Biodegradable plastic bags can still carry load after 3 years in soil, sea

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

The research published in Environmental Science & Technology examined the degradation of five plastic bag materials widely available from high street retailers in the United Kingdom.

Plastic bag materials were exposed to air, soil and sea, environments which it 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 plastic bag materials had completely disintegrated into fragments.

However, the biodegradable, oxo-biodegradable and conventional plastic formulations remained functional as carry 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 the soil after 27 months.

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

Imogen Napper, who led the study, said: "After three years, I was really amazed that any of the bags could still hold a load of shopping. For a biodegradable bag to be able to do that was the most surprising. When you see something labelled in that way, I think you automatically assume it will degrade more quickly than conventional bags. But, after three years at least, our research shows that might not be the case."

In the research, scientists quote a European Commission report in 2013 which suggested about 100 billion plastic bags were being issued every year, although various Governments (including the UK) have since introduced levies designed to address this.

Many of these items are known to have entered the marine environment, with previous studies having explored their impact on coastal sediments and shown they can be broken down into microplastics by marine creatures.