Search

Background: Metabolic functions typically increase with human activity, but optimal methods to characterize activity levels for real-time predictions of ventilation volume (l/min) during exposure assessments have not been available. Could tiny, triaxial accelerometers be incorporated into personal level monitors to define periods of acceptable wearing compliance, and allow the exposures (μg/m 3 ) to be extended to potential doses in μg/min/kg of body weight?, Objectives: In a pilot effort, we tested: 1) whether appropriately-processed accelerometer data could be utilized to predict compliance and in linear regressions to predict ventilation volumes in real time as an on-board component of personal level exposure sensor systems, and 2) whether locating the exposure monitors on the chest in the breathing zone, provided comparable accelerometric data to other locations more typically utilized (waist, thigh, wrist, etc.)., Methods: Prototype exposure monitors from RTI International and Columbia University were worn on the chest by a pilot cohort of adults while conducting an array of scripted activities (all <10 METS), spanning common recumbent, sedentary, and ambulatory activity categories. Referee Wocket accelerometers that were placed at various body locations allowed comparison with the chest-located exposure sensor accelerometers. An Oxycon Mobile mask was used to measure oral-nasal ventilation volumes in-situ. For the subset of participants with complete data (n= 22), linear regressions were constructed (processed accelerometric variable versus ventilation rate) for each participant and exposure monitor type, and Pearson correlations computed to compare across scenarios., Results: Triaxial accelerometer data were demonstrated to be adequately sensitive indicators for predicting exposure monitor wearing compliance. Strong linear correlations (R values from 0.77 to 0.99) were observed for all participants for both exposure sensor accelerometer variables against ventilation volume for recumbent, sedentary, and ambulatory activities with MET values ~<6. The RTI monitors mean R value of 0.91 was slightly higher than the Columbia monitors mean of 0.86 due to utilizing a 20 Hz data rate instead of a slower 1 Hz rate. A nominal mean regression slope was computed for the RTI system across participants and showed a modest RSD of +/-36.6%. Comparison of the correlation values of the exposure monitors with the Wocket accelerometers at various body locations showed statistically identical regressions for all sensors at alternate hip, ankle, upper arm, thigh, and pocket locations, but not for the Wocket accelerometer located at the dominant-side wrist location (R=0.57; p=0.016)., Conclusions: Even with a modest number of adult volunteers, t he consistency and linearity of regression slopes for all subjects were very good with excellent within-person Pearson correlations for the accelerometer versus ventilation volume data. Computing accelerometric standard deviations allowed good sensitivity for compliance assessments even for sedentary activities. These pilot findings supported the hypothesis that a common linear regression is likely to be usable for a wider range of adults to predict ventilation volumes from accelerometry data over a range of low to moderate energy level activities. The predicted volumes would then allow real-time estimates of potential dose, enabling more robust panel studies. The poorer correlation in predicting ventilation rate for an accelerometer located on the wrist suggested that this location should not be considered for predictions of ventilation volume.

Personal exposures, indoor and outdoor concentrations, and questionnaire data were collected in three retirement center settings, supporting broader particulate matter (PM)--health studies of elderly populations. The studies varied geographically and temporally, with populations studied in Baltimore, MD in the summer of 1998, and Fresno, CA in the winter and spring of 1999. The sequential nature of the studies and the relatively rapid review of the mass concentration data after each segment provided the opportunity to modify the experimental designs, including the information collected from activity diary and baseline questionnaires and influencing factors (e.g., heating, ventilation, and air-conditioning (HVAC) system operation, door and window openings, air exchange rate) measurements. This paper highlights both PM2.5 and PM10 personal exposure data and interrelationships across the three retirement center settings, and identifies the most probable influencing factors. The current limited availability of questionnaire results, and chemical speciation data beyond mass concentration for these studies, provided only limited capability to estimate personal exposures from models and apportion the personal exposure collections to their sources. The mean personal PM2.5 exposures for the elderly in three retirement centers were found to be consistently higher than the paired apartment concentrations by 50% to 68%, even though different facility types and geographic locations were represented. Mean personal-to-outdoor ratios were found to 0.70, 0.82, and 1.10, and appeared to be influenced by the time doors and windows were open and aggressive particle removal by the HVAC systems. Essentially identical computed mean PM2.5 personal clouds of 3 micrograms/m3 were determined for two of the studies. The proposed significant contributing factors to these personal clouds were resuspended particles from carpeting, collection of body dander and clothing fibers, personal proximity to open doors and windows, and elevated PM levels in nonapartment indoor microenvironments.

