Effect of Azo Dyes on Survivorship,Oxygen Consumption Rate,and Filtration Rate of the Freshwater Cladoceran Moina macrocopa

Toxicity of the azo dyes Procion Red MX-5B (PR), Procion Yellow HE-4R (PY), and Congo Red (CR) on the freshwater cladoceran Moina macrocopa was studied. The 4-day LC₅₀ values for PR, PY, and CR were 59.0, 9.50, and 0.16 mg/L, respectively. Reproduction was a more sensitive endpoint than mortality. The onset of reproduction was delayed at azo dye concentrations ≥ 0.01 mg/L. The total number of young produced over 7 days was reduced by 49.8% in PR, 44.5% in PY, and 69.0% in CR. No reproduction was recorded at PY concentrations ≥ 100 mg/L and CR concentrations ≥ 1.0 mg/L. A significant decrease in oxygen consumption rate was observed after 4 days of exposure to azo dyes at concentration equivalent to 25% of the 4-day LC₅₀. The effect of CR on oxygen consumption rate was observed after 4 days of exposure to a concentration equivalent to 10% of the 4-day LC₅₀. Filtration rate was a more sensitive endpoint than oxygen consumption rate. For all three dyes, filtration rate was reduced after 4 days of exposure to concentrations equivalent to 10% of the 4-day LC₅₀. Based on mortality, reproduction, oxygen consumption, and filtration, the order of toxicity was CR > PY > PR.