Chemical Used in Plastics Manufacturing
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Two reports that came out this fall have reignited the debate over the safety of long-term, low-dose exposures of humans to bisphenol A, or BPA. This organic chemical compound is used to synthesize DGEBA, a building block for an epoxy resin commonly used as food and beverage can liners. BPA is also used to make dental sealants and fillings as well as polycarbonate plastic bottles, some tableware and utensils, eyeglass lenses, medical devices, and a whole array of consumer products.
The first report, published by the National Toxicology Program’s Center for the Evaluation of Risks to Human Reproduction (NTP-CERHR), evaluated potential health threats of BPA, which mimics the hormone estrogen, to human reproduction and development.
“The report concludes that there is some concern for adverse effects on the brain, behavior and prostate gland in fetuses, infants and children at current BPA exposures,” says Prof. Susan Woskie of UMass Lowell’s Department of Work Environment, one of the expert panelists who prepared the NTP-CERHR paper.
“There is minimal concern for effects on the mammary glands and the early onset of puberty for females. There is negligible concern that exposure of pregnant women to BPA would result in birth defects, mortality or decreased birth weight and growth. There is also negligible concern for reproductive effects in adults, though the level of concern is elevated to minimal for occupational exposures. These terms ߝ ‘some,’ ‘minimal’ and ‘negligible’ ߝ are part of the language required in NTP-CERHR evaluation.”
Following the NTP-CERHR expert panel report, the American Medical Association (AMA) published in its journal a study by a team of British and American researchers that links urinary concentrations of BPA to medical disorders and laboratory abnormalities in adults. The investigation, which involved a survey of 1,455 American men and women aged 18 through 74 years, concluded that “higher urinary concentrations of BPA were associated with an increased prevalence of cardiovascular disease, diabetes, and liver-enzyme abnormalities. These findings add to the evidence suggesting adverse effects of low-dose BPA in animals.”
“BPA has been found in 95 percent of the urine samples collected and has been found in a large fraction of breast milk samples as well as in outdoor and indoor air samples,” says Woskie. “It’s important that studies be conducted to understand the most important sources of human exposure to BPA so that elimination efforts can be targeted at the most important contributors. For example, levels of BPA in residential drinking water wells and community water sources have not been systematically studied and we know little about fetal and neonatal exposures.”
The authors of the study in the AMA journal acknowledge that “independent replication and follow-up studies are needed to confirm [their] findings and to provide evidence on whether the associations are causal.”
In response, the American Chemistry Council stated that, due to inherent limitations in the study, the findings cannot support a conclusion that BPA causes any disease. “The weight of scientific evidence,” it says, “continues to support the conclusion of governments worldwide that bisphenol A is not a significant health concern at the trace levels present in some consumer products.”
“BPA is not a monomer or co-monomer for the vast majority of plastics,” says Prof. Robert Malloy, chair of UMass Lowell’s Plastics Engineering Department. According to Malloy, monomers are building blocks for polymers. “All plastics are based on polymers,” he says. “Once the monomer reacts to form a polymer, it no longer exists as a monomer but is now chemically locked in as a link in the polymer chain.”
Malloy says there are two primary ways that monomers like BPA can show up in a plastic product, either internally or possibly on the surface. “The first way is as ‘residual monomer,’ ” he says. Here the polymerization process was not sufficiently completed so some BPA can remain as a residual ingredient. “Plastics manufacturers, however, use advanced polymerization techniques and quality control to ensure residual monomers are at safe levels,” he says.
“In addition, most plastics are not very permeable and any residual monomer is not likely to leach out at any significant rate under normal circumstances. That said, residual monomer could be present, but generally at very low concentrations. The questions, of course, are ‘How low?’ and ‘What is a safe level?’ I’m not sure anyone knows.”
A second way, he says, BPA could show up is if the plastic produced from BPA monomer was somehow “depolymerized.” For example, an item made of BPA-based polycarbonate could undergo hydrolysis, a type of depolymerization, when exposed to hot water or steam in the presence of alkaline or other chemicals that might catalyze such a reaction.
“This could be a concern when putting something like a polycarbonate baby bottle in a dishwasher with alkaline detergent,” he says. “Baby toys and food-contact items are always a concern when chemicals are involved simply due to the infants’ small body masses and their development. This would not be a concern for me for other polycarbonate applications like automobile headlamps, CDs, or even five-gallon water-cooler containers.” Malloy notes that manufacturers such as Nalgene have voluntarily removed polycarbonate products from the marketplace once this issue came to light.
Woskie says that as far as she knows, the U.S. Food and Drug Administration has no immediate plans of banning or phasing out BPA in plastics manufacturing. “In April, Canada banned baby bottles containing BPA, and several states in the U.S., including California and New York, have had legislators propose bans on BPA-containing products,” she says.
“However, the California proposal was defeated and the others have not gotten very far in the legislative process. In Congress, Senate Democrats introduced a bill to ban BPA from all products made for infants and children up to age seven, and to have the Centers for Disease Control study the health effects of BPA for children and adults. I don’t believe this bill has gotten out of the committee yet.”
If you want to minimize your exposure to BPA, Woskie says there are a number of steps you can take. “For example, you can limit your consumption of canned foods since these products are likely to have [DGEBA] epoxy lining that can potentially leach BPA,” she says. “Of particular concern is the use of canned infant formula. It would be prudent to use powdered formula and mix it yourself rather than liquid pre-mixed formula in cans.” She also suggests minimizing your intake of canned pasta with tomato sauce or soup with a tomato base, as well as canned citrus products and canned carbonated and alcoholic drinks.
Malloy notes that coating cans prevents corrosion that would otherwise result in spoilage of large quantities of food as well as illnesses due to food poisoning. “The likelihood of DGEBA-based epoxy lining leaching residual BPA,” he says, “depends on a number of factors, including the purity of DGEBA, the acidity or alkalinity of the cans’ contents, whether they are water or oil based, and the method of can sterilization used.”
Woskie recommends avoiding microwaving food in polycarbonate containers or using them to store acidic or hot liquids. “It would be better to use ceramics or glass instead,” she says. “Dispose of any polycarbonate if it becomes cracked or worn.”
Woskie also suggests avoiding using polycarbonate bottles for infants. “Some companies are replacing polycarbonates with BPA-free alternatives such as a Tritan™ copolyester and polyamide (PA) products, but I don’t think we know enough about these products yet to determine if they are safer or just an alternative,” she says.
To learn more about the chemical itself, go to www.bisphenol-a.org.