'There is no safe level': Study finds 35 per cent of Aussie backyards contaminated with lead

If you’re growing food at home, consider getting your soil tested for lead. New research published in April suggests there’s a substantial risk the heavy metal is lurking in your garden at unsafe levels.

Thirty-five per cent of participants contributing soil samples to Macquarie University’s ongoing VegeSafe program had at least one sample with lead exceeding Australian residential guidelines of 300mg/kg. 

While many of us are somewhat aware of the issue, the study – the largest known of its kind – is a further wake-up call to gardeners. Sampling over 5000 homes (so far) across all states of the country, it represents at least 65 per cent of where the population lives, says Mark Taylor, the head of the program and a professor of Environmental Science and Human Health at Macquarie University.

Properties most at risk of elevated lead were older, painted homes, in traffic-congested areas and closest to the city. Front yards tended to be higher in lead than backyards. 

Why is lead such an issue? 

Lead occurs naturally in the earth’s crust at an average concentration of 10 parts per million (ppm). The higher accumulation in garden soil is predominantly a legacy of our former use of leaded petrol and lead-based paints deteriorating into the soil, Taylor explains. “It’s elemental and it does not go away,” he says. “Which is why we find it.” 

Lead transfers from our gardens to us through inhalation or ingestion of lead-containing dust, soil or other small particles, and through consuming our own produce including backyard eggs containing lead, Taylor says. A new, soon-to-be-published study led by the professor shows an association between the lead levels in soil, chickens and their eggs. 

Research is clear on the negative impacts of lead on our bodies, Taylor says. Of concern to parents, it interferes with the neurological development of children. “It causes deficit of IQ, behavioural problems, ADHD, and oppositional type behaviours,” he says. Other research links lead exposures to early dementia and cardiovascular and kidney problems. These occur at very low-level exposures, even below current safe thresholds, he says. “There is no safe level.”

Solutions to get you gardening worry-free 

First, get your soil assessed. Anyone in Australia can send five samples of garden dirt for analysis through Macquarie University’s VegeSafe program for a donation of $20. Those living in high-risk locations and in former or current industrial or high-traffic areas should especially get their soil tested. To check out levels in your area, visit Map My Environment.

If your soil is contaminated, the only real way to get rid of lead is to dig up the dirt and replace it, Taylor says. Given the impracticality, and cost of that, he recommends building raised beds and bringing in fresh soil. Any open soil areas of the garden should be covered with grass, mulch, pavers or ground covers.

“Don’t scalp the grass on the lawn – that generates dust,” he says. “Basically, keep the outdoors outdoor and indoors indoor.” Wash any edibles from the garden before eating. Make sure to take your shoes off indoors and don’t put the vacuum dust into the compost, he adds. 

Also, crank the compost. Research shows compost creates soil conditions that limit the uptake of lead and other heavy metals into plants.

Some plants, such as sunflowers, are able to absorb heavy metals from the soil, but it’s a lengthy process and “it doesn’t just magically disappear”, Taylor says. “That has to go into landfill at some point. So it just gets moved from one place to another.”

The overriding message from the VegeSafe team is to carry on gardening. “There’s a significant benefit of growing your own veggies,” Taylor says. “The objective is to empower people to make sure that they produce veggies in clean soils.”