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The Effects Of Microplastics In The Deep Sea

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Introduction

There is a large-scale accumulation of plastic waste in the marine environment, it is without a doubt a sink for microplastic build up. Plastics have been known to pollute the marine environments since the early 1970s. Nowadays, many everyday items are made up of plastics as they are cost effective, light but resistant and easy to manufacture. These characteristics make them appealing to use for a vast spectrum of biotechnological processes. This is the reason why plastic production and pollution has drastically increased the past few decades. Despite there being in increase in microplastic awareness in communities the past 10 years, it still represents a big threat as there is increasing evidence of its negative effects on the marine environment.

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Today this poses an increasing scientific concern due to the durability of plastic and their resistance to degradation. Due to this plastic debris travel substantial lengths before they settle and they accumulate every year from a growing quantity of sources. Plastics enter the marine environment due to their inconsistent disposal and it affects the marine biota unfavourably. Degradation of plastics causes them to brake into small fragments which are known as microplastics. A lot of microplastic particles are found to be of similar size to certain marine organisms, therefore microplastic ingestion has become quite common in a variety of invertebrates.

The international framework on the matter is complicated therefore to steer away from microplastic pollution it is essential take up bottom-up processes. What are microplastics and what effects do microplastics in the ocean have on many organisms and the environment? The development of this project will be answering this question, providing a definition for microplastics and how they are produced, including their chemical structures. It will also provide information on how these small pieces of plastic in the marine habitats affect the environment as a whole.

How Are Microplastics Created

The word plastic derives from the Latin word “plasticus” which means “capable of shaping or moulding”. Plastics are low cost materials presenting hundreds of different compounds that are based on polymers, which are very resistant, cost efficient and easy to produce. Polymers are materials made of multiple repeating units. Polymers are determined according to their chain-like conformation, which establishes their chemical and physical properties during and after manufacturing.

A big range of chemical additives are added into plastic polymers to provide particular properties, such as phthalates which are added to them to make them more durable, stable flexible and transparent. Phthalates are the most frequently used plasticizers and they are classified as either high or low, determined by their molecular weight. High phthalates comprise of those with 7 to 13 Carbon atoms in their chemical backbone, which makes them more durable. Low phthalates comprise of those with 3 to 6 Carbon atoms in their chemical backbone, which are frequently used in cosmetics, inks and medical devices. Certain addtives are designed to make the polymer more stable and less susceptible to degradation. The additives aren’t typically covalantly bonded to the polymer, which means is is probable for them to be leaching out of the plastics as they start to degrade and get into the marine habitat. Microplastics are small particles of plastic, which are smaller than 5mm.

They are classified in two main types, primary and secondary: Primary microplastics are made to be a small size and secondary microplastics are fragments of bigger plastic products, which suffer fragmentation which are often found in the marine environment (Barnes, 2010). An example of primary microplastics are microbeads, are extremely small fragments of plastic, smaller than 1mm which are added to many health and beauty products, for instance shampoos, toothpastes and facial cleansers. An increasing number of products are now using microbeads in body care products.

As for secondary microplastics, through photo-degradation, sunlight begins to oxidize the chemical structure or weathering from wind, waves cause plastics to break into really small fragments. All polymers are likely to degrade as time goes by, and the molecular mass and structure determines their speed of degradation. Many studies estimate that plastics can take up to several hundred years to biodegrade and others estimate it takes thousands of years. Plastics are polymers which are big chains which are sometimes three-dimensional networks of recurring organic units called monomers. Each polymer has a monomer, but they are all quite simple at that basic one-unit level, they can bond to one another on each side. Although in reality, the chains can occasionally be hundreds of thousand units long. To be able to make a polymer all you need is a molecule that can simply bond to another homogenous molecule at two points. Chemists want different things out their plastics, whether it’s them being strong, stretchy, colourful or transparent.

Monomers can be attached together in one of two ways: condensation polymerisation or addition polymerisation. Firstly, addition polymerisation has three fundamental steps, which are initiation, propagation and termination. Polystyrene and polyethylene are an example of this. Addition polymerisation is the continuous addition of alenekene monomers to eachother (Ouellette, 2015). As for condensation polymerisation, a little molecule is removed as the monomers join together. Some polyesters and nylon are an example of this. Condensation polymerisation is when two functional groups are joined together, for instance a carboxylic acid and an alcohol and creates another small molecule of water.

