A fluidized bed aerosol generator was connected to a 13-stage cascade impactor (nanoMOUDI) for the size fractionation of urban dust (<10 µm), followed by the gravimetric analysis of loaded PTFE filter samples. This method was used to characterize the PM₁₀ (thoracic) fraction of road dust sampled from expressways, arterial roads and local roads in Toronto, Canada. The fine particle fractions (<1.8 µm) of all the studied samples accounted for 51–72% of the resuspended PM₁₀ (by weight). Elemental analysis using ICP-MS and ICP-OES revealed an overall trend of element enrichment in the <1.8 µm fraction compared to the coarse fraction (1.8–10 µm) of the road dust. By contrast, archived house dust samples displayed the reverse trend for most elements. The lung bioaccessibility of target elements (Al, B, Ba, Co, Cr, Fe, La, Mn, Mo, Sb, Sr, Ti, V and Zn) was assessed for each road dust fraction using 0.1 M ammonium citrate (pH 4.4) to simulate intracellular fluid and Gamble solution (pH 7.2) to simulate interstitial lung fluid. The <1.8 µm fraction of local road dust displayed significantly higher bioaccessibility (p < 0.05) for Zn when using Gamble solution, and for seven out of the 14 target elements when using ammonium citrate. These results show the importance of characterizing the fine fraction of road dust.

Understanding bioaccessibility, defined as the fraction of an element that is soluble under gastrointestinal conditions, has become an important component of human health risk assessments. This study investigated the impact of humidity on the bioaccessibility of lead (Pb), zinc (Zn), cobalt (Co) and selenium (Se) in house dust. Three dust samples (two vacuum samples and NIST 2584 Indoor Dust) were weathered in an oxygenated humidity chamber for four months. Bioaccessibility was determined in original and weathered samples using a simulated gastric extraction followed by Inductively-Coupled Plasma Optical Emission Spectrometry (ICP-OES) and/or Mass Spectrometry (ICP-MS) as required. Exposure to humid conditions significantly increased bioaccessibility in all samples by 45–93% for Pb and by 21–65% for Zn. In contrast, bioaccessibility of Se was significantly decreased in all three weathered samples (by 75–93%), whereas bioaccessibility of Co displayed a variable response (16% increase; no significant change; 35% decrease respectively). Synchrotron XAS analysis of Pb speciation in the original and weathered dust samples determined that Pb transformed from less bioaccessible inorganic species towards more bioaccessible organic species under humid conditions. These results indicated that chemical transformations in damp microenvironments where house dust accumulates, such as window troughs or the base of carpets, may increase the bioaccessibility of particle-bound elements. Changes in bioaccessibility caused by weathering were shown to be significant in the context of the nationally representative Canadian House Dust Study (n = 1025). The national datasets indicated that bioaccessibility is element-dependent (median 59% for Pb; 67% for Zn; 33% for Co; and 13% for Se). Variations in the frequency distributions were attributed to site-specific differences in speciation and the varied bioaccessibility of individual species. The importance of speciation in determining overall bioaccessibility was further demonstrated by measurements of dozens of Pb, Zn and Co compounds that could feasibly occur in house dust. It was concluded that interactions between these elements and the organic matter content of house dust are key to understanding element bioaccessibility and accumulation behaviour in the indoor environment.

Wipe sampling is the USA regulatory protocol for determination of “dust lead loadings” in residential environments. Few studies have applied the wipe sampling method to metals other than lead (Pb) for the purpose of residential exposure assessments. This study was undertaken to develop and expand the wipe method for quantifying additional metal(loid)s including arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), and antimony (Sb); and to provide information on typical background loadings for these metals in urban Canadian homes. A total of 932 wipe samples, 220 field blanks, and 220 duplicate wipes were collected from 222 homes located in three cities in Ontario, Canada using the ASTM 1728 standard. The wipes were digested using a modified version of the ASTM 1644 standard for Pb, which prescribes a hot nitric acid/hydrogen peroxide digestion. The key modification was the addition of hydrofluoric acid to improve recoveries of the target elements, and determination using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Generally, a large proportion of the results fell below the limits of detection (LOD) and quantification (LOQ). To distinguish “elevated” metal loadings from loadings characterized as “urban background”, an upper background threshold for each element was derived using a normality (Q–Q) plot. LOQ was determined to be the appropriate minimum threshold based on quality assurance criteria. It is concluded that wipes are a useful sampling option to investigate multi-element loadings in residential environments.