Concentrations, enrichment and bioaccessibility of heavy metals in household dust in Singapore

Abstract

This study examines the concentrations, enrichment and bioaccessibility of potentially toxic elements in household dust in Singapore. The fine dust fraction (<63?m) collected from 49 houses were analyzed for Al, As, Cd, Cr, Cu, Fe, Mn, Pb and Zn using the USEPA’s Method 3051A. Household dust was enriched relative to measured crustal concentrations in the order of Zn(Enrichment factor=236) > Pb(156) > Cu(75) > Cr(40) > Mn(31) > Fe(4), sugesting the influence of various anthropogenic activities such as industries and automobiles on heavy metal concentrations. Heavy metals can be transported into houses by long-range atmospheric transport or adherence onto skin, clothing and shoes of humans. Indoor sources of heavy metals such as the burning of incense also contribute to the heterogeneous elemental composition of household dust, resulting in location-specific heavy metal concentrations. Comparison with guideline values by the Wisconsin’s (USA) Department of Natural Resources highlights the spatial variation of heavy metal contamination across Singapore. Higher metal concentrations in <20?m particles from this study compared to the larger (and partially inclusive) <63?m fraction present a potential health risk to the population, which is aggravated by the increased likelihood of inhalation. Bioaccessibility, determined through an in-vitro model reflects the amount of metals that can potentially be absorbed by the human body. It was found in the order of Zn(mean=76%) > Cu(51%) > Mn(44%) > Fe(7%) > Al(3%). Besides being the most bioaccessible metal, high concentrations of Zn beyond recommended thresholds pose a health risk.