A second primary school in Sydney's north is among four additional sites that have returned positive results for asbestos contamination.
The NSW Environment Protection Agency on Saturday confirmed Allambie Heights Public School in northern Sydney, two residential estates under construction in the city's southwest and Munn Park in Millers Point tested positive for traces of asbestos-laden mulch.
A single piece of bonded asbestos was found in one garden bed at Allambie Heights Public School, the Department of Education confirmed.
"That garden bed ... was already cordoned off," department secretary Murat Dizdar told reporters.
"We did operate on Friday with face-to-face teaching and learning and we'll be able to do the same on Monday.
"The area has been made safe for our staff, students and community."
A further three private properties returned positive results for asbestos but are not being identified for privacy reasons and are not publicly accessible, EPA chief executive Tony Chappel said.
Liverpool West Public School was shuttered on Monday due to a positive result.
Authorities have since identified four more schools for precautionary testing following inspections of seven on Friday.
They are Domremy College in Five Dock, Edmondson Park Public School in Edmondson Park, St Michael's Catholic Primary School in Daceyville and Trinity Catholic Primary School in Kemps Creek.
North Sydney Public School, one of the seven inspected, returned negative tests.
The risk to human health remained low if asbestos was bonded and not disturbed, the EPA chief said.
Meanwhile, the University of Sydney has been identified as a potential contamination site and will test this weekend.
The grounds of Sydney Olympic Park Authority have undergone testing after the EPA identified landscaping on a median strip.
"The initial batch of testing there are all negative," Mr Chappel said.
He assured the public the site will be safe for Taylor Swift and Blink-182 concerts which will definitely proceed.
The City of Sydney is also undertaking precautionary testing on a number of parks.
Since bonded asbestos was found at Rozelle Parklands in Sydney's inner west in early January, the criminal investigation has grown into the largest in the EPA's history.
Entities that contribute to or cause pollution under NSW law are responsible for the full cost of remediating and cleaning up that pollution, Mr Chappel said.
"We are not concerned about companies providing mulch off the shelves that's contaminated," he said.
"Bunnings, Mitre10 and other nursery store products are not in question here."
Greenlife Resource Recovery is the "common link" between all positive detections across Sydney and Nowra, although the company denies its product was contaminated under its watch.
"Greenlife is confident mulch leaving our facility is free of asbestos contamination," it said in a statement, adding recycled mulch is independently tested by a laboratory approved by National Authorities Testing Australia.
The company is challenging a NSW Environment Protection Authority prevention order in court, saying its testing has shown mulch stockpiled at its facility was free of asbestos contamination.
The number of positive sites grew to at least 32 on Saturday with more than 300 sites already tested.
About one in 10 sites have returned positive results from the testing, the EPA said.
