The study, published as an open-access paper in Food Chemistry: X, was led by Huijing Lan and colleagues including senior author Yan Xu, with analytical work carried out at Jiangnan University. The team selected Nongxiangxing Baijiu as a proof-of-concept system for good reason: its aroma arises from a large and diverse set of volatile compounds generated during solid-state fermentation, distillation, and aging, and its evaluation tradition explicitly prizes complexity-related attributes such as richness, layering, and persistence. Unlike cross-style comparisons, where differences may simply reflect broad stylistic variation, comparing products within the same aroma style asks a sharper question: can chemistry distinguish products sharing the same characteristic compounds but differing in perceived depth?

The researchers analyzed 21 commercial Nongxiangxing Baijiu samples at 52% alcohol by volume, drawn from eight representative Chinese brands and spanning high-, medium-, and low-tier products as declared by their manufacturers. They quantified 140 volatile compounds chosen from prior quantitative and gas chromatography-olfactometry studies, using three complementary analytical methods tailored to different compound classes and abundances. High-abundance compounds such as major esters and alcohols were measured by direct-injection gas chromatography with flame ionization detection. Compounds requiring headspace enrichment were captured by solid-phase microextraction coupled to GC-MS, while trace-level analytes such as pyrazines, lactones, and sulfur compounds were concentrated by dispersive liquid-liquid microextraction and quantified by tandem mass spectrometry. Calibration curves, built in matrix-matched ethanol solutions with isotope-labeled internal standards, showed coefficients of determination from 0.9131 to 1.0000 and recoveries between 80.1% and 129.6%.

The heart of the work lies in how those raw concentration tables were transformed into perceptually meaningful dimensions. The framework rests on three pillars. The first, functional complexity, asks how broadly the volatile profile spans odor quality space. Each of the 140 compounds was passed through a machine-learning odor prediction model, the principal odor map framework of Lee and colleagues, which generated probability scores for 138 odor descriptors from molecular structures supplied as SMILES strings. As a consistency check, the ten highest-ranked predictions for each compound were compared with annotations in the Good Scents database: at least one database annotation appeared among the top predictions for 99.29% of compounds. The 138 descriptors were then collapsed into twelve semantic aroma categories, including fruity, floral, woody, baked, and herbal, and Shannon entropy was used to measure how evenly a compound’s predicted odor information spreads across those categories.

The second pillar addresses time. Odor persistence, the tendency of an odorant to linger, was predicted for every compound by a hybrid graph neural network trained on a curated fragrance dataset that uses the historical relative-persistence scale of Poucher. The model combined a two-layer graph attention network with a multilayer perceptron, fed by six physicochemical descriptors plus a 2048-bit molecular fingerprint, and achieved a mean absolute error of 5.43 with a coefficient of determination of 0.93 in five-fold cross-validation. High-persistence predictions clustered among medium-chain fatty acids and their esters, lactones, aromatic aldehydes, phenolics, and terpenoid alcohols, compounds such as octanoic acid, decanoic acid, ethyl caprate, beta-damascenone, gamma-decalactone, and vanillin. Notably, several of these overlap with compounds reported in Baijiu empty-cup aroma studies, which examine the fragrance that lingers in a finished glass, lending supporting consistency to the predictions.

The third pillar is structural. Drawing on four established molecular complexity metrics, SCScore, the CM and Cse indices of Proudfoot, and Spacial-Score, the team scored each compound for atom connectivity, branching, ring systems, heteroatom composition, and stereochemical richness, then combined the four normalized metrics with equal weight. Terpenes, terpenoid alcohols, lactones, phenolics, and related aromatics scored highest, reflecting their ring systems and multiple functional groups. This echoes an earlier finding that structurally more complex odorants tend to evoke a broader range of olfactory notes, suggesting molecular architecture may constrain the perceptual space a volatile compound can occupy. Across all three pillars, compound-level scores were aggregated to the sample level using log-transformed concentrations as weights, a choice designed to retain abundance information while preventing a handful of dominant esters from swamping the whole profile.

