The findings are particularly alarming because the impairment appears to accumulate silently over time. The researchers, led by José Maria Viana dos Santos and Márcio Nakanishi, found that odor identification scores declined steadily with years on the job. Workers with olfactory impairment had an average tenure of 10.2 years at the pumps, compared with just 5.9 years among those with normal smell. A statistical correlation analysis confirmed a moderate negative relationship between years of exposure and olfactory performance, and a multivariable regression model that accounted for age and smoking history revealed that each additional year of work increased the odds of olfactory dysfunction by roughly 15 percent. Notably, age itself was not significantly associated with impairment, suggesting that the effect is driven by exposure rather than simple aging.

What makes the study especially compelling is the gap between objective test results and subjective awareness. Only 27 of the 116 participants, or 23.3 percent, believed that their work was affecting their sense of smell. Yet among the 68 workers with objectively confirmed dysfunction, 48, or 70.6 percent, reported no such perception. Several participants were reportedly surprised by their results and attributed any perceived changes to aging or recurring nasal problems rather than to their workplace. This pattern of underrecognition echoes earlier hypotheses in occupational health literature that chemical-induced olfactory disorders are frequently subclinical and go unreported unless they become severe, which limits the effectiveness of surveillance programs that rely solely on workers noticing and reporting symptoms.

The exposure at issue is a complex cocktail of volatile organic compounds. Gasoline vapors contain BTEX, a group of aromatic hydrocarbons comprising benzene, toluene, ethylbenzene, and xylene. Benzene is the most notorious member of this group: it is classified as carcinogenic to humans, with strong evidence linking it to acute myeloid leukemia, and it is present in gasoline as an inherent component that cannot simply be substituted away. Although humans can typically detect benzene by its sweet smell at concentrations of roughly one to five parts per million, the study’s authors emphasize that odor perception is an unreliable safety indicator. Individual sensitivity varies widely, olfactory adaptation can dull the warning signal after repeated exposure, and workers cannot depend on their noses to alert them to hazardous airborne concentrations.

The biological plausibility of fuel-vapor-induced smell loss is well grounded in toxicology. The olfactory epithelium, the specialized tissue lining the upper nasal cavity where odor detection occurs, is remarkably metabolically active and rich in cytochrome P450 enzymes, which can bioactivate inhaled xenobiotics into reactive metabolites. Chronic inhalation of solvents may damage olfactory receptor neurons and their supporting cells through oxidative stress, inflammation, and mucosal irritation. Benzene and its metabolites are known to induce oxidative stress and DNA damage, and biomonitoring studies of Brazilian gas station workers have documented genotoxic effects consistent with such exposure. The authors caution, however, that their findings should not be interpreted as direct evidence of DNA damage in the olfactory mucosa; for solvent mixtures and volatile organic compounds, irritation and inflammation of the nasal lining are considered more plausible mechanisms than direct nerve uptake, a pathway more clearly established for ultrafine particles. The irritant properties of petrochemical vapors may also provoke chronic rhinitis, and workers in Brazilian biomonitoring studies have frequently reported nasal irritation and nosebleeds, consistent with mucosal toxicity.

Importantly, the pattern of errors on the smell test suggests that the damage is not simply a matter of becoming desensitized to fuel odors. While gasoline was correctly identified by 69.8 percent of participants, the odors most frequently misidentified by impaired workers were apple, eucalyptol, and orange, none of which are fuel-related, while garlic, clove, and cinnamon were recognized by most participants. This non-selective pattern of loss indicates that selective adaptation to gasoline odor alone is unlikely to explain the dysfunction, strengthening the case that the vapors are causing genuine injury to the olfactory system rather than mere familiarity effects.

The study’s methodology deserves attention because it showcases a new generation of field-deployable sensory testing. Conventional standardized smell assessments, such as the University of Pennsylvania Smell Identification Test and Sniffin’ Sticks, are well validated but require trained personnel, consume considerable time, and are costly to administer at scale. The researchers instead used the MultiScent-20, an automated digital device developed in São Paulo, Brazil, which delivers 20 microencapsulated odor stimuli through a tablet interface in a four-alternative forced-choice format. Each participant taps a start button, receives a five-second burst of scent carried by a controlled airflow, and selects the matching option from four choices on the touchscreen. The entire test takes roughly 10 to 15 minutes, scores itself automatically, and can be self-administered. Validation studies have shown high test-retest reliability and strong concordance with Sniffin’ Sticks, with a correlation of approximately 0.88, making the device well suited for workplace screening campaigns that would be impractical with traditional methods.

