WASHINGTON, DC -- A panel of academic, government and industry scientists has determined that there is "credible evidence" that some hormone like chemicals can affect test animals at very low levels well below the "no effect" levels determined by traditional testing. However, other credible studies failed to observe such low dose effects, reported the panel, which found no obvious reason for the different outcomes.
The 36 member panel reviewed the chemicals, called environmental estrogens and endocrine disruptors, at the request of the U.S. Environmental Protection Agency (EPA). After reviewing dozens of prior studies, the panel concluded that these hormone like chemicals deserve greater scrutiny and additional research.
Plastic trash bags and many other common plastic products can contain hormone disrupting chemicals (Photo not included)
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.
Because of years of controversy over some of the studies and their meaning, the review has attracted attention from environmentalists, industry, government and academic scientists worldwide.
"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," said Dr. Kenneth Olden, director of the National Toxicology Program and the National Institute of Environmental Health Sciences.
"This permitted a statistical reanalysis of the data, rather than merely a reliance on the conclusions of published papers," Olden said. "In fact, some of the data are from papers still to be published."
Under current regulations, studies are undertaken at three or four levels where each dose may be two to four fold less than the next highest. The highest dose at which no effect on the animals is observed is called 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.
Some pesticides contain hormone disrupting chemicals (Photo not included)
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 of the review committee found there was "credible evidence" of bodily changes, such as in increased prostate weight, in some rodents exposed to low levels of bisphenol A.
However, "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 was not asked by EPA to make that judgment - it found evidence that increases in prostate weight and changes in female reproductive organs can occur in rodents or other test animals from low doses of estrogen. Several other estrogenic compounds, including the insecticide methoxychlor and a dietary component derived from soy known as genistein, can also cause such changes.
Five types of studies were recommended for a group of chemicals related to testosterone, called androgens and antiandrogens. These chemicals include the fungicide vinclozolin, which appeared to cause changes in the reproductive organs of both female and male offspring when pregnant rats were exposed to the chemical.
The panel said the 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 obtaining 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.
Hormone disrupting chemicals have been linked to unusual sexual characteristics in some species. Here, University of Idaho professor James Nagler examines chinook salmon from the Columbia River's Hanford Reach (Photo not included)
The panel also suggested to the EPA that it consider which strains and ages of rodents are best for such tests.
The National Toxicology Program, which is headquartered at the National Institute of Environmental Health Sciences in North Carolina, released the experts' draft report on Monday. The draft will be available for 60 days to collect comments from other scientists, industry representatives and consumers, before the report is sent to the EPA.
The comments will not change the report but will be attached to it, said Dr. Ronald Melnick of NIEHS, who chaired the peer review organizing committee.
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