A polymer is a chemical which is characterised by having extremely long molecules. This tends to give polymers useful properties such as flexibility and elasticity. The most common polymers are the materials generically referred to as plastics and these are wonderful in many ways. They are inexpensive, durable and versatile and we use them for an endless variety of applications, from polythene shopping bags to polyester clothing. However, in several ways, polymers also have a significant environmental impact.
Polymers are made from monomers; smaller chemical compounds which are linked together to form longer molecules. Polythene, for example, is made by reacting the simple molecule ethylene (CH2CH2) such that it joins to itself repeatedly. The majority of these monomers are derived from petrochemicals. In fact, about 4 per cent of the oil produced worldwide goes to making polymers. This use of a substantial quantity of a precious non-renewable resource is one environmental consequence of plastics.
Since most polymers are not "natural" but rather synthetic, they are generally not biodegradable. Many plastics also do not readily break down due to natural forces, such as high temperatures or sunlight. In some ways, this resilience is a positive aspect of plastics since it enables us to make durable, long lasting polymer items, but when plastics are thrown away, they create significant problems by piling up in landfills. Approximately one quarter of all domestic trash in landfill sites is composed of various polymers.
The manufacture of plastics often involves the use of toxic or environmentally harmful chemicals. Until relatively recently, for example, the manufacture of polystyrene foam involved the application of chlorofluorocarbons, which are powerful ozone-depleting compounds. Traces of the chemical bisphenol A in common plastics such as polycarbonate water bottles has also caused concern since this compound has been linked to potential health problems. Phthalates, commonly added to some polymers to improve tensile properties, have been flagged as hormone disrupters in humans.
Plastics which are dispersed into the natural environment can cause many problems for wildlife who interact with them. Almost 200 species of animals have been found to have ingested plastic. This leads to serious health hazards such as clogged digestive systems in the animals and also in some cases illness due to toxic chemicals leached out of the plastics. Other animals become physically entangled in plastic debris and are unable to swim, fly or eat.