Marine Litter
What is it?
Marine litter is defined as any persistent, manufactured or processed solid material that is discarded, disposed of or abandoned in marine and coastal environments. The main categories are plastic, paper, metal, textile, glass and rubber. Plastics are recognised as the most substantial pollutant in our oceans, accounting for 92% of all marine litter in our seas. Since their invention, plastics and their usage has been implemented across all aspects of human life. They have become essential to society.
Plastics save us fuel and reduce CO2 emissions by providing light materials that are used in car and plane construction.
Plastics contribute to high performing insulation material which consequently reduces energy consumption.
Plastics allow for storage and increased longevity of food, therefore enhancing food safety and security.
Plastics also enable storage of sterilised medical equipment and innovative development of medical procedures which ultimately saves lives.
The world's first fully synthetic plastic was invented in 1907, the problem of plastic waste therefore, is relatively new. Since then it is believed over 8000 million metric tonnes of plastic has been produced, from which only 9% has been recycled, 12% has been incinerated and the remaining 79% has ended up accumulating in our natural environment, either in landfill or dumped as waste.
Production rates of plastic are expected to double in the next few decades. Currently over 10 million tonnes of plastic enters our ocean annually and with these increasing production rates, it is therefore likely that plastic accumulation in our oceans will increase dramatically too. Marine plastic can be classified by their size into:
Macroplastics: Those over 5mm in size
Microplastics: Those between 1-5mm in size
Nanoplastics: Those less than 1mm in size
Plastics are also widely diverse in their characteristics, they can be grouped into five different categories: Foams, Fragments, Fibres, Sheets, Pellets.
Where does it come from?
Plastic in our ocean come from many different places. They have both land based and sea based sources.
Land based sources include poor waste disposal, stormwater run off either into rivers or straight into the ocean, flooding, industry by products (such as industrial pellets) and ineffective water treatment works.
Sea based sources include the direct dumping of waste and degradation of marine macroplastics through processes such as wind, weathering, UV radiation and wave action. This creates fragments and particles of microplastic and nanoplastic size.
What happens to it?
Macro, micro and nanoplastics become distributed across our oceans. Where plastic ends up in our oceans can separated into:
1) Where they end up within the ocean
2) Where they are distributed across the worlds oceans
Within the ocean
Within the ocean, plastics are distributed throughout the water column, on the seafloor and at the sea surface. They can also be found in coastal beach sediments and estuary river mouths. Plastic characteristics play an important role in their ocean distribution.
Those with lower densities float and are more likely to be found at the sea surface or somewhere in the water column.
Those with higher densities sink and are more likely to end up on the seafloor.
Other ecological processes such as biofouling affects ocean distribution. Biofouling is the accumulation of microorganisms, plants, algae or small animals on a materials surface. Common examples are what you find on the bottom of ships: algae, limpets and barnacles. These can similarly be seen on turtle shells and whales. When this bioaccumulation occurs on plastic particles it increases their weight and can cause them to sink even if they would normally float.
Across the world
Where plastics are found across the world is known as the global spatial distribution. Areas known to have input hotspots are found to have high concentrations of plastic in their coastal seas. Input hotspots are locations where high volumes of plastic enter the ocean in terms of:
1) Quantity of plastic pollutant
2) Number of plastic pollutant sources
3) Both
An, example of this is Hong Kong, a city previously reported to have some of the highest marine microplastic pollution amounts on record. China is classed globally as the biggest plastic producer yet 3/4 of their waste is unmanaged resulting in a huge unregulated input hotspot for marine plastic pollution.
Plastics also travel great distances across the world. Ocean currents, surface storms, winds and waves all contribute to moving plastic around the world. Specific circular ocean currents known as gyres are responsible for concentrating plastic in localised areas. The most notorious of these are known as the great Pacific garbage patches: an accumulation of marine litter in the North Pacific Ocean, one on the West side and one on the East. These garbage patches are trapped and contained by the ocean currents.
The combination of marine plastic sources, high quantity inputs and diverse distribution processes within the oceans have resulted in marine plastics now contaminating every marine environment. They are classed as “ubiquitous” across marine ecosystems, the consequence of which, is marine plastics can now come into contact with a huge variety of marine organisms and animals.
