Depletion of gamma isomer from benzene hexachloride cattle-dipping fluids

Abstract

A differential loss of the isomers from BHC cattle-dipping fluid was demonstrated, the concentration of the gamma isomer decreasing faster than that of the total of all isomers. Parallel with the reduction in gamma-BHC content, the toxicity of the fluid for cattle ticks also lessened. This depletion of the gamma isomer occurred not only in field dipping vats, but also during laboratory storage of dipping fluid contaminated with animal waste products and soil. A decrease in the gamma isomer concentration was always accompanied by a chloride increase, which was evidence of at least a partial breakdown of the BHC molecule, but in field dipping samples the chloride increase was not a quantitative measure of gamma isomer depletion. Autoclaving failed to prevent depletion in subsequently stored samples, and refluxing BHC in suspensions containing cattle dung produced a rapid destruction of the gamma isomer, and a large chloride increase. Over certain ranges, the rate of depletion was related to both temperature and dung concentration. When suspensions of BHC and dung were adjusted to a number of different pH values and stored, no decrease in gamma isomer concentration occurred in those below pH 5. The addition of certain chemicals also reduced the rate of depletion, and in most cases this was associated with a lowering of the pH. This finding suggests a practical method of preventing depletion of gamma-BHC in cattle-dipping vats.