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^-1 ), loadings (μg m^-2 ), and loading rates (ng m^-2 d^-1 ). 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).

Keywords: actinides; dissipative losses; exposure assessment; indoor environments; lanthanides; rare earth metals.