Effect Measure

“Microwave safe”: Not

The team of investigative reporting team of Susanne Rust and Meg Kissinger at the Milwaukee Journal-Sentinel just keeps rolling along, this time with an amazing story about how microwave safe plastics are leaching bisphenol-A (BPA) at potentially unsafe levels. We are saying potentially unsafe because we really know little about the effects of hormone mimics like BPA except that at levels currently found in BPA containing plastics in contact with food and liquids produce biological effects in test systems and a recent analysis of a representative survey of US adults showed an association between self-report of heart disease and adult onset diabetes (Type II) and blood abnormalities in liver function tests (see our post here). That’s preliminary but the animal data are pretty consistent. BPA is not something we want to expose our children or ourselves to and consumers are voting with their feet, trying to avoid BPA containing products. But to avoid them, a consumer has to have accurate information. When they see a label on a product that says “microwave safe,” they can be forgiven if they interpret this to mean it’s OK to heat the item in the microwave. Rust and Kissinger decided to see if it was true. They took ten “microwave safe” products, used them as directed and sent the results to a laboratory to measure BPA:




The newspaper’s test results raise new questions about the chemical and the safety of an entire inventory of plastic products labeled as “microwave safe.” BPA is a key ingredient in common household plastics, including baby bottles and storage containers. It has been found in 93% of Americans tested.

The newspaper tests also revealed that BPA, commonly thought to be found only in hard, clear plastic and in the lining of metal food cans, is present in frozen food trays, microwaveable soup containers and plastic baby food packaging.

Food companies advise parents worried about BPA to avoid microwaving food in plastic containers, especially those with the recycling No. 7 stamped on the bottom.

But the Journal Sentinel’s testing found BPA leaching from containers with different recycling numbers, including Nos. 1, 2 and 5. (Susanne Rust, Meg Kissinger, Milwaukee Journal-Sentinel)

Not surprisingly the trade association for the chemical industry, the American Chemistry Council, says it is nonsense and that the newspaper does a “serious disservice by drawing a conclusion about product safety that simply cannot be drawn from either this study or the overall body of scientific research.” The argument seems to be the same one they used with the FDA: that the levels are too low to matter. But the FDA was recently rebuked by an independent panel for not heeding abundant scientific data that biological effects are possible at the doses found in the Journal-Sentinel tests.

So was the law broken when these products were “microwave safe”? No. Because there is no regulation that governs whether you can put “microwave safe” on your product. The newspaper targeted their testing to products most likely to be consumed by infants and children, replacing the food by a mixture of alcohol and water (a standard laboratory practice that removes the variation in food content as a variable and may underestimate the amount of leaching). The highest leaching was found in a can of Enfamil liquid infant formula and a Rubbermaid plastic food-storage container. Dispolable frozen-food containers had the lowest amount of leaching. Here is the list of the ten products tested:

  • Munchkin bowls
  • Gerber Graduates Pasta Pick-ups
  • Rubbermaid Premier food storage container
  • Gerber 2nd Foods Hawaiian Delight dessert
  • Campbell’s Just Heat & Enjoy tomato soup
  • Enfamil liquid baby formula
  • Hormel chili
  • Stouffer’s macaroni and cheese and Stouffer’s lasagna
  • Playtex VentAire baby bottles also were tested, but the company has since reformulated the product to eliminate bisphenol A

Canada is banning sale, advertising or import of BPA containing products to infants and children. The US FDA, after first declaring BPA safe, is now being forced to re-evaluate. They will take their time and probably nothing will happen until we get an administration truly interesting in keeping us safe from corporations (63 ore days, in case you lost count). Demands for action are rising, nonetheless, and companies aren’t waiting:

Increasingly, consumer groups are calling for BPA to be banned. Last month, the consumer watchdog Environmental Working Group sent letters to infant formula makers, asking them to stop packaging their products in containers made with BPA.

The attorneys general in New Jersey, Connecticut and Delaware sent letters to 11 companies that make baby bottles and baby formula containers, asking that they voluntarily stop using BPA.

Six U.S. senators have called for a federal ban on the chemical, and more than 35 lawsuits have been filed in recent years against companies using BPA, claiming the chemical has caused physical harm.

Companies are beginning to proactively back away from BPA. In April, after Canada’s announcement of a ban, several corporations said they would stop producing and selling certain products made with BPA. The companies and retailers include Nalgene, Wal-Mart, Toys “R” Us, Playtex and CVS pharmacies.

