Biodegradable bags still pose a serious eco-threat

File photo: AP

File photo: AP

Published May 8, 2019

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Cape Town – Biodegradable bags can hold a full load of shopping three years after being discarded in the environment.

This is according to the International Marine Litter Research Unit at Plymouth University in the UK.

The researchers have published a study in Environmental Science and Technology.

The team, under the guidance of unit head, Professor Richard Thompson OBE, had examined the degradation of different plastic bags widely available from retailers including compostable bags, two forms of biodegradable bags and conventional carrier bags.

These were left exposed to air, soil and sea - environments which they could potentially encounter if discarded as litter - and monitored at regular intervals. Deterioration was considered in terms of visible loss in surface area and disintegration as well as assessments of more subtle changes in tensile strength, surface texture and chemical structure.

After nine months in the open air, all the materials had completely disintegrated into fragments.

The compostable bag completely disappeared from the experimental test rig in the marine environment within three months but, while showing some signs of deterioration, was still present in soil after 27 months. 

But, the big shock was that the biodegradable, oxo-biodegradable and conventional plastic formulations remained functional as carrier bags after being in the soil or the marine environment for over three years.

The research team said their results raise several questions, including whether environmental and weather conditions were a realistic means of decomposing bags when they are thrown away, even if they were labelled “biodegradable”.

Important, too, is the confusion of the use of the term biodegradable; the researchers believe it lulls consumers into thinking the bag will disappear if thrown away.

These issues are top-of-mind for South African National Bottled Water Association chief executive Charlotte Metcalf, whose members package either in glass or PET bottles.

“Plastic in all its forms is one of the major pollutants of our water bodies and landmasses. Ways must be found to curtail pollution but calls for outright bans or adoption of unproven, untested alternatives are grossly overrated as solutions.

“A holistic strategy that results in investing in solutions that encourage behaviour change coupled with the implementation of considered, well-thought through new technologies is closer to the answer,” said Metcalf. 

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