Lethal and sublethal effects of Cadmium on Daphnia (Crustacea: Cladocera)

Acute and chronic toxicity studies were performed to determine the effects of cadmium on Daphnia pulex, Leydig 1860 emend. Richard 1896, D. magna Straus 1820, and D. parvula, Fordyce 1901, three cladocerans commonly found in fresh water. Test specimens were exposed to several series of concentrations of cadmium sulfate for 96 hours in the acute toxicity studies. The 24-, 48-, 72- and 96-hour 50 percent lethal doses (LDSO's) were calculated by probit analysis using a computer program. Mortality was defined as immobilization. The 96-hour LD50's for D. pulex ranged from 0.213 to 0.064 mg/liter. The 96-hour LD50 could not be determined for D. parvula; however, the 72-hour LD50 was 0.183 mg/liter. The 96-hour LD50 for D. magna was 0.086 mg/liter. All LD50's were reported in terms of the salt concentration. Daphnia pulex was selected for long-term (chronic) study and was exposed to two concentrations of cadmium sulfate (0.012 and 0.025 mg/liter) at two temperatures (15.5 and 19.5 C). Molting, hatching of young, number of young, and mortality were observed every six hours for four weeks. Molting appeared to be a critical time for Daphnia exposed to cadmium sulfate. Dosed animals showed significantly higher mortality rates and produced 50 percent fewer young than the controls. The experimental temperatures did not alter the toxicity of cadmium.