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2 Theoretical Framework

2.1 Description of Plastic and Microplastic Marine Debris, Persistence and Interaction of

Chemical Characteristics of Plastic

Plastic is created from organic and inorganic raw materials which are usually obtained from oil, coal and natural gas. Plastic consists of long chain polymeric molecules, which make most of the plastics persistent. Depending on the monomers during the polymerization process, different types of plastic are produced. This process can lead to strong or weak hydrocarbon-bond creation. Polystyrene has a crystalline structure and is comprised of strong hydrocarbon-bonds. Whereas other plastics, such as polyethylene, consist of weaker hydrocarbon-bonds which appear like entangled strings as an amorphous structure.

Thermoplastics can repeatedly be thermally softened and hardened by cooling; those plastics can be remoulded and reused practically indefinitely. Those plastics are used for packaging, food containers and other household products. Thermoplastics which are heat resistant and more durable can be used in automobiles, machineries and electrical products.

Another group of plastic, called thermosetting plastics, harden permanently after being heated. Those have higher melting points and are used for high-heat resistant products.

(Goryska, 2009). Plastic is an inexpensive, lightweight, strong, durable and corrosion resistant material (Ivar do Sul & Costa, 2013). It is extremely stable (Shimao, 2001) and resistant to biodegradation (Mitchell et al., 2004). Most of the synthetic polymers are buoyant in water, for example PE and PP, whenever those particles are buoyant enough to float on seawater. Polymers which are denser than seawater, for example PVC, might settle.

Microbial films can develop on those submerged plastics and change their physiochemical properties (Ivar do Sul & Costa, 2013).

Microplastic

Microplastic is defined as small plastic particles conventionally assumed to range between 333 µm and 5 mm. Recent research shows that the size frequency of plastic debris is highly skewed towards smaller particles (Browne, Galloway, & Thompson, 2007). These small plastic particles can be found all around the world in high amounts, not only near highly industrialised or urban areas but also in remote and low industrialised places (Goryska, 2009).

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The first source of microplastic is fragmentation which takes place through chemical

weathering and mechanical erosion. The degradation process is more likely to take place on land, and not in the sea, due to a higher solar radiation and mechanical erosion. In the marine environment, fragmentation could take place through wave action and abrasion from sediment particles. Another source is in cleaning products where it is used as an abrasive scrubber. These make up the smallest plastic particles (Goryska, 2009). Microplastic is easily transported with sewage through the waste water treatment facilities where it enters the aquatic habitat (Goryska, 2009). Microscopic plastic debris, such as fragments or fibres, are widely spread in the marine environment and accumulates in the pelagic, demersal and benthic zones (Mitchell et al., 2004).

The Effects of Microplastic Pollution

There is very little information about the impacts of plastics on the marine environment. It is known that various turtles, seabirds and other marine mammals are affected by plastic litter. Microplastic can be found in mussels as well (Goryska, 2009) and has been detected in fish, probably taken up through their diet which had previously

accumulated plastic. Mussels and fish are food sources for humans, which pose a threat to human health (Goryska, 2009). Microplastics can be ingested by a variety of marine

organisms and could be transferred along the food web.

The effects of microplastic ingestion of marine organisms are divided into three categories:

- Physical clogging and damage of feeding appendages or the digestive tract - Leaching of plastic component chemicals into the organism after digestion - Ingestion and accumulation of adsorbed chemicals by the organism

Ingestion of microplastic that mimics natural food fails to provide nutrition proportionate to its weight or volume. It can lead to starvation due to false feeling of satiation and irritation of stomach lining. With that the individual fails to store fat necessary for migration and

reproduction. Moreover, thin packaging film has the potential to inhibit gas exchange in the gills which might interfere with O2 uptake and CO2 sequestration. (Moore, 2008)

Furthermore, there is a chance of plastic debris changing the composition of the sea floor which would interfere with inhabitants of the sediment. It also fills up and destroys nursery habitat with marine litter, so less new life is able to emerge (Moore, 2008).

