Quantal Response Of Freshwater Shrimp ( Desmocaris trispinosa ) To Toxicity Of Azo Dyes

The quantal-response of freshwater shrimp ( Desmocaris trispinosa ) to the toxicity of five azo dyes was studied. Generally, increase in percentage mortality of the organisms was obtained with increases in concentration of the toxicants and exposure time. The median lethal concentration 50 (LC 50 ) and median lethal concentration 50 (LC 50 ) values were obtained from the concentration-mortality and time-mortality probit graphs, respectively. Based on the LC 50 and LT 50 values, the dyes were ranked in order of toxicity: Mordant Black 11>Acid Orange 10>Direct Red 28>Direct Orange 31>Direct Red 23. Differences in quantal effect of the toxicants was attributed to their molecular weight, dye content and/or impaired oxygen transfer through the respiratory apparatus of the organisms due to adsorption of the dye molecules on their gill surface. Evidence of bioaccumulation of the toxicants in guts and tissues of the shrimps was obtained and its implication to human health was discussed. KEY WORDS: Toxicity, azo dyes, Desmocaris trispinosa, quantal response, bioaccumulation Global Journal of Environmental Sciences Vol.4(1) 2005: 41-45