Biodegradable teabags don’t readily breakdown in garden compost and labelling should be made clearer to prevent them being thrown away in domestic compost heaps according to a new study from the Universities of Bath and Plymouth. These ‘biodegradable’ teabags can harm earthworms and instead should be disposed of via industrial compositing.
Persistent plastic
Some teabags consist of plastic alternatives such as polylactic acid (PLA), which is derived from sources like corn starch or sugar cane. Although bio-based with a lower carbon footprint compared to conventional plastics, PLA doesn’t degrade in soil – rather it requires industrial composting conditions.
The study analysed three widely available teabags made using different compositions of PLA. They were buried in soil for seven months to replicate environmental conditions teabags might be exposed to if discarded inappropriately due to lack of clear labelling. Researchers used a range of analytical techniques to examine how the teabags changed visibly and structurally. Teabags made solely from PLA remained completely intact, but those made from a combination of cellulose and PLA degraded into smaller pieces. They lost between 60% and 80% of their overall mass and the PLA component remained.
“In response to the plastic waste crisis, biodegradable plastics such as PLA are being used in an increasing range of products,” says lead author Dr Winnie Courtene-Jones, Post-Doctoral Research Fellow at the University of Plymouth. “This study highlights the need for more evidence on the degradation and possible effects of such materials before their use becomes even more widespread, and to prevent the generation of alternative problems if they are not properly disposed of.”
Threat to earthworms
Researchers also analysed the impact of teabags on Eisenia fetida, a species of earthworm which has a critical role in soil nutrient turnover. Being exposed to three different concentrations of teabag discs, equivalent to the mass of half, one and two teabags, caused up to 15% greater mortality. Reproduction was also adversely affected by some concentrations of PLA.
“In this study PLA-based teabags did not fully deteriorate, and it seems that composting worms may be harmed by them,” says Dr Mick Hanley, Associate Professor in Plant-Animal Interactions at Plymouth and senior author. “The lack of clear labelling can lead to consumers disposing of teabags in their compost, where any limit to complete degradation of the material raises the potential for plastics to enter the soil when compost is added to the garden, with potential impacts on garden wildlife and uptake by food plants.”
Customer confusion
The findings emphasise the importance of understanding alternative materials, their impacts and how to dispose of them, and for accurate disposal information to be clearly displayed on product packaging, the researchers say. Theres a high chance customers could be confused about terms like ‘plant-based’ or ‘biodegradable’, and only one of the tested teabags’ packaging said they were not home compostable.
Dr Fannie Burgevin from the University of Bath’s Department of Chemistry says: “Current labels on packaging such as biodegradable or compostable can be misleading for the public. Therefore, it is imperative that scientists, policy makers and manufacturers work together so that the public has an easy access to information and learn how to dispose of those new types of plastic.”
The research, conducted as part of BIO-PLASTIC-RISK, builds on previous work which found some products labelled as biodegradable, like carrier bags, do not disintegrate after as much as three years in the environment.
Professor Richard Thompson OBE FRS, Head of Plymouth’s International Marine Litter Research Unit and lead of BIO-PLASTIC-RISK said: “Even if consumers understand how to dispose of these products only around half of households in the UK currently have access to the necessary waste streams for the type of composting required. It is essential we learn from the mistakes we made with plastic materials by testing and labelling these novel materials in relation to the prevailing waste management infrastructure.”
News Reference
Courtene-Jones, W. et al (2024) Deterioration of bio-based polylactic acid plastic teabags under environmental conditions and their associated effects on earthworms, Science of the Total Environment.