Critical Review of Health Impacts of Wildfire Smoke Exposure

Associations between fine particulate matter and in-home blood pressure during the 2022 wildfire season in Western Montana, USA

Wildfires continue to increase in size, intensity, and duration. There is growing evidence that wildfire smoke adversely impacts clinical outcomes; however, few studies have assessed the impact of wildfires on household air quality and subclinical cardiovascular health indicators. We measured continuous indoor and outdoor fine particulate matter (PM2.5) concentrations from July-October 2022 at 20 residences in the rural, mountainous state of Montana in the United States. We used a combination of satellite-derived smoke plume data from the National Oceanic and Atmospheric Administration's Hazard Mapping System and household-level daily mean PM2.5 concentrations to classify wildfire-impacted days. One participant from each household self-reported in-home blood pressure (BP) on weekly electronic surveys. We used linear mixed-effects regression models to assess associations between air pollution exposures (PM2.5 concentrations; number of wildfire-impacted days) and systolic BP (SBP) and diastolic BP (DBP). Models were adjusted for potential time-variant confounders including temperature, humidity, and self-reported exercise. Compared to survey periods with 0 wildfire days, SBP was 3.83 mmHg higher (95% Confidence Interval [95% CI]: 0.22, 7.44) and DBP was 2.36 mmHg higher (95% CI: -0.06, 4.78) during periods with 4+ wildfire days. Across the entire study period, a 10 µg m-3 increase in indoor PM2.5 was associated with 1.34 mmHg higher SBP (95%CI: 0.39, 2.29) and 0.71 mmHg higher DBP (95% CI: 0.07, 1.35). We observed that wildfire-impacted days and increasing household-level PM2.5 concentrations are associated with higher in-home BP. Our results support growing literature which indicates that wildfires adversely impact subclinical cardiovascular health. Clinical and public health messaging should emphasize the cardiovascular health impacts of wildfire smoke and educate on exposure-reduction strategies such as indoor air filtration.

Asthma medication usage after environmental exposure to wildfire smoke: A systematic review

Asthma is a chronic respiratory condition exacerbated by exposure to particulate air pollution. Smoke from landscape fires has been associated with increased mortality, asthma-related admissions to emergency and other hospital departments, and uptake in primary care services. With climate change and more frequent landscape fires, healthcare systems must prepare for disaster, including surges in asthma medication demand. Past reviews have not resolved the direction and magnitude of the association between PM2.5 exposure during landscape fires and asthma medication use. The aim of this review was to investigate the relationship between exposure to landscape fire smoke and the use of asthma medications. We conducted a systematic review of PubMed, Scopus, and Web of Science, identifying peer-reviewed articles that examined asthma medication usage following environmental exposure to landscape fire smoke. After a full-text review, we identified twelve articles, three from Canada, three from the USA and six from Australia, with five being retrospective cohort studies. Despite differences in study design, outcome and exposure assessment, the included studies reported a consistent increase in asthma medication use after exposure to wildfires. There is consistent evidence that exposure to wildfire smoke is associated with an increase in the use of reliever medications, particularly salbutamol. Increases in other asthma management medications were also consistently identified. Increases in demand for asthma medications after exposure to wildfire smoke highlight the urgent need to address the growing frequency and intensity of wildfires driven by climate change.

Impact of occupational exposure to wildfire events on systemic inflammatory biomarkers in Portuguese wildland firefighters

While occupational exposure as a firefighter is considered a dangerous occupation, research on the underlying mechanisms remains limited, particularly in wildland firefighters. Inflammation, a key effect of wildfire exposure, plays a significant role in the development of various diseases. The current study aims to investigate the impact of wildland firefighting exposure on the levels of pro-inflammatory systemic biomarkers. A pre-post study design investigated 59 wildland firefighters comparing data collected after participation in a wildfire event (Phase II) with data obtained before wildfire season (Phase I). Data on demographics, lifestyle, health and occupational-related factors were assessed. Exposure factors, such as fire combat (e.g., exposure duration), were also registered. Inflammatory biomarkers (i.e. interleukin-6 [IL-6], interleukin-8 [IL-8], tumor necrosis factor α [TNF-α] and high-sensitivity C-reactive protein [hs-CRP]) and hydroxylated polycyclic aromatic hydrocarbons metabolites (1-OHNaph+1-OHAce, 2-OHFlu, 1-OHPhen, 1-OHPyr) were analysed in blood and urine samples, respectively. Serum IL-8 and IL-6 levels were significantly increased after wildland fire combat. IL-8 levels were 2.62 times higher (95 % CI: 1.96-3.50; p < 0.01), whereas IL-6 levels were 1.25 times higher (95 % CI: 1.00-1.57; p = 0.04). Furthermore, IL-8 levels were significantly correlated with urinary 2-hydroxyfluorene levels and fire combat duration (>12 h). In addition, the mean hs-CRP level, in both phases, was above 3.0 mg/L, indicating a potential risk for cardiovascular events. Given the long-term health implications of firefighting occupational exposure, biomonitoring and early detection of occupational risks are essential for protecting firefighters' health. Protective measures must be urgently implemented to enhance occupational health and strengthen preventive strategies in this sector.

Satellite data to support air quality assessment and management

Satellite data have long been recognized as valuable for air quality applications. These applications are in a stage of rapid growth: new geostationary satellites provide hourly or sub-hourly data; improvements in algorithms convert measured wavelengths into retrievals of atmospheric constituents; advances in machine learning support improved estimates of near-surface pollution; and growing interest among air quality managers has led to a range of new satellite data applications. Considering mainly activities in the United States under the Clean Air Act, we discuss proven applications relevant to air quality management, including: informing epidemiological studies and health risk assessments for setting regulatory standards; evaluating regulatory models; constraining emissions inventories; supporting Exceptional Event Demonstrations through tracking wildfire plumes and other sources; characterizing emission patterns and ozone-forming chemistry for State Implementation Plans; improving air quality forecasting; and tracking long-term trends to evaluate regulatory impact. Air quality professionals are increasingly using satellite data for these and related analyses, but barriers remain. This review provides a summary of satellite products used in applications for air quality and related health assessments; progress in using satellite observations for deriving surface-level air quality information across scales; and their use in air quality management.Implications: The review covers advancements in satellite data for air quality applications over the last 15 years. Success with satellite applications, especially for PM2.5 and NO2, include use in health risk assessment, constraining emissions inventories, and supporting tracking short- and long-term trends with regulatory relevance. Solutions co-developed between researchers and practitioners show promise for continued improvements in the use and value of satellite data for air quality applications.

Wildfire-Related Air Pollution and Infectious Diseases: Systematic Review and Meta-Analysis

Amid the global rise in wildfire events, the health impacts of wildfire-related air pollution are increasingly scrutinized. While numerous reviews have examined the link between air pollution and infectious diseases, reviews specifically focusing on wildfire-related air pollution and infectious diseases remain scarce. To address this gap, we conducted a comprehensive search in MEDLINE, EMBASE, Scopus and Web of Science databases up to December 31, 2023, using PRISMA (Preferred Reporting Items for Systematic Reviews & Meta-Analyses) guidelines. Search terms included synonyms of wildfire and infectious diseases. Peer-reviewed epidemiological studies that reported any association or trend between wildfire air pollution and infectious diseases were selected against eligibility criteria. Risk of bias and quality of included studies were assessed using modified risk of bias and quality assessment tools. Our review included 30 studies, predominantly from developed countries including the United States (USA), Australia, and Canada. Most focused on respiratory infectious diseases (n = 29), including 9 specifically on the coronavirus disease 2019 (COVID-19). The majority examined short-term wildfire air pollution (n = 27) (exposure of one month or less). Twenty-three studies reported effect estimates for the meta-analysis. We found that a 10 μg/m3 increase in short-term wildfire PM2.5 (particulate matter with a diameter of 2.5 micrometer of less) exposure was associated with a 15% increase in COVID-19 infections (relative risk [RR] = 1.15; 95% confidence interval [CI]: 1.09-1.21; heterogeneity (I 2): 83%), a 3% increase in respiratory diseases (RR = 1.03; 95% CI: 1.01-1.05; I 2: 0%) and a 3% increase in acute upper respiratory infection combined with acute bronchitis (RR = 1.03; 95% CI: 1.02-1.05; I 2: 62%). Medium-term exposure (more than a month but less than a year) to wildfire smoke was associated with 20% rising hospitalization for systemic fungal infections like coccidioidomycosis (95% CI: 5-38%). The current research exclusively examines respiratory infections in developed countries. Future high-quality primary studies should prioritize understanding the impact of wildfire-related air pollution on various infectious diseases.

Global disparities in indoor wildfire-PM2.5 exposure and mitigation costs

Wildfires have become more frequent and severe, and evidence showed that exposure to wildfire-caused PM2.5 (fire-PM2.5) is associated with adverse health effects. Fire-PM2.5 exposure occurs mainly indoors, where people spend most of their time. As an effective and timely approach of mitigating indoor PM2.5 pollution, air purifiers incur notable associated costs. However, the long-term global population exposure to indoor fire-PM2.5 and the economic burden of using air purifiers remain unknown. Here, we estimated the indoor fire-PM2.5 concentration and the cost of reducing indoor PM2.5 exposure, along with the extra cost incurred because of fire-PM2.5, at a resolution of 0.5° by 0.5° globally during 2003 to 2022. Our findings revealed 1009 million individuals exposed to at least one substantial indoor wildfire-air pollution day per year. We identified pronounced socioeconomic disparities in the costs of mitigating indoor PM2.5 exposure, with low-income countries bearing a disproportionately higher economic burden, emphasizing the critical need for addressing these disparities.

