Suzanne Beauchemin

Canadian house dust study: lead bioaccessibility and speciation.

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.

Influence of Matrix Composition on the Bioaccessibility of Copper, Zinc, and Nickel in Urban Residential Dust and Soil

ABSTRACT This study examines factors affecting oral bioaccessibility of metals in household dust, in particular metal speciation, organic carbon content, and particle size, with the goal of addressing risk assessment information requirements. Investigation of copper (Cu) and zinc (Zn) speciation in two size fractions of dust (< 36 μ m and 80–150 μ m) using synchrotron X-ray absorption spectroscopy (XAS) indicates that the two metals are bound to different components of the dust: Cu is predominately associated with the organic phase of the dust, while Zn is predominately associated with the mineral fraction. Total and bioaccessible Cu, nickel (Ni), and Zn were determined (on dry weight basis) in the < 150 μ m size fraction of a set of archived indoor dust samples (n = 63) and corresponding garden soil samples (n = 66) from the City of Ottawa, Canada. The median bioaccessible Cu content is 66 μ g g−1 in dust compared to 5 μ g g−1 in soil; the median bioaccessible Ni content is 16 μ g g−1 in dust compared to 2 μ g g−1 in soil; and the median bioaccessible Zn content is 410 μ g g−1 in dust compared to 18 μ g g−1 in soil. For the same data set, the median total Cu content is 152 μ g g−1 in dust compared to 17 μ g g−1 in soil; the median total Ni content is 41 μ g g−1 in dust compared to 13 μ g g−1 in soil; and the median total Zn content is 626 μ g g−1 in dust compared to 84 μ g g−1 in soil. Organic carbon is elevated in indoor dust (median 28%) compared to soil (median 5%), and is a key factor controlling metal partitioning and therefore bioaccessibility. The results show that house dust and soil have distinct geochemical signatures and should not be treated as identical media in exposure and risk assessments. Separate measurements of the indoor and outdoor environment are essential to improve the accuracy of residential risk assessments.

Lead Speciation in House Dust from Canadian Urban Homes Using EXAFS Micro-XRF and Micro-XRD

X-ray absorption fine-structure (XAFS) spectroscopy, micro-X-ray fluorescence (μXRF), and micro-X-ray diffraction (μXRD) were used to determine the speciation of Pb in house dust samples from four Canadian urban homes having elevated Pb concentrations (>1000 mg Pb kg(-1)). Linear combination fitting of the XAFS data, supported by μXRF and μXRD, shows that Pb is complexed in a variety of molecular environments, associated with both the inorganic and organic fractions of the dust samples. The inorganic species of lead identified were as follows: Pb metal, Pb carbonate, Pb hydroxyl carbonate, Pb oxide, and Pb adsorbed to iron oxyhydroxides. Pb carbonate and/or Pb hydroxyl carbonate occurred in all four dust samples and accounted for 28 to 75% of total Pb. Pb citrate and Pb bound to humate were the organic species identified. The results of this study demonstrate the ability of XAFS to identify Pb speciation in house dust and show the potential to identify Pb sources from new homes versus older homes. Understanding Pb speciation and how it influences bioaccessibility is important for human health risk assessment and risk management decisions which aim to improve indoor environmental health.

Lead speciation in indoor dust: a case study to assess old paint contribution in a Canadian urban house

