The study from North Carolina State University and the National Institute of Environmental Health Sciences (NIEHS) found that exposure to levels of BPA that US authorities have currently judged to be harmless over the course of a lifetime triggered reproductive problems in female rats.
BPA is a chemical found in baby bottles, water bottles, canned foods and an array of other consumer products. Its use is the subject of intense debate. A number of US states have banned its use in containers for infants and the Food and Drug Administration is currently reviewing its opinion that the substance poses no threat to human health.
The research group discovered that female rats exposed to a 50-microgram/kilogramme of body weight (µg/kg) dose of the chemical in their first four days of life experienced the early onset of puberty. Those exposed to 50 milligrams per kilogramme (mg/kg) during the same four-day period “developed significant ovarian malformations and premature loss of their estrus cycle”, said a statement from the group.
Exposing female rats during the first four days of life is significant because this is a “sensitive developmental window for the animals, similar to a sensitive developmental stage that takes place for humans when they are still in the womb”, explained the NC/NIEHS.
Dr. Heather Patisaul, lead researcher and assistant professor of biology at NC State, said: "The 50 mg/kg level is important because it is equivalent to the U.S. Environmental Protection Agency's 'Lowest Observable Adverse Effect Level' for BPA. So, by definition, we should not have seen significant effects at or below this level, but we did."
Patisaul also said the 50 µg/kg is significant because this is the EPA’s listed reference dose for BPA. This means it is the level the EPA says a person can be exposed to on a daily basis without any expectation of adverse effects following a lifetime of exposure.
The research group acknowledged the fact that because the experiments were carried out on rats, this makes it “difficult" to determine its applicability to humans. However, Patisaul stressed that it added to “a growing body of evidence that exposure to low doses of BPA during development can impact female reproductive health."
But the American Chemistry Council (ACC) has dismissed the study as being of “very limited relevance to human health”.
Dr Steven Hentges, of the ACC, said “It is a continuing disappointment to see that researchers conduct studies that involve injection of laboratory animals with BPA. This experimental technique has recently been acknowledged by the NIEHS to have very limited value for assessing human health effects since people are orally exposed to BPA, not by injection. It is well-known that BPA is efficiently metabolized and rapidly eliminated from the body after oral exposure.”
Hentges said the researchers were wrong to suggest the study is significant because it used a quantity equal to the EPA reference dose for BPA because this level is applicable to oral doses only and not to injection exposure.