Wildfire smoke impacts respiratory health more than fine particles from other sources: observational evidence from Southern California

Impact of occupational exposures in patients with chronic obstructive pulmonary disease: current understanding and knowledge gaps

PURPOSE OF REVIEW

Chronic obstructive pulmonary disease (COPD) is thought of as a disease caused by tobacco exposure, but numerous occupational exposures have been identified as risk factors for development of disease and exacerbations, although these remain underappreciated and underdiagnosed. We highlight evidence of occupational exposures and how they relate to COPD, while also looking at gaps in how the changing workplace might affect the occupational COPD landscape.

RECENT FINDINGS

Historical exposures linked to COPD included inorganic dusts like coal and silica and organic dusts like cotton and wood. Other data associated agricultural exposures, cleaning agents, air pollution, and construction work with COPD. As the workplace has evolved to include more work from home and growing industries like ridesharing and delivery, items like radon and indoor and outdoor air quality must be factored into the equation as occupational exposures with the potential to cause COPD and increase its morbidity. Despite this, causal conclusions with many risk factors are challenging due to the complex interaction between patient susceptibilities and environmental factors, both occupation-related and nonoccupation related.

SUMMARY

Additional studies are needed, not only to better evaluate occupational exposures and COPD pathogenesis, but also to look at more solution-oriented areas like precision medicine and interventions targeting a healthier workplace.

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.

Source-resolved black carbon and PM2.5 exposures during wildfires and prescribed burns

Changes in climate and land-use have significantly increased both the frequency and intensity of wildland fires globally, exacerbating the potential for hazardous impacts on human health. A better understanding of particle exposure concentrations and scenarios is crucial for developing mitigation strategies to reduce the health risks. Here, PM2.5 and black carbon (BC) concentrations were monitored during wildland fires between 2022 and 2024, in fire-prone areas in Catalonia (NE Spain), by means of personal monitors (AirBeam2 and Micro-aethalometers AE51 and MA200). Results revealed that exposures to combustion aerosols (PM2.5 and BC) were significant and comparable during wildfires and prescribed burns (mean PM2.5 during wildfires = 152 μg/m3 vs. 110-145 μg/m3 for prescribed burns). Overall, BC/PM2.5 ratios showed a large variability as a function of the monitoring scenario, indicating varying contributions from mineral aerosols to the emissions mix originating from fire management and extinction tasks. Specifically, mop-up tasks (final extinction tasks involving stirring top soil using handheld tools) were identified as a significant contributor to PM2.5 exposures, with 1-min PM2.5 peak concentrations reaching up to 1190 μg/m3. These results may be especially valuable for emissions modelling. Source apportionment of multi-wavelength BC datasets provided deeper insights into emissions and their impact on exposure profiles: line operators (who control the fire perimeter) were predominantly exposed to biomass burning smoke BCbb (61%) when compared to BC from fossil-fuel combustion (BCff = 39%), while torchers (in charge of initiating technical fires using fossil-fuel drip-torches) were predominantly exposed to BCff (77% vs. 23% BCbb). These findings highlight the value of portable monitors in the assessment of wildfire emissions and impacts on human exposure and environment. The combination of these tools, reporting data in real-time and with high time-resolution, is key to the design and implementation of effective mitigation strategies for environmental and health concerns related to wildland fires.

Associations of Wildfire-Derived Particulate Matter with Hospitalization, Emergency Department Visits and Mortality: A Systematic Review and Meta-Analysis

Epidemiological studies on wildfire smoke exposure and its associated disease morbidities and mortalities are rapidly accumulating in recent years. However, the findings of the existing studies have not been quantitatively evaluated with a conclusion. We conducted a systematic review and meta-analysis for the studies focused on associations of wildfire-sourced particles (PM2.5 and PM10) with cardiorespiratory diseases and mortality. We reviewed all literatures related to wildfire particles (PM2.5 and PM10) and cardiorespiratory disease morbidities [hospital admission, emergency department (ED) visits] and mortality (all-cause and cause-specific) from 1 January 2000 to 1 August 2024. Meta-analyses were conducted to summarize Relative Risks (RRs) and 95% confidence intervals (CIs) across studies when at least three studies were available for a particular exposure-outcome. All articles were assessed for risk of bias using a standard tool (Grading of Recommendations Assessment, Development and Evaluation, GRADE) for quality assurance. Studies (N=45) were increasingly published between the years of 2020-2024 and from North America (N=21) and Australia (N=11) where wildfires are common. In the meta-analysis of over 124 million patients, wildfire smoke was consistently associated with increased risk of all-cause mortality (RR: 1.02, 95% CI 1.01-1.03 for PM2.5 per 10 μg/m3) and respiratory outcomes, including hospital admission (1.04, 95% CI 1.02-1.05 for wildfire PM2.5 and 1.01, 95% CI 1.00-1.02 for wildfire PM10) and ED visits (1.04, 95% CI 1.02-1.06 for wildfire PM2.5). Associations between wildfire PM2.5 and cardiovascular diseases were inconclusive (mortality: 1.02, 95% CI 1.01-1.03; hospital admission: 1.01, 95% CI 1.00-1.02; ED visit: 1.01, 95%CI: 0.98-1.04). Current studies provide evidence of an increased risk of hospitalization and ED visits for respiratory diseases and all-cause mortality due to wildfire PM2.5 and PM10 exposures worldwide. Future research is needed to explore health effects of wildfire exposure on cardiovascular diseases.

Wildfire and wood smoke effects on human airway epithelial cells: A scoping review

BACKGROUND

Wildfires, which occur naturally but are increasingly intensified by climate change, release a complex mixture of organic and inorganic pollutants. These emissions have significant public health implications, contributing to increased morbidity and mortality. Epidemiological and clinical studies have consistently shown that exposure to wildfire smoke exacerbates respiratory conditions such as chronic obstructive pulmonary disease (COPD) and asthma. There are many epidemiological studies of the potential impact of smoke on human health; however, there are remarkably few in vitro studies, and an investigation of the underlying mechanisms of wildfire and wood smoke exposure on airway epithelial cells is required to better understand their toxicity and significance.

OBJECTIVES

This scoping review aimed to critically examine studies on the association between wildfire and wood smoke exposure and airway epithelial cell responses.

METHODS

We conducted a systematic search of relevant studies that used a combination of keywords related to wood smoke, wildfire, and epithelial cells and were published up to May 2024. Studies were retrieved from MEDLINE, PubMed, Google Scholar, and Web of Science.

RESULTS

Twenty-three studies fulfilled our inclusion criteria and were included. This review highlights inflammation, oxidative stress, and cytotoxicity as key impacts of wildfire and wood smoke on airway epithelial cells, causing lung damage. More studies are needed to understand these effects and guide prevention strategies.

DISCUSSION

This scoping review underscores the need for further research to better understand the complex biological endpoints associated with exposure to wildfire/wood smoke, informing strategies to mitigate health effects, ultimately improving health and well-being of population exposed to wildfire/wood smoke.

Toxicological screening of PM2.5 from wildfires involving different biomass fuels

Wildfires are becoming increasingly frequent and severe, particularly in Southern Europe. In addition to their immediate environmental and socioeconomic impacts, wildfires release significant amounts of particulate matter (PM), which poses serious health and ecological risks. Gaseous (CO and CO2) and PM2.5 samples were collected directly from smoke plumes, and the modified combustion efficiency (MCE) was calculated to characterise combustion conditions. This study aims to assess the cytotoxicity, mutagenicity and ecotoxicity of PM2.5 collected during wildfires in Portugal, with a focus on how varying biomass types and combustion conditions impact these effects. Ecotoxicity assessments using Aliivibrio fischeri showed that PM2.5 samples ranged from toxic to extremely toxic, with mixed vegetation burns (eucalyptus, acacia, ferns) exhibiting the highest toxicity levels. Cytotoxicity tests on human lung epithelial cells (A549) demonstrated a dose-dependent decrease in metabolic activity and no membrane damage, while mutagenicity assays identified direct-acting mutagens from smouldering acacia debris combustion, specifically inducing frameshift mutations in Salmonella typhimurium strain TA98. Root growth inhibition tests showed no toxicity, with some samples, instead, promoting growth probably due to nutrient content. Peroxidase activity responses indicated that, at higher concentrations, the enzyme function could be reduced if defence mechanisms are overwhelmed or stimulated due to high nutrient levels. These findings highlight the complex and varying toxicological profiles of wildfire PM, emphasising the need for further research.

