Erin O. Semmens

The outdoor air pollution and brain health workshop

Accumulating evidence suggests that outdoor air pollution may have a significant impact on central nervous system (CNS) health and disease. To address this issue, the National Institute of Environmental Health Sciences/National Institute of Health convened a panel of research scientists that was assigned the task of identifying research gaps and priority goals essential for advancing this growing field and addressing an emerging human health concern. Here, we review recent findings that have established the effects of inhaled air pollutants in the brain, explore the potential mechanisms driving these phenomena, and discuss the recommended research priorities/approaches that were identified by the panel.

Relationship between Radiation Exposure and Risk of Second Primary Cancers among Atomic Bomb Survivors

Radiation exposure is related to risk of numerous types of cancer, but relatively little is known about its effect on risk of multiple primary cancers. Using follow-up data through 2002 from 77,752 Japanese atomic bomb survivors, we identified 14,048 participants diagnosed with a first primary cancer, of whom 1,088 were diagnosed with a second primary cancer. Relationships between radiation exposure and risks of first and second primary cancers were quantified using Poisson regression. There was a similar linear dose-response relationship between radiation exposure and risks of both first and second primary solid tumors [excess relative risk (ERR)/Gy = 0.65; 95% confidence interval (CI), 0.57-0.74 and ERR/Gy = 0.56; 95% CI, 0.33-0.80, respectively] and risk of both first and second primary leukemias (ERR/Gy = 2.65; 95% CI, 1.78-3.78 and ERR/Gy = 3.65; 95% CI, 0.96-10.70, respectively). Background incidence rates were higher for second solid cancers, compared with first solid cancers, until about age 70 years for men and 80 years for women (P < 0.0001), but radiation-related ERRs did not differ between first and second primary solid cancers (P = 0.70). Radiation dose was most strongly related to risk of solid tumors that are radiation-sensitive including second primary lung, colon, female breast, thyroid, and bladder cancers. Radiation exposure confers equally high relative risks of second primary cancers as first primary cancers. Radiation is a potent carcinogen and those with substantial exposures who are diagnosed with a first primary cancer should be carefully screened for second primary cancers, particularly for cancers that are radiation-sensitive.

Coarse particulate matter and airborne endotoxin within wood stove homes

Emissions from indoor biomass burning are a major public health concern in developing areas of the world. Less is known about indoor air quality, particularly airborne endotoxin, in homes burning biomass fuel in residential wood stoves in higher income countries. A filter-based sampler was used to evaluate wintertime indoor coarse particulate matter (PM₁₀₋₂.₅) and airborne endotoxin (EU/m³, EU/mg) concentrations in 50 homes using wood stoves as their primary source of heat in western Montana. We investigated number of residents, number of pets, dampness (humidity), and frequency of wood stove usage as potential predictors of indoor airborne endotoxin concentrations. Two 48-h sampling events per home revealed a mean winter PM₁₀₋₂.₅ concentration (± s.d.) of 12.9 (± 8.6) μg/m³, while PM₂.₅ concentrations averaged 32.3 (± 32.6) μg/m³. Endotoxin concentrations measured from PM₁₀₋₂.₅ filter samples were 9.2 (± 12.4) EU/m³ and 1010 (± 1524) EU/mg. PM₁₀₋₂.₅ and PM₂.₅ were significantly correlated in wood stove homes (r = 0.36, P < 0.05). The presence of pets in the homes was associated with PM₁₀₋₂.₅ but not with endotoxin concentrations. Importantly, none of the other measured home characteristics was a strong predictor of airborne endotoxin, including frequency of residential wood stove usage.

