Answer to Question #3170 Submitted to "Ask the Experts"

Q

Recently, at my place of work, a pregnant worker in her first trimester had used an older model Litton microwave oven to heat her food. She was likely near (within 0.5 metres) the oven for approximately two to three minutes while it was "operating." A short time later, when another worker was attempting to heat up her lunch, it was noted that the food did not heat up. Our maintenance person was nearby at the time and decided to use a small handheld microwave tester, manufactured by Universal Enterprises, to test the microwave. The microwave was activated and the tester was placed at the door. The meter went to full-scale deflection, which was 2 (no units, but I'm assuming that it was measuring in mW/cm²). The microwave was brought in by the vending machine provider and was a temporary unit. Unfortunately, the vending machine representative removed and disposed of the microwave before I could determine the model, wattage, and date of manufacture of the unit. My questions to you are: (1) Is this a cause for concern for the pregnant worker? (2) Have any studies or evidence been documented that cite any deleterious effects on the embryo from microwave exposure? (3) How can I calculate the maximum amout of microwave radiation that is generated by various microwaves, perhaps using the power ratings, the 2.45 GHz operating frequency, power level of cooking, time of cooking, etc.? (4) Is there a formula? (5) Is there a maximum allowable limit for commercial microwave oven radiation? Any assistance you could give me in fielding these questions would be extremely helpful to this first-time mother. To my knowledge there is no family history of birth defects, she has not experienced any reproductive problems, and she is in good health. At this point, she is just anxious in regard to her potential exposure.

A

The US Food and Drug Administration (FDA) has a regulation on microwave oven leakage. In Title 21—Food and Drugs, Chapter I—Food and Drug Administration, Department of Health and Human Services, it states:

"PART 1030—PERFORMANCE STANDARDS FOR MICROWAVE AND RADIO FREQUENCY EMITTING PRODUCTS: (c) Requirements—(1) Power density limit. The equivalent plane-wave power density existing in the proximity of the external oven surface shall not exceed 1 milliwatt per square centimeter at any point 5 centimeters or more from the external surface of the oven, measured prior to acquisition by a purchaser, and, thereafter, 5 milliwatts per square centimeter at any such point."

The power leakage from the microwave oven cannot be high at 50 cm away from the oven, since the power is inversely proportional to the square of distance. A recently published review paper in Bioelectromagnetics (Volume 24, Supplement 6, Page S174-S186, 2003) on "Radiofrequency Fields and Teratogenesis" indicated in the conclusion of the review: "In overall conclusion, excessive temperature elevations, whether from RFEMF exposure or more conventional heating are teratogenic, and no valid experimental evidence was found for the occurrence of nonthermal teratogenic effects."

Therefore, unless the exposure caused excessive heating, the fetus cannot be affected. If the fetus were excessively heated, the mother would have detected it. Since there was no excessive heating sensation perceived by the mother, I do not believe that the fetus was affected at all.

To answer your questions:

1. There is no concern for the pregnant worker.
2. Answered above.
3. The maximum power output depends on the power rating of the magnetron. It should be stated in the user's manual.
4. Cooking is controlled by both power-level setting (if there are choices, such as defrosting and full-power cooking) and cooking time. They are set by the users.
5. See answer above in the FDA regulation.

C-K Chou, PhD