The debate concerning the harmful effects to the marine environment caused by plastics and micro-plastics, is gaining significant global momentum. This has resulted in some notable, legislated commitment to the reduction of plastic waste. For example: the UK government will ban all sales of single-use plastics, including plastic straws, from 2019; several Australian States have banned single-use plastic shopping bags; and the City of Seattle has banned the use of plastic drinking straws. The growing public concern about marine plastic pollution is likely to continue and cause further reductions in the use of single-use plastic consumables. The current focus of attention is on the marine environment and is, at times, driven by public sentiment rather than detailed scientific research. Consequently, it tends to under-emphasise the threat and damage associated with single-use plastics and micro-plastics in the terrestrial environment.
There is now a growing body of scientific knowledge about plastic and micro-plastic pollution in the marine environment. This research, although still incomplete, is driving the design and development of practical methods of combatting the environmental threat. Our understanding of the effects of single-use plastics and micro-plastics on land, however, is limited. How these pollutants enter the terrestrial environment, where they end up, the effects on ecosystems and possible second and third order effects in the food chain remain largely unknown.
The core components of most plastics are petroleum based. In manufacturing plastics in common use, chemicals are mixed with the raw petroleum to create plastic compounds used to make items like drinking straws, shopping bags and the water-proofing substance used in disposable coffee cups. The manufacturing process changes the petroleum-derived plastic from a biomaterial, whose cells would normally biodegrade and decay away, into a material unrecognized by the organisms that normally break down organic matter.
In many parts of the world, particularly in countries where waste reduction and management regimes are not robust or closely followed, waste is concentrated in landfill sites. Plastics dumped in landfill pose a risk, because they can create serious consequences for the health of people and animals that rely on water drawn from the under-lying water table. Evidence suggests that carcinogens and toxins slowly build-up in landfill. This is the result of plastics interacting with water and the chemicals produced when the surrounding litter breaks down, or when in contact with hydrocarbons. They can also come from rainwater affected by atmospheric pollutants. When these chemicals seep underground to reach the water table, groundwater quality can be severely degraded, to the extent that it is unfit for consumption.
Plastic waste can be transported in waterways, storm drains and associated infrastructure, where it can disrupt the hydraulic flow, resulting in blockages and flooding. In the built environment, infrastructure damage caused by plastics can be costly to repair and increases maintenance costs. Wind will also carry plastic waste from one place to another, increasing the accumulation of land litter. When plastics are burnt, intentionally or by accident, poisonous chemicals are released into the atmosphere. In 2008, the World Health Organization recognised airborne toxic pollutants as a contributing factor to 40 per cent of deaths in the western Pacific region. The traditional practice in that region of burning waste to reduce litter, is a major reason for the high death rate.
Single-use plastics can have a major effect on the terrestrial food chain. Plastic bags and food containers often carry food particles and scents that appeal to animals, attracting them to eat the plastic. The plastic becomes permanently lodged in the animals’ digestive tracts, blocking the passage of food and leading to death by starvation or infection. Birds and large mammals in particular, such as sheep, goats, cattle and even camels, are recorded as being found dead after consuming plastic bags. Additionally, birds use pieces of plastic in their nest building. In a nest, newly hatched chicks will peck away at pieces of plastic, which they may swallow. Ecosystems are further damaged when plastic litter piles up along the shores of lakes and inland water bodies, disrupting the nesting patterns of waterfowl. This will have flow-on effects on other animals in the food chain, such as small insects and frogs, which are a prime source of food for higher carnivores and reptiles inhabiting wetlands.
While much of the contemporary debate concerning the environmental effects of plastic pollution focuses on natural ecosystems, it is important to note that little is known about its effect on human health. Terrestrial plastic contaminants have the potential to readily enter the human food chain through agricultural livestock. There is a growing proliferation of single-use plastic waste particles, which make their way into cities and towns and the ecosystems that support the natural and agricultural environments. Recently reported evidence suggests that micro-plastic contamination is as ubiquitous on land and in freshwater as in the marine environment, but too little is known about its effects in both freshwater and terrestrial ecosystems.