Heating plastics in the microwave may cause chemicals to leach into your foods.
Plastic is everywhere. It’s in bowls, wraps, and a host of bottles and bags used to store foods and beverages. But in recent years more people have been asking whether exposing our food (and ourselves) to all of this plastic is safe.
Studies have found that certain chemicals in plastic can leach out of the plastic and into the food and beverages we eat. Some of these chemicals have been linked to health problems such as metabolic disorders (including obesity) and reduced fertility. This leaching can occur even faster and to a greater degree when plastic is exposed to heat. This means you might be getting an even higher dose of potentially harmful chemicals simply by microwaving your leftovers in a plastic container.
The question is, should you be concerned? And if so, can you do anything to reduce your exposure?
We asked Dr. Russ Hauser, chair of the Department of Environmental Health and the Frederick Lee Hisaw Professor of Reproductive Physiology at the Harvard T.H. Chan School of Public Health to help us sort through this issue and give us some advice on how to reduce any potential risks.
The first thing to know, says Dr. Hauser, is that plastic is not one thing. “There are many different types of plastics,” he says. Different types of plastic have different names based on their composition — such as polypropylene, polyethylene, polyethylene terephthalate, and polycarbonate — and contain a variety of chemicals with different properties, such as plasticizers, antioxidants, and colorants.
Generally, there are several chemicals in plastics that are considered worrisome because they have been shown to be harmful to people who are exposed over the long term. “We’re talking about very low-dose chemical exposures,” says Dr. Hauser. “But even though single exposures to a specific chemical are small, if they occur repeatedly over long periods of time, their effects may add up, leading to a variety of adverse health outcomes down the road. Furthermore, and most importantly, we are exposed to many chemicals simultaneously (i.e., chemical mixtures) that may have additive adverse effects.” At particular risk are pregnant women and their fetuses. Many of these chemicals cross the placenta, so the fetus is exposed. Experts say childhood exposure is also of high concern.
Among the more troubling chemicals are phthalates and bisphenol A (BPA). Both are endocrine disrupters, which are substances that interfere with the actions of human hormones, says Dr. Hauser.
Phthalates are known to toxicologists as male reproductive toxicants (harmful substances). But this group of chemicals is also known to have ill effects in females. Phthalates, sometimes referred to as plasticizers, are often used to make vinyl plastics soft and flexible. They are widely used in baby toys, food processing equipment and materials, medical devices, and vinyl building products, in addition to other items. A 2003-04 analysis by the CDC and the National Health and Nutrition Examination Survey (NHANES) found that exposure to phthalates was widespread in the U.S. population. Adult women had higher exposure than men, likely because some phthalates are also found in many cosmetics as well as personal care products such as soaps, shampoo, and body washes.
BPA has gotten a lot of attention in recent years because studies have shown it has reproductive and other health effects in both humans and rodents. It’s most often used to make a hard type of plastic called polycarbonate, which is found in products like DVDs. It’s also a component of epoxy resins, which are used for numerous purposes, such as lining the inside of food storage cans. While there has been some controversy about how harmful BPA may be, says Dr. Hauser, there’s little question that there is widespread general exposure to the chemical. That same 2003-04 CDC/NHANES report estimated that 93% of people in the United States ages 6 and older had the chemical in their urine.
While these two chemicals get the most attention, there are many other chemicals in plastics that may be related to health problems, including processing aids, antioxidants, and colorants, says Dr. Hauser.
Is it safe to microwave plastic?
Depending on the type of plastics you are using, heating them in the microwave can release various chemicals into the foods or liquids that you are cooking, says Dr. Hauser. Fatty foods, particularly meats and cheeses, seem more prone to absorbing high amounts of these chemicals.
Some plastics are deemed by the FDA to be microwave-safe. To get the FDA’s designation, manufacturers must test the containers, estimating how long the container will be in the microwave, how much a person is likely to eat from the container, and the anticipated temperature of the food inside. Provided the amount of chemicals leaching from the container into the food is estimated to be lower than the maximum allowable amount, the container is considered microwave-safe. But that doesn’t necessarily guarantee safety.
