COPPER MOLLUSCICIDES FOR CONTROL OF SCHISTOSOMIASIS .2. COPPER PHOSPHATE CONTROLLED RELEASE GLASS

Dissolution of copper phosphate controlled release glass (CRG) yields a solution with about half the total phosphate as polyphosphate-copper species with less than 10 phosphate units and about half as more highly condensed species. The polyphosphates break down slowly by hydrolysis. As a consequence of the formation of copper-polyphosphate complexes the proportion of the total copper present as Cu2+(aq) is less in the short term than that in solutions derived from CuSO4: solutions from CRG are thus less toxic toward the schistosome host Biomphalaria glabrata. Increasing pH results in a reduction in toxicity partly because of the precipitation of an incompletely characterized copper phosphate. The formation of polyphosphate-copper complexes by the CRG allows more copper to exist in the aqueous phase in the presence of clay than would be the case with solutions containing the same mass of copper derived from CuSO4. Though this complexed copper is probably of low toxicity, copper adsorbed onto clay particles may under some conditions be highly toxic. The relevance of the results to snail control is discussed.