Recent studies have found animals have ingested plastic items mistaking them for food, they have become entangled in marine plastic (most frequently discarded fishing nets) and they have also been exposed to new toxins from manmade chemicals within the plastics themselves. These are known as ecological impacts and are of high concern due to their increasingly detrimental impacts on the environment that are both direct and indirect.
Where is it?
Understanding the complexity of measuring marine plastics and the lack of standardised method or units, gives an explanation as to why mapping the distribution of marine plastic is an almost impossible task.
This being said, the scientific method of a meta-analysis (reviewing data from multiple scientific publications) and reviewing literature can give a fairly good idea of where marine plastics are distributed across the world and can be presented to some extent on a distribution map.
Using all microplastic research published in 2017 and 2018, that reported the quantity of marine microplastics as the average “number of microplastic items per kilogram of sediment” as a unit, I was able to create this map:
The coloured circles represent the number of items of microplastic found in 1 kg of sand in that location.
This map also enables us to identify areas where there has been minimal research on microplastic pollution: particularly North and South America, parts of Asia, Africa and the Caribbean. It is possible that in some of these areas such as Africa, Southern Asia and South America the lack of research is due to the prioritisation of work effort and funding into combating socioeconomic issues. These continents host multiple developing countries with relative poverty and high rates of unemployment. It is therefore likely that ecological issues present little concern in comparison to human needs.
With regards to spatial distribution of marine plastic across the world, there is a lot of work to be done and a pressing need to standardise research to enable global collaboration and the opportunity to effectively tackle marine pollution worldwide.
How is it measured?
Measuring plastics is complicated. Macroplastics, microplastics and nanoplastics must all be measured separately. The method for sampling macroplastics which include plastics of great size will be widely different to the methods used to sample micro or even nanoplastics, whose size can be hard to see with the naked eye.
Measuring marine plastics should also be separated based on what area within the ocean is being studied. The methods of sampling plastic found on the seafloor, within the water column, on the sea surface or in beach sediments are vastly different due to the need for different approaches and equipment.
It is therefore incredibly hard to have a method to measure marine plastics as a whole, due to the need to isolate:
1) What plastics you are measuring
2) Where you want to measure them from
Problems
Because measuring marine plastic is so complicated, scientists have not yet agreed on a uniform method to measure any specific marine plastic in any specific area of the ocean. The majority of scientific research into marine plastic distribution across the world utilises widely differing methods and units in which to report findings.
As a result it is not very easy to draw any conclusions about which areas of world are more contaminated than others. Therefore, to understand the distribution of marine plastics across the world, similarities have to be found between scientist’s work. The more frequently a similarity is found, the more likely it is to be true and so the more confident we can be in the assumptions made from our findings.
A good example of this is in the Mediterranean Sea, multiple studies on all sized marine plastics in the Mediterranean have equally concluded:
There are many major city input hotspots
The Mediterranean is a closed sea compared to the open oceans and this results in high marine plastic accumulation
The East side is more contaminated in the West side due to currents within the Mediterranean sea
Even though the studies have all used widely differing methods, equipment, locations and units, the overall conclusions made are all in agreement. It can therefore be assumed with some degree of confidence that these conclusions are accurate.
A reviewing process is currently the best way we can hope to understand spatial distribution of marine plastics until a ground breaking global collaboration agreement on a uniform method successfully occurs. With such exponential increase in both plastic production and marine plastic pollution, it is crucial to standardise our research methods to improve accuracy and robustness of scientific findings. This will allow scientists to provide sufficient motivation for the government and public alike to make changes to benefit our oceans and reduce pollution.
How is it harmful?
How marine plastics are starting to affect the marine environment is actually widely unknown. While research into this is increasing, major hurdles exist: this primarily is the scientific complexity of plastic impacts and this is due to:
1) The vast number of methods by which marine plastics can cause harm
2) The thousands of different organisms and habitats they can affect
3) The dramatically different ways in which each species respond
As a result trying to quantify (put the value to) the threat that marine plastics pose is practically impossible.
There are three general areas in which scientists analyse how marine plastics are affecting our oceans health: entanglement, ingestion and exposure.