Climate-Driven Escalation of Global PM2.5 Health Burden from Wildland Fires

Wildland fires constitute a major source of ambient fine particulate matter (PM2.5), significantly impacting air quality and public health. As the climate becomes warmer and drier, fire frequency is projected to rise, yet how the associated health impacts of fire-sourced PM2.5 (FPM2.5) respond to climate change remains vague. In this study, we modeled the global concentration and associated premature deaths of FPM2.5 over the past two decades. Our results reveal an upward trend in FPM2.5 concentrations globally, contributing to an increase in premature deaths from 156,000 to 241,000 between 2000 and 2021, alongside population growth and aging. Substantial variations are observed on a regional scale, but most regions experience increasing exposure levels, suggesting an increased impact of FPM2.5. Further regression analysis indicates that climate change plays a critical role in these trends, accounting for 56% of the net changes in FPM2.5-related premature deaths. Warming and drought emerge as key drivers of climate-induced health risks, with slightly different contributions to the FPM2.5 concentration and the associated premature deaths. Our findings underscore the urgent need to integrate climate adaptation strategies with fire management to mitigate the growing health burden caused by FPM2.5 worldwide.

Impacts of wildfire smoke PM2.5, greenspace and terrain ruggedness on life expectancy in the contiguous United States

Wildfire smoke PM2.5 has been associated with many adverse health effects. However, little is known about its impact on life expectancy. This study investigated the impact of wildfire smoke PM2.5 and its interaction with greenspace and terrain ruggedness on life expectancy in the contiguous United States. By analyzing life expectancy estimates during the 2010 to 2015 period in 66,263 census tracts with multi-level regression models adjusted for income, age, race, and population density, we found that life expectancy was negatively associated with the concentration of smoke PM2.5 and the number of smoke days. Specifically, the increase of 1 μg/m3 in the annual daily average smoke PM2.5 levels is associated with a decrease in life expectancy by 1.10 years (regression coefficient β = -1.10, 95 % confidence interval (CI): [-1.21, -0.99]). For every extra smoke day, life expectancy might decrease by 0.021 years (β = -0.021, 95 % CI: [-0.024, -0.018]). Additionally, the interaction of greenspace with smoke PM2.5 negatively affected life expectancy (β = -0.29, 95 % CI: [-0.38, -0.21]). No significant relationship was observed between life expectancy and terrain ruggedness. The generalized additive model revealed that the impact of smoke PM2.5 on life expectancy varied across concentration levels. The sensitivity analysis confirmed that the results were robust. Our study suggests that wildfires not only have a direct negative effect on life expectancy but also diminish the beneficial impact of greenspace, potentially turning its positive effects detrimental.

Evaluating public exposure to airborne particulates from major incident fires: A back trajectory plume modelling approach

Major incident fires at industrial facilities, particularly waste sites, pose a significant risk to public health because of the large amounts of hazardous airborne pollutants released into the ambient environment. Monitoring carried out during these fires is limited in spatial resolution, meaning that the full extent of population exposure is difficult to estimate. In this study, we overcome these limitations by using a novel back-trajectory plume modelling approach, applied to PM10 emission data from a significant tyre fire that occurred in the UK in 2010. This approach allows the calculation of an hourly emission rate that is then used in the forward modelling mode to predict hourly plume concentrations. An analysis of the modelled plume indicated that, as a reasonable worst case, up to 8000 residents in areas adjacent to the fire may have been exposed to PM10 concentrations that are deemed hazardous. Moreover, a vulnerability analysis showed that the exposed population had disproportionately poorer health than the national average, thus raising concerns about environmental justice. This work highlights the need to improve regulatory controls for waste sites located near urban areas and for further research on population exposure and the health impacts of major incident fires.

Environmental risk factors for all-cause dementia, Alzheimer's disease dementia, vascular dementia, and mild cognitive impairment: An umbrella review and meta-analysis

BACKGROUND

Mitigation of environmental risk factors for neurocognitive disorders could reduce the number of incident cases. We sought to synthesize the literature on environmental risk factors for dementia and mild cognitive impairment.

METHODS

We conducted an umbrella review and meta-analysis. Multiple databases were systematically searched to identify systematic reviews and meta-analyses of longitudinal studies examining environmental risk factors for dementia or mild cognitive impairment. We used random effects multi-level, meta-analytic models to synthesize risk ratios for each risk factor while accounting for overlap in the studies within reviews. As a secondary objective, we examined risk factors for two common phenotypes of dementia: Alzheimer's disease dementia and vascular dementia.

RESULTS

A total of 19 reviews containing 37 meta-analyses were included umbrella review. We found 9 factors where exposure was associated with higher risks of all-cause dementia: fine particulate matter, particulate matter, nitrogen dioxide, nitrogen oxides, carbon monoxide, shift work, night shift work, chronic noise, and extremely-low frequency magnetic fields. Neighbourhood greenness was associated with a lower risk of all-cause dementia. In a narrative review, we found that exposure to sulfur dioxide, proximity to roadways, ionizing radiation, aluminum, solvents, pesticides, and environmental tobacco smoke were also associated with dementia. We also found that fine particulate matter, extremely-low frequency magnetic fields, sulfur dioxide, chronic noise, and pesticides were related to Alzheimer's disease dementia. Fine particulate matter, particulate matter, and chronic noise were related to vascular dementia. No systematic review reported on mild cognitive impairment.

CONCLUSION

Achieving stronger air quality targets has the potential to reduce population-level dementia risk. Neighbourhood (i.e., greenness and chronic noise) and occupational (i.e., shift work) characteristics are associated with dementia and are viable public health intervention points. Additional research should examine the relationship between other environmental risk factors and mild cognitive impairment and specific types of dementia.

The heterogenous molecular characteristics of biomass-pyrogenic smoke dissolved organic matters (BPS-DOMs) binding with PAHs: Novel insights from combined analysis of FT-ICR MS and fluorescence variation

Biomass-pyrogenic smoke dissolved organic matter (BPS-DOM) can co-deposit with polycyclic aromatic hydrocarbons (PAHs), thereby altering their environmental behavior and fate in surface environments. However, the heterogeneous molecular characteristics of BPS-DOM binding with PAHs remain unclear. This study systematically elucidates the binding characteristics of PAHs (phenanthrene and pyrene), with various molecular compositions in BPS-DOM, utilizing FT-ICR MS and fluorescence variation analysis. CHO compounds in BPS-DOM, characterized by high aromaticity and abundant CO bonds, significantly enhance PAHs binding by promoting π-π electron donor-acceptor interactions. In contrast, CHON compounds with higher aliphaticity inhibit pyrene binding by competing for binding sites on BPS-DOM. Furthermore, the binding sequence of different fluorescent molecules follows the order of CHO→CHOS→CHON for phenanthrene and CHO→CHON→CHOS for pyrene. This was primarily due to the larger conjugated aromatic structures of CHO compounds, which provide stronger π-π interaction sites for PAHs binding. The difference in binding sequences between phenanthrene and pyrene is primarily attributed to phenanthrene's reliance on π-π electron donor-acceptor interactions induced by -SO and -N = O, while pyrene binding depended on π-π interactions driven by larger conjugated aromatic structures. These results provide an important theoretical foundation for further understanding the molecular-level interactions between BPS-DOM and PAHs.

Impacts of Aging and Relative Humidity on Properties of Biomass Burning Smoke Particles

Quantifying changes in the properties of smoke aerosols under varying conditions is important for understanding the health and environmental impacts of exposure to smoke. Smoke composition, aerosol liquid water content, effective density (ρeff), and other properties can change significantly as smoke travels through areas under different ambient conditions and over time. During this study, we measured changes in smoke composition and physical properties due to oxidative aging and exposure to humidity. We found that smoke aging led to SOA formation and increases in ratios of organic carbon to elemental carbon. Aerosol liquid water content increased with increasing relative humidity (RH), and aged smoke took up more water than fresh smoke at all humidity levels, likely due to a combination of changes in aerosol surface polarity at low and medium RH and increases in surface area with aging at high RH. Growth factors ranged from 1.06 ± 0.08 for fresh smoke at low RH to 1.32 ± 0.08 for aged smoke at high RH. Oxidative aging and exposure to humidity led to increases in ρeff. For 100 nm particles, ρeff ranged from ∼1.2 for fresh smoke at low RH to ∼1.6 for aged smoke at high RH. Results from these experiments suggest that exposure to humidity leads to smoke restructuring and compaction and/or changes in surface chemistry.

