Relationships between House Characteristics and Exposures to Metal(loid)s and Synthetic Organic Contaminants Evaluated Using Settled Indoor Dust.

This study investigates associations between house characteristics and chemical contaminants in house dust, collected under the nationally representative Canadian House Dust Study (2007−2010). Vacuum samples (<80 µm fraction) were analysed for over 200 synthetic organic compounds and metal(loid)s. Spearman rank correlations between contaminant concentrations in dust and presence of children and pets, types of flooring, heating styles and other characteristics suggested a number of indoor sources, pointing to future research directions. Numerous synthetic organics were significantly associated with reported use of room deodorizers and with the presence of cats in the home. Hardwood flooring, which is a manufactured wood product, emerged as a source of metal(loid)s, phthalates, organophosphate flame retardants/plasticizers, and obsolete organochlorine pesticides such as ∑DDT (but not halogenated flame retardants). Many metal(loid)s were significantly correlated with flame-retardant compounds used in building materials and heating systems. Components of heating appliances and heat distribution systems appeared to contribute heat-resistant chemicals and alloys to settled dust. Carpets displayed a dual role as both a source and repository of dust-borne contaminants. Contaminant loadings (<80 µm fraction) were significantly elevated in heavily carpeted homes, particularly those located near industry. Depending on the chemical (and its source), the results show that increased dust mass loading may enrich or dilute chemical concentrations in dust. Research is needed to improve the characterisation of hidden indoor sources such as flame retardants used in building materials and heating systems, or undisclosed ingredients used in common household products, such as air fresheners and products used for companion animals.

Selection of metric for indoor-outdoor source apportionment of metals in PM2.5 : mg/kg versus ng/m3.

Trends in the elemental composition of fine particulate matter (PM2.5 ) collected from indoor, outdoor, and personal microenvironments were investigated using two metrics: ng/m3 and mg/kg. Pearson correlations that were positive using one metric commonly disappeared or flipped to become negative when the other metric was applied to the same dataset. For example, the correlation between Mo and S in the outdoor microenvironment was positive using ng/m3 (p < 0.05) but negative using mg/kg (p < 0.05). In general, elemental concentrations (mg/kg) within PM2.5 decreased significantly (p < 0.05) as PM2.5 concentrations (µg/m3 ) increased-a dilution effect that was observed in all microenvironments and seasons. An exception was S: in the outdoor microenvironment, the correlation between wt% S and PM2.5  flipped from negative in the winter (p < 0.01) to positive (p < 0.01) in the summer, whereas in the indoor microenvironment, this correlation was negative year-round (p < 0.05). Correlation analyses using mg/kg indicated that elemental associations may arise from Fe-Mn oxyhydroxide sorption processes that occur as particles age, with or without the presence of a common anthropogenic source. Application of mass-normalized concentration metrics (mg/kg or wt%), enabled by careful gravimetric analysis, revealed new evidence of the importance of indoor sources of elements in PM2.5 .

Detection of Carbon Nanotubes in Indoor Workplaces Using Elemental Impurities.

This study investigated three area sampling approaches for using metal impurities in carbon nanotubes (CNTs) to identify CNT releases in workplace environments: air concentrations (µg/m3), surface loadings (µg/cm2), and passive deposition rates (µg/m2/h). Correlations between metal impurities and CNTs were evaluated by collecting simultaneous colocated area samples for thermal-optical analysis (for CNTs) and ICP-MS analysis (for metals) in a CNT manufacturing facility. CNTs correlated strongly with Co (residual catalyst) and Ni (impurity) in floor surface loadings, and with Co in passive deposition samples. Interpretation of elemental ratios (Co/Fe) assisted in distinguishing among CNT and non-CNT sources of contamination. Stable isotopes of Pb impurities were useful for identifying aerosolized CNTs in the workplace environment of a downstream user, as CNTs from different manufacturers each had distinctive Pb isotope signatures. Pb isotopes were not useful for identifying CNT releases within a CNT manufacturing environment, however, because the CNT signature reflected the indoor background signature. CNT manufacturing companies and downstream users of CNTs will benefit from the availability of alternative and complementary strategies for identifying the presence/absence of CNTs in the workplace and for monitoring the effectiveness of control measures.

Evaluating the capabilities of aerosol-to-liquid particle extraction system (ALPXS)/ICP-MS for monitoring trace metals in indoor air.

