NIH Press Release
National Institute of Environmental
Health Sciences

Wednesday, Jan. 8, 1997

Tom Hawkins
(919) 541-1402
Home: (919) 782-3009

Experimental Support for Link to 'Gator Abnormalities
Two Pesticides in Spill Shown To Block Natural Hormones

A new study links residual DDT and another pesticide, dicofol, to the declining populations of alligators in Florida's Lake Apopka, near Orlando, and to the males' abnormal testes and small penises and the female alligators' reproductive tract abnormalities.

Both pesticides have been speculated as possible causes. They were among the chemicals in a major spill in the lake in 1980. The new research shows how the two pesticides could interfere with the action of natural hormones on animal cells.

The research, published today in Environmental Health Perspectives, the journal of the National Institute of the Environmental Health Sciences, was conducted by scientists Peter M. Vonier, D. Andrew Crain, John A. McLachlan, Louis J. Guillette Jr., and Steven F. Arnold at the Tulane-Xavier Center for Bioenvironmental Research in New Orleans.

They tested a series of synthetic chemicals in the laboratory to see to what degree they block the alligators' sex hormones, estrogen and progesterone.

Hormones in animals, including humans, act by attaching to specialized molecules in the cell called receptors. These then relay the hormone "messages" to the cell. If a synthetic or other natural chemical mimics the attachment of the hormones, it can block or modify these messages -- and normal development and reproduction may be thwarted.

In the study, DDT (which was banned from most U.S. uses in 1972) and similar chemicals produced from it by the body, as well as dicofol (used to kill mites) and other chemicals and combinations of chemicals showed binding to the hormone receptor sites.

The researchers believe the study provides further support for a role for these pesticides in the alligators' reproductive problems.

The research was supported by an Environmental Protection Agency cooperative agreement, a W. Alton Jones Foundation grant, the Department of Zoology at the University of Florida, and the Tulane-Xavier Center for Bioenvironmental Research.

Senior author John McLachlan can be reached at (504) 585-6910.