Participants living in rural homes cooking primarily with biomass fuels experienced daily indoor PM concentrations that were 6-fold higher than participants living in the urban households in Puno. These PM exposures were up to 5.5-fold higher than the 24-hour World Health Organization (WHO) safe air quality standard of 25 μg/m3. Measurements of ambient PM concentrations show that background ambient PM concentrations are not likely to contribute heavily to the exposures experienced by those cooking with biomass. There has been a growing interest in the health effects of the coarse fraction, defined as the fraction of particles between 2.5 μm and 10 μm in diameter [30, 31]. Results of gravimetric analyses demonstrate that biomass fuel smoke had a slightly higher proportion of fine PM. In contrast, PM in urban households contain a slightly higher proportion of coarse PM, most likely contributed by ambient PM from outdoor sources. Our results are comparable to concentrations found in other studies conducted in regions where biomass fuel use is highly prevalent . On average, rural participants in our study reported cooking with a traditional cookstove for 32 years, indicating that women in this region experience extremely high lifetime cumulative exposures to biomass smoke. Furthermore, since children are often present inside the kitchen during cooking, lifetime exposure may be even higher than our estimates, especially for women. These high cumulative exposures to biomass fuel smoke signify that individuals in this region are at elevated risk of many communicable and non-communicable chronic diseases associated with exposure to environmental pollutants found in biomass smoke.
While PM and CO concentrations were somewhat elevated in homes without chimneys as compared to rural homes with chimneys, we did not see a significant difference in these concentrations, indicating that locally constructed chimneys were minimally effective at reducing exposures to biomass smoke in our population. Chimney design and installation varied considerably across households. Specifically, we observed chimneys that were both vertically and horizontally oriented, constructed of a variety of materials including polyvinyl chloride pipe, adobe, and brick. Some stoves were placed in a recessed area of the kitchen wall while others were not. While observing differences in exposures resulting from different forms of chimney construction is beyond the scope of this study, it is important to highlight the importance of instruction and supervision for proper construction of chimneys at the local level for future policy and implementation studies. There is a strong need to incorporate technical assistance for appropriate construction of chimney stoves in cookstove intervention programs and to evaluate the effectiveness of chimney design.
Data from our census demonstrate that at the time of our study, government-sponsored cookstove intervention programs had yet to reach many communities in the region of Puno, with only 2.4% of households reporting participation in the national improved cookstove program through JUNTOS . Similarly, only five participants in our sample reported having an improved stove, and none reported having received this stove from the JUNTOS program. Only 22% of households in our census reported having chimneys in their kitchens. While it is still unclear exactly what an effective improved cookstove intervention should consist of, attention should be given to this region of Peru where there is a dire need for effective cookstove intervention programs.
We found that eNO and SpO2 changed significantly in rural participants after cooking as compared to before cooking; however, the magnitudes of these changes were negligible and not biologically meaningful. Although eCO levels were weakly but significantly correlated with 24-hour CO concentrations, we found a significant difference in eCO levels between urban and rural participants. This reflects the differences in indoor CO concentrations found in urban and rural kitchens. These differences remained after eliminating the only daily smoker from the analysis. The low prevalence of current and lifetime daily smoking suggests that differences in these levels can be attributed to differences in exposure to biomass fuel smoke. While urban participants were slightly older than rural participants, we do not believe that this affected the differences in eCO levels. Other studies have also demonstrated the utility of eCO as a biomarker for biomass smoke [33, 34]. However, its utility may be limited somewhat by the relatively short half-life of CO in the body, approximately two to 4.5 hours, depending on initial exposure . In our study, since we measured eCO immediately before and after cooking in rural households, we were able to capture eCO levels within this critical window. We saw a significant difference in eCO levels between urban and rural participants, but did not observe a significant difference before as compared to after cooking. These observations suggest that eCO could represent a useful personal biomarker for long-term, chronic exposure to biomass fuel smoke. An exploration of concentrations of CO generated under different combustion conditions is an important validation step that would be needed to employ eCO as a marker for biomass combustion. However, in our study, biomass composition and combustion conditions were similar in all rural homes and the use of LPG was predominant in our urban homes. Therefore a discussion of the potential contributions of CO generated by different sources or combustion processes were beyond the scope of this analysis. eCO is simple and inexpensive to measure, requiring the participant to simply hold his or her breath for 20 seconds and then exhale fully into the machine. This simplicity is particularly useful because the instrument can be taken to the homes of the participants, instead of requiring the participant to travel to a local clinic for measurement. Hence, eCO may represent a useful and practical biomarker for biomass fuel smoke exposure and warrants further exploration for use in cookstove intervention studies.
