The chemical industry has long insisted that bisphenol A levels in people are so low as to not be a concern. But a new assessment has found the estrogen-like chemical used to make plastic is present in humans at levels similar to those shown to be harmful in animal experiments.
The assessment, appearing in the current edition of the journal Reproductive Toxicology, is likely to raise further health concerns about the controversial chemical. Although bisphenol A has been known for decades to act like a hormone, companies have been using it to make everything from polycarbonate plastic baby bottles and office water jugs to dental sealants and the resin linings on the insides of most tin cans.
Bisphenol A manufacturers have said the trace amount leaching into food and beverages isn't dangerous to people because it's quickly metabolized into a form that loses its ability to act like a female sex hormone.
While the authors of the new assessment agreed that people break down some of the bisphenol A they absorb, they said since so many plastics and other products containing it are in use that "virtually everybody" in developed countries has chronic, low-level exposure to the chemical and measurable amounts of its biologically active version.
Typical readings are about two parts per billion in blood. Although this is an extremely small amount, hormones are active at this level, and at even lower concentrations.
Based on the amounts being found in people and what is known about the metabolism of bisphenol A from animal experiments, it also appears that human exposures are above the current U.S. safety limit, according to the assessment.
The reason for this is not known, although there is speculation that people are gaining additional exposures beyond those known to be coming from foods and beverages, possibly through breathing in the air in buildings containing plastics and through dust.
The assessment was based on the results of an expert panel of scientists sponsored by the U.S. National Institute of Environmental Health Sciences.
Its lead author was Frederick vom Saal, a biologist at the University of Missouri and one of the world's leading authorities on bisphenol A, but it was also signed by 37 other top experts on the chemical.
The researchers, in the assessment, said they are "confident" in concluding that one reason bisphenol A is dangerous is because it is capable of altering the normal functioning of genes, turning them on and off at inappropriate times.
They believe this property is one reason exposure to the chemical leads to changes in the prostate, testes, mammary glands, brain structure and behaviour of laboratory animals, particularly at low doses during sensitive points of fetal development and adult life.
"The wide range of adverse effects observed of low doses of BPA in laboratory animals exposed both during development and in adulthood is a great cause for concern with regards to the potential for similar adverse effects in humans," the assessment said.
It said some recent human health trends have been similar to bisphenol A results found in laboratory animal tests, including increases in breast and prostate cancers, earlier onset of puberty in girls, Type 2 diabetes, obesity and neurobehavioural problems, such as attention deficit and hyperactivity disorders.
Health Canada and Environment Canada are currently evaluating bisphenol A, after placing it on a list of potentially dangerous chemicals in long-term use that were grandfathered in the 1980s from detailed safety assessments.
Bisphenol A is sometimes identified on consumer products by the plastic industry symbol of a recycling triangle containing the number seven.
The conclusions of the assessment were disputed by the plastics industry.
"Over all, claims that bisphenol A, in particular [ biologically active] bisphenol A, is present in blood at significant levels are not supported by the weight of the evidence," said Steven Hentges, spokesman at the American Plastics Council, which represents major makers of the chemical.
The industry trade group says one of the testing methods used for determining bisphenol A in humans is flawed, although those participating in the expert panel said they didn't rely on the disputed technology. Instead, they used the results of 14 studies using other testing methods.
The new research has prompted calls for restrictions on the use of bisphenol A.
"We'd like to see some immediate action on this chemical, on food and beverage containers in particular," said Kapil Khatter, president of the Canadian Association of Physicians for the Environment.
He said the federal review process could take up to five years to complete, and he said Ottawa shouldn't wait that long to reduce human exposures to the chemical through consumer items.
Source: TheGlobeandMail.com
Posts
No comments:
Post a Comment