Toxicity of cadmium and zinc to miracidia of Schistosoma mansoni

The specific objectives of this study were to elucidate metal toxicity to h atching, survival and avoidance behaviour of Schistosoma mansoni miracidia. The toxicity of cadmium, zinc, and cadmium/zinc mixtures at concentrations ranging from 10000 to 10 mug/l was investigated. Metal mixture toxicity in vestigation nas undertaken with equal concentrations of the metals. The hat ching of miracidia from eggs was inhibited by concentrations of 1000-10000 mug/l of single metals. Metal mixtures had no effect on egg hatching. Survi val of miracidia was reduced by increasing metal concentration except at co ncentrations of 10 mug/l for single metal toxicity where survival was incre ased above the control. Miracidia demonstrated a rapid avoidance behaviour when briefly exposed to heavy metals. The mechanisms of metal toxicity to m iracidia are briefly discussed.