When the three components were summed into TACI, the 21 samples ranged from 438.69 to 513.57, with the highest value in a high-tier product of brand NXX4 and the lowest in the low-tier product of brand NXX6. Six of the eight brands showed a monotonic increase in TACI with commercial tier, and in several brands the higher-tier products displayed broader contributions beyond the sweet, alcoholic, and fruity core, extending into woody, floral, vegetal, and herbal territory. But the association was not universal. In brand NXX7, the middle-tier product ranked highest on every component index, while NXX6 showed almost no tier separation. The authors are careful to note that commercial grades reflect market positioning rather than standardized quality benchmarks, and that aging and blending can reshape volatile composition in ways that do not necessarily raise the index.

The crucial test came against human perception. Nine professional Baijiu tasters, each with more than eight years of experience, scored six representative samples on a nine-point complexity scale under blind, randomized conditions, having been instructed to judge complexity as an overall attribute of aromatic diversity, layering, harmony, and persistence rather than mere intensity. The correlation between TACI and the panel’s mean scores was strikingly positive: Pearson’s r of 0.84 with a coefficient of determination of 0.70. With only six sample-level observations, however, the authors insist this is an exploratory association, not confirmatory validation. The result is nevertheless a tantalizing sign that an algorithmic digest of gas chromatograms can approximate something as elusive as what a master taster senses in a glass.

The study is candid about its limits. The odor descriptor predictions come from a pretrained black-box model that may not fully translate to perception in a complex ethanol matrix; persistence values derive from fragrance references rather than Baijiu-specific measurements; the three components share the same concentration matrix, which inflates their mutual correlations; and equal-weight integration was chosen as a transparent baseline rather than a claim about perceptual equivalence. OAV-based weighting was deliberately avoided because matrix-matched odor thresholds were not consistently available, though the authors acknowledge that future work should test odor thresholds, alternative descriptor groupings, and component weights. Cumulative uncertainty across the pipeline was not quantified. Still, the framework offers something the field has lacked: a transparent, scalable, chemistry-grounded index that complements rather than replaces sensory evaluation. If validated on larger and more diverse collections, the approach could extend beyond Baijiu to other aroma-rich fermented beverages, giving producers and researchers alike a common quantitative language for one of flavor science’s most stubborn abstractions.

Subject of Research: A computational volatile-based aroma complexity index for strong-aroma-type Chinese Baijiu

Article Title: A volatile-based aroma complexity index for Nongxiangxing baijiu

Article References: Lan, H., Zheng, J., Zhao, D., Su, J., Lu, Y., Chen, S., & Xu, Y. (2026). A volatile-based aroma complexity index for Nongxiangxing baijiu. Food Chemistry: X, 39, Article 104440. https://doi.org/10.1016/j.fochx.2026.104440

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104440

Keywords: baijiu, aroma complexity, food chemistry, volatile compounds, gas chromatography, machine learning, odor prediction, Shannon entropy, sensory evaluation, flavor science, distilled spirits, odor persistence

The research team, led by Xiangui Wang and Tianzhu Shi of the Moutai Institute, selected eight representative finished baijiu samples: two from Renhuai in Guizhou Province, the spiritual home of the style, and one each from Xishui, Chishui, Jinsha, Zunyi, and Guiyang in Guizhou plus Gulin in Sichuan. Sauce-flavor baijiu is made through a famously grueling process described as nine distillations, eight fermentations, and seven rounds of distillation, relying on high-temperature Daqu starter cultures, solid-state fermentation, and repeated cycles that stretch across a full year. The researchers analyzed the spirits using gas chromatography with flame ionization detection, a workhorse technique that separates volatile compounds in a heated capillary column and measures them with high sensitivity. The method performed strongly across all nine target aldehydes, with correlation coefficients between 0.996 and 0.999, detection limits as low as 0.02 milligrams per liter, recoveries between roughly 96 and 99 percent, and repeatability within about 3 percent, giving the team confidence that the regional patterns they observed were real chemistry rather than analytical noise.

