sequent weathering processes of lead tailings preferentially produce lead in fine particles, or perhaps the majority of tracked particles are very fine lead particles deposited from air.

The dilution effect of indoor-derived organic-rich particles on the concentrations of crustal elements associated with tracked-in soils has been analyzed by Trowbridge and Burmaster (1997). For a series of crustal elements with no significant indoor sources (aluminum, cerium, iron, hafnium, lanthanum, manganese, sodium, phosphorus, scandium, samarium, thorium, and vanadium), the geometric mean (GM) dilution ratio (defined as the ratio of the concentration of the crustal element in house dust to its concentrations in yard soil) was 0.42, with a geometric standard deviation (GSD) of 1.44. A ratio of 1 would indicate that indoor dust is entirely of outdoor origin, whereas a ratio of 0 implies that outdoor soil does not contribute to indoor dust. The U.S. Environmental Protection Agency (EPA) default value for this ratio in the IEUBK model (defined as the MSD parameter, or the mass fraction of soil in dust, grams [g] of soil/g of dust) is 0.70 (EPA 1998), which is higher than the apparent dilution values noted above. However, IEUBK model runs conducted in support of the HHRA (Tables 6-11a-h) used measured concentrations of lead in household dust and yard soil.

As a means of further exploring the relationships between the crustal elements and lead in soil and dust, we evaluated the analytical results of the sampling campaigns that included measurements of iron, manganese, and lead in yard soils, entryway mats, and vacuum bag dust (data provided by the Idaho Department of Health and Welfare from FSPA06). The data included residences in the towns of Kingston, Osburn, Mullan, Silverton, and Wallace, along with residences in the Side Gulches, Nine-Mile, and Burke. To minimize the potential impacts of different sampling techniques and geographical regions on the exploratory analysis, we restricted the evaluation to the basin towns and used only the top surface-soil samples (0 to 0.08 feet) from the borehole samples of the yards (thereby excluding surface grab samples and hand auger samples). The soil concentration, assumed to be representative for the multiple yard samples obtained at each residence, was calculated as the GM of the samples. A total of 37 residences had paired measurements of the crustal elements and lead in the soil, mat, and vacuum bag media. Three residences included data outliers for one or more of the soil constituents and therefore were removed from the analysis, leaving 34 residences for the analysis. The resulting concentration data for the soils, mats, and vacuum bags were then used to calculate ratios for mat/ soil, vacuum bag/mat, and vacuum bag/soil. These ratios are presented in Table E-1.

The concentrations of iron and manganese in yard soils exhibit less variability than that of lead, which is reasonable given that the crustal

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