2000 Progress Report: Field and Laboratory Studies of the Effects of Polychlorinated Biphenyls and Other Persistent Organic Pollutants on Thyroid Function During Avian DevelopmentEPA Grant Number: R827400
Title: Field and Laboratory Studies of the Effects of Polychlorinated Biphenyls and Other Persistent Organic Pollutants on Thyroid Function During Avian Development
Investigators: McNabb, F.M. Anne
Institution: Virginia Polytechnic Institute and State University
EPA Project Officer: Carleton, James N
Project Period: August 1, 1999 through July 31, 2001 (Extended to December 31, 2003)
Project Period Covered by this Report: August 1, 1999 through July 31, 2000
Project Amount: $256,587
RFA: Endocrine Disruptors (1999) RFA Text | Recipients Lists
Research Category: Economics and Decision Sciences , Health , Safer Chemicals , Endocrine Disruptors
Objective:The objectives of this study are to: (1) evaluate the current status of thyroid function in developing Herring gulls (Larus argentatus) from Great Lakes sites with different chemical pollutant exposures; and (2) determine, using laboratory studies on developing chickens (Gallus domesticus), if the disruption of avian thyroid function by polychlorinated biphenyls (PCBs; key contaminants at many Great Lakes sites) is similar mechanistically to that in laboratory mammals. Herring gulls, a fish-eating, top-predator, have been used as a sentinel species to monitor the concentrations and biological effects of environmental contaminants in the Great Lakes for more than 25 years. Past research has focused on mortality, developmental abnormalities and reproductive effects of chemical pollutants in the lakes. Studies of thyroid histology and developmental effects suggest that thyroid function is disrupted in these gulls. This study examines the thyroid status of developing gulls in the Great Lakes and employs a laboratory model and specific PCB congeners (PCBs are key contaminants in the lakes) to examine the mechanisms whereby PCBs may disrupt thyroid function in birds (oviparous vertebrates) in comparison to their known mechanisms of disruption in mammals.
Progress Summary:Our studies of embryonic and prefledgling herring gulls collected in 1998 and 1999, at Great Lakes sites with differing amounts of PCB contamination (1.5 to 21.2 ppm total PCBs in egg homogenates), indicate that whole-body thyroid hormone (TH) availability is not altered at high PCB sites compared to the reference site. Likewise, the enzymatic conversion of T4 to T3 in brain is not altered between sites, suggesting hormone supply to this critical tissue is not altered by differences in high PCB pollutant exposure. However, thyroid gland function is affected at the high PCB sites, with pipping embryos and prefledglings showing somewhat different alterations. Pipping embryos from high PCB sites have significantly decreased thyroid TH content/mg and TH content/gland but thyroid mass is not altered in comparison to embryos from the reference site. Prefledgling gulls (4 weeks of age) from the high PCB sites have significantly increased thyroid gland mass (suggestive of increased pituitary thyrotropin resulting from hypothalamic-pituitary-thyroid stimulation and decreased thyroid gland TH content/mg. The net effect of these alterations is no difference in TH content/thyroid gland in birds from the high PCB sites compared to the reference sites. Currently we are investigating whether liver uridine disphosphate glucuronosyltransferase (UDP-GT) activity, an enzyme that may be induced by PCB exposure and that is important in T4 metabolism and excretion, is altered at the high PCB sites compared to the reference site.
We also are investigating the effects of specific PCB congeners on thyroid function in laboratory studies of chicken embryos and chicks. The first compound we have used is PCB-126 (3,3',4,4',5 pentachlorobiphenyl), a coplanar, dioxin-like congener which was injected into chicken eggs prior to incubation. Embryos exposed to PCB-126 (doses from 0.0512 to 0.8 ppb) did not show any relationship between increasing PCB dose and plasma TH concentrations, brain 5'deiodinase activity, or thyroid gland mass or hormone stores. There was a trend toward increasing UDP-GT activity with increasing PCB dose. PCB-126 appears to exert toxic effects before the appearance of any potential effects on thyroid function. Currently we are measuring UDP-GT in fowl chicks exposed to PCB -126 and will soon begin studies using non-coplanar PCBs (PCB-153) and PCB mixtures (Aroclor 1254). Understanding of whether PCBs affect thyroid function in birds in the same or different ways to those in mammals requires evaluations of different aspects of thyroid function with exposure to different types of PCBs.