Biodegradable plastic bags are still capable of carrying full loads of shopping after being exposed in the natural environment for three years, a new study shows.

Researchers from the University of Plymouth examined the degradation of five plastic bag materials widely available from high street retailers in the UK.

They were then left exposed to air, soil and sea, environments which they could potentially encounter if discarded as litter.

The bags were monitored at regular intervals, and 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.

However, 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 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.

Writing in Environmental Science and Technology, researchers from the University’s International Marine Litter Research Unit say the study poses a number of questions.

The most pertinent is whether biodegradable formulations can be relied upon to offer a sufficiently advanced rate of degradation to offer any realistic solution to the problem of plastic litter.