The toxic contamination in land where several Auckland preschools now stand carries minimal health risks, worried parents have been told.

"There is cause for concern, but no cause for alarm," Auckland City Deputy Mayor Bruce Hucker said last night after a private meeting between council officials, health officials and about 70 parents.

Parents last week withdrew 30 children from the Auckland Central Playcentre in Freemans Bay after tests revealed the presence of benzo-a-pyrene, which can cause respiratory upsets, skin irritation and, on rare occasions, cancer.

Between one in 100,000 children and one in 10 million children could contract cancer, Dr Hucker said.

"It's a very low risk ... [but] it's sensible for children to have their blood tested for lead, a marker for benzo-a-pyrene."

He said the council had agreed to give a grant to the Auckland Playcentre Association to reimburse parents for the $21 test.

Interim results yesterday showed that the site of Freemans Bay Early Learning Centre would need to be treated, but that would not be finalised until today.

Dr Hucker said there was no risk once the sites were cleaned, and the council would continue monitoring.

"Two of our grandchildren attended [affected] sites, so I'm personally assessing this information very carefully."

Rae Wilkin, who has researched the dangers of benzo-a-pyrene - which is from a chemical group identified in a Columbia University report as a possible cause of "chromosomal aberrations" and childhood cancers - told the Herald she was worried the council was "politicising" the matter at the expense of public safety. "If any of my grandchildren were there, I would be really worried about it."

She said the council was wrong to ban the media from last night's meeting, as it was important the public learned as much as possible about the chemical.

In all, 185 council-owned sites are thought to be contaminated.