Participants in rural areas who had a chimney installed in their homes tended to be younger than those living in homes without a chimney by about 9 years. Furthermore, rural participants who occasionally cooked LPG were younger by 9 years. While these differences may simply be a result of chance given the relatively small sample size, they also may reflect a trend for younger families to adopt these technologies. Younger families may also represent a willing target population for intervention.
Not surprisingly, we found that kitchen PM concentrations increased with the number of hours participants reported cooking on a typical day. In addition, although not statistically significant, we found that using dung for fuel also increased PM concentrations. We were unable to separate the effects of different types of biomass fuels (e.g. wood, dung, crop waste) on PM concentrations because most participants used multiple fuel sources for cooking. Since we excluded LPG households from the analysis, the increase in PM levels compares households that used dung with households that used other forms of biomass. Thus, our results suggest that dung use leads to a modest increase in exposure to PM even as compared to other biomass fuels. Contrary to our expectations, we found that kitchens with thatched roofs had slightly higher levels of indoor PM than other roof materials such as corrugated metal. These results could be due to the fact that thatched roofs were often tightly constructed and may have resulted in less ventilation than metal roofs. Furthermore, thatched roofs can hold a considerable amount of previously deposited PM, which can come loose when agitated or brushed by people working inside the kitchen. There has been considerable interest in the potential for using CO as a proxy for PM2.5 in biomass fuel studies . Our results support this relationship in that kitchen CO concentrations were positively and significantly correlated with PM2.5 concentrations in rural households.
An important strength of our study is that two or more trained observers were present during the cooking period in rural homes, allowing us to directly record household characteristics and cooking behaviors rather than relying on self-report. There are also limitations to our study. First, concentrations measured in a household kitchen may not represent personal exposures. In particular, we may be underestimating personal exposures to environmental pollutants in urban participants given that they are likely exposed to higher concentrations of ambient PM when outside the home. Outdoor PM concentrations in rural areas are quite low, and thus kitchen exposures are likely to be the predominant source of PM exposure for rural participants. However, time spent indoors is a significant modifier of personal exposure. Second, we only recorded kitchen concentrations of household air pollution for a 24-hour period. Given the high intra-household variation found in other studies , longer monitoring periods would have provided more data to evaluate this variability. Third, we were unable to stay for the full duration of fuel combustion, and in most instances we were unable to determine whether participants remained in the kitchen until the fire was completely extinguished.
It is possible that participants changed their cooking behaviors as a result of our presence in their homes. Regardless, we believe that this effect was not a great source of error and we prefaced all of our visits by emphasizing that we wanted them to cook as they normally do.
Another important strength of our study is that we conducted gravimetric PM2.5 measurements concurrent with passive, real-time nephelometric measurements in order to validate and generate a calibration equation for passive measurements against a gold standard. Real-time optical devices, such as the pDR-1000 used in this study, are thought to overestimate PM2.5 mass compared to gravimetric assessments . We found in our study that the pDR-1000 tended to underestimate PM at very low concentrations as compared to gravimetric measurements and overestimated PM at higher concentrations, following a logarithmic function. There are important limitations to the validation component of our study. First, due to logistical limitations, we pre- and post-calibrated pumps in the study office, as opposed to calibrating immediately before and after deployment in the field, which may have led to variable accuracy in recorded pump flow. Second, we observed breakthrough PM on many of the filters, meaning that our calibration equation most likely yields conservative concentration estimates after correction. However, our study is valuable and novel in that it investigates the use of a real-time optical instrument (the pDR-1000) that is simple to use in a setting where it is logistically challenging to carry out the gold standard (gravimetric) measurement method.