Metabolic fate of [U-14C]pentachlorophenol in a lactating dairy cow

A lactating Holstein-Friesen dairy cow was administered a single oral dose of [U-14C]pentachlorophenol (PCP). To better simulate chronic exposure conditions on a typical dairy farm, the cow was fed 0.2 mg/kg body wt/day technical PCP for 95 days prior to [U-14C]PCP administration and for the 4 days postadministration. Both absorption and elimination of PCP obeyed first-order kinetics and had half-lives of 4.3 and 43 h, respectively. Over the 76-h postadministration, 75% of the radiolabel was eliminated in urine, 5% in milk, and 5% in feces. The radiolabel was distributed widely into various tissues, but the highest levels were in liver, kidneys, and lungs. Skeletal muscle and adipose tissue contained among the lowest levels. In milk, the fat fraction contained the greatest amount of the radiolabel but the whey fraction represented the largest pool (62.2%). In whey and casein, both conjugated and unconjugated forms were quantified. There was no evidence of phase 1 metabolism of PCP, whereas phase 2 metabolism (conjugation) was highly evident. In urine, two-thirds of the PCP was present in a conjugated form, whereas in serum about 80% was present as unconjugated PCP. These data suggest that efficient conjugation and elimination of PCP prevent its accumulation in cattle tissues