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Environmental Contaminants & Gators

Before instituting the program to collect eggs to supply the alligator farming industry, the State of Florida asked a group of researchers to determine how many alligators could be taken from the wild without harming the population.

In the late 1970’s and 1980’s Lake Apopka was considered a prime place for alligators.  Scientists counted 1,500 to 2,000 in a single night.  So with the assumption that Apopka was good place for alligators the researchers began to collect eggs from the lake.

Alligators lay clutches of 30-45 eggs and though some are lost to predation, well over half the eggs hatch in the wild.  Take the healthy eggs into the lab and nearly all eggs hatch.

When the Apopka eggs were hatched in the lab, only a fifth produced live young.  Of the animals that hatched, half died shortly afterwards.

By the late 1980’s it was clear that something was very wrong with the alligators in Lake Apopka.  Dead alligators were often found floating on the lake, or washed ashore.  From 2,000 a night, counts were down to 150 a night.

To find out what was wrong Dr. Louis Guillette in UF’s Department of Zoology decided to do a controlled experiment.  In 1992, they collected eggs from Lake Apopka and another lake, Lake, Woodrufff, where the alligator population was thriving.  When the eggs hatched many of the Apopka hatchlings died in the first few days, whereas the Woodruff young survived.

Apopka alligators had atypical hormone levels.  Male had strikingly high estrogen levels and very low testosterone levels.  In fact the Apopka males had the testosterone levels of a normal female — over three times lower than a normal male’s level from Lake Woodruff.  Apopka males also had poorly developed testes and undeveloped penises.

Convinced that he had made a mistake in the experimental protocol, Guillette repeated the research the next year.  This time some of the healthy eggs from Lake Woodruff were painted with DDT or DDE.  Others were left unpainted.

All the unpainted eggs hatched but only ¾ of the ones painted with chemicals did.  More importantly, the levels of DDE and the hormone balances of the hatchlings from the painted eggs were comparable with the animals hatched from the Lake Apopka eggs.

Scientists hypothesized that the problem was environmental contamination.  The problem was worst in the part of the lake near the former Tower Chemical Company.  In 1980, Lake Apopka had been the site of a severe chemical spill that left it one of Florida’s most polluted lakes.  A waste pond at the Tower Chemical Company overflowed, spilling large amounts of the pesticides DDT and DICOFOL into the lake.  Soon after, 90% of Apopka’s alligators disappeared.  Tissue samples showed high levels of ppDDE – a breakdown product of DDT.

DDT, DDE and DICOFOL are three of several dozen man-made chemicals capable of imitating naturally occurring hormones, in this case the female hormone estrogen.

Environmental contaminants such as these can act as ‘gender-bending’ chemicals— acting as hormone or antihormones.  They can alter sex determination and hormone concentrations later in life.

Recently Guillette has found abnormal hormone levels and smaller penises in alligators from other lakes, including Lake Okeechobee and Lake Griffin.  These are average Florida lakes, not adjacent to superfund sites.  This finding suggests the background level of contamination could cause permanent changes to developing young – at least in alligators.


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Wildlife of Florida 2011
Wildlife of Florida 2011
Fiona Sunquist
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Wildlife of Florida: Lizards
Fiona Sunquist
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