Mr. McGuire (Walter Brooke): I just want to say one word to you -- just one word.

Ben (Dustin Hoffman):

Yes, sir.

Mr. McGuire:

Are you listening?

Ben: Yes, I am.

Mr. McGuire: "Plastics."

-- "The Graduate," 1967

I have received several frightening e-mails warning me against using plastics in the microwave oven. Specifically, if plastic wrap touches the hot food, can toxic chemicals leach out of the plastic into the food?

The answer is "maybe," but it ain't gonna kill ya. This is a classic example of alarmists pouncing on a situation in which all the scientific facts are not yet known and jumping to the worst possible conclusions. I suppose they think they're doing a public service by scaring the wits out of as many people as possible. (God bless the Internet.)

The word "plastics" is as ambiguous today as it must have sounded to poor Ben Braddock in 1967. There are literally hundreds of chemically different plastics in commercial use, having in common only that they are polymers: made of huge molecules that are in turn made up of repeating groups of atoms. While generalizations can therefore be misleading, all plastics are "microwave safe" because their huge molecules don't absorb microwave energy.

Here are the most common plastics used in food packaging. The abbreviations and numbers are their identification codes for recycling purposes. You'll find them within the triangular recycling symbol on the bottoms of plastic containers.

Polyethylene terephthalate (PET or PETE, #1); polyethylene (PE), both high-density polyethylene (HDPE, #2) and low-density polyethylene (LDPE, #4); polyvinyl chloride (PVC, #3); polypropylene (PP, #5) and polystyrene (PS, #6), better known by the trade name Styrofoam; and miscellaneous others, primarily polycarbonate (PC, #7). These plastics can turn up either as rigid containers such as margarine tubs; milk, water and juice bottles and refrigerator storage containers (these are usually made of PET, HDPE, PVC, PP or PS); or as thin films or "food wraps," such as supermarkets use to wrap meat and cheese and home cooks use for a variety of purposes. The clingy wraps are usually PVC or PVDC (polyvinylidene chloride), while the non-clingy ones are LDPE.

End of chemistry lesson. Now let's see what's being alleged, what's known and what's unknown about the dangers of plastics in microwave ovens. There are at least two e-mail scare stories making the rounds on the Internet. The messages conclude with the telltale signature of an Internet urban legend: "Please pass this on to your friends and family."

What's alleged:

One widely circulated story quotes a certain Dr. Edward Fujimoto "of Castle Hospital," who on a morning television news program in Hawaii warned that plastics heated in the microwave oven release dioxins, chemical by-products of the manufacture of disinfectants and herbicides, including the infamous Agent Orange defoliant used in Vietnam. Some anonymous person saw this program, ran to his or her computer and set off the exponential spread of this "important health information" on the Internet.

What's known:

Fujimoto is not an MD, a toxicologist or a plastics chemist, but the director of a Wellness and Lifestyle Medicine Department at Hawaii's Castle Medical Center. There is no evidence that plastics used in microwaving foods contain dioxins or that any dioxins have been detected in foods heated in contact with them. Small amounts of dioxins can be present in bleached paper, but U.S. paper mills comply voluntarily with the FDA's limits on the dioxin content of food-contact papers.

But how dangerous are dioxins, anyway? The Encyclopedia Britannica says, "In the early 1980s . . . toxicologists mistakenly concluded from studies on laboratory animals that [dioxin] was one of the most toxic of all man-made substances. . . Subsequent research, however, discounted most of these inferences, which were based on the effects of very high doses of [dioxin] on guinea pigs and other peculiarly susceptible animals . . . Epidemiological studies on industrial workers exposed to [dioxins] over many years show that it has a weak carcinogenic effect at high-dose exposures and no effect whatsoever at low-dose exposures."

What's unknown:

Although some plastics produce dioxins when burned, it is not known whether dioxins are formed at the much lower temperatures of microwaved foods. The Britannica's summary notwithstanding, however, the toxicity of low-dose dioxins remains an open book.

What's alleged:

Another widely circulated Internet story tells about Claire Nelson, a 10th-grade student in Mississippi, who decided to see whether dangerous levels of DEHA or di(2-ethylhexyl)adepate, a component of some plastic wraps, migrated from the plastic into hot foods with which it was in contact in a microwave oven. Several studies had already found traces of DEHA in plastic-wrapped cheese. With the help of Jon Wilkes, an FDA scientist, she microwaved samples of four plastic wraps immersed in olive oil and found surprisingly high levels of DEHA in the oil.

What's known:

Claire Nelson is real, and she really did that experiment, which was published in a scientific journal and won an American Chemical Society award. (Eat your hearts out, all you science fair contestants.) DEHA, a suspected but not proven carcinogen, is a plasticizer: a chemical that the plastics manufacturers add, notably to PVC, to make it soft and flexible. Without DEHA, a film made of PVC would be hard and brittle and wouldn't cling well to itself or other surfaces. But plasticizers are not necessary in making films of LDPE -- the non-clingy kind of household food wrap. Before Nelson's experiment, amounts of DEHA up to 153 parts per million had been found in the cheese studies, but she found up to 500 parts per million in her olive oil. DEHA is soluble in fats, so hot olive oil would be expected to extract the maximum amount of it.

What's unknown:

While several DEHA experiments have been done on rodents, no universally accepted standard exists for the maximum safe amount of DEHA in foods for humans. Very few studies have yet been done to determine how much, if any, DEHA migrates into the surfaces of different foods under microwaving conditions.

What to do:

Even if DEHA is proven to be a carcinogen in large doses, the odds of any individual's getting cancer from a microwaved meal (or 100 microwaved meals) are infinitesimally small. A risk is only a probability, not a certainty. If your risk of getting cancer from food were raised from one in a million to one in 999,000, there would be little to lose any sleep over.

Nevertheless, until more is known about these issues, here are some prudent measures you can take:

* If you have to cover a microwaved dish of fatty food with plastic wrap, especially a clingy wrap, try to avoid its touching the food. Or use wax paper instead.

* Best of all, do what I do: cover the food with an inverted paper plate. It's inherently safe (the FDA monitors all paper products intended for food use), it efficiently prevents spattering and yet it is loose enough to let steam escape.

* Don't microwave food in restaurant takeout containers made of PS (Styrofoam). They might melt, and melted plastics can bleed harmful chemicals, if there are any, more easily than solids can.

* Don't microwave food in margarine tubs made of HDPE, not because of any toxicity, but because they will warp and make a mess of the food.

* Don't microwave food in food storage bags and produce bags from the supermarket. While they're made of polyethylene (PE), which is considered chemically harmless, they can melt easily. Bits of plastic aren't pleasant to chew on.

Please pass this on to your friends and family.

Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author, most recently, of "What Einstein Told His Cook: Kitchen Science Explained" (W.W. Norton, $25.95). He can be reached at wolke@pitt.edu.