How
the FDA tests plastic chemicals for safety
The FDA tests plastic chemicals for use in microwave ovens carefully because
it knows some substances used in manufacturing plastics can, at high
temperatures, diffuse out of the
plastic into contained food. These
substances, called plasticizers, can harm humans. Hence the care.
The tiny plasticizer molecules move around in the plastic due to their
thermal energy. In fact, plasticizer molecules have such small molecular
weights that the heated molecules can bop out of the plastic into contained
food, much like water molecules leave a boiling pot of water and enter the air
above the pot. The higher the the plasticizer's temperature, the faster
the molecules move. This random thermal movement is called diffusion.
The FDA tests chemicals used to manufacture various plastic containers to
make sure the amount of plasticizers that diffuses into the food is less
than a maximum allowable amount. The maximum allowable diffusion for a
microwave-safe container or plastic wrap is 100 to 1000 times less per
pound of body weight than the amount shown to harm laboratory animals over a
life time of use.
Container manufacturers then use only chemicals that the FDA authorizes for a
"specific type of use and under specific conditions of use (time temperature),"
emails
Edward J. Machuga of the FDA Office of Food Additive Safety. These
chemicals have passed the maximum-allowable-diffusion tests, and manufacturers
can therefore label containers or wraps using such plastics as "microwave safe"
on the manufacturer's container box.
The FDA tests include such steps as estimating:
- the ratio of plastic surface area to food
- how long the container will be in the microwave
- how often a person will eat from the container
- how hot the container might get during microwave heating
Further Reading:
Guidance for Industry: Microwave-only containers, FDA, April 2002; December
2007
(Answered 11 Jan. 2010)
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