The US National Toxicology Program, a federal agency within the National Institutes of Health, has issued a public consultation document in which it questions the safety of a commonly occuring chemical present in everyday consumer plastics such as baby bottles, CDs, food cans and other products.
The main area of concern is that the chemical, called bisphenol A, which has estrogen-like properties, may harm the development of the brain and reproductive organs of fetuses and young children.
Titled Draft NTP Brief on Bisphenol A, the 69 page document is primarily the work of the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR), which describes itself as giving “timely, unbiased, scientifically sound evaluations of the potential for adverse effects on reproduction or development resulting from human exposures to substances in the environment”.
Bisphenol A is an industrial chemical that is used to make polycarbonates, a range of plastics found in everyday consumer products such as refillable beverage bottles, impact resistant safety equipment, plastic dinnerware, protective linings in food cans, compact disks, and epoxy resins used to coat food cans, bottle tops and water pipes.
Polycarbonates are typically hard and see through, and carry the recycling code “7”, often with the letters “PC”.
Bisphenol A is also used to make materials found in dental composites and sealants.
Bisphenol A is not used to make the softer more flexible plastics such as single-use water bottles.
The chemical formula of Bisphenol A is C15H16O2 and it has a molecular weight of 288.29.
In 2004, the US produced about 2.3 billion pounds of bisphenol A, mostly for use in polycarbonates and resins, said the NTP report.
Bisphenol A has been getting a lot of attention in recent years because human exposure is now widespread and animal studies have raised concerns about the chemical’s potential to harm human reproductive organs and growth.
Bisphenol A is described as “weakly estrogenic” said the NTP report, and it is also suspected of having biological effects on other hormonal processes such as those involving androgens and thyroid hormones.
The main way people are exposed to bisphenol A is through the diet, says the report. Although air, dust and water, for instance in skin contact while swimming or bathing, are also ways to come into contact with the chemical, the majority of exposure is through food and drink. The chemical migrates from the food or beverage container that could be coated in epoxy resin or made from polycarbonate.
The degree to which the chemical migrates into food and beverage from the container depends more on the temperature than the age ofthe container, with higher migration rates occurring at higher temperatures.
Bisphenol A can also be found in breast milk, which is thought to occur when the mother has had dental work using sealants or composites containing the chemical.
Workers can also be exposed to bisphenol A during manufacturing of the compound and products that contain it.
Addressing the question of whether current human exposures of bisphenol A are high enough to cause concern, the report suggests it is “possible”. At high doses, the evidence from animal studies clearly shows adverse effects on development, including reduced survival, lower birth weight, reduced growth of offspring early in life and delayed puberty.
However, the report said that estimated exposures in pregnant women, fetuses and young children are equivalent to “low” doses in animal studies, and these showed that the chemical affects “the brain and behavior, prostate and mammary gland development, and early onset of puberty in females”.
Taken together these findings show “limited evidence that bisphenol A has adverse effects on development”, said the report.
The NTP highlights three conclusions at the end of the report:
- The NTP said it had “some concern for neural and behavioral effects in fetuses, infants, and children at current human exposures”. And the agency also had concerns about human exposure effects on “the prostate gland, mammary gland, and an earlier age for puberty in females”.
- The NTP said it had “negligible concern that exposure of pregnant women to bisphenol A will result in fetal or neonatal mortality, birth defects or reduced birth weight and growth in their offspring”.
- And finally, the agency said it had “negligible concern that exposure to bisphenol A causes reproductive effects in non-occupationally exposed adults and minimal concern for workers exposed to higher levels in occupational settings”.
The CERHR reviewed over 500 studies in preparing the report.
The NTP was careful to point out that the report is not a comprehensive review of the scientific literature on the chemical, and does not replace the risk assessments carried out by the regulatory federal agencies.
The National Toxicology Program is an inter-agency organization within the auspices of the US Department of Health and Human Services. Its headquarters are at Research Triangle Park (RTP), North Carolina, at the National Institute of Environmental Health Sciences, a component of the National Institutes of Health.
“Draft NTP Brief on Bisphenol A.”
CAS No 80-05-7, April 14, 2008
National Toxicology Program, US Dept of Health and Human Services
Sources: NTP, CDC.
Written by: Catharine Paddock, PhD