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USE OF METAL- AND FLUORESCEIN-TAGGED MATERIALS TO STUDY SETTLED PARTICLES EXPOSURE PATHWAYS
Citation:
Harper, S L., J. T. Antley, J. Giglio, AND R. W. Vanderpool. USE OF METAL- AND FLUORESCEIN-TAGGED MATERIALS TO STUDY SETTLED PARTICLES EXPOSURE PATHWAYS. Presented at American Chemical Society 221st National Meeting, San Diego, CA, April 1-5, 2001.
Impact/Purpose:
The objective of this task is to develop and employ PM measuring tools for EPA researchers and regulators to use to characterize the exposure of humans to PM of outdoor origin in both outdoor and indoor environments. Achieving these objectives will improve the scientific foundation for risk assessments of PM in future reevaluations of the NAAQS and in assessing exposure of humans to PM.
Description:
Through the use of ten size ranges of tagged materials (Antley et. al., 2000a), inductively coupled plasma- mass spectrometry (ICP-MS) and flourometry are being used to study the movement of settled particles in the indoor environment, exposure pathways, and the collection efficiency of surface samplers. Particle-bound contaminants in housedust and tracked-in soil represent potentially significant exposure hazards for both children and adults. Children and adults can be exposed to housedust by direct dermal contact to dust on floors (hard surface and carpeting) and elevated horizontal surfaces (furniture and countertops), and by inhalation from housedust resuspended by normal activities such as walking on flooring, especially carpeting. Additionally, young children may add an ingestion route if mouthing activities are included. The movement of housedust from the original source (settling from air, track-in from outside) to the ultimate exposure location is a function of particle size and dust character. During this migration, the dust and soil may become contaminated with liquid-applied pesticides, or the particles, such as lead-based paint or particle-form pesticides.
Estimates of exposure of this settled and tracked-in dust are typically obtained from surface samplers. Representativeness of the sample collected to the actual contamination to which humans are exposed must be known. Research indicates that this exposure is related to the particle size. To date, the collection performance of many surface samplers for various sizes of particle-bound contaminants have not been well characterized and therefore the representativeness of the samples being collected is uncertain.
A laboratory technique has been developed (Antley et. al., 2000b) to generate reference surfaces of particles of known characteristics which consists of a dry particle distribution system using tagged materials of sizes ranging from <1 to 500 micrometers physical diameter (< 1 micron to 850 microns aerodynamic diameter). The computer-controlled positioning system is capable of moving the aerosolization system over the test surface to generate spatially uniform deposits for total surface loading of 0.100 to 19.600 g/m2 with deposition uniformity of 20% CV or less. The deagglomerated particles are deposited at natural terminal settling velocities on hard or soft surfaces. These surfaces are then used for studies of surface sampler characteristics and dermal transfer and may be used for resuspension, re-entrainment, and particle mobility and fate studies.
Use of a different metal for each particle size fraction allows for use of polydisperse mixtures while retaining the ability to perform assessments as a function of particle size. Internal standards are used as performance indicators for the ICP-MS as well as indicators of loss during sample collection and processing. Use of fluorescein tagged materials for discrete particle size range experiments permits the analyses of masses lower than gravimetric determinations of untagged materials.
This work has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and administrative review process and approved for presentation and publication. Mention of tradenames or commercial products does not constitute endorsement or recommendation for use.