Article – Microplastics

Microplastics Dr Stephanie Matthews

What is it?  

How many pieces of plastic have you swallowed today? Does it matter?

Charles Darwin (1809-1882) lived in a world where plastic did not exist. It hadn’t been invented yet. Today, the estimate is that for every man woman and child on the planet, there is more than a ton of plastic. What does a ton of plastic look like? It depends on the density, ranging from feather lite polystyrene to hard PVC. An average ton of plastic would be perhaps 20 black bags of waste. This is the plastic we can see, but what about the plastic we can’t see because it is too small. 

All plastic originates from crude oil. By a combination of polymerisation and condensation, the carbon molecules in the oil are transformed into different types of plastic. (See table) Plastic never goes away, but it can ‘disappear’ because it gets broken down into smaller and smaller pieces, mainly in the oceans. When it gets to less than 5mm in diameter it is defined as Microplastic, but it is often much smaller than this. For comparison, a grain of rice is about 5mm, a salt crystal is 15 times less than this at 0.3mm. A human hair is about 0.1mm diameter. When does plastic become invisible to the human eye, or a light microscope? These very small pieces are called nanoplastics.

There are different ways of classifying microplastics. One way is to ask: Were the plastics made to be this way? In this case they are primary microplastic. If the small pieces derive from breakdown of bigger pieces, eg plastic bottles, then they are secondary.

Primary microplastics include nurdles, Micro-beads and particles made to use in air blasting cleaning. The plastics industry make billions of tiny nurdles  each year which are 1-5mm diameter little lumps of plastic. These are used as the starting point for almost all manufactured plastics, such as bottles and bags. Nurdles hit the headlines in 2017(1) when a shipping container spilt about 2 billion of these into the sea in South Africa. Nurdles now account for a significant amount of beach and ocean plastic pollution.

Designer Microbeads, developed in the 1980’s are little bits of plastic made specially for the cosmetic industry. These are up to 1mm in diameter and are used in toothpastes, exfoliating soaps and scrubs.

Secondary microplastic, from the breakup of ‘big’ plastic mainly happens in the oceans under the influence of light, wave motion and oxidation. The bits of plastic get smaller and smaller but they are still plastic and instead of forming a garbage patch, they produce a sort of plastic soup.

Microplastic fibres don’t fit neatly into either the primary or secondary category. The fibres are deliberately made this size, so are primary, but are then manufactured into clothing, fishing nets and road tyres. Many fibres are released into the environment during this process. But the fibres also come off the finished product, so are secondary. It has been estimated that about 700,000 fibres are released with each washing machine load wash.(2) The worst offenders are thought to be the fleece type materials. (3)

But primary or secondary, does it matter? Microplastic is everywhere: In the sea, rivers, the air, dust, in our food, and the  global microplastic load is increasing daily, and it is ‘invisible’ to us but tasty delicacies for marine and freshwater animals.(4, 5)

Biodegradable plastic – a new dangerous source of microplastic

Crude oil, as seen after oil spills at sea, will biodegrade. Unfortunately, once the oil has been turned into plastics, and purposely designed to be indestructible, biological systems don’t recognise them, they won’t biodegrade and can’t be digested.

If that is the case, why is some plastic called ‘biodegradable’? Other confusing terms are eco plastic, natural synthetic, recyclable,  renewable,  sustainable, natural plastic, and oxo-biodegradable, disposable, renewable degradable, compostable. Stop! 

These jargon terms are springing up in clever marketing departments to sell products without recourse to accurate definition. Some claims are true but are being swamped in the mire of confusion. 

If a substance biodegrades, it’s not plastic. In fact, it may turn out to be worse than obvious plastic as it could make people lazy about usage and disposal. It will also be a source of microplastic, or in this case even smaller pieces –  nano plastics.

The misnamed ‘Biodegradable plastic’ is made up of the synthetic plastic polymers and starch like polymers. In the right conditions, the starch like parts will decompose leaving the plastic bits which are are synthetic polymers, styrene monomer, dimer and trimer, and these end up in the oceans.(7)

If a substance does genuinely fully biodegrade, make up another word. Plasti-gone? Ecoplast? Plastaway? But don’t call it plastic. And specify the conditions under which it will biodegrade. (8)

So have you eaten any microplastic today?

It is highly likely that the answer is yes. A study, (9) albeit quite a small study, found microplastic in the poo of everyone tested, on average about 1,000 bits of plastic a day. The study is very small and needs to be repeated but throws up many questions. Where did the plastics come from? Was the plastic in the food, packaging or was it airborne and land on the food before it was eaten? Do the plastics stay in the gut and just get pushed out again in the poo? Do they escape from the gut into the blood stream or lymphatic system and get to other organs? Do they cause any damage? Can plastic be inhaled?

Microplastics have been found in bottled water, beer , table salt and seafood (10, 11). In the bottled water, 93% of the bottles contained particles at a concentration of about 10 particles per litre which were around 0.1mm diameter, but about 350 particles per litre which were much smaller. Some bottles contained 10,000 particles. The International Bottled Water Association took issue with the findings, saying they were not peer-reviewed and not based on sound science. 

In studies on animals, the highest concentrations of microplastics were found in the stomach and intestines, but smaller amounts have also been detected in blood, lymph and the liver.

If you have eaten any microplastic, can it harm you?

The answer simple – it is not known. But it is very important to find out, and as soon as possible. 

There are three main possible ways that the microplastic could harm humans directly.  The first is that the tiny particles and fibres, sometimes five times thinner than a human hair, could get to places they shouldn’t be after ingestion or inhalation. If they get into the blood stream or the lung, they could then lodge in other organs and cause reactions like inflammation, or disrupt the immune system. 

