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July 20, 2009
Volume 87, Number 29
pp. 28 - 29

Can Conundrum

Chemists come up short in attempts to remove bisphenol A from food can liners

Melody Voith

Melody Voith/C&EN
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Environmental activists, regulators, and even soccer moms are becoming alarmed about possible health effects from human exposure to bisphenol A, a key monomer in polycarbonate plastics and epoxy resins. But while many manufacturers of plastic bottles are now touting their BPA-free status, efforts to remove BPA from the epoxy resin liners in food and beverage cans are shrouded in silence.

The main problem, say packaging insiders, is the lack of a ready replacement for epoxy that meets the canned food industry’s needs. Epoxy liners have been used in cans since the 1950s, helping preserve everything from peas to tomatoes to soda. Existing food-grade substitutes are not popular because they cannot be used as broadly, are more expensive, or both.

Another reason the chemical industry is not keen to phase out BPA-containing can liners is because BPA is a $6 billion global industry, says Alex Millar, a materials analyst at Nerac, a product research advisory firm. BPA is made by firms including Dow Chemical, Hexion Specialty Chemicals, and Bayer MaterialScience. According to the National Institutes of Health, approximately 940,000 tons of BPA are produced in the U.S. per year. About 21% is used in epoxy resins and most of the rest goes to polycarbonate.

Defenders of BPA, led by trade groups such as the North American Metal Packaging Alliance and the American Chemistry Council, assert that cans lined with epoxy do not affect human health. Very little unreacted BPA is left in the epoxy manufacturing process, NAMPA says, explaining that “BPA and other materials are reacted to form high-molecular-weight epoxy polymers, which are further cross-linked during the curing process to form a chemically resistant coating.” ACC asserts that exposure to BPA from can coatings is less than 0.00011 mg per kg of body weight per day, less by a factor of 450 than the 0.05 mg maximum acceptable dose set by the Environmental Protection Agency.

Nevertheless, published reports about suspected health effects threaten to make BPA-containing cans unpopular in the marketplace. Last month, the Endocrine Society released a 56-page position paper stating that exposure to BPA, “particularly in development, increases the risk of mammary cancer, obesity, diabetes, and reproductive and neuroendocrine disorders.” And Food & Drug Administration Commissioner Margaret Hamburg told the House Energy & Commerce Committee that her agency will review the safety of BPA.

While food packaging makers and their chemical suppliers publicly promote the safety of BPA, they are privately looking for alternatives, Millar contends. “In the background they’re working on something but won’t come out with a new product unless there is regulation or a huge backlash.” The public is not likely to hear about breakthroughs, he says, because the formulations “tend to be trade secrets. Each company that makes these can linings has its own take on how to make them. It’s pretty difficult to get to those guys.”

So far, public attention has focused on BPA in polycarbonate baby bottles and sports water containers. Concerns about BPA in food cans have been relatively muted. But further attention from the government and health researchers might compel packaging firms to commercialize any innovation they have on the shelf. “They would be willing to bring out a new product if that’s what the science says they must do,” Millar says.

The food industry, for its part, would readily adopt a reliable epoxy replacement, Millar says, but it would first have to cross high safety and performance hurdles. They like epoxy because it stands up well to food processing. For example, cans of low-acid food are steam-heated in a process called retorting to kill the spores of the botulism bacteria. Can manufacturers claim that epoxy resin is stable even when canned food is heated to 240 °F.

“When we started looking for alternatives, we couldn’t find a can manufacturer making a lining without BPA.”

Linings made with BPA give a wide range of canned goods their long shelf life and good food safety record. Without any lining, a typical aluminum or steel can creates a strong air and light barrier all by itself. But eventually, contact between the food and the metal will corrode the packaging, leading to spoilage or microbial contamination. Corrosion would rapidly ruin high-acid foods, such as tomatoes. Low-acid foods like peas may last longer but are more likely to harbor toxin-producing bacteria such as Clostridium botulinum.

Its strengths have made epoxy resin so ubiquitous that avoiding it is close to impossible. Michigan-based Eden Foods, an organic food producer, switched to a BPA-free can for beans in 1999. “When we started looking for alternatives, we couldn’t find a can manufacturer making a lining without BPA,” recalls Sue Becker, Eden’s vice president for marketing. “We asked for a custom-made, BPA-free can to be made for us.”

Eden’s bean can, which comes from Ball Corp., has a baked-on oleoresin enamel lining made from oils and resins extracted from plants. Although the oleoresin lining was common in the pre-BPA era, Eden says, the “new-old” cans cost 14% more than standard cans. That premium boosts the retail price of a can of beans by 3 to 5 cents.

The oleoresin lining does not stand up to high-acid foods, so Eden is still looking for a BPA-free can for its tomatoes. The shelf life of the leading contender is six months, while the bean can lasts two years. Becker says Eden would like to see larger food companies put pressure on suppliers to find alternatives and, at least in the meantime, adopt BPA-free cans for their low-acid foods. Her message for other food companies: “Don’t use your tomatoes as an excuse for your beans.”

Major food makers are not moving quickly to adopt non-BPA linings, complains Green Century Capital Management, an advisory firm for environmentally responsible investing. In a survey it conducted of 20 packaged-food companies, 11 reported that they are “exploring alternatives” to BPA, but none presented clear plans or time frames for phasing it out.

“We’ve been working with some companies that are talking with suppliers and increasing pressure on can manufacturers to find a solution feasible for all can linings,” says Emily Stone, shareholder advocate at Green Century. “We understand it is a supply-chain issue, but the can has the food company’s brand name on it, and that’s a risk.”

One company that did not receive the survey is Goya Foods, a food processor and distributor of Hispanic foods. In an e-mailed response to a C&EN query, Senior Vice President Joseph F. Perez wrote, “Yes, we are working with the coatings industry, Valspar among others, as well as can-making companies, for example, Silgan Containers, for alternative coating options.” Neither Valspar nor Silgan responded to requests for comment.

The quest for a BPA substitute has sent many firms to the consulting firm Packaging & Technology Integrated Solutions. “They all want the magic packaging material,” says PTIS senior scientist Aaron Brody. “We haven’t found it yet.” Brody suggests looking to Japan, where canned-goods makers voluntarily reduced BPA starting in 1998. Many switched to polyethylene terephthalate (PET) polyester linings like those made by Toyo Seikan. Another option might be polypropylene-lined cans, Brody suggests.

But even these choices may not be enough. “The adhesive used to adhere polyester to the can may contain BPA, though it wouldn’t migrate easily,” Brody says. Between polyester and polypropylene, polyester resists corrosion better, he says, and both stand up to high temperatures. The likely impact of using either one as a can liner would be much higher costs, Brody offers.

Ironically, in recent years the most popular innovations in shelf-stable food packaging include polypropylene “cans” as well as pouches made of layered PET films. Rather than line metal cans with the polymers, food makers may just opt out of cans altogether. “We are moving away from cans—there hasn’t been any growth in the past 20 years or so. But polypropylene containers are growing,” Brody reports.

Still, grocery stores will continue to stock food in metal cans for years to come, so the search for an alternative liner will continue, predicts Green Century’s Stone. “Just like with the sports bottle industry, where brands such as Nalgene and Camelback are trying to one-up each other on BPA-free designations,” she says, “canned food companies that move quickly will find themselves winning in the consumer arena.”

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2011 American Chemical Society
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