Health New Zealand Te Whatu Ora Southern medical officer of health Dr John Eastwood said while lead had been used for thousands of years, it was only "since the 1940s, and more recently since the 1990s, that we’ve really started to understand the risk of lead to child development".
A child’s development could be impaired even at low levels, Dr Eastwood said.
However, he said recent changes to the Dunedin City Council’s resource consent processes for subdivision or land use should not be a cause for alarm.
The council this month introduced a new step in its consent processes for many pre-1945 houses after an analysis found lead paint in the surrounding soil could be seven times higher than contamination standards allow.
Although he was not a technical expert in regards to lead absorption, Dr Eastwood, a paediatrician by training, said the major source of lead in the environment that had an effect on children was lead in petrol — and lead had been removed from petrol decades ago.
Nowadays, risky behaviour related to lead exposure was not gardening in an area where lead-paint residue could be present but instead activities such as making a lead sinker in the garage at home.
The risk facing families from lead in the garden was minimal, he said.
"I will acknowledge that there is a ‘public awareness’ matter for families, pregnant women and families, living in parts of New Zealand where there is likely to be lead-based paint contaminating the soil," he said.
"Parents should be advised to not allow their children to be eating dirt from the garden, that’s basically it."
Developers and others have warned the council’s new approach to managing the risk from lead exposure could have wide-ranging, costly consequences and could hinder attempts to increase residential density in the city.
Terramark planning manager Darryl Sycamore said for sites that historically used lead-based paint, and in particular pre-1945 homes, uncertainty around lead contamination could affect property values.
He said the ability to on-sell property once it was identified and recorded as being on a contaminated site could be affected.
Mr Sycamore questioned why the issue of lead contamination in gardens was only dealt with at the resource consent levels.
When he raised his concerns with the Otago Daily Times, the council said the issue was not unique to Dunedin or New Zealand, but wider questions about public health should be referred to Health New Zealand.
Dr Eastwood said the public health risk arose when soil was disturbed, and when houses were knocked down.
"It’s like a lot of things: it’s like asbestos in buildings, until you actually demolish the building, there’s a minimal risk.
"When a house is being demolished, or a property is being developed, it is entirely prudent to be testing the soil at that time.
"It’s beyond my brief to talk about economic issues, cost issues, but if we might extrapolate ... it seems prudent to me, the DCC’s approach for it to be done each time a house is applying for a resource consent rather than trying to remove the soil from the whole of South Dunedin.
"Do you really think as a country, or a city, we can afford to remove all contaminated soil from South Dunedin? No.
"So, the pragmatic approach is to do it as needed, which is when someone applies for resource consent to develop a block of land, or demolish some houses and develop a block of land — to assess the risk at that time."
