Old Paint Increases Lead Bioavailability In Dust

The dust sitting around a home can contain the neurotoxic metal lead from construction materials, old paint, batteries, and other materials. Canadian government researchers recently surveyed lead levels and sources in house dust across the country. They found that houses with old paint have more bioavailable lead in the dust (Environ. Sci. Technol., DOI: 10.1021/es104056m). Their results also suggest people don't know how to handle removing lead-containing paint when they renovate their homes, one expert says.

In the 1970s, the U.S. and Canadian governments banned lead in paint. But by then, many homes already had walls coated in paint with high lead levels. Scientists have yet to find a lead exposure level so low that it doesn't cause neurological harm to children, according to the U.S. Agency for Toxic Substances and Disease Registry.

Pat Rasmussen from Health Canada and colleagues set out to study the lead found in dust in urban Canadian homes. House dust is the major means of lead exposure for children, the researchers note. Scientists debate whether lead-based paints or other sources, such as soils tracked in from outdoors, are the major contributors of lead in this dust.

The team collected samples from vacuum cleaners in 1,025 randomly selected homes. Using X-ray absorption spectroscopy, the team found that about 90% of the homes had dust levels below 250 µg per gram of dust, which the researchers considered to be the typical exposure level for an average person. The remaining 10% of the homes had what the researchers called elevated lead levels, with some samples reaching 975 μg/g.

To identify the metal's source and estimate its bioavailability, the researchers used a synchrotron-based X-ray spectroscopy technique that they recently developed (Environ. Sci. Technol., DOI: 10.1021/es2001503). The method pinpoints the chemical form of lead present in their samples.

In the dust samples, they found nine lead species and traced two, lead carbonate and lead hydroxyl carbonate, to old paints. Since the scientists knew which forms of lead were more bioavailable than others, they estimated the amount of bioavailable lead in each of the dust samples. They determined that homes with elevated lead also had more bioavailable forms of the metal than background homes did. This increased bioavailability was due to the two compounds from old paint, the researchers report.

Rufus Edwards of the University of California, Irvine's School of Medicine is troubled by the study's results, particularly its finding that a majority--about 70%--of the homes with elevated lead levels underwent renovations recently. He thinks this result suggests people aren't aware of how to safely remove lead paint from older homes.