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Hormonal Havoc
"Better living through chemistry" hasn't turned out to be the case for Florida alligators with subsized penises, Great Lakes fish with exploding thyroids and women worldwide with reduced fertility. Scientists are now increasingly pointing to such aberrations as evidence of the endocrine-disrupting effects of chemical pollution throughout our environment. They say PCBs, pesticides, dioxin and thousands of other common contaminants are mimicking natural hormones - most often estrogen - in fish, wildlife and humans.
"The food chain is the major route of exposure," says Citizens for a Better Environment's Greg Karras. Most endocrine-disruptors are fat soluble, accumulating in human and animal fat tissue over a lifetime. And most can cross the placental barrier from mother to fetus. Once inside the body, the chemical impostors masquerade as natural hormones, interacting with a receptor molecule like a key with a lock and triggering molecular activity that scrambles genetic messages, blocks or amplifies genetic activity or interferes with the hormonal system.
Often these effects don't show up as defects in adults - instead the adults either fail to reproduce or produce offspring that cannot thrive. For example, very few male western gulls frequented breeding colonies in a DDT-contaminated area off the Southern California coast. Avian toxicologist Dr. Michael Fry, who studied the colonies, hypothesized that pollutants in gull eggs were "chemically neutering" male embryos. His egg injection studies revealed males with partly ovarian testes. In the same area, female gulls nested with females, and together laid more than the usual number of eggs. Fry attributes all these abnormalities to DDT's estrogenic effects.
Similar effects are turning up in the heavily contaminated Great Lakes ecosystem - producing salmon that fail to mature, terns and cormorants born without eyes and eagle chicks whose twisted beaks keep them from eating. In humans, women whose mothers took the synthetic estrogen hormone DES during pregnancy suffer a host of reproductive disorders and cancers while DES-exposed sons show increased incidence of undescended testicles and lowered sperm counts.
Local scientists are starting to wonder whether similar chemical-induced chaos is occurring in the Bay-Delta ecosystem. "It seems plausible that pollutant concentrations in some parts of the Estuary could be high enough to cause endocrine disruption. Researchers just haven't looked for it," says Jay Davis, a Ph.D. candidate in Fry's laboratory at UC Davis' Center for Ecological Health Research. Davis took a first step across this research gap by doing a baseline study of the levels of dioxin-like compounds in double-crested cormorants. He found that the median concentration of these compounds in the birds is at the "threshold for toxicity," and that some individuals are "way above" this threshold. His data also show apparently high levels of egg mortality and/or infertility among cormorants nesting on the Richmond Bridge, but the scope of the study stopped short of linking these aberrations to estrogenic effects.
Cormorants feed almost exclusively on fish, and it is here that Fry thinks Bay Area scientists should begin the search for estrogenic impostors. He points to a recent S.F. Regional Board study that found elevated levels of DDT, PCBs, dioxin/furans, dieldrin and chlordanes - all documented endocrine disruptors - in Bay-caught fish. "People should be concerned if they're eating fish. Cormorants are extremely good bioindicators for humans - the only difference is they don't read the warnings against eating fish," says Fry.
It's not just familiar contaminants like DDT that have scientists thinking. Kim Hooper of Cal EPA's Hazardous Materials Lab says scientists should examine another class of estrogenic chemicals - the alkylphenol polyethoxylate surfactants contained in everything from plastics and detergents to spermicides and cosmetics. Like PCBs and DDT, surfactants can bioaccumulate in fat tissues. But unlike the chlorinated compounds, surfactants are water soluble and biodegrade into nonylphenols, which are highly estrogenic. "The ambient concentration of nonylphenols in water can be quite low, but fish can easily take them up just by swimming around, making them available to the fish's own estrogen receptors and to anything that eats the fish," says Hooper. In England, male rainbow trout exposed to nonylphenols in sewage effluent became feminized - their testes shrank, their livers grew, and they began to produce egg yolk proteins, clear indications of estrogenic activity, says Hooper.
Conventional wastewater treatment doesn't remove nonylphenols from effluent - and routine monitoring doesn't look for them. "Nonylphenols could be a major source of contaminants to the Bay," says Hooper, "but they haven't been studied the way PCBs or dioxin have." Hooper says newly developed assays could inform needed studies, including a version that uses bioengineered yeast strains to mark estrogenic activity in water and sediments.
Dealing with this problem may require completely new models for environmental testing and monitoring, which typically don't measure endocrine-disrupting effects, and environmental risk assessment, which has historically focused on acute toxicity and cancer risk to directly exposed individuals. Traditional strategies for pollution prevention may come under scrutiny as well. "It's not economically feasible to chase these chemicals around the environment. The only safe solution is to stop production of them all together," says Karras.
Contacts: Jay Davis and Dr. Michael Fry (916)752-1201; Kim Hooper (510)540-3499; Greg Karras (415)243-8373
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