The Brazilian context amplifies the significance of the findings. National legislation in Brazil prohibits self-service fueling, which means attendants handle every refueling and bear the full burden of cumulative vapor inhalation, eight hours a day. Regulatory guidelines such as NR-09 mandate biological monitoring of benzene exposure using urinary trans,trans-muconic acid, and Brazilian studies have shown that even at ambient benzene concentrations below one part per million, workers exhibit elevated biomarkers of benzene-related biological effects. Yet protective measures remain strikingly inadequate: in the study, only 3 of 116 participants, or 2.6 percent, reported using personal protective equipment, even though 62.8 percent of those asked believed such equipment was necessary. Workers cited discomfort, inconvenience, interference with customer service, and lack of employer enforcement as reasons for non-use, and 63 percent were aware of benzene-related health risks.

The safety implications extend beyond health into hazard detection itself. Gas station workers may rely on smell as one of several warning cues to detect fuel leaks and spills, thereby reducing fire and explosion risks, and case reports have documented incidents of ignition near gasoline spills involving individuals with anosmia. Reduced smell sensitivity also diminishes the ability to detect smoke, gas leaks, or spoiled food in daily life. In some countries, such as Germany, intact olfactory function is formally required for specific occupations involving gas detection, but no such requirement exists for gas station workers in Brazil, leaving workers with impaired smell effectively less able to perceive odor-related dangers on the job.

The authors argue that their results should prompt a broadening of occupational surveillance frameworks, which currently focus almost exclusively on hematological and carcinogenic endpoints of benzene toxicity, toward sensory outcomes. They recommend periodic olfactory screening for solvent-exposed workers, engineering controls such as stage II vapor recovery systems at fuel pumps, job rotation to limit continuous exposure, worker education about the sensory effects of fuel vapors, and longitudinal studies to track long-term outcomes. They also suggest that respirators with organic vapor cartridges should be available for high-exposure tasks like tank cleaning and spill response, even if sustained routine use remains impractical without cultural change. The study does carry limitations: its cross-sectional design precludes definitive causal inference, individual exposure levels were not measured, and only current workers were evaluated, raising the possibility that the most affected individuals had already left the job. Still, the consistency of the findings with international evidence, including an Indonesian study that found 77.5 percent of gas station employees with olfactory dysfunction compared with none of the unexposed controls, suggests the problem transcends borders. For a workforce that keeps the world’s vehicles fueled, the message is sobering: the very vapors they breathe every day may be eroding one of the senses they need to stay safe, long before they notice anything is wrong.

Subject of Research: Olfactory dysfunction among gas station workers chronically exposed to fuel vapors containing benzene and other volatile organic compounds

Article Title: Olfactory dysfunction among gas station employees exposed to fuel vapors using digital odor identification testing

Article References: Viana dos Santos, J. M., & Nakanishi, M. (2026). Olfactory dysfunction among gas station employees exposed to fuel vapors using digital odor identification testing. iScience, 29(11), Article 117786. https://doi.org/10.1016/j.isci.2026.117786

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117786

Keywords: olfactory dysfunction, gas station workers, benzene, BTEX, fuel vapors, occupational health, volatile organic compounds, smell testing, hyposmia, anosmia, MultiScent-20, Brazil

The review, conducted by Mahlodi Esther Masekela, systematically mapped the literature on BTEX emissions from household firewood combustion published between 1994 and 2025, following the Arksey and O’Malley scoping framework and adhering to PRISMA-ScR reporting guidelines. Searches across ScienceDirect, Web of Science, Google Scholar, and Scopus identified 583 records, which were screened down to just five eligible peer-reviewed studies. That tiny number is itself a striking finding: after three decades of research, only a handful of investigations have quantitatively characterized BTEX emissions from the specific firewood species burned in domestic cookstoves, and the review’s central concern is what those few studies leave out.