Coexposure to extreme heat, wildfire burn zones, and wildfire smoke in the Western US from 2006 to 2020

Climate change drives three heat-related hazards: extreme heat (EH), wildfire burn zones (WFBZs), and wildfire smoke (WFS). Using daily census tract-level data from 2006 to 2020, we investigated when, where, and whom these hazards coexposed in 11 Western US states. Among 18,106 tracts, at least one hazard occurred an average of 32 days (581,867 tract-days) annually. EH-WFS coexposure increased over the study period and was the most frequent coexposure (annual average of 38,218 tract-days). EH-WFS-affected regions varied year to year. WFBZ-involved coexposures were spatially confined and did not increase over time. On average, the most tract-days of EH-WFBZ-WFS coexposure took place in California, Arizona, and Oregon. Among census tracts most exposed to EH-WFBZ-WFS, populations disproportionately consisted of people of older age, with disabilities, and living in poverty. American Indian and Alaska Native individuals disproportionately faced all coexposures. As climate change accelerates, tracking coexposure to multiple hazards can help target resources to protect health.

Racial-ethnic composition of U.S. school districts, wildfire smoke PM2.5 levels, and reduced in-person learning among schoolchildren and adolescents during the COVID-19 pandemic

Background

In 2023, the U.S. Biden administration called for an "all-hands-on-deck" response to address chronic absenteeism and disrupted learning among primary and secondary school students due to school closures and remote learning during the pandemic. To identify student populations that might benefit from interventions, this study examined the racial-ethnic composition of school districts as a predictor of wildfire smoke PM2.5 levels and in-person student visits to schools.

Methods

In a lagged cross-sectional study, multivariable logistic regression was employed to investigate school district quartiles of mean percentages of non-White students as predictors of: 1) mean levels of wildfire smoke PM2.5 > 35 μg/m3 during school days for grade 3-8 students; and 2) being above the median for the mean decline in in-person K-12 student attendance (vs. pre-pandemic) during the 2020-2021 and 2021-2022 school years.

Results

The highest (vs. lowest) quartile for the district-level percentage of non-White students predicted a nearly 3-fold higher odds (adjusted odds ratio, AOR = 2.78; 95 % CI = 2.07-3.74; P < .001) of high wildfire smoke exposure and 5-fold higher odds (AOR = 4.95; 95 % CI = 3.84-6.38; P < .001) of substantially reduced in-person learning levels. Successively higher odds for both outcomes were observed in higher quartiles (P for trend < .001). Similar patterns were seen when percentages of Asian-, Black-, and Hispanic-American students were modeled simultaneously.

Conclusions

Districts with higher percentages of non-White students showed elevated odds of high wildfire smoke PM2.5 levels and distance learning. Distributing portable air filtration devices in these districts could be a cost-effective intervention to address these concomitant risks and mitigate learning loss among children and adolescents in the USA.

Occupational exposure to wildland firefighting and its effects on systemic DNA damage

BACKGROUND

Portugal is among the European Union countries more devastated by forest fires. Wildland firefighters are at the forefront of this battle, facing exposure to a wide range of harmful pollutants. Epidemiological studies have highlighted a potential link between occupational firefighting exposure and several diseases, including cancer. To date, very few studies have explored the biological mechanisms associated with such exposure. The present longitudinal study aims to assess changes in early effect biomarkers following wildland firefighters' occupational exposure to a real wildfire event.

METHODS

Paired blood samples from 59 healthy Portuguese wildland firefighters were collected at two different time points: before wildfire season and after a fire event during wildfire season. Sociodemographic variables (e.g., age, sex) and work-related factors (e.g., years of service) were assessed via a self-reported questionnaire. Levels of early effect biomarkers, such as primary DNA damage and oxidative DNA damage (oxidised purines) were assessed via comet assay. DNA double-strand breaks (DSBs) were evaluated by phosphorylated H2AX (γH2AX). Moreover, hydroxylated polycyclic aromatic hydrocarbon metabolites (OHPAHs) and metal(loid)s were quantified in urine samples. The influence of urinary OHPAHs, urinary metal(loid)s, and other exposure-related factors (e.g., firefighting duration) on changes (Δ) in early effect biomarkers (post-vs. baseline levels) was investigated.

RESULTS

Firefighting activities led to a significant increase in both primary DNA damage and oxidative DNA damage by 22 % (95 % CI: 1.11-1.35; p < 0.05) and 23 % (95 % CI: 1.04-1.45; p < 0.05), respectively. Results from linear regression revealed that per each unit increase of urinary 2-hydroxyfluorene (2-OHFlu) (μmol/mol creatinine), the risk of ⧍ oxidative DNA damage increased by 20 % [FR: 1.20 (1.09-1.32); p < 0.01]. Additionally, each unit increase in urinary cesium (Cs) (μg/L) resulted in a significant 4 % increase in Δ primary DNA damage [FR: 1.04 (1.01-1.06); p < 0.05] and a 3 % increase in Δ oxidative DNA damage [FR: 1.03 (1.01-1.05); p < 0.05]. Post-exposure levels of γH2AX were significantly correlated with urinary 2-OHFlu levels assessed after firefighting (r = 0.30; p < 0.05). Furthermore, exposure duration and reported breathing difficulties during firefighting were significantly associated with increased levels of primary DNA damage.

CONCLUSION

Results obtained provide insights into the potential human health effects of wildland firefighting occupational exposure at the genetic and molecular levels, offering new and important mechanistic data. These findings are crucial for implementing health and safety measures, recommendations, and best practices to mitigate occupational risks and protect the health of wildland firefighters.

Smoke Exposure and Respirator Use Among Wildland Firefighters: A Narrative Review

Climate change contributes to warm, dry conditions, which leads to longer and more active fire seasons. Wildland firefighters work long hours in smoky conditions without regulations requiring respiratory protection. Wildfire smoke has many toxic components, including high levels of fine particulate matter (PM2.5). Regular monitoring for short- and long-term health outcomes in wildland firefighter populations is uncommon. However, extrapolating from knowledge about the individual components of smoke, it is likely that the firefighters' health is negatively affected. Firefighters are routinely exposed to dangerous levels of smoke, which may lead to both acute and chronic health consequences. Current guidelines from Occupational Safety and Health Administration (OSHA), the U.S. Forest Service (USFS), and the Interagency Standards for Fire and Fire Aviation Operations do not recommend respirator use for wildland firefighters. The methodologies used to quantify exposure and harm likely underestimate actual risks. Although there are no respirators that can filter all known harmful components of wildfire smoke, this review examines the potential benefit of respirator use by reducing some of the most harmful components of the smoke. Smoke exposure among wildland firefighters needs to be further characterized and quantified. Regulations should be reassessed to accurately reflect the exposure and potential harm that firefighters face. This narrative review gathers information from peer-reviewed scientific literature, government publications, news articles, and personal conversations with both public- and private-sector professionals. The objectives are to describe the likely health effects of wildland firefighting, evaluate the evidence behind current respiratory protection guidelines, and propose potential solutions.

Radiative cooling in New York/New Jersey metropolitan areas by wildfire particulate matter emitted from the Canadian wildfires of 2023

Wildfire particulate matter from Canadian forest fires significantly impacted the air quality in the northeastern United States during the summer of 2023. Here, we used real-time and time-integrated instrumentation to characterize the physicochemical properties and radiative effects of wildfire particulate matter reaching the metropolitan areas of New Jersey/ New York during this extreme incident. The radiative forcing of -352.4 W/m2 derived here based on the measured optical properties of wildfire particulate matter explains, to some extent, the ground level temperature reduction of about 3 °C observed in New Jersey/ New York City during this incident. Such negative radiative forcing in densely populated megacities may limit natural ventilation, increase the residence time of wildfire particulate matter and background air pollutants, exacerbating public health risks. This study highlights the importance of radiative effects from wildfire particulate matter in densely populated areas and their potential implications for climate, air quality and public health.

Gestational exposure to particulate matter from urban wildfires is associated with changes in circulating oxylipins but not flame retardants 7 to 13 months post-exposure

Exposure to fine particulate matter (PM2.5) from wildfire smoke has been linked to immune dysregulation underlying multiple health conditions, but data on the long-term effects of these exposures during gestation are lacking. Smoke PM2.5 from wildfires occurring in urban areas is of particular concern because it can carry persistent chemicals within household furniture or soil, as well as polyaromatic hydrocarbons (PAHs) from combusted materials. The present study investigated the long-term associations between wildfire PM2.5 and serum polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), PAHs and lipid mediators (i.e., oxylipins) involved in immune regulation in participants from the B-SAFE (Bio-Specimen Assessment of Fire Effects) study, which enrolled women pregnant during or shortly after the 2017 Tubbs Fire in California (n = 140). Serum samples were collected and assayed 7 to 13 months post-exposure, at which point 20 women were still pregnant and 120 women were postpartum. Adjusted linear regression models revealed a significant positive association between increasing PM2.5 (μg/m3) exposure and serum concentrations of benzo[k]fluoranthene, a PAH (β = 0.866, P = 0.0403, [95 %CI: 0.0389, 1.69]). No significant associations were observed between PM2.5 exposure and serum PBDEs, PCBs or other PAHs. Increased exposure to PM2.5 was associated with lower serum concentrations of lipoxygenase (LOX)-derived free oxylipins and increased concentrations of LOX-derived oxylipins esterified to circulating lipids. These findings provide new evidence of long-term effects of gestational wildfire PM2.5 exposure on serum benzo[k]fluoranthene levels and the turnover of oxylipins involved in immunity via the LOX pathway. Additional studies are warranted to better understand the impact of these changes on maternal and child health.

