What Are the Dangers of Freezing Plastic Containers?

Having plastic food containers on hand in the kitchen provides convenience. You can cook a large pot of stew, chili or other dish and pack any leftovers from your meal into plastic containers and freeze them. They're available for you to pull out of the freezer, heat up and have a quick meal. But media attention has focused on plastic containers and their safety. There are claims that chemicals in plastic containers may seep into the foods that they're holding.

Plastic Types

• There are seven types of plastic that are considered food-grade. Polycarbonate is a clear plastic that resembles glass. This plastic replaces glass in many types of food storage containers and is also used to make some reusable water bottles. Polystyrene most often forms Styrofoam food containers, such as meat trays and egg cartons. Polypropylene is harder and holds its shape at higher temperatures. It's used for food lids and many microwave-safe containers. Low-density Polyethylene is clear and flexible. This plastic forms flexible squeeze bottles. Polyvinyl chloride or PVC forms freezer bags and plastic wrap. Milk bottles are commonly made from high-density polyethylene. Soda and water go to market in PET, or Polyethylene terephthalate.

The Claims

• Many media outlets and mass emails circulated information that freezing plastic bottles releases cancer-causing dioxins and other chemicals. Much of the controversy surrounds plastic water bottles. Both single-use and reusable water bottles contain PET. Some also contain high-density polyethylene, or HDPE. The claim is that the freezing process stretches the plastic and causes the release of dioxins and bisphenol A -- or BPA, a chemical commonly added to plastic to retain its flexibility.

The Facts

• The facts don't support that claim, however. First, according to Dr. Lynn Goldman, a pediatrician and epidemiologist and a professor at Johns Hopkins University, food-grade plastics don't contain dioxins, so there's no risk of dioxin contamination in freezing plastic containers. Second, while some food containers contain BPA, they do so in minute amounts. BPA plastic is commonly found in the seams and linings of metal food cans and the flexible plastic seal on drink and juice lids. Most food container manufacturers remove BPA during production. ANy BPA that remains in the plastic is not affected by the freezing process. According to Dr. Goldman, freezing a container would actually prevent chemicals from moving into the food or drink because the cold temperature tends to limit chemical release.

Risks

• There is one other risk to freezing plastic containers. At very low temperatures, PVC and PET containers become brittle. Some containers, such as water bottles or plastic wrap, may tear or break as food or fluid inside expands during freezing. In addition, dropping or jarring a frozen plastic food container may crack or break the item.