Toxicity of azo dyes to the freshwater shrimp (Desmocaris trispinosa). – C. J. Ogugbue and N. A. Oranusi
The toxicity of five azo dyes to freshwater shrimp (Desmocaris trispinosa) was investigated. The organisms were exposed to various concentrations (0.1mgl-1 – 1000mgl-1) of Mordant Black 17, Direct Red 2, Direct Blue 14, Reactive Red 4 and Reactive Yellow 2. Mortality increased with increase in concentration of each toxicant and with increase in exposure time. The 96h LC50 for the 5 dyes obtained from the concentration-mortality probit graphs were: Mordant Black 17 (2.48mgl-1); Direct Red 2 (4.96mgl-1); Direct Blue 14 (11.33mgl-1); Reactive Red 4 (11.47mgl-1) and Reactive Yellow 2 (732.75mgl-1). The 96hLT50 of the dyes were also determined from the time-mortality probit graphs. Based on the values, the toxicity of the dyes was ranked as: Mordant Black 17>Direct Red 2>Direct Blue 14>Reactive Red 4>Reactive Yellow 2. Differences in toxicity of the dyes were attributed to their molecular weight, impurities and/or impaired oxygen transfer through the respiratory apparatus of the organisms due to adsorption of the dye molecules on their gill surface. The supernatant obtained from dead and macerated shrimps were coloured which could have resulted from the accumulation of the dye in the tissues of the shrimp. The human health risk of consumption of shrimps from environments contaminated with dye wastewater effluent is discussed.
Keywords: Azo dyes, toxicity, Desmocaris trispinosa, LC50, human health.