Furthermore the two main categories of plastics are thermoplastics and thermosets. Thermoplastics soften when they are heated, therefore can be re-shaped before they harden again as they cool down. Thermosets on the other hand cannot be re-shaped because they will decompose when heated rather than melt. They are produced by altering natural polymers, they are chemically cross linked throught a process which is referred to as curing. This process produces a very dense chemical structure that allows it to be rigid and brittle. Having said this, thermosets can’t be re-shaped therfore they become much more difficults to re-process than thermoplastics. Nonetheless these tend to have a much longer shelf life.

Many different types of thermoplastics exist, but the ones which are made with just 4 monomers; Styerene, propylene, ethylene and vinyl chloridec made up nearly 90% of thermoplastics manufactured in the mid 1900s (National Reasearch council, 1994). This is still true to this day. Popular thermoplastics and what they are usually used for are shown in the table above. Many of these products are single use plastics, which explains how plastic pollution is vastly increasing. Plastic is unfortunately not percieved as a valuable resource but rather as disposable. Plastic waste has been a cause of economic damage in certain countries as it decreases tourism. Cleaning plastic pollution from marine environments would require an extortianate amount of money. Poorer countries frequenty burn plastic for many reasons, some of which are cooking and to create heat. But this exposes their population to toxic emissons. Disposing of plastic this way frees dangerous gases, such as dioxin and furan (Giacovelli, 2018). Recent studies have found that 79% of all plastic waste now settles in dumps landfills or the environment and only 12% has been remanufactured and 9% has been recycled.

Although plastics are know to take a very long time to biodegrade there are a few processes behind the breakdown of polymers. These processes are:

  • Hydrolysis: Here, the plastic is stored in acidic or moist conditions, and chain scission may happen through hydrolysis of the main chain. This takes place in polymers with functional groups which are reactive to the effects of water (Kahar, 2017).
  • Mechanical Procedures: The polymer is dependent on mechanical change or stress that then causes an alteration in the polymer properties.
  • Photo-oxidative Methods: The soaking up of radiation by polymers, or their contaminants, which is caused by subjection to sunlight or big energy radiation may result in the severing of chemical bonds within polymers that results in photo-degradation. This is much more likely if the polymers contain some semi-conductive properties in the visible light region.
  • Thermo-oxidative Procedures: With very high temperatures. The polymer is heated and goes through oxidation in the primary chain of the polymer. Essentially, the backbone of the polymer gets chemically modified.
  • Additional Chemical procedures: For these processes, corrosive gases, liquids or chemicals are utilized to deteriorate the polymer. Pollutants of the atmosphere, and acids like sulfuric, Hydrochloric and nitric will strain and decompose the majority of polymers through oxidation and chain scission. Close to hydrolytic or oxidative procedures (Kahar, 2017).
  • Ultrasonic Methods: In this case the polymer goes through an ultrasonic environment, and its chains can vibrate at the frequency of the environment and can cleave and be dislodged.

Having said this the most secure method to decompose plastic is the biological one because it is the one that does not harm the environment, which would involve be tiny organisms called bacteria and fungi that play an important role in helping the degradation process. But it is not as straight forward as that as plastics have very strong bonds and their molecular weight is big, which is why they do not readily decompose naturally in the environment.

Microplastics in Oceans

Nearly 71% of our planet is water, which is why it is concerning when plastics pollution has been found in all marine environments. Microplastics are distributed in all of the five main compartments of the ocean: the shoreline, the surface, the water column, the seafloor and the biota. Which causes a big concern for the health of the marine environment (UNESCO, 2017).

Plastics have been known to pollute the marine environments since the early 1970s. Microplastics that are usually found in the oceans are polystyrene (PS), polyethylene (PE) and polypropylene (PP).

Polystyrene is an inexpensive hard plastic, used very commonly to make plastic cups, computer cases, TVs and kitchen appliances etc. It is produced by polymerization of the monomer styrene. The second most commonly manufactured polymer, after polyethylene. It is a transparent thermoplastic. Polystyrene is a hydrocarbon as it is composed simply of carbon and hydrogen atoms. In polystyrene each repeat unit has a big pendant group instead of one of the H’s.