The core methodological problem is the mismatch between study design and real-world fuel use. Four of the five included studies—80 percent—examined only single firewood species, burning one taxonomically distinct wood type at a time. But households in low- and middle-income countries rarely do this. Research in South Africa has documented that families typically use bundles containing up to six different tree species, while studies in Ethiopia have found that mixed fuels, principally wood combined with animal dung, are the most common cooking fuels. Laboratory work has shown that blending fuels fundamentally alters both the total volatile organic compound concentrations and the relative proportions of individual compounds, meaning single-species emission profiles may simply not represent what happens in a real kitchen.

Geography compounds the problem. Four of the five studies were conducted in high-income countries, mostly in Europe—Portugal, Sweden, and Finland—plus one in the United States, while only a single study, from South Africa, represents the low- and middle-income country context. This distribution is starkly inverted relative to the disease burden: firewood accounts for roughly 25 to 60 percent of energy consumption in middle-income countries and up to 60 to 95 percent in developing contexts, while high-income countries derive less than 5 percent of their energy from wood, largely burning it in modern stoves designed to minimize emissions. All five studies were conducted in countries with less than 10 percent primary reliance on polluting fuels and cookstoves, meaning the existing evidence comes almost exclusively from low-exposure settings while the populations facing the highest exposures in Africa and Asia remain critically under-represented. Africa’s air quality monitoring density—just 0.03 monitors per million inhabitants—leaves BTEX emission factors and source profiles largely absent precisely where they are most urgently needed.

Setting matters just as much as species. Most of the reviewed studies were conducted in purpose-built laboratory combustion facilities, and none achieved a full rating for real-world setting representativeness in the review’s quality appraisal. The only study that approached household realism, the South African investigation in Senwabarwana, used a simulated kitchen structure and still could not capture the full variability of actual kitchen geometry, ventilation, and occupant behavior. This matters because field studies of other products of incomplete combustion have repeatedly shown that real-world emissions exceed laboratory measurements and display far greater variability, reflecting inconsistent stove operation, fluctuating fuel quality, and diverse user behaviors that controlled experiments systematically exclude. When laboratory data are used for population-level exposure assessment without field validation, the review warns, health burden estimates risk being systematically biased.

The synthesis also revealed a consistent chemical hierarchy that cuts across geography and methodology. Benzene was the most consistently reported and highest-emitting BTEX compound in every study, with emission profiles generally following the pattern benzene, then toluene, then ethylbenzene, then xylenes. Among studies reporting comparable emission factors in milligrams per kilogram, benzene values ranged from 108 mg/kg for European beech to 1,500 mg/kg for birch logs—a 13.9-fold difference across single-species combustion alone, though the review cautions that differences in adsorbent chemistry between the studies’ sampling methods may account for some of this spread. Benzene’s dominance echoes broader literature on residential wood combustion and suggests it may be a fundamental feature of firewood combustion chemistry rather than a species-specific artifact, arising from the thermal degradation of lignin, the principal aromatic precursor in wood. Still, with only two studies providing complete four-compound profiles, the review frames this pattern as preliminary rather than definitive.

Reporting practices added further obstacles to comparison. Only two of the five studies reported a complete BTEX profile; three omitted ethylbenzene entirely, and one reported benzene only. Ethylbenzene, a Group 2B possible carcinogen that is relatively more abundant in biomass-burning profiles and can help distinguish those emissions, was systematically absent from 60 percent of the studies, potentially due to co-elution with xylene isomers and intermittent detection. The studies also used incompatible metrics: four reported emission factors, which characterize fuel or stove performance, while others reported ambient concentrations relevant to health risk assessment. These quantities are not interchangeable, and the review argues that both are needed simultaneously to serve source characterization and exposure assessment alike. Analytical approaches further fragmented the evidence, spanning adsorbent-based gas chromatography, whole-air canister sampling, and Fourier-transform infrared spectroscopy, each with distinct trade-offs in detection limits, sample stability, and susceptibility to interference.

The health stakes are considerable. Households in low- and middle-income countries typically cook three times a day, four to six hours per session—roughly 21 meals per week, far above the global average—implying chronic exposure far exceeding the 365-day threshold used in toxicology. Benzene targets the hematopoietic system, with prolonged exposure linked to aplastic anemia and leukemia, while toluene is associated with cognitive impairment and cardiac sensitization, and xylenes with headaches and memory deficits. Simultaneous co-exposure complicates matters further: BTEX compounds compete for shared metabolic pathways involving the enzyme CYP2E1, producing less-than-additive metabolism but potentially greater-than-additive neurological effects as unmetabolized parent compounds persist in the bloodstream. With benzene concentrations measured at combustion sources running thousands of times above the World Health Organization’s most stringent risk-based reference level, and BTEX vapors persisting indoors for one to fourteen days, poorly ventilated kitchens may never fully clear between cooking episodes.

