Fate of DDT in Larvicide Suspensions

Abstract

The toxicity of DDT in aqueous-acetone suspensions to mosquito larvae is affected by the volume of suspension and the type of the test container. To learn whether the differences are due to settling, settling rates for different concentrations of DDT suspensions were determined. Settling does take place at the 1-p.p.m. level but not at 0.01 p.p.m., a concentration approximating that normally used in mosquito larvicide tests. In further studies of such suspensions, a high proportion of the DDT was found deposited on the inner walls of glass, aluminum, or paper containers when the liquid phase was withdrawn within minutes after preparation of the suspensions. The concentration of the DDT in suspension was thereby reduced. Another surprising finding was that more than 50% of the DDT from 0.01-p.p.m. suspensions was lost by volatilization with the liquid phase during 24 hours. This volatilization plus the deposition on the walls of the container appear to account for the loss of DDT from larvicide test suspensions. A physicochemical explanation for these findings is presented.