The effect of wildfire smoke on children's health: A systematic review

BACKGROUND

With wildfires increasing globally due to climate change, children may be more behaviourally exposed and more physiologically vulnerable to adverse health outcomes.

OBJECTIVE

To complete a comprehensive investigation of epidemiological studies examining respiratory and non-respiratory impacts of wildfires to identify research gaps and inform decision-making to protect children's health.

DATA SOURCES

The databases searched were PubMed, Embase, Scopus and Google Scholar.

STUDY SELECTION AND DATA EXTRACTION

Global epidemiological studies that investigated individuals under the age of 18 and were published from January 2006 to July 2024 were eligible to be included. Studies were included if they had wildfire days, smoke, or pollutants as the main exposure and had an outcome related to children's health. Though a meta-analysis was not possible, results were reported qualitatively through summaries of evidence tables and noteworthy results and the magnitude of the associations for each outcome was reported.

RESULTS

Twenty-four studies were selected. Sixteen studies examined respiratory outcomes and 11 studies included non-respiratory outcomes. A meta-analysis was not conducted, and consistent conclusions could not be made due to the heterogeneity and the small number of studies. Most respiratory-related studies found positive associations between wildfire exposure and adverse respiratory outcomes. All non-respiratory outcomes, except physical activity, had positive associations with wildfire exposure. For most non-respiratory outcomes, only one study evaluated each outcome. Higher-risk children were asthmatic, obese, under the age of five, in low-income countries or with a low socio-economic status.

CONCLUSIONS

There is consistent evidence that wildfire exposure is associated with adverse respiratory health in children, globally. There is less consistent evidence for the effect of wildfire exposure on non-respiratory outcomes. Further long-term research on non-respiratory outcomes in children, specifically physical activity, academic success and mental health is needed, especially in high-risk populations.

Polycyclic aromatics-derived benzene carboxylic acids (BPCAs) as a fast predictor of the genotoxicity of combustion particles

Polycyclic aromatic compounds (PAC) are common toxics in combustion particles. Numerous studies on health effects of PAC mixtures focused on limited compounds. It's still challenging to quantify complex PAC mixtures in combustion particles. Recently, benzene polycarboxylic acids (BPCAs) method, which involves conversion of PAC mixtures into a few BPCAs, has been used to quantify complex PAC mixtures in particles. In this study, in vitro biossays were used to evaluate the toxicity of extractable organic matter (EOM) in combustion particles. Analysis with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) identified ~1000 molecules, mostly aromatics (84.47 ± 5.32 %), that positively associate with the EOM toxicity (p < 0.05). We further employed BPCAs method to quantify PAC mixtures in the EOM of combustion particles, and observed the toxicity (especially genotoxicity) of EOM linearly increases with the abundance of PAC mixtures (r2: 0.68-0.89, p < 0.05), as it is shown by a data set referring to all source types including biomass burning, coal combustion and vehicle exhaust. The genotoxicity of PAC mixtures in EOM of combustion particles was estimated to be 10-13 times that of benzo[a]pyrene at the same mass concentration. Target analysis of 48 PAC was carried out, but a weaker relationship is found for the toxicity of EOM and the abundance of 48 PAC. Taken together, we suggest PAC-derived BPCAs as a fast predictor of the genotoxicity of combustion particles, which could be promising in routine monitoring of PAC pollution in the air.

Probing Interactions at the Organic-Inorganic Interface of Biomass Burning Aerosol: Reactivity of Organic Tracer Species with Different Iron Oxide Mineral Phases

As wildfire events become more frequent, there is a need to better understand the impact of smoke on the environment and human health. Smoke, or biomass burning aerosol (BBA), can undergo atmospheric processing changing its chemical and optical properties. We examined the interactions between four lignin pyrolysis products (catechol, syringol, syringic acid, and vanillic acid) and three BBA-relevant iron oxide mineral phases (hematite, maghemite, and magnetite) using attenuated total reflectance-Fourier transform infrared spectroscopy and dissolved iron measurements to better understand how atmospheric processing changes concentrations of soluble iron, iron oxidation state, and brown carbon abundance. Reductive dissolution was the primary dissolution mechanism for catechol and syringol, which led to a substantial amount of iron release (p < 0.05), whereas syringic and vanillic acids had little impact on dissolution. Comparisons with other BBA relevant compounds highlight the importance of both steric and electronic structures in the reductive dissolution process. The maghemite and magnetite phases, which are more likely to be present in BBA, released significantly more dissolved iron than hematite (p < 0.05), emphasizing the need to use BBA relevant iron oxide proxies in laboratory studies. This work provides insight into observations of iron dissolution and transformation of organics in BBA.

Lung function may recover after coal mine fire smoke exposure: a longitudinal cohort study

BACKGROUND AND OBJECTIVE

The 2014 Hazelwood coal mine fire exposed residents in nearby Morwell to high concentrations of particulate matter <2.5 µm (PM2.5) for approximately 6 weeks. This analysis aimed to evaluate the long-term impact on respiratory health.

METHODS

Adults from Morwell and the unexposed town of Sale completed validated respiratory questionnaires and performed spirometry, gas transfer and oscillometry 3.5-4 years (round 1) and 7.3-7.8 years (round 2) after the fire. Individual PM2.5 exposure levels were estimated using chemical transport models mapped onto participant-reported time-location data. Mixed-effects regression models were fitted to analyse associations between PM2.5 exposure and outcomes, controlling for key confounders.

RESULTS

From 519 (346 exposed) round 1 participants, 329 (217 exposed) participated in round 2. Spirometry and gas transfer in round 2 were mostly lower compared with round 1, excepting forced vital capacity (FVC) (increased) and forced expiratory volume in 1 second (minimal change). The effect of mine fire-related PM2.5 exposure changed from a negative effect in round 1 to no effect in round 2 for both pre-bronchodilator (p=0.005) and post-bronchodilator FVC (p=0.032). PM2.5 was not associated with gas transfer in either round. For post-bronchodilator reactance and area under the curve, a negative impact of PM2.5 in round 1 showed signs of recovery in round 2 (both p<0.001).

CONCLUSION

In this novel study evaluating long-term respiratory outcomes after medium-duration high concentration PM2.5 exposure, the attenuated associations between exposure and respiratory function may indicate some recovery in lung function. With increased frequency and severity of landscape fires observed globally, these results inform public health policies and planning.

Evidence for cytotoxicity and mitochondrial dysfunction in human lung cells exposed to biomass burning aerosol constituents: Levoglucosan and 4-nitrocatechol

Biomass burning (BB) emissions are one of the largest sources of carbonaceous aerosol, posing a significant risk as an airway irritant. Important BB markers include wood pyrolysis emissions, such as levoglucosan (LG) that is an anhydrous sugar bearing a six-carbon ring structure (i.e., 1,6-anhydro-β-D-glucopyranose). Atmospheric chemical aging of BB-derived aerosol (BBA) in the presence of nitrogen oxides (NOx) can yield nitro-aromatic compounds, including 4-nitrocatechol (4NC). There is building evidence that NOx-mediated chemical aging of BBA poses a more serious exposure effect than primary pyrolysis emissions. This study provides a comparative toxicological assessment following the exposure to important BBA marker compounds in human lung cells (i.e., A549 and BEAS-2B) to determine whether aromatic 4NC is more toxic than BBA-bound anhydrous carbohydrate (i.e., LG). We determined inhibitory concentration-50 (IC50) and examined reactive oxygen species (ROS) changes, mitochondrial dysfunction, and apoptosis induction in the two cell lines following exposure to LG and 4NC in a dose-response manner. In the BEAS-2B cells, estimated IC50 values for 4NC were 33 and 8.8 μg mL-1, and for LG were 2546 and ∼3 × 107 μg mL-1 at 24 h and 48 h of exposure, respectively. A549 cells exhibited a much higher IC50 value than BEAS-2B cells. LG exposures resulted in mitochondrial stress with viability inhibition, but cells recovered with increasing exposure time. 4NC exposures at 200 μg mL-1 resulted in the induction of apoptosis at 6 h. Mitochondrial dysfunction and ROS imbalance induced the intrinsic apoptotic pathway induction following 4NC exposures. While increased ROS is caused by LG exposure in lung cells, 4NC is a marker of concern during BB emissions, as we observed apoptosis and high mitochondrial ROS in both lung cells at atmospherically-relevant aerosol concentrations. It may be associated with higher airway or inhalation pathologies in higher BBA emissions, such as wildfires or during wood combustion.

