A cross-sectional study of determinants of indoor environmental exposures in households with and without chronic exposure to biomass fuel smoke

Abstract

Background: Burning biomass fuels indoors for cooking is associated with high concentrations of particulate matter (PM) and carbon monoxide (CO). More efficient biomass-burning stoves and chimneys for ventilation have been proposed as solutions to reduce indoor pollution. We sought to quantify indoor PM and CO exposures in urban and rural households and determine factors associated with higher exposures. A secondary objective was to identify chronic vs. acute changes in cardiopulmonary biomarkers associated with exposure to biomass smoke.

Methods: We conducted a census survey followed by a cross-sectional study of indoor environmental exposures and cardiopulmonary biomarkers in the main household cook in Puno, Peru. We measured 24-hour indoor PM and CO concentrations in 86 households. We also measured PM2.5 and PM10 concentrations gravimetrically for 24 hours in urban households and during cook times in rural households, and generated a calibration equation using PM2.5 measurements.

Results: In a census of 4903 households, 93% vs. 16% of rural vs. urban households used an open-fire stove; 22% of rural households had a homemade chimney; and <3% of rural households participated in a national program encouraging installation of a chimney. Median 24-hour indoor PM2.5 and CO concentrations were 130 vs. 22 μg/m3 and 5.8 vs. 0.4 ppm (all p<0.001) in rural vs. urban households. Having a chimney did not significantly reduce median concentrations in 24-hour indoor PM2.5 (119 vs. 137 μg/m3; p=0.40) or CO (4.6 vs. 7.2 ppm; p=0.23) among rural households with and without chimneys. Having a chimney did not significantly reduce median cook-time PM2.5 (360 vs. 298 μg/m3, p=0.45) or cook-time CO concentrations (15.2 vs. 9.4 ppm, p=0.23). Having a thatched roof (p=0.007) and hours spent cooking (p=0.02) were associated with higher 24-hour average PM concentrations. Rural participants had higher median exhaled CO (10 vs. 6 ppm; p=0.01) and exhaled carboxyhemoglobin (1.6% vs. 1.0%; p=0.04) than urban participants.

Conclusions: Indoor air concentrations associated with biomass smoke were six-fold greater in rural vs. urban households. Having a homemade chimney did not reduce environmental exposures significantly. Measures of exhaled CO provide useful cardiopulmonary biomarkers for chronic exposure to biomass smoke.

Figure 1

Plot of log-transformed gravimetric PM_2.5 concentrations vs. log-transformed passive nephelometric PM concentrations. The red line represents the calibration equation: Gravimetric PM_2.5 = e ^{1.5 + 0.6 × ln(nephelometric PM)}.

Figure 2

Median (left) and maximum (right) average concentrations of indoor PM by hour of the day. Curves are stratified by site and chimney construction (urban, rural with chimney, and rural without chimney). The y-axis represents summaries of average hourly concentrations (in μg/m³) of indoor PM across households. We calculated these household summaries for each hour of the day, as indicated in the x-axis.

Figure 3

Median indoor CO concentrations by hour of the day. Curves are stratified by site and chimney construction (urban, rural with chimney, and rural without chimney). The y-axis represents median values of indoor CO (ppm) across households. We calculated these household summaries for each hour of the day, as indicated on the x-axis.

Figure 4

Boxplots of 24-hour indoor PM concentrations by household characteristics among rural participants. Presence of a chimney (panel A), use of dung while cooking (panel B), number of hours cooking (panel C), having a thatch roof (panel D).

Figure 5

Boxplots of cardiopulmonary outcomes stratified by site (rural vs. urban). Displayed are exhaled nitric oxide (eNO), exhaled CO (eCO), carboxyhemoglobin from exhaled breath (eHBCO), carboxyhemoglobin from pulse co-oximetry (SpHbCO), pulse oximetry (SpO₂) and heart rate stratified by site (rural vs. urban).