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 outcomes.
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.
Materials provided by NIH/National Institute Of Environmental Health Sciences. Note: Content may be edited for style and length.
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