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corticoid mimic or stressor (Hayes et al. 1997). However, studies are needed of altered hormone concentrations or modifications of the endocrine system of free-living amphibians to explore whether deformities observed in the wild are related to hormonal modification.

Reptiles

Alligators

The American alligator of Lake Apopka, Florida, is one of the most cited examples of a wildlife population affected by environmental toxicants, including HAAs. The work on the alligator in Florida's wetlands began as the population rebounded as a result of protection under the terms of the Endangered Species Act. Studies of the reproductive biology of alligator populations began in the late 1970s to determine whether this animal could sustain annual harvests for their hides. During this work, most of the study lakes showed reduced egg viability and elevated embryonic mortality (Masson 1995). Lake Apopka exhibited a massive reduction in neonatal and juvenile populations and extremely high embryonic and neonatal mortality in the early 1980s (Woodward et al. 1989, 1993). Chapter 10 discusses the population effects in detail.

Lake Apopka is Florida's most polluted lake (EPA 1979a; Schelske and Brezonik 1992). Contamination of the lake has come from extensive agricultural activities around the lake and from sewage and runoff from several municipalities. In addition, there was an accidental release of the pesticide dicofol (contaminated with up to 15% DDT and its metabolites) (Clark 1990) and sulfuric acid (EPA, unpublished report) in 1980 from the Tower Chemical Company. Water samples obtained after the spill showed DDT concentrations ranging from nondetectable to 433 µg/L and dicofol concentrations of 66-150 µg/L (EPA, unpublished report). Sediment sample concentrations of DDT were 31-1611 µg/ kg, dry weight, and of dicofol were 6,400-31,000 µg/kg, dry weight (EPA, unpublished report). One report from sampling conducted in 1993 (EPA 1994b) indicates that DDT and its breakdown products were still elevated in sediment samples, as was the pesticide toxaphene.

A study by Heinz et al. (1991) identified high concentrations of various persistent pesticides and their metabolites in alligator eggs collected between 1984 and 1985 from Lake Apopka (Table 5-2). With the exception of toxaphene, dieldrin, and chlordane, the pesticides and metabolites bind to the alligator estrogen receptor (Vonier et al. 1996). No correlation was found between elevated concentrations of organochlorine compounds and poor egg viability (Heinz et al. 1991). However, the mean concentrations of p,p'-DDE observed, 5.8 ppm wet weight (1984; range, 3.4-7.6 ppm) and 3.5 ppm wet weight (1985; range, 0.89-29 ppm), are above the concentrations known to reduce hatching success and cause deformities (Cooper 1991). Studies by EPA (1994b) have shown that juvenilecontinue