Causes of plastic pollution
100% of plastic pollution is attributable to humans. 100% human. At the heart of the problem is one of plastic’s most valued properties: its durability. Combined with the throwaway culture that has grown up around plastic products, this means that we are using materials that are designed to last, but for short-term purposes. About 50% of plastic is used for single-use disposable applications, such as packaging, agricultural films and disposable consumer items. The increasingly short lifetime of products that use plastic, especially electronic goods, means that more plastic waste is being produced in today’s upgrade-and-dispose culture. A key example of this is the mobile phone: its plastic components contain several toxic substances known to be harmful to human health.
Types of plastic pollution
Plastic waste can be categorised under a variety of approaches.
Plastic debris can be categorised as either primary or secondary. Primary plastics are in their original form when collected. Examples of these would be bottle caps, cigarette butts, and microbeads. Secondary plastics, on the other hand, account for smaller plastics that have resulted from the degradation of primary plastics.
Another commonly-used categorisation is to distinguish between pre- and post-consumer plastic waste. Pre-consumer plastic waste is produced during manufacturing or converting processes, while post-consumer plastic waste is produced after a product is consumed or used. Pre-consumer plastic waste often consists of small pellets that are used to make larger plastic objects.
At sea, plastic waste is often categorised into macro- (over 20mm diameter), meso- (5-20mm diameter) and micro- (under 5mm diameter) plastics.
Macroplastics can be further categorised according to type of object, for example, bottle, bag or lid.
Microplastics are a significant issue in plastic waste, partly because they are more difficult to monitor, and partly because they may have greater impacts at a chemical and physical level on ecosystems and human health, owing to their size and large volume-to-surface area ratio.
In the ocean as well as on land, plastics tend to fragment into smaller particles. This can be aided by the action of ultraviolet (UV) radiation, waves and wind. In landfills, acidity and chemicals can break down plastics. In the sea, water absorbs and scatters UV so plastics floating near the surface will break down more rapidly than those at depth. For those on the seabed, breakdown is significantly slower since there is no UV radiation and temperatures are colder.
Recent scientific reviews have raised the concept of nanoplastics. These are engineered plastic nanoparticles derived from post-consumer waste via degradation. Although they have not been quantified yet the reviews suggest there is little doubt that weathering of plastic can produce nanoscale particles, which could potentially be easily absorbed by phytoplankton and zooplankton. The potential to spread throughout the food chain then becomes a certainty – including humans.
How is plastic made?
Plastics are made from carbon-based compounds. The materials used in the production of plastics are natural products such as cellulose, coal, natural gas, salt and crucially, crude oil. Crude oil itself being a highly complex mix of thousands of different compounds.
The production of plastic begins with a distillation process in an oil refinery
The distillation process involves the separation of heavy crude oil into lighter groups called fractions. Each fraction is a mixture of hydrocarbon chains (chemical
compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules. One of these fractions, naphtha, is the crucial element for the production of
The two major processes used to produce plastics are called polymerisation and polycondensation, and they both require specific catalysts. In a polymerisation reactor, monomers like ethylene and propylene are linked together to form long polymers chains. Each polymer has its own properties, structure and size depending on the various types of basic monomers used.
There are many different types of plastics, and they can be grouped into two main polymer families:
- Thermoplastics (which soften on heating and then harden again on cooling)
- Thermosets (which never soften when they have been moulded)
Human activity driving plastic pollution
Sources of plastic waste are plentiful and the nature and extent of plastic polution varies considerably by region across the world. For example, the shipping and fisheries industries are significant contributors in the East Asian Seas region and the southern North Sea, whereas tourism is a major source of plastic pollution in the Mediterranean region.
Although it is important to try and determine sources of plastic waste for developing and monitoring prevention actions and policy, it should be remembered that the distinction between land-based and sea-based sources is irrelevant for prevention, as all plastic is produced on land. If we are to reduce overall amounts of plastic waste, the land is where the greatest efforts need to be made i.e. we need to tackle the root of the problem.
What drives the demand for plastic production? The following data was based on a 2008 study of EU countries plus Norway and Switzerland.
Building and construction: 6%
WEEE (waste electrical and electronic equipment): 5%
Domestic housewares, leisure,sports: 3%
Plastic waste on land
There is little information on the amounts, rates, fate or impacts of plastic waste on land, whereas there has been a major effort to quantify impacts on shorelines and sea.
On land, if waste is not recycled or recovered, it is mostly disposed of in landfill sites where, although not visible, it may still come to the surface as ‘debris’. In addition, the conditions within landfill may cause the chemicals contained within plastic to become more readily available to the environment This is a particular concern in developing countries where landfill management is not as closely monitored as in developed nations.
Plastic pollution from land to sea
It is currently estimated that 80% of plastic waste in the sea is from land-based sources.
The main landbased sources of marine plastic waste include storm water discharge, combined sewer overflows, tourism related litter, illegal dumping, industrial activities e.g. plastic resin pellets, losses from accidents and transport, and blowing from landfill sites.
The ocean-based sources tend to be commercial fishing, recreational boaters, merchant/military/ research vessels, losses from transport, offshore oil and gas platforms.
The final sting in the tail: plastic itself is bad enough but the plastic manufacturing process also introduces many more polluting chemicals into the mix.
These additives inclde:
Colourants: for coloured plastic parts.
Antioxidants: for plastic processing and outside application where weathering resistance is needed.
Foaming agents: for expanded polystyrene cups and building board and for polyurethane carpet underlayment.
Plasticisers: used in wire insulation, flooring, gutters, and some films.
Lubricants: used for making fibers.
Anti-stats: to reduce dust collection by static electricity attraction.
Antimicrobials: used for shower curtains and wall coverings.
Flame retardants: to improve the safety of wire and cable coverings and cultured marble.