The main source of high lead levels found in homes in western Sydney is not interior lead paint but lead from soils, according to a Macquarie University research investigation. Garden soils have accumulated lead mainly as a result of decades of emissions from vehicles running on leaded petrol. Other sources of lead include the deterioration of exterior leaded paint.

The preliminary findings were made by Mark Laidlaw and Mark Taylor from Macquarie University, whose international collaborators include researchers at Colorado State University and the University of Texas at El Paso. Over a 15-month period, Mark and Mark collected data from paint samples, surface and subsurface soils, interior dust collected by vacuum cleaning, settled interior and attic dust, and exterior atmospheric dust obtained from four inner western Sydney houses and one in an area of low density bushland 28 kilometres northwest of Sydney. None of the houses had exterior paint, except on gutters and windows.

Mark and Mark analysed their samples for total metal content (arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc) and lead isotopes, and used x-ray absorption spectroscopy at the Australian Synchrotron (see image at right) to obtain lead spectra from each sample. The researchers then used the distinctive lead spectra, which vary according to the different lead compounds present in the samples, rather like fingerprints to determine where the lead inside the homes had come from.

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