Superfund Research Program
The Effects of Chlorinated Hydrocarbons on Wildlife
SBRP-funded researchers have documented reduced fertility, reduced fecundity and abnormal sexual development in alligators and fish in several central Florida lakes. Since 1995, Dr. Tim Gross has led a team of scientists at the University of Florida (UF) conducting field and laboratory studies to establish the causes of these reproductive failures and identify the causal links between specific adverse effects and exposure to individual chlorinated hydrocarbons (CHCs) or mixtures of CHCs.
In initial studies, Dr. Gross' team found higher concentrations of chlorinated pesticides, including p,p'-DDE, toxaphene, dieldrin and chlordanes in alligators and largemouth bass from CHC-impacted lakes than those found at reference sites. They determined that alligator and fish females with high levels of pesticides exhibited a variety of health effects related to reproduction and development of offspring. Alligators from impacted sites produced smaller eggs and embryos often failed to develop normally. Although bass were able to spawn, they often produced juveniles that died during early developmental stages. The UF team discovered that land reclamation activities, specifically flooding of land previously used for farming, had resulted in the introduction of persistent pesticides resident in the soil into the aquatic ecosystem. They hypothesized this contamination played critical roles in developmental toxicity and endocrine disruption in fish and wildlife. They communicated these findings to risk assessors at the Florida Department of Environmental Protection, and changes were made in the practice of flooding farmland including determination of soil pesticide levels and soil remediation, if necessary, prior to flooding.
The patterns of reproductive impacts observed by the UF scientists indicate that adverse effects are likely the result of complex processes affecting several stages of life and several species. Laboratory studies involving 60 or 90 day exposure of largemouth bass to p,p'-DDE through implanted slow-release pellets resulted in lowered plasma sex steroid concentrations and gonad size. Similar treatment with dieldrin had little or no effect. Although the exposed fish were able to spawn, p,p'-DDE exposure resulted in significant developmental mortality and reduction in survival to the swim-up stage. The work is significant because it demonstrates that maternal exposure to pesticides affects the development of the offspring.
In field epidemiology studies of alligator populations, the UF researchers observed high egg hatchability for reference lakes and decreased hatch rates for the CHC-impacted sites. Low rates of egg hatching in alligators were shown to be due to fertilization failure as well as early embryonic mortality. Embryos that did develop from contaminated sites showed an overall retardation of development. The researchers are also studying differences in egg-shell thickness, yolk and albumen constituents and embryonic histopathology between clutches from reference sites and CHC-contaminated sites. Preliminary analyses suggest that the presence of high concentrations of chlorinated pesticides correlates with low concentrations of thiamine in the eggs.
The researchers continued to evaluate these associations under laboratory treatment conditions. Experimental exposure to single chemicals did not have the same effect on the alligators observed in the wild. However, alligators in captivity treated with a mixture of four chlorinated pesticides had a clutch viability rate of approximately 19%, compared with 42% for captive controls. These studies were the first to utilize captive adult alligators to test an environmentally relevant hypothesis and preliminary results follow the same trend of effects observed in natural environments. The significance of this work is that it provides evidence of a cause-and-effect relationship between maternal exposure to a complex mixture of chlorinated pesticides and developmental mortality in alligators. This study also indicates some similarity in reproductive impacts on alligators and fish living in high CHC impacted sites, and suggests the potential for similar mechanisms of endocrine disruption and resultant decreased egg quality or developmental toxicity and mortality.
In the course of this work, the researchers developed tools for monitoring the effects of endocrine-disrupting environmental chemicals:
- Monoclonal antibodies were developed to detect vitellogenin, a protein that is of key importance in fish reproduction, in largemouth bass. This protein is produced by the liver after estrogen stimulus, and it triggers the process of yolk accumulation in the developing egg. Two of these antibodies have been made into ELISA kits and are available to other researchers for monitoring environmental estrogens in naturally CHC-exposed fish.
- A technique for nanoinjection of fish eggs with single chemicals as well as mixtures was developed. This technique can be applied to different fish species and has the advantage, over whole animal studies, of being capable of testing hundreds of chemicals in a relatively short period of time and at low cost to the researcher.
These new sensitive tools have the potential to impact public health and influence decision making at Superfund sites by providing rapid methods to determine whether or not endocrine-disrupting chemicals are present. The tools can be used for initial screening of sites, prior to more extensive chemical analysis and can also be used to monitor clean-up of previously impacted sites.
This research is important because it is well documented that adverse effects on sensitive species may serve as surrogates for health effects in humans. There is continued uncertainty about exactly how these findings apply to human health, but it is clear that compounds that produce such profound effects on wildlife will have ecological effects that will eventually impact humans. Also, direct effects of these chemicals may occur in humans, particularly in sensitive sub-populations.
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To learn more about this research, please refer to the following sources:
- Gross TS, Rauschenberger RH. 2003. Triazines. In: Endocrine Disruptors: Biological Basis for Health Effects in Wildlife and Humans. Oxford University Press, NY.
- Sepulveda MS, Quinn BP, Denslow ND, Holm SE, Gross TS. 2003. Effects of pulp and paper mill effluents on reproductive success of largemouth bass. Environ Toxicol Chem 22(1):205-213. PMID:12503766
- Arnold BS, Sepulveda MS, Rotstein DS, Gross TS, Davis LM, Glenn TC, Clark GC. 2002. Use of DNA analysis to study early embryonic mortality in Flordia alligators. In: Proceedings of the 16th Working Meeting of the Crocodile Specialist Group, October 7-10. Gainsville, FL.
- Gross TS. 2002. Chlorinated Hydrocarbons as Hormonally-Active Agents and Developmental Toxicities in Alligators and Fish. In: Proceedings of the EPA (Environmental Protection Agency) Risk-Assessors Conference, April. Phildelphia, PA.
- Gross TS, Arnold BS, Sepulveda MS, McDonald K. 2002. Endocrine disrupting chemicals and endocrine active agents. Chapter 39 in: Handbook of Ecotoxicology, 2nd Edition. Lewis Publishers, Boca Raton, FL. pp.1033-1098.
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