Invitro Toxicity of Binary Mixtures of Glyphosate and 2, 2 Dichlorovinyl Dimethyl Phosphate on Bacterial Isolates

The in vitro toxicity of glyphosate (Gly) and 2, 2 Dichlorovinyl dimethyl phosphate (DDVP) single compound and binary mixtures was assessed against Pseudomonas sp. and Bacillus sp. isolated from Otamiri River, Imo state, Nigeria was investigated. The toxicity response was assessed using the inhibitory effect of the single and binary mixtures on isolates dehydrogenase activity; and 2,3,5 triphenyltetrazolium chloride (TTC) was used as the artificial electron acceptor. The binary mixtures were composed using fixed ratios of glyphosate and 2, 2 Dichlorovinyl dimethyl phosphate in ratios of 20% Gly:80% DDVP, 40% Gly: 60% DDVP, 50% Gly: 50% DDVP, 60% Gly: 40% DDVP and 80% Gly: 20% DDVP. Results obtained showed that the isolates exhibited different degrees of logistic and sigmoidal toxicity trends with areas of hormesis at low concentrations of the toxicants. Furthermore, isobolographic analysis on the toxic interaction of the mixtures presented both synergism and antagonism, based on the relative ratio of the component mixtures. Increasing concentration of glyphosate in the binary mixture caused a shift in the interaction effect from antagonism to synergism. Our findings showed that isolates exhibited tolerance to glyphosate and 2,2 dichlorovinyl dimethyl phosphate and their binary mixtures exposure at concentration range of 0-1000mg/L; above which has deleterious effects on the aquatic organisms. It is evident that there are considerable differences in pesticide sensitivity among the bacterial species and that the presence of glyphosate and 2, 2-dichlorovinyl dimethyl phosphate in the aquatic environment may present toxicological risk to microbial diversity.