The effect of concentration on the performance of two DDT cattle-dipping formulations

Abstract

Dipping trials with two supelcooled melt formulations of DDT, in which the DDT concentrations were raised progressively to four times the usual strength, showed that whilst more DDT was deposited both on the hair of calves and on bush ticks (Haemaphysalis bispinosa Neumann) as the DDT concentration was increased and the dip aged, the toxicity to ticks of both formulations increased only during the early stages of each trial. Clearly the size and shape of the DDT crystals which developed in both dips and the degree of crystal aggregation were important factors which influenced the deposition of DDT and its toxicity. Of the forms of DDT present, the toxicity is attributed mainly to microcrystals of colloidal dimensions. Additions of formulation would serve to maintain but not increase the concentration of these microcrystals. Differences in performance of the dips is ascribed to the composition of the soaps (i.e. surface active agents) in the formulations. The experiments emphasize the importance of the nature of the deposit, and indicate that increases in dip concentration will not necessarily give better biological performance.