What is polypropylene (PP)?
Polypropylene (PP) is known for its high melting point, which makes it ideal for holding hot liquids that cool in the bottles (for example, ketchup and syrup). It can be manufactured to be flexible or rigid. PP is used to make containers for yogurt, margarine, takeout meals, and deli foods. It is also use for medicine bottles, bottle caps, and some household items. It is identified as number 5.
What is polystyrene (PS)?
Polystyrene (PS) can be rigid or foamed. It is most commonly used for protective packaging (for example, foam packaging for furniture, electronics, and other delicate items), food serving packaging (for example, cups, plates, bowls, cutlery, meat and poultry trays, and rigid food containers), bottles, and food containers. It is identified as number 6.
What is bisphenol A?
Bisphenol A (BPA) is a widely produced chemical used primarily for the production of polycarbonate plastics and epoxy resins. More than 6 billion pounds of BPA are produced and used each year for this purpose. The use of this chemical is so profound that it was detected in the urine in 93% of the population over 6 years of age.
Polycarbonate plastics are typically hard and clear and are marked with the resin identification code number 7. As mentioned previously, the number 7 is considered the "other" category and includes chemicals other than bisphenol A, as well. Nalgene water bottles were made with BPA until recently. They are being voluntarily pulled from the shelves and replaced by bottles that are BPA-free made with a relatively new plastic called Tritan copolyester. Other sources of polycarbonate are food and drink packaging, including infant bottles, toddler sipping cups, tableware, and food containers. Epoxy resins are used to line metal products such as canned foods, bottle tops, and water supply pipes.
The health risks of BPA have been receiving considerable attention. It has long been known that previous studies done on lab animals showed that BPA can cause genetic damage. BPA was approved for use with humans because the amount given to the animals was not comparable to what humans consume. For example, the intake of BPA is expressed in milligrams (mg) per kilogram (kg) of body weight (bw) per day. The highest estimated daily intake (exposure) for humans is
- less than 0.0147 mg/kg bw/day for children;
- less than 0.0015 mg/kg bw/day for adults; and
- 0.0100 mg/kg bw/day for workers exposed to this chemical.
Studies done on laboratory rodents have shown that high doses of BPA during pregnancy and lactation can reduce survival, birth weight, and growth of offspring early in life, and delay the onset of puberty. The doses given were significantly higher than the estimated human exposures:
- Delayed puberty: greater than 50 mg/kg bw/day
- Growth retardation: greater than 300 mg/kg bw/day
- Survival: greater than 500 mg/kg bw/day
BPA has also been linked to cancer, diabetes, and obesity in animals. The American Chemistry Council states that "consumers would have to eat more than 500 pounds of food and beverages in contact with polycarbonate plastic or epoxy resins every day of their lives to exceed exposure levels determined to be safe by the European Food Safety Authority and the U.S. Environmental Protection Agency." There is no way to know for sure if humans would have the same reaction that the animals have had, but there is enough evidence to be concerned and warrant further studies.
The highest estimated intakes of bisphenol A occur in infants and children. Their intake is greatest because pound for pound they eat, drink, and breathe more than adults. BPA is found in the plastic baby bottles and the linings of cans of powdered and liquid formula. Their exposure is also increased by the objects that they put in their mouth. It's important to note that bisphenol A has been detected in the blood of pregnant women and in the breast milk of lactating women.
One thing that many people seem to agree on is that high temperatures can cause BPA to leach into the food or beverage. In one study, boiling water was placed in hard plastic water bottles. The rate of release of BPA with the boiling water was compared with room-temperature water. With room-temperature water, BPA was released at a rate of 0.2 to 0.8 nanograms per hour. The BPA was released 15 to 55 times faster with the boiling water, with a rate of 8 to 32 nanograms per hour. The concern about this has led Canadian retailers to pull all baby bottles made with BPA from the shelves. In the United States, many manufacturers and retailers are beginning to do the same.