Chemical Evolution of Biomass Burning Aerosols across Wildfire Plumes in the Western U.S.: From Near-Source to Regional Scales

The atmospheric processing of biomass burning organic aerosol (BBOA) and its implications for tropospheric aerosol physicochemical properties remain uncertain. To address this gap, we investigate the chemical transformation of BBOA from wildfire events in the western U.S., using data from aerosol mass spectrometers aboard the DOE G-1 aircraft and at the Mt. Bachelor Observatory (∼2800 m a.s.l.) during the summers of 2013 and 2019. This study captures dynamic changes in submicron particulate matter (PM1) concentrations and chemical profiles within wildfire plumes that span a broad range of atmospheric ages, from fresh emissions (<30 min) to plumes transported for several days. As plumes age, the oxidation state of organic aerosols (OA) increases, accompanied by the formation of secondary aerosol components such as phenolic secondary OA (SOA) species, carboxylic acids, and potassium sulfate. Early plume evolution is marked by the evaporation of semivolatile components and the formation of alcohol and peroxide functional groups, while extended aging produces more oxidized species, including carboxylic acids and carbonyl compounds. Normalized excess mixing ratios (NEMRs) of OA to CO demonstrate a complex interplay between evaporation, SOA formation, and oxidative loss. Using positive matrix factorization (PMF), we identify distinct BBOA types representing various stages of atmospheric processing and assess the contributions of primary BBOA and secondary BBOA formed through atmospheric reactions. These findings shed light on the intricate mechanisms governing the evolution of BBOA characteristics within wildfire plumes, providing critical insights to improve atmospheric modeling of BBOA and better assess the environmental and climatic impacts of wildfire emissions.

Geographic patterns in wildland fire exposures and county-level lung cancer mortality in the United States

BACKGROUND

Emissions from wildfire plumes are composed of modified biomass combustion by-products, including carcinogens. However, studies of the association between wildland fires (WF; includes wildfires, prescribed burns, and resource management fires) exposure and lung cancer are scant. We evaluated geographic patterns in these exposures and their association with lung cancer mortality (LCM) rates across the conterminous United States (US).

METHODS

We extracted data from the Monitoring Trends in Burn Severity program (1997-2003) and derived county-level exposure metrics: WF density by area, WF density by population, the ratio between total burned land area and county area, and the ratio between total burned land area by population. We obtained sex-specific, county-level LCM rates for 2016-2020 from the National Center for Health Statistics. Counties with fewer than 10 cases were suppressed. To account for cigarette smoking, we first modeled residual values from a Poisson regression between cigarette smoking prevalence and sex-specific, age-adjusted LCM rates. We then used Lee's L statistic for bivariate spatial association to identify counties with statistically significant (p < 0.05) associations between WF exposures and these residuals. In a sensitivity analysis, we applied a false discovery rate correction to adjust for multiple comparisons.

RESULTS

We observed geographic variation in bivariate associations between large WFs and subsequent LCM rates across US counties while accounting for ever cigarette smoking prevalence. There were positive (high WF exposures and high LCM rate) clusters for males and females in counties within the mid-Appalachian region and Florida, and modest differences across WF metrics in the cluster patterns were observed across the Western US and Central regions. The most positive clusters were seen between WF density by area and LCM rates among women (n = 82 counties) and a similar geographic pattern among men (n = 75 counties). Similar patterns were observed for males and females in the western US, with clusters of high WF exposures and low LCM rates. After adjusting for multiple comparisons, a positive cluster pattern among both sexes persisted in Kentucky and Florida with area-based exposure metrics.

DISCUSSION

Our analysis identified counties outside the western US with wildfires associated with lung cancer mortality. Studies with individual-level exposure-response assessments are needed to evaluate this relationship further.

The state of wildfire and health research: emerging trends, challenges and gaps

BACKGROUND

The increasing frequency and severity of wildfires, exacerbated by climate change, population growth and land use changes, have escalated public health risks. These events are associated with respiratory and cardiovascular diseases and adverse mental health outcomes. Vulnerable populations, including children, older people and those with pre-existing health conditions, face particularly high risks.

METHODS

This study evaluates the existing literature on wildfire-related health impacts. Key variables include publication frequency, geographic distribution, collaborative networks and funding patterns.

RESULTS

Findings reveal a concentration of research in high-income regions, particularly North America and Europe, with limited studies from wildfire-prone but under-represented areas such as Latin America, Oceania, Africa and the Caribbean. This geographical disparity restricts comprehensive understanding and effective public health responses to wildfire impacts. The analysis also underscores the need for interdisciplinary approaches.

CONCLUSIONS

Wildfires continue to pose significant global public health challenges. There is a critical need for more inclusive research efforts, enhanced international collaboration and a stronger focus on health-specific outcomes, especially in under-represented regions. Expanding research in these areas is essential to inform effective public health policies and interventions that address the health risks posed by wildfires worldwide.

Awareness of wildfire smoke among U.S. adults with and without asthma

OBJECTIVE

To describe awareness of ambient wildfire smoke among U.S. adults with and without asthma.

METHODS

We analyzed data from the summer wave of the 2021 ConsumerStyles survey, a nationally representative survey of 4085 U.S. adults. Respondents self-reported their asthma status and awareness of wildfire smoke where they lived in the past 12 months. We linked survey responses by zip code of residence with satellite-detected wildfire smoke plume data that estimated the daily maximum smoke plume density over the preceding year. We estimated associations between asthma status and awareness of wildfire smoke across categories of maximum smoke plume density and days with medium- or heavy-density smoke as prevalence ratios (PRs) with 95% confidence intervals (CIs) using predicted marginal probabilities from logistic regression models.

RESULTS

Over 98% of the estimated population of U.S. adults lived in a zip code affected by ≥1 day of medium- or heavy-density wildfire smoke, which occurred on an average of 16 days in the past year. Awareness of wildfire smoke was reported by 19% of U.S. adults and was higher among adults with than without asthma (PR: 1.25; 95% CI: 1.01, 1.55), including in zip codes affected by heavy-density smoke (PR: 1.30, 95% CI: 1.04, 1.63) and with 22 or more days of medium- to heavy-density smoke (PR: 1.22, 95% CI: 1.01, 1.47).

CONCLUSIONS

Although awareness of wildfire smoke was higher among U.S. adults with than without asthma, low percentages of awareness overall indicate a need for health communication about wildfire smoke and its health risks.

Wildfire Smoke Exposure and Cause-Specific Hospitalization in Older Adults

Importance

The escalating intensity of wildfires in the western US is increasing exposure to smoke pollution. Previous studies of wildfire smoke and health have primarily focused on mortality and respiratory and cardiovascular events, with limited research on broader health impacts or on the shape of concentration-response curves.

Objective

To characterize the associations between exposure to smoke-specific fine particulate matter (PM2.5) and cause-specific hospitalizations among older adults in the western US.

Design, Setting, and Participants

This retrospective cohort study used Medicare inpatient claims data from 2006 to 2016 linked with machine learning-derived smoke-specific PM2.5 to assess associations between smoke PM2.5 and hospitalization rates. Participants included Medicare beneficiaries aged 65 years or older who lived in a western US state (ie, Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, or Wyoming). Analyses were conducted from October 2023 to February 2025.

Exposures

Daily county-level smoke-specific PM2.5 concentrations were estimated from machine learning models trained on monitor and satellite data.

Main Outcomes and Measures

Daily county-level rates of unscheduled hospitalization for each of 13 broad cause categories. To characterize the association between each cause of hospitalization and smoke PM2.5, distributed lag models were fitted with hospitalization rates modeled as a function of same-day smoke PM2.5 exposure and exposures on each day of the preceding week, using splines on exposure to allow for nonlinearity.

Results

The study included 10 369 361 individuals (mean [SD] age, 74.7 [7.9] years; 4 862 826 male [46.9%]; 5 506 535 female [53.1%]; 373 252 Black [3.6%]; 420 577 Hispanic [4.1%]; and 8 365 607 White [80.7%]), 57 million person-months of follow-up, and 4.7 million unscheduled hospitalizations. Smoke PM2.5 concentration-response curves for respiratory hospitalizations and cardiovascular hospitalizations were flat at lower concentrations but showed increasing trends at concentrations above 25 μg/m3. On average, daily hospitalizations (per 100 000) increased by 2.40 (95% CI, 0.17 to 4.63) for respiratory concerns when increasing same-day and preceding week smoke PM2.5 concentrations from 0 to 40 μg/m3; hospitalizations for cardiovascular concerns increased by 2.61 (95% CI, -0.09 to 5.30), a difference that was not statistically significant. No associations were observed for other causes of hospitalization.

Conclusions and Relevance

In this cohort study, exposure to high levels of smoke pollution was associated with an increase in hospitalizations for respiratory diseases. These findings underscore the need for interventions to mitigate the health impacts of wildfire smoke exposure.

