Blood lead levels among Port Pirie children are at a decade high, according to the latest SA Health data.

The "accepted" national blood lead level is 5 micrograms per decilitre (μg/dL), but new figures show the mean blood lead level for two-year-olds in Port Pirie is 7.8μg/dL.

That is an increase of 1.6 micrograms since 2020.

Meanwhile, children aged under four recorded the second-highest blood lead levels in the decade, at 5.7μg/dL.

That was eclipsed only in 2019 when Port Pirie's smelter operator, Nyrstar, was found in breach of its Environment Protection Authority (EPA) license.

Nyrstar's lead emissions also increased in the second half of 2020, despite a $291 million smelter upgrade that was intended to halve lead-in-air pollution.

Director of Scientific Services at SA Health, David Simon, said Monday's increase in blood lead levels among young children was a direct result of the higher atmospheric lead levels recorded over those years.

The latest data from the EPA showed a drop in lead-in-air levels in Port Pirie since then.

SA Health has been tracking blood levels since 1984, which Dr Simon said were far higher than Monday's levels.

"Back in 1987, only 2 per cent of the population in Port Pirie had a blood lead level below 10 micrograms," he said.

Lead levels will 'take years' to come down

The downtrend in lead-in-air emissions has been coupled with tougher conditions imposed on Nyrstar by the EPA in 2020, which required the operator to reduce its annual lead emissions by 20 per cent.

However, Dr Simon said it would take children several years to shake their elevated blood lead levels.

"The report shows – like in the last quarter of last year – that our children are growing up in an environment that is being completely inundated with lead," he said.

National health guidelines state that blood lead levels above 5μg/dL should be investigated.

The World Health Organization reports there is no safe level of exposure, and Dr Simon said the lower the level, the better.

"Lead is a neurotoxin. It affects the developing brain in particular. Children are at risk of not reaching their full potential IQ-wise if they're exposed to lead," Dr Simon said.

Indeed, according to a 2019 Macquarie University study, some 13 IQ points are lost with every 10μg/dL of lead in the blood.

There were nine children in Port Pirie who recorded a blood lead level equal to or exceeding 20μg/dL in the first half of 2021, which was higher than the same period last year.

Nyrstar admits 'further work' needed

In a statement, Nyrstar said SA Health's latest report demonstrated that "further work is required to reduce blood lead levels."

However, the company said it was making progress in reducing its emissions.

"This reflects a 31 per cent reduction in lead-in-air across the whole monitoring network, which is the same reporting period as the First Half 2021 Blood Lead Report.

"Nyrstar is optimistic there will be reduced blood lead levels in the future."