Hexachlorobenzene I. Uptake, distribution and excretion of hexachlorobenzene (HCB) in growing lambs

The uptake, distribution, and excretion of hexachlorobenzene (HCB) was studied in young male (castrated) lambs. Lambs were exposed for 90 days at a dietary concentration of 0, 0.01, 0.1 and 1.0 ppm. Tissue concentration of HCB were monitored by periodic omental biopsy and by post-slaughter collection of tissues at 90 and at 300 days. Blood samples were collected by venipuncture each time that biopsies or sacrifice occurred. Findings of the 300 days duration study were: (1) the growth rate of the exposed lambs was unaffected by the exposure to the dietary HCB, (2) adipose tissue concentrations reached a level approximately ten times that in the diet at the end of the 90-day exposure period, (3) HCB concentration was higher in the omental fat than in the perirenal fat at 90 days but not at 300 days, (4) a good portion of the apparent decresae in HCB in the fat following cessation of exposure is due to dilution (by increasing carcass fat), (5) the apparent half-life of HCB was approximately 90 days and was not dose-dependent at the exposure rates studied, and (6) the highest HCB concentrations in other tissues were in the brain and liver. The study demonstrated that the omental biopsy provides an excellent means of estimating body fat burden of this lipid soluble pesticide, although it tends to provide an overestimate during actual dietary exposure. The finding that the bioconcentration of and the depletion from the adipose tissues were independent of dose enables prediction of the degree to which food animals might become contaminated if allowed to feed on HCB-contaminated pastures or feed stuffs, and of the time which will be required for such residues to decrease to negligible levels. This predictive ability is of obvious benefit to both the food animal producer and the consumer. Since the HCB is apparently much more stable in the body than is indicated by the depletion half-life of 90 days in these growing lambs, it follows that environmental contamination of grazing lands or animal feeds is of far greater consequence for adult animals which would not be likely to experience the growth dilution of carcass residues.