PpDDE and Lake Apopka Alligators and Birds

Although we generally consider that the problems of some chemicals like DDT are behind us, the situation in Lake Apopka demonstrates that this is not the case. Furthermore, ecological risk assessments sometimes fail to consider adequately how contaminants from normal agricultural uses ("brown-farms") that ended nearly 30 years ago can still elicit adverse effects on wildlife. In Lake Apopka, Florida, reproductive problems in alligators (Alligator mississippiensis)

and other species have been well documented. This 12,500-hectare lake is polluted with contaminants from agricultural activities around the lake, sewage treatment from a nearby town, and a "spill" in 1980 at Tower Chemical Company. Although this spill reportedly resulted in contamination of the lake with dicofol, DDT, and sulfuric acid, some confusion exists about the actual contaminants released into the lake [158]. Shortly after this spill, there was a 90 % decline in the alligator population that persisted from 1980-1984 and the population remains depressed to date. Alligator egg clutch viability was depressed due to an embryonic mortality rate of 80% in the first month after fertilization [140]. In addition, juvenile alligators continue to display endocrine and morphological abnormalities [15,140]. Lake Apopka female alligators displayed polyovular follicles in their ovaries with multinucleated oocytes, males exhibited plasma testosterone levels one-third those of Lake Woodruff males (the reference site), phalli were 24% smaller than Lake Woodruff male alligators, and abnormal structures were observed within the seminiferous tubules of the testes [143]. In addition, testicular estradiol synthesis was elevated threefold in Lake Apopka males over males from Lake Woodruff. Freshwater turtles from this lake show developmental abnormalities of the gonad and plasma sex steroids similar to those seen in alligators [141].

An initial analysis of the contaminants in alligator eggs from Lake Apopka indicate that these reptiles are exposed to several pesticides, with p,p'-DDE being the most abundant, occurring at levels (5.8 ppm in alligator eggs) [159] above those known to reduce embryo viability in avian eggs [140]. In addition to p,p'-DDE, these eggs contained not detectable (ND) to 1.8 ppm p,p'-DDD, 0.02-1.0 ppm dieldrin, and ND to 0.25 ppm chlordane. More recently, Guillette et al. [16] detected 16 (of 18 measured) organochlorine pesticides or metabolites and 23 (of 28 measured) congener-specific PCBs in juvenile alligator serum from Lake Apopka, Orange Lake, and Lake Woodruff National Wildlife Refuge (the two reference sites). Lake Apopka alligators had higher levels of p,p'-DDE, dieldrin, mirex, endrin, chlordane, total DDTs, and total PCBs vs alligators from the other lakes, and the Lake Apopka alligators had lower serum testosterone and smaller phalli (adjusted for body size) than animals from Lake Woodruff, replicating effects seen in earlier studies in a different cohort of animals [143].

The fact that p,p -DDE displays antiandrogenic activity in mammalian in vitro and in vivo assays led Guillette et al. [141] and Kelce et al. [106] to hypothesize that the small phallus size could result from an antiandrogenic effect of p,p'-DDE in juvenile male alligators. On the other hand, Guillette et al. [141] proposed that the increase in testicular abnormalities could result from an "es-trogenic environment" created by the mixture of pesticides in the tissues through inhibition of testosterone action via the AR, by lowering plasma levels of testosterone, and increasing synthesis of testicular estradiol. They also noted that polyovular follicles with multinucleated oocytes is pathognomonic of in utero DES exposure in female mice, suggesting that some estrogenic effector may be present in the Lake Apopka ecosystem.

Beginning in 1998, wildlife populations at Lake Apopka suffered a new, major and unanticipated insult from pesticide contaminants that had persisted in the soil of muck farms since their use was banned [133,160]. As part of the Lake

Apopka Restoration Project, muck farms on the northern end of the lake were flooded in 1998, which inadvertently mobilized pesticide residues that had accumulated for decades. Since the flooding, thousands of piscivorous birds (pelicans, wood stork, herons, etc.) have been found dead or dying around the lake. Tissue residue analyses from the moribund animals reveals lethal levels of pesticides including, p,p'-DDE, toxaphene, dieldrin, and chlordane. One great blue heron fat sample contained 2.3 % (23,000 ppm) p,p'-DDE alone. The effects on other fish and wildlife species or humans who fish in the lake have not been rigorously evaluated at this time. It seems likely that other species will be adversely affected as well. If some way is found to reduce the release of pesticides into the lake and partially remediate this problem, one would anticipate that reproductive problems in fish and wildlife will persist well after the residues decline below lethal levels. If the restoration project continues to mobilize these pesticides into the biota of the lake, it is unclear how these contaminants can be controlled. Clearly, the lack of concern about the EDC issue [160], which was raised by some scientists prior to the flooding, and lack of consideration of the lethal and reproductive effects of pesticides on fish and wildlife populations in the risk assessment process, coupled with the failure to adequately sample these farms for residues, led to this disaster, one that should not be repeated, especially as consideration is being given to restoration of the nearby Everglades ecosystem.

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