Rare earth elements and select actinoids in the Canadian House Dust Study

Abstract

Nationally representative baseline data are presented for rare earth elements (REE), thorium (Th) and uranium (U) in house dust sampled from 1025 urban homes, in units of concentrations (μg g ), loadings (μg m ), and loading rates (ng m d ). Spearman rank correlations indicate that, in addition to outdoor sources, consumer products and building materials can influence indoor dust concentrations of REE, Th, and U. Correlations (P<.01) with numbers of occupants, dogs, and cats suggest soil track-in. Correlations (P<.01) with hardwood floors suggest release of REE additives used in pigments and coatings during daily wear and tear. Concentrations of light REE are elevated in smokers' homes compared to non-smokers' homes (P<.001), suggesting that a key source is "mischmetal," the REE alloy used in cigarette-lighter flints. Indoor sources include geological impurities in raw materials used in consumer products, such as U and Th impurities in bentonite clay used in cat litter, and REE impurities in phosphates used for a variety of applications including dog food and building materials. Median gastric bioaccessibility (pH 1.5) of most REE in dust ranges from about 20% to 29%. Household vacuum samples correlate with fresh dust samples from the same homes (P<.001 for all investigated elements).

Selection of metric for indoor‐outdoor source apportionment of metals in PM 2.5 : mg/kg versus ng/m 3

“…Metals in source media, which are typically measured in mg/kg, contribute to airborne PM through a variety of release, dissipation, resuspension, and combustion processes. Settled house dust has proven to be a sensitive indicator of indoor sources 15 , 87 , 88 and a useful medium for estimating indoor inhalation exposures where sample collection is limited by inadequate resources. 89 , 90 …”

“…Metals in source media, which are typically measured in mg/ kg, contribute to airborne PM through a variety of release, dissipation, resuspension, and combustion processes. Settled house dust has proven to be a sensitive indicator of indoor sources 15,87,88 and a useful medium for estimating indoor inhalation exposures where sample collection is limited by inadequate resources. 89,90 Strong indoor-outdoor correlations (r > 0.6) for many PM 2.5 elements in the Windsor study homes (Appendix S6) provide evidence of particle infiltration from outdoor sources, but this observation does not necessarily mean an absence of indoor sources (discussed further in Appendix S5).…”

Toward setting public health guidelines for chemicals in indoor settled dust?

“…Loading (µg/m 2 ) was judged by the group to be a better indicator of exposure because it combines the dustiness of the indoor environment and the concentration of the compound in dust 8 . Studies with lead have suggested dust loading correlates better with children's blood levels than does the concentration 9,10 .…”

“…Studies with lead have suggested dust loading correlates better with children's blood levels than does the concentration 9,10 . Its measurement could be achieved with a wipe or with a specific vacuum cleaner, 2,8,11,12 on a measured surface area. One limitation is the spot measurement of loading is influenced by the delay between last cleaning and sampling.…”

“…Concentration (µg/g) more clearly identifies presence of sources and is less influenced by the delay since the last cleaning. A strength is this value could be obtained from the analysis of dust easily collected in the bag of a vacuum cleaner (household or specific) 2,8,12 . Estimates of intake and dose, however, still necessitate the use of a default, age‐specific dust intake rate in mg/day 15…”