BOSTON – Mothers often boil baby bottles with the caps on to warm liquids and disinfect the container, but such safeguards could be doing more harm than good.According to new studies released by environmental health organizations in the U.S. and Canada, the toxic chemical bisphenol A (BPA) leaches from plastic baby bottles when heated.Last week, the state Senate passed a bill that would replace toxic chemicals like BPA with safer alternatives where feasible. Elizabeth Saunders, a spokesman for the environmental advocacy group Clean Water Action, said the bill’s swift passage in the House ensures better protection for Massachusetts families from toxic chemicals found in common household goods.The study, “Baby’s Toxic Bottle: Bisphenol A Leaching from Popular Baby Bottles,” was commissioned by Environmental Defense of Canada. It contributes to a growing body of evidence that calls for immediate protective action to reduce public exposure to BPA, especially for infants and children.BPA, a synthetic sex hormone that mimics estrogen, is used to make hard polycarbonate plastic. Ninety-five percent of all baby bottles on the market are made with BPA.The U.S. study shows that when new bottles are heated, those manufactured by Avent, Evenflo, Dr. Brown’s and Disney/First Years leached between 4.7 – 8.3 parts per billion of BPA. Recent research on animals indicates that BPA can be harmful by disrupting development at doses below these levels. Studies conducted on laboratory animals and cell cultures have linked low doses of BPA to obesity, diabetes, thyroid disease, breast cancer, prostate cancer and other illnesses.BPA exposure is widespread and has been found in 95 percent of Americans tested.Boston Common Assets Management, a founding member of the Investors Environmental Health Network, has engaged Philips Electronics, Novartis and Playtex on this issue and claim Philips has been looking at alternatives to BPA since January 2007, including the feasibility of manufacturing a BPA-free baby bottle.In addition to baby bottles, BPA is used to make hard plastic used in some toddler sippy cups, polycarbonate water bottles such as some Nalgene bottles, dental sealants, and the linings of many food and beverage cans, including all infant formulas. Patagonia and Whole Foods have stopped selling products containing BPA.The full study, “Baby’s Toxic Bottle: Bisphenol A Leaching from Popular Baby Bottles,” is available to download for free on the Web site www.babystoxicbottle.org. The Canadian version of the study is available at www.toxicnation.ca.