Lake Apopka is located in central Florida about 11 kilometers northwest of Orlando. It covers an area of approximately 125 square kilometers, and is located in both Orange County and Lake County. Before the lake’s marshes were eradicated from the lake it spanned approximately 52,000 acres—after drainage of the marshes it was reduced to 31,000 acres. It is a shallow lake with average depths between 5 and 6 feet, and at present can be classified as a hypereutrophic system (Thomas, 1999).
Recently, Lake Apopka has drawn national attention with the worst case of wildlife pesticide poisoning in the United States in decades. More than 800 birds died after a portion of pesticide-contaminated farmland, bought by the St. Johns Water Management District, was re-flooded to recreate a marsh system. This area, and other farmland areas located primarily on the northern shore of the lake, has received high doses of pesticides for many years. The method of flooding the fields at different times of the year requires that the water, at some point, be discharged into Lake Apopka. This practice has introduced massive amounts of dissolved fertilizers and pesticides to the lake. Despite the continuous inputs of pesticides, the lake had never experienced large bird kills like this before. Louis J. Guillette, Jr., a University of Florida biologist, thinks that the pesticide contamination of Lake Apopka has had adverse effects on the endocrine systems of the local wildlife (Gillis, 1995).
The endocrine system is important, for it controls the release of hormones into the body by various organs and glands such as the pancreas, ovaries and testis, and thyroid, pituitary and adrenal glands—which all act to influence the rate of functioning of almost all the body’s cells. Mechanisms of endocrine disruption include chemical interference with the oestrogen receptor, therefore acting as either an oestrogen or an anti-oestrogen. Similar chemical interruptions can occur on other receptors—either activating or inactivating the receptor.
Guillette has studied firsthand such influences on the population of alligators, and feels all to certain that disruptions in the endocrinology of other organisms are also occurring. Alligators have been examined and found to have shrunken penises, and in some instances have possessed both male and female sexual organs. Gross, Denise A. et al (1995) studied largemouth bass in Lake Apopka, and three other lakes in Florida, and found the fish from Lake Apopka to have significantly higher concentrations of estrogens. Other research that has been conducted supports the claim that pesticides exposure does, effectively, feminize organisms.
The destructive potential of pesticides are not solely limited to there feminizing capabilities, for there have been instances where birds have been born with such severely malformed beaks that they were incapable of eating (Williams, 1999).
The farms surrounding Lake Apopka are responsible for the introduction
of many types of pesticides and chemicals into the Lake Apopka system.
Compounds like the organochlorine pesticides DDT, DDE, and dicofol (mixture
of the pesticides DDT and DDE), polychlorinated biphenyls (PCBs), dioxin
and diethlstibestrol (DES) contribute to the disruption of the endocrine
systems of organisms (Gillis, 1995). Other discharged chemicals include
dieldrin and aldrin, furans and phthalates (The Lancet, 1995). Most
of the more dangerous or threatening pesticides were banned in the 1970s
and 1980s—pesticides such as dicofol, DDT, aldrin-dieldrin, and toxaphene.
These organochlorines alter both sodium and potassium concentrations in
neurons within an organism, affecting impulse transmission and causing
muscles to twitch spontaneously. In 1992 a nationwide study by the
EPA found DDE—a metabolite of DDT—at more than 90 percent of the sampling
sites. So despite the ban on many pesticides, some still persist
in the natural environment. See Table 1 for a list of compounds,
some of which have been banned, and other of which should be banned.
TABLE 1. Chemicals With Widespread Distribution In The Environment Reported
To Have Reproductive and Endocrine Disrupting Effects
Herbicides Fungicides Insecticides Nematocides Industrial Chemicals
2,4-D 2,4,5-TAlachlorAmitroleAtrazineMetribuzinNitrofenTrifluralin Benomyl HCBMancozebManebMetiram-complexTributyl tinVinclozinZinebZiram Beta-HCH CarbarylChlordaneDicofolDieldrinDDT & metabolitesEndosulfanHeptachlor & H-epoxideLindane (Gama-HCH)MalathionMethomylMethoxychlorMirexOxychlordaneParathionSynthetic pyrethroidsToxapheneTransnonachlor Aldicarb DBCP Cadmium Dioxin (2,3,7,8-TCDD)LeadMercuryPBBsPCBsPentachlorophenolPenta- to nonylphenolsPhthalatesPolycarbonatesStyrenes
*Taken from Wildlife Federation, 1997.
Method and Materials
Gross, Denise A. et al (1995) conducted a study to determine whether largemouth bass of Lake Apopka have incidences of malformed reproductive systems due to the fact that it has been exposed to a variety of contaminants that are potentially endocrine disruptors. This involved the capture of 24 fish (12 females and 12 males) from each of the following lakes: Lake Apopka, Griffin, Jessup and Woodruff, on which tests were performed to reveal estrogen, testosterone, and 11-keto-testoterone levels. Fish samples were also tested for concentrations of pesticides.
