Eco-Friendly Gifts Blog: What Happens To Plastic In The Ocean?
With an estimated 'rubbish truck full' of waste entering the ocean every minute, marine plastic pollution is a crisis that cannot be ignored.
A contributing factor to the overwhelming scale of plastic pollution in the aquatic environment, is the fact that most of the plastic does not readily biodegrade.
In this blog, we are going to look at what happens to plastic in the ocean, and how it affects the marine environment.
What Is Plastic?
Plastic is quite a misunderstood material, so let's go into a bit of depth about what exactly 'plastic' is.
First of all, 'plastic' is not one material. There are many different types of plastic, ranging in base sources and characteristics.
'Plastic' as most of us know it, is referring to 'conventional plastic'.
These plastics are produced from fossil fuels, and do not have the ability to biodegrade.
Common examples of conventional plastics included PET (polyethylene terephthalate), HDPE (high density polyethylene) and PP (polypropylene).
Plastic materials are made from polymers, which are long chains of repeating molecular sequences, known as monomers.
In the example of polypropylene, the monomer is propylene.
Through the process of polymerisation, the propylene monomers bond together to form polypropylene.
Plastic In The Ocean
Because there is a lack of efficient systematic processes available globally to deal with plastic waste, much of it is ending up in the natural environment.
In the marine environment, wildlife populations are being harmed by plastic debris, primarily through ingesting plastic waste floating on the ocean surface.
When conventional plastics enter the natural environment, they degrade very slowly over time.
In the marine environment, temperatures are not high, and are usually ambient. Therefore, the most common mechanisms for non biodegradable plastics to degrade are thermal degradation, photo degradation and hydrolysis.
There is not one universal mechanism for 'plastic' to break down from, because the molecular structures are unique to each type of polymer.
To give a range of different polymers, and how they break down in the marine environment, we have selected three different plastics: PET, PE and PLA.
Polyethylene Terephthalate, in the ambient temperatures present in the natural marine environment, will primarily degrade via photodegradation and hydrolysis.
Thermal degradation will still continue to take place, but at a slow rate due to the ambient temperature.
There is a difference between how plastics degrade on the ocean surface, and in the ocean depths.
The main reason for this difference is the lack of UV light on the ocean floor.
Because of this lack of UV light, photo degradation will not take place. Instead, hydrolysis and thermal degradation will continue to occur.
Because temperatures are, on average, lower on the ocean floor compared to the ocean surface, it can be expected that the rate at which thermal degradation occurs will also decrease.
Onto the next plastic: polyethylene.
We are talking about both high density and low density polyethylene, as they roughly respond to the same external factors that bring about degradation.
PE will degrade in the natural environment, but extremely slowly.
PE will only break down via thermal degradation, at appreciable rates, if sunlight is present. This is assuming that temperatures are less than 100 degrees celsius, which is a fairly safe assumption to make.
In situations where there is both no sunlight, and no oxygen, then PE will be unlikely to break down via thermal degradation.
This is due to the lack of sunlight and oxygen meaning the necessary temperature to degrade PE anaerobically will have to equal, or be in excess of, 350 degrees celsius.
As well as the plastic polymers themselves, additives that are produced to give the plastic material different characteristics, also can enter the natural environment. Many additives can leach from the plastic, as a result of not being chemically bonded to the plastic polymers.
PLA is a bioplastic, which can biodegrade, be industrially composted, as well as being produced from renewable resources.
Polylactic acid, similar to PET, will degrade first by thermal degradation, photo degradation and hydrolysis.
PLA can degrade without oxygen present, but temperatures will need to be far higher than what's found in the natural environment (at least 230 degrees celsius).
Because hydrolysis of PLA starts to occur at around 30 degrees celsius, it is unlikely for hydrolysis to be the dominant method of degradation.
Instead, photo degradation is the most likely way for PLA to break down in the natural marine environment.
It is possible for conventional plastics to biodegrade, but it is still a field that is poorly understood, with more research needed in order to understand more. Below is a list of microorganisms that can biodegrade certain types of plastic.
Biodegradation of conventional plastics is extremely slow, and it is by no means guaranteed to happen in the natural environment, with regards to quick biodegradation times.
