Tricia Hogbin said she decided to get her backyard tested after reading about the effects of growing vegetables in lead-contaminated soil.

"I thought I'd get our backyard soil tested because we have a vegetable garden and our two-year-old plays in the garden," Mrs Hogbin said.

"I sent a sample to a lab and it came back with high levels, more than double what would be safe for a backyard."

Vegetable gardens are becoming more common with people turning to organic food and trying to save money.

Health authorities say high lead levels can harm people and vegetables can absorb lead, threatening people's health when eaten.

A Hunter New England Health report said children were at risk from playing in bare soil with high lead concentrations.

"Play should be restricted to areas with a grass barrier or to soil known to have lower lead levels," the report said.

Black slag from the old Pasminco smelter was used over 90 years as fill in many Newcastle properties, but Mrs Hogbin said the source of lead in her garden was not confirmed.

"It could have been an incinerator or someone burning copper logs or timber with lead painted on," she said.

Mrs Hogbin said her family had their blood levels tested and "they came back fine".

She has sent eight more soil samples to a Sydney-based lead advisory service for testing, costing about $250, to establish the extent of the contamination.

Hunter New England Health recommends that clean soil be put in lead-contaminated gardens before vegetables are grown. Clean soil should be 10 centimetres deep and vegetables should be washed before eating.