Microplastics

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.

Nurdles

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.

Research released in 2021 by University of Waikato master of science student Anita Lewis found extremely high levels of microplastics across the Bay of Plenty moana. Every area she tested showed evidence of microplastics, and high levels were found in shellfish.

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.

Future research

Scientists have started a 5-year research project, Aotearoa Impacts and Mitigation of Microplastics (AIM²) investigating how microplastic contamination affects our native species, environment, taonga and health in Aotearoa New Zealand.

Read more about the impacts of microplastics in How harmful are microplastics?