Gross, Timothy S. et al (1995) collected plasma fat tissues from nesting female alligators in Lake Apopka and Lake Woodruff, and analyzed them for sex steroid and pesticide concentrations. Eggs were also collected and incubated at 39 degrees Celsius—which the temperature at which a male to female ratio of 1:1 is attained. After hatching chorioallantoic fluids were tested for estrogen and testosterone concentrations.
Louis Guillette collected alligator eggs from a clean lake and incubated them at a temperature high enough to produce more males than females—20 percent females and 80 percent males. He then painted another batch of eggs with DDE, incubated them and observed the results.
The experiment conducted by Gross, Denise A. et al (1995) concluded that male largemouth bass did in fact have lower concentrations of testosterone, whereas female largemouth bass had higher concentrations of estrogen.
Related to this experiment was a study carried out by Gross, Timothy S. et al (1995) that found similar results not for fish but for alligators of Lake Apopka. Alligators of Lake Woodruff were found to have higher clutch viability than those located in Lake Apopka. High pesticide levels in the chorioallantoic fluids were found to correlate to decreased clutch viability. In addition, Lake Apopka alligator neonates were found to have increased concentrations of estrogen, while levels of testosterone decreased.
Guillette believes that Lake Apopka has an estrogen problem, for the results to his experiment showed distorted sex ratios for the hatchlings. About 20 percent of the hatchlings were females, 20 percent were males, and the remaining 20 percent were “intersex”—they had very simple sex organs that, more than likely could not function correctly.
The feminization of alligators in Lake Apopka produced a decline in their populations. In the early 1980s, population counts of between 1,200 to 2,000 alligators were often recorded for a single night. But by the late 1980s population counts had dropped to about 150 (Gillis, 1995).
An organism’s systems are most sensitive when they are underdevelopment, therefore, contact with compounds at a young age, or developing stage can have adverse effects on the endocrine system. It seems that abnormal development of the reproductive system is a result of the introduction of various chemical compounds (Lebanc, 1998). Abnormalities of the endocrine system—such as “reduced phallus size, reduced plasma androgens and abnormal plasma levels” (Crain et al, 1998)—have been observed in alligators located in wetland areas that have not received significant pesticide introductions. This demonstrates the ability that some compounds have to persist in the environment, and resist metabolism into compounds with less possibility for endocrine disruption.
The wildlife populations at Lake Apopka appear to be under extreme threat from endocrine disrupting compounds. Birds, alligators, fish, and turtles are a few of the organisms that have been studied and found to be affected by various compounds entering the Lake Apopka ecosystem. Study after study seem to indicate which compounds are responsible for a particular endocrine system disruption, but as of yet no solid plan for their removal has been implemented.
Crain, D. A., N. Noriega, P. M. Vonier, S. F. Arnold, J. A. McLachlan, and L. J. Guillette, Jr. 1998. Cellular bioavailability of natural hormones and environmental contaminants as a function of serum and cytosolic binding factors. Toxicol. Indus. Health 14, 261-273.
Gillis, A. M. 1995. What Cautionary Tales Can Lake Apopka Tell? ZooGoer 24(4).
Gross, D. A., T. S. Gross, B. Johnson and L. Folmar. 1995. Characterization of Endocrine-Disruption and Clinical Manifestations in Large-Mouth Bass from Florida Lakes. Society of Environmental Toxicology and Chemistry, Pensacola, FL. Pp. 185.
Leblanc, G. A. 1998. The state of the debate: while scientists agree that some synthetic chemicals can mimic hormones, consensus on a course of action remains elusive. Forum for Applied Research and Public Policy, v.13, 3, 6(5).
Williams, T. 1999. Lessons From Lake Apopka. Audubon; July 1999, v.101, 4, 64-72.
Male reproductive health and environmental oestrogens. 1995. The Lancet, April 15, v345, n8955, p933(3).
Myers, R. L. and J. J. Ewel. 1990. Ecosystem of Florida. University of Central Florida Press, Orlando, FL.
Luoma, J. R. 1995. Havoc in the hormones (contaminated animal populations exhibit abnormal behavior). Audubon; July-August, v97, n4, p60(8).
Thomas, J. 1999. The Story of Lake Apopka—A Historic Review. Florida Naturalist, 3rd Quarter 1999, 6-7.
Unlu, K. 1994. Assessing Risk of Ground-Water Pollution From Land-Disposed Wastes. Journal of Environmental Engineering, Vol. 120, No. 6, 1578-1594.
Gross, T. S., H. F. Percival, K. Rice, C. L. Abercrombie, P. W. Wilkinson, L. Folmar and A. Woodward. 1995. Evaluation of Reproductive Function in Adult Female Alligators from Contaminated and Control Lakes in Florida. Society of Environmental Toxicology and Chemistry, Pensacola, FL. Pp. 184.
Gross, Timothy S. and Louis J. Guillette, Jr. 1991.
Developmental abnormalities of the reproductive system of alligators from contaminated and control lakes in Florida. Presented as testimony before U.S. House Subcommittee on Health and Environment (Washington, DC, October 21, 1993).