Physiological stress response of <i>Macrobrachium vollenhoevenii</i> (Herklots 1857) to interacting effects of binary mixtures of industrial effluents

Abstract

The toxicities of effluents from paint and textile industrial establishments in Lagos State, Nigeria and their binary mixtures based on predetermined (1:1) and equitoxic (4:3) ratios were evaluated against the juvenile stage of prawn, Macrobrachium vollenhoevenii in laboratory bioassays. On the basis of derived toxicity indices, the paint effluent with 96 h LC50= 54.73 ml/L was found to be 1.33 times less toxic than the textile effluent (96 h LC50= 40.99 ml/L) when acting alone against M. vollenhoevenii. In the joint toxicity tests, the binary mixtures in a predetermined ratio (1:1) with 96 h LC50= 49.45 ml/L was 1.16 times more toxic than the equitoxic mixtures (4:3) with 96 h LC50= 57.7 ml/L. The interactions between binary mixtures showed significant departures from the action of individual constituent effluent when acting singly, and depended largely upon the proportions of additions of the mixture components. On the basis of synergistic (Synergistic Ratio, SR) and concentration-addition models (Relative Toxicity Unit, RTU), the relationship between binary mixtures (1:1) of paint and textile effluents against M. vollenhoevenii were in conformity with models of synergism and antagonism (SR= 1.11, 0.83; RTU=
0.97) while equitoxic mixtures (4:3) conformed to antagonism (S.R =0.94, 0.71, RTU =0.84) model. Furthermore, the isobologram model showed that both binary mixtures conformed to sub-additive
action. Symptoms of toxicosis observed in the test organisms include loss of equilibrium, agitated swimming, spiral movement, followed by weakness, periods of quiescence and death. It is concluded
that the incorporation of joint action toxicity evaluation with bio-monitoring tools are clearly relevant in setting effective and realistic environmentally safe limits of pollutants or verifying ecological
significance of existing water criteria meant to protect aquatic biota.