Atmospheric concentrations of lead peak during winter in New Zealand urban centres - and levels of arsenic have crossed national and international guidelines in some places.
That's according to a new GNS Science investigation, which analysed the makeup of tiny particles that are ubiquitous in the air.
As lead has been removed from petrol for more than 20 years, the main source of the elevated levels is likely to be the burning of old wood containing lead and treated timber containing arsenic in domestic fires.
The study suggested that enough contaminated timber was being burned to potentially cause chronic illness to some people.
Study leader Perry Davy of GNS Science said the most likely source of the treated timber was off-cuts from renovations and demolitions.
"The peaks didn't always correspond with the coldest weather, suggesting some of the burning is opportunistic," Davy said.
"These studies show that air in New Zealand urban centres is not as clean as we would like to think."
In fact, some of the winter measurements were more like the air we expect to encounter in polluted overseas cities, he said.
The study found the highest average concentrations were in Nelson and Richmond, Wainuiomata, Hastings and Christchurch.
Other urban centres from Whangarei to Invercargill also showed elevated levels during winter.
What was unknown was the exposure risk in and around the homes that were burning contaminated timber, where the concentrations could be many times higher and posed a health risk for children.
A further issue was the disposal of domestic fire ash that contains residual arsenic, copper and chromium.
When ash was placed on gardens, it represented an additional exposure pathway through the consumption of vegetables grown in contaminated soils.
Councils were responsible for the management of air quality and most councils banned the burning of CCA-treated timber.
"Several councils have embarked on enforcement and community education programmes, but there is clearly more work to do in this area," Davy said.
GNS Science uses ion beam technology to analyse tiny particles on air filters that most councils collect at air quality monitoring sites around towns and cities.
The analysis not only identifies dozens of different elements, but also their concentrations in the air we breathe and that information can be used to identify the sources.
Councils use this information to help develop mitigation measures to improve the quality of air in urban centres.
The new findings follow a study showing how extremely high levels of lead in Kiwi cities in the 1970s and 1980s lowered the IQ and life prospects of today's adults.
Research from the University of Otago's internationally recognised Dunedin Study released today showed that among more than 500 Dunedin children who grew up in the era of leaded petrol, those exposed to lead had a lower IQ and social standing by the age of 38, relative to peers who had less exposure.
It showed the effects were "slight but significant", also revealing the higher the blood-lead level was in childhood, the greater the loss of IQ points and job prospects as adults.
New Zealand lead levels were consistently higher than international standards during the 1970s and 1980s, largely because of vehicle exhaust fumes.
Leaded petrol was finally phased out completely in 1996.
An Otago University researcher not involved in the study blamed oil companies and complicit politicians for lead not being banned earlier and said the research had important lessons for today's politicians.
Of the just over 1000 Dunedin Study participants, who were all born in 1972 and 1973, 565 had blood-lead tests at age 11. About half of those tested had more than 10mcg of lead per decilitre of blood.
That half had IQ scores on average 4.25 points lower than their less lead-exposed peers when tested again 27 years later at age 38.
They also attained occupations with a lower socio-economic status than those of their parents.
Additional reporting - Otago Daily Times