When conventional plastics degrade, they break down into smaller and smaller pieces of plastic, as opposed to natural components such as CO2, biomass and water.
Microplastics are formed, and then nanoplastics after that.
Biodegradable plastics such as PHA polymers do have the potential to biodegrade.
However, just because the potential is there, does not mean that all of the PHA material will biodegrade. Instead, some of the material could be broken down the by abiotic methods previously mentioned.
It has been found that nanoplastics formed from PHA still have a negative effect on the microorganisms local to the environment of the degrading PHA.
This shows the importance of having large scale systematic processes to ensure that no plastic, or any waste for that matter, ends up in the natural environment.
Large scale processes such as industrial composting are great examples of what should be taking place.
Microplastics can be primary or secondary.
Primary microplastics were created below the maximum size of 5 mm in all dimensions, whereas secondary microplastics have formed as a result of larger pieces of plastic degrading.
A common source of microplastics entering the natural marine environment is from washing clothes. Many items of clothing internationally are produced from polyester, a category of plastic polymers.
When clothes are washed, the polyester microfibers in the clothing are released into the water system. From there, it is easy for the microplastic particles to make their way into the natural marine environment.
When microplastics, primary or secondary, enter the natural marine environment, they have the potential to enter the marine food chain at the lower trophic levels.
Organisms such as zooplankton ingest the microplastics, which are then ingested by it's predator on the next highest trophic level. This process continues all the way up the food chain, and that includes us.
We are, in effect, eating our own plastic waste.
Health Defects From Microplastics
Microplastics have the potential to accumulate in the body, which has prompted studies to be carried out focusing on the effects microplastics have on health.
It was found that immune cells that come into contact with microplastics, die three times faster than immune cells that did not come into contact with microplastics.
This could lead to people becoming sick from having their immune systems compromised by microplastics.
Nanoplastics are smaller than microplastics, with a maximum size of 100 nanometers (There are 1,000,000,000 nanometers in a meter).
Nanoplastic particles are so small that they have the potential to accumulate in the bloodstream, vital organs as well as the blood-brain barrier.
It has been studied that organisms ingesting nanoplastics actually alter their behaviour. This is thought to be because of nanoplastics passing through the blood brain barrier, and influencing brain activity to the point of behaviour change.
On the smallest levels, zooplankton were fed nanoplastic particles. 50% of these zooplankton died as a result.
The zooplankton that survived were then fed to carp. These carp changed their behaviour in the ways of swimming slower, losing more weight than normal as well as exploring less of their environment.
These carp were then studied, and it was found that nanoplastics had built up in the brain, and as a result, changed the carps behaviour.
Gyres And Plastic Pollution
Gyres are large rotating currents in our oceans.
There are five of them, with the most famous arguably being the North Pacific Gyre, due to it containing the Great Pacific Garbage Patch.
As a result of the circular currents of the gyres, plastic waste accumulates at the centre of each circular current.
The great pacific garbage patch is not some huge pile of oceanic plastic comparable to a massive floating landfill site.
Much of the plastic in the north pacific gyre is not visible on the surface, due to a large percentage of the garbage patch being made up of microplastics.
Persistent Organic Pollutants
It is not just the plastic polymers themselves that have a negative effect on the environment, it is what the plastic carries.
Hydrophobic persistent organic pollutants are attracted to plastic debris, due to it being a solid surface. This means that POPs have the potential to accumulate on plastic debris, and thrive.
As well as attracting persistent organic pollutants, plastic also has the potential to carry pathogens.
When plastic debris comes into contact with coral reefs, it has the potential to abrade the skin of the coral.
When this happens, the pathogens being carried on the plastic can enter the reef, spreading disease and slowly killing the reef from the inside out.
A study was carried out, which showed that coral reefs that had come into contact with plastic had an 89% chance of being diseased, compared to just 4% of reefs that had not come into contact with plastic.
Plastic In The Ocean
In conclusion, we can see that there are many possible journeys that plastic can take when it arrives in the natural marine environment.
Through ingestion, both microplastics and macroplastics can have detrimental effects on the health of marine organisms, large and small.
In order to combat oceanic plastic pollution, there must be immediate action undertaken by governments internationally.
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