Exposure of humans to high levels of wood smoke is associated with adverse health effects including asthma, respiratory disease and cardiovascular disease. In the US alone, more than 100,000 people annually are exposed to elevated woodsmoke levels from wildfires, prescribed burns and agricultural field burning. 70,000 - 80,000 people involved in wildland fire fighting also receive substantial occupational exposure to woodsmoke. Investigating the relationship between woodsmoke exposure and adverse health effects is hindered by inadequate methods of exposure assessment which leads to exposure misclassification, and the setting of community-impact-driven guidelines for managed fires suffers from a lack of exposure-response data. The primary objective of this proposal was to develop biological markers of human exposure to woodsmoke. Preliminary work has shown that levels of a number of methoxylated phenolic compounds are increased in urine following woodsmoke exposure. It was our hypothesis that the dose-dependent increase in urinary methoxyphenols observed following ingestion or inhalation of woodsmoke combustion products can be related in a quantitative manner to environmental woodsmoke, and thereby provide a biomarker basis for assessment of woodsmoke exposure in occupationally and environmentally exposed populations. The first aim of this project was to modify existing analytical methodology to permit sensitive, specific and accurate determination of methoxyphenols in biomass smoke. We successfully developed a sensitive and robust assay for determination of methoxyphenols in samples of ambient air particulate matter. Deuterated standard compounds are added to the environmental samples prior to extraction to determine analyte recoveries in each sample. Analytical figures of merit for the assay, as applied to ambient PM2.5 and PM10 samples are: Recovery = 63-100%, precision = 2-6%; analytical limit of detection (SIN 2) = 0.002 ug/mL; limit of quantitation = 0.07-0.45 ng/m3 (assuming a 14 m3 sample). The improved method was applied to ambient PM samples collected between 1999-2000 in Seattle, WA. Particle-bound methoxyphenol concentrations in the range <0.1 to 22 ng/m3 were observed and the methoxyphenols were present almost exclusively in the fine (PM2.5) size fraction. We also demonstrated that XRF analysis of samples of atmospheric PM collected on Teflon filters significantly reduced the levels of methoxyphenols measured in the PM samples in subsequent assay of the same filters. Therefore XRF analysis of filters, commonly undertaken to obtain trace element concentrations for use in source apportionment analyses, would preclude the subsequent analysis of those filters for methoxyphenols and other similarly semi-volatile or reactive organic chemicals. In addition, we developed a microanalytical method suitable for the quantitative determination of the sugar anhydride levoglucosan in low-volume samples of atmospheric fine particulate matter. The method incorporates two sugar anhydrides as quality control standards. The recovery standard sedoheptulosan (2,7 -anhydro-B-D-altro- heptulopyranose) in 20 uL solvent is added onto samples of the atmospheric fine particulate matter and aged for 1 hr prior to ultrasonic extraction with ethylacetate/triethylamine. The extract is reduced in volume, an internal standard added (1,5-anhydro-D-mannitol), and a portion of the extract derivatized with 10% by volume N-trimethylsilylimidazole. The derivatized extract is analyzed by gas chromatography- mass spectrometry (GCMS). The recovery of levoglucosan using this procedure was 69 :t 6% from 5 filters amended with 2 ug levoglucosan, and the reproducibility of the assay is 9%. The limit of detection is approximately 0.1 ug/mL, which is equivalent to approximately 3.5 ng/m3 for a 10 L/minute sampler or approximately 8.7 ng/m3 for a 4 L/minute personal sampler (assuming 24hr integrated samples). The second aim of this project was to determine the range of woodsmoke exposures above which urinary methoxyphenol excretion in humans is reflective of woodsmoke exposure. Methoxyphenol exposure and excretion was examined in a variety of populations with different levels of exposure to biomass smoke. Significant associations between woodsmoke exposure and urinary methoxyphenol excretion were only observed for populations with very high woodsmoke exposures (Managed exposure study, Guatemala study, wildland firefighters). Urinary methoxyphenol excretion was not associated with woodsmoke exposure for residents