Responses of Prepubertal Female Rats to Environmental PCBs with High and Low Dioxin Equivalencies

An extract of landfill soil containing high levels of polychlorinatedbiphenyls (PCBs) was refined by alumina-charcoal column chromatographyto remove coplanar PCBs and high relative levels of PCDFs. Bothextracts were administered ip in corn oil to immature femalerats on Days 21 and 22 of age. Rats were terminated on Day 23and organ weights, enzyme activities, and serum thyroxine (T4)were measured. The change in characteristics caused by charcoal-strippingwas confirmed by comparing hepatic microsomal 7-ethoxyresorufinO-deethylase (EROD), 7-pentoxyresoru-fin O-depentylase (PROD),7-benzyloxyresorufin O-dearylase (BROD), and UDP glucuronyltransferase (UDPGT) activities. EROD and 4-nitrophenol (4-NP)UDPGT activities, estimates of aryl hydrocarbon (Ah) receptoragonists present, peaked at 140 mg/kg soil extract, decliningat 210 mg/kg; these activities in rats treated with the charcoal-refinedsoil extract were not induced at low doses, but increased linearlyfrom 70 to 210 mg/kg. Conversely, PROD and BROD activities weremodestly induced at 7 to 70 mg/kg of either soil extract; however,at higher doses induction was threefold higher in rats receivingthe charcoal-filtered extract. Liver weights increased in apattern similar to EROD induction. At all doses, the weak uterotropicresponse was greater in rats receiving the charcoal-filteredextract, probably due to removal of antiestrogenic Ah receptoragonists by the charcoal. Serum total T4 declined similarlyin rats receiving either extract to about 40% of control valuesat the highest doses. Short-term integrated bioassays such asthis are useful in detecting multiple complex interactions andcan be used to define the net effects of mixtures with changingcompositions for improved risk assessment.