Pollutants in house dust as indicators of indoor contamination

This review summarizes occurrence of organic and inorganic contaminants in house dust and the contribution of house dust as a marker of indoor exposure. Several studies have identified house dust as an important route of toxicant exposure. Often levels of pollutants found in house dust, including compounds banned long ago, are significant sources of exposure for the general population, especially children. House dust is a sink and repository for semivolatile organic compounds and particle-bound matter. Analyses of compounds in house dust are a measure of indoor contamination but may also provide valuable information for assessment of human indoor exposure. The objective of analyzing house dust are to describe the extent, distribution, and determinants of exposure, to identify possible sources of indoor contamination, or to record elevated indoor exposure leading to intervention or sanitation. House dust and compounds adsorbed to house dust may enter the human body by inhalation of suspended and resuspended particles, through nondietary ingestion of dust, through ingestion of particles adhering to food, surfaces in the homes, and on the skin as well as by absorption through the skin. The quantity of dust inhaled and deposited in the differing parts of the alveolar tract is dependent on the aerodynamic diameter. Exposure to house dust does not exclusively and may not even predominantly occur via inhalation, however. For instance, ingestion of house dust particles adhering to food, objects, and the skin or direct absorption through the skin may be primary routes of exposure (Lewis et al. 1994). Samples referred to as "house dust" vary significantly because house dust may be of different origin, amount, and composition and the method of sampling the dust influences the properties of the sample used for analysis. Passive and active sampling methods are described and discussed. For the analysis of organic pollutants in house dust, the < or = 63-microns fraction should be favored because variances caused by inhomogeneity of the subsample are low. Results from studies on house dust are presented for polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), plasticizers (phthalates, phenols), flame retardants, other organic xenobiotics, and inorganic constituents. If available, medians as a measure of the average concentration and the 90th or 95th percentiles are added as reference values. The review of the literature points out that ingestion of house dust may be a major route of exposure to pesticides for infants and toddlers. So far, only a few guideline values or limiting values for house dust exist. For lead in house dust, the health risk is regulated only in the U.S. and for PAH in the Federal Republic of Germany. Risk associated with the ingestion of contaminated dust by small children (age, 1-6 years; mean body weight, 16 kg) can be estimated using the chronic oral reference dose (RfD) and a daily intake of 100 mg house dust. The tentative benchmark house dust concentrations that are believed to be without health effect for small children were calculated for several compounds from their current RfD. Comparison with the maximum concentrations reviewed for chlorpyrifos, DDT, and diazinon indicates that the tolerable exposure concentration in house dust might be exceeded and that chlorpyrifos especially can be considered as a potential hazard to householders. The role of house dust as an exposure source is gaining more attention over the years but several open questions related to health remain to be resolved. Pesticides applied outside or within the household that are absorbed and preserved by house dust can lead through the everyday activities of children and infants to increased exposure. Residential exposure including house dust residues contribute to combined exposure from dietary and nondietary sources. It is justified to shift more attention to indoor pollution by house dust contamination and to improve the risk assessment of nondietary ingestion, but any health-based standard must be accompanied by a specific dust sampling method.