Microplastics are very small plastic particles generally less than 5 mm in size. Some people also distinguish microplastics from even smaller plastics, termed nanoplastics, that are less than one-thousandth of a millimetre wide.
What are microplastics?
Primary microplastics are small plastic particles manufactured for specific uses, for example, microbeads used in personal care products such as facial cleansers, toothpaste and cosmetics. Microplastics are sometimes added to these products to replace traditional natural ingredients such as pumice, oatmeal and almonds. Tiny particles of abrasive plastic are also commonly used in industrial cleaning products. Another common primary microplastic is glitter. Most glitters used for art or body decoration are plastic based.
Secondary microplastics are plastics originating from the fragmentation of larger plastic items. Examples include fibres from synthetic clothing and fragments of items such as plastic bags and bottles. Most non-biodegradable plastics will eventually disintegrate and form microplastics.
Transportation also contributes to the production of microplastics, including the wear and tear of vehicle tyres and brakes and the chipping of paints and coatings, especially from road markings.
Many synthetic textiles in our clothing contribute to microplastic pollution, for example, polar fleece is made from PET plastic and many polycottons use polyester fibres made from plastic. These textiles release tiny plastic fibres when washed. These plastic microfibres are then released into wastewater.
Plastic resin pellets or nurdles, used as the raw materials in the production of plastic products, are another significant source of primary microplastics. They are typically cylindrical and a few millimetres in diameter, generated in massive quantities and transported to production facilities around the globe. Nurdles are commonly lost if they are poorly stored or mishandled during transportation and processing. As a result, nurdles are now often found in the marine environment, particularly near cities and industrial areas. Nurdles were first seen in New Zealand waters in the 1970s.
Microplastics in the environment
In 2014, it was estimated that the ocean contained 15–51 trillion microplastic particles, not counting those that have sunk to the seabed or have been deposited on shorelines worldwide. It can be extremely difficult to remove microplastics that are lost into the environment. It is likely that these microplastics have been accumulating in the environment since the origin of plastic materials.
Microplastics are found across many environments, including on New Zealand’s coastlines, particularly in the urban centres of Auckland, Wellington and Christchurch. Globally, secondary microplastics, especially wear from tyre abrasion and fibres released from synthetic clothing, are found to be the greatest type of microplastics in sediments, soils and marine and freshwater samples.
Both primary and secondary microplastics can be transported to freshwater and marine environments when they are washed into stormwater and wastewater systems. Synthetic fibres and fragments account for the majority of the microplastics found in discharge from wastewater treatment plants. Garments made of synthetic materials such as polyester and nylon fleece can release up to 1,900 fibres per wash. An American study of 17 wastewater treatment plants found on average 4 million microplastic particles were being discharged daily from each wastewater treatment plant, while a Scottish study found 65 million microplastic particles were being released daily from a single wastewater treatment plant.
Microplastic in New Zealand
An investigation by Scion found significant levels of microplastics in Auckland’s waterways and coastlines, especially polyethylene, polyethylene terephthalate and polypropylene. Concentrations were higher on the west coast than the east coast. A large proportion of the microplastics were fibres, consistent with international studies suggesting that wear and washing from textiles is a significant source of microplastics in the environment.
Modern wastewater treatment plants are designed to capture and remove large pieces of plastics and other debris from water during treatment processes. However, they are generally not designed to remove microplastics, which can pass through the treatment process and into the environment. For example, plastic-based glitters are frequently found entering and leaving municipal wastewater plants and are therefore being discharged into the environment.
Any microplastics that are removed during wastewater treatment can end up in sewage sludge and enter the environment if this sludge is used on land including as fertiliser in agriculture.
To reduce the amount of primary microplastics entering the environment, some countries, including New Zealand, ban the use of microbeads in some consumer products such as those designed to be washed down the drain.
Microplastics on land
The fate of microplastics on land is not well studied, but research is demonstrating that these particles are accumulating in dust and soils and have been detected in air. Microplastics on land may be retained in the soil or washed into rivers and streams during periods of rain. On land, known problem areas include farms where plastic rope, silo wrap, sheeting, packaging and netting is left to accumulate and fragment into agricultural soil.
Scientists have started a 5-year research project investigating how microplastic contamination affects our native species, environment, taonga and health in Aotearoa New Zealand. Read more about the impacts of microplastics in
Nature of science
Issues like the effects of microplastics in our ecosystems are gaining interest with the general public. The increasing pressure is on science to find answers in order for policy makers to make informed decisions about the regulation of different plastics.
In the activity Plastic – reuse, recycle or rubbish game, students have to sort plastic items into three categories: reuse, recycle and rubbish. The game encourages students to observe and consider how they use and reuse plastics in their everyday lives.
One of the few facilities able to recycle plastics into new products in New Zealand is Flight Plastics.
When we throw something away, how do we know where ‘away’ is? The Sustainable Seas National Science Challenge is developing online tools to help us find out. Ocean Plastic Simulator is an interactive computer simulation that shows where plastic is likely to end up when it is dropped in the ocean.
Plastic is a wicked problem. It’s incredibly useful, but it’s also a huge environmental issue. A helpful resource is Thinking about plastic – planning pathways which includes our interactive planning pathway – use this to begin a cross-curricular look at plastics.
Listen to a podcast from Nanogirl’s Great Science Adventures on how microplastics gets into the sea.
Read about microplastic pollution in the environment in Plastic particles falling out of the sky with snow in the Arctic and Nurdle invasion creates environmental headache.
To aid the identification of nurdles, download this chart.
Did you know that our clothing and cars can contribute to the microplastic problem? Take a look at these news articles – Are washing machines to blame for Auckland's microplastic scourge? and Nanogirl Michelle Dickinson: Driving your car drives up microplastic pollution.
The text for this article is from the Royal Society Te Apārangi expert advice summary Plastics in the Environment: Te Ao Hurihuri – The Changing World and has been released under CC BY 3.0 NZ. To explore the original document and the references cited, download a copy.