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Vacuum samples were collected from 1025 randomly selected urban Canadian homes to investigate bioaccessible Pb (Pb(S)) concentrations in settled house dust. Results indicate a polymodal frequency distribution, consisting of three lognormally distributed subpopulations defined as "urban background" (geomean 58 μg g(-1)), "elevated" (geomean 447 μg g(-1)), and "anomalous" (geomean 1730 μg g(-1)). Dust Pb(S) concentrations in 924 homes (90%) fall into the "urban background" category. The elevated and anomalous subpopulations predominantly consist of older homes located in central core areas of cities. The influence of house age is evidenced by a moderate correlation between house age and dust Pb(S) content (R(2) = 0.34; n = 1025; p < 0.01), but it is notable that more than 10% of homes in the elevated/anomalous category were built after 1980. Conversely, the benefit of home remediation is evidenced by the large number of homes (33%) in the background category that were built before 1960. The dominant dust Pb species determined using X-ray Absorption Spectroscopy were as follows: Pb carbonate, Pb hydroxyl carbonate, Pb sulfate, Pb chromate, Pb oxide, Pb citrate, Pb metal, Pb adsorbed to Fe- and Al-oxyhydroxides, and Pb adsorbed to humate. Pb bioaccessibility estimated from solid phase speciation predicts Pb bioaccessibility measured using a simulated gastric extraction (R(2) = 0.85; n = 12; p < 0.0001). The trend toward increased Pb bioaccessibility in the elevated and anomalous subpopulations (75% ± 18% and 81% ± 8%, respectively) compared to background (63% ± 18%) is explained by the higher proportion of bioaccessible compounds used as pigments in older paints (Pb carbonate and Pb hydroxyl carbonate). This population-based study provides a nationally representative urban baseline for applications in human health risk assessment and risk management.

Soil ingestion rates calculated using a tracer-based mass balance approach may carry considerable study errors, insensitivities, and "artefacts" of analysis that result in significant uncertainty. These same soil ingestion rates are often used as surrogates for dust ingestion rates. Therefore, a more direct and mechanistic method was developed to estimate soil and dust ingestion rates. The soil and dust ingestion rates were calculated using measures of: particle loading to indoor surfaces; fraction transferred to the hands; hand surface area; fraction of hand surface area that may be mouthed or contact food; frequency of hand-to-mouth events, amount dissolved by saliva; and exposure time. Adapted specifically for the Canadian context, estimated mean indoor dust ingestion rates range from 2.2 mg/d for teenagers to 41 mg/d for toddlers; mean soil ingestion rates range from 1.2 mg/d for seniors to 23 mg/d for children. Combined soil and dust ingestion rates ranged from 3.8 mg/d for seniors to 61 mg/d for toddlers. These ingestion rates are lower than values adopted by most agencies. These ingestion rates are mechanistic, can be adjusted on a site-specific basis, can be modified into an hourly rate and are presented as a more realistic alternative to traditional mass balance approaches.

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Dermal absorption of heavy metal soil contaminants was tested in vitro with chloride salts of radioactive nickel (Ni-63) and mercury (Hg-203). Aqueous soil suspensions, spiked with either Ni-63 or Hg-203, were applied to fresh viable human breast skin tissue in Bronaugh diffusion cells perfused with Hanks HEPES buffered (pH 7.4) receptor containing 4% bovine serum albumin (BSA). Receptor fractions were collected every 6 h for 24 h when skin was soap washed. Tests were conducted concurrently in triplicate with and without soil for each skin specimen. Mean percent dermal absorption including the skin depot for Ni-63 was 1 and 22.8% with and without soil, respectively, while for Hg-203, values of 46.6 and 78.3% were obtained. Excluding the skin depot and considering only absorption in receptor, there was 0.5 and 1.8% absorption of Ni-63 with and without soil, respectively, and 1.5 and 1.4% for Hg-203. The potential bioavailability of the skin depot is discussed in relation to dermal exposure to these metals in contaminated soil.