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A panel of academic, government and industry scientists has determined that
there is "credible evidence" that some hormone-like chemicals can affect test
animals' bodily functions at very low levels well below the "no effect"
levels determined by traditional testing.
However, the panel reported that, in some cases, other credible studies failed
to observe such low-dose effects and there is no obvious reason for the different
The 36-member panel said the chemicals, called "environmental estrogens"
and "endocrine disruptors" deserve greater scrutiny and additional research.
Some of the hormones, like estrogen and testosterone, occur naturally. Other,
chemically related substances are manufactured for packaging, plastics and
other products of modern life.
The National Toxicology Program, which is headquartered at the National Institute
of Environmental Health Sciences in Research Triangle Park, N.C., released
the experts' draft report today for 60 days of comment by other scientists,
industry and consumers before sending the advice to the Environmental Protection
Agency, which had requested the panel review. The comments will not change
the report but will be attached to it, Ronald Melnick, Ph.D., of NIEHS said.
Dr. Melnick chaired the peer review organizing committee.
Because of years of controversy over some of the studies and their meaning,
Dr. Melnick said the review has attracted attention from environmentalists,
industry, as well as government and academic scientists worldwide.
Kenneth Olden, Ph.D., director of the NIEHS and NTP, said, "In a first for
this kind of review, the panel was able to obtain the raw data from nearly
all of the studies. Nearly 100 percent of the scientists were able to cooperate
in this. This permitted a statistical reanalysis of the data, rather than
merely a reliance on the conclusions of published papers.
"In fact, some of the data are from papers still to be published."
The panel found enough evidence of low level effects to recommend additional
studies of low level doses of bisphenol A, a plastics building block used
for a wide line of products, from safety helmets and impact resistant eye
glass lenses to food packaging. A subpanel said there was "credible evidence"
of bodily changes, such as in increased prostate weight, in some rodents exposed
to low levels of bisphenol A, but "due to the inability of other credible
studies... to observe low dose effects... and the consistency of these negative
studies, the subpanel is not persuaded that a low dose effect of BPA has been
conclusively established as a general or reproducible finding."
While the panel stopped short of finding any of the effects to be either
harmful or benign it wasn't asked by EPA to make that judgement
it found evidence that increases in prostate weight and/or changes in female
reproductive organs can occur in rodents or other test animals from low doses
of estrogen, the so-called female hormone, and from several other estrogenic
compounds, including the insecticide methoxychlor and a dietary component
derived from soy known as genistein.
Five types of studies were recommended for a group of chemicals which are
related to the so-called male hormone, testosterone, and are called androgens
and antiandrogens. These chemicals include the fungicide vinclozolin, which
when pregnant rats were exposed to it appeared to cause changes in the reproductive
organs of both female and male offspring.
The panel said EPA should obtain the best advice of experts who design tests
and then consider rewriting the "guidelines" that industry must follow in
having their new products tested before EPA approval. The panel said that
additional multi-generational studies might use a range of different dosages
to better determine if any reproductive problems result in the offspring or
grand-offspring of exposed animals.
The panel also suggested to EPA that it consider the best strains and ages
of rodents for such tests.
Under current regulations, studies are undertaken at three or four levels
where each dose may be two- to four-fold less than the other. The highest
dose at which no effect on the animal is seen is considered the "no effect"
level. But the panel said the raw data suggested that at even lower levels,
an effect might occur, so that the traditional study may need to be re-thought.
The full NTP report can be found at http://ntp-server.niehs.nih.gov.
NIEHS is one of the National Institutes of Health. NIEHS and NTP are part
of the U.S. Department of Health and Human Services.