Practical considerations for using low-cost sensors to assess wildfire smoke exposure in school and childcare settings

BACKGROUND

More frequent and intense wildfires will increase concentrations of smoke in schools and childcare settings. Low-cost sensors can assess fine particulate matter (PM2.5) concentrations with high spatial and temporal resolution.

OBJECTIVE

We sought to optimize the use of sensors for decision-making in schools and childcare settings during wildfire smoke to reduce children's exposure to PM2.5.

METHODS

We measured PM2.5 concentrations indoors and outdoors at four schools in Washington State during wildfire smoke in 2020-2021 using low-cost sensors and gravimetric samplers. We randomly sampled 5-min segments of low-cost sensor data to create simulations of brief portable handheld measurements.

RESULTS

During wildfire smoke episodes (lasting 4-19 days), median hourly PM2.5 concentrations at different locations inside a single facility varied by up to 49.6 µg/m3 (maximum difference) during school hours. Median hourly indoor/outdoor ratios across schools ranged from 0.22 to 0.91. Within-school differences in concentrations indicated that it is important to collect measurements throughout a facility. Simulation results suggested that making handheld measurements more often and over multiple days better approximates indoor/outdoor ratios for wildfire smoke. During a period of unstable air quality, PM2.5 over the next hour indoors was more highly correlated with the last 10-min of data (mean R2 = 0.94) compared with the last 3-h (mean R2 = 0.60), indicating that higher temporal resolution data is most informative for decisions about near-term activities indoors.

IMPACT STATEMENT

As wildfires continue to increase in frequency and severity, staff at schools and childcare facilities are increasingly faced with decisions around youth activities, building use, and air filtration needs during wildfire smoke episodes. Staff are increasingly using low-cost sensors for localized outdoor and indoor PM2.5 measurements, but guidance in using and interpreting low-cost sensor data is lacking. This paper provides relevant information applicable for guidance in using low-cost sensors for wildfire smoke response.

Will terrestrial biomes survive in the face of greenhouse gas emissions spillover: Insights from G20 countries

The emission of greenhouse gases (GHGs) presents localized concerns with far-reaching global repercussions, as the impacts of climate change extend beyond geographical boundaries. Despite global efforts, the cumulative effect of these endeavors falls short of the emission reduction benchmarks set by the Paris Agreement. Within this context, the study employs a time-varying parameter vector autoregressive frequency connectedness measure to examine GHG emission spillovers among G20 countries from 1971 to 2020. This method enables the analysis of connectedness intensity across both short and long time horizons. The findings reveal the time-varying nature of GHG emissions, with long-run connectedness contributing significantly more to total connectedness than short-term connectedness. The overall emission landscape remained largely unchanged until the Paris Agreement, with only slight declines observed later, including during the COVID-19 period. GHG spillovers notably impact terrestrial biome protection initiatives in G20 countries, particularly at lower quantiles. At the same time, temperature changes affect these initiatives primarily within the interquartile range, not at the extreme frequencies. Additionally, the spillover effects are asymmetric between large and smaller economies. The findings will be important for redefining GHG emission protocol policies and actionable standards for G20 countries.

Quantifying the association between pregnancy exposure to biomass-attributable PM2.5 and the risk of preterm birth and stillbirth: A case-control study in Sydney, Australia for 2010-2020

Biomass combustion, including wildfires and residential wood burning, is a significant source of particulate matter (PM2.5) in Australia, with potentially distinct health effects due to its unique chemical composition. This study aimed to quantify the association between exposure to ambient biomass-attributable PM2.5 and the risk of preterm birth and stillbirth across pregnancy windows in Sydney, Australia, from 2010 to 2020. We conducted case-control studies nested within a cohort of 578,391 singleton pregnancies, including 29,954 preterm births and 2,928 stillbirths. Controls were randomly selected using risk-set sampling. Daily all-source PM2.5 estimates at a 5 km resolution were obtained from a previous study. Days exceeding the 95th percentile of all-source PM2.5 at statistical area level 4 without significant dust storm pollution were classified as biomass-affected days. For these days, biomass-attributable PM2.5 was estimated using the remainder component from a seasonal trend decomposition, with the seasonal and trend components representing nonbiomass-attributable PM2.5. Conditional logistic regressions were used to analyze associations between biomass-attributable PM2.5 exposure and outcomes, adjusting for area-level socioeconomic factors, temperature, humidity, and temporal and seasonal trends. The odds ratio for preterm birth per interquartile range increase in biomass-attributable PM2.5 was 1.002 (95% CI = 0.997, 1.007) for the entire pregnancy average exposure, with similar null results across trimesters. For stillbirth, the odds ratio was 1.002 (95% CI = 0.985, 1.019) for the entire pregnancy average exposure, with comparable null findings across trimesters. These results suggest that in Sydney, biomass-attributable PM2.5 exposure during pregnancy may not increase the risk of preterm births or stillbirths.

Neurometabolomic impacts of wood smoke and protective benefits of anti-aging therapeutics in aged female C57BL/6J mice

Background

Wildland fires have become progressively more extensive over the past 30 years in the United States, routinely generating smoke that deteriorates air quality for most of the country. We explored the neurometabolomic impact of biomass-derived smoke on older (18 months) female C57BL/6J mice, both acutely and after 10 weeks of recovery from exposures.

Methods

Mice were exposed to wood smoke (WS) 4 hours/day, every other day, for 2 weeks (7 exposures total) to an average concentration of 448 μg particulate matter (PM)/m3 per exposure. One group was euthanized 24 hours after the last exposure. Other groups were then placed on 1 of 4 treatment regimens for 10 weeks after wood smoke exposures: vehicle; resveratrol in chow plus nicotinamide mononucleotide in water (RNMN); senolytics via gavage (dasatanib + quercetin; DQ); or both RNMN with DQ (RNDQ).

Results

Among the findings, the aging from 18 months to 21 months was associated with the greatest metabolic shift, including changes in nicotinamide metabolism, with WS exposure effects that were relatively modest. WS caused a reduction in NAD + within the prefrontal cortex immediately after exposure and a long-term reduction in serotonin that persisted for 10 weeks. The serotonin reductions were corroborated by behavioral changes, including increased immobility in a forced swim test, and neuroinflammatory markers that persisted for 10 weeks. RNMN had the most beneficial effects after WS exposure, while RNDQ caused markers of brain aging to be upregulated within WS-exposed mice.

Discussion

Taken together, these findings highlight the persistent neurometabolomic and behavioral effects of woodsmoke exposure in an aged mouse model. Further examination is necessary to determine the age-specific and species-determinant response pathways and duration before complete resolution occurs.

The 2025 Los Angeles Wildfires and Outpatient Acute Healthcare Utilization

January 2025 brought devastating wildfires to Los Angeles (LA) County, California, causing poor air quality, destroying homes and businesses, and displacing thousands of people. We used electronic health record data from 3.7 million Kaiser Permanente Southern California members to promptly determine if the 2025 LA Fires increased outpatient acute healthcare utilization. We created exposure categories using the maximum wildfire burn zone reached by an LA or Ventura County wildfire as of January 16, 2025. Highly-exposed members resided in census tracts located <20km from burn zones and moderately-exposed members lived in tracts ≥20km but within LA County. We identified daily outpatient and virtual acute care visits in five categories: all-cause, cardiovascular, injury, neuropsychiatric, and respiratory. We conducted 2-stage interrupted time-series analyses using machine-learning algorithms to determine if and by how much the 2025 LA Fires increased acute healthcare utilization. Across the week following the January 7 LA Fires ignitions, virtual respiratory visits were 41% (95% empirical confidence interval [eCI]: 26%, 56%) higher and 34% (95% eCI: 17%, 52%) higher than expected in highly- and moderately-exposed groups, respectively, totaling 3,221 excess visits. Similarly, both exposure groups had approximately 35% more virtual cardiovascular visits than expected over the same period. Among highly-exposed members, outpatient and virtual injury visits and outpatient neuropsychiatric visits were ≥ 18% higher than expected on January 7. Substantial increases in acute healthcare utilization driven primarily by virtual care-seeking were observed following the LA Fires. As disruptive climate events increase, such data are essential to inform healthcare preparedness and response.

Pollution and toxicity of heavy metals in wildfires-affected soil and surface water: A review and meta-analysis

Wildfires, both natural and man-made, release and mobilize hazardous substances such as heavy metal(loids) (HM), which are known carcinogens. Following intense rainfall events, HM bound to soil organic matter are transported from the soil to surface water, resulting in water quality degradation. This study reviews the pollution status of HM in wildfire-affected soil and surface water, as well as their toxic effects on aquatic organisms and humans. The rate of HM release during wildfires depends on factors such as the type of tree burned and fire severity. The mobility of HM from soil to surface water is influenced by soil pH, organic matter content, rainfall intensity, and duration. The risk priority number (RPN) analysis indicates that both wildfire-affected soil and surface water require remediation to address HM contamination. HM concentrations in both soil and surface water decrease over time due to soil erosion, wind, storm events, and the depletion of burnt residues. The greatest percentage changes in HM concentrations in burned soils compared to unburned soils were observed for vanadium (340%), nickel (260%), and arsenic (110%). In surface water, the highest increases were seen for iron (740%), vanadium (530%), and aluminium (510%). Wildfire-affected water has been shown to cause toxic effects in aquatic organisms, including DNA damage, oxidative stress, and lipid peroxidation. The consumption of HM-contaminated water and fish poses significant health risks to humans. Therefore, post-fire monitoring of wildfire-affected areas is essential for designing treatment plants, assessing risks, and establishing maximum allowable HM concentrations in water.

