Experts call for tougher standards on compostable products

With Aotearoa New Zealand’s ban on single-use plastics driving consumers towards products they believe are sustainable and compostable, new research from the University of Auckland reveals that not all compostable products are as eco-friendly as they claim.

In 2023, the Ministry of Environment commissioned researchers at the University to investigate how compostable products affect soil health. Three new reports have been published detailing the findings, potential consequences and recommendations for regulating these products, aiming to improve compostable product practices in Aotearoa with a focus on soil health and cultural relevance.

Compost is usually added to soil to enhance its fertility and support the growth of food crops. Therefore, it is crucial to ensure that the compost is free from toxic substances, not only to preserve soil health but also to maintain the quality of the food produced.

As part of the study, researchers tested ten products – including paper cups, bin liners, pizza boxes and food trays – for harmful substances such as plastics, heavy metals, endocrine disrupting chemicals and PFAS (per- and poly-fluoroalkyl substances, also known as “forever chemicals”).

The analysis revealed that many products contained these contaminants, which could threaten soil and groundwater health if composted in large quantities, according to researchers Associate Professor Lokesh Padhye, Associate Professor Melanie Kah, Dr Gabriela Baron and PhD candidate Nargiss Taleb.

A cardboard pizza box, for example, contained all the chemical classes tested in the study, also raising concerns about the potential for these chemicals to transfer into food through the packaging.

Although some products contained only low levels of contaminants, a concerning finding involved an unlined fibre tray labelled ‘compost me’, which had high levels of total fluorine and PFOA, a banned chemical listed on the Stockholm Convention.

“We need to be cautious about composting items with unknown chemical additives, as contaminants like PFAS and plastic polymers can persist in the environment for decades, posing long-term risks to soil and groundwater health,” says Padhye.

He says that additives are often used to maintain the functionality of compostable products, such as preventing soggy plates or crumbling pizza boxes. However, he says that some of these products might prove equally or more harmful in the longer term than single-use plastics, making this a case of ‘regrettable substitution’.

“Consumers often pay a premium for compostable products, but they might not always be worth the extra cost. The higher price tag of these products can be justified by their perceived environmental benefits, but if the additives used in these products render them toxic to the soil health, then it defeats the very purpose these products are marketed for.

“This misalignment between consumer expectations and the actual environmental impact highlights the need for greater transparency and stricter regulations regarding the use of additives in compostable products”.

There is also an important distinction between home and industrial composting, says Padhye.

Many people mistakenly think that products labelled as compostable can break down in their home compost. However, industrial composting uses higher temperatures and controlled conditions that are not achievable at home. This misconception can result in improper disposal practices, where products may not decompose as intended.

Padhye says that the reports will help shape future regulations for compostable products in Aotearoa.

“Manufacturers should be responsible for certifying their products and ensuring they are tested to confirm that chemical levels are within safe limits.

“Labelling is another significant issue in New Zealand, as we lack clear guidelines on how terms like ‘green’ and ‘sustainable’ can be used. Consumers often make purchasing decisions based on the marketing claims on the products, without knowing if they truly meet those claims.”

The reports also advocate for a Te Ao Māori perspective on soil health. In Te Ao Māori, soil is seen as an ancestor deeply connected to human well-being. This cultural view highlights the need for policies that align with Māori values and knowledge to ensure composting practices fully respect and protect soil health.

The researchers also developed a guide to help stakeholders in Aotearoa navigate decision-making processes across the different stages of the life cycle of compostable products.

“This is New Zealand’s first attempt to create guidelines for compostable products,” Padhye says. “While testing only ten products doesn’t cover the entire market, we aimed to include a diverse range of products to gain a clearer understanding of the issue. What we can confidently report is that nearly all the products we tested contained some concerning chemicals, and there is an urgent need to improve consumer education, reduce greenwashing and enact regulatory framework in this space.”