying concentration.