Brisbane City Council is investigating claims the free dog-waste bags may not be fully biodegradable, as both it and its suppliers have claimed.

Independent scientific testing of the bags has revealed they are made almost entirely of plastic and will not break down as expected.

The revelation is an embarrassment to Lord Mayor Campbell Newman, who claims the environment as one of his top priorities, and comes amid growing calls for bans or levies on

plastic bags.

BCC estimates it supplies 100,000 to 150,000 of the bags a month, meaning about a million bags could have been used since the contract with the supplier, The Dog Tidy Company,

began in December.

The company sells cartons of 2000 bags online for $72.50, meaning they could have cost ratepayers as much as $38,000 since the contract began.

Under the terms of the tender, the bags were supposed to contain no more than two per cent polyolefin - a plastic resin.

However, tests by a European laboratory have revealed they are almost entirely polyethylene, a type of polyolefin plastic, and supplemented with only 10 per cent of the more

compostable starch.

The report, seen by The Courier-Mail, concluded the bags would not comply with current "compostability standards" nor meet Australian biodegradability standards.

A BCC spokesman said the council was made aware of "allegations" surrounding the bags more than a week ago and had since written to its suppliers asking them to address the

concerns.

He said a further independent analysis of the bags had been ordered.

"Should this further analysis show the supplier has not complied with the conditions of their tender, council will take appropriate action," the council spokesman said.

Melbourne-based Dog Tidy Company was reluctant to comment yesterday, but said the bags were bought from an overseas supplier.

"We just go by the standards and what they give us and we've got to look into it," a spokesman said.

Clean Up Australia Day chairman Ian Kiernan said so-called "degradable" bags containing only a small portion of vegetable matter were worse for the environment than

non-degradable bags as they broke into pieces.

"It's a fraud and these people are doing more damage to the environmental issue as well as the environment than if they were doing nothing," he said.

Dog owners can be fined $37.50 for not carrying a bag while walking their pets and $150 for failing to pick up droppings.

The Gold Coast, Redlands and Sunshine Coast councils said they did not use Dog Tidy Company bags.