Aldehydes occupy a fascinating dual role in baijiu. At moderate levels they contribute fruity, aged, and harmonious notes that drinkers associate with maturity and quality; in excess they produce the sharp, pungent bite that can make a harsh spirit. The most influential of them, acetaldehyde, forms during fermentation and oxidation and carries fruity freshness in small doses but stings at high concentrations. Acetal, its chemical partner, arises when acetaldehyde binds with ethanol and delivers a softer, sweeter fruit character that moderates harshness. Furfural, a heat-derived compound born from sugars and amino acids under the intense thermal conditions of solid-state distillation, contributes caramel, roasted, almond-like notes and adds mouthfeel fullness. Because each of these compounds follows a different formation pathway, their relative abundances act like a recording of the conditions under which the spirit was made, from fermentation intensity to distillation control to the distiller’s cut points.

The regional results were striking. Gulin, the sole Sichuan production region in the study, recorded the highest total aldehyde content and by far the highest acetaldehyde level at 945.42 milligrams per liter, compared with a low of just 295.00 milligrams per liter in Zunyi. Acetal followed the same pattern, peaking at 540.86 milligrams per liter in Gulin. Because all other regions sit within Guizhou, the researchers attribute this co-elevation not to geography alone but to differences in production practices, particularly distillation control and liquor-cutting criteria, alongside fermentation intensity, storage, and blending habits. Furfural told a different story entirely, reaching its highest levels in Chishui at 296.93 and Jinsha at 293.49 milligrams per liter while staying comparatively low in Gulin, evidence that its formation does not track acetaldehyde and acetal but responds to its own set of process conditions.

Branched-chain and aromatic aldehydes added further layers of regional identity. Jinsha showed the strongest accumulation of amino acid-derived branched aldehydes, with its 3-methylbutyraldehyde concentration roughly 3.1 times that of the leading Renhuai distillery. Most intriguingly, phenylacetaldehyde, an aromatic compound linked to floral and honey-like notes, reached 9.63 and 9.62 milligrams per liter in the two Renhuai samples, approximately six to twenty times higher than any other region, where levels stayed below 1.70 milligrams per liter. Even more telling, the two Renhuai distilleries, one large and one medium-sized, produced nearly identical phenylacetaldehyde levels and highly similar overall profiles. This suggests a powerful within-region consistency in flavor chemistry, as though the shared microbial ecology, climate, and craft traditions of a single town imprint a common chemical signature on spirits from different producers.

To test whether these patterns could actually discriminate origins, the team deployed principal component analysis and orthogonal partial least squares discriminant analysis, two multivariate statistical techniques that compress many chemical measurements into a visual map of sample relationships. The first two principal components alone explained 92.6 percent of total variance, and the supervised OPLS-DA model separated Gulin and Jinsha dramatically from the rest while still resolving the tightly clustered Renhuai, Xishui, and Zunyi samples. A 200-permutation test confirmed the model was robust rather than overfitted. Variable importance projection identified acetaldehyde as the single strongest discriminator, with a VIP score of 2.03, followed by acetal at 1.54 and furfural at 1.22. Although phenylacetaldehyde contributed less to the global model because its elevated concentrations were confined to just two samples, the researchers argue it holds genuine potential as a Renhuai-specific marker, one that larger datasets could validate for authentication purposes.

Sensory relevance was assessed through odor activity values, calculated by dividing measured concentrations by published odor thresholds in ethanol-water matrices similar to baijiu. Nearly every aldehyde exceeded its threshold, confirming that these compounds are not passive bystanders but active contributors to aroma. Acetaldehyde showed odor activity values ranging from 246 in Zunyi to 788 in Gulin, acetal ranged from 70 to 259, and furfural from 3 to 7, all above the threshold of 1 in every sample. Propionaldehyde, isobutyraldehyde, and 2-methylbutyraldehyde posted values in the hundreds to thousands, while phenylacetaldehyde’s values of 37 in both Renhuai products dwarfed the 2 to 6 seen elsewhere, quantifying just how sensorially distinctive the region’s spirits are. Because thresholds shift with ethanol concentration and matrix composition, the authors frame these values as screening estimates, but the regional disparities in odor activity align neatly with the known stylistic reputations of the different production towns.

