Chemicals Causing Havoc
In Human Body
Environment News Service (ENS)

WASHINGTON, DC, August 6, 1999 (ENS) - Too little is known about the effects of exposure to low doses of chemicals that change the balance of hormones in the human body, says a new report from a National Research Council committee. These chemicals include polychlorinated biphenyls (PCBs) and the pesticide DDT. In high doses they are known to have harmful effects.
Called endocrine disrupters, these chemicals may affect reproduction and development, the nervous system, the immune system, the incidence of cancer, and other aspects of the biology of humans and wildlife.
New studies should be conducted that follow groups of at-risk subjects from conception through adulthood, the Committee on Hormonally Active Agents in the Environment recommends.
"Determining the risk to humans from contact with these chemicals in the environment is difficult because ordinary exposure to these agents has not been routinely monitored," said committee chair Ernst Knobil, the Ashbel Smith Professor and H. Wayne Hightower Professor in the Medical Sciences, Medical School, University of Texas, Houston. "Determining what these exposures actually are is therefore of primary importance."
Hormonally active agents include a wide variety of chemicals that mimic the actions of sex hormones and have been associated with adverse reproductive and developmental effects in wildlife.
The pesticide DDT, for instance, acts like the human hormone estrogen, and so is called an estrogen mimic. In 1972, the Environmental Protection Agency banned all uses of DDT, except for public health emergencies.
Exposure to hormonally active agents can occur from a variety of sources. For example, eating food that is contaminated with PCBs or DDT, and using commercial products such as cleaners, pesticides, and food additives are ways in which people may come in contact with these chemicals.
PCBs are a family of man-made chemicals that contain 209 individual compounds with varying toxicity. Because of their insulating and nonflammable properties, PCBs have been used widely as coolants and lubricants in transformers, capacitors, and other electrical equipment. The manufacture of PCBs stopped in the United States in 1977 because of evidence that PCBs accumulate in the environment and may cause health hazards for humans.
Laboratory studies are needed to determine whether hormonally active chemicals used in pesticides, cleaning solutions, and skin care products have any affect on the immune system, the committee said.
The majority of the evidence available is based on studies done on wildlife and laboratory animals. Very little is known about how the compounds affect humans. In every area of investigation, the committee said information about how humans are affected is sketchy and more well-designed studies are needed.
Do They Cause Cancer?
Some researchers believe that exposure may increase the incidence of breast cancer. There are also concerns that endocrine disrupters may play a role in the reported declines in sperm counts, increased rates of testicular and prostate cancer, and other male reproductive disorders.
The committee said that although some endocrine disrupters have been associated with tumors of the thyroid, pituitary, and adrenal glands in lab animals, an evaluation of the available data does not support an association between breast cancer and adult exposure to the chemicals.
A recent study reported an association between the pesticide dieldrin and breast cancer. Still, additional epidemiological and laboratory studies are needed to help confirm or refute this possible relationship, the committee said.
The current literature does not support associations between hormonally active agents in the environment and other hormonally sensitive cancers such as testicular, prostate, and endometrial cancer, the report says. But few studies have measured the levels of these chemicals in adult humans in relation to cancer risk, and no studies have been conducted to examine associations between the risk of cancer and exposure to them during fetal development.
Reproduction and Development
Adverse reproductive and developmental effects have appeared in wildlife and laboratory animals due to exposures to some hormonally active agents. In humans, fetal exposure to pesticides and other pollutants from the mother's consumption of contaminated fish or other foods can cause lower birth weights and premature births. Exposure has been linked to lower IQs and memory deficits and delayed neuromuscular development.
No links between endocrine disrupters and increases in the incidence of male reproductive disorders in humans, such as testicles that have not descended to the scrotum and testicular cancer could be confirmed, the committee said.
Evidence exists that links fetal exposure to high concentrations of PCBs from industrial accidents, and exposure to PCBs and some pesticides found in fish and other foods, with abnormalities in the developing nervous system.
Monkeys exposed to hormonally active agents while in the womb and during nursing have lapses in brain function when examined 14 months after exposure. Rats and mice exposed to the chemicals before birth suffer impaired movement and learning ability.
Several endocrine disrupters affect a variety of elements of the immune system in laboratory animals, the committee reported. There is evidence that birds of the Great Lakes exhibited immune system dysfunction after exposure to the chemicals, as did captive seals that were fed contaminated fish from the Baltic Sea. Such immunosuppression is believed to be the reason for the increased incidences of bacterial and viral infections in seals in similarly contaminated waters.
Ecological Effects
Hormonally active agents (HAAs) in the environment probably have contributed to declines in some wildlife populations, the committee said. Fish and birds of the Great Lakes and alligators of Lake Apopka in Florida have been affected. The chemicals are also likely to blame for diseases and deformities in mink in the United States, river otters in Europe, and marine mammals in European waters, the committee said.
These contaminants, along with inbreeding, may have contributed to the low birth rate of the endangered Florida panther, and the increase of embryonic death and deformities observed in snapping turtles of the Great Lakes.
Only 30 to 50 panthers still remain in Florida, making this one of the rarest and most endangered mammals in the world. (Photo courtesy U.S. Fish & Wildlife Service) "It is difficult to determine a clear causal relationship between these changes and exposure to HAAs given all of the other environmental factors involved," the committee said, and called for more wildlife studies on population size and life expectancy.
Such research should examine the links between chemical exposures and alterations in key developmental stages to understand how they affect populations in the long term.
The study was funded by the U.S. Environmental Protection Agency, the National Biological Service of the U.S. Department of the Interior, and the Centers for Disease Control and Prevention.
The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.