THE TOXICITY RANKING OF FOUR HEAVY METALS OF INDUSTRIAL SOURCE TO SIX RESIDENT ANIMALS OF A TROPICAL ESTUARINE LAGOON

摘要

Following the identification of the most prominent heavy metals in industrial effluents, drainage channels and in the sediments, water and animals of the Lagos lagoon, the relative toxicity of four of these heavy metals to six animals from the Lagos Lagoon was investigated, adopting standard semi-static bioassay methods. These metals were ranked in order of toxicity thereby providing a toxicity scale based on 96-h LC_(50) values. Within limits of slight variations, Hg was the most toxic to all test species followed by Cu, Mn and Fe in a descending order of toxicity against T. guineensis, Mugil sp. T. fuscatus, N. senegalensis, C. africanus and Cypris sp. The ecotoxicological implications of the results and the need for appropriate environmental management strategies to be informed by such data are discussed while stressing the need to complementarily use the results of chemical and biological surveys to avoid misleading conclusions. Relevant recommendations to ensure better management of this important tropical estuarine lagoon within a sustainable framework are made.