Effects of heavy metals on survival and growth of Biomphalaria glabrata Say (Gastropoda: Pulmonata) and interaction with schistosome infection

The effects of dissolved Pb, Cd and Hg on growth and survival of adult Biomphalarin glabrata Say, uninfected and infected with Schistosoma mansoni Sambon, were examined. Pb at concentrations from 0.25-100 mu M, Cd from 0.075-0.25 mu M and Hg from 0.25-1 mu M significantly reduced growth and survival of normal snails. With each metal the effects increased with increasing concentration. The LC 25 at 2 wks exposure was 82 +/- 19, 0.22 +/- 0.04 and 0.94 +/- 0.13 mu M (x +/- S.E.) for Pb, Cd and Hg, respectively. Snails exposed to heavy metals continued to be reproductively active, but the egg production was highly variable and no significant effect of heavy metal exposure was demonstrated. Infection also decreased survival and growth of snail hosts and infected individuals exposed to heavy metals displayed the greatest mortality. The LC 25 for infected snails at 2 wks exposure was 8 +/- 3, 0.9 +/- 0.02 and 0.29 +/- 0.08 for Pb, Cd and Hg respectively. A significant interaction between heavy metal exposure and infection was apparent. Infected snails were not reproductively active. Cercarial shedding by infected snails was significantly reduced in the presence of heavy metals and by 6 wks shedding had ceased at the highest metal concentrations.