In a statement released on Tuesday the National Health and Medical Research Council (NHMRC) says that any person with more than 5 micrograms per decilitre of blood should have the source of their lead exposure "investigated and reduced, particularly if the person is a child or pregnant woman."

It has been estimated that up to 100,000 Australian children could have blood lead levels that breach the new standard, although no-one knows exactly how many are affected as widespread testing is not done. But soil-testing in inner-city areas such as Marrickville, Leichhardt and Willoughby have found shockingly high levels of lead and other contaminants, linked to past activities such as lead paint use, heavy traffic or industrial usage.

Despite this, the research council  has stopped short of recommending widespread screening programs or soil testing, and maintains there is not enough evidence to definitively prove that lead levels below 10 micrograms per decilitre cause problems such as low IQs, or behavioural or health issues.

One lead contamination expert says the new recommendations don't go far enough, warning Australia is being more conservative than overseas regulators and more must be done to protect children at risk.

Mark Taylor, a professor of Environmental Science at Macquarie University, said the guidelines focused more on minimising the effects of exposure to lead, than preventing the exposure from happening at all.

"Organisations like the United Nations Environment Programme, the US Environmental Protection Agency ... they all have completely different views on this, they all talk about causality," he said. "I think they [the research council ] have been very cautious in the way they have constructed their advice".

In an opinion piece  written with fellow lead expert Bruce Lanphear​, and published on the academic website The Conversation on Tuesday afternoon, Professor Taylor argued that the research council's approach of targeting only children at high-risk of lead exposure failed to protect the millions of children who were suffering small but still important deficits because of exposure to lead and other toxins.

"Unless there is a threshold, the high-risk approach will inevitably fail to protect the majority of those affected, albeit at lower levels," they wrote.

The US department of health says there is sufficient evidence to state that blood lead levels above 5 micrograms cause decreased academic achievement and IQ, and increased attention and behavioural problems. Some academics have even argued that the amount of lead in the environment is directly correlated to crime rates 20 years later – when the people exposed as children reach adulthood.

But Sophie Dwyer, who headed the research council's  lead working group, said any problems caused by blood lead levels below 10 were not likely to be obvious at an individual level, and showed up only as broad averages across a population.

"IQ as a measure has substantial variability, even with the individual person from test to test, which makes it difficult to interpret the significance of these small differences in IQ between these populations," she said. "In the view of the lead working committee the evidence ... is at quite a subtle level, a low level – there would be far more significant influences on factors such as crime or educational achievement than lead".

She said it was likely that exposure to "background" levels of lead would lead most people to have a level of about 5 micrograms, and so anything above that meant there was some extra exposure that could be prevented.

"Lead is not beneficial to human health and can be harmful to the human body, and as such it should be minimised as much as possible," she said.

In some parts of NSW such as Broken Hill, where mining has caused high levels of lead contamination, child lead levels have risen. But research council head Anne Kelso said overall lead levels in the population had fallen, which was good news for public health.

Sources of lead exposure in the home

• Paint from houses built before the 1970s, particularly when tampered with during renovations 
• Dust and soil near busy roads, which is contaminated from leaded petrol and can be walked into the house.
• Old household items using lead piping, some pottery or lead crystal.