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.

Polluted Air from Canadian Wildfires and Cardiopulmonary Disease in the Eastern US

Importance

Intense wildfires affecting residential populations are increasingly frequent. However, the adverse cardiopulmonary consequences to patients from remote wildfire smoke exposure is uncertain.

Objective

To investigate the association between wildfire smoke originating in Western Canadian provinces with cardiopulmonary disease burden in sociodemographically heterogenous populations in the Eastern US.

Design, Setting, and Participants

This case-only study used International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes for cardiopulmonary diseases extracted from the University of Maryland Medical System in June 2023 vs June 2018 and June 2019. Data were analyzed from September 2023 to September 2024.

Exposures

High air pollution episodes where the concentration of particulate matter with aerodynamic diameter below 2.5 μm (PM2.5) exceeded the toxic National Ambient Air Quality Standard (35 μg/m3) (referred to as "hotspot days") on contiguous days.

Main Outcomes and Measures

The number of patients with inpatient, ambulatory, and emergency department clinical encounters during assigned hotspot days in June 2023 compared with matching days in June of control years. Adjustments for covariates for comparisons between groups were made with χ2 tests and multivariable logistic regression.

Results

Statewide air quality analysis identified June 6-8 and 28-30 as 6 hotspot days with an increase in PM2.5 by 9.4-fold and 7.4-fold, respectively, in Baltimore City compared with all other days in 2023. After adjusting for calendar days across years, the cohort included 2339 cardiopulmonary clinical encounters in June 2023 (mean [SD] age, 68 [15] years; 1098 female [46.9%]; 710 Black [30.4%], 1528 White [65.3%]) and 3609 encounters in June 2018-2019 (mean [SD] age, 65 [15] years; 1690 female [46.8%]; 1181 Black [32.7%], 2269 White [62.9%]). The proportion of clinical encounters occurring during hotspot days in June 2023 was 588 of 2339 days (25.1%) vs 806 of 3609 days (22.3%) in control years (χ2 = 6.07; P = .01), with an adjusted odds ratio (aOR) of 1.18 (95% CI, 1.03-1.34; P = .02). Restricting this analysis to cardiac diseases, there was a 20% increase in adjusted odds for a clinical encounter (aOR, 1.20; 95% CI, 1.01-1.42; P = .04). Patients with cardiopulmonary encounters on hotspot days had greater socioeconomic advantage vs control years by ADI score (mean [SD] score, 39.1 [21.1] vs 41.0 [23.7]; P = .05).

Conclusions and Relevance

In this case-only study of a large medical system, we identified an increased cardiopulmonary disease burden for residents of Maryland that was likely associated with contemporaneous wildfire smoke-based infiltration of polluted or toxic air originating from Western Canada up to 2100 miles remotely.

Airborne antibiotic resistome from sludge dewatering systems: Mobility, pathogen accessibility, cross-media migration propensity, impacting factors, and risks

Bioaerosol contamination was considered as a potential health threat in sludge dewatering systems (SDSs), while emission and risk of airborne antibiotic resistome remain largely unclear. Herein, seasonal investigations of fine particulate matter (PM2.5) were conducted using metagenomics-based methods within and around different SDSs, together with an analysis of sewage sludge. Featured with evident seasonality, antibiotic resistance genes (ARGs) in SDS-PM2.5 also possessed greater accumulation, transfer, and pathogen accessibility than those in ambient air PM2.5. Mobile ARGs in SDS-PM2.5 mainly encoded resistance to tetracycline, and most were flanked by integrase. Some pathogenic antibiotic resistant bacteria (PARB), including Enterobacter asburiae, Escherichia coli, Enterococcus faecium, and Staphylococcus aureus, also carried mobile genetic elements in SDS-PM2.5. Dewatering behavior actuated > 50.56% of ARG subtypes and > 42.86% of PARB in sewage sludge to aerosolize into air. Relative humidity, temperature, and PM2.5 concentration collectively drove the evolution of bacterial community and indirectly promoted the antibiotic resistance of SDS-PM2.5. SDS-PM2.5 posed more serious resistome risks than sewage sludge and ambient air PM2.5, and the highest levels were discovered in winter. These findings underline the role of dewatering behavior in facilitating resistome's aerosolization, and the need to mitigate this potential air pollution.

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.

Intersections between climate change and antimicrobial resistance: a systematic scoping review

Climate change and antimicrobial resistance (AMR) present crucial challenges for the health and wellbeing of people, animals, plants, and ecosystems worldwide, yet the two are largely treated as separate and unrelated challenges. The aim of this systematic scoping Review is to understand the nature of the growing evidence base linking AMR and climate change and to identify knowledge gaps and areas for further research. We conducted a systematic search of the peer-reviewed literature in Scopus, Web of Science, and PubMed on 27 June, 2022. Our search strategy identified and screened 1687 unique results. Data were extracted and analysed from 574 records meeting our inclusion criteria. 222 (39%) of these reviewed articles discussed harmful synergies in which both climate change and AMR exist independently and can interact synergistically, resulting in negative outcomes. Just over a quarter (n=163; 28%) of the literature contained general or broad references to AMR and climate change, whereas a fifth (n=111; 19%) of articles referred to climate change influencing the emergence and evolution of AMR. 12% of articles (n=70) presented positive synergies between approaches aimed at addressing climate change and interventions targeting the management and control of AMR. The remaining literature focused on the shared drivers of AMR and climate change, the trade-offs between climate actions that have unanticipated negative outcomes for AMR (or vice versa), and, finally, the pathways through which AMR can negatively influence climate change. Our findings indicate multiple intersections through which climate change and AMR can and do connect. Research in this area is still nascent, disciplinarily isolated, and only beginning to converge, with few documents primarily focused on the equal intersection of both topics. Greater empirical and evidence-based attention is needed to investigate knowledge gaps related to specific climate change hazards and antimicrobial resistant fungi, helminths, protists, and viruses.

Biomass burning in Peninsular Southeast Asia intensifies meteorological drought in Southwest China

Biomass burning in Peninsular Southeast Asia (BB-PSEA) affects the climate in downwind regions, especially precipitation (PRE) in southern China. However, the impact of BB-PSEA on the meteorological drought in Southwest China (SWC), where closes to PSEA and often occurs seasonal drought, have not been clear yet. We selected a severe drought event in SWC from January to April 2010 and conducted sensitivity simulations using WRF-Chem (Weather Research and Forecasting model coupled with Chemistry) to evaluate the impact of BB-PSEA on the meteorological drought in SWC. Comparisons with observations revealed that the model performed well in simulating the spatiotemporal evolution of the drought in SWC. BB-PSEA increased the drought severity by 0.01-0.75 levels, enlarged drought areas by about 10%, and prolonged the drought duration mainly by one month in SWC. The impact of BB-PSEA on the drought in SWC in March/April was almost tenfold that in January/February, due to the higher emissions of BB-PSEA in March/April. The mechanism that BB-PSEA influenced drought predominantly involved the reduction of PRE, potential evapotranspiration (PET), and moisture fluxes in SWC. BB-PSEA aerosols warmed the air at 600-800 hPa and cooled the air near the surface in SWC, which stabilized the atmosphere and suppressed PRE and reduced PET in SWC. BB-PSEA aerosols also increased the sea surface temperature in South China Sea and the geopotential heights in the north of the Bay of Bengal, where the moisture sources of SWC originated from. This perturbation reduced the moisture fluxes across the west and south boundaries of SWC, resulting in the reduction of the water vapor content and PRE in SWC. Through elucidating the impact of BB-PSEA on the drought in SWC, this study clarified how BB-PSEA affected the climate in the downwind region and provided new understanding for drought prediction in SWC.