Efficacy of interventions targeting household air pollution from residential wood stoves

Wood is commonly used for residential heating, but there are limited evidence-based interventions for reducing wood smoke exposures in the indoor environment. The Asthma Randomized Trial of Indoor Wood Smoke (ARTIS) study was designed to assess the efficacy of residential interventions to reduce indoor PM exposure from wood stoves. As part of a three-arm randomized placebo-controlled trial, two household-level interventions were evaluated: wood stove changeouts and air filtration units. Exposure outcomes included indoor measures such as continuous PM2.5, particle counts, and carbon monoxide. Median indoor PM2.5 concentration was 17.5 μg/m3 in wood-burning homes prior to interventions. No significant reductions in PM2.5 concentrations were observed in the 40 homes receiving the placebo filter intervention. Sixteen homes received the wood stove changeout and showed no significant changes in PM2.5 or particle counts. PM2.5 concentrations were reduced by 68% in the filter intervention homes. Relative to placebo, air filtration unit homes had an overall PM2.5 reduction of 63% (95% CI: 47–75%). Relative to the wood stove changeout, the filtration unit intervention was more efficacious and less expensive, yet compliance issues indicated a need for the evaluation of additional strategies for improving indoor air quality in homes using wood stoves.

Indoor particulate matter in rural, wood stove heated homes.

Ambient particulate matter (PM) exposures have adverse impacts on public health, but research evaluating indoor PM concentrations in rural homes in the United States using wood as fuel for heating is limited. Our objectives were to characterize indoor PM mass and particle number concentrations (PNCs), quantify infiltration of outdoor PM into the indoor environment, and investigate potential predictors of concentrations and infiltration in 96 homes in the northwestern US and Alaska using wood stoves as the primary source of heating. During two forty-eight hour sampling periods during the pre-intervention winter of a randomized trial, we assessed PM mass (<2.5μm) and PNCs (particles/cm(3)) in six size fractions (0.30-0.49, 0.50-0.99, 1.00-2.49, 2.5-5.0, 5.0-10.0, 10.0+μm). Daily mean (sd) PM2.5 concentrations were 28.8 (28.5)μg/m(3) during the first sampling period and 29.1 (30.1)μg/m(3) during the second period. In repeated measures analyses, household income was inversely associated with PM2.5 and smaller size fraction PNCs, in particular. Time of day was a significant predictor of indoor and outdoor PM2.5 concentrations, and infiltration efficiency was relatively low (Finf (sd)=0.27 (0.20)). Our findings demonstrate relatively high mean PM concentrations in these wood burning homes and suggest potential targets for interventions for improving indoor air quality and health in rural settings.

Household reporting of childhood respiratory health and air pollution in rural Alaska Native communities

Background Air pollution is an important contributor to respiratory disease in children. Objective To examine associations between household reporting of childhood respiratory conditions and household characteristics related to air pollution in Alaska Native communities. Design In-home surveys were administered in 2 rural regions of Alaska. The 12-month prevalence of respiratory conditions was summarized by region and age. Odds ratios (ORs) were calculated to describe associations between respiratory health and household and air quality characteristics. Results Household-reported respiratory health data were collected for 561 children in 328 households. In 1 region, 33.6% of children aged <5 years had a recent history of pneumonia and/or bronchitis. Children with these conditions were 2 times more likely to live in a wood-heated home, but these findings were imprecise. Resident concern with mould was associated with elevated prevalence of respiratory infections in children (ORs 1.6–2.5), while reported wheezing was associated with 1 or more smokers living in the household. Reported asthma in 1 region (7.6%) was lower than national prevalence estimates. Conclusions Findings suggest that there may be preventable exposures, including wood smoke and mould that affect childhood respiratory disease in these rural areas. Additional research is needed to quantify particulate matter 2.5 microns in aerodynamic diameter or less and mould exposures in these communities, and to objectively evaluate childhood respiratory health.