Polystyrene Structure

Polyethylene is the simplest of all commercial polymers. Over 80 million tons of it are produced every year. A molecule of polyethylene is a long chain of carbon atoms with two hydrogen atoms attached to each carbon. In addition to the carbon backbone, only hydrogen atoms are used to obtain four covalent bonds per carbon atom. In addition, it is transparent and thermoplastic. Although it can be converted into a thermoset, which means it can change chemically during a curing process and cannot be melted down and re-formed. This is done by introducing cross links between those polymer chains. Polyethylene’s strength can also be varied by changing the size of the molecules.

Even though polyethylene ends in ene it is not an Alkene, because all the double bonds get broken to form new sigma bonds. It is a polimerised alkene but the molecule itself is an alkane. Polyethylene structure:

Polypropylene is produced by addition polymerization of Propene. Polypropylene an extremely useful polymer, it has two functions, both as a plastic and as a fibre. It is one of the most versatile polymers available. Like the previous polymers it is thermoplastic. Due to its outstanding properties it is suitable to replace different materials such as metals, glass and other polymers.

Polypropylene Structure

Microplastic pollution in the oceans has become of increasing concern the past few decades, this is due to an increase in plastic awareness due to it being portrayed in the media. What we see are shocking images of trash accumulating on the sea surface and coastlines and marine animals that are being suffocated by plastic bags, being caught in nets. Bur what is even more worrying is the pieces of plastic which cannot be seen by the naked eye, which are microplastics.

As previously stated, plastics are well suited for a variety of application due to their strong, cheap, diverse, light and generally transparent material. Traditional materials such as cartons, glass and metals are being replaced by low cost plastic packaging of equal if not higher quality design. These particles of plastic which range from just a few μm to 500μm are regularly found in sea water and represent a growing proportion of plastic litter. Persistent organic pollutants (POPs) that prevail globally in the oceans at very small concentrations are picked up by microplastics via partitioning. Due to the hydrophobic nature of POPs they it makes it easier for them to have a much higher concentration in the microplastic debris than that in the seawater. Following the contamination of these plastics their ingestion by many marine species allows the POPs to enter the food web (Andrady, 2011).

Plastic particles absorb hydrophobic POPs, which results in much higher concentrations than those in sea water which is nearby. Microplastics are more likely to absorb waterborne contaminants in comparison to meso/macroplastics due to its bigger surface area to volume ratio. During the production of polymers chemicals might be introduced to give it a big range of properties. Certain additives, plasticizers for instance have been known to cause health concerns, they are commonly used due to them being colourless and odourless esters that improve the elasticity of a material. One of the most evident benefits of plasticizers is it’s guarantee for good performance for up to five decades. But with recent studies, it has been discovered that certain types of plasticizers can interact with the hormone system of mammal (Koester, 2015).

The migration of additives in a polymer is dependent on several factors. Organic compounds are commonly used additives in polymers to enhance the properties of the emerging product. The freed additives into the environment is an undesirable outcome as the living organisms are vulnerable to the exposed additives. Polymers themselves have a 3-dimentional structure in which the additives are spread. Molecules of small size have been known to move out of a polymer by leaching onto an organism or into the water.

The degradation of plastic polymers is extremely slow due to their non polar structure and their big molecular weight. Therefore they build up the ocean and have a negative impact on the marine environment. Additionally the circumstances the polymer is open to plays a part in its breakdown. The speed in which polymers are brokendown by UV light (photodegradation) can hugely differ depending on their location. Throughout photodegradation, sunlight causes the chemical structure to oxidise, and that divides carbon, carbon-oxygen, carbon-clodrine and amide bonds in polymers. In water the photodegration of polymers takes much longer than in the air (Andrady, 2011). As the majority of plastic ends up in the marine environment, which means it becomes even more resistant to decomposition. The degradation of plastic items can differ quite a lot between one item and the other. For example, it can take 450 years for a plastic bottle or a disposable diaper to decompose, whereas a Styrofoam cup takes 50 years which is significantly less.

Two types of decomposition exist, biotic and abiotic. Abiotic decomposition is when a substance gets broken down as a result of a physical or chemical reaction. Those plastic polymers are resistant due to their non molar structure and big molecular weight. Which signifies that they are not susceptible to environmental degradation and this is common in plastics. Whereas biotic decomposition is when a substance gets broken down by living organisms. When it comes to plastics the atoms are joined together by strong links. Therefore, bacteria have difficulty breaking these links and the plastics do not deteriorate. This explains why plastics take so long to decompose and certain scientists believe that certain plastics never fully decompose but rather gradually break down into smaller fragments of plastic, which is one of the ways microplastics are born.