Black carbon and particulate matter concentrations amid central Chile's extreme wildfires

The increase in the frequency and severity of global wildfires has been largely influenced by climate change and land use changes. From February 2 to 6, 2024, central Chile experienced its most devastating wildland-urban interface wildfire in history, severely impacting the Valparaíso region. This catastrophic event, which led to extensive forest destruction, the loss of thousands of homes, and over a hundred human fatalities, directly impacted the area surrounding the campus of Federico Santa María Technical University. In that period, an air quality monitoring campaign was set up on the campus to measure black carbon (BC) and particulate matter (PM) during the wildfire season. The monitoring station was located directly within the smoke plume, allowing for the collection of unprecedented air quality data. Extremely high concentrations of BC at 880 nm were reported during the wildfires, with a daily mean (±σ) of 14.83 ± 19.52 μg m-3. Peak concentrations measured at 880 nm and 375 nm reached 812.89 μg m-3 and 1561.24 μg m-3, respectively. The maximum daily mean BC concentrations at these wavelengths were 55 and 99 times higher, respectively, compared to the pre-event period. The mean Ångström absorbing coefficient during the event was 1.66, indicating biomass burning as the primary BC source, while the maximum BC/PM2.5 ratio (at 375 nm) reached 57 %. From February 2 to 5, 2024, PM concentrations exceeded the Chilean air quality standard by 82 % and 198 % for coarse and fine particles, respectively. These levels are 4.7 and 6.0 times higher than the World Health Organization's recommendations. These elevated concentrations persisted for up to three days after the fire was extinguished. This study provides unique evidence of the rapid deterioration of regional air quality during a wildfire event using in situ measurements, serving as a stark reminder of the far-reaching consequences of a warming climate.

Wildfire Seasons, Prenatal PM2.5 Exposure, and Respiratory Infections by Age 1 Year: A Population-Based Case-Control Analysis of Critical Developmental Windows

The 2017 and 2018 wildfire seasons in British Columbia (BC), Canada were unprecedented. Among all the pollutants in wildfire smoke, fine particulate matter (PM2.5) poses the most significant risk to human health. There is limited research on prenatal wildfire smoke exposure and its impacts on infant health. We used a population-based nested case-control design to assess the association between daily PM2.5 exposures during specific developmental windows and the occurrence of otitis media or lower respiratory infections by age 1 year, including infections associated with dispensations of the antibiotic amoxicillin. We observed the strongest association between per 10 μg/m3 increase in PM2.5 exposure and otitis media during the fourth window of eustachian tube development (weeks 19-28) with an OR [95% confidence interval] of 1.31 [1.22, 1.41]. Similarly, the canalicular stage of lower respiratory tract development (weeks 18-27) was associated with the highest odds of lower respiratory infections, with an OR of 1.21 [1.15, 1.28]. Measures to reduce wildfire smoke exposure during pregnancy are warranted.

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.

Molecular insight into biomass-burning smoke water-soluble organic matter binding with Cd(II): Comprehensive analysis from fluorescence EEM-PARAFAC, FT-ICR-MS and two-dimensional correlation spectroscopy

The deposition of biomass-burning smoke water-soluble organic matter (BBS-WSOM) significantly affects the environmental behavior of heavy metals in aqueous environments. However, the interactions between BBS-WSOM and heavy metals at the molecular level remain unknown. This study combined FT-ICR-MS, fluorescence spectrum, FTIR, and two-dimensional correlation spectroscopy to anatomize the molecular characteristics of BBS-WSOM binding with Cd(II). The results show that CHO and CHOP compounds were responsible for the fluorescence response of BBS-WSOM at Ex: 225 nm and 275 nm/Em: 325 nm, and abundant proteins or CHON compounds were responsible for the fluorescence response of BBS-WSOM at Ex: 225-250 nm/Em: 350-450 nm and Ex: 300-350 nm/Em: 350-450 nm, which was very different from the fluorescence molecules in natural organic matters. Fluorescence change after Cd(II) addition indicated that CHOP and CHOS compounds enhanced BBS-WSOM binding with Cd(II). Differently, the CHON compounds could weaken the binding of other compounds with Cd(II). Different compounds binding with Cd(II) generally followed the order: CHON/CHOS compounds>CHOP compounds>CHO compounds, and the chemical groups binding with Cd(II) generally followed the prioritization: -COO-> -NH/SO>P = O/P-O>aromatic ring>CO>C-OH of phenol/alcohol>C-O-C. This study provides a profound insight into the interaction between BBS-WSOM and Cd(II) at the molecular level.

Fine Particulate Matter, Its Constituents, and Spontaneous Preterm Birth

Importance

The associations of exposure to fine particulate matter (PM2.5) and its constituents with spontaneous preterm birth (sPTB) remain understudied. Identifying subpopulations at increased risk characterized by socioeconomic status and other environmental factors is critical for targeted interventions.

Objective

To examine associations of PM2.5 and its constituents with sPTB.

Design, Setting, and Participants

This population-based retrospective cohort study was conducted from 2008 to 2018 within a large integrated health care system, Kaiser Permanente Southern California. Singleton live births with recorded residential information of pregnant individuals during pregnancy were included. Data were analyzed from December 2023 to March 2024.

Exposures

Daily total PM2.5 concentrations and monthly data on 5 PM2.5 constituents (sulfate, nitrate, ammonium, organic matter, and black carbon) in California were assessed, and mean exposures to these pollutants during pregnancy and by trimester were calculated. Exposures to total green space, trees, low-lying vegetation, and grass were estimated using street view images. Wildfire-related exposure was measured by the mean concentration of wildfire-specific PM2.5 during pregnancy. Additionally, the mean exposure to daily maximum temperature during pregnancy was calculated.

Main Outcomes and Measures

The primary outcome was sPTB identified through a natural language processing algorithm. Discrete-time survival models were used to estimate associations of total PM2.5 concentration and its 5 constituents with sPTB. Interaction terms were used to examine the effect modification by race and ethnicity, educational attainment, household income, and exposures to green space, wildfire smoke, and temperature.

Results

Among 409 037 births (mean [SD] age of mothers at delivery, 30.3 [5.8] years), there were positive associations of PM2.5, black carbon, nitrate, and sulfate with sPTB. Adjusted odds ratios (aORs) per IQR increase were 1.15 (95% CI, 1.12-1.18; P < .001) for PM2.5 (IQR, 2.76 μg/m3), 1.15 (95% CI, 1.11-1.20; P < .001) for black carbon (IQR, 1.05 μg/m3), 1.09 (95% CI, 1.06-1.13; P < .001) for nitrate (IQR, 0.93 μg/m3), and 1.06 (95% CI, 1.03-1.09; P < .001) for sulfate (IQR, 0.40 μg/m3) over the entire pregnancy. The second trimester was the most susceptible window; for example, aORs for total PM2.5 concentration were 1.07 (95% CI, 1.05-1.09; P < .001) in the first, 1.10 (95% CI, 1.08-1.12; P < .001) in the second, and 1.09 (95% CI, 1.07-1.11; P < .001) in the third trimester. Significantly higher aORs were observed among individuals with lower educational attainment (eg, less than college: aOR, 1.16; 95% CI, 1.12-1.21 vs college [≥4 years]: aOR, 1.10; 95% CI, 1.06-1.14; P = .03) or income (<50th percentile: aOR, 1.17; 95% CI, 1.14-1.21 vs ≥50th percentile: aOR, 1.12; 95% CI, 1.09-1.16; P = .02) or who were exposed to limited green space (<50th percentile: aOR, 1.19; 95% CI, 1.15-1.23 vs ≥50th percentile: aOR, 1.12; 95% CI, 1.09-1.15; P = .003), more wildfire smoke (≥50th percentile: aOR, 1.19; 95% CI, 1.16-1.23 vs <50th percentile: aOR, 1.13; 95% CI, 1.09-1.16; P = .009), or extreme heat (aOR, 1.51; 95% CI, 1.42-1.59 vs mild temperature: aOR, 1.11; 95% CI, 1.09-1.14; P < .001).

Conclusions and Relevance

In this study, exposures to PM2.5 and specific PM2.5 constituents during pregnancy were associated with increased odds of sPTB. Socioeconomic status and other environmental exposures modified this association.

Abiotic and biotic-controlled nanomaterial formation pathways within the Earth's nanomaterial cycle

Nanomaterials have unique properties and play critical roles in the budget, cycling, and chemical processing of elements on Earth. An understanding of the cycling of nanomaterials can be greatly improved if the pathways of their formation are clearly recognized and understood. Here, we show that nanomaterial formation pathways mediated by aqueous fluids can be grouped into four major categories, abiotic and biotic processes coupled and decoupled from weathering processes. These can be subdivided in 18 subcategories relevant to the critical zone, and environments such as ocean hydrothermal vents and the upper mantle. Similarly, pathways in the gas phase such as volcanic fumaroles, wildfires and particle formation in the stratosphere and troposphere can be grouped into two major groups and five subcategories. In the most fundamental sense, both aqueous-fluid and gaseous pathways provide an understanding of the formation of all minerals which are inherently based on nanoscale precursors and reactions.