“It’s hard to say without knowing the exact structure of the plastics and any additives in the plastic,” says Dr. Hauser. So, sometimes it’s better to err on the side of caution. “I think a good recommendation is to try to avoid heating foods in plastic,” says Dr. Hauser.
More questions remain
While microwaves accelerate chemical leaching from plastic, this isn’t the only way that chemicals from plastic can wind up in your food or drinks. “Even if it’s not microwaved, chemicals can still enter food stored in plastic containers or bags,” says Dr. Hauser. “There were studies done a few years ago in Japan that show that plastics used to store foods and liquids allowed chemicals to leach into the foods and liquids.”
Dr. Hauser was involved in another study that found liquids stored in plastic bottles that are subject to heat and sunlight passed chemicals into the liquids. And acidic foods, like tomatoes, can also absorb chemicals from the linings of food cans. Even vinyls or plastics used in homes or offices can release gases, putting measurable amounts of chemicals, such as phthalates, into the air over time. In the same way, plastic vapors can introduce chemicals to food, even if the plastic isn’t touching the food, albeit in smaller amounts than would occur with direct contact. This might happen if you use a plastic splatter lid over a bowl in the microwave.
Reducing risks from plastics may require regulatory changes
Even the most diligent efforts won’t totally eliminate your exposure to harmful chemicals in plastics. That won’t happen without changes in manufacturing, says Dr. Russ Hauser, of the Harvard T.H. Chan School of Public Health.
There are groups moving toward that goal. The Food Packaging Forum, a charitable foundation based in Zurich, Switzerland, works with experts to better understand scientific information that potentially affects the safety of food packaging. The group is working with manufacturers and others to make food packaging safer for consumers and to reduce plastic waste for environmental reasons, says Dr. Hauser, who sits on the organization’s scientific advisory board. But the problem won’t be instantly solved.
Packaging is designed to promote safety by preventing microbial growth and spoilage. “It’s hard to completely replace plastic because of the ease and also the protection that it does afford,” says Dr. Hauser. Finding safe and suitable alternatives is a challenge. Dr. Hauser believes the government should step in and create policies regarding chemicals in food packaging. The Environmental Protection Agency requires some toxicological testing of chemicals before they come to market.
“But the manufacturer may only test a chemical for limited health effects,” says Dr. Hauser. For example, he says, it might not test for subtle effects on fetal brain development. By contrast, the European Union has made steps toward more aggressively regulating chemicals through a program called REACH — short for Registration, Evaluation, Authorization, and Restriction of Chemicals — which began more than a decade ago. “Before they put a new chemical on the market, they subject it to more rigorous testing than is required in the United States,” says Dr. Hauser.
Are you safe if you use plastics that are free of problematic chemicals such as phthalates and BPA?
Again, it’s hard to say whether plastics that don’t contain such chemicals are risk-free, says Dr. Hauser. Often what happens when a manufacturer removes a problematic ingredient from plastic is that it substitutes another chemical that we know little about, he says. For example, if a manufacturer takes phthalates out of its vinyl plastic recipe, it still needs something that will make the plastic soft, so it replaces the phthalates with another softening chemical. The problem is that often the new chemical hasn’t been shown to be safer; there is just little or no evidence about its risk. “Initially, companies looking to avoid using BPA in products switched to a different chemical called bisphenol S, or BPS,” he says. “Much less was known about it at the time. But more recently it’s been shown to be harmful as well.”
A 2011 study published in Environmental Health Perspectives reported that when scientists tested commercially available plastic products labeled as BPA-free, almost all of them leached out chemicals known to have estrogenic activity, meaning that they mimicked human estrogen. Some of the chemicals had even more estrogenic activity than the BPA they replaced.
So, is there anything you can do to protect yourself and cut down on exposure? Here are two good practices:
Use heat wisely. Plastics release more chemicals when heated, so avoid heating foods in plastic containers in the microwave.
Skip packaging. When possible, opt against buying products that are stored in plastics.