2001 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, 2000 through July 31, 2001
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, 1999, and 2000, at Great Lakes sites with differing amounts of PCB contamination indicate that whole-body thyroid hormone (TH) availability is not altered at some high PCB sites compared to the reference site (based on yolk-sac PCBs). Thyroid gland function is affected markedly 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.
To date, our studies of two coplanar PCBs (PCB 126 and 77) in chicken embryos (injection onto the air cell at the beginning of incubation) have caused the expected pattern of dose-related mortality and immune system responses (measured by K. Grasman), thus indicating that the PCBs did enter the body by this exposure method. Surprisingly, there was little effect of either PCB 126 or 77 on thyroid variables in pipped embryos or in chicks hatched from PCB-injected eggs. Thyroid assessments in these studies have included plasma T and T3, thyroid gland T4 and T3 content, brain 5'deiodinase activity, and liver UDP-GT. Currently, we are completing analyses of embryonic and chick experiments using Aroclor 1254, a PCB mixture used in many of the published studies of PCB effects in birds and a commonly used industrial PCB that has been released in many environmental locations. We also will do studies with some non-coplanar PCBs that account for a high proportion of environmental PCBs.
To aid in understanding the role of UDP-GT activity in PCB alterations in thyroid function during development, we have developed an assay for avian tissues and have completed a descriptive study of UDP-GT development in precocial birds. For these studies, we used Japanese quail (available from our breeding colony) that are precocial and have a pattern of thyroid development identical to that in chickens. This study will help us to understand how sampling age needs to be considered in relation to studies of these enzymatic responses to pollutant chemicals.