Public health teams are visiting five Dunedin primary schools where raised levels of lead have been found.
The Southern District Health Board has moved quickly to investigate after GNS Science found the lead in soil samples as part of a wider study.
The primary schools are Bathgate Park, George Street Normal, Mornington, North East Valley and Opoho.
Medical officer of health Marion Poore said the highest sample level was 595mg of lead per kg of soil, which is above the recommended government standard for home gardens (210mg) but below that for public parks (880mg).
She said there was no specific standard for schools.
The health risk was low but still needed to be investigated, so the DHB was taking a conservative and precautionary approach, Dr Poore said.
The schools have been warned and staff have begun visiting to gather more information about where the lead was found, and if children could have been exposed.
Dr Poore said further soil testing would be ordered if needed.
She said the DHB was not surprised at the discovery, as these schools were generally older buildings painted with lead-based paints, and there had been a lot of lead in the air from leaded petrol.
Some of the schools were Enviroschools, with gardens on-site where students could grow fruits and vegetables.
But Dr Poore said, to her understanding, the gardens were a recent addition and were tended using soil brought from outside the schools.
Any vegetables produced by any of the schools should still be washed thoroughly before being eaten, she said.
A recently published study revealed Dunedin children's exposure to lead in the 1970s and 1980s could be linked to a drop in their intelligence level as adults.