Responses of prepubertal female rats to environmental PCBs with high and low dioxin equivalencies.

An extract of landfill soil containing high levels of polychlorinated biphenyls (PCBs) was refined by alumina-charcoal column chromatography to remove coplanar PCBs and high relative levels of PCDFs. Both extracts were administered ip in corn oil to immature female rats on Days 21 and 22 of age. Rats were terminated on Day 23 and organ weights, enzyme activities, and serum thyroxine (T4) were measured. The change in characteristics caused by charcoal-stripping was confirmed by comparing hepatic microsomal 7-ethoxyresorufin O-deethylase (EROD), 7-pentoxyresorufin O-depentylase (PROD), 7-benzyloxyresorufin O-dearylase (BROD), and UDP glucuronyl transferase (UDPGT) activities. EROD and 4-nitrophenol (4-NP) UDPGT activities, estimates of aryl hydrocarbon (Ah) receptor agonists present, peaked at 140 mg/kg soil extract, declining at 210 mg/kg; these activities in rats treated with the charcoal-refined soil extract were not induced at low doses, but increased linearly from 70 to 210 mg/kg. Conversely, PROD and BROD activities were modestly induced at 7 to 70 mg/kg of either soil extract; however, at higher doses induction was threefold higher in rats receiving the charcoal-filtered extract. Liver weights increased in a pattern similar to EROD induction. At all doses, the weak uterotropic response was greater in rats receiving the charcoal-filtered extract, probably due to removal of antiestrogenic Ah receptor agonists by the charcoal. Serum total T4 declined similarly in rats receiving either extract to about 40% of control values at the highest doses. Short-term integrated bioassays such as this are useful in detecting multiple complex interactions and can be used to define the net effects of mixtures with changing compositions for improved risk assessment.