I have received the following e-mail. Is there any truth to it?

"Johns Hopkins has recently sent this out in their newsletters. This information is being circulated at Walter Reed Army Medical Center . . . . Don't freeze plastic water bottles with water in them as this releases dioxin from the plastic. Dioxin carcinogens cause cancer [sic] . . . Pass this on to your family and friends."

That last sentence, "Pass this on to your family and friends," is often the telltale signature of an Internet urban legend. This particular one erupted when one Edward Fujimoto was interviewed on KHON-TV in Honolulu on Jan. 23, 2002, and made some alarming statements about plastics. (I wrote about this in my Nov. 13 column of that year.) Your e-mail message has been circulating ever since, picking up such creative embellishments along the way as the purported imprimaturs of Johns Hopkins University and Walter Reed Army Medical Center.

In a word, the message is baloney. Dioxins are a class of probably carcinogenic chemicals, some of which are released when certain plastics are burned. But the simple fact is that there are no dioxins in plastic bottles. Period.

A more recent Internet story has it that reusing plastic water bottles is dangerous because toxic chemicals in them will poison the water. More baloney. There are no toxic chemicals in polyethylene terephthalate (PET) water bottles. Even if there were, do you suppose they would be lying in wait without contaminating the original contents until such time as the bottle is refilled, whereupon they would leap out to poison the unsuspecting refiller? Instead of continually buying little bottles of water at $8 a gallon to keep in my car, I refill one bottle repeatedly from my kitchen tap. If it's good enough to drink in the house, it's good enough to drink in the car. (I don't use that philosophy for my cocktails.)

There is a grain of truth in one of these plastics legends, however. If a clingy kitchen plastic wrap containing the plasticizer di(2-ethylhexyl) adepate, or DEHA, should be in contact with a fatty food while it is being heated in the microwave oven, small amounts of DEHA can migrate from the plastic into the fat. Even so, there is no evidence that DEHA poses a significant risk to humans in the amounts that could possibly enter the food from the plastic.

Plastic wrap manufacturers don't list the chemical identities of their plastics on the packages, so to play it safe, I cover my microwaved food with an inverted paper plate.

Can you please discuss whether grapefruit has unique effects on metabolism? For example, I've read that grapefruit interferes with the absorption of certain medications. I'm also curious about the acidity of grapefruit compared to that of other citrus fruits. Though I think it's highly acidic, a co-worker maintains that it is very sweet, which is why aspartame is made from it.

Any co-worker who thinks grapefruit is sweet should never be trusted to make the office coffee. Grapefruit juice is more acidic (sour) than orange juice, but not as sour as lemon or lime juice. And puh-leeze! Aspartame is not made from grapefruit.

But grapefruit juice does have a surprising effect on certain drugs: it increases, not decreases, their absorption. Grapefruit juice contains chemicals that inhibit an enzyme system called CYP 3A4, which catalyzes the metabolism of many drugs in the small intestine. If less of a drug dose is metabolized, more of it is available for absorption into the bloodstream, so that its effects -- and perhaps also its side effects -- can be intensified. So taking a drug within a few hours after ingesting grapefruit juice can make the drug more potent.

Individuals differ widely in their sensitivity to this grapefruit effect, and not all drugs are affected. Among the more common drugs whose actions can be intensified by grapefruit juice are the cholesterol-lowering statins atorvastatin (Lipitor), lovastatin (Mevacor) and simvastatin (Zocor). Plus sildenafil (Viagra).

(All right, gentlemen, I know what you're thinking. But washing Viagra down with a glass of grapefruit juice is not recommended.)

To check your medications for grapefruit counteractions go to http://powernetdesign.com/ grapefruit/general/ GJDIsummary.pdf or ask your pharmacist the next time you refill your prescription.

Correction: In a recent Labelingo, I sanctioned a reader's opinion that it was silly to homogenize nonfat or skim milk because it contains virtually no fat. I have since been informed that according to an Oct. 31, 2001, regulation of the U.S. Department of Agriculture, "All fluid milk and milk products . . . shall be homogenized."

LABELINGO: Perspicacious reader Jay Weingart of Olney writes, "I purchased Sprouted Grain Tortillas, manufactured by the Food For Life Baking Company. Emblazoned across the package is Ezekiel 4:9: 'Take thou also unto thee Wheat, and Barley, and Beans, and Lentils, and Millet, and Spelt, and put them in one vessel, and make bread of it . . . ' Hopefully, the Food For Life Baking Company neglected the remainder of the chapter because Verse 12 says, 'And thou shalt eat it as barley cakes, and thou shalt bake it with dung that cometh out of man, in their sight.' What would the FDA say about that?"

Relax, Jay. Ezekiel was merely suggesting that we bake it using dried human dung as a fuel, not as an ingredient. Dried cow manure was used as a fuel in biblical times and is still used in many parts of the world.

I'll stick with charcoal.

(Have you noticed any silly things on food labels? Send your Labelingo contributions, along with your name and town, to Food 101, Food Section, The Washington Post, 1150 15th Street, N.W., Washington, D.C., 20071 or to the e-mail address below.)

Robert L. Wolke (www.professor science.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). He can be reached at wolke@pitt.edu.