Isotopic ratio analysis in residential lead-based paint and associated surficial dust

Objectives: This investigation assessed the contribution of lead in lead-based paint (7 samples) to lead-laden dust (8 samples) in a single suburban vacant residence using isotopic ratio analysis, Methods: Interior/exterior lead-based paint surface concentration was measured by X-ray fluorescence while dust and scrapings were analyzed chemically for total lead content and by mass spectrometry for the associated isotopic ratios. Results: Four out of 5 comparisons of paint (7 samples) and dust (8 samples) for a given location did not match isotopically, In the one location where the isotopic ratio of the paint and dust samples matched closely, some portions of the paint were not intact. One explanation for the isotopic ratio match is that the dust sample may have actually been contaminated with paint flecks. This explanation appears likely since the isotopic ratio for the lead in the dust and paint sample were not in the modern average range of US environmental lead, strongly indicating a local point source of the lead in this dust sample, namely the paint at this location. Lead dust samples whose isotopic ratio lies in the modern average range for US environmental lead cannot be correlated to the paint which is beneath them, since the isotopic ratio of lead in the dust may actually be a composite of many sources of lead over time, as suggested by an isotopic ratio in the modern average range. Conclusions: From the samples from this one house, the data dispute the contention that intact lead-based paint chalks and creates lead-contaminated dust on its surface. While leaded household dust may contribute to children's lead exposure, intact paint need not contribute to surficial lead-laden dust. Isotopic ratio measurements can be useful for point-source determination by virtue of sample match and by placement of the ratio on the spectrum of isotopic ratio values for lead. Point-source assessment based on isotopic ratio was either strengthened or weakened by placement outside or within the average range for US environmental lead, respectively.