In a recent study, we found that 40 percent of the 203 Sydney homes sampled contained lead in their garden soil over 300 milligrams/kg (mg/kg) according to Australian health guidelines.
It is a danger because soil lead can stick to edible plants or absorb it. A second way of exposure is when soil dust contaminated with lead enters homes and is accidentally consumed. Lead is a neurotoxin which affects development.
VegetSafe and urban agriculture
In Australia, urban agriculture is growing in popularity. Nearly half (48%) of all metropolitan households are growing edible produce.
The majority of lead contamination results from the use of lead paint and petrol (now banned) as well as previous industrial emissions. Scientists and regulators know about these legacy issues, but the public is not informed.
In 2013, we launched the VegeSafe community science initiative to help urban gardeners evaluate contamination risks associated with soils in their gardens. The program provides free soil metal testing to participants.
Participants receive a report detailing their soil metal test results, along with advice on what to do if the soils have high metal concentrations. Over 1,300 Australian homes and community gardens have received 5,500 soil metal testing free of charge. This is the largest study and program of its kind.
What did we discover?
In addition to the 40 percent of Sydney gardens that contained soil levels above the Australian health guideline of 300 mg/kg, one in seven houses had soil lead levels higher than 1,000 mg/kg. The soil metal concentrations are typically highest around drip lines.
The highest soil lead concentrations occurred in the City of Sydney and former local governments of Leichhardt Municipal Council and Marrickville Council. These areas had soil lead concentrations of 960 mg/kg on average, and 883 mg/kg.
Soil lead concentrations in vegetable garden soils at 141 Sydney homes. This map represents one of the four areas surrounding homes in this study (front yard drip line, backyard and vegetable garden). Source: Rouillon et al. 2016
Lead contamination is more common in homes with painted exteriors that were built before 1970. Homes 80 years and older have the highest lead levels. Lead-rich paint that contained up to 50 percent lead before 1970 is most likely the cause. By 1997, the amount of lead in paint had been reduced to less than 1,000 mg/kg (0.1%).
In our study, we observed the positive environmental impact of the removal of lead paints and leaded gasoline (removed by 2002). The soil in the gardens of newer houses contains the least amount of lead. The soil lead concentration decreases as you move away from Sydney city centre where there are older homes, more traffic and industries.
The cross-section of a typical inner Sydney residential home, with the median soil Pb concentrations (lead), for painted homes pre-1970, non-painted homes pre-1970, post-1970 and reference homes. As was the case with most homes, the vegetable garden is located at the back of the backyard. Source: Rouillon et al. 2016
Lead exposure can be especially harmful to children, as their skeletal and neurological systems are still developing. Adults can also be adversely affected by sub-clinical lead exposures. Studies have shown that increased blood tension and hypertension is associated with such exposures.
Toxicological evidence shows that exposure also reduces the quality of semen and prolongs pregnancy. Lead is harmful to all human systems, and it should be avoided at all costs.
According to our study, lead contamination is higher in soils around painted homes. Many Australian homes built before 1970 still have paint with lead content up to 50% on the exterior walls, fences and eaves, as well as doors, window frames, and door frames.
Exposure is a major risk when lead-based paint degrades or is improperly removed. Many home renovators expose themselves unknowingly and others to lead hazards due to their lack of knowledge.