Ask a Toxicologist: Is it safe to microwave food in plastic containers?

When was the last time you microwaved food in a plastic container?Image used with permission. Source: http://www.drfranklipman.com/

At some point in my life, I switched many of my plastic food storage containers to glass containers. Someone told me, perhaps my mom, that microwaving food in those plastic containers could cause bad chemicals from the plastic to leach into my food.

Does that really happen and what are the health consequences? With the splendors of PubMed at my fingertips and some free time, I decided to find out. As in my previous post on Teflon, I’ll follow the basic steps of toxicity assessment to organize my findings.

Hazard Identification and Characterization: What is the culprit? What does it do?

Bisphenol A, or BPA, is commonly used in the production of polycarbonate plastics; it is one of the most commonly produced chemicals in the world. Plastics made with BPA have been used in food packaging products since the 1960s and are used almost everywhere. In fact, the 2003-2004 National Health and Nutrition Examination Survey found detectable levels of BPA in 93% of Americans aged six years or older.Image used with permission. Source: http://www.oberk.com

Studies have found that BPA interacts with estrogen receptors, as well as other receptors in the body, potentially mimicking actions of the estrogen hormone. Estrogen is a key hormone involved in the development of reproductive organs (particularly in women), bone growth, cardiovascular health, and proper human development from embryos to adolescents. Because estrogen is a key endocrine signaling hormone involved in proper function of the body, disrupting its balance through exposures to chemicals that mimic the effects of estrogen could have negative health effects. Many of these adverse effects could even happen at low doses. Exposures to endocrine-disrupting chemicals are of particular concern for babies and young children, who are more sensitive during their period of human development.

Since the heightened public awareness of BPA in baby bottles during the early 2000s, companies have produced BPA-free plastic products and can linings. However, the BPA in these products has most likely been replaced with other chemicals, such as Bisphenol S and F (BPS and BPAF), which may be just as hormonally-active and endocrine-disrupting as BPA! Thus, the food containers labeled BPA-free may still be a source of endocrine-disrupting chemicals.

There are many other chemicals that go into the process of creating plastics that could be of concern. For our purposes today, I will limit our discussion to BPA and BPA-substitutes.

Exposure Assessment: How, how much, how often?

In our situation here, exposure to BPA and/or BPA-substitutes would occur through ingestion of food or water contaminated with chemicals released after microwaving plastic storage containers. So do chemicals leach from plastics after microwaving? If so, is there enough chemical leached to cause a response from the estrogen receptor? The amount of BPA or related chemicals released by the plastic depends on the temperature of the plastic, the acidity/basicity of the container’s contents, and physical stresses and damage to plastic.

Based on their assessment of the literature in 2015, the European Food Safety Authority (EFSA) established that the safe BPA intake limit is 4 ug/kg of body weight/day. The EFSA concluded that current dietary exposure to BPA is 4-15 times less than the safe limit. The US Food and Drug Administration does not list a specific intake limit but does state that, based on its most recent safety assessment, BPA is safe at the current levels in foods. Other studies have reported that microwaving baby bottles or water bottles increased the amount of BPA released, but these levels did not result in release of BPA at levels that exceed the EFSA standard.

Regarding BPA-substitutes, Dr. George Bittner and his team at the University of Texas in Austin have conducted a comprehensive study on BPA-free products. They stressed the plastic under various conditions: exposing to UV light, microwaving, and autoclaving (extreme heating and steaming similar to what happens in a dishwasher). 

BPA flow chart. Illustration by Mimi Huang.After collecting the chemicals released from the stressed plastics, they tested if the extracted chemicals interacted with the estrogen receptor, by exposing estrogen-responsive cells that would proliferate upon activation of the estrogen receptor. If the cells proliferated, the product was concluded to leach chemicals with estrogen activity (EA).

The researchers found that many BPA-free products leached chemicals that were estrogen active. Thirty-one out of 40 products leached EA chemicals after exposure to UV light, 4 out of 16 after microwaving, and 5 out of 24 after autoclaving. What’s exciting is that they found plastic products that did not leach estrogen-active chemicals, even after exposure to various stresses. Thus, plastics can be made in a way that eliminates our exposure to estrogen-active chemicals!

Limitations: What’s missing?

A positive reading on the cell-based estrogen activity test used by Bittner and his team is not necessarily indicative of what will happen when the body is exposed to the same compound. The body is generally pretty good at breaking down and getting rid of foreign chemicals; therefore, if a compound was tested in animals, it may not show as much estrogen activity as predicted by the cell-based test.

The study published by Bittner et al. did not identify or quantify the amount of chemicals extracted from the plastics. Not knowing the identities of the leached chemicals is not a necessarily a concern because the chemicals, regardless of what they were, caused estrogen activity. What is a concern is that we do not know the concentrations of the chemicals causing these effects. While the study does simulate real-life use of plastics to some extent, we cannot be sure that the concentrations being assessed in this study are relevant to what we would be exposed to at home.

Risk Assessment: The Bottom Line

Is it safe to microwave food in plastic containers?

