The Big Compost Experiment: Using citizen science to assess the impact and effectiveness of biodegradable and compostable plastics in UK home composting

Abstract

Compostable and biodegradable plastics are growing in popularity but their environmental credentials need to be more fully assessed to determine how they can be a part of the solution to the plastic waste crisis. We present results and analysis on home compostable packaging. This type of packaging requires the citizen to be able to correctly identify the packaging as “home compostable,” to have composting facilities at home, and to successfully compost the plastic. Using a citizen science approach, we engaged with 9,701 UK citizens geographically spread across the UK to examine their capability, opportunity, and motivation to do this. Of this cohort 1,648 citizens performed home compost experiments to test the environmental performance of compostable plastics. We report on the type of plastics they tested and their disintegration under real home composting conditions. The results show that the public are confused about the meaning of the labels of compostable and biodegradable plastics. 14% of sampled plastic packaging items tested were certified “industrial compostable” only and 46% had no compostable certification. Of the biodegradable and compostable plastics tested under different home composting conditions, the majority did not fully disintegrate, including 60% of those that were certified “home compostable.” We conclude that for both of these reasons, home composting is not an effective or environmentally beneficial waste processing method for biodegradable or compostable packaging in the UK.

The difficult relationship between science, citizen science, and mass communication. A negative example

“…The figures shown by Purkiss et al (2022) are not accompanied by any statistical analysis, because they are the result of a deliberately qualitative approach. It is not an experiment that studies the interaction of materials with a composting process.…”

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Recently, an article titled "The Big Compost Experiment: Using citizen science to assess the impact and effectiveness of biodegradable and compostable plastics in UK home composting" (Purkiss et al, 2022) caused quite a stir. I must acknowledge that I was a reviewer of this article and after a long exchange with the authors, I advised the Editor to publish it.

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“…When this citizen science experiment was communicated to citizens, it became a media tsunami that defamed a system based on standards and accredited certifiers. Purkiss et al (2022) describe the results of a citizen science experiment involving the treatment of plastic items certified as "home compostable" in home composting bins by volunteers. As known, garden and kitchen wastes can be composted in composting bins.…”

The performance and environmental impact of pro-oxidant additive containing plastics in the open unmanaged environment—a review of the evidence

“…The other issue raised by our review is the choice of testing sites and how this related to the generality of claims about the performance of PAC plastics. Recently, work showed that 60% of home-compostable plastics did not fully biodegrade in UK home composting conditions [ 65 ]. The research showed that the biodegradable plastics experienced very different conditions in the home setting, and yet a single type of laboratory test was being used to certify composability.…”

Automatic identification and classification of compostable and biodegradable plastics using hyperspectral imaging

“…The advantages of compostable packaging are realized when these types of packaging are industrially composted and do not enter the environment or pollute other waste streams or the soil (Purkiss et al, 2022). Currently, most compostable plastics are treated as a contaminant in the recycling of conventional plastics such as HDPE and PET, reducing their value.…”