Again, kudos to Rust and Kissinger at the Milwaukee Journal-Sentinel. They’ve done on a pittance what the US FDA has failed to do. It’s not money. It’s the will do it.


  1. #1 M. Randolph Kruger
    November 17, 2008

    Revere, what is the test in humans for BPA? Blood, urine, liver output obviously. Doing a liver punch is a bit extreme of course but what does it take to find out how much you have in you.

    I use glass but until the first noise of the 90’s I was a microwave freak.

  2. #2 revere
    November 17, 2008

    Randy: I’m not an expert but I know it is measured in the urine via HPLC-MS. It occurs both in free and conjugated forms there and is usually reported as total. Probably not easy to find a lab to do it, though.

  3. #3 Paul
    November 17, 2008

    OMG!! The melamine problem should have alerted us that the FDA is broken. This needs to be fixed ASAP before we are all sick.

    The FDA thought they could get away with BPA in the water bottles in another republican administration, but later reversed…

  4. #4 Anna
    November 17, 2008

    More a question- what about the autoclaved Nalgene bottles used to water lab animals? Is this even of consequence? Does the container have to be full of a substance to leach the BPA into? Excuse my ignorance, SVP.

  5. #5 M. Randolph Kruger
    November 17, 2008

    Hey, remember the cuzzin runs a testing lab for the Mid South. Just needed to know what to look for.

    Paul, I believe it was the FDA that alerted us to the problem initially.

    I have a second question Revere. So you nuke the plastic in the microwave, what about dishwashers and the like. That produces mighty damned hot air inside to kill the bacteria that might be left in the drying cycle. Is that just waiting for us to load it up with something later on and then hit it again with the nuke thus doubling the effect?

  6. #6 revere
    November 17, 2008

    Anna: Whether you nuke or autoclave the bottles, some BPA will leach out, but if it leaches into waste water it isn’t going into your food or drinking water. But it appears BPA leaches more from older plastic than brand new plastic, so stressing it with microwave or hot water heating may make it easier for BPA to leach out. But I don’t know the data on this, just general observations I have heard from people who work on this.

  7. #7 Anna
    November 17, 2008


    That makes sense. I guess for microisolator-kept animals the water is autoclaved separately from the bottles themselves (is that still the protocol?) My question was if the animals were consuming regular quantities of BPA via water from the nalgene bottles, what would the possible interference on tox or other studies be as a result, given the now known effects.

  8. #8 LindaCO
    November 18, 2008

    D’oh! I love Stouffer’s mac and cheese *sigh*.

    Are there any plastics that are safe to microwave things in? Thank you for this informative post.

  9. #9 zevkvakti.com
    November 19, 2008

    thanks post nice blog

  10. #10 Chris
    November 19, 2008


    I always transfer things from the plastic containers into a pyrex bowl or jug for microwaving. (I used to do it because it had convenience advantages, but I’m not going to stop after reading this!)

  11. #11 phytosleuth
    November 20, 2008

    Just visited a relative at an independent living care facility for elders. I had lunch with them and noticed that they all brought a plastic container with them to save the extra food they didn’t eat. They freeze these leftovers and then thaw them out later for dinners…you guessed it, in a microwave oven.

  12. #12 per
    November 21, 2008

    hmm. “kudos to Rust and Kissinger”.
    so what did they do, and what did they find ? This page (http://dev.www.jsonline.com/watchdog/watchdogreports/34532859.html) appears to contain their findings.

    lo, and behold, the highest level of BPA is at 3 microgrammes per kilogramme (ppb). Needless to say, there isn’t a control water sample, so you cannot tell if this is all just an artefact; a minor detail.

    Assuming 4kg for a new-born baby, and 0.9kg for food, you end up with less than a microgramme per kg of BPA. Or 50 times less than government regulations.

    and that is for the stuff with the highest level BPA, using worst case scenarios for intake. The other containers had much lower levels of BPA, with 7/10 more than 10x lower.

    but isn’t it amazing how bad it seems when you talk about hundreds of parts per trillion; hundreds of parts ! and isn’t a trillion such a big number ! Well, why, it must be a problem.

    good to see that the bloggers maintain their critical analysis of good science.

  13. #13 revere
    November 21, 2008

    per: Also good to see you keep up with the literature. This has been discussed quite a bit here and elsewhere, especially as regards low dose biological effects. You might want to check the NTP Report on the subject. Or you might not. Since you rely on government regs for your scientific facts, it might not interest you.