Depressed nestling growth during exposure to smoke from distant wildfires

Human and animal populations increasingly encounter smoke pollution as climate change enhances the frequency and intensity of wildfires. Most work on smoke effects in animals has studied populations close to fires, populations experiencing small, prescribed burns, or animals in the lab. In June of 2023, smoke from distant Canadian wildfires quickly elevated particulate matter (PM2.5) pollution in a wild house wren (Troglodytes aedon) population for three days before returning to baseline levels. Compared to previous years, nestlings experiencing three days of elevated PM2.5 within the first 6 days of life weighed less on days 6 and 10 after hatching and had shorter tarsometatarsus bones, a sign of smaller skeletal size. In contrast, nestlings that hatched before or after this event did not differ in size from previous years. Although sublethal, these effects may have important consequences for survival and reproduction. As wildfire activity increases, more wildlife populations are at risk of smoke-related fitness consequences, even those distant from the blaze.

The Camp fire and perinatal health: an example of the generalized synthetic control method to identify susceptible windows of exposure

The November 2018 Camp fire was the most destructive wildfire in California history, but its effects on reproductive health are not known. We linked California birth records from 2017-2019 to daily smoke levels using US EPA Air Quality System (AQS) PM2.5 data and NOAA Hazard Mapping System smoke plume polygons during the Camp fire. In the main analysis, pregnancies were considered exposed if they had median AQS PM2.5 levels above 50 μg/m3 for at least 7 days during November 8-22, 2018. We calculated rates of preterm birth and the infant sex ratio based on week of conception and used the generalized synthetic control method to estimate the average treatment effect on the treated and to propose a novel approach to identify potential critical weeks of exposure during pregnancy. We found associations between Camp fire-related smoke exposure and rates of preterm birth, with a risk difference (RD) of 0.005 and a 95% confidence interval (CI) of 0.001-0.010. Exposure during week 10 of pregnancy was consistently associated with increased preterm birth (RD, 0.030; 95% CI, 0.004-0.056). We did not observe differences in the infant sex ratio. Camp fire smoke exposure was associated with increased rates of preterm birth, with sensitive windows in the first trimester. This article is part of a Special Collection on Environmental Epidemiology.

Wildfire smoke and health impacts: a narrative review

OBJECTIVE

Air pollution emission associated with wildfires is a global concern, contributing to air quality deterioration and severely impacting public health. This narrative review aims to provide an overview of wildfire smoke (WFS) characteristics and associated impacts on adults' and children's health.

DATA SOURCE

Literature review based on a bibliographic survey in PubMed (National Library of Medicine, United States), SciELO (Scientific Electronic Library Online), and Google Scholar databases. Observational, cross-sectional, longitudinal, and review studies were considered, prioritizing peer-reviewed articles published in the last 10 years (2014-2024).

DATA SYNTHESIS

Wildfire smoke (WFS) contributes to the deterioration of air quality, resulting in increased exposure to air pollution especially in wildland-urban interfaces. WFS contains particulate matter (PM) in a range of sizes and chemical compositions, as well as multiple toxic gasses. The health impacts of WFS are systemic, affecting the respiratory, cardiovascular, and neurological systems. Exposure to WFS is associated with inflammatory and oxidative stress, DNA damage, epigenetic modulations, and stress-disorders in adults and children. Children may be at an increased risk of WFS respiratory impacts, due to their smaller airways and developing lungs.

CONCLUSION

Wildfires are increasing in frequency and intensity, resulting in thousands of premature deaths and hospitalizations worldwide, each year. Preventive measures against wildfire spread must be reinforced, considering the increasing trends of global warming and extreme weather events. Adaptation strategies should be undertaken especially in wildland-urban interface regions, including the improvement of early warning systems, improvement of health care facilities and household preparedness and promotion of risk communication campaigns.

[Wildfires and their respiratory impact]

INTRODUCTION

Largely due to climate change, wildland fires are currently increasing in extent and frequency. While particles from fire smoke exhibit higher toxicity, those identified in wildland urban interface (WUI) areas, which are exacerbated by household and vehicle emissions, are even more toxic.

STATE OF THE ART

This review article is based on English-language papers published by peer-reviewed journals. Since a previous review article was published in 2018, only papers since 2017 have been selected. The respiratory impacts of wildfires in the general population include irritative symptoms, exacerbation of chronic respiratory diseases (asthma, rhino-sinusitis, COPD…) and excess short and probably long-term mortality. Among firefighters, the short-term impact of wildfires on respiratory function has yet to be clearly established. Asthma prevalence, asthma exacerbation rates and chronic obstructive pulmonary disease (COPD) occurrence seem to be higher than in other occupational groups. That said, the different studies have not highlighted excess mortality. As regards cancer, while mesothelioma incidence has clearly increased, lung cancer incidence generally has not.

PERSPECTIVES

Two areas require clarification: first, short-term respiratory impact according to the characteristics of inhaled smoke; the long-term impact of exposure to particles from fire smoke.

CONCLUSION

Forest fires have become increasingly worrisome, in terms of both their negative health impact and their detrimental contribution to climate change.

Emergency department visits in California associated with wildfire PM2.5: differing risk across individuals and communities

The threats to human health from wildfires and wildfire smoke (WFS) in the United States (US) are increasing due to continued climate change. A growing body of literature has documented important adverse health effects of WFS exposure, but there is insufficient evidence regarding how risk related to WFS exposure varies across individual or community level characteristics. To address this evidence gap, we utilized a large nationwide database of healthcare utilization claims for emergency department (ED) visits in California across multiple wildfire seasons (May through November, 2012-2019) and quantified the health impacts of fine particulate matter <2.5 μm (PM2.5) air pollution attributable to WFS, overall and among subgroups of the population. We aggregated daily counts of ED visits to the level of the Zip Code Tabulation Area (ZCTA) and used a time-stratified case-crossover design and distributed lag non-linear models to estimate the association between WFS and relative risk of ED visits. We further assessed how the association with WFS varied across subgroups defined by age, race, social vulnerability, and residential air conditioning (AC) prevalence. Over a 7 day period, PM2.5 from WFS was associated with elevated risk of ED visits for all causes (1.04% (0.32%, 1.71%)), non-accidental causes (2.93% (2.16%, 3.70%)), and respiratory disease (15.17% (12.86%, 17.52%)), but not with ED visits for cardiovascular diseases (1.06% (-1.88%, 4.08%)). Analysis across subgroups revealed potential differences in susceptibility by age, race, and AC prevalence, but not across subgroups defined by ZCTA-level Social Vulnerability Index scores. These results suggest that PM2.5 from WFS is associated with higher rates of all cause, non-accidental, and respiratory ED visits with important heterogeneity across certain subgroups. Notably, lower availability of residential AC was associated with higher health risks related to wildfire activity.

Interventions for reducing exposure to air pollution from landscape fires in a changing environment: A systematic review

Emissions from more frequent and prolonged landscape fires (wildfires, risk reduction fires, agricultural burning) can expose populations to high levels of air pollution and exacerbate a range of health conditions. This systematic review aims to map, evaluate, and synthesise the scientific literature reporting interventions that can reduce exposure to landscape fire smoke (LFS). Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we searched PubMed, Scopus and Web of Science and reviewed relevant literature published until March 2024. Thirty-three studies from four countries met the eligibility criteria. Of the interventions evaluated, air filtration was the most frequently reported, and included use of portable air cleaners (PACs) with high efficiency particulate air (HEPA) filters, ventilation systems with standard and upgraded filters, and low-cost fan filter units (FFU). The effectiveness of PACs for fine particulate matter (PM2.5) reduction ranged between 54 %-92 %. In naturally ventilated residences, concentrations of PM2.5 were 0-44 % lower indoors, and depended on the duration of LFS, building operation, and permeability. Mechanical ventilation with minimum efficiency reporting value (MERV) 5/8 filters in buildings reduced LFS PM2.5 levels by 18-58 %; however, use of higher rated filters (e.g., MERV 12/13) achieved reductions of up to 87 %. Communication interventions, including smartphone apps and alerts/messages from various media sources (e.g., radio, television, internet) had mixed results; nevertheless, inclusion of spirometry and asthma control surveys during app use could improve health outcomes for vulnerable groups. The efficacy of facemasks (N95/P2) was up to 94 % for single pass PM2.5 removal, although they were relatively underutilised. Clean air shelters in public buildings can potentially provide a place for exposure reduction and social support, but have not been sufficiently tested during LFS events. Further research is needed on the effectiveness of interventions during prolonged smoke events, and in low- and middle-income countries.

Wildfire Smoke, the Clean Air Act, and the Exceptional Events Rule: Implications and Policy Alternatives

In recent years, increasing wildfire activity in the western US and Canada has driven declining air quality in some regions of the US. Under EPA's Exceptional Events Rule, states are allowed to exempt daily pollution monitor readings impacted by wildfire smoke from determinations of compliance with Clean Air Act air quality standards. As a result, wildfire smoke is leading to a growing divergence between actual and regulatory air quality. This paper reviews treatment of wildfire smoke under the Clean Air Act and the Exceptional Events Rule. It presents quantitative evidence on the effect of the rule on fulfillment of air quality standards, and an analysis of the degree to which smoke that currently leads to air quality violations is driven by out-of-state fires and fires on federal lands. We suggest a modification to the Exceptional Events Rule under which wildfire emissions would be excluded from air quality regulations only if states adopt government-defined best fire management policies, and we discuss the legal and practical feasibility of such a change.

