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2A - Mixture toxicity (MOP/88) Determination of types of interactions exhibited by binary mixtures of heavy metals tested against the hermit crab, Clibanarius africanus. OTITOLOJU, Adebayo1, DON-PEDRO, Kio1, 1 University of Lagos, Dept. of Zoology, Marine Biology & Fisheries, Akoka, Lagos, Nigeria ABSTRACT- Single and joint action toxicity of heavy metal compounds (Zn, Cu and Cd) was carried out against the hermit crab, Clibanarius africanus in laboratory bioassays. On the basis of the 96hLC50 values, Copper (98hLC50 = 4.342mg/l) was found to be most toxic followed by Cd and Zn (96hLC50 = 29.801mg/l) in a decreasing order of toxicity. The evaluation of the metal compounds in mixtures of Zn-Cu, Zn-Cd and Cd-Cu in pre-defined ratios of 4:1, 3:2, 1:1, 2:3 and 1:4 (wt/wt) respectively revealed that interactions between Zn-Cu and Zn-Cd test mixtures were in conformity with the models of antagonism (reduction in toxicity of constituent metals). The computed synergistic ratios (S.R) and relationship between experimentally observed/predicted 96hLC50 values (RTU) were consistently below 1, indicating antagonistic interactions. However, with regards to Cd-Cu test mixtures, interactions between these metals were mainly in conformity with the model of synergism. The computed S.R. and RTU values were largely above 1, indicating synergistic interactions. The isobolic representation of the toxicity data also gave similar classification of the type of interactions existing between the constituent metals as observed for the other two models (Synergistic Ratios and Concentration-addition model). The importance of joint action evaluations for the management and protection of aquatic ecosystems particularly in the setting up of water quality criteria aimed at protecting aquatic lives was discussed. Key words: heavy metals, joint action, isobole, water quality criteria |