This study investigates the application of the Aerosol-to-Liquid Particle Extraction System (ALPXS), which uses wet electrostatic precipitation to collect airborne particles, for multi-element indoor stationary monitoring. Optimum conditions are determined for capturing airborne particles for metal determination by inductively coupled plasma-mass spectrometry (ICP-MS), for measuring field blanks, and for calculating limits of detection (LOD) and quantification (LOQ). Due to the relatively high flow rate (300 L min(-1)), a sampling duration of 1 hr to 2 hr was adequate to capture airborne particle-bound metals under the investigated experimental conditions. The performance of the ALPXS during a building renovation demonstrated signal-to-noise ratios appropriate for sampling airborne particles in environments with elevated metal concentrations, such as workplace settings. The ALPXS shows promise as a research tool for providing useful information on short-term variations (transient signals) and for trapping particles into aqueous solutions where needed for subsequent characterization. As the ALPXS does not provide size-specific samples, and its efficiency at different flow rates has yet to be quantified, the ALPXS would not replace standard filter-based protocols accepted for regulatory applications (e.g., exposure measurements), but rather would provide additional information if used in conjunction with filter based methods. Implications: This study investigates the capability of the Aerosol-to-Liquid Particle Extraction System (ALPXS) for stationary sampling of airborne metals in indoor workplace environments, with subsequent analysis by ICP-MS. The high flow rate (300 L/min) permits a short sampling duration (< 2 hr). Results indicated that the ALPXS was capable of monitoring short-term changes in metal emissions during a renovation activity. This portable instrument may prove to be advantageous in occupational settings as a qualitative indicator of elevated concentrations of airborne metals at short time scales.

Canadian House Dust Study: population-based concentrations, loads and loading rates of arsenic, cadmium, chromium, copper, nickel, lead, and zinc inside urban homes.

The Canadian House Dust Study was designed to obtain nationally representative urban house dust metal concentrations (µg g(-1)) and metal loadings (µg m(-2)) for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Consistent sampling of active dust of known age and provenance (area sampled) also permitted the calculation of indoor loading rates (mg m(-2) day(-1) for dust and µg m(-2) day(-1) for metals) for the winter season (from 2007 to 2010) when houses are most tightly sealed. Geomean/median indoor dust loading rates in homes located more than 2 km away from industry of any kind (9.6/9.1 mg m(-2) day(-1); n=580) were significantly lower (p<.001) than geomean (median) dust loading rates in homes located within 2 km of industry (13.5/13.4 mg m(-2) day(-1); n=421). Proximity to industry was characterized by higher indoor metal loading rates (p<.003), but no difference in dust metal concentrations (.29≥p≤.97). Comparisons of non-smokers' and smokers' homes in non-industrial zones showed higher metal loading rates (.005≥p≤.038) in smokers' homes, but no difference in dust metal concentrations (.15≥p≤.97). Relationships between house age and dust metal concentrations were significant for Pb, Cd and Zn (p<.001) but not for the other four metals (.14≥p≤.87). All seven metals, however, displayed a significant increase in metal loading rates with house age (p<.001) due to the influence of higher dust loading rates in older homes (p<.001). Relationships between three measures of metals in house dust - concentration, load, and loading rate - in the context of house age, smoking behavior and urban setting consistently show that concentration data is a useful indicator of the presence of metal sources in the home, whereas dust mass is the overriding influence on metal loadings and loading rates.

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.

Buoyancy-corrected gravimetric analysis of lightly loaded filters.

Numerous sources of uncertainty are associated with the gravimetric analysis of lightly loaded air filter samples (< 100 microg). The purpose of the study presented here is to investigate the effectiveness and limitations of air buoyancy corrections over experimentally adjusted conditions of temperature (21-25 degrees C) and relative humidity (RH) (16-60% RH). Conditioning (24 hr) and weighing were performed inside the Archimedes M3 environmentally controlled chamber. The measurements were performed using 20 size-fractionated samples of resuspended house dust loaded onto Teflo (PTFE) filters using a Micro-Orifice Uniform Deposit Impactor representing a wide range of mass loading (7.2-3130 microg) and cut sizes (0.056-9.9 microm). By maintaining tight controls on humidity (within 0.5% RH of control setting) throughout pre- and postweighing at each stepwise increase in RH, it was possible to quantify error due to water absorption: 45% of the total mass change due to water absorption occurred between 16 and 50% RH, and 55% occurred between 50 and 60% RH. The buoyancy corrections ranged from -3.5 to +5.8 microg in magnitude and improved relative standard deviation (RSD) from 21.3% (uncorrected) to 5.6% (corrected) for a 7.2 microg sample. It is recommended that protocols for weighing low-mass particle samples (e.g., nanoparticle samples) should include buoyancy corrections and tight temperature/humidity controls. In some cases, conditioning times longer than 24 hr may be warranted.