Mulch laden with asbestos has been detected in at least 22 sites across NSW after bonded asbestos was first found at the Rozelle Parklands in Sydney’s inner west in January.

More than 100 sites across Sydney have since been tested, leading to at least 13 positive results for bonded asbestos.

The latest discovery at a school in Liverpool resulted in hundreds of students learning from home before being shifted to another public school nearby while the mulch is removed.

Education Minister Prue Car said the clean-up would take longer than expected because the mulch had been incorrectly placed.

“We’ve obviously got a lot of a serious investigating to do about what happened at the actual construction of this (playground) upgrade,” she said.

“There is supposed to be soil underneath the mulch in the garden bed, but instead of doing that the contractor in question has in fact just put metre of mulch.”

Ms Car said the contractor in question was being investigated by the NSW Environment Protection Authority (EPA).

“It is a seriously unlawful act to contaminate mulch with something like asbestos,” she said.

The NSW opposition has called for a register of all sites at risk of possible asbestos contamination in mulch to be made available to the public.

Opposition environment spokeswoman Kellie Sloane said a central register of all sites under investigation by the state’s environmental watchdog would give the public greater transparency and peace of mind.

“The public has a right to know if playgrounds and public spaces in their suburbs are under investigation for asbestos contamination,” she said on Wednesday.

“The first time people hear about a contaminated site shouldn’t be when fences are going up or the media reports it.”

Sloane said the register should inform the public in real time and give them the assurance to go about their daily lives.

The EPA issued landscaping supply company, Greenlife Resource Recovery, with a prevention notice after the watchdog determined it supplied the mulch used at Rozelle.

The supplier has been linked to all 22 sites across Sydney found with asbestos-tainted mulch.

The company said its testing showed mulch stockpiled at its facility was free of asbestos contamination and it was confident the material was also clean when delivered to contractors for landscaping.

The EPA probe has grown to involve 120 investigators, who are working to trace the supply of mulch.

NSW EPA chief executive Tony Chappel said the whole supply chain was under scrutiny.

– AAP