One-third of global population at cancer risk due to elevated volatile organic compounds levels

The study addresses the global health risks posed by ambient volatile organic compounds (VOCs), which are precursors to PM2.5 and ozone and have direct adverse effects, including respiratory morbidity and long-term cardiovascular, neurological, reproductive, and carcinogenic impacts. While specific VOCs such as benzene and formaldehyde are recognized carcinogens with quantified lifetime risks at low concentrations, most prior assessments have been limited to local, regional, or national scales due to sparse monitoring and measurement complexity. There is a lack of global, long-term, consistent assessments of VOC exposure and associated cancer risks, particularly in less developed regions. This work aims to fill that gap by simulating global surface NMVOC concentrations from 2000 to 2019, selecting ten hazardous VOCs for health risk assessment (including three carcinogens: benzene, formaldehyde, acetaldehyde), and estimating lifetime inhalation cancer risks and cancer burdens at regional, national, and global scales to reveal exposure disparities across income groups.

Previous studies have quantified VOC levels and health risks primarily at sub-global scales. Xiong et al. evaluated VOC sources and risks in eight Canadian cities (2013–2018), finding elevated inhalation cancer risks, especially near traffic and industrial sites. Strum et al. analyzed 41 hazardous air pollutants across 200+ US sites, identifying formaldehyde and benzene as major cancer risk contributors, but noted that monitor-based estimates may not reflect population-wide risks. Satellite-based approaches (e.g., OMI) have been used to infer surface formaldehyde and related cancer risks; Zhu et al. found up to 6,600 lifetime cancer cases in the US due to outdoor formaldehyde, despite satellite values being lower than ground observations on average. Global-scale assessments remain rare; one recent modeling study estimated BTEX-induced preterm births in 2015. Given substantial changes in NMVOC emissions over the past two decades, a global, temporally consistent evaluation of VOC exposure and health risks has been lacking, motivating the present study.

The authors used the CESM2 (version 2.2.0) CAM6-Chem global chemistry–climate model with MOZART-TS1 chemistry and MAM4 aerosols to simulate global surface NMVOC and individual VOCs for 2000–2019. Simulations were run at 0.9° × 1.25° (lat–lon) with specified dynamics using MERRA-2 meteorology, in 5-year intervals with the first year as spin-up. Anthropogenic NMVOC emissions were taken from CEDS v2021_04_21 for eight sectors and 11 regions; individual emissions for 22 VOC species (including benzene, toluene, xylenes, formaldehyde, acetaldehyde, methanol, propylene, methyl ethyl ketone, acetonitrile, hydrogen cyanide, among others) were derived by scaling CEDS NMVOCs using CMIP6 sector/species fractions and regridded to model resolution. Intermediate-VOC and semi-VOC emissions were parameterized (20% of NMVOC and 60% of primary organic aerosol, respectively). Biomass burning emissions were from CMIP6 (BB4CMIP). Model evaluation used in situ VOC observations from the US, Canada, and Europe (details in Supplementary Discussion). Population-weighted annual concentrations were computed using GPWv4 population data (regridded to 0.1° for country analysis). Cancer risk assessment focused on inhalation exposure to three carcinogens (benzene, formaldehyde, acetaldehyde), with age-specific calculations from the third trimester to age 70 incorporating age sensitivity factors, intake rates (breathing rate/body weight), exposure duration, and time at residence. Residential inhalation dose and lifetime inhalation cancer risk (LICR) were computed per grid cell and age group and summed to obtain integrated LICR. Cancer burden (CB) was calculated as LICR × population, representing potential excess lifetime cancer cases; uncertainties and 95% CIs were derived using variability in intake parameters. Analyses aggregated to global, regional (11 macro-regions), and national levels.

