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Compost - a hidden source of plastic pollution

24 May 2018

Microplastics Compost 2018
Microplastics Compost 2018

The extensive use of all kinds of plastic in food production is a ticking time bomb because of the risks it poses to the environment and human health, says ESR Environmental Scientist Olga Pantos.

Dr Pantos says there is a growing public awareness of the risks posed by plastic in the marine environment but there is not the same level of knowledge about the risks plastics pose in the soil.

One potentially hidden source of plastic moving into the environment is via compost.

Dr Pantos says that even consumers who want to do the right thing with their plastic waste get confused about what they can recycle and what should go to waste.

Labelling is often hard to read and often even harder to understand.  She says increased use of biopolymers and plastic alternatives in food packaging makes it likely that the amount of plastic in green waste is increasing.

While some consumers might think they are making good decisions by choosing compostable and biodegradable labelled products, they can be just as harmful to the environment as conventional plastic if they are not disposed of properly.

Putting these products into compost may mean they are simply degrading to smaller pieces of plastic and making their way into the food chain.

 A recent study in Germany found compost from supermarket waste had close to 900 pieces of microplastic in a one-kilogram sample. 

Once that plastic gets into the compost it can have an impact on the biological function of the soil.  Dr Pantos says the nature of plastics makes them effective in absorbing chemical contaminants, making them more toxic.

She says consumers are starting to become aware of the hidden plastic content in apparently harmless items like tea bags but she says there is still a lot to learn about how to make good choices as a consumer.

She says that per capita New Zealanders generate some of the highest amounts of plastic waste in the world.

Globally over 311 million tonnes of plastic was produced and most of that is single-use.

Olga Pantos is a senior scientist at ESR Food, water and Biowaste group – based in Christchurch.

She was involved in the recent survey of marine microplastics in Wellington.