Probably for the general adult, but avoid doing so if possible. It’s always better to reduce exposure if you can!

Microwaving BPA containing plastics resulted in release of some BPA, though not exceeding the established safe level. Studies show that exposure to low doses of BPA could have effects on human health, particularly during early stages in life. Some BPA-free plastics do release chemicals with estrogen activity after microwaving. The health effects of exposure to many BPA-substitutes and other chemicals used in plastic production may be similar to that of BPA. The scientific research on both BPA-substitutes and BPA is ongoing, which will help clarify what exposure level is indeed safe.


If you are concerned, the NIEHS has recommendations for limiting exposure to BPA and related compounds:

  • Don’t microwave polycarbonate plastic food containers. Polycarbonate is strong and durable, but over time it may break down from over use at high temperatures.
  • Plastic containers have recycle codes on the bottom. Some, but not all, plastics that are marked with recycle codes 3 or 7 may be made with BPA.
  • Reduce your use of canned foods.
  • When possible, opt for glass, porcelain or stainless steel containers, particularly for hot food or liquids.
  • Use baby bottles that are BPA free.

Edited by Lydia Morris and Jaime Brozowski

ToxCast and ToxPI: Emerging Tools for Toxicity Testing in the 21st Century

Hindsight is always 20/20, especially in the field of science. Given what we know now, it seems crazy that people used to think the world was flat. The realm of toxicology is filled with similar stories (see “pregnancy-boosting” DES and super-insecticide DDT). In the mid-twentieth century America, realization of the harmful effects of chemicals like DES and DDT contributed to rising concern about potential risks to human and environmental health associated with chemicals. Consequently, in efforts to better monitor and understand what chemicals may be harmful to humans and the environment, Congress enacted the Toxic Substance Control Act in 1976, enabling the US Environmental Protection Agency (EPA) to inventory and regulate chemicals being sold or manufactured in the US. As of 2014, 84,000 chemicals are in use in the United States (EPA TSCA). Continue reading

Ask a Toxicologist: Is it safe to use Teflon pans?

As a young adult living in Carolina, I have come to associate summer with intolerable heat, delicious watermelon, and…the start of wedding season. Two friends of mine got married recently in May. A few months before, as they were making their registry, they encountered a troubling question. As they held the Bed, Bath and Beyond scanner in their hand, they wondered: should we scan the Teflon pans? The lure of easy frying and convenient cleanup wrestled with their faint anxieties about Teflon that came perhaps from a vague conversation with some environmentalist friend or that one article that popped up on a news feed a few months ago. Concerned, they brought me their question:

Is it safe to use non-stick frying pans and cookware?

Before I answer, let me give a quick overview of how us toxicologists approach these kinds of questions. Hopefully, then you can follow a similar procedure and determine for yourself the health risks of other products!

When assessing safety of any chemical or component, there are two types of information that needs to be gathered: hazard characterization and exposure assessment. In other words, what is the toxic compound and what toxic effects might it cause (hazard characterization)? Then, are people exposed to the compound? If so, how does it get into the body? And how much? Is the amount people are exposed to enough to cause harmful effects (exposure assessment)? Toxicologists design experiments to generate these two types of information.

Risk-Assessment

Integrating these pieces of information allows us to make our best estimate of the risk of chemicals being toxic to humans, a form of risk assessment. These are only estimates since much of this information is sometimes difficult to obtain practically (you can’t expose humans to potentially toxic compounds in a study!). Thus, we must rely on animal studies, testing individual cells, and computer models.

Now, lets apply this method to non-stick pans.

Problem/Question

Is it safe to use non-stick frying pans and cookware?

Hazard Characterization

What makes pans non-stick? What is the potentially toxic component?

The most common non-stick coating used to coat pots and pans is Teflon, a chemical mixture of perfluorochemicals (chemicals with lots of fluoride atoms). Developed by DuPont chemical company in 1938, these chemicals are extremely non-polar, meaning they do a very good job repelling other chemicals. As such, Teflon is used as an additive to paints, fabrics, carpets, and clothing. It is also used to treat materials to make them resistant to oils (like the inside of microwave popcorn bags). The primary chemical in Teflon, polytetrafluoroethylene (PTFE), has a high melting point (327 ºC), making it ideal for cooking applications. However, when heated to temperatures above 350 ºC (662 ºF), PTFE begins to degrade, releasing fine particles and a variety of gaseous compounds that can cause damage to the lungs when inhaled (Waritz 1975).

What is the route of exposure? How are we exposed to PTFE?

Inhalation of the PTFE-fumes from overheating a non-stick pan is one method of exposure. Since we use these pans to cook food, we might suppose that people could be ingesting PTFE, say if some of the coating gets into the food cooked in the pan. We want to estimate risk for the worst-case scenario so we will consider both routes of exposure.

What is known about the harmful effects, or toxicities, of PTFE?

