Combined effects of three metals were assessed through toxicological tests in binary and one tertiary mixtures. Death and changes in body weight were used as biological responses to the toxicity. Test solutions were prepared with metal salts grade Merck Analar at 65%. Concentrations were derived from the Congolese official standards from Mining Code and Regulations. These were 500 ppb fof Cd, 5000 ppb for Pb and 5000 ppb for Al. Acute tests were 96-h exposures of the Mosquito fish Gambusia affinis and chronic tests were based on the 35-d exposures. During the chronic exposure, fish were daily fed with the powder of the earthworm Eisenia fetida.Results allowed to conclude that:- Legal standards from the Congolese code were toxic to fish. They should be reduced or lowered.- Mixtures of Cd and Pb develop synergism and remain very toxic to aquatic organisms.- Mixtures of both metals with the Al in binary or tertiary combinations showed antagonism.This information provides useful tools to water quality managers.
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