Development of an Integrated Platform to Assess the Physicochemical and Toxicological Properties of Wood Combustion Particulate Matter

Abstract

Wood burning contributes to indoor and ambient particulate matter (PM) pollution and has been associated with increased morbidity and mortality. Here, we present an integrated methodology that allows to generate, sample, and characterize wood smoke derived from different moisture contents and representative combustion conditions using pine wood as a model. Flaming, smoldering, and incomplete combustion were assessed for low-moisture pine, whereas both low-moisture pine and high-moisture pine were investigated under flaming conditions. Real-time monitoring of carbon monoxide, volatile organic compounds, and aerosol number concentration/size in wood smoke was performed. The PM was size-fractionated, sampled, and characterized for elemental/organic carbon, organic functional groups, and inorganic elements. Bioactivity of PM was assessed by measuring the sterile alpha motif (SAM) pointed domain containing ETS (E-twenty-six) transcription factor (SPDEF) gene promoter activity in human embryonic kidney 293 (HEK-293T) cells, a biomarker for mucin gene expression. Findings showed that moisture content and combustion condition significantly affected the organic and inorganic elemental composition of PM_0.1 as well as its bioactivity. Also, for a given moisture and combustion scenario, PM chemistry and bioactivity differed considerably with PM size. Importantly, PM_0.1 from flaming combustion of low-moisture pine contained the highest abundance of the oxygenated saturated aliphatic functional group [H-C-O] and was also biologically most potent in stimulating SPDEF promoter activity, suggesting the role of organic compounds such as carbohydrates and sugar alcohols (that contain [H-C-O]) in driving mucus-related respiratory outcomes. Our platform enables further well-controlled parametric studies using a combination of in vitro and in vivo approaches to link wood burning parameters with acute and chronic inhalation health effects of wood smoke.

Fig. 1.

Schematic of the integrated platform and methodology for the systematic investigation of wood combustion emissions and their detailed physicochemical and toxicological characterization.

Fig. 2.

Real-time monitoring of evolved carbon monoxide (panels A, B, C) and total gaseous volatile organic compounds (TVOC) (panels D, E, F) as a function of time (or temperature) during the combustion of pine wood during the three different burning conditions, F: flaming (A, D), S: smoldering (B, E), and IC: incomplete combustion (C, F). Data represent mean ± standard deviation across three separate woodburning experiments (n=3).

Fig. 3.

Real-time monitoring of emitted nanoparticle number concentration (panels A, B, C) and mobility size distribution (panels D, E, F) during the combustion of pine wood under three different burning conditions, F: flaming (A, D), S: smoldering (B, E), and IC: incomplete combustion (C, F) using a Scanning Mobility Particle Sizer Spectrometer (SMPS) covering aerosol mobility diameters between 5 – 300 nm. Panels A-C display the total nanoparticle number concentration as a function of time (or temperature), whereas panels D-F display the nanoparticle number-size distributions captured at the timepoint of peak nanoparticle emission, for the three different burning conditions. GMD: geometric mean diameter; GSD: geometric standard deviation. Data represent mean ± standard deviation across three separate woodburning experiments (n=3).

Fig. 4.

Organic functional group characterization of sampled wood smoke particles generated from the combustion of pine wood under different conditions. Pie charts show the relative abundances of the different protons associated with the respective functional groups characterized by 1-D ¹H-NMR spectroscopy (calculated as mole fraction of the functional H based on the total non-exchangeable functional organic hydrogen, where each functional H concentration is the mean of analytical triplicates (n=3) measured on one PM suspension). The following functional groups of non-exchangeable organic hydrogen were quantified: (i) saturated aliphatic hydrogen [H-R]; (ii) allylic hydrogen [H-C-C=]; (iii) saturated oxygenated hydrogen, including α-hydrogen to hydroxyl, ether and ester group [H-C-O]; (iv) acetalic and vinylic hydrogen ([O-CH-O]+[H-C=]); (v) aryl hydrogen [H-Ar]; and (vi) carbonyl hydrogen [H-C=O]. PW: pine wood; PW-MC: pine wood with higher moisture; F: flaming; S: smoldering; IC: incomplete combustion; DEN: thermal denuder.

Fig. 5.. SPDEF promoter activities of wood smoke PM.

(A) Wood smoke PM_0.1 size fractions derived from flaming, smoldering and incomplete combustion of lower moisture (6%) pine wood were tested at 10, 100 and 1000 ng/mL concentrations each; (B) Wood smoke PM_0.1 size fraction derived from flaming combustion of higher moisture (24% MC) pine wood and its water-soluble component obtained by filtration of the PM_0.1 aqueous extract were tested at 10, 100 and 1000 ng/mL concentrations each; (C) Wood smoke PM_0.1, PM_0.1-2.5 and PM_2.5-10 size fractions derived from flaming combustion of lower moisture (6%) pine wood were tested at 10, 100 and 1000 ng/mL concentrations each; (D) Water-soluble component obtained by filtration of the PM_0.1 aqueous extract derived from flaming combustion of lower moisture (6%) pine wood was tested at 10, 100 and 1000 ng/mL equivalent PM concentrations; and (E) Denuded wood smoke PM_0.1 that remained after thermal denudation of the PM_0.1 derived from flaming combustion of lower moisture (6%) pine wood was tested at 10, 100 and 1000 ng/mL concentrations for SPDEF promoter luciferase activity in HEK-293T cells. SPDEF promoter construct in PGL3 basic vector was transfected into HEK-293T cells one day prior to treatment with PM or vehicle control from blank substrates (FC, PUF) or untreated control (NT). SPDEF promoter activity in the cell lysates was measured by luminometer. For each figure, the mean ± standard error of mean is graphed (two separate woodburning experiments × biological triplicates: n=6), with significant differences at *p<0.05, **p<0.01, and ***p<0.001 from untreated control (NT).