New Delhi, May 28 (IANS): Not all biodegradable tea bags made using corn starch or sugar cane, and touted as the best alternatives against plastic, degrade in soil, a new study showed on Tuesday, noting their potential to harm terrestrial species and the environment.

Researchers from the universities of Plymouth and Bath in the UK looked at commonly available teabags made using three different compositions of polylactic acid (PLA), which were buried in soil for seven months.

The teabags made solely from PLA were completely intact.

However, the two types of tea bags made from a combination of cellulose and PLA broke down into smaller pieces, losing between 60 and 80 per cent of their overall mass with the PLA component remaining.

Winnie Courtene-Jones, the lead author from the University of Plymouth, noted that biodegradable plastics such as PLA are being used in an increasing range of products in response to the plastic waste crisis.

However, "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," Winnie, a postdoctoral research fellow at the varsity, added.

The team also examined the impacts of the discs cut from the teabags on a species of earthworm, Eisenia fetida, which has a critical role in soil nutrient turnover as it consumes organic matter.

The results published in the journal Science of the Total Environment showed that being exposed to three different concentrations of teabag discs -- equivalent to the mass of half, one, and two teabags -- resulted in up to 15 per cent greater mortality, while some concentrations of PLA had a detrimental effect on earthworm reproduction.