Polystyrene foam cups contain styrene - a chemical compound that is increasingly suspect. In the 12th edition of its Report on Carcinogens, the National Toxicology Program (NTP) stated that styrene is "reasonably anticipated to be a carcinogen," and the International Agency for Research on Cancer has classified styrene as a "possible human carcinogen." However, in spite of these classifications, polystyrene foam continues to be widely used for coffee cups, egg cartons, and salad boxes as well as disposable bowls, plates and trays. A hard version of polystyrene is used to make plastic cutlery, yogurt and cottage cheese containers, cups and clear salad bar containers.
Styrene poses the greatest danger to humans who are exposed to it in the workplace. It is used in the manufacture of a wide array of products, everything from boats, car and truck parts, to bath tubs and shower stalls with glass fiber-reinforced polyester composite plastics. While the NTP describes evidence that styrene can cause cancer as "limited," it reports that the occupational hazards include an increased risk for leukemia and lymphoma as well as genetic damage in white blood cells of workers exposed to the chemical. Beyond that, styrene also has been associated with respiratory problems among workers exposed to it as well as with "styrene sickness," a combination of headache, fatigue and feelings of drunkenness. Styrene causes lung tumors in several strains of mice.
Styrene isn't known to leach out of hard plastics, but some evidence suggests that it can leach out of foam food containers and cups when food or drinks are hot – not when they're cold. Based on what we now know, you're probably safe using styrene foam cups for cold drinks, but I wouldn't use them for hot coffee or tea, and I would avoid using plastic containers for hot foods. You can recognize styrene foam cups at a glance. To find out whether other food containers are made with polystyrene, look for the number 6 inside the recycling symbol.
Apart from the dangers styrene may pose to human health, it also poses a risk to the environment. According to the Environmental Protection Agency, of the nearly 20 million pounds of waste styrene generated annually, about 17.8 million pounds winds up in the air and 1.7 million pounds gets into surface waters. The National Resources Defense Council notes that polystyrene foam from coffee cups and other food containers are clogging landfills and turning up in the ocean, where sea birds and marine animals swallow it.
You would be doing the environment (and possibly your health) a favor by reducing use of containers made with polystyrene. Using your own coffee cup or mugs for your drinks and your own containers for foods is better for the planet. As for recycling the material, some recyclers won't take foam containers because they're so light - the profit in recycling is calculated by weight. The end result is that the styrene foam containers blow away, often into the ocean, where they don't disintegrate.
Andrew Weil, M.D.