Prescribed burn related increases of population exposure to PM2.5 and O3 pollution in the southeastern US over 2013-2020

Ambient air quality across the southeastern US has improved substantially in recent decades. However, emissions from prescribed burns remain high, which may pose a substantial health threat. We employed a multistage modeling framework to estimate year-round, long-term effects of prescribed burns on air quality and premature deaths. The framework integrates a chemical transport model with a data-fusion approach to estimate 24-h average PM2.5 and maximum daily 8-h averaged O3 (MDA8-O3) concentrations attributable to prescribed burns for the period 2013-2020. The Global Exposure Mortality Model and a log-linear exposure-response function were used to estimate the premature deaths ascribed to long-term prescribed burn PM2.5 and MDA8-O3 exposure in ten southeastern states. Our results indicate that prescribed burns contributed on annual average 0.59 ± 0.20 µg/m3 of PM2.5 (∼10 % of ambient PM2.5) over the ten southeastern states during the study period. On average around 15 % of the state-level ambient PM2.5 concentrations were contributed by prescribed burns in Alabama (0.90 ± 0.15 µg/m3), Florida (0.65 ± 0.19 µg/m3), Georgia (0.91 ± 0.19 µg/m3), Mississippi (0.65 ± 0.10 µg/m3) and South Carolina (0.65 ± 0.09 µg/m3). In the extensive burning season (January-April), daily average contributions to ambient PM2.5 increased up to 22 % in those states. A large part of Alabama and Georgia experiences ≥3.5 µg/m3 prescribed burn PM2.5 over 30 days/year. Additionally, prescribed burns are responsible for an average increase of 0.32 ± 0.12 ppb of MDA8-O3 (0.8 % of ambient MDA8-O3) over the ten southeastern states. The combined effect of prescribed burn PM2.5 exposure, population growth, and increase of baseline mortality over time resulted in a total of 20,416 (95 % confidence interval (CI): 16,562-24,174) excess non-accidental premature deaths in the ten southeastern states, with 25 % of these deaths in Georgia. Prescribed burn MDA8-O3 was responsible for an additional 1,332 (95 % CI: 858-1,803) premature deaths in the ten southeastern states. These findings indicate significant impacts from prescribed burns, suggesting potential benefits of enhanced forest management strategies.

Megafire smoke exposure jeopardizes tree carbohydrate reserves and yield

The global incidence of megafires is on the rise, leading to extensive areas being shrouded in dense smoke for prolonged periods, spanning days or weeks1. Here, by integrating long-term regional observations of non-structural carbohydrate content in trees across California's Central Valley with spatiotemporal satellite data, we present compelling evidence that dense smoke plumes negatively impact carbohydrate stores in three tree species: Prunus dulcis, Pistacia vera and Juglans regia. Our findings show that the presence of smoke causes a significant decrease in total non-structural carbohydrates, with reductions in the accumulation of both soluble sugar and starch reserves. This decline in carbohydrate levels persists through the trees' dormancy period into the next season's bloom, culminating in a reduced yield. Our results highlight a previously unrecognized wildfire threat that could affect plant health and ecosystem stability in both agricultural and natural environments.

Effects of fine particulate matter from wildfire and non-wildfire sources on emergency-department visits in people who were housed and unhoused in San Diego County (CA, USA) during 2012-20: a time-stratified case-crossover study

BACKGROUND

Being unhoused can increase vulnerability to adverse health effects due to air pollution. We aimed to quantify changes in emergency-department visits during and after exposure to wildfire-specific and non-wildfire particulate matter 2·5 μm or less in diameter (PM2·5) in San Diego County (CA, USA) in people who were both unhoused and housed.

METHODS

For this time-stratified case-crossover study, we used data on exposure to wildfire-specific PM2·5 in California and individual-level data for people admitted to the emergency departments of two hospitals (UC San Diego Health emergency departments at La Jolla and Hillcrest, San Diego) in San Diego County between July 1, 2012, and Dec 31, 2020. People with a postcode outside of San Diego County were excluded. Demographic information was age group, race or ethnicity, and transport to the emergency department. Wildfire-specific PM2·5 concentration at the postcode level was previously estimated using an ensemble model that combined multiple machine-learning algorithms and explanatory variables obtained via data on 24-h mean PM2·5 concentrations from the US Environmental Protection Agency Air Quality System. Conditional logistic regression models were applied, adjusting for specific humidity, wind velocity, and maximum temperature extracted from the US Gridded Surface Meteorological Dataset. Housing status was established by registration staff or triage nurses on arrival at the emergency department. For people who were unhoused, exposure was defined based on the weighted mean PM2·5 concentration at the city level proportional to the number of people who were unhoused in each specific city across urban centres in San Diego County. For people who were housed, we used residence postcode to measure exposure. We assessed the association between PM2·5 from wildfire and non-wildfire sources and emergency-department visits in people who were housed and unhoused.

FINDINGS

There were 587 562 emergency-department visits at the two hospitals, 76 407 (13·0%) of which were by people who were unhoused. People who were housed had a higher exposure to overall PM2·5 (24-h mean over the study period of 9·904 mg/m3, SD 3·445) and non-wildfire PM2·5 (9·663, 2·977) than people who were unhoused (9·863, 3·221; 9·557, 2·599). However, people who were unhoused had a higher exposure to wildfire-specific PM2·5 (0·305, 1·797) than people who were housed (0·240, 1·690). Overall PM2·5 exposure was associated with increased odds of emergency-department visits for both people who were housed (odds ratio 1·003, 95% CI 1·001-1·004 per 1 μg/m3 PM2·5 for 0-3 days after exposure) and people who were unhoused (1·004, 1·000-1·008 for 0-3 days after exposure). We found that non-wildfire PM2·5 was associated with emergency-department visits among people who were housed (1·003, 1·002-1·005 for 0-3 days after exposure) and wildfire-specific PM2·5 was associated with emergency-department visits in people who were unhoused (1·006, 1·001-1·011 for 0-3 days after exposure).

INTERPRETATION

People who were unhoused in San Diego County were more likely to visit emergency departments after exposure to increased wildfire-specific PM2·5. As the intensity and frequency of wildfires increase, understanding risk factors for vulnerable populations, such as people who are unhoused, is crucial to develop effective adaptation strategies.

FUNDING

US National Institutes of Health, National Institute on Aging.

Residential exposure to Aspergillus spp. is associated with exacerbations in COPD

BACKGROUND

Sensitisation to Aspergillus fumigatus is linked to worse outcomes in patients with COPD; however, its prevalence and clinical implications in domestic (residential) settings remains unknown.

METHODS

Individuals with COPD (n=43) recruited in Singapore had their residences prospectively sampled and assessed by shotgun metagenomic sequencing including indoor air, outdoor air and touch surfaces (a total of 126 specimens). The abundance of environmental A. fumigatus and the occurrence of A. fumigatus (Asp f) allergens in the environment were determined and immunological responses to A. fumigatus allergens determined in association with clinical outcomes including exacerbation frequency. Findings were validated in 12 individuals (31 specimens) with COPD in Vancouver, Canada, a climatically different region.

RESULTS

157 metagenomes from 43 homes were assessed. 11 and nine separate Aspergillus spp. were identified in Singapore and Vancouver, respectively. Despite climatic, temperature and humidity variation, A. fumigatus was detectable in the environment from both locations. The relative abundance of environmental A. fumigatus was significantly associated with exacerbation frequency in both Singapore (r=0.27, p=0.003) and Vancouver (r=0.49, p=0.01) and individuals with higher Asp f 3 sensitisation responses lived in homes with a greater abundance of environmental Asp f 3 allergens (p=0.037). Patients exposed and sensitised to Asp f 3 allergens demonstrated a higher rate of COPD exacerbations at 1-year follow-up (p=0.021).

CONCLUSION

Environmental A. fumigatus exposure in the home environment including air and surfaces with resulting sensitisation carries pathogenic potential in individuals with COPD. Targeting domestic A. fumigatus abundance may reduce COPD exacerbations.

