August 4, 1999
Study Inconclusive on Chemicals' Effects
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By GINA KOLATA
Apanel of experts convened to study a class of environmental contaminants known as "endocrine disrupters" has concluded that not enough is known about them to determine whether they cause health problems at the low levels in which they typically occur in the environment.
The panel, convened by the National Research Council at the request of Federal agencies and Congress, said in its report released Tuesday that as yet there is insufficient evidence to say the chemicals are causing human cancers and other problems, like infertility. While high concentrations of such compounds, like the hormone diethylstilbesterol and the pesticide DDT, can be harmful to health, the panel wrote, "the extent of harm caused by exposure to these compounds in concentrations that are common in the environment is debated."
No easy answers about a class of contaminants.
In fact, the panel seemed to take pains to refer to the compounds not as endocrine disrupters but rather as "hormonally active agents." The experts said much more research was needed before the dangers of day-to-day exposures to the contaminants can be ascertained but added that scientists did not agree on what exposure levels should be studied or even how to screen for the compounds and their possible influences in people.
"This field is rife with uncertainty," said Dr. Ernst Knobil, who was chairman of the panel. Dr. Knobil, a professor in the medical school at the University of Texas-Houston Health Science Center, added, "It's an exceedingly complex environmental issue and there are no easy answers."
Concerns about endocrine disrupters have been growing for nearly a decade based on a series of observations and deductions. Certain pesticides, like DDT and PCB's and chemicals in plastics, mimic the hormone estrogen. Wildlife that had been exposed to the chemicals in high concentrations were harmed. And women whose mothers had taken high doses of the synthetic estrogen diethylstilbesterol when they were pregnant -- in the hope of preventing miscarriages -- developed vaginal cancers.
The fear was that as use of these chemicals rose, humans were being harmed in subtle and not-so-subtle ways.
The panel's report was requested four years ago by Congress, the Environmental Protection Agency, the Department of the Interior and the Centers for Disease Control and Prevention.
Congress has directed the Environmental Protection Agency to screen compounds for hormonal effects, and today the agency praised the council's report, especially its endorsement of screening and its call for additional research.
"It's a very important report," said J. Charles Fox, who is an assistant administrator there. "It is very consistent with the research agenda we have developed and in fact the report endorses many of the recommendations that we have developed to deal with the potential threat to health and the environment."
The report elicited mixed reactions from scientists, ranging from praise by those who were concerned about the compounds to withering criticism from skeptics of the endocrine disrupter hypothesis.
"I'm amazed and I'm pleased," said Dr. Theo Colborn, a senior program scientist at the World Wildlife Fund and whose book, "Our Endangered Future," helped make "endocrine disrupters" a national issue. She said she was delighted that the expert panel did not dismiss suspicions about endocrine disrupters and that it agreed with her that at high doses, the chemicals can injure people and animals. With the evidence at hand, she said, it is wise to follow the precautionary principle: limit exposure as much as possible while research continues.
"This is a growing field," Dr. Colborn said. "Just because we don't have the evidence does not mean there are no effects."
By contrast, Dr. Elizabeth M. Whelan, president of the American Council on Science and Health, said she was dismayed by the report. The endocrine disrupter hypothesis, she said, "has never been grounded in any reality." It is easy to call for more research in the absence of evidence of danger, she said. But, she added, that does not help people who need to know if they should, or should not, be worried about the food they eat, the water they drink, the air they breathe, and the plastics they use.
"I am now convinced that one of the major problems is that scientists are unwilling to use the four-letter word, 'safe.' " Dr. Whelan said. The council is mostly financed by foundations but also receives some of its money from industry groups.
Committee members emphasized that they were a diverse group, and said they had struggled to write a report that all could endorse.
"It is signed off by the most ardent advocates as well as the most ardent objectors," of the endocrine-disrupter hypothesis, Dr. Knobil said.
In chapter after chapter, the report examines suspicions about the chemicals, and evidence for the suspicions. In the process, it raises questions about virtually every aspect of the field, starting with the description of the chemicals themselves.
Dr. Knobil explained that even when high doses of the chemicals elicited adverse health effects, it was never clear that the effects were due to endocrine hormone disruptions. DDT, for example thinned the eggshells of birds. "What is the endocrinologic basis of eggshell thinning?" Dr. Knobil asked. "No one has come up with one yet.
"If you don't know the mechanism, you can't ascribe the effect to endocrine disruption," Dr. Knobil said. The group decided to call the chemicals "hormonally active agents," instead. They defined such chemicals as any that had hormonal effects in a laboratory test.
A problem that plagued the group was how to deal with questions of exposure level. In general, the chemicals are present in the environment in minuscule quantities whereas the known effects occurred at high concentrations. Moreover, the human body is virtually awash in a sea of naturally occurring hormonally active agents that are present in much greater amounts than the chemicals in question. These range from hormones made by the body, like estrogen and testosterone, to hormones in pills, like birth control pills, to hormone-like substances in plants that people eat.
It is possible that chemicals like pesticides and chemicals in plastics interact with these much more abundant hormones in the body, but no one can say for sure, the report said.
"We need some quantitative assessments of these interactions," Dr. Knobil said, "and then we need to come to informed and intelligent conclusions about what the risks are."
The difficulties in getting a handle on the risks posed by the chemicals extended from epidemiology to basic biochemistry.
The chapter of the report on "Screening and Monitoring" began: "There are no generally accepted, validated methods to screen for or monitor exposure to chemicals that could cause adverse hormonal activity -- largely because of the complexity of the endocrine system."
The chapter on "Neurological Effects" states in its introduction that some scientists proposed that the chemicals act on fetuses and cause neurological damage. But, the group wrote: "In humans, particularly, a number of difficulties are associated with the investigation" of neurological effects, "including the recognition that such effects may be quite subtle, and the possibly long delay between exposure and outcome."
One of the most often cited concerns about the chemicals is that they are causing epidemics of breast cancer and male reproductive system problems, including hypospadia, in which the urethra opens at the bottom rather than the top of the penis, undescended testes, and lowered sperm counts.
The panel wrote that studies to date did not support an association between exposure to the chemicals and breast cancer in women or hypospadia, or undescended testes in men. The sperm data, the group concluded, were "controversial." The panel members wrote in that they had not agreed among themselves about whether sperm counts really were declining.
If the public really does want to get definitive answers to the questions of whether endocrine disrupters are a major public health threat, the studies that would be necessary could last for decades and require huge investments from the Federal government. Is it the best way to spend resources?
That is not a question for his group, Dr. Knobil said. That, he said, "is a matter for policymakers to decide."
The report can be obtained from the Academy at
www.nationalacademies.org. Printed copies of the report may be obtained from the National Academy Press, 2101 Constitution Avenue N.W., Washington, 20418.
