Studies of the Contamination of Lake Apopka

      The alligator population at Lake Apopka in central Florida declined dramatically between 1980 and 1987. Endocrine-disrupting chemicals and  DDT metabolites have been implicated in the alligators' reproductive failure. The DDT metabolite hypothesis is based largely on the observation of elevated concentrations of p,p-DDE and p,p-DDD in alligator eggs obtained from Lake Apopka in 1984 and 1985. 
      Lake Apopka is significantly contaminated with a variety of chemicals including anthropogenic nutrients, organochlorine pesticides, and multiple congeners of polychlorinated biphenyls(PCBs). 

      According to Thea M. Edwards, Gunnar Toft, and Louis J. Guillette of the Department of Biology in Florida, "Our laboratory has previously documented a number of reproductive abnormalities in alligators from Lake Apopka, compared with alligators captured from Lake Woodruff, a nearby reference lake. We conducted the present study to investigate if another native vertebrate, Gambusia holbrooki (eastern mosquitofish), is similarly affected." So for these researchers to conduct this study, first adult female mosquitofish were collected from Lake Apopka and Lake Woodruff monthly for 16 months in order to document seasonal and lake-associated variation in reproductive patterns. What was found during this study was that in contrast to fish from Lake Woodruff, females from Lake Apopka exhibited earlier and more synchronized spring ovarian recrudescence, increased body size, increased fecundity, increased adjusted hepatic weight, and more extreme fluctuations in muscle estradiol concentrations in most months. Endocrine disruption, consistent with other studies and Lake Apopka's pollution profile, is one explanation for these findings. Other environmental and physiological factors are also addressed. However, the higher fecundity among Apopka females suggests that, unlike Apopka alligators, Apopka mosquitofish are not 
impacted at the population level.


Sources:

Guillette LJ, Jr, Gross TS, Masson GR, Matter JM, Percival HF, Woodward AR. Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida. Environ Health Perspect. 1994 Aug;102(8):680–688.

Edwards, Thea M., Louis J. Guillette, and Gunnar Toft. "Seasonal reproductive patterns of female Gambusia holbrooki from two Florida lakes." The Science of the Total Environment 408.7 (2010): 1569+. Health Reference Center Academic. Web. 7 Nov. 2012.