The review concludes that the effect of mixed-species combustion on BTEX emissions remains an unresolved gap in the literature, and it calls for future studies designed around the mixed fuel bundles and fuel stacking practices—wood co-burned with coal, charcoal, crop residues, and dung—that actually characterize household energy use in low- and middle-income settings, conducted within real homes rather than laboratories. Standardized full-profile BTEX reporting, integration of combustion frequency and ventilation data, and field-based exposure measurements are identified as priorities. Until the evidence base aligns with the conditions under which exposure actually occurs, the review warns, the populations bearing the greatest burden from firewood smoke will remain the least represented in the science meant to protect them.

Subject of Research: Methodological gaps in BTEX emission studies from household firewood combustion and their implications for indoor air pollution exposure assessment.

Article Title: Methodological Gaps in BTEX Emission Studies from Household Firewood Combustion: Implications for Exposure Assessment and Indoor Air Pollution

Article References: Masekela, M. E. (2026). Methodological Gaps in BTEX Emission Studies from Household Firewood Combustion: Implications for Exposure Assessment and Indoor Air Pollution. Environmental Challenges, Article 101665. https://doi.org/10.1016/j.envc.2026.101665

Image Credits: AI Generated

DOI: 10.1016/j.envc.2026.101665

Keywords: BTEX, benzene, firewood combustion, indoor air pollution, household energy, exposure assessment, scoping review, LMICs, volatile organic compounds, clean cooking, wood smoke, public health

Microbial bioremediation, the use of naturally occurring microorganisms to degrade contaminants, is widely regarded as one of the most promising and sustainable strategies for BTEX removal. But designing effective bioremediation strategies requires knowing precisely which genes and pathways are present at a contaminated site, and—crucially—which specific BTEX compounds the resident microbes are equipped to degrade. That is far harder than it sounds. The enzymes that initiate BTEX degradation belong to large protein families in which closely related members can target strikingly different substrates. Generic functional annotation pipelines, which assign genes to broad families based on sequence similarity, often cannot tell these near-identical enzymes apart. The result is annotation noise: environmental surveys that detect ‘a degradation gene’ but cannot say whether it acts on benzene, toluene, or neither.

A team of researchers at Carnegie Mellon University, working with a bioinformatics specialist in Pittsburgh, has now built a tool designed to close this gap. The software, called BTEXgenie, is described in a peer-reviewed study published in BMC Genomics. Led by June Qu and Catherine R. Armbruster of Carnegie Mellon’s Department of Biological Sciences, together with Arkadiy I. Garber of Middle Author Bioinformatics, the project set out to create an annotation resource with substrate-specific resolution: one that can distinguish between closely related BTEX-degrading enzymes with different catalytic specificities rather than lumping them into vague functional categories.

The technical heart of BTEXgenie lies in profile hidden Markov models, or HMMs—a statistical framework that has become the workhorse of modern protein annotation. Unlike simple pairwise sequence comparison, a profile HMM captures the consensus of an entire protein family, recording which positions in a multiple sequence alignment are conserved, which tolerate substitutions, and where insertions and deletions commonly occur. This makes HMMs exquisitely sensitive to distant but genuine family members. What sets BTEXgenie apart is the curation of its models: rather than relying on broad, automatically generated family definitions, the team built custom HMMs from alignments of experimentally validated BTEX degradation proteins, anchoring every model to enzymes whose substrates and activities have been confirmed in the laboratory.

That curation pays off dramatically in benchmarking. When the researchers tested BTEXgenie against the widely used KEGG KOfam HMM database across genes involved in BTEX degradation pathways, the new tool achieved an overall sensitivity of 84.36 percent, compared with just 40.74 percent for KOfam—an improvement of 43.62 percentage points. Sensitivity, in this context, measures how many true degradation genes a method successfully recovers. Notably, the gain did not come at the cost of accuracy: BTEXgenie maintained a specificity of 92.28 percent, only marginally below KOfam’s 93.63 percent. In practical terms, BTEXgenie found nearly twice as many genuine degradation genes while producing a comparable rate of false positives—a combination that until now has been difficult to achieve with general-purpose annotation resources.