Microplastic has the potential of toxicity due to additives and monomers (Setälä, Fleming-Lehtinen, & Lehtiniemi, 2013). It can be highly carcinogenic, reproducing abnormalities in humans, invertebrates and rodents (Goryska, 2009). Plastic can absorb hydrophobic

substances such as PAHs and PCBs which can threat the whole food chain because plastic

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is present in all sizes and depths of the ocean (Frias et al., 2010). PCB congeners for example are not only carcinogenic agents; they are also endocrine disrupters which can affect the immune, reproductive, nervous and endocrine system of animals (Frias et al., 2010).

When exposed to salts in water, polycarbonate might accelerate leaching of the bioactive Bisphenol-A monomer (Moore, 2008). All of these substances could impact the sea-surface micro-layer ecosystems (Frias et al., 2010).

Microplastic especially in fibre form poses threats to organisms that consume them as they can cause clogging in the digestive tract, become translocated to different tissues within the organism, and undergo accumulation (Mathalon & Hill, 2014).

Filter feeders may also take up contaminated particles and with that transport the pollutants upwards onto organisms in higher trophic levels. Chronic negative health effects resulting from ingestion of these organisms can also be experienced by humans. (Frias et al., 2010)

“However, the great majority of people during their lifetime are exposed to complex mixtures of organic compounds at low concentrations. Thus, long-term exposure may be more important in terms of overall public health than short-term exposure.”1

Existing Studies

As Figure 4 shows, research regarding microplastic pollution has already been

conducted worldwide, especially in industrial countries. A lot of studies have been carried out regarding the pollution of sediment and chemical pollution (Ivar do Sul & Costa, 2013).

Microplastics in species have been researched; some of these reports dealt with accumulation of the microplastic within an ecosystem as “Trophic level transfer of

microplastic: Mytilus edulis (L.) to Carcinus meanas (L.)” by Paul Farrell and Kathryn Nelson or “Accumulation and fragmentation of plastic debris in global environments” by David K. A.

Barnes et al. in 2009.

1Frias, J.P.L.; Sobral, P.; Ferreira, A:M.: Organic pollutants from two beaches of the Portuguese coast, 2010 , page 5,

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Figure 4 Microplastic Studies in the World (Ivar do Sul & Costa, 2013)

Environmental and Economic Impact and Health

Presently, the average Greek eats 26 kilograms of seafood per year and this is expected to increase by another kilo by 2030. Other Mediterranean countries show similar behaviour (France 32 kg/capita/year, Italy 26 kg/capita/year, Portugal 59 kg/capita/year and Spain 39 kg/capita/year) (Pierre Failler, 2007). Research showed that 90 percent of the samples from the Mediterranean Sea contain plastics. The movement of the plastic is fairly unknown but microplastic is available to every level of the food web from the primary producer to higher trophic levels. The impact on population levels as a result of ingestion of small plastic particles is undocumented but it is clear that microplastic pollution is threatening the Mediterranean Sea (Ivar do Sul & Costa, 2013). This is a result of being a semi-enclosed sea surrounded by highly industrialised and densely populated countries. Thus chemical pressure is high in the Mediterranean Sea. These chemical contaminants are causing

alteration to marine ecosystems impacting individuals, population, species and food webs by entering at different trophic levels (Cresson, et al., 2014).

Plastic usage increased from 1950 with 1.5 million tons to 245 million tons in 2008 (Rios, Jones, Moore, & Naravan, 2010). The production of plastic depletes a significant proportion of the world’s non-renewable resources. The plastic themselves have a limited durability and longevity and then are thrown away; this increases pressure on the resources. The plastic debris currently poses a significant hazard to wildlife (Krause, von Nordheim, & Brägen,

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2006). Based on the present trend, animals and humans are at risk due to microplastic pollution. Microplastic particles will continue their slow, intricate paths towards the bottom of the ocean and at some point become buried in sand or mud for centuries. Scientists need to find economic and logistical ways to remove this pollutant (Ivar do Sul & Costa, 2013).