Some plastic bottles are believed to be potentially hazardous to human health, because they contain chemicals which could cause health problems. As a quick rule of thumb, hard plastics numbered 2, 4, or 5 are generally believed to be safe, while plastics labeled 1, 3, and 7 are believed to be potentially hazardous, especially if they are reused. Because of concerns about the safety of plastic bottles, some consumers prefer to use metal or glass bottles for their beverages.
Several chemicals used in the manufacture of certain plastics are of concern. The first is bisphenol-A (BPA) which is known to be an endocrine disrupter, meaning that it causes a hormone imbalance. BPA has been linked to cancers in lab animals, and there is some concern that it could also cause cancers in humans. BPA is most notably present in Lexan, a hard plastic which carries the number 7; Lexan bottles were often sold as an environmentally friendly long-use water bottle before the risks of BPA were fully realized.
Another chemical of concern in plastic bottles is Bis(2-ethylhexyl)phthalate (DEHP), a chemical which is used as a plasticizer. DEHP is present in flexible plastics with numbers like 1 and 3; these plastics are often designed for single use, and not intended for extended re-use. DEHP is also believed to have a potential for endocrine disruption, and it has been linked with obesity in some studies. Other chemicals used in the manufacture of plastics can include things like chlorine, which are not generally good for human health.
The chemicals present in plastic bottles can leach into their contents in a number of ways. Extended regular use can result in leaching, and leaching can be accelerated by damage to the bottle, heat exposure, and cleaning agents. As chemicals leach into the contents of the bottle, they pose a risk to anyone drinking from the bottle, who might ingest those chemicals unwittingly. For people who use a lot of plastic bottles, long-term exposure through leaching could lead to health problems in the future.
Plastics labeled with a “1” are designed to be used once, and then recycled. Such plastics are generally believed to be safe for a single use, which explains why they are widely used to package soft drinks, but some people feel that they should not be re-used. Reuse of these plastic bottles could put consumers at risk of leaching and DEHP exposure.