One of the most significant findings concerns anaerobic BTEX degradation. While the aerobic breakdown of aromatic hydrocarbons is comparatively well characterized, many BTEX-contaminated sites are oxygen-limited, and anaerobic degradation—driven by nitrate-, sulfate-, iron- or methane-cycling microbes—is where much of the real-world remediation action happens. The genes underpinning these anaerobic pathways, including the remarkable fumarate addition enzymes that activate benzene without oxygen, are poorly represented in standard databases. BTEXgenie improved the detection of anaerobic BTEX degradation genes that were entirely absent from KOfam annotations, opening a window onto microbial processes that conventional pipelines simply miss.

To validate the tool beyond benchmarks, the team applied it to real environmental metagenomes—the collective genetic material sequenced directly from contaminated and uncontaminated sites. BTEXgenie recovered pathway patterns that matched reported site characteristics and known degradation potential, suggesting the tool can deliver biologically meaningful pictures of in situ microbial capability rather than laboratory-only performance. For researchers studying polluted aquifers, petroleum reservoirs or marine seeps, this means a metagenomic dataset can now be interrogated not just for ‘hydrocarbon genes’ in the abstract, but for the specific aerobic and anaerobic routes by which benzene, toluene, ethylbenzene and xylene might be dismantled in that environment.

The developers also paid close attention to usability, an often-neglected dimension of bioinformatics software. Beyond raw gene annotation, BTEXgenie supports downstream interpretation through built-in visualization modules: KEGG pathway-based displays map detected functions onto canonical degradation routes, making it easy to see which steps of a pathway are complete and which are missing, while Circos-based visualizations show the genomic distribution of hits across genomes. The tool was refined through user testing, and its documentation walks researchers through annotation and interpretation without requiring deep programming expertise. Supplementary materials released with the paper include detailed tables of the enzyme units used to build the models, their mappings to KEGG Orthology identifiers, Pfam domains and eggNOG or COG annotations, and comparisons with existing hydrocarbon-annotation resources such as CANT-HYD, HADEG and AromaDeg.

The validation framework itself is a model of rigor. The team compiled a reference set of 65 genomes from organisms with experimentally validated BTEX degradation capabilities and documented the presence, absence, or unknown status of each BTEXgenie model—and of 15 well-characterized BTEX-associated enzymes—across that panel. This ground-truthing exercise distinguishes BTEXgenie from tools built purely on computational inference, because every substrate-specific claim traces back to enzymes whose behavior has been measured. It also provides a template for how future substrate-specific annotation resources might be constructed for other pollutant classes, from chlorinated solvents to plastics.

The broader significance of the work extends beyond BTEX itself. As DNA sequencing becomes cheaper, environmental metagenomics is generating an overwhelming torrent of data from contaminated sites worldwide, and the bottleneck has shifted from data collection to interpretation. Tools that embed expert curation and experimental validation into automated annotation pipelines offer a path through that flood, converting raw sequence into actionable ecological and engineering insight. For bioremediation practitioners, BTEXgenie could help identify sites where monitored natural attenuation is feasible, guide the design of bioaugmentation or biostimulation strategies, and track whether degradation potential changes as remediation proceeds. For microbial ecologists, it offers a sharper lens on one of nature’s most consequential metabolic capabilities: the capacity of microorganisms to dismantle the hydrocarbons that humans have scattered across the biosphere. The study, supported by a grant from the Richard King Mellon Foundation and published open access, makes the tool freely available to the research community, and its developers hope it will become a standard component of the environmental genomics toolbox.

Subject of Research: Development of a curated profile HMM-based tool for substrate-specific annotation of microbial BTEX degradation genes

Article Title: BTEXgenie: a curated and user-friendly tool for profile HMM-based substrate-specific annotation of BTEX degradation genes

Article References: Qu, J., Garber, A. I., & Armbruster, C. R. (2026). BTEXgenie: a curated and user-friendly tool for profile HMM-based substrate-specific annotation of BTEX degradation genes. BMC Genomics. https://doi.org/10.1186/s12864-026-13297-3

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13297-3

Keywords: BTEX, bioremediation, hidden Markov models, functional annotation, metagenomics, environmental microbiology, BTEXgenie, hydrocarbon degradation, anaerobic degradation, genomics, pollution, microbial ecology