Endocrine Disruptors and Host Resistance in Lake Apopka Alligators

EPA Grant Number: R826127
Title: Endocrine Disruptors and Host Resistance in Lake Apopka Alligators
Investigators: Schoeb, Trenton R. , Klein, Paul A. , Brown, Mary B. , Gross, Timothy S.
Institution: University of Florida , Florida Caribbean Science Center
Current Institution: University of Florida , United States Geological Survey [USGS]
EPA Project Officer: Klieforth, Barbara I
Project Period: January 3, 1998 through January 2, 2001
Project Amount: $598,253
RFA: Endocrine Disruptors (1997) RFA Text |  Recipients Lists
Research Category: Endocrine Disruptors , Human Health , Safer Chemicals


Declines in populations of wildlife species, such as that of the American alligator in Lake Apopka, Florida, have been associated with reproductive effects of endocrine- disrupting environmental contaminants. Recently, concern has arisen that endocrine disruptors also can have other adverse effects, including altered immunity and decreased resistance to disease, and that organisms may be especially susceptible to such effects during embryonic and fetal development. Such effects could contribute to the increased mortality that has been reported among Lake Apopka alligator hatchlings. In preliminary studies, the thymuses, spleens, and bone marrow of neonatal alligators hatched from eggs from Lake Apopka were found to be poorly developed, or hypoplastic. Such hatchlings also were found to have significantly decreased antibody responses to sheep erythrocytes in comparison with alligators hatched from eggs from Lake Woodruff, a relatively uncontaminated "reference" lake. The predominant contaminant in the tissues and eggs of Lake Apopka alligators is p,p'-DDE, with lesser amounts of other pesticide residues such as chlordane, dieldrin, endosulfan, and toxaphene. Abnormal development in hatchling Lake Apopka alligators could be due to these substances, which have estrogenic activity, inasmuch as the synthetic estrogen DES is myelotoxic and developmentally immunotoxic in rodent models, and other immunotoxic contaminants such as TCDD and PCBs are not present at high levels in Lake Apopka.

The objective of this study is to study effects of in ovo treatment with putative endocrine disruptors on basic measures of specific and nonspecific immune functions and on host resistance to a natural infectious disease of alligators, which will provide a stringent assessment of the biological significance of alterations in measures of immunity. The hypothesis to be tested is that alligators hatched from eggs from Lake Apopka, or from reference lake eggs treated with contaminants found in Lake Apopka alligators will have decreased (i) T dependent antibody responses; (ii) T cell proliferative responses; (iii) blood, marrow, or lymphoid organ cell counts or activity; or (iv) resistance to the recently recognized alligator pathogen, Mycoplasma lacerti. Most previous research on endocrine disruptors has focused on reproductive and endocrine effects. This work will address concerns that endocrine disruptors could have adverse effects on the immune system, especially during development, and that such effects could adversely affect the health of wildlife species, and therefore by implication that of humans and domestic animals.


The approach will be to treat groups of alligators in ovo with p,p'-DDE and other endocrine disrupting contaminants alone and in combination. Hapten-specific antibody responses will be determined by class-specific ELISA in hatchlings immunized at up to 6 months of age. T cell mitogen response assays, one-way mixed lymphocyte reactions, and bacterial phagocytosis and killing by spleen and peripheral blood cells will be studied, and numbers of B, T, and adherent cells in spleen, marrow, thymus, and peripheral blood will be determined. Effects of contaminants on resistance to M. lacerti will be assessed in experiments of similar design in which groups of alligators hatched from treated lake eggs will be inoculated with M. lacerti and studied for severity of pneumonia and arthritis and for numbers of mycoplasmas in affected organs and tissues.

Expected Results:

Our expected results are that hatchlings from eggs from Lake Apopka, and from eggs treated with at least some of the contaminants, will have decreased measures of immune function and host resistance. However, the results will be of interest even if the anticipated results are not obtained, as this would suggest involvement of other causes that have not yet been investigated.

Publications and Presentations:

Publications have been submitted on this project: View all 5 publications for this project

Supplemental Keywords:

health effects, ecological effects, organics, pathogens, bacteria aquatic, biology, pathology, Florida, FL, agriculture., RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Toxics, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Health Risk Assessment, Environmental Chemistry, Ecosystem/Assessment/Indicators, exploratory research environmental biology, State, Endocrine Disruptors - Environmental Exposure & Risk, pesticides, endocrine disruptors, Risk Assessments, Southeast, Biochemistry, Physical Processes, Biology, Endocrine Disruptors - Human Health, ecological effects, ecological exposure, adverse outcomes, aquatic ecosystem, wildlife, reptile, host resistance, exposure, chemical mixtures, 2, 3, 7, 8-Tetrachloro-dibenzo-p-dioxin (TCDD), Chlordane, Lake Apopka, FL, fetal development, animal models, developmental processes, immune system response, pathogen, Lake Apopka Alligators, Florida, biological effects, DDE

Relevant Websites:


Progress and Final Reports:

  • 1998
  • 1999 Progress Report
  • Final Report