Effects of lead, mercury and cadmium on the extramolluscan larval stages of Schistosoma mansoni (Sambon).

The effects of the heavy metal pollutants, lead, mercury and cadmium on the survival and behaviour of miracidia and cercariae of Schistosoma mansoni were examined. Concentration ranges of 100-900 microM lead chloride, 0.25-20 microM mercuric chloride and 0.25-9.0 microM cadmium chloride were tested. Inversely proportional relationships between metal concentration and survival were evident with all the metals. The LC50 of miracidia was 600 microM for lead, 1 microM for mercury and 2.5 for cadmium. The LC50 of cercariae was 600 microM for lead, 6 microM for mercury and 2.5 microM for cadmium. Movement and behavior of miracidia and cercariae were severely affected by exposure at the higher end of the concentrations of heavy metals tested. Infectivity of cercariae to mice was reduced by nearly half when cercariae were pre-exposed to lead, mercury or cadmium for five hours at the LC50 concentrations, compared with the infectivity of unexposed cercariae.