The problem of plastics Plastic is a polymeric material—that is, a material whose molecules are very large, often resembling long chains made up of a seemingly endless series of interconnected links. Natural polymers such as rubber and silk exist in abundance, but nature’s “plastics” have not been implicated in environmental pollution, because they do not persist in the environment. Today, however, the average consumer comes into daily contact with all kinds of man-made plastic materials that have been developed specifically to defeat natural decay processes—materials derived mainly from petroleum that can be molded, cast, spun, or applied as a coating. Since synthetic plastics are largely nonbiodegradable, they tend to persist in natural environments. Moreover, many lightweight, single-use plastic products and packaging materials, which account for approximately 50 percent of all plastics produced, are not deposited in containers for subsequent removal to landfills, recycling centres, or incinerators. Instead, they are improperly disposed of at or near the location where they end their usefulness to the consumer. Dropped on the ground, thrown out of a car window, heaped onto an already full rubbish bin, or inadvertently carried off by a gust of wind, they immediately begin to pollute the environment. Indeed, landscapes littered by plastic packaging have become common in many parts of the world. (Illegal dumping of plastic and overflowing of containment structures also play a role.) Studies from around the world have not shown any particular country or demographic group to be most responsible, though population centres generate the most litter. The causes and effects of plastic pollution are truly worldwide. According to the trade association PlasticsEurope, world plastic production grew from some 1.5 million tons in 1950 to an estimated 260 million tons in 2007. Compared with materials in common use in the first half of the 20th century, such as glass, paper, iron, and aluminum, plastics have a low recovery rate. That is, they are relatively inefficient to reuse as recycled scrap in the manufacturing process, due to significant processing difficulties such as a low melting point, which prevents contaminants from being driven off during heating and reprocessing. Most recycled plastics are subsidized below the cost of raw materials by various deposit schemes, or their recycling is simply mandated by government regulations. Recycling rates vary dramatically from country to country, with only northern European countries obtaining rates greater than 50 percent. In any case, recycling does not really address plastic pollution, since recycled plastic is “properly” disposed of, whereas plastic pollution comes from improper disposal. Plastic pollution in oceans and on land Since the ocean is downstream from nearly every terrestrial location, it is the receiving body for much of the plastic waste generated on land. It has been estimated that 6.4 million tons of debris end up in the world’s oceans every year and that some 60 to 80 percent of that debris, or 3.8 to 5 million tons, is improperly discarded plastic litter. Plastic pollution was first noticed in the ocean by scientists carrying out plankton studies in the late 1960s and early 1970s, and oceans and beaches still receive most of the attention of those studying and working to abate plastic pollution. Floating plastic waste has been shown to accumulate in five subtropical gyres that cover 40 percent of the world’s oceans. Located at Earth’s midlatitudes, these gyres include the North and South Pacific Subtropical Gyres, whose eastern “garbage patches” (zones with high concentrations of plastic waste circulating near the ocean surface) have garnered the attention of scientists and the media. The other gyres are the North and South Atlantic Subtropical Gyres and the Indian Ocean Subtropical Gyre. In the ocean, plastic pollution can kill marine mammals directly through entanglement in objects such as fishing gear, but it can also kill through ingestion, by being mistaken for food. Studies have found that all kinds of species, including small zooplankton, large cetaceans, most seabirds, and all marine turtles, readily ingest plastic bits and trash items such as cigarette lighters, plastic bags, and bottle caps. Sunlight and seawater embrittle plastic, and the eventual breakdown of larger objects makes it available to zooplankton and other small marine animals. In addition to being nonnutritive and indigestible, plastics have been shown to concentrate pollutants up to a million times their level in the surrounding seawater and then deliver them to the species that ingest them. In one study, levels of polychlorinated biphenyl (PCB), a lubricant and insulating material that is now widely banned, were shown to have increased significantly in the preen gland oil of streaked shearwaters (Calonectris leucomelas) after these seabirds had been fed plastic pellets culled from Tokyo Bay for only one week.
Posted on: Fri, 02 Aug 2013 08:55:49 +0000
Trending Topics
Recently Viewed Topics
© 2015