ARTICLE pubs.acs.org/est
Canadian House Dust Study: Lead Bioaccessibility and Speciation Pat E. Rasmussen,*,†,‡ Suzanne Beauchemin,§ Marc Chenier,†,‡ Christine Levesque,† Lachlan C. W. MacLean,† Leonora Marro,† Heather Jones-Otazo,|| Sanya Petrovic,^ Lauren T. McDonald,† and H. David Gardner†,‡ †
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Exposure and Biomonitoring Division, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Colombine Driveway, Ottawa, Ontario, Canada K1A 0K9 ‡ Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 § Natural Resources Canada, CANMET-MMSL, 555 Booth Street, Ottawa, Ontario, Canada K1A 0G1 Regions and Programs Branch, Health Canada, 180 Queen Street West, Toronto, Ontario, Canada M5V 3L7 ^ Contaminated Sites Division, Healthy Environments and Consumer Safety Branch, Health Canada, 269 Laurier Avenue West, Ottawa, Ontario, Canada K1A 0K9
bS Supporting Information ABSTRACT: Vacuum samples were collected from 1025 randomly selected urban Canadian homes to investigate bioaccessible Pb (PbS) concentrations in settled house dust. Results indicate a polymodal frequency distribution, consisting of three lognormally distributed subpopulations defined as “urban background” (geomean 58 μg g1), “elevated” (geomean 447 μg g1), and “anomalous” (geomean 1730 μg g1). Dust PbS 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 PbS content (R2 = 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 (R2 = 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.
’ INTRODUCTION House dust is described as playing a dual role in environmental exposures to lead (Pb): it is both a transport medium, facilitating the transfer of outdoor contaminants in airborne particles, soil, and street dust to the indoor environment,1,2 and an exposure medium, with ingestion of house dust providing the major pathway of Pb exposure for young children.35 Results of a recent (2007- 2009) Canadian biomonitoring survey6 linked elevated blood Pb levels with older housing stock (>50 years old). Elevated dust Pb may occur in older homes due to the extensive past use of Pb compounds in paint and plumbing,7,8 but actual exposure depends on the presence of peeling paint inside and outside, home remodelling, paint removal, effectiveness of cleaning, and frequency of cleaning.5,8 Published 2011 by the American Chemical Society
The present study characterizes bioaccessible Pb in urban Canadian house dust sampled from 2007 to 2010 as part of the population-based Canadian House Dust Study (CHDS). The CHDS was designed to obtain statistically robust, nationally representative baseline estimates for Pb and other chemical constituents of settled dust in urban Canadian homes. As defined by Horsch,9 baseline data need to be collected “to identify the starting point from which progress is examined”; this will enable future decision-makers to evaluate the progress of Pb reduction Received: December 3, 2010 Accepted: April 29, 2011 Revised: April 5, 2011 Published: May 12, 2011 4959
dx.doi.org/10.1021/es104056m | Environ. Sci. Technol. 2011, 45, 4959–4965
Environmental Science & Technology programs and risk management policies. Pilot studies in Ottawa, Canada,10,11 a city generally characterized as an “urban background” setting, indicated that geomean Pb concentrations are 5-fold higher in house dust compared to exterior dust and soil. These results pointed to the need to obtain a nationally representative measure of Pb concentrations in house dust. One difficulty in defining incremental (i.e., above typical background) exposures and risks associated with contaminated sites has been the lack of quantitative population-based information on typical residential exposures. Therefore, an important application of the present study is to provide a point of comparison for human health risk assessments (HHRA) at contaminated sites. House dust is an organic-rich matrix (1837% organic C) with an affinity for metals,12 which serves as a useful sampling medium for detailed chemical, isotopic, and mineralogical investigations aimed at identifying and mitigating potential Pb sources.1316 Solid sample dust speciation studies, using a combination of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS) analyses, and synchrotron-based microprobe techniques, have shown that Pb speciation of Pb-contaminated dust in older Canadian homes (>50 yr) is dominated by pigments and other compounds used in paints at that time.7,17 Childhood exposure estimates are improved by understanding the solubility of dust Pb in the gut (bioaccessibility), which is controlled by the chemical or mineral form (speciation) of the Pb.1820 Thus in addition to the main goal of establishing a nationally representative baseline for urban Canadian homes, the present study uses synchrotron-based X-ray techniques to identify Pb compounds in elevated dust Pb samples and examines the relationship between solid sample Pb speciation and bioaccessibility.
’ METHODS Study Design. A three-stage stratified sampling design was developed with the goal of obtaining a random and representative population-based sample of single family homes in large Canadian cities (population >100,000). Existing information on the variability of dust Pb concentrations in Ottawa households10 and Canadian Census data21 indicated that sampling approximately 1000 homes across Canada would be required to obtain a statistically robust urban estimate. In the first stage, Canadian provinces and territories were divided into five regions from which a random sample of 13 cities was selected using proportional allocation (Figure 1). In the second stage, a sample of 8 to 10 dissemination areas (DAs) was randomly selected from each city. In the third stage, a simple random sample of addresses within each DA was generated for mailing out letters of invitation. Results for the Canadian House Dust Study are not reported on a municipal or regional basis, as the statistical design requires that results are aggregated for Canada as a whole. The sampling plan was rigorously designed to provide a nationally representative sample; therefore, subsets of samples from individual cities are not intended to be representative of those cities. Likewise, samples collected in a given province or region are not representative of that province or region. Study participation was anonymous. Dust Sampling. Sampling was conducted in the winter seasons from January 2007 to March 2010. The household visits each lasted two hours, during which the consultant conducted wipe sampling as described elsewhere,22 followed by vacuum sampling and completion of a short questionnaire limited to
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Figure 1. Sampling Design: Canadian provinces and territories were divided into five regions 1. BC, AB, and YT; 2. SK, MN, and NT; 3. ON and NU; 4. QC; and 5. PE, NS, NB, and NL from which 13 cities with population >100,000 were randomly selected for sampling.
questions related to dust composition (e.g., heating practices, dates of construction and renovation activity, location relative to exterior sources, tobacco use, and hobbies). Participants were requested to refrain from vacuuming activities for one week prior to household visits. Settled dust samples were collected from bare floors and carpets following the German vacuum protocol23 Verein Deutscher Ingenieure, in which a composite sample of fresh (active) dust is collected from dry living areas of the home, including bedrooms, family rooms, offices, hallways, and finished basements. A Pullman-Holt High-Efficiency Particulate Air (HEPA) vacuum sampler (model 102 ASB-12PD) was used, in which dust particles follow a direct pathway from the floor to the vacuum bag, without passing internal mechanical parts, thus avoiding potential contamination of the sample. The bag is specified to capture 99.97% of all particles g0.3 μm. In many homes only small amounts of dust were available, and therefore small sample masses (
