Plastic-Lined Containers Can Release Nanoparticles At High Temperature

Nylon cooking bags and plastic-lined cardboard cups are conveniences many people rely on, but a new study in ACS' Environmental Science & Technology suggests that they are an underappreciated source of nanoparticles. They report that the plastic in these products release trillions of particles into each litre of water that they come in contact with. That sounds like a lot, but the team notes that these levels are under the regulatory limits for consumption.

Food-grade plastics come into contact with a variety of foods and drinks that people consume every day. For instance, nylon cooking bags help keep food moist in the oven and make clean-up easier for slow cookers. Likewise, plastic-lined paper cups are designed to keep liquids hot and prevent them from leaking out. Previous studies have shown that some plastic materials, including polypropylene baby bottles and polyethylene terephthalate tea bags, can shed microscopic and nanoscale particles into heated liquids, though the human health implications of ingesting these particles are unclear. So, Christopher Zangmeister and colleagues wanted to see whether food-grade plastic films can also be a source of small plastic particles.

The researchers poured room temperature or hot water into nylon slow cooker bags and low density polyethylene-lined cardboard cups from different retailers. After keeping the slow cooker hot for an hour, the researchers found that 35 trillion plastic nanoparticles leached into the litre of water in each bag. When the team put hot liquid in 12-fluid-ounce cups for 20 minutes, 5.1 trillion plastic nanoparticles per litre leached out. Both materials released considerably fewer nanosised particles into room temperature water. Finally, the researchers calculated that a person would have to drink 13 cups of hot water from a plastic-lined cup or half a litre of water from the cooking bag to consume the equivalent of one nanoplastic particle for every seven cells in a person's body. 

New plastics are usually “BPA-free” and labelled accordingly, but what about all of those plastic containers you already have in your kitchen or that you come across at thrift stores and yard sales? How can you tell if they’re BPA-free?

BPA (bisphenol-a) is found in polycarbonate plastics, which are hard, clear (or clear-tinted), unbreakable plastics. They’ve been used since the 1960s to make products like water bottles, food-storage containers, drinking glasses, pitchers, and baby bottles.

Know Your Plastics

You can assume that any opaque plastics are BPA-free. So, if you can't see through it, that’s the first step in identifying BPA-free plastics in your home.

For any plastics that fit the description of being hard, clear (or clear-tinted) and unbreakable, flip them over and look for a recycling number. Polycarbonate plastics will have a number 7 on them, but they’re not the only plastic that gets labelled with a 7, so you’ll need to do a bit more investigating.

If you see a label indicating that the container is handwash only, it’s probably made of acrylic and therefore OK to keep.

If the container doesn’t have a recycling number on it and you bought it before July of 2012, it’s best to assume that it contains BPA and to get rid of it.

Metal containers, especially aluminium water bottles, are sometimes lined in BPA to improve the taste of the water. If you feel any plastic lining inside a container that isn't marked as BPA-free, it's best to throw it away. These types of linings are especially prone to scratching.

Safety

Polycarbonates get a lot of attention due to concerns over BPA, but it’s important to remember that it isn’t the only plastic that can leach chemicals into your food. While you’re going through your plastic containers, go ahead and toss any that are scratched or damaged. Worn containers pose a higher leaching risk.

Other leaching risks Include:

• Microwaving food in plastic containers
• Storing acidic foods (like tomato sauce) in plastic because the acidity could draw chemicals into your food
• Placing foods in containers while they're still hot
• Scrubbing containers too vigorously or with scrubbers that can cause scratches
• Routinely exposing your containers to high temperatures, including washing them in the dishwasher
• Using containers over an extended period.

A good idea is to switch to using glass in your kitchen; you won't have to worry about any of these concerns because of glass:

• Is microwave-safe (not that we recommend cooking in the microwave).
• Is dishwasher-safe
• Won't stain
• Doesn't wear out
• Won't leach chemicals into your food if it becomes scratched or is exposed to high temperatures