Developmental efforts and experimental data that focused on quantifying the transfer of particles on a mass basis from indoor surfaces to human skin are described. Methods that utilized a common fluorescein-tagged Arizona Test Dust (ATD) as a possible surrogate for housedust and a uniform surface dust deposition chamber to permit estimation of particle mass transfer for selected dust size fractions were developed. Particle transfers to both wet and dry skin were quantified for contact events with stainless steel, vinyl, and carpeted surfaces that had been pre-loaded with the tagged test dust. To better understand the representativeness of the test dust, a large housedust sample was collected and analyzed for particle size distribution by mass and several metals (Pb, Mn, Cd, Cr, and Ni). The real housedust sample was found to have multimodal size distributions (mg/g) for particle-phase metals. The fluorescein tagging provided surface coatings of 0.11-0.36 ng fluorescein per gram of dust. The predominant surface location of the fluorescein tag would best represent simulated mass transfers for contaminant species coating the surfaces of the particles. The computer-controlled surface deposition chamber provided acceptably uniform surface coatings with known particle loadings on the contact test panels. Significant findings for the dermal transfer factor data were: (a) only about 1/3 of the projected hand surface typically came in contact with the smooth test surfaces during a press; (b) the fraction of particles transferred to the skin decreased as the surface roughness increased, with carpeting transfer coefficients averaging only 1/10 those of stainless steel; (c) hand dampness significantly increased the particle mass transfer; (d) consecutive presses decreased the particle transfer by a factor of 3 as the skin surface became loaded, requiring approximately 100 presses to reach an equilibrium transfer rate; and (e) an increase in metals concentration with decreasing particle size, with levels at 25 microns typically two or more times higher than those at 100 microns--consistent with the earlier finding of Lewis et al. for the same sample for pesticides and polycyclic aromatic hydrocarbons (PAHs).

Two collaborative studies have been conducted by the U.S. Environmental Protection Agency (EPA) National Exposure Research Laboratory (NERL) and National Health and Environmental Effects Research Laboratory to determine personal exposures and physiological responses to particulate matter (PM) of elderly persons living in a retirement facility in Fresno, CA. Measurements of PM and other criteria air pollutants were made inside selected individual residences within the retirement facility and at a central outdoor site on the premises. In addition, personal PM exposure monitoring was conducted for a subset of the participants, and ambient PM monitoring data were available for comparison from the NERL PM research monitoring platform in central Fresno. Both a winter (February 1-28, 1999) and a spring (April 19-May 16, 1999) study were completed so that seasonal effects could be evaluated. During the spring study, a more robust personal exposure component was added, as well as a more detailed evaluation of physical factors, such as air-exchange rate, that are known to influence the penetration of particles into the indoor environment. In this paper, comparisons are made among measured personal PM exposures and PM mass concentrations measured at the NERL Fresno Platform site, outside on the premises of the retirement facility, and inside selected residential apartments at the facility during the two 28-day study periods. The arithmetic daily mean personal PM2.5 exposure during the winter study period was 13.3 micrograms/m3, compared with 9.7, 20.5, and 21.7 micrograms/m3 for daily mean overall apartment, outdoor, and ambient (i.e., platform) concentrations, respectively. The daily mean personal PM2.5 exposure during the spring study period was 11.1 micrograms/m3, compared with 8.0, 10.1, and 8.6 micrograms/m3 for the daily mean apartment, outdoor, and ambient concentrations, respectively.

Experimental considerations are discussed for conducting controlled studies of the dispersion of contaminants released near a mannequin. A 183 cm x 183 cm cross section wind tunnel was modified to study the low velocity range of 10 to 100 cm/sec (20 to 200 ft/min). Installation of a removable biplanar slat grid produced turbulent intensities up to 15%. The results of validation testing for selected experimental components are reported, including (1) a minimum, unambiguous velocity measurement capability of 2.0 cm/sec (4.0 ft/min); (2) a minimum required integration interval for velocity and contaminant measurements of at least 3 min; (3) a determination that smoke streamline plume settling may be a problem at velocities < or = approximately 15 cm/sec (approximately 30 ft/min); (4) a determination that a 14% tunnel blockage by the mannequin was not of consequence for frontal measurements; and (5) a finding that the biplanar grid produced turbulence spectra representative of low velocity indoor settings. A deceleration zone was noted that extended 50 cm upstream from the mannequin, with freestream velocities reduced 50 to 60%, 2.5 cm from the chest. A contaminant tracer released as a point source 60 cm upstream typically dispersed laterally only 10 to 15 cm and diluted by a factor of 10(4) before reaching the chest.