You may feel good about reusing your plastic margarine tubs for microwaving leftovers or using plastic grocery bags for food storage in the spirit of reuse or recycle, but are they safe practices?

Not according to the U.S. Department of Agriculture. Here is what experts with USDA's Meat and Poultry Hotline have to say about these and other food packaging questions.

Q. Is it safe to microwave-heat foods in margarine tubs or cottage cheese containers?

A. No. Cold food storage containers are intended for those uses only. They have not been tested or approved for any other use, including cooking. Do not use these types of containers for heating food. They are not heat stable and chemicals from the plastic may migrate into the food during heating.

Q. What about the use of plastic and other packaging materials in the microwave oven?

A. Microwave foods in packaging materials only if the package directs, and then only one time. Or, frozen foods may be partially defrosted and then transferred to a glass or ceramic container or plate to complete cooking. If using plastic wrap, make sure it doesn't touch the food and don't reuse the wrap. Wax paper is a safe alternative cover for microwaving foods.

Q. Is it safe to use plastic grocery or trash bags for food storage?

A. This is not a recommended practice, especially for plastic trash bags. They generally are not made of food grade plastic, and chemicals from them may leach into the food, especially raw food such as fresh produce.

Q. What about packaging that accidently gets cooked in a conventional oven, such as the giblet bag inside a turkey?

A. The giblet bag and the absorbent pad that comes with it are clearly not intended to be cooked, however if this happens and the packaging materials remain unaltered (that is, they don't melt or come apart), the giblets should not be used, but the turkey surrounding will not pose an imminent health hazard. However, if the packaging materials have melted or changed shape, USDA experts recommend against using the turkey for food safety reasons.

Q. Is it safe to reuse plastic water bottles?

A. Bottles used for soft drinks, juice, milk, water and peanut butter are made from No. 1 or No. 2 plastics. These containers are recommended for single use only. Don't continue to reuse them with food or water.

For more information on the safety of food packaging materials, call USDA's Meat and Poultry Hotline toll-free at 1-888-MPHotline.

* Sheila Ryan is an agent for family and consumer science with the Yakima County office of Washington State University Cooperative Extension.