When synthetic materials or plastics get littered, they begin to break down into much smaller plastics and once they do, these small plastic particles will eventually make their way into the ocean (Hugh, 2018). These microplastics are so small, they are not picked up during water filtration. And many household products contribute to microplastics ending up in the marine environment, whether it’s small microbeads from toothpaste or shampoo that gets washed down the drain, or fibres from synthetic clothing that get washed into the environment. The deep sea is the most diverse habitat on the planet and microplastics are easily ingested due to their small size by many taxa, including fish, invertebrates, zooplankton and marine mammals. Contaminants that are contained in microplastics are easily transferred to marine animals after ingestion. Hundreds of marine species have been found to contain plastic. It is difficult for many marine species to differentiate these microplastics from their actual food. It also becomes virtually impossible not to ingest it as marine species are surrounded by it. This microplastic ingestion can lead to their undernourishment. It has also been proven that microplastics can store, transport and release toxic chemicals, especially when plastic is exposed to UV rays in water. Primary and low- trophic level organisms are the most vulnerable when it comes to microplastics ingestion. Following ingestion microplastics can be egested as faeces, be transferred to other tissues or taken up by the epithelial lining in the gut. This gravely affects the quality of life for the fauna (Diepens, 2018).

Coral reefs are also deeply affected by microplastic built up. This is concerning as coral reefs provide shelter for many aquatic organisms and provide protection to coastlines from harmful effects of storms and powerful waves. Moreover they are the main source of nitrogen and crucial nutrients for oceanic food chains and play an important role helping nitrogen and carbon fixing. They obtain their energy from photosynthesis by symbiotic algae inside their tissues, but they also obtain this energy from ingesting small organisms that live in the oceans, which often have previously ingested the microplastics, and this damages corals and affects their overall health. It is clear that microplastics within the marine environment have profound environmental consequences. Microplastics have shown an impact on coral reef growth, which slows noticeably when there is a high concentration of microplastics.

In addition seabirds are also affected by this marine pollution as they feed off of fish and inevitably pick up and swallow small fragments of plastic. Studies find that 90% of seabirds have pieces of plastic in their gut. Furthermore, larger marine animals are also affected by microplastic debris. 60.5% of sea turtles in Brazil are contaminated by microplastic build-up and their digestive track. And Also, whales are prone to microplastic ingest a big number of microplastics as they swim with their mouths open and take in large quantities of water that essentially contain small organisms. They then filter out the water, but the living organisms stay on the baleen along with the microplastics and are then swallowed. Because of this the plastics accumulate in the intestines and stomach which isn’t heathy for the whales. The factor most closely correlated with degradation varied between polymer types. This may be a result of the different functional groups within the polymer. The difference in polymer structure results in different labile functional groups.

And these microplastics make their way through the food chain and indirectly get ingested by humans once they consume seafood that has been exposed to these plastics. They are passed on from species to species. Due to the toxicity they can be hazardous to human health. Having said that humans are exposed to large quantities of plastic in their everyday life, whether it’s synthetic materials, or plastic food and beverage containers. There are certain species that vomit the solid parts of their diet, like gulls and cormorants. And this benefits them as plastic does not accrue in their gastro-intestinal tract in comparison to other seabirds that do not regurgitate their food. Research shows that the dangerous effect of microplastic ingestion by humans is that it can alter chromosomes, which could cause infertility and cancer.

Conclusion

Water makes up almost 3/4 of our planet, which contains five oceans and microplastics have been found in virtually all marine habitats, which include the deep sea, the seafloor, the sea surfaces and the plastic litter on the beaches. Therefore, it should not come as surprise that microplastic pollution in the oceanic environment affects our whole planet. Microplastics are created in one of two ways, they are either purposefully made to be Scientific research on this topic emphasize that every piece of plastic that is currently being produced ends up in the environment and in most cases it’s in the marine environment. Polymers are hardly ever used in their pure form and the vast majority contains additives. These additives get liberated and can create other marine pollutants, which causes harm to marine wildlife and habitats.

Marine organisms are undernourished, the growth of coral reefs is impaired but also other species that feed on seafood suffer the consequences. This devastating reality is due to the high resistance and durability of plastics, which take a tremendous amount of time to decompose, especially in water. We continue to dismiss these facts and keep producing plastic and ignore all the harm they are causing the environment. To be able to maintain the biodiversity of our oceans, actions need to be taken urgently.

14 May 2021

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