Plastic (cont.)
What is low-density polyethylene (LDPE)?
Low-density polyethylene (LDPE) is used for its toughness, flexibility, and
relative transparency. LDPE is used to make bottles that require extra
flexibility. To take advantage of its strength and toughness, it is used to
produce grocery bags and garbage bags, squeezable bottles, shrink wrap, stretch
films, and coating for milk cartons. It can also be found in toys, container
lids, and packaging. It is identified as number 4.
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. The study did not include anyone under 6 years
of age, so the level in their urine is unknown.
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.
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.
Next: What should I do when using plastics? »
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