The chronic toxicity of technical and analytical pentachlorophenol in cattle. I. Clinicopathology

The objectives of this study in female yearling Holstein cattle were to define the toxic effects of (1) long-term exposure to analytical pentachlorophenol (aPCP), and (2) to determine the influence of the contaminants in technical pentachlorophenol (tPCP) in the toxic syndrome. Four groups of three heifers each were exposed for 160 days to aPCP, tPCP, or a mixture thereof in the feed. A fifth group of three animals served as unexposed controls. All treated cattle received the same amount of PCP; 20 mg/kg/day for 42 days which was reduced to 15 mg/kg/day for the remainder of the study because of a suspected decrease in body weight gain in all PCP-exposed animals compared to controls. Fat and liver samples for chemical analyses were collected at the end of the study. Major findings in the tPCP-exposed heifers included a dose-related decrease in body weight, decreased feed efficiency, progressive anemia, a dose-related increase in liver and lung weights, and a decrease in thymus weight. The most conspicuous lesion was market villous hyperplasia of the urinary bladder mucosa in two of three animals exposed to the highest level of tPCP. There were minimal hepatic lesions although hyperplasia of the mucosal lining of the gali bladder and bile duct was noted in some animals exposed to tPCP. Animals exposed to aPCP were, in general, comparable to the controls. Hepatic mixed function oxidases were increased by aPCP, but more so by tPCP. A decrease in thyroxine concentration was found in all PCP-treated cattle. Immunologic studies suggested a progressive tPCP dose-related enhancement in the lymphoproliferative response, an in vitro correlate for cell-mediated immunity. Observed effects on humoral immune parameters were equivocal. The results of this study indicate that toxicity of PCP in cattle is primarily attributable to its contamination with toxic impurities.