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 extra cts were administered ip in corn oil to immature female rats on Days 2 1 and 22 of age, Rats were terminated on Day 23 and organ weights, enz yme activities, and serum thyroxine (T4) were measured. The change in characteristics caused by charcoal-stripping was confirmed by comparin g hepatic microsomal 7-ethoxyresorufin O-deethylase (EROD), 7-pentoxyr esorufin O-depentylase (PROD), 7-benzyloxyresorufin O-dearylase (BROD) , and UDP glucuronyl transferase (UDPGT) activities. EROD and 4-nitrop henol (4-NP) UDPGT activities, estimates of aryl hydrocarbon (Ah) rece ptor 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 fro m 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 do ses induction Was threefold higher in rats receiving the charcoal-filt ered extract, Liver weights increased in a pattern similar to EROD ind uction. At all doses, the weak uterotropic response was greater in rat s receiving the charcoal-filtered extract, probably due to removal of antiestrogenic Ah receptor agonists by the charcoal. Serum total T4 de clined similarly in rats receiving either extract to about 40% of cont rol 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 compositio ns for improved risk assessment. (C) 1996 Society of Toxicology.