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.

DDT Polymorphism and the Lethality of Crystal Forms

“…In fact, DDT is one of many molecular crystals that twist around the growth direction . DDT crystal habits of varied lethality have been described, but all were unindexed and presumed to be manifestations of the same crystal phase . DDT has always been considered monomorphic, crystallizing in the polar space group Pca 2 1 , Z =4.…”

Physico‐chemical studies of pesticides. IV.solubilised pesticides

“…[1][2][3][4][5][6] In contrast pesticides dissolved (solubilised) in aqueous soap (surface-active agent) solutions form thermodynamically stable systems and thus possess considerable advantages. The location of the solubilised compound, and its effect on the size and shape of the micelle, have been the subject of considerable investigati~n.~-~ Although McBain & Hutchinsong have discussed the application of solubilised pesticides in agriculture, the amount of soap required to ' stabilise ' emulsions and suspensions is usually much less than that required to solubilise the same quantity of toxicant and, possibly for this reason, the use of pesticides applied wholly in solubilised form has been limited in practice.…”