Via inhalation

Numerous case studies in the 1900s have documented flu-like symptoms after inhalation of PTFE fumes by workers in PTFE-using factories and by people overheating non-stick pans in the kitchen. This condition is called polymer fume fever, or “Teflon flu”, and presents with temporary, intense, but not serious symptoms such as fever, shivering, sore throat and coughing. These cases of Teflon flu are due to acute (short-term) exposures to PTFE fumes; no studies have been done looking at the long-term effects of brief, repeated PTFE-fume exposure, as would be the case in cooking using non-stick pans for a lifetime.

Birds were found to be particularly susceptible to the PTFE fumes, based on some reports that pet birds were dying after their owners left a coated pan heating on the stove. Indeed, parakeets and Japanese quails died after exposure for 4 hours to PTFE fumes generated at 330 ºC (626 ºF). In summary, inhalation toxicity becomes a concern when PTFE is heated to high temperatures which releases toxic particles and gases that could result in polymer fume fever. These effects are more prominent, if not lethal, in birds than in humans.

Via ingestion

PTFE is inert in its solid form, meaning it won’t react with other chemicals, which is what makes it such as great non-stick coating. As such, the minimal PTFE you would ingest will likely pass through the digestive tract without harm. However, another fluorinated compound, PFOA (perfluorooctanoic acid), is commonly used in the process of making PTFE and may be residual in non-stick coating components. After repeated heating and cooling, it is possible that the PFOA could migrate into the food. Research suggests that PFOA interferes with hormonal balances as well as reproduction and fetal development.

Exposure assessment

So if PTFE is the hazardous component, do non-stick pans generate these toxic PTFE-fumes when I use them in the kitchen?

Typical temperatures for frying foods range from 130 ºC for fish fillets to 280 ºC for steak (266 ºF, 536 ºF, respectively) and the maximum temperature for most household ovens is 500 ºF. Given that PTFE degrades above 350 ºC (662 ºF), I would presume that the temperatures typically used to cook foods do not generate sufficient PTFE-fumes to cause polymer fume fever. Many of the case studies reporting polymer fume fever were results of unattended heating and of heating empty non-stick pans. Furthermore, most kitchens have reasonable ventilation that would protect the user. Altogether, non-stick pans could produce PTFE-fumes if used improperly. Typical cooking practices will probably not generate a significant amount of these fumes.

What about PFOA? How much PFOA is there? How much PFOA comes from non-stick pans?

While PFOA is used in the production of non-stick coatings, it is thought that there is minimal PFOA in PTFE. DuPont removed PFOA from Teflon production in 2013 as a part of the 2010/2015 PFOA Stewardship Program, an initiative by eight manufacturing companies organized by EPA to reduce PFOA emissions and use in production (EPA).

PFOA is hard to degrade and it can remain in the environment and the human body for a long time. Thus, repeated exposure to small amounts of PFOA could build up over time and cause toxicity. In fact, PFOA has been detected in the blood of almost all US residents (Post). To determine how much PFOA could come from non-stick coatings, Begley and his team at the U.S. FDA designed an experiment to investigate the possibility of PFOA transfer from PTFE-coated pans to food. Using the most conservative estimates, they found that minimal amounts of PFOA transferred from PTFE cookware, even after intensive heating of the pans. Thus, it is more likely that humans are exposed to PFOA through other means than by ingestion of residual PFOA from food cooked in a non-stick pan.

Limitations

A very important section! All research has its limitations. We can’t measure everything, our tests aren’t perfect, and we can’t account for all the variables when designing the experiments. Thus, every risk assessment needs to identify and address the caveats. The biggest question that is not answered by research is the long-term effect of exposure to small amounts of PTFE and PFOA. This kind of exposure is more representative of how people come into contact with Teflon and its toxic components.

Risk Assessment: And the answer is…

In conclusion, to my dear newlywed friends and other interested readers, is it safe to use non-stick frying pans and cookware? Assuming you use your cookware appropriately, i.e. not heating it excessively and unattended, always heating the pan with something in it, not scratching off the Teflon and consuming it for dinner, using non-stick pans is relatively safe for humans. Risk of “Teflon flu” due to inhalation of fumes during typical kitchen use is minimal. Ingestion of PTFE is not reported to be toxic and residual PFOA in PTFE-coated pans is minimally transferred to food. However, long-term exposure studies to PTFE-fumes and PFOA have not been conducted so we can’t say that it is completely safe. Regardless, you should keep Larry the bird away from the kitchen.

If you wish to avoid the Teflon risk altogether, stainless steel and cast-iron pans are recommended alternative, albeit not necessarily non-stick, cooking options.

Teflon infographic

Other resources

Environmental Working Group. “Healthy Home tips: Tip 6- Skip the non-stick to avoid the dangers of Teflon”  http://www.ewg.org/research/healthy-home-tips/tip-6-skip-non-stick-avoid-dangers-teflon

EPA website on PFOA and Fluorinated Telomers (aka PFTE and Co.) http://www.epa.gov/oppt/pfoa/

Disclaimer: The views and opinions expressed in this article are those of the author alone and are not intended for medical diagnoses/advice. They also do not necessarily reflect those of SWAC or the UNC at Chapel Hill.


Peer edited by Zan Isgett & Lindsay Walton

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