Rare earth elements in house dust: loading rates versus concentrations

Importance and objectives: The Canadian House Dust Study (CHDS) provides nationally representative baseline information about the geochemistry of urban house dust. House dust contains a wide variety of compounds from both... [ view full abstract ]

Importance and objectives: The Canadian House Dust Study (CHDS) provides nationally representative baseline information about the geochemistry of urban house dust. House dust contains a wide variety of compounds from both indoor and outdoor sources, and is a useful medium for assessing residential exposures. In this study, element loading (ng/sq m/day) is examined as a function of the dust loading (mg/sq m/day) and the element concentration (µg/g) in the settled dust, with focus on the rare earth elements (REE).

Methodologies: “Active” or fresh dust was collected from 1025 urban homes according to sampling protocols developed to obtain different measures of elements in house dust – concentration and loading rate - which provided complementary types of information for risk assessments. REE were determined in the <80 micron fraction, using INAA for Sc-21 and ICP-MS for Y-39, La-57, Ce-58, Pr-59, Nd-60, Sm-62, Eu-63, Gd-64, Tb-65, Dy-66, Ho-67, Er-68, Tm-69, Yb-70 and Lu-71.

Main results: Loading rates for all REE are significantly higher (p <0.01) in homes occupied by smokers than in homes occupied by non-smokers, which is partly attributable to the significantly higher dust loading rate in homes of smokers (geomean = 12.6 mg/sq m/day) compared to homes of non-smokers (geomean = 9.2 mg/sq m/day).

Conclusions: Concentration data are useful for identifying sources of REE in the home, including building materials and consumer products. However it is dust levels within the home and the dustiness of the external environment that are the important drivers of exposure.