Perceptions of and Responses to Wildfire Smoke Among New York State Residents: A Cross-Sectional Study

Exposure to wildfire smoke (WFS) is associated with detrimental physical and mental health. Periods of sustained WFS are predicted to increase with climate change, affecting populations globally. Using a retrospective cross-sectional study, we assessed perceptions of and responses to WFS in a cohort of New York State (NYS) residents in Summer 2023. Data were collected using an online survey from October to November 2023. Descriptive statistics summarized respondent experiences, while exploratory analyses identified high-risk populations using chi-square and t-tests. Our sample consisted of 609 primarily healthy, white, and well-educated individuals who spent most of their time in NYS during Summer 2023. Of the 99% that reported experiencing WFS, 92% received and 91% sought out WFS-related air quality information. While only 25% reported a WFS-related illness, 87% experienced at least one symptom with WFS, frequently citing watery eyes (63%), irritated throat (50%), and headaches (49%), with women reporting symptoms more frequently than men (89.1% vs. 81.6%; p = 0.034). A majority (93%) reported taking mitigation actions, including avoiding outdoor activities (75%) and wearing masks (54%). Our results highlight widespread impacts of wildfires in NYS during Summer 2023, with nearly all respondents reporting sustained periods of WFS. Most reported at least one adverse health symptom despite taking preventative measures, indicating that current protective strategies may be insufficient and more effective interventions are needed.

Wildland fire smoke adds to disproportionate PM2.5 exposure in the United States

Wildland fire (i.e., prescribed fire and wildfire) smoke exposure is an emerging public health threat, in part due to climate change. Previous research has demonstrated disparities in ambient fine particulate matter (PM2.5) exposure, with Black people, among others, exposed to higher concentrations; yet it remains unclear how wildland fire smoke may contribute to additional disproportionate exposure. Here, we investigate the additional PM2.5 burden contributed by wildland fire smoke in the contiguous United States by race and ethnicity, urbanicity, median household income, and language spoken at home, using modeled total, non-fire, and fire PM2.5 concentrations from 2007 to 2018. Wildland fires contributed 7% to 14% of total population weighted PM2.5 concentrations annually, while non-fire PM2.5 concentrations declined by 24% over the study period. Wildland fires contributed to greater PM2.5 exposure for Black and American Indian or Alaska Native people, and those who live in non-urban areas. Disproportionate mean non-fire PM2.5 concentrations for Black people (9.1 μg/m3, compared to 8.7 μg/m3 overall) were estimated to be further exacerbated by additional disproportionate concentrations from fires (1.0 μg/m3 , compared to 0.9 μg/m3 overall). These results can inform equitable strategies by public health agencies and air quality managers to reduce smoke exposure in the United States.

Shifting the Conversation on Wildland Fire Smoke Exposures: More Smoke Within and Across Years Requires a New Approach to Inform Public Health Action

With the increase in acres burned from wildfire over the last few decades, wildfire smoke is an increasing global public health threat. To date, wildfire smoke research, risk communication, and public health action has focused on short-term (or daily) smoke exposures. However, the patterns of wildfire smoke exposure are transitioning to include longer duration and repeated exposures occurring within and across years. Epidemiologic and experimental studies represent important lines of evidence that have informed risk communication and public health actions for short-term smoke exposures; however, they have yet to provide the science needed to refine public health approaches to include other dynamic exposure durations such as repeated, episodic, or cumulative. This commentary provides an overview of methodological approaches used and recent findings from epidemiologic and experimental studies that examined longer duration, repeated smoke exposures. Based on the current science, we recommend that future epidemiologic and experimental studies of wildfire smoke examine multiple exposure metrics to capture the duration, frequency, and intensity of exposures. Such studies would improve the science produced to best support the needs of the public as we strive to further protect public health in a world projected to have more smoke.

Cancer Risk and Estimated Lithium Exposure in Drinking Groundwater in the US

Importance

Lithium is a naturally occurring element in drinking water and is commonly used as a mood-stabilizing medication. Although clinical studies have reported associations between receiving lithium treatment and reduced cancer risk among patients with bipolar disorder, to our knowledge, the association between environmental lithium exposure and cancer risk has never been studied in the general population.

Objectives

To evaluate the association between exposure to lithium in drinking groundwater and cancer risk in the general population.

Design, Setting, and Participants

This cohort study included participants with electronic health record and residential address information but without cancer history at baseline from the All of Us Research Program between May 31, 2017, and June 30, 2022. Participants were followed up until February 15, 2023. Statistical analysis was performed from September 2023 through October 2024.

Exposure

Lithium concentration in groundwater, based on kriging interpolation of publicly available US Geological Survey data on lithium concentration for 4700 wells across the contiguous US between May 12, 1999, and November 6, 2018.

Main Outcome and Measures

The main outcome was cancer diagnosis or condition, obtained from electronic health records. Stratified Cox proportional hazards regression models were used to estimate the hazard ratios (HRs) and 95% CIs for risk of cancer overall and individual cancer types for increasing quintiles of the estimated lithium exposure in drinking groundwater, adjusting for socioeconomic, behavioral, and neighborhood-level variables. The analysis was further conducted in the western and eastern halves of the US and restricted to long-term residents living at their current address for at least 3 years.

Results

A total of 252 178 participants were included (median age, 52 years [IQR, 36-64 years]; 60.1% female). The median follow-up time was 3.6 years (IQR, 3.0-4.3 years), and 7573 incident cancer cases were identified. Higher estimated lithium exposure was consistently associated with reduced cancer risk. Compared with the first (lowest) quintile of lithium exposure, the HR for all cancers was 0.49 (95% CI, 0.31-0.78) for the fourth quintile and 0.29 (95% CI, 0.15-0.55) for the fifth quintile. These associations were found for all cancer types investigated in both females and males, among long-term residents, and in both western and eastern states. For example, for the fifth vs first quintile of lithium exposure for all cancers, the HR was 0.17 (95% CI, 0.07-0.42) in females and 0.13 (95% CI, 0.04-0.38) in males; for long-term residents, the HR was 0.32 (95% CI, 0.15-0.66) in females and 0.24 (95% CI, 0.11-0.52) in males; and the HR was 0.01 (95% CI, 0.00-0.09) in western states and 0.34 (95% CI, 0.21-0.57) in eastern states.

Conclusions and Relevance

In this cohort study of 252 178 participants, estimated lithium exposure in drinking groundwater was associated with reduced cancer risk. Given the sparse evidence and unknown mechanisms of this association, follow-up investigation is warranted.

Physical Health Symptoms and Perceptions of Air Quality among Residents of Smoke-Damaged Homes from a Wildland Urban Interface Fire

The Marshall Fire was a wildland urban interface (WUI) fire that destroyed more than 1000 structures in two communities in Colorado. High winds carried smoke and ash into an unknown number of buildings that, while not incinerated, were significantly damaged. We aimed to understand whether smoke or ash damage to one's home was associated with physical health impacts of the fire event for people living in and around the fire zone whose homes were not completely destroyed. We analyzed data collected from participants who responded to Wave 1 (six months postfire; N = 642) or Wave 2 (one-year postfire; N = 413) of the Marshall Fire Unified Research Survey. We used self-reported exposure to smells and ash in their homes as measures of exposure and also created spatial exposure measures based on proximity to destroyed structures. Reporting a headache was statistically significantly associated with all exposure metrics (self-reported and spatial proximity), and reporting a strange taste in one's mouth was also significantly associated with having more destroyed buildings within 250 m of the home. Study findings can inform response planning for future WUI fires to protect the health of residents of smoke-damaged homes.

Perceived wildfire risk and past experiences with wildfire smoke influence public support for prescribed burning in the western conterminous United States

BACKGROUND

Prescribed burning is an important fuel management tool to prevent severe wildfires. There is a pressing need to increase its application to reduce dry fuels in the western United States, a region that has experienced many damaging wildfires. Public support for this practice is tempered by concern around smoke impacts and escape risks. This study aims to understand how recent experiences with wildfire smoke and perceived risk of smoke events affect public support for prescribed burning.

METHODS

Data were from the May 2023 Household Emergency Preparedness Survey, an online panel survey of 1,727 adults in 12 western conterminous states, applying survey weights to reflect the underlying population demographics. In weighted logistic regression models, we evaluated associations between predictor variables (past experiences with smoke, wildfire risk perception) and support for prescribed burns in general or near a respondent's neighborhood, adjusting for age, race/ethnicity, gender, education, household income, and wildland urban interface status. Mediation models were used to assess whether perceived risk of smoke exposure mediates the relationship between recent smoke experience and support for prescribed burning.

