Plastic pollution is the excessive accumulation of plastic products in the environment, adversely affecting wildlife, wildlife habitat and humans. Since plastics are inexpensive and durable, its production by humans is high. The chemical structure of most plastics renders them resistant to many natural processes of degradation, and as a result they are slow to degrade. These two factors together have led to a high accumulation of non-biodegradable plastic in the environment.
The annual global food production is around 3 billion tonnes, out of which about 1 billion tonnes is wasted and the rest is either consumed or bio-degraded in a few years' time. But as far as plastics are concerned, the world produces about 400 million tonnes of plastics every year. Between 1950 and 2018, an estimated 4.5 billion tonnes of plastic waste have been dumped on land and water bodies, including oceans. During the same period of 68 years, the world has burnt around 500 million tonnes of plastic, which produced toxic by-products, including many carcinogenic gases and other compounds, making this Earth a polluted and hazardous place. Plastics therefore endanger land, air and water and pose a serious threat to life itself.
Some researchers suggest that by 2050 there could be more plastic by weight than fish, in the oceans. Plastics can harm living organisms, particularly marine animals, either by mechanical effects such as entanglement in plastic objects, or problems related to ingestion of plastic waste, or through exposure to chemicals in plastics that interfere with their physiology. Humans are also affected by plastic pollution, through disruption of various hormonal mechanisms.
Plastic pollution has the potential to poison animals, which can then adversely affect human food supplies. The book, 'Introduction to Marine Biology' by Richard Turner et al, describes plastic pollution as being highly detrimental to large marine mammals, posing as the "single greatest threat" to them. Some marine species, such as sea turtles, were found to contain large quantities of plastic in their stomachs. When this occurs, the animal typically starves, because the plastic blocks the animal's digestive tract. Marine mammals sometimes become entangled in plastic products such as nets, which can harm or kill them.
Types of Plastic Debris
There are three major forms of plastic that contribute to plastic pollution: microplastics, mega-plastics and macro-plastics. Mega and micro plastics have accumulated in highest densities in the Northern Hemisphere, and are concentrated around urban centres and water fronts. They can be found off the coast of some islands because of currents carrying the debris. Both mega-plastics and macro-plastics are used in packaging, footwear, and other domestic items that have been washed off ships or discarded in landfills. Fishing-related items are more likely to be found around remote islands. These may also be referred to as micro-, meso-, and macro debris.
Micro-debris is plastic between 2 mm and 5 mm (millimetre) in size. Plastic debris that starts off as meso- or macro-debris can become micro-debris through degradation and collisions that break it down into smaller pieces. Micro-debris is more commonly referred to as nurdles. Nurdles are recycled to make new plastic items, but they easily end up released into the environment during production because of their small size. They often end up in ocean waters through rivers and streams. Micro-debris that come from cleaning and cosmetic products are also referred to as scrubbers. Because micro-debris and scrubbers are so small in size, filter-feeding organisms often consume them.
Plastic debris is categorised as macro-debris when it is larger than 20 mm. These include items such as plastic grocery bags. Macro-debris is often found in ocean waters, and can have a serious impact on native organisms. Fishing nets have been the prime pollutants. Even after they have been abandoned, they continue to trap marine organisms and other plastic debris. Eventually, these abandoned nets become too difficult to remove from the water because they become too heavy, having increased in weight upto 6 tonnes.
Decomposition of Plastic
Many kinds of plastics exist, depending on their precursors and the method for their polymerisation (a chemical reaction). Depending on their chemical composition, plastics and resins have varying properties related to contaminant absorption and adsorption. Polymer degradation takes much longer as a result of saline environments and the cooling effect of the sea. It is estimated that a foam plastic cup will take 50 years, a plastic beverage holder will take 400 years, a disposable nappy will take 450 years, and a fishing line will take 600 years to degrade.
Chlorinated plastic can release harmful chemicals into the surrounding soil, and then seep into groundwater or other surrounding water sources and also the ecosystem. This can cause serious harm to the species that drink the water. Landfill areas contain many different types of plastics. In these landfills, there are many micro-organisms which speed up the bio-degradation of plastics. These micro-organisms include such bacteria as pseudomonas, nylon-eating bacteria, and flavobacteria. The breakdown of biodegradable plastics releases methane, a very powerful greenhouse gas that contributes significantly to global warming.
In 2012, it was estimated that there were approximately 165 million tonnes of plastic pollution in the world's oceans. One type of plastic that is of concern in terms of ocean plastic pollution is nurdles. Nurdles are manufactured plastic pellets (a type of microplastic) used in the creation of plastic products and are often shipped as cargo. Many billions of nurdles are spilled into the oceans each year, and it has been estimated that globally, around 10% of beach litter consists of nurdles.
The toxins that are components of plastic include di-ethylhexyl phthalate, which is a toxic carcinogen, as well as lead, cadmium, and mercury. Plankton, fish, and ultimately the human race, through the food chain, ingest these highly toxic carcinogens and chemicals. Consuming the fish that contain these toxins can cause cancer, immune disorders, and birth defects.
A 2017 study found that 83% of tap water samples taken around the world contained plastic pollutants. This means that people may be ingesting between 3,000 and 4,000 microparticles of plastic from tap water per year.
Biodegradable and Degradable Plastics
The use of bio-degradable plastics has many advantages and disadvantages. Biodegradables are biopolymers that degrade in industrial composters. Biodegradables do not degrade as efficiently in domestic composters, and during this slower process, methane gas may be emitted.
There are also other types of degradable materials that are not considered to be biopolymers, because they are oil-based, similar to other conventional plastics. These plastics are made more degradable through the use of different additives, which help them degrade when exposed to UV rays or other physical stressors. Although biodegradable and degradable plastics have helped reduce plastic pollution, there are some drawbacks. One issue concerning both types of plastics is that they do not break down very efficiently in the natural environment. Therefore, degradable plastics that are oil-based may break down into smaller fractions, after which point, they do not degrade further.
Every year, June 5th is observed as World Environment Day to raise awareness and increase government action on the pressing issue. This year, India is the host to the World Environment Day and the theme is 'Beat Plastic Pollution' with focus on single-use or disposable plastics. The Minister of Environment, Forest and Climate Change of India, invited people to take care of their Green Social Responsibility and urged them to take up Green Good Deeds in everyday life.
The billions of items of plastic wastes choking our oceans, lakes, and rivers, and piling up on land is a real and growing threat to human health. They are absolute threats to plants and wildlife too. Plastic pollution can make human beings an endangered species in our own planet.
by Dr R. Jagannathan, Editorial Advisor