Residents in older homes may experience increased lead (Pb) exposures due to release of lead from interior paints manufactured in past decades, especially pre-1960s. The objective of the study was to determine the speciation of Pb in settled dust from an urban home built during WWII. X-ray absorption near-edge structure (XANES) and micro-X-ray diffraction (XRD) analyses were performed on samples of paint (380–2,920xa0mg Pb kg−1) and dust (200–1,000xa0mg Pb kg−1) collected prior to renovation. All dust samples exhibited a Pb XANES signature similar to that of Pb found in paint. Bulk XANES and micro-XRD identified Pb species commonly found as white paint pigments (Pb oxide, Pb sulfate, and Pb carbonate) as well as rutile, a titanium-based pigment, in the <150xa0μm house dust samples. In the dust fraction <36xa0μm, half of the Pb was associated with the Fe-oxyhydroxides, suggesting additional contribution of outdoor sources to Pb in the finer dust. These results confirm that old paints still contribute to Pb in the settled dust for this 65-year-old home. The Pb speciation also provided a clearer understanding of the Pb bioaccessibility: Pb carbonatexa0>xa0Pb oxidexa0>xa0Pb sulfate. This study underscores the importance of taking precautions to minimize exposures to Pb in house dust, especially in homes where old paint is exposed due to renovations or deterioration of painted surfaces.

Impact of humidity on speciation and bioaccessibility of Pb, Zn, Co and Se in house 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.

Contributions of natural arsenic sources to surface waters on a high grade arsenic-geochemical anomaly (French Massif Central)

The subwatershed studied drains a non-exploited area of the St-Yrieix-la-Perche gold mining district (French Massif Central) and it is located on an arsenic (As) geochemical anomaly. In this context, it is important to know the geochemical processes involved in the transfer of As from solid environmental compartments to the aquatic system. The stream showed a temporal variation of dissolved As (As(d)) content from 69.4 μg.L(-1) in the low flow period to 7.5 μg.L(-1) in the high flow period. Upstream, ground- and wetland waters had As(d) concentrations up to 215 and 169 μg.L(-1), respectively. The main representative As sources were determined at the subwatershed scale with in-situ monitoring of major and trace element contents in different waters and single extraction experiments. The As sources to stream water could be regrouped into two components: (i) one As-rich group (mainly in the low flow period) with groundwater, gallery exploration outlet waters and wetland waters, and (ii) one As-poor group (mainly in the high flow period) with rainwaters and soil solutions. In the soil profile, As(d) showed a significant decrease from 52.4 μg.L(-1) in the 0-5 cm superficial soil horizon to 14.4 μg.L(-1) in the 135-165 cm deep soil horizon. This decrease may be related to pedogenic processes and suggests an evolution of As-bearing phase stability through the soil profile. Quantification of As(d) fluxes at the subwatershed scale showed that groundwater was the major input (>80%) of As(d) to surface water. Moreover, natural weathering of the As-rich solid phases showed an impact on the As release, mainly from superficial soil horizons with runoff contributing about 5% to As input in surface water.

Chemical transformations of lead compounds under humid conditions: implications for bioaccessibility

This short communication documents chemical transformations caused by weathering of two Pb compounds that commonly occur in house dust. Chamber experiments were designed to simulate humid indoor environment conditions to determine whether Pb compounds undergo chemical transformations influencing bioaccessibility. Reference compounds of Pb metal (12xa0% bioaccessibility) and Pb sulfate (14xa0% bioaccessibility) were subjected to an oxygenated, humidified atmosphere in closed chambers for 4xa0months. X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) spectroscopy were used to characterize the main Pb species, and the change in Pb bioaccessibility was determined using a simulated gastric acid digestion. At the end of the weathering period a small amount of Pb carbonate (9xa0% of total Pb) appeared in the Pb sulfate sample. Weathering of the Pb metal sample resulted in the formation of two compounds, hydrocerussite (Pb hydroxyl carbonate) and Pb oxide, in significant amounts (each accounted for 26xa0% of total Pb). The formation of highly bioaccessible Pb carbonate (73xa0% bioaccessibility), hydrocerussite (76xa0% bioaccessibility), and Pb oxide (67xa0% bioaccessibility) during weathering resulted in a measurable increase in the overall Pb bioaccessibility of both samples, which was significant (pxa0=xa0.002) in the case of the Pb metal sample. This study demonstrates that Pb compounds commonly found in indoor dust can ‘age’ into more bioaccessible forms under humid indoor conditions.