Prenatal Exposure to Source-Specific Fine Particulate Matter and Autism Spectrum Disorder

In this study, associations between prenatal exposure to fine particulate matter (PM2.5) from 9 sources and development of autism spectrum disorder (ASD) were assessed in a population-based retrospective pregnancy cohort in southern California. The cohort included 318,750 mother-child singleton pairs. ASD cases (N = 4559) were identified by ICD codes. Source-specific PM2.5 concentrations were estimated from a chemical transport model with a 4 × 4 km2 resolution and assigned to maternal pregnancy residential addresses. Cox proportional hazard models were used to estimate the hazard ratios (HR) of ASD development for each individual source. We also adjusted for total PM2.5 mass and in a separate model for all other sources simultaneously. Increased ASD risk was observed with on-road gasoline (HR [CI]: 1.18 [1.13, 1.24]), off-road gasoline (1.15 [1.12, 1.19]), off-road diesel (1.08 [1.05, 1.10]), food cooking (1.05 [1.02, 1.08]), aircraft (1.04 [1.01, 1.06]), and natural gas combustion (1.09 [1.06, 1.11]), each scaled to standard deviation increases in concentration. On-road gasoline and off-road gasoline were robust for other pollutant groups. PM2.5 emitted from different sources may have different impacts on ASD. The results also identify PM source mixtures for toxicological investigations that may provide evidence for future public health policies.

Wildland Fire-Related Smoke PM 2.5 and Cardiovascular Disease ED Visits in the Western United States

Background

The impact of short-term exposure to fine particulate matter (PM 2.5 ) due to wildland fire smoke on the risk of cardiovascular disease (CVD) remains unclear. We investigated the association between short-term exposure to wildfire smoke PM 2.5 and Emergency Department (ED) visits for acute CVD in the Western United States from 2007 to 2018.

Methods

ED visits for primary or secondary diagnoses of atrial fibrillation (AF), acute myocardial infarction (AMI), heart failure (HF), stroke, and total CVD were obtained from hospital associations or state health departments in California, Arizona, Nevada, Oregon, and Utah. ED visits included those that were subsequently hospitalized. Daily smoke, non-smoke, and total PM 2.5 were estimated using a satellite-driven multi-stage model with a high resolution of 1 km. The data were aggregated to the zip code level and a case-crossover study design was employed. Temperature, relative humidity, and day of the year were included as covariates.

Results

We analyzed 49,759,958 ED visits for primary or secondary CVD diagnoses, which included 6,808,839 (13.7%) AFs, 1,222,053 (2.5%) AMIs, 7,194,474 (14.5%) HFs, and 808,396 (1.6%) strokes. Over the study period from 2007-01-01 to 2018-12-31, the mean smoke PM 2.5 was 1.27 (Q1: 0, Q3: 1.29) µg/m 3 . A 10 µg/m 3 increase in smoke PM 2.5 was associated with a minuscule decreased risk for AF (OR 0.994, 95% CI 0.991-0.997), HF (OR 0.995, 95% CI 0.992-0.998), and CVD (OR 0.9997, 95% CI 0.996-0.998), but not for AMI and stroke. Adjusting for non-smoke PM 2.5 did not alter these associations. A 10 µg/m 3 increase in total PM 2.5 was linked to a small increased risk for all outcomes except stroke (OR for CVD 1.006, 95% CI 1.006-1.007). Associations were similar across sex and age groups.

Conclusion

We identified an unexpected slight lower risk of CVD ED visits associated with short-term wildfire smoke PM 2.5 exposure. Whether these findings are due to methodological issues, behavioral changes, or other factors requires further investigation.

Wildfire-related PM2.5 and cause-specific cancer mortality

Wildfires have devastating effects on society and public health. However, little evidence from population-based cohort has been performed to analyze the relationship of wildfire-related PM2.5, an important component of wildfire smoke, with cancer-specific mortality. We aimed to explore this relationship and identify vulnerable populations in UK with lower levels of wildfire-related PM2.5 exposure. The study consisted of 492394 participants (age: 38-73 years) recruited by UK Biobank during 2004-2010. The cumulative wildfire-related PM2.5 within 10 kilometers of residence over three years was used as exposure, which was assessed by chemical transport and machine learning models. A time-varying Cox regression was utilized to explore the relationship of exposure with diverse cancer-specific mortality outcomes. Subgroup analyses of a range of potential modifiers were performed. Each 10 μg/m3 increment of 3-year cumulative exposure was related to a 0.4 % greater risk of total cancer (95 %CI: 1.001-1.007), a 1.1 % greater risk of lung cancer (95 %CI: 1.004-1.018), and a 2.7 % greater risk of lip, oral cavity and pharynx (LOP) cancer (95 %CI: 1.005-1.049). Higher vulnerability in the wildfire-related PM2.5-lung cancer relationship was found among participants being retired than those with other employment status. Even lower levels of exposure to PM2.5 from wildfires were related to elevated mortality risks for cancer from total, lung, LOP, highlighting the importance of wildfire prevention and control. Further investigations are warranted to enrich and extend existing knowledge in this field.

Impacts of wildfire-season air quality on park and playground visitation in the Northwest United States

A significant cost of wildfires is the exposure of local and regional populations to air pollution from smoke, which can travel hundreds of miles from the source fire and is associated with significant negative health consequences. Wildfires are increasing in frequency and intensity in the United States, driven by historic fire management approaches and global climate change. These influences will take many decades or longer to reverse, so the main opportunities for mitigating health effects involve minimizing human exposure through changes in behavior or infrastructure. One key recommendation for reducing pollution exposures during wildfire smoke events is to limit time and physical activity outdoors, but there is limited evidence on the extent to which people make this change. We estimate how use of parks and playgrounds changes with air quality during wildfire season in the northwest United States. We find small reductions in park and playground visits on moderately polluted days, and large reductions, to 50-60% of baseline visits, when pollution levels are high. Disaggregating results by neighborhood characteristics, we find a significantly greater behavioral response to moderate levels of air pollution in neighborhoods with higher socio-economic status, although responses to high levels of pollution are similar across neighborhood types.

Robust differential gene expression patterns in the prefrontal cortex of male mice exposed to an occupationally relevant dose of laboratory-generated wildfire smoke

Wildfires have become common global phenomena concurrent with warmer and drier climates and are now major contributors to ambient air pollution worldwide. Exposure to wildfire smoke has been classically associated with adverse cardiopulmonary health outcomes, especially in vulnerable populations. Recent work has expanded our understanding of wildfire smoke toxicology to include effects on the central nervous system and reproductive function; however, the neurotoxic profile of this toxicant remains ill-explored in an occupational context. Here, we sought to address this by using RNA sequencing to examine transcriptomic signatures in the prefrontal cortex of male mice modeling career wildland firefighter smoke exposure. We report robust changes in gene expression profiles between smoke-exposed samples and filtered air controls, evidenced by 2,862 differentially expressed genes (51.2% increased). We further characterized the functional relevance of these genes highlighting enriched pathways related to synaptic transmission, neuroplasticity, blood-brain barrier integrity, and neurotransmitter metabolism. Additionally, we identified possible contributors to these alterations through protein-protein interaction network mapping, which revealed a central node at ß-catenin and secondary hubs centered around mitochondrial oxidases, the Wnt signaling pathway, and gene expression machinery. The data reported here will serve as the foundation for future experiments aiming to characterize the phenotypic effects and mechanistic underpinnings of occupational wildfire smoke neurotoxicology.

Wildfires and Human Health

This JAMA Insights explores the adverse effects of wildfires on human health and health care systems and offers suggestions on how clinicians can help mitigate the health threats posed by wildfires.

Autoimmune Diseases Following Environmental Disasters: A Narrative Review of the Literature

Environmental disasters are extreme environmental processes such as earthquakes, volcanic eruptions, landslides, tsunamis, floods, cyclones, storms, wildfires and droughts that are the consequences of the climate crisis due to human intervention in the environment. Their effects on human health have alarmed the global scientific community. Among them, autoimmune diseases, a heterogeneous group of disorders, have increased dramatically in many parts of the world, likely as a result of changes in our exposure to environmental factors. However, only a limited number of studies have attempted to discover and analyze the complex association between environmental disasters and autoimmune diseases. This narrative review has therefore tried to fill this gap. First of all, the activation pathways of autoimmunity after environmental disasters have been analyzed. It has also been shown that wildfires, earthquakes, desert dust storms and volcanic eruptions may damage human health and induce autoimmune responses to inhaled PM2.5, mainly through oxidative stress pathways, increased pro-inflammatory cytokines and epithelial barrier damage. In addition, it has been shown that heat stress, in addition to increasing pro-inflammatory cytokines, may also disrupt the intestinal barrier, thereby increasing its permeability to toxins and pathogens or inducing epigenetic changes. In addition, toxic volcanic elements may accelerate the progressive destruction of myelin, which may potentially trigger multiple sclerosis. The complex and diverse mechanisms by which vector-borne, water-, food-, and rodent-borne diseases that often follow environmental diseases may also trigger autoimmune responses have also been described. In addition, the association between post-disaster stress and the onset or worsening of autoimmune disease has been demonstrated. Given all of the above, the rapid restoration of post-disaster health services to mitigate the flare-up of autoimmune conditions is critical.

