Plastics consist of various types of large polymers, or
resins—organic molecules made by chemically linking
monomer molecules produced mostly from oil and natural
gas (Figure 15-4, p. 375). About 46 different types
of plastics are used in consumer products, and some
products contain several kinds of plastic.
Many plastic containers and other items are thrown
away and end up as litter on roadsides, beaches (Figure
21-11), and oceans and other bodies of water. Each
year they threaten millions of seabirds, marine mammals
(Figure 11-5, p. 254), and sea turtles, which can
mistake a floating plastic sandwich bag for a jellyfish or
get caught in discarded plastic nets (Figure 11-10, right,
p. 260). About 80% of the plastics in the ocean are blown or washed in from beaches, rivers, storm drains,
and other sources, and the rest gets dumped into the
ocean from vessels and fishing boats.
Plastics discarded on beaches or dumped into the
ocean from ships can disintegrate into particles the size
of sand grains that resemble the prey of a variety of organisms.
These particles can fill the stomachs of birds
and other sea creatures and cause dehydration, malnutrition,
and eventually starvation. Because tiny plastic
particles can accumulate as they move through food
webs, some level of plastic is found in most of the seafood
people eat.
Currently, only about 4% by weight of all plastic
wastes in the United States is recycled. As American
comedian Lily Tomlin observes, “We buy a wastebasket
and take it home in a plastic bag. Then we take
the wastebasket out of the bag, and put the bag in the
wastebasket.” The percentage of plastic waste that is recycled
is low for three reasons. First, many plastics are
hard to isolate from other wastes because the many
different resins used to make them are often difficult
to identify, and some plastics are composites of different
resins. For example, a plastic ketchup bottle might
have as many as six different layers of plastics bonded
together. Most plastics also contain stabilizers and other
chemicals that must be removed before recycling.
Second, recovering individual plastic resins does not
yield much material because only small amounts of any
given resin are used in each product.
Third, the inflation-adjusted price of oil used to
produce petrochemicals for making plastic resins is
low enough to make the cost of virgin plastic resins
much lower than that of recycled resins. An exception
is PET (polyethylene terephthalate), used mostly
in plastic drink bottles. However, PET collected for recycling
must not have other plastics mixed with it; a
single PVC (polyvinyl chloride) bottle in a truckload of
PET can render it useless for recycling. Despite its economic
value, only about 20% of the PET used in plastic
containers in the United States is recycled. However,
in 2007, Coca-Cola announced a goal of reusing or recycling
100% of the PET bottles it sells in the United
States.
Progress is being made in the recycling of plastics
(Individuals Matter, above) and in the development of
more degradable bioplastics (Science Focus, at right).