Reducing indoor air pollutants with air filtration units in wood stove homes

BACKGROUND Biomass burning has been shown to be a major source of poor indoor air quality (IAQ) in developing and higher income countries across the world. Specifically, wood burning for cooking and heating contributes to high indoor concentrations of fine (particles with aerodynamic diameters<2.5μm; PM2.5) and coarse (particles with aerodynamic diameters <10μm and >2.5μm; PMc) particulate matter. Endotoxin, predominantly found within the coarse fraction of airborne particulate matter, is associated with proinflammatory effects and adverse outcomes among susceptible populations. The aim of this study was to assess the efficacy of air filter interventions in reducing indoor PM2.5, PMc, and PMc-associated endotoxin concentrations in homes using a wood stove for primary heating. RESULTS Homes (n=48) were randomized to receive in-room air filtration units with either a high efficiency filter (i.e. active) or a lower efficiency fiberglass filter (i.e., placebo). The active filter intervention showed a 66% reduction in indoor PM2.5 concentrations (95% CI: 42.2% to 79.7% reduction) relative to the placebo intervention. Both the active and the placebo filters were effective in substantially reducing indoor concentrations of PMc (63.3% and 40.6% average reduction for active and placebo filters, respectively) and PMc-associated endotoxin concentrations (91.8% and 80.4% average reductions, respectively). CONCLUSIONS These findings support the use of high efficiency air filtration units for reducing indoor PM2.5 in homes using a wood stove for primary heating. We also discovered that using lower efficiency, lower cost filter alternatives can be effective for reducing PMc and airborne endotoxin in homes burning biomass fuel.

Measured Pulmonary and Systemic Markers of Inflammation and Oxidative Stress Following Wildland Firefighter Simulations.

Objective: A controlled human exposure study was conducted to investigate the impact of inhalational exposures to wood smoke PM2.5 on measured concentrations of airway and systemic inflammatory biomarkers. Methods: Mimicking wildland firefighter activities, 10 participants were exposed to three doses of wood smoke PM2.5 (filtered-air, 250 &mgr;g/m3, and 500 &mgr;g/m3) while exercising on a treadmill. Exhaled breath condensate (EBC) and blood plasma samples were obtained pre-, immediately post-, and 1-hour postexposure. 8-isoprostane, pH, and myeloperoxidase were measured in EBC, while H2O2, surfactant protein D, and pentraxin-3 (PTX3) were measured in both EBC and plasma. Results: Only pH, 8-isoprostane, and PTX3 displayed significant changes when comparing pre- and postexposures. Conclusions: Markers of inflammation and oxidative stress, including PTX3, pH, and 8-isoprostane in EBC and/or plasma, are sensitive to wood smoke inhalation, with further investigations warranted.

Estimating the number of vulnerable people in the United States exposed to residential wood smoke.