RESULTS

Approximately two-thirds of the population supported prescribed burning in general, and more than half supported prescribed burning near their neighborhood. 44% reported experiencing a smoke event in the past 3 years, which increased the odds of support for prescribed burning in general (OR = 2.03, 95%CI 1.51-2.74) and near their neighborhood (OR = 1.59, 95% CI 1.20-2.09). High perceived risk of future smoke impacts was associated with support for prescribed burns in general (adjusted OR = 1.66, 95% CI = 1.15-2.39) and near their residence (adjusted OR = 1.72, 95%CI = 1.23-2.39). Although only trending towards significance, perceived future risk mediated 16.9% (p = 0.066) of the association between recent smoke experience and support for prescribed burning nearby. Among those who experienced recent smoke events, reporting high degrees of overall smoke impacts or outdoor air quality impacts were positively associated with support for prescribed burns.

CONCLUSIONS

Recent experience with wildfire smoke and perceived future risk are strongly associated with support for prescribed burns. Educational campaigns can apply these findings to improve public support toward prescribed fire activities and funding to reduce wildfire risks and protect public health.

Systematic review of impacts of occupational exposure to wildfire smoke on respiratory function, symptoms, measures and diseases

BACKGROUND

Wildfire smoke contains numerous hazardous air pollutants which pose serious health risks to humans. Despite this, there has been a limited focus on the assessment of the acute physiological and longer-term respiratory effects of wildfire exposure on firefighters and other emergency workers. Therefore, we undertook a systematic review of the evidence about the respiratory impacts of occupational wildfire smoke exposure among wildfire fighters (WFF).

METHODS

Eligible studies from Medline, Embase and Scopus databases were included if they described the relationship between wildfire exposure and respiratory function, symptoms, measures and diseases amongst emergency personnel or firefighters who had responded to wildfires.

RESULTS

Twenty-six articles met the inclusion criteria. 24 out of 26 (22 out of 23 moderate/high quality) studies provided evidence of adverse respiratory effects, including reduced lung function, increased airway dysfunction and airway inflammation, upper and lower respiratory tract symptoms and increased asthma incidence related to wildfires or prescribed burns exposure among WFF and police responders. Fourteen out of 19 studies showed statistically significant declines in spirometry measures of lung function (mostly short-term studies). Two studies using complex lung function tests showed a significant effect on peripheral airway function.

DISCUSSION

This review found a convincing body of evidence that occupational exposure to wildfires or prescribed burns has both acute and possibly longer-term respiratory effects among WFFs and some other emergency personnel. Given that these events are increasing, more needs to be done to identify those most at risk and mitigate these risks.

Evaluating Chemical Transport and Machine Learning Models for Wildfire Smoke PM2.5: Implications for Assessment of Health Impacts

Growing wildfire smoke represents a substantial threat to air quality and human health. However, the impact of wildfire smoke on human health remains imprecisely understood due to uncertainties in both the measurement of exposure of population to wildfire smoke and dose-response functions linking exposure to health. Here, we compare daily wildfire smoke-related surface fine particulate matter (PM2.5) concentrations estimated using three approaches, including two chemical transport models (CTMs): GEOS-Chem and the Community Multiscale Air Quality (CMAQ) and one machine learning (ML) model over the contiguous US in 2020, a historically active fire year. In the western US, compared against surface PM2.5 measurements from the US Environmental Protection Agency (EPA) and PurpleAir sensors, we find that CTMs overestimate PM2.5 concentrations during extreme smoke episodes by up to 3-5 fold, while ML estimates are largely consistent with surface measurements. However, in the eastern US, where smoke levels were much lower in 2020, CTMs show modestly better agreement with surface measurements. We develop a calibration framework that integrates CTM- and ML-based approaches to yield estimates of smoke PM2.5 concentrations that outperform individual approach. When combining the estimated smoke PM2.5 concentrations with county-level mortality rates, we find consistent effects of low-level smoke on mortality but large discrepancies in effects of high-level smoke exposure across different methods. Our research highlights the differences across estimation methods for understanding the health impacts of wildfire smoke and demonstrates the importance of bench-marking estimates with available surface measurements.

Concentration of particulate matter and atmospheric pollutants in the residential area of Kathmandu Valley: A case study of March-April 2021 forest fire events

Forest fires have become more intense and frequent in recently changing climates. The wide variety of pollutants released by forest fire include greenhouse gases, photochemically reactive compounds, and fine and coarse particulate matter. This study investigated the impact of forest fire events on air quality in the Kathmandu Valley during March-April 2021 using ground air quality monitoring stations and satellite data. The three fire periods were studied (a) Pre-fire from 21st - 23rd March (b) first-fire episode from 24th -27th March and (c) second fire episode from 1st - 5th April of 2021. The concentrations of PM2.5 reached to maximum 199 μg/m3 during pre-fire period, 371 μg/m3 and 280 μg/m3 during first and second fire event respectively. The second fire episode had lower PM2.5 concentration despite higher fire counts (449) compared to the first episode suggesting influence of fire activities near to vicinity of Kathmandu valley during second fire episode. There was a two-day lag between the beginning of forest fire events and an increase in PM2.5 levels in Kathmandu. Satellite observation showed varying patterns for different pollutants. HCHO levels responded quickly to fire activity, while AOD and CO levels increased after a few days. Also, low wind speed, low temperature, and low relative humidity additionally elevated these pollutants in Kathmandu. This study emphasizes the extent of the impact of forest fires on air quality and the importance of considering meteorological and satellite data to understand the distribution of pollutants during such events.

Encountering Prescribed Fire: Characterizing the Intersection of Prescribed Fire and Wildfire in the CONUS

Prescribed fire is applied across the United States as a fuel treatment to manage the impact of wildfires and restore ecosystems. While the recent application of prescribed fire has largely been confined to the southeastern US, the increase in catastrophic wildfires has accelerated the growth of prescribed fire more broadly. To effectively achieve wildfire risk reduction benefits, which includes reducing the amount of smoke emitted, the area treated by prescribed fire must come into contact with a subsequent wildfire. In this study, we applied timely and consistent geospatially resolved data sets of prescribed fires and wildfires to estimate the rate at which an area treated by prescribed fire encounters a subsequent wildfire. We summarize these encounter rates across time intervals, prescribed fire treatment area, and number of previous prescribed fires and by region. On all U.S. Forest Service lands across the Conterminous US (CONUS) 6.2% of prescribed fire treated area from 2003-2022 encountered a subsequent wildfire in 2004-2023. Encounter rates were highest in western US forests, which tend to be more impacted by wildfire than the eastern US, and lower in the eastern US. Encounter rates increased with treatment area in the southeastern US but were relatively flat in the northwest. For the CONUS, encounter rates increased with longer time intervals, associated with diminished potential for reducing wildfire severity, between prescribed fire and the subsequent wildfire area burned. Our results provide timely information on prescribed fire and wildfire interactions that can be leveraged to optimize analyses of the trade-offs between prescribed fire and wildfire.

Air Pollution and Temperature in Seizures and Epilepsy: A Scoping Review of Epidemiological Studies

PURPOSE OF THE REVIEW

Seizures and epilepsy can be debilitating neurological conditions and have few known causes. Emerging evidence has highlighted the potential contribution of environmental exposures to the etiology of these conditions, possibly manifesting via neuroinflammation and increased oxidative stress in the brain. We conducted a scoping review of epidemiological literature linking air pollution and temperature exposures with incidence and acute aggravation of seizures and epilepsy. We systematically searched PubMed, Embase, Web of Science, and APA PsycINFO databases for peer-reviewed journal articles published in English from inception to February 7, 2024.

RECENT FINDINGS

We identified a total of 34 studies: 16 examined air pollution exposure, 12 ambient temperature, and six examined both air pollution and ambient temperature. Most studies were conducted in Asia (China, Taiwan, South Korea, and Japan). Nearly all studies retrospectively derived acute (daily average), ambient, and postnatal exposure estimates from ground monitoring systems and ascertained epilepsy cases or seizure events through record linkage with medical records, health registry systems, or insurance claims data. Commonly assessed exposures were particulate matter (PM2.5, PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), and daily mean ambient temperature. Overall, the main findings across studies lacked consistency, with mixed results reported for the associations of air pollutants and temperature metrics with both seizure incidence and acute aggravations of epilepsy.

Wildfire Smoke: Health Effects, Mechanisms, and Mitigation

Wildfires are becoming more frequent and intense on a global scale, raising concerns about their acute and long-term effects on human health. We conducted a systematic review of the current epidemiological evidence on wildfire health risks and a meta-analysis to investigate the association between wildfire smoke exposure and various health outcomes. We discovered that wildfire smoke increases the risk of premature deaths and respiratory morbidity in the general population. Meta-analysis of cause-specific mortality and morbidity revealed that wildfire smoke had the strongest associations with cardiovascular mortality (RR: 1.018, 95% CI: 1.014-1.021), asthma hospitalization (RR: 1.054, 95% CI: 1.026-1.082), and asthma emergency department visits (RR: 1.117, 95% CI: 1.035-1.204) in the general population. Subgroup analyses of age found that adults and elderly adults were more susceptible to the cardiopulmonary effects of wildfire smoke. Next, we systematically addressed the toxicological mechanisms of wildfire smoke, including direct toxicity, oxidative stress, inflammatory reactions, immune dysregulation, genotoxicity and mutations, skin allergies, inflammation, and others. We discuss wildfire smoke risk mitigation strategies including public health interventions, regulatory measures, and personal actions. We conclude by highlighting current research limitations and future directions for wildfire research, such as elucidating the complex interactions of wildfire smoke components on human health, developing personalized risk assessment tools, and improving resilience and adaptation strategies to mitigate the health effects of wildfires in changing climate.