The round-by-round analysis, conducted on base spirits from rounds one through seven of the 2024-2025 production cycle, revealed dynamic behavior invisible in finished products. Acetaldehyde and acetal both followed a general rise-fall-rise trajectory across the seven rounds, but the timing of peaks varied sharply by region: Guiyang peaked at round five, Jinsha at round six, Gulin at round seven for acetaldehyde, while Zunyi dominated acetal in early rounds and Jinsha surged in rounds five through seven. Furfural marched to a different drummer, accumulating steadily with round number, moderate through rounds one to three and accelerating after round four to reach maximum levels at round seven in most regions. Pearson correlation analysis across regions showed furfural with the strongest cross-regional consistency, acetaldehyde the most sensitive to local environment and process, and acetal falling in between. These patterns carry practical weight, since the late-round accumulation of furfural could support round-based grading, while the fluctuating acetaldehyde and acetal profiles inform blending strategy and the assessment of aging potential.

The study’s authors are candid about its limits: nine targeted aldehydes cannot capture the full flavorome, the sample set of eight products cannot represent every distillery, and the chemical focus leaves microbiome interactions and human sensory judgment for future work combining two-dimensional gas chromatography, metagenomics, and formal sensory panels. Still, the implications are considerable. In an era when geographic indication protection and anti-counterfeiting matter enormously to premium spirits markets, a simple gas chromatographic measurement of three aldehydes offering probabilistic origin verification is a genuinely valuable tool. The work also reframes the romance of terroir in scientific terms: the distinctive character of a Renhuai bottle versus one from Jinsha is written in measurable molecular ratios, shaped by local climate, microbial communities, and generations of refined craft. For consumers, the next glass of sauce-flavor baijiu may taste the same as always, but science now knows exactly where that taste comes from.

Subject of Research: Regional variation and round-by-round dynamics of aldehydes in sauce-flavor baijiu from the Chishui River Basin

Article Title: Regional differences and round-by-round dynamics of aldehydes in sauce-flavor baijiu from the Chishui River Basin

Article References: Wang, X., Yang, D., Yuan, X., Zeng, D., Wu, D., Xu, H., & Shi, T. (2026). Regional differences and round-by-round dynamics of aldehydes in sauce-flavor baijiu from the Chishui River Basin. Food Chemistry: X, 39, Article 104443. https://doi.org/10.1016/j.fochx.2026.104443

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104443

Keywords: sauce-flavor baijiu, aldehydes, Chishui River Basin, acetaldehyde, furfural, origin identification, gas chromatography, fermentation, odor activity values, food chemistry, baijiu authentication, distillation rounds

The research team, led by Ahmeed Olalekan Ashade of Lagos State University of Science and Technology together with colleagues at Lagos State University and Elizade University, set out to isolate bacteria capable of degrading hydrocarbons while tolerating heavy metals and producing surface-active biomolecules. Such a combination of traits has been sparsely reported in the literature, particularly for West African freshwater systems, even though co-contamination by petroleum and metals is the norm rather than the exception in polluted industrial waterways. The work builds on the group’s earlier metagenomic surveys, which showed that Ologe Lagoon harbors a diverse array of prokaryotic phylotypes with potential biotechnological value.

To capture these hardy microbes, the researchers identified three sampling points reflecting different levels of human disturbance: an industrial-contaminated site, a human-activities site, and a presumed-undisturbed reference site. Surface water was collected in sterile flasks and sediments were retrieved from the lagoon floor using an Ekman grab