CHARACTERIZING THE SOURCES OF PARTICULATE LEAD IN HOUSE DUST BY AUTOMATED SCANNING ELECTRON-MICROSCOPY

Automated scanning electron microscopy procedures have been devised for apportioning the sources of lead in household dust. Source particles were sampled from auto exhausts, road dusts, garden soils, mineralized soils, paints, lead smelters, a waste incinerator, electrical materials, and lead oxide reference materials. A source signature library containing size and elemental data on more than 8300 individual lead-containing source particles was created. A divisive hierarchical cluster analysis was used to identify 101 groups of compositionally similar source "type" particles in the source library data. These groups formed the basis for an extended classification scheme. A simple descritpive apportionment procedure was defined to deal with the classification results generated by this scheme. The wide dispersion of lead in the house dust matrix necessitated the development of separation and preconcentration techniques involving density and size fractionation. Analysis results for house dusts suggest that paint, road dust, and garden soil may all be important lead sources. These contributions are a function of particle size, and the importance of the contributions is dependent on whether the apportionment is based on particle population or estimated particle volume.