Rogalsky et al. (2014) recently estimated the number of homes and individuals at risk of adverse health effects from exposure to emissions from residential wood combustion in the United States. We appreciate the importance of this topic, particularly to rural and underserved communities. We also understand the authors’ emphasis on low-income individuals because this population generally has more difficulty accessing health care services and fewer resources available to improve indoor air quality. However, several factors suggest that the indication of 500,000–600,000 low-income persons exposed to household air pollution (HAP) from the burning of solid fuels may be a very conservative estimate, substantially underestimating the public health importance of residential wood combustion. First, the estimate of Rogalsky et al. (2014) was limited by their use of the census-based figure of 2.8 million homes using wood as a primary heating fuel. The U.S. Energy Information Agency (2012) noted that another 8.8 million homes use wood stoves or wood-burning fireplaces as a secondary source of heating. Limited data are available on the frequency of use of wood burning as a secondary heating source and the associated exposure to indoor particulate matter (PM), but the 11.6 million homes with an estimated 2.58 persons per household (U.S. Census Bureau 2012) suggest that closer to 30 million people in the United States live in a home where wood burning is used for heating, rather than the 6.5 million people reported by Rogalsky et al. Second, the authors’ estimate of at-risk persons was limited to those with co-occurrence of in-home wood burning as a primary heating source and households below the Federal Poverty Level (FPL) (i.e., 900,000 people that meet both criteria). However, at-risk individuals, including children and the elderly, also reside in homes that are above the FPL threshold. Third, Rogalsky et al. suggested that 53–65% of wood-burning homes in high-poverty communities may exceed health-based standards, but this estimate is based on few studies, with poverty assessed only at the community level. Finally, the authors focused only on direct indoor fugitive emissions in homes using wood stoves, but exposure risk is not limited to those living in homes with wood-burning appliances. As indicated in several published studies, communities with a high proportion of residential wood-burning households may also have elevated concentrations of ambient wintertime PM (Ward and Lange 2010). Moreover, analyses of infiltration efficiencies suggest that exhausted wood smoke can contribute substantially to indoor PM concentrations in both wood-burning and non–wood-burning homes (Barn et al. 2008), resulting in a higher proportion of homes and their residents experiencing risk from biomass combustion–derived PM. Rogalsky et al. (2014) should be commended for acknowledging these and other limitations in their discussion, and we appreciate the opportunity to provide additional information on these points. Here we offer an alternative framework for estimating the number of people in the United States exposed to high levels of PM associated with wood burning. Approximately 11.6 million homes in the United States use wood as a primary or secondary source of heat. Of these, 4.8 million homes have wood stove appliances (U.S. Energy Information Agency 2012). Because of the uncertain frequency of fireplace use, we have not included homes with fireplaces in our estimate, although they likely are important sources of indoor PM. Rather than limiting our estimate to those homes below the FPL, we define our at-risk population as the susceptible individuals living within these homes (i.e., children and the elderly). With approximately 0.63 children 65 years of age per household (U.S. Census Bureau 2012), we estimate that within the United States alone, approximately 4.8 million susceptible individuals live in homes with substantial exposures to wood smoke–derived PM, an order of magnitude greater than the 0.5–0.6 million estimate of Rogalsky et al. (2014). This estimate is conservative because it does not account for infiltration into non–wood stove households experiencing HAP generated from neighboring wood-burning homes, nor does it account for all household residents that are vulnerable due to chronic health conditions. As with any estimates of at-risk populations, there is an important balance to strike between underestimating the risk and artificially inflating the public health importance. We suggest that Rogalsky et al. (2014) erred toward the former. Our estimates are based on a different framework with respect to exposure potential and susceptible populations. Whether the true number of individuals in the United States at risk for adverse health effects from exposure to wood smoke is closer to 0.5 million or 4.8 million, it remains clear that this is an important environmental exposure that disproportionately impacts rural populations.

Base Camp Personnel Exposure to Particulate Matter During Wildland Fire Suppression Activities

Wildland fire base camps commonly house thousands of support personnel for weeks at a time. The selection of the location of these base camps is largely a strategic decision that incorporates many factors, one of which is the potential impact of biomass smoke from the nearby fire event. Biomass smoke has many documented adverse health effects due, primarily, to high levels of fine particulate matter (PM2.5). Minimizing particulate matter exposure to potentially susceptible individuals working as support personnel in the base camp is vital. In addition to smoke from nearby wildland fires, base camp operations have the potential to generate particulate matter via vehicle emissions, dust, and generator use. We monitored particulate matter at three base camps during the fire season of 2009 in Washington, Oregon, and California. During the sampling events, 1-min time-weighted averages of PM2.5 and particle counts from three size fractions (0.3–0.5 microns, 0.5–1.0 microns, and 1.0–2.5 microns) were measured. Results showed that all PM size fractions (as well as overall PM2.5 concentrations) were higher during the overnight hours, a trend that was consistent at all camps. Our results provide evidence of camp-based, site-specific sources of PM2.5 that could potentially exceed the contributions from the nearby wildfire. These exposures could adversely impact wildland firefighters who sleep in the camp, as well as the camp support personnel, who could include susceptible individuals. A better understanding of the sources and patterns of poor air quality within base camps would help to inform prevention strategies to reduce personnel exposures.