Water and baby bottles made from polycarbonate plastic release a potentially dangerous chemical called bisphenol A much faster when boiling water is poured into them, researchers say in a new study.
Scientists from the University of Cincinnati found that when hard plastic drinking bottles were exposed to boiling water, BPA was released 55 times more rapidly and in higher amounts than when they were filled with room temperature water.
When the bottles were filled with cool water, the rate of BPA release ranged from 0.2 to 0.8 nanograms per hour. After the bottles were exposed to boiling water, rates increased to 8 to 32 nanograms per hour.
And they found that the age of the bottles didn't matter: well-used bottles were just as likely to leach the chemical, which has been called a hormone disruptor, as newer ones.
"Bottles used for up to nine years released the same amount of BPA as new bottles," study author and associate professor Scott Belcher said of his team's experiments.
The study is published in the journal, Toxicology Letters.
The finding is important for parents with bottle-fed children, since many plastic baby bottles are made of polycarbonate plastic and parents are advised to repeatedly sterilize the bottles in boiling water for long periods. According to the study, following that advice would make the bottles release BPA faster.
The finding may also be significant to hikers who may use the bottles from which to drink hot chocolate or other hot beverages.
Bisphenol A has been the focus of much scrutiny in recent years, with worries that the chemical mimics estrogen. There are fears the chemical can cause earlier onset of puberty in girls, declining sperm counts, and raise the risk of breast and prostate cancer.
"There is a large body of scientific evidence demonstrating the harmful effects of very small amounts of BPA in laboratory and animal studies, but little clinical evidence related to humans," Belcher said in a statement.
"There is a very strong suspicion in the scientific community, however, that this chemical has harmful effects on humans."
Health Canada is currently conducting a "high priority" evaluation of the chemical. The agency notes that while BPA is not bioaccumulative (meaning it doesn't persist in the environment or build up in fat stores), it was recently classified for reproductive toxicity by the European Commission and can cause harm to aquatic organisms.
Health Canada is expected to publish its conclusions on BPA in May.
BPA is used in the manufacture of a wide variety of plastic consumer products, including water bottles. It's also used as a component of composite resin dental materials, and in resins that line food and beverage cans.
Polycarbonate plastic food and beverage containers that contain BPA are labeled #7 inside a triangle-shaped recycling symbol on the bottom of the bottle.
However, not all containers with the recycling symbol #7 are made with BPA.
Late last year, Mountain Equipment Co-op became the first retailer in Canada to stop selling some products that contain BPA "until guidance is provided by the Government of Canada on the health risks posed by BPA."
Vancouver-based Lululemon Athletica later also decided to pull water bottles containing BPA from the shelves of its athletic and yoga wear stores.