Application of Synchrotron X-ray Techniques for the Determination of Metal Speciation in (House) Dust Particles

An overview of synchrotron radiation-based X-ray absorption and scattering techniques for characterizing the speciation of metals in complex, heterogeneous samples, such as house dust, is presented. The complementary techniques are demonstrated on a house dust sample elevated in Pb (1,670 mg kg−1). The X-ray techniques successfully identified the speciation and sources of Pb in house dust samples, and provided an explanation for the observed high Pb bioaccessibility. Ultimately, this approach has the potential to fingerprint the various sources of metals and metalloids in houses (outdoor vs. indoor) and help determine any transformation processes that these compounds may undergo inside a building. Understanding these sources and processes will have important implications for risk management within the indoor environment.

Initial biochar properties related to the removal of As, Se, Pb, Cd, Cu, Ni, and Zn from an acidic suspension

This study tests the influence of a diverse set of biochar properties on As(V), Se(IV), Cd(II), Cu(II), Ni(II), Pb(II), or Zn(II) removal from solution at pH 4.5. Six commercial biochars produced using different feedstock and pyrolysis conditions were extensively characterized using physical, chemical, and spectroscopic techniques, and their properties were correlated to anion and cation removal using multiple linear regression. H/total organic C (TOC) ratio and volatile matter were positively correlated to cation removal from solution, which indicate interactions between metals and non-aromatic C. Defining the correlation of ion removal with specific OC functional groups was hindered by the inherent limitations of the spectroscopic techniques, which was exacerbated by the heterogeneity of the biochars. Ash was negatively correlated to Se(IV) and positively correlated to Cd(II), Cu(II), and Ni(II) removal from solution. Interference from soluble P in biochars may partly explain the low Se(IV) removal from solution; and Ca-, P-, and Fe- containing compounds likely sorbed or precipitated Pb(II), Cd(II), Cu(II), Ni(II) and Zn(II). Furthermore, Ca-oxalate identified using X-ray diffraction in willow, may be responsible for willows increased ability to remove Cd(II), Ni(II), and Zn(II) compared to the other 5 biochars. It was clear that both OC and inorganic biochar components influenced metal(loid) and Se(IV) removal from solution. The non-aromatic and volatile OC correlated to removal from solution may be readily available for microbial degradation, while Mg, N, P, and S are required for biological growth. Biological metabolism and uptake of these compounds may inhibit or destabilize their interaction with contaminants.

Differentiating Inorganics in Biochars Produced at Commercial Scale Using Principal Component Analysis

Characterizing the inorganic phase of biochar, beyond determining element concentration, is needed for appropriate application of these materials because mineral forms also influence element availability and behavior. Inorganics in 13 biochars (produced from Poultry litter, switchgrass, and different types of wood) were characterized by proximate analysis, chemical analysis, powder X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) spectroscopy. Principal component analysis (PCA) was used to compare biochars and characterize associations between elements. The biochars were produced using commercial-scale reactors and represent materials with properties relevant to field application. Bulk inorganic concentration and composition were responsible for differentiating biochars after PCA of chemical data. In comparison, differentiation based on PCA of diffractogram fingerprints was more nuanced. Here, contributions from cellulose and turbostratic crystalline C influenced separation between samples. It was also sensitive to mineral forms of Ca (whewellite and calcite). Differences in crystalline C and Ca minerals separated two biochars generated from the same willow feedstock using the same pyrolysis conditions at different temperatures. PCA of 606 SEM-EDX point scans revealed that inorganics belong to four main clusters containing Ca, Fe, [Al, Si], and [Cl, K, Mg, Na, P, S] consistent with XRD identification of calcite, magnetic Fe-oxide, silicates, and sylvite. It further suggested that amorphous P-containing minerals associated with Ca (not identified through XRD) were constituents of willow and poultry litter-derived biochars. However, unlike PCA of XRD, it was not able to differentiate the two biochars derived from willow. The three analysis methods provided different perspectives on the properties of the biochar inorganic phase. Combining information from multiple methods is needed to better understand the inorganic composition of biochars.