  14. #14 per
    November 22, 2008

    “Since you rely on government regs for your scientific facts…”
    well, if you don’t have anything constructive to say, abuse often fills a gap, doesn’t it ?

    according to the wikipedia page, there are only two studies showing an effect at 1 microgramme per kg and below. The concerns raised in both of these studies were dismissed by the NTP CERHR study.

    clearly, revere will be aware that the NTP CERHR study used a 5-stage grading of concern, and that the highest grading of concern was the mid-stage “some concern” for developmental neuro/behavioural tox endpoints. Revere is also aware just how weak a level of concern this is, and how much crap research (think prostate) was dismissed as not a basis for concern.

    oh, but that is the boring bit about science, and details again. The journal sentinel article, combined with the NTP report, makes a case that there is no concern. But hey; that is a boring detail next to “HUNDREDS OF TRILLIONTHS”. Mind you, if you are prepared to say “the animal data is consistent”, your attention to the scientific literature is obviously world-class and incisive.

  15. #15 revere
    November 22, 2008

    per: Kind of thin skinned, per. This is the intertoobz, you know. As you know, there were two NTP panels. I discussed this with the chair of one of them, Fred vom Saal. You chose to cite the one that had significant questions of conflict of interest (the SAI issue). I don’t mind your snarky comments. That’s par for the course on blogs. I am amused you are so offended about them when they used in reference to you. Thin skinned.

    You obviously know this is not just “a blogger” weighing in on this. vom Saal, who is an acknowledged BPA expert, is quoted three times in the article and many other scientists are concerned about BPA at these levels, even if you aren’t. You act as if this is a piece of junk science when it is quite clearly, at the very least, contested science (and I am being generous here). I assume you have no particular scientific expertise in this matter and no stake in it. I therefore suggest you read the relevant literature before commenting in the way you have. Just a suggestion. You are still welcome here. But expect to get push back.

  16. #16 per
    November 23, 2008

    Two NTP panels ? The panel convened by the NTP was the CERHR panel, and that gave rise to an official and scrutinised report.

    The other panel is a bunch of self-appointed experts, many with known conflicts of interest, which got a bit of funding from the NIEHS. It is chutzpah to describe this as an NTP panel.

    It is worth noting that Vom Saal has a large number of conflicting interests in this issue, including financial interests; surely you must agree it is important to mention when someone has a self-interest in an issue ? Vom Saal’s recent editorial in JAMA lists a large number of areas where Vom Saal has an apparent conflict.

  17. #17 per
    November 23, 2008

    i did raise an issue about the science that you blogged about. If you look at the data that the journal sentinel looked at, at worst, it shows exceptionally low levels of exposure. In fact, much lower than most of (what you describe as) the contested literature.

    if you are going to rely on data which uses doses of less than a microgramme per kilogramme, then you should ‘fess up to the scientific issues, and stand behind the papers that show an effect at 25 ng/kg. You should be able to defend how you can get an estrogenic effect even when the dose is so low.

    I think your issue of whether the low dose effects are junk science, or contested science, is very interesting. The FDA view is currently that it is junk science, though they are reviewing that. The FDA is not alone, and i find it surprising to imagine that FDA would take that view without good reason. Certainly, reasons for imagining that much of it is junk are in the public domain.

    what is more, I managed all of that without insulting you :-)

  18. #18 Stephanie
    January 2, 2009

    I guess my child could be the face of what COULD happen- regarding BPA. There is NO hx of diabetes anywhere in our family tree. Healthy, healthy baby. Dx with diabetes at age 14 months. MAYBE because fed with BPA bottles that were microwaved (with formula or breast-milk) every 3 hrs AND sterilized numerous times/day??? Like I said, my child could very well be the face of what COULD happen. If I could change anything I would have used GLASS bottles. A bit more expensive money-wise, but NOT compared to the price HE has to pay: a life he now has to lead, numerous insulin injections, blood glucose tests 10 or more times each day, what he can or can not do or eat. What’s that old adage.. prevention is better than cure!
    Not to mention the guilt I have to live with the rest of my life.

  19. #19 Michael Frederic
    March 9, 2010

    Hello, my name is Mike Frederic and I am currently a college student studying for my AA Degree. I am working on a term paper for Enviromental Science on,” The Safety of Microwave Oven Usage” and one of the requirements is to get feedback from legitimate sources on the pros and cons of microwave uage. After reading your article, I was wondering if I could get any feedback from you about the subject.
    I would appreciate anything you have to offer.I can be reached at axisofjustice@live.com