House dust has been consistently shown to be a primary route of exposure to numerous environmental contaminants, in particular pesticides, lead and other metals, and allergens, and as a surrogate measure of exposure to these contaminants. These contaminants are often found in greater concentrations indoors through their accumulation from both originating indoors, and entry from outdoor sources. This increases the potential exposure to children who are at greater risk through: ingestion due to lower body weight (typically 1/5 that of an adult), frequent hand-to-mouth activity (ingesting about 2.5 times as much dust as an adult, from 10 to 1300 mg/day), and possibly enhanced uptake such as seen with lead ingestion by children; direct inhalation, and; dermal contact from an increased surface to volume ratio and greater body contact with surfaces. These potential pathway sources and routes of exposures place children and other family members at risk from exposure to contaminants at home. Lead concentrations in house dust have been shown correlated with particle size, although again with inconsistent results. All of these investigations have been limited in sample size, and have only been performed for urban locations.
Vacuum cleaner bags containing occupant collected household dust were obtained during two prior studies covering three different environmental areas: a rural lead mining waste superfund site and a control (non-lead mining waste superfund area), and an urban environment. In both studies household vacuum cleaner bags were collected from all study participants when available (i.e. if they had a vacuum cleaner). To investigate the variation in particle size and associated lead concentrations, household vacuum bag contents will be sieved into five size fractions, and each size fraction weighed and analyzed on-site for lead content. Additionally analysis will be performed for presence of additional metals.
The presence alone of lead in house dust as a particulate, or as an adhesion or adsorbent to a particulate is important. But the relationship of the contaminant concentration and/or loading to the size fraction of the house dust and location may be a much better indicator and surrogate for potential exposure. Fine particles are more likely to stick to hands and be ingested or inhaled, through hand-to-mouth behavior or close contact with source material. Intervention measures that preferentially address a selected particle size, surface or location may not succeed if the particle size, surface or location is not related to the exposure of concern. The study methodology has been designed to address some of these issues.