Children's blood-lead tests are no longer being done by Nyrstar smelter for analysis by health authorities.
This was changed on January 1 so that SA Pathology provides the results.
Before that, tests were being performed by both entities with the smelter results said to be "slightly" lower than the pathology department's.
The Recorder asked the health department about possible distortions in year-to-year comparisons.
Health's director of scientific services, Dr David Simon, confirmed that year-to-year comparisons had looked at analysis by the smelter in 2018 and by the pathology department in 2019.
"It could have magnified the increase by a small amount, perhaps by one microgram per decilitre," he said.
But he said this had no effect on the numbers of children with blood-lead levels of concern above 10 or 20 micrograms per decilitre.
He said the health department still worked with the families of children in this range to reduce their readings.
The switch in analysis from Nyrstar to the pathology department had resulted from:
- Concerns that there was "conflict between the polluter and the child"
- The pathology department had a far simpler method of analysis
- It avoided two laboratories doing the same tests.
Dr Simon said "double-check" tests for the pathology department were done by New South Wales Pathology on the same machine.
He said blood-lead testing was not done "to see whether Nyrstar is going its job", but to target help to affected families.
"Nyrstar has 12 air monitors around town and the Environment Protect Authority at least three," he said pointing to alternate indicators of lead pollution.
It was agreed that children's blood-lead results could be biased because children with low levels were sometimes withdrawn from the program by their parents.
"We suggest that is not a bad idea by the parents," Dr Simon said.
But he conceded that consecutive quarters of testing could contain a greater number of high-level children.
"There is a bias, but in the report we say that all reports show a bias," he said.
Asked why all children were not tested, he replied that public health programs were unable to force parents to test their children unless the children were exposed to lead. "It would be like testing a teenage for bowel cancer. You just wouldn't do it," he said.
Asked why each quarterly result was not compared with the previous quarter, he said this was not done and it was too hard to do so because of weather changes between test times.
Dr Simon was asked whether he had a conflict of interest in commenting on results when he had written a scientific paper titled Living in a Sea of Lead.
"No, I don't because the purpose of writing that paper was to put into peer group literature how children were being exposed to lead from birth," he replied.
He said a study had been done in Adelaide pointing to this factor, but previously it had been unclear whether exposure happened at, say, two, three or six months.
Originally, Port Pirie children had been tested monthly.
This was modified to enable health to work with families from birth.
His paper had been quoted around the world.
"It is a paper that helped to re-evaluate the Environmental Health Centre program and put in place the regime we have today," he said.
The third-quarter analysis for this year shows what health says is "deterioration" in the children's blood-lead levels. The average level for two-year-olds increased from 5.8 micgrograms per decilitre at this time last year to 6.6, continuing a trend seen earlier this year.
Dr Simon said it was "most concerning" that there was an increase in the number of children at high risk of health effects with levels equal to or above 20.
This had risen to 15 children from 12 at the same time last year.
The results also showed the overall average level of all children tested had risen from 4.1 to 5.6.
"The results are ... expected given the prolonged high lead-in-air emissions between 2016 and 2018, carrying a big amount of lead-contaminated dust across the city," Dr Simon said.
"There are some early signs that the deterioration in levels may be starting to reduce.
"This could be linked to the fact that children are less likely to be exposed to lead in winter as they spend more time indoors and wet weather suppresses dust in the environment along with the reported reduction in average lead-in-air this year.
"The Environmental Health Centre will work with the community to monitor the situation as we move closer to dry, windy conditions in summer."
Interventions are offered to children with elevated blood-lead levels, but, given the known effect of lead on children's developing brains, preventing exposure in the first place is said to be the chief aim.
"Case workers work closely with parents and caregivers of children with elevated blood-lead levels to help families to reduce lead exposure," Dr Simon said.
Since 2010, the number of children tested in each quarter has varied between about 180 and 277.