Compostable Plastic Bags Trialled in South Australia as Bans Loom in other States

It sounds too good to be true — a plastic bag made from corn starch that breaks down with food waste and leaves no remnant plastic to make its way into the oceans.

These "compostable" light-weight bags for fruit and vegetables are being trialled in two South Australian supermarkets.

Shani Wood from the City of Holdfast Bay said the bags were made in Japan from 100 per cent organic matter, including "98 per cent corn starch".

"The idea is that you use the bags to line your kitchen organic basket and put that bag into the green organics bin to be turned into compost, instead of being put into the garbage bin to be put into landfill," Ms Wood said.

If disposed incorrectly and the bags end up in waterways, she said they would not harm marine life, even if they consumed it.

But while the bags appear as a greener alternative to the reuseable heavy-duty plastic or so-called "green bags" offered by retailers, Professor Peter Halley from the University of Queensland expressed caution.

"They are definitely a good start, but we need to be looking at the entire use of resources, energy, water, CO2 emissions during production and disposal to get a material's true effect on the environment," he said.

The university's head of chemical engineering said it was important to look at the entire life cycle of the material, even if compostable bags break down fast in water provided the corn starch was water soluble