The temporal trend and disparity in short-term health impacts of fine particulate matter in California (2006-2019)

Most epidemiological studies assume that the relationship between short-term air pollution exposure and health outcomes is constant over time, which ignores potential changes in population composition and particulate matter emission sources. Limited studies have assessed changes in the relationship between fine particulate matter (PM2.5) and adverse health outcomes over time, with mixed results. Additionally, there is a need to identify which subgroups are disproportionately impacted over time by PM2.5-related health consequences. Therefore, we aimed to examine whether temporal trends exist in the relationships between daily PM2.5 exposure and circulatory and respiratory acute care utilization in California from 2006 to 2019. We further assessed whether certain subpopulations are more susceptible to PM2.5 exposure by demographic characteristics and extreme wildfire frequency. Daily PM2.5 concentrations estimated from a stacked ensemble model and daily cause-specific acute care utilization and demographic data from the California Department of Health Care Access and Information. We analyzed this relationship using modified two-stage Bayesian hierarchical models, where we first did not consider temporal trends, then stratified by two periods, and finally flexibly considered non-linear changes over time. Increases in circulatory (0.56 %; 95 % credible interval (CI): 0.17 %, 0.96 %) and respiratory acute care utilization risk (2.61 %; 95%CI: 2.29 %, 2.94 %) were found with every 10 μg/m3 increase in PM2.5 on the same day and previous two days. These risks were found to increase over time, where 0.13 % (95%CI: 0.02 %, 0.22 %) and 1.40 % (95%CI: 1.24 %, 1.54 %) increases were identified for circulatory and respiratory acute care utilizations, respectively, from the first (2006-2012) to second period (2013-2019). Differences by age, sex, race/ethnicity, and extreme wildfire frequency were noted. These findings confirm that air pollution guidelines should consider the dynamic nature of epidemiological dose-response and can provide insight for targeted air pollution control and adaptation policies designed to reduce PM2.5 exposure, particularly for the most susceptible subpopulations.

Fire Smoke Elevated the Carbonaceous PM2.5 Concentration and Mortality Burden in the Contiguous U.S. and Southern Canada

Despite emerging evidence on the health impacts of fine particulate matter (PM2.5) from wildland fire smoke, the specific effects of PM2.5 composition on health outcomes remain uncertain. We developed a three-level, chemical transport model-based framework to estimate daily full-coverage concentrations of smoke-derived carbonaceous PM2.5, specifically Organic Carbon (OC) and Elemental Carbon (EC), at a 1 km2 spatial resolution from 2002 to 2019 across the contiguous U.S. (CONUS) and Southern Canada (SC). Cross-validation demonstrated that the framework performed well at both the daily and monthly levels. Modeling results indicated that increases in wildland fire smoke have offset approximately one-third of the improvements in background air quality. In recent years, wildland fire smoke has become more frequent and carbonaceous PM2.5 concentrations have intensified, especially in the Western CONUS and Southwestern Canada. Smoke exposure is also occurring earlier throughout the year, leading to more population being exposed. We estimated that long-term exposure to fire smoke carbonaceous PM2.5 is responsible for 7,462 and 259 non-accidental deaths annually in the CONUS and SC, respectively, with associated annual monetized damage of 68.4 billion USD for the CONUS and 1.97 billion CAD for SC. The Southeastern CONUS, where prescribed fires are prevalent, contributed most to these health impacts and monetized damages. Given the challenges posed by climate change for managing prescribed and wildland fires, our findings offer critical insights to inform policy development and assess future health burdens associated with fire smoke exposure.

Firefighters' occupational exposure to air pollution: impact on COPD and asthma-study protocol

INTRODUCTION

Firefighting continues to be among the most hazardous yet least studied occupations in terms of the impact of exposure to occupational disease. In particular, firefighters are at increased risk of adverse health effects due to exposure to significant levels of potentially harmful substances, namely carbon monoxide, particulate matter and formaldehyde, during their professional duties.This paper reports an epidemiologic study aiming to reduce the gaps in assessing the long-term effects of air pollution exposure to forest fires' combat on firefighters, namely regarding chronic obstructive pulmonary Disease (COPD) and asthma.

METHODS AND ANALYSIS

Based on the implementation in an area with high forest fires (in Portugal), the study will analyse firefighters' exposure to fire emissions by measuring air pollutants with personal exposure monitors during forest fire combat through a retrospective cohort study (exposed vs non-exposed). Moreover, based on answers to validated questionnaires and medical examinations to be performed by medical doctors, the study will assess the prevalence, incidence and exacerbation of COPD and asthma in firefighters, thus considering both short-term and long-term effects. Based on the results above referred, the study aims to evaluate the impact of exposure and inhalation dose of air pollutants during forest fires' combat on the development of the above-referred chronic diseases. The approximate number of participants in the study will never be less than 186, guaranteeing 80% of study power (significant at a 5% level).

ETHICS AND DISSEMINATION

The study has been approved by the Ethical Committee of Centro Hospitalar Universitário São João. The results will be published in international and national journals and conferences, allowing the results obtained to be communicated to the scientific community. Moreover, up-to-date data will be disseminated to stakeholders and decision-makers to help them decide on triggering official control measures.

Preoperative Exposure to Fine Particulate Matter and Risk of Postoperative Complications: A Single Center Observational Cohort Bayesian Analysis

Background

While exposure to fine particulate matter air pollution (PM 2.5 ) is known to cause adverse health effects, its impact on postoperative outcomes in US adults remains understudied. Perioperative exposure to PM 2.5 may induce inflammation that interacts insidiously with the surgical stress response, leading to higher postoperative complications.

Methods

We conducted a single center, retrospective cohort study using data from 49,615 surgical patients living along Utah's Wasatch Front and who underwent elective surgical procedures at a single academic medical center from 2016-2018. Patients' addresses were geocoded and linked to daily Census-tract level PM 2.5 estimates. We hypothesized that elevated PM 2.5 concentrations in the week prior to surgery would be associated with an increase in a bundle of major postoperative complications. A hierarchical Bayesians regression model was fit adjusting for age, sex, season, neighborhood disadvantage, and the Elixhauser index of comorbidities.

Results

Postoperative complications increased in a dose-dependent manner with higher concentrations of PM 2.5 exposure, with a relative increase of 8% in the odds of complications (OR=1.082) for every 10ug/m 3 increase in the highest single-day 24-hr PM 2.5 exposure during the 7 days prior to surgery. For a 30 fold increase in PM 2.5 (1 ug/m 3 to 30ug/m 3 ) the odds of complication rose to over 27% (95%CI: 4%-55%). The association persisted after controlling for comorbidities and confounders; our inferences were robust to modeling choices and sensitivity analysis.

Conclusions

In this large Utah cohort, exposure to elevated PM 2.5 concentrations in the week before surgery was associated with a dose-dependent increase in postoperative complications, suggesting a potential impact of air pollution on surgical outcomes. These findings merit replication in larger datasets to identify populations at risk and define the interaction and impact of different pollutants. PM 2.5 exposure is a potential perioperative risk factor and, given the unmitigated air pollution in urban areas, a global health concern.

Landscape fire PM2.5 and hospital admissions for cause-specific cardiovascular disease in urban China

There is a growing interest in the health impacts of PM2.5 originating from landscape fires. We conducted a time-series study to investigate the association between daily exposure to landscape fire PM2.5 and hospital admissions for cardiovascular events in 184 major Chinese cities. We developed a machine learning model combining outputs from chemical transport models, meteorological information and observed air pollution data to determine daily concentrations of landscape fire PM2.5. Furthermore, we fitted quasi-Poisson regression to evaluate the link between landscape fire PM2.5 concentrations and cardiovascular hospitalizations in each city, and conducted random-effects meta-analysis to pool the city-specific estimates. Here we show that, on a national scale, a rise of 1-μg/m3 in landscape fire PM2.5 concentrations is positively related to a same-day 0.16% (95% confidence interval: 0.01%-0.32%) increase in hospital admissions for cardiovascular disease, 0.28% (0.12%-0.44%) for ischemic heart disease, and 0.25% (0.02%-0.47%) for ischemic stroke. The associations remain significant even after adjusting for other sources of PM2.5. Our findings indicate that transient elevation in landscape fire PM2.5 levels may increase risk of cardiovascular diseases.

Clair JM, Warneke C, Wolfe GM, Womack C. Evolution of Reactive Organic Compounds and Their Potential Health Risk in Wildfire Smoke

Wildfires are an increasing source of emissions into the air, with health effects modulated by the abundance and toxicity of individual species. In this work, we estimate reactive organic compounds (ROC) in western U.S. wildland forest fire smoke using a combination of observations from the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign and predictions from the Community Multiscale Air Quality (CMAQ) model. Standard emission inventory methods capture 40-45% of the estimated ROC mass emitted, with estimates of primary organic aerosol particularly low (5-8×). Downwind, gas-phase species abundances in molar units reflect the production of fragmentation products such as formaldehyde and methanol. Mass-based units emphasize larger compounds, which tend to be unidentified at an individual species level, are less volatile, and are typically not measured in the gas phase. Fire emissions are estimated to total 1250 ± 60 g·C of ROC per kg·C of CO, implying as much carbon is emitted as ROC as is emitted as CO. Particulate ROC has the potential to dominate the cancer and noncancer risk of long-term exposure to inhaled smoke, and better constraining these estimates will require information on the toxicity of particulate ROC from forest fires.