Seeing through the smoke: The effects of wildfire fine particulate matter (PM2.5) exposure on standing and lying behavior in Holstein heifer calves

Wildfires are burning more acres annually, contributing to air pollution across the United States. Air pollutants, such as particulate matter (PM2.5), have health implications for humans and animals, and are known to alter behavior in several species, but effects of wildfire PM2.5 on dairy calf behavior are unknown. The present study aimed to understand how dairy calf standing and lying behavior is affected by wildfire PM2.5. Holstein heifer calves (n = 13) were monitored for the first 90 d of life, concurrent with the 2022 wildfire season. Hourly PM2.5 concentrations and meteorological conditions, which were used to calculate temperature-humidity index (THI), were recorded. Wildfire and wind trajectory mapping was used to determine the contribution of wildfires to spikes in PM2.5. Calf activity data were recorded every minute using accelerometers and analyzed as total hourly and daily standing and lying times, standing and lying bouts, and duration of bouts. Additionally, the responses of calves to the initial 24-h period of each of 2 separate exposures to wildfire smoke were assessed. Wildfire PM2.5 exposure was associated with reduced daily standing time and bout duration, increased daily total lying time, and increased, albeit not significantly, daily standing bouts. Percent of time standing hourly was increased, whereas percent of time lying hourly was decreased by wildfire PM2.5. The initial 24 h of each smoke exposure was characterized by decreased standing and increased lying time, but there was a greater change in behavior during the first event compared with the second event. These results indicate that exposure to wildfire PM2.5 induces a behavioral response, which may diminish with repeated exposures. Future research should aim to understand the health and welfare implications of the behavioral responses to wildfire PM2.5.

Significant chlorine emissions from biomass burning affect the long-term atmospheric chemistry in Asia

Biomass burning (BB) is a major source of trace gases and particles in the atmosphere, influencing air quality, radiative balance, and climate. Previous studies have mainly focused on the BB emissions of carbon and nitrogen species with less attention on chlorine. Reactive chlorine chemistry has significant effects on atmospheric chemistry and air quality. However, quantitative information on chlorine emissions from BB, particularly the long-term trend and associated atmospheric impacts, is limited both on regional and global scales. Here, we report a long-term (2001-2018) high-resolution BB emission inventory for the major chlorine-containing compounds (HCl, chloride, and CH3Cl) in Asia based on satellite observations. We estimate an average of 730 Gg yr-1 chlorine emitted from BB activity in Asia, with China contributing the largest share at 24.2% (177 Gg yr-1), followed by Myanmar at 18.7% and India at 18.3%. Distinct seasonal patterns and significant spatial and interannual variability are observed, mainly driven by human-mediated changes in agricultural activity. By incorporating the newly developed chlorine emission inventory into a global chemistry-climate model (CAM-Chem), we find that the BB-chlorine emissions lead to elevated levels of HCl and CH3Cl (monthly average up to 2062 and 1421 parts per trillion by volume (pptv), respectively), subsequently resulting in noticeable changes in oxidants (up to 3.1% in O3 and 17% in OH radicals). The results demonstrate that BB is not only a significant source of air pollutants but also of oxidants, suggesting a larger role of BB emissions in the atmospheric chemistry and oxidation process than previously appreciated. In light of the projected increase in BB activity toward the end of the century and the extensive control of anthropogenic emissions worldwide, the contribution of BB emissions may become fundamental to air quality composition in the future.

Physicochemical Characterization of the Particulate Matter in New Jersey/New York City Area, Resulting from the Canadian Quebec Wildfires in June 2023

The global increase in wildfires, primarily driven by climate change, significantly affects air quality and health. Wildfire-emitted particulate matter (WFPM) is linked to adverse health effects, yet the toxicological mechanisms are not fully understood given its physicochemical complexity and the lack of spatiotemporal exposure data. This study focuses on the physicochemical characterization of WFPM from a Canadian wildfire in June 2023, which affected over 100 million people in the US Northeast, particularly around New Jersey/New York. Aerosol systems were deployed to characterize WFPM during the 3 day event, revealing unprecedented mass concentrations mainly in the WFPM0.1 and WFPM0.1-2.5 size fractions. Peak WFPM2.5 concentrations reached 317 μg/m3, nearly 10 times the National Ambient Air Quality Standard (NAAQS) 24 h average limit. Chemical analysis showed a high organic-to-total carbon ratio (96%), consistent with brown carbon wildfires nanoparticles. Large concentrations of high-molecular-weight PAHs were found predominantly bound to WFPM0.1, with retene, a molecular marker of biomass burning and a known teratogen, being the most abundant (>70%). Computational modeling estimated a total lung deposition of 9.15 mg over 72 h, highlighting the health risks of WFPM, particularly due to its long-distance travel capability and impact on densely populated areas.

Climate change and public health in California: A structured review of exposures, vulnerable populations, and adaptation measures

California faces several serious direct and indirect climate exposures that can adversely affect public health, some of which are already occurring. The public health burden now and in the future will depend on atmospheric greenhouse gas concentrations, underlying population vulnerabilities, and adaptation efforts. Here, we present a structured review of recent literature to examine the leading climate risks to public health in California, including extreme heat, extreme precipitation, wildfires, air pollution, and infectious diseases. Comparisons among different climate-health pathways are difficult due to inconsistencies in study design regarding spatial and temporal scales and health outcomes examined. We find, however, that the current public health burden likely affects thousands of Californians each year, depending on the exposure pathway and health outcome. Further, while more evidence exists for direct and indirect proximal health effects that are the focus of this review, distal pathways (e.g., impacts of drought on nutrition) are more uncertain but could add to this burden. We find that climate adaptation measures can provide significant health benefits, particularly in disadvantaged communities. We conclude with priority recommendations for future analyses and solution-driven policy actions.

Seasons of smoke and fire: preparing health systems for improved performance before, during, and after wildfires

Increased frequency, intensity, and duration of wildfires are intensifying exposure to direct and smoke-related hazards in many areas, leading to evacuation and smoke-related effects on health and health systems that can affect regions extending over thousands of kilometres. Effective preparation and response are currently hampered by inadequate training, continued siloing of disciplines, insufficient finance, and inadequate coordination between health systems and governance at municipal, regional, national, and international levels. This Review highlights the key health and health systems considerations before, during, and after wildfires, and outlines how a health system should respond to optimise population health outcomes now and into the future. The focus is on the implications of wildfires for air quality, mental health, and emergency management, with elements of international policy and finance also addressed. We discuss commonalities of existing climate-resilient health care and disaster management frameworks and integrate them into an approach that addresses issues of financing, leadership and governance, health workforce, health information systems, infrastructure, supply chain, technologies, community interaction and health-care delivery, before, during, and after a wildfire season. This Review is a practical briefing for leaders and health professionals facing severe wildfire seasons and a call to break down silos and join with other disciplines to proactively plan for and fund innovation and coordination in service of a healthier future.

Respiratory Diseases Associated With Wildfire Exposure in Outdoor Workers

Wildfires, including forest fires, bushfires, and landscape fires, have become increasingly prevalent, fueled by climate change and environmental factors and posing significant challenges to both ecosystems and public health. This review article examines the relationship between wildfires and respiratory diseases in outdoor workers, with a main focus on airway disease. In addition to the expected effects of direct thermal respiratory injuries and possible carbon monoxide poisoning, there are associations between wildfires and upper and lower respiratory effects, including infections as well as exacerbations of asthma and chronic obstructive pulmonary disease. A few studies have also shown an increased risk of new-onset asthma among wildfire firefighters. Outdoor workers are likely to have greater exposure to wildfire smoke with associated increased risks of adverse effects. As wildfires become increasingly prevalent globally, it is crucial to understand the various dimensions of this association. Furthermore, this review addresses preventive measures and potential interventions to alleviate the airway burden on individuals during and after work with wildfires events.