The second way microplastics can harm is due to the baggage they are carrying. Microplastics are not the only manmade things floating around in the water. There are also organic chemicals which were made as pesticides, herbicides, dyes, and many other uses. These  organic molecules also persist in the environment, typically up to 20 years, and have been given the name ‘POPS” or Persistent Organic Pollutants. Because of the chemistry of microplastics, the POPS get absorbed into, and stick onto, the microplastics. The smaller the plastic particle, relatively the more POP it can hold. The POPS are toxic, after all, many were invented to kill insects and plants. The result is that the plastics attract the other polluting chemicals to them, acting like sponges, thus concentrating the toxic chemicals before they are eaten by the marine animals. By sticking to microplastics, the POPS can reach a million times more concentrated than in the surrounding water. Potentially hazardous chemicals, used in the manufacture the plastic can also leach out of the microplastic.

Additives to plastics

List of POPS  



fluorinated substances like perfluoroalkylates, 

HCH or hexachlorocyclohexane, 

PCB’s or Polychorinated biphenyls

A third way that microplastic can be directly dangerous is because bacteria, known to be harmful to humans, eg Vibrio, which can cause severe gastroenteritis and septicaemia, hitch a ride on microplastic particles in the oceans. (12) Vibrio infections are most often associated with eating raw shellfish and ingestion of the contaminated microplastics can lead to infection in the person eating the shellfish. 

We don’t know if microplastics directly harm humans,  and we can’t ask humans to eat microplastics because it would not be ethical, so it is a difficult subject to study. There is evidence however that microplastics and their hitch hikers can harm animals. 

Experiments show that microplastics damage marine animals as well as turtles and birds. They can block digestive tracts, diminish the urge to eat, and alter feeding behaviour, all of which reduce growth and reproductive output. The fish that had ingested the treated plastic suffered liver damage and were less able to cope with drugs, pesticides, and other pollutants. In birds, the ingestion of plastic has been found to affect the villi lining the gut and disrupt iron absorption. Oysters exposed to tiny pieces of polystyrene—the stuff of take-out food containers—produce fewer eggs and less motile sperm.

The styrene monomers and polymers from the misnamed ‘biodegradable’ plastic are not found in naturally in Nature, and disturbingly, there is a possibility that some have been shown to cause cancer, and have been found in seawater around the world at up to 150 parts per million. 

The chemicals associated with the microplastics, such as  the persistent Organic Pollutants (POPS) and  Bisphenol A, are known to affect hormones. There are disturbing links to low sperm count, miscarriage, heart disease and diabetes and breast cancer. (ref 14)

A particular worry is the research that showed the tiny fibres crossed into the brain in fish and caused reduced feeding and premature death. (ref 15)

What can be done?  

Consumer power

The plastic we can see, and the plastic that is ‘invisible’  is having major impacts on our health and food security. Already individuals and governments are taking action. Defeatist critics are saying such actions are too late and inadequate to deal with a problem that has reached epic proportions. 

It’s time to prove the critics wrong.

Reference list

  1. “Nurdles KZN, SA. Project Duration: Long Term”. Coast KZN. 2019

2. Release of synthetic microplastic fibres from domestic washing machines: Effects of fabric type and washing. Napper I.E. and Thompson R.C. Marine Pollution Bulletin vol 112, Nov 2016, pp 39-45

3. Micropollution from textiles: A literature review. Henry B. Et al. SIFO Project report no. 1-2018

4. Microplastic ingestion by riverine macroinvertebrates. Windsor F.M. et al Science of the total environment. Vol 646, 2019, pp 68-74.

5. Plastic microfibre ingestion by deep-sea organisms    M. L. Taylor et al ,   ScientificReports6,  Articlenumber:33997(2016) 

6. Link to page on TYD site

7.  A systematic review of epidemiologic studies of styrene and cancer (2018)

James J. Collins & Elizabeth Delzell 

8. how things biodegrade

9.  Duncombe, J. (2018), Microplastics found in human stool, Eos, 99,

10. Kosuth, M., S. A. Mason, and E. V. Wattenberg (2018). Anthropogenic contamination of tap water, beer, and sea salt. PLOS One, 

11. Liebezeit G. and E. Liebezeit (2014) Synthetic particles as contaminants in German beers. Food Additives & Contaminants, 31, 1574-157

12.  Dangerous hitchhikers? Evidence for potentially pathogenic Vibrio spp. on microplastic particles. Inga V. Kirstein et al, Marine Environmental Research, 2016, 

13. Damstra, T. (2002). Potential Effects of Certain Persistent Organic Pollutants and Endocrine Disrupting Chemicals on Health of Children. Clinical Toxicology. 40(4), 457–465.

14. Vandenberg L.N. et al (2012) Hormones and endocrine disrupting chemicals: low dose effects and non monotonic dose responses. Endocrine Reviews 33(3): 378-455

SOURCES, FATE AND EFFECTS OF MICROPLASTICS IN THE MARINE ENVIRONMENT: PART TWO OF A GLOBAL ASSESSMENT  A report to inform the Second United Nations Environment Assembly  GESAMP Working Group 40 2nd phase ISSN: 1020-4873 

Microplastics as contaminants in the marine environment: A review

15. Brain damage and behavioural disorders in fish induced by plastic nanoparticles delivered through the food chain. Mattsson K. Et al. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-10813-0

16. This bag is 100% biodegradable. Alex Gray, 4th May, World Economic Forum.


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