Entanglement
Entanglement of sea birds and marine animals in large plastic litter (nets, ropes, lines, buoys, bags and tarpaulins) has been documented since the early 1970s and the number of affected species is continuously increasing. The risk of entanglement for marine animals tends to be higher in areas that have high accumulated quantities of discarded fishing gear. Such places include subtropical gyres such as the East and West Northern Pacific garbage patches.
Entanglement also causes injury in growing animals. Ropes, netting and lines that are tangled around bodies and limbs cut into tissue as the animals continues to grow. These injuries can be gruesome and sometimes fatal, from the infection or size of the injury itself or from restricted movement resulting in starvation or predation.
On the whole, entanglement is highly detrimental to a wide diversity of animals and many species are seeing huge declines in population numbers as a direct effect of marine plastic entanglement.
Ingestion
Small sized plastics can be easily swallowed by numerous marine animals and are taken into the body: this is a process defined as ingestion. This is probably the most common way nanoplastics and microplastics come into contact with marine animals and usually occurs as the particles are mistaken for food or accidentally swallowed in the water along with their food.
The way in which an animal feeds has been found to have the most effect on how many plastic particles an animal will ingest, for example: shellfish such as oysters feed by filtering water through their bodies and this feeding mechanism has been found to result in high amounts of particle ingestion.
To any animal that has ingested plastic, the particles hold no nutritional value, yet they frequently take up a large proportion of the digestive system. These marine animals are consuming foreign, artificially manufactured objects and their bodies natural reaction is to try and remove it. This is done through the energetically costly process of egestion which not only removes the plastic but also eliminates a proportion of the animals much needed nutrients too. A rapidly growing list of species have been found to have ingested plastic, including many iconic animals such as seals, dolphins, whales, sharks, sea birds and sadly all marine species of turtle.
Exposure
While marine plastic entanglement and ingestion studies are currently dominating scientific studies, further research is developing to begin to understand the effects of plastic exposure. This is defined as the presence of plastic within a marine environment or within an organism itself.
Recent research has recognised that such exposure has many highly detrimental effects and our present understanding and knowledge is only scratching the surface. So far microplastic exposure has been found to cause physical, behavioural and toxicological effects.
Physical effects: The physical effects of exposure have been found in the form of an increased stress response leaving affected individuals more susceptible to sickness and infection.
Behavioural effects: Reduce swimming and movement is a behavioural effect of particle exposure and is found across numerous marine animals from vertebrates to invertebrates. Reduced movement influences an individual’s ability to survive by decreasing their ability to catch prey as well as increasing their chance of being predated upon.
Toxicological effects:
1) Plastics contain thousands of variations of chemical additives such as plasticizers and flame retardants. The combinations of these chemicals is what gives each type of plastic it's desirable characteristics such as flexibility, rigidity, hard wearing, nondegrading, the list is endless as are the combination of chemicals. As plastics breakdown and degrade in the ocean these chemicals escape through a process known as leaching. These chemicals leach into both the marine environment or into the bodies of those that have ingested plastic particles.
2) Marine plastics particles are also found to attract pollutants via a chemical attraction, this is the result of the composition of particles. These pollutants include heavy metals, PCBs and PAHs, all of which are known to be harmful to life. These are classed as adhered toxins.
3) Finally plastic particles themselves provide a new habitat within the ocean, one that can be utilised by pathogens: bacteria, viruses and fungi. These live on the surface of the plastics and therefore move across the ocean with them, allowing them to invade new marine environments and animals. The variety of toxicological impacts of marine plastics hold the potential to cause serious damage to ocean health.
The chemicals, toxins and pathogens have the ability to act synergistically (in combination), to cause significantly higher damage than if acting individually. The combined cumulative effect of these pollutants also decrease the affected organisms ability to cope with further environmental stress such as increased temperatures or noise pollution. Research has shown that marine plastics are lowering immunity and tolerance to these environmental stressors as well as providing new stressors such as toxins and pathogens.
In January 2018 the European Chemical Health Agency called for an urgent evaluation of the risks that marine plastics pose to both the environment and human health. The diverse and complex ways that marine plastics are threatening all oceans and the organisms within them provides a bleak outlook for the species already suffering from environmental change.
How does it affect humans?
