Researchers from Macquarie University in Sydney have been testing backyard soil since 2013 as part of a study to help people know what risks are tied to their vegetable patches.

More than 17,250 samples have been tested so far from 3609 homes.

More than one-third - 35 per cent - of homes have soils with neurotoxic trace metal lead levels above the Australian residential guideline of 300 mg/kg.

More homes in Sydney had higher levels compared to Melbourne and Brisbane.

Research assistant Kara Fry says there a specific risk factors.

"These are inner city homes, older homes, timber-painted buildings. Those are the criteria that are more likely to have elevated lead levels in their soil," she told AAP on Wednesday.

"We also found, particularly in these inner-city areas, they're more likely to have lead uptake in vegetables higher than Australian guidelines.

"They may also be correlated with adverse effects for children below two-years-old, that are exposed to the soil."

The team also runs a program which analyses dust collected by household vacuums.

"We generally find what's outside makes its way in," Ms Fry said.

About 40 per cent of people involved in the soil study have taken remedial action.

That includes methods to reduce exposure to soil such as planting in raised garden beds, mulching exposed soil and washing hands.

"Mulching really helps because that stops what's going inside the house, stops the generation of dust from wind," Ms Fry said.

The study has this week been published in science journal Environment International.

Australians across the country can send the team soil samples to be tested, and are asked for a $20 donation in return.

Research is also being done on backyard chickens and their eggs for levels of trace metals, particularly lead.

Australian Associated Press