Ask A Scientist: Is Microwaving Plastic Wrap Bad?

A Gentle Reader asks: "Will you take blog suggestions and answer science questions?" Of course! Any time, dear readers; I regard it as my sacred calling to spread the word of science understanding. So, the first question:

"What exactly is the risk to one's health of microwaving food with saran wrap on top?

There are two things most often cited as health risks of heating plastic: dioxin(s) and phthalates. Here's my scientific summary: dioxins are not in plastic and are not formed in the microwave. Phthalates are present in many plastics; they have no demonstrated effect at low levels. There are proven effects in rats, but at higher levels than we eat. The risk appears to be low, as in less than getting run over by a truck. If you're really worried about it, use a paper towel or paper plate or wax paper on top of your food in the microwave. Actually, use wax paper anyways: it decomposes.

1. Dioxin: In short, don’t worry about it (in your plastic wrap).

Dioxin describes a class of chemicals made of two benzene rings connected by two oxygens. They are often halogenated (that is, they contain chlorine or fluorine) and the chemical TCDD is commonly referred to as ‘dioxin’.

Dioxin is in fact very bad for you; it was a contaminant in Agent Orange, causing thousands of birth defects. Adult exposure is also very bad for you (ask Yuschenko). It can do a variety of nasty things to your biochemistry, interfere with immune function, or increase the risk of cancer, although a relatively high dose is necessary for any nasty or long-term effects. We’re talking chemical spill or employment at Monsanto, not everyday exposure. The first sign of dioxin exposure is usually chloroacne, which is what’s on Yuschenko’s face.

SC Johnson informs us that their products have no chlorine or dioxin. But do they form dioxin during cooking??? you ask. No. Monochlorinated dioxin is formed ‘as low as 400 C’ in a chemical study; an old CNN article cites a minimum of 300 C in the presence of metallic catalysts (during trash burning) for dioxin formation.

The EPA told us (2000 data) that the greatest atmospheric dioxin levels come, in fact, from backyard burning. The FDA also informs us that “although dioxin is an environmental contaminant, most dioxin exposure occurs through the diet, with over 95% coming through dietary intake of animal fats”. Since dioxin is stored in fat, it bioaccumulates up the food chain; age and fat/meat consumption are strong predictors of total body dioxin levels.

So in brief:

• There is no dioxin in Saran wrap, and likely not in other brands.
• Dioxin will not form in a microwave, unless it is on fire.
• If you’re really worried about dioxin, avoid Russian spies and become a vegetarian.

Monday: Part 2, Phthalates

[Note: I am not a medical professional; this should not substitute for medical advice or treatment. This is intended as an academic summary of the evidence available. For medical needs, please consult your physician.]