Question by Nona Siegel

Many plastic drinking bottles, including the colorful Nalgene bottles, are made from polycarbonate plastic. If you look on the bottom of the bottle and see a number 7 recycling triangle, it's made of polycarbonate plastic. Polycarbonate plastic is a polymer made from a chemical called bisphenol A (BPA). BPA is an endocrine disruptor and in animal studies has been associated with reproductive abnormalities including lower sperm counts, hormonal changes, enlarged prostate glands and pre-cancerous changes in the breast and prostate. We don't have very much data on whether BPA could be causing the same problem in humans but over 90 percent of the general population carries residues of BPA in their bodies.  
 
It's likely that beverages stored in polycarbonate plastic contain some amount of BPA, especially when they contain acidic substances or when they are stored at warm temperatures or for prolonged periods of time. Containers that are older and have become discolored or cracked also are likely to leach more BPA. A better option for storing beverages is to use an unlined stainless steel container. Unlined stainless steel containers like Kleen Kanteen are easily recyclable, so they have less impact than plastics. 
 
It hasn't received as much attention as the Nalgene bottles but BPA is used to line the inside of metal food and soda cans and leaches from the can liner into the food. So you may be getting more BPA by eating canned food and drinking canned soda than from drinking out of a polycarbonate bottle. Acidic foods like tomato sauces and soda absorb more BPA. To reduce your exposure, drink less canned soda and eat less canned food, especially those that are tomato-based.