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Is Putting A Plastic Container In the Microwave Really That Bad?

03/11/2015 10:54 am ET
Krasyuk via Getty Images

How bad is putting a plastic container in the microwave? When you bring your lunch to work in one and you don't feel like transferring it to glass or paper before you heat it up, are you endangering yourself?

While the risks of putting plastics, BPA-free or otherwise, in the microwave are still up for debate, one thing is certain: Glass and ceramic are always a safe option. But if you want to get into the nitty-gritty, here's what you need to know.

According to the FDA, you should only use plastic containers that "have been labeled for microwave oven use." A container fits this category if it is labeled "microwave safe," if the package contains an image of a microwave, or if the instructions direct you to use the microwave.

If you don't see any indication that the plastic container is safe for the microwave, you may want to reconsider nuking it. The FDA says that some plastics run the risk of melting in the microwave.

One threat surrounding plastic containers that's gotten a lot of attention in recent years is a chemical called bisphenol-A (BPA). The National Institute Of Environmental Health Sciences says that BPA can leach into food from food storage containers.

As Harvard Medical School's Harvard Health Publication explains, BPA is "plasticizer" used in the making of hard, clear plastic. It's also found in some metal food cans. In 2012, the FDA banned the use of BPA in baby bottles and drinking cups, but today allows for low exposure to the chemical in adults. Before a product hits the market, the FDA reviews it to make sure it meets standards for what it deems to be safe levels of BPA. The FDA has concluded that exposure to five micrograms of BPA per kilogram of body weight per day qualifies as safe.

BPA has been used in food packaging since the 1960s, and since that time, the FDA has been continually reviewing studies on the chemical, "including those addressing possible low-dose effects." In the fall of 2014, the FDA concluded, after reviewing 300 scientific studies, that it didn't need to revise its current safety standard for BPA in food containers.

This year the European Food Safety Authority (EFSA) declared BPA exposure causes no harm at current levels, but scientists and food safety organizations are still expressing concern over the chemical. Professor Ulla Hass of Denmark's National Food Institute, for example, recommends the tolerable daily intake (TDI) be "lower than one-fifth of the EFSA recommended limit.”

Potentially negative effects of BPA have focused, though not exclusively, on pregnant women and children. Exposure to BPA has been said to possibly cause reproductive disorders, and exposure during pregnancy may lead to lung problems in children. In a study by Columbia University, childhood exposure to low doses of BPA indicated a greater risk for children to develop asthma later on in life. Exposure to low doses of the chemical could also increase susceptibility to prostate cancer in men, as well as increase the risk of breast cancer in women. Ana Soto, Professor of Integrative Physiology & Pathobiology at Tufts University, told USA Today that, "it's possible that BPA exposure makes fetuses more sensitive to estrogen, a hormone that drives the growth of most breast cancers." The article continues, "In that way, BPA could indirectly increase the risk of breast cancer later in life."

While the debate over safety levels of exposure to BPA continues, many companies have removed BPA from their products entirely.

Good Housekeeping conducted a study on heating food in plastic containers. They assembled a collection of plastic food storage items -- including frozen dinner packaging, microwave-safe containers, wraps and bags -- and sent them off to an independent lab. The lab tested for BPA in 30 products and showed that 27 of them did not contain BPA. Only the following three consisted of low levels of BPA: Rubbermaid Easy Find Lids, Rubbermaid Premier containers and Glad Storage Zipper Bags. (The study also tested for phthalates, another potentially hazardous chemical found in soft plastic, like plastic wrap, and concluded that one product, Glad Press'n Seal wrap, "had low levels of both phthalates and BPA.")

Next the study evaluated if BPA seeped into food stimulants -- which are used to stand in for real food. No BPA was found in any of the food stimulants. Finally, Good Housekeeping experimented with real food and tested whether or not the three products that contained low levels of BPA would leach the chemical into the food. The results showed that no BPA transferred into the food after the containers had been heated in the microwave. While this may be good news from Good Housekeeping, the publication didn't test every plastic container on the market, and it only tested for BPA -- not other chemicals.

Scientific American reports that a chemical called bisphenol-S (BPS) is a common replacement for BPA because it's thought to be "more resistant to leaching." However, the chemical has its own set of problems. In January of this year, The Washington Post highlighted a study conducted by University of Calgary scientists that showed adverse effects of BPS. The chemical often used in "BPA-free" products lead to abnormal brain cell growth and hyperactivity in zebrafish, the study found. (Zebrafish are a common "biomedical model for understanding embryonic brain development" since zebrafish "possess very similar developmental processes as humans," UToday writes.)

What's more, BPS isn't the only problematic chemical in plastic. A day after The Washington Post reported on the BPS study, it published a follow-up article that noted other potentially hazardous chemicals in plastic. Tests done on hundreds of plastic products put through "real world" scenarios, including getting warmed in the microwave, showed that estrogenic chemicals seeped out of 95 percent of the plastic products. The problem, Deborah Kurrasch, the lead scientist on the BPS study, pointed out, is that, "A lot of the alternative chemicals have not been adequately tested because they don’t have to be... A compound is considered safe [by the FDA] until proven otherwise.”

Good Housekeeping's study only focused on BPA seeping out from plastic heated in the microwave. There are still many unknowns about chemicals used in BPA-free products. It's important to note that "microwave-safe" doesn't necessarily mean BPA-free, and BPA-free doesn't mean it's necessarily safe to put the plastic in the microwave.

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