Toxicity of binary mixtures of sodium dodecyl sulfate and heavy metals to Acinetobacter seifertii from tropical river sediment

Tel.+2348035086155 The toxicities of Sodium Dodecyl Sulfate (SDS) and heavy metal ions (Ni2+, Co2+, Cd2+, Zn2+ and Pb2+), as individual and SDS + metal ion binary mixtures to Acinetobacter seifertii isolated from Otamiri river sediment, Owerri, in southeastern Nigeria were assessed, on the basis of dehydrogenase activity (DHA) inhibition. The responses of the bacterium to the toxic effects of the toxicants were concentration-dependent. The EC50S observed ranged from 0.011 ± 0.000 mM for Cd2+ to 2.810 ± 0.140 mM for SDS. The EC50S of the individual toxicants were statistically different from each other. The heavy metals were more toxic than SDS and the decreasing order of toxicity was Cd2+ > Co2+ > Zn2+ > Pb2+ > Ni2+ > SDS. Fixed ratio mixtures based on EC50 equieffect concentration ratio (EECR50 mixtures) and arbitrary combinations (ABCR mixtures) were designed to assess the combined toxicities of SDS and metals. All the dose-response relationships of the ABCR and EECR50 mixtures and the individual toxicants could be described by logistic function. Toxicities predicted from concentration addition (CA) and independent action (IA) models were statistically different from the experimentallyderived toxicities. In SDS + Ni2+ binary mixture, CA and IA models overestimated the toxicity at low concentrations, while under estimating at high concentrations. Furthermore, both models predicted identical toxicities in SDS + Ni2+ and SDS + Co2+ mixtures and there was also no statistical difference between CA and IA-predicted EC50S for the two binary mixtures. In all but ABCR3 mixture ratio of SDS + Cd2+ mixture, both models significantly predicted lower toxicities. SDS + Zn2+ binary mixture was hormetic at low concentrations. The binary mixtures were generally synergistic to A. seifertii. This synergistic interaction of SDS and metals ions highlights the environmental implications of SDS and metal ions co-contamination.