- Emissions and concentrations: Global NMVOC emissions increased by 10.2% from 133.6 Tg (2000) to 147.2 Tg (2019). Largest relative increases occurred in Sub-Saharan Africa (SSA, +75.9%), Rest of Asia (ROA, +44.0%), and China (+21.5%); decreases occurred in the US (−36.4%) and Western Europe (−44.8%). Sectorally, energy (+33.4%) and solvent (+32.2%) emissions rose, while transportation (−24.7%) and residential/commercial/other (−6.8%) fell; by 2014, energy and solvent surpassed transportation and RCO contributions. - Surface concentrations: Global annual mean NMVOC rose from 19.3 µg m−3 (2000) to a peak 21.2 µg m−3 (2015) and 21.0 µg m−3 (2019); hazardous VOCs (HVOC) rose from 7.8 to 8.8 µg m−3. China exhibited the highest NMVOC concentrations (35.0–41.5 µg m−3), followed by India (31.8–38.1), Latin America (26.6–33.8), and ROA (19.5–28.8). ROA had the highest percentage increase in NMVOC concentrations (+32.1%), while WEurope (−43.3%) and the US (−15.6%) decreased most. - Species patterns: Methanol was the most abundant HVOC (~30% of HVOC), reflecting growth in industrial and solvent sources. Formaldehyde and acetaldehyde together contributed ~34–36% of HVOC and increased over ROA, China, India, and Canada; Canada saw +23.9% (formaldehyde) and +23.3% (acetaldehyde), consistent with secondary formation from oil and gas precursor emissions. BTEX share declined from 19.5% (2000) to 17.6% (2019); benzene decreased in WEurope (−34.1%), US (−24.1%), and China (−5.0%), but increased in ROA (+78%) and SSA (+50%). - Cancer risk (LICR): Globally, integrated LICR rose from 4.2×10−6 (2000) to 4.4×10−6 (2015/2019). Benzene posed the highest risk (global mean LICR ≈ 2.6×10−5), implying ~26 per million lifetime cancer risk; formaldehyde ~13–14 per million; acetaldehyde ~0.31–0.35 per million. The 0–2 years age group had the highest excess lifetime risks due to higher susceptibility and intake rates. - Population exposure: Between 36.4% and 39.7% of the global population was exposed to LICR > 1×10−6 from the three carcinogens; 26.3–29.3% were exposed to benzene-related LICR > 1×10−6. China had very high exposed fractions (82.8–84.3%); India 49.4–55.8%; ROA increased from 32.9% to 47.3%; SSA from 18.6% to 30.5%. Europe had low exposed fractions (1.7–5.8%); US decreased substantially but ~4.5% remained exposed in 2019. - Cancer burden (CB): Global CB attributable to the three carcinogens was 0.60 (95% CI: 0.40–0.81) million in 2000; 0.64 (0.42–0.86) in 2005; 0.69 (0.46–0.93) in 2010; 0.79 (0.52–1.06) in 2015; and 0.85 (0.56–1.14) million in 2019. Benzene contributed 72.2–74.1% of integrated CB, formaldehyde 20.5–22.0%, acetaldehyde 5.4–5.8%. China, India, ROA, and SSA accounted for 80.8–84.4% of global CB; US and WEurope contributed only 3.9–2.3% and 3.8–2.1%, respectively. - Country rankings: China and India had the highest CBs. Increases in rank for Indonesia, Pakistan, Nigeria, the Democratic Republic of the Congo, and Brazil reflected rising emissions, population, and events like fires/agricultural burning. Several major oil-producing countries (e.g., Bahrain, Qatar, UAE, Kuwait, Nigeria) exhibited high benzene-related risks exceeding US EPA’s upper risk bound. - Disparities and drivers: High-income regions saw 15.4–21.6% reductions in integrated and benzene-related CBs (2000–2019), driven by 11.4–40.6% emission reductions and corresponding LICR decreases. Formaldehyde CB sometimes increased due to population growth and secondary formation (notably over Canadian oil sands). Low and low-middle-income countries experienced increases in CB (integrated +7.9% to +141%; benzene +4.0% to +166%), with SSA showing the fastest growth due to +79.5% population and +69–73% VOC emission increases. Open agricultural burning and wildfires amplified formaldehyde and benzene burdens in several regions.

The study demonstrates that global VOC emissions and concentrations have risen unevenly across regions, translating into substantial and unequal cancer risks and burdens. By quantifying LICR and CB at fine spatial scales and aggregating to countries and regions, the work reveals pronounced disparities: while high-income regions reduced benzene and overall VOC risks through emission controls, low-to-middle-income regions experienced increasing risks driven by rapid population growth, industrialization, transportation and energy sector expansion, and biomass burning. The findings support targeted mitigation: prioritizing benzene emission reductions in less developed regions to quickly reduce both individual and population-wide cancer risks, and focusing on controlling secondary formaldehyde formation in high-income regions where primary emissions have already declined. The results underscore environmental injustice in exposure to carcinogenic VOCs and highlight the need for policy interventions tailored to regional sources and socioeconomic contexts.

Using CEDS emissions with the CESM2 CAM6-Chem model, the study provides a 20-year global assessment of VOC concentrations, lifetime inhalation cancer risks, and population-wide cancer burdens from key carcinogenic VOCs. Approximately one-third of the global population was exposed to unacceptable lifetime cancer risks (LICR > 1×10−6) from benzene, formaldehyde, and acetaldehyde between 2000 and 2019, with especially high exposure in China and rising risks in low- and low-middle-income regions. Benzene dominated the global cancer burden, while secondary formaldehyde remains a concern in developed regions. The authors propose differentiated mitigation strategies: benzene-focused reductions for low-to-middle-income countries and controls on secondary formaldehyde formation for high-income countries. These results inform long-term health burden evaluations of global VOC exposure and policies to reduce exposure disparities. Future improvements should incorporate additional VOCs and exposure pathways (e.g., dermal/ingestion), indoor sources, country-specific exposure parameters, and higher-resolution modeling and observations in under-monitored regions.

- Additivity assumption for mixed VOC carcinogenic effects; potential synergistic or antagonistic interactions are not captured. - Risk estimates limited to 10 hazardous VOCs (3 carcinogens) out of 22 modeled, likely underestimating total cancer risk. - Only inhalation exposure considered; dermal and ingestion pathways and indoor sources (e.g., volatile chemical products) excluded. - Uniform exposure parameters across some regions due to lack of country-specific data (e.g., assumed similarities between China and ROA, and between US and Western Europe). - Uncertainties in emission inventories, model configuration, and simulations; sparse ground-based measurements in regions like SSA, ROA, and NAME limit evaluation. - Coarse horizontal resolution (0.9°×1.25°) may not capture local gradients and exposure variability within grid cells, potentially biasing risk estimates.