of Seattle, W A (typical PM exposures approximately 10-15 ug/m3 PM2.5), or for farmers exposed to wheat stubble smoke (70-1800 ug/m3 PM2.5 for up to 3 hours). Background urinary methoxyphenol concentrations in unexposed or pre-exposure samples were substantial and variable; cohorts in which dietary exposure to woodsmoke chemicals was controlled (i.e. restricted diet and managed exposure subjects) had substantially lower urinary methoxyphenol concentrations than did subjects with no dietary restrictions. We developed an exposure variable based on the sum of the 5 urinary methoxyphenol concentrations that showed the strongest association with woodsmoke exposure in our managed exposure study (see aim 3). Based on our managed exposure study, the intercept of the personal PM2.5 vs urinary biomarker regression indicated that the threshold for detection of an acute exposure event would be approximately 600 ug/m3 woodsmoke Thus we conclude that the prerequisites for the successful use of urinary methoxyphenols as biomarkers of exposure to woodsmoke are either that the woodsmoke exposure are substantial (woodsmoke PM concentrations of the order of 600 ug/m3), or that dietary consumption of methoxyphenols is suppressed such that lower levels of woodsmoke exposure may be reflected in urinary methoxyphenol excretion. Aim 3 of this project was to investigate the dose-response relationship for urinary methoxyphenol excretion in individuals with elevated exposure to woodsmoke. To accomplish this aim we conducted managed human exposures to woodsmoke from an open fire. Personal exposures (PM2.5 mean 1,500 ug/m3) varied 3.5 fold. Most methoxyphenols had measurable pre-exposure levels. Propylguaiacol, syringol, methylsyringol, ethylsyringol and propylsyringol had peak urinary concentrations after the wood smoke exposure. Eight subjects had peak urinary elimination of methoxyphenols within 6 hours (tl/2 3-5 hr), whereas one had delayed elimination. Several metrics for urinary excretion were evaluated. Analyte concentration was greatly affected by diuresis. Excretion rate and analyte concentrations normalized by creatinine gave a clearer signal and were equivalent in predictive ability. 12-hr average creatinine- normalized concentrations of each of the 5 methoxyphenols gave a Pearson correlation >/= 0.8 with their particle-phase concentration. The sum of urinary concentrations for the 5 methoxyphenols versus levoglucosan on personal filters gave a regression coefficient of 0.75. This sum versus particulate matter 2.5 gave a regression coefficient of 0.79. The signal to noise (12-hr post exposure average/pre-exposure average) ranged from 1.1-8 for the 5 methoxyphenols. Finally, occupational woodsmoke exposures and urinary methoxyphenol excretion were measured in a cohort of 20 wildland firefighters. PM exposures ranged from 630-2700 ug/m3, while levoglucosan exposures were 0.3-210 ug/m3. Levoglucosan was not significantly correlated with PM mass on the filter samples, indicating significant non-woodsmoke contributions to PM concentrations in this cohort. Urinary methoxyphenol concentrations were 1.2 to 13 fold greater in post-exposure vs pre- exposure urine samples, and this difference was significant for 14 of the 20 compounds (paired t-test). For six of the most abundant guaiacol-type methoxyphenols we observed a significant correlation between the cross shift increase in urinary methoxyphenol concentrations and personal exposure to levoglucosan; cross-shift changes in urinary concentrations of the syringol-type methoxyphenols were not significantly associated with PM or levoglucosan exposures, however. We speculate that exposure to syringol type methoxyphenols was low in the firefighter study because primarily softwood species were being burned, and softwood smoke is deficient in syringol-type methoxyphenols. These data demonstrate that in a real world occupational exposure situation urinary methoxyphenol excretion was positively associated with woodsmoke exposures.
Wood; Fuels; Organic-compounds; Phenolic-compounds; Air-quality-monitoring; Air-quality; Phenols; Fire-fighters; Fire-hazards; Smoke-inhalation; Particulate-dust; Dust-particles; Dust-inhalation; Dust-exposure; Airborne-particles; Airborne-dusts; Farmers; Agricultural-workers; Agricultural-industry; Exposure-assessment; Exposure-limits; Biological-monitoring
Department of Environmental and Occupational Health Sciences, School of Public Health and Community Medicine, University of Washington, Box 357234, Seattle, Washington 98195-7234