Human health is likely to be detrimentally affected by marine plastics through what scientists call trophic transfer. Trophic transfer of marine plastic is where animals at the bottom of the food chain (at a low trophic level) ingest plastic. This animal is then ingested by a predator that is higher up the food chain (at a higher trophic level) and as a result the predator has indirectly ingested microplastic.
Scientists are becoming increasingly concerned as nanoplastics (less than 1mm in size) have recently been found to move easily across the gut lining and move into the cells and tissues of an organism.
This has been found to have occurred in a large range of different animals and it is therefore very plausible to suggest that this is not just isolated to marine animals but could well be occurring in human bodies too.
A UK study found 40 - 60% of marine plastic particles found within mussels from Wales, Scotland and England waters, as well as imported supermarket mussels were of a size small enough to be translocated from the human gut into tissue cells.
A European study estimated the average seafood consumer could ingest up to 11,000 particles a year from shellfish alone. With increasing exposure of human populations to marine plastics occurring through processes such as trophic transfer, it is becoming more acceptable to think that we may begin to exhibit some of the detrimental exposure effects demonstrated so far in marine organisms.
Can it be stopped?
One huge problem faced by governments, scientists and the general public across the world is the fact marine plastics arise from multiple untraceable sources and once within the ocean, micro and nanoplastics especially are impossible to remove. It is therefore much more effective to target the source of the input instead, yet this is easier said that done. Across the world there are widely varying standards of waste management and an international standardisation of waste management and recycling is not feasible.
Significantly more scientific research needs to be undertaken to identify and assess the most effective ways to mitigate marine plastic pollution and litter.
What has been done?
Public education is a powerful tool that is key to driving positive change. Public awareness has resulted in improved waste management and the banning of plastic production in locations all over the world. Documentaries, films, podcasts and websites targeted to provide scientific education are become more easy to access and increasingly popular.
In 2017, Sir David Attenborough captured the publics hearts and minds with his documentary Blue Planet II. The final episode focused on the impacts of marine microplastics and reached over 37 million people in the UK alone. 62% of the surveyed audience stated they wanted to make changes to their daily life to help reduce plastic impact in our oceans. On top of this, in 2018 the Collins dictionary announced the word of the year to be “single-use” in reference to single use plastics.
The last few years have shown that increased public awareness and support is successfully driving positive change alongside scientific research and subsequent understanding. The worldwide public movement to ban the production and use of cosmetic microbeads to benefit our oceans, is a strong example of how public opinion and the demand of the public can help to drive positive environmental change. The UK, USA, Canada, France, New Zealand, Sweden and Taiwan have all now banned microbeads from rinse off cosmetics.
What can I do?
As previous public movements in driving positive change have proved to be both successful and powerful, one of the most important things that you can do as individual is to educate yourself, which, if you’ve made it to this page, you’ve already taken a step in the right direction. There is such increasingly accessible information across social media platforms, websites, podcasts and within film and tv, that a little computer browsing is likely to present you with multiple websites and articles on ocean pollution education. The best place to start, is on this very website.
To actively contribute to positive environmental change on a day to day basis, one of the best ways is to implement “reduce”, “reuse” and ”recycle”.
Reduce: Plastic alternatives such as glass, metal, paper, carboard, fabric and even compostable materials are becoming more widely available and positively looked upon. Choosing plastic free items or plastic alternative items, especially when it comes to supermarket shopping is one of the most positive impacts we can have as individuals: loose vegetables, glass jars and metal tins are just a suggestion.
Reuse: Information regarding reusing plastic items is increasing with suggestions of using milk bottles as seed planters, plastic peanut butter jars for snack storage or even using a mixture of general single use plastics for DIY crafts or art.
Recycle: The most important part of recycling is to correctly group the recycling according to the local councils requirements.
Most places around the country are unable to recycle black plastic: So any food from supermarkets (eg meats, fish, ready meals) that are contained in black plastic is unable to be recycled.
Dirty plastic also cannot be recycled. In fact any recyclable item (glass/metal/plastic) cannot be recycled if it is dirty: E.g dirty milk bottle, juice bottles, food packaging, pasta sauce jar, baked bean tins etc.
Failing to clean recyclable items and putting them in the wrong recycling groups are classic examples of waste mismanagement and part of the reason why plastic that could be recycled ends up in normal rubbish and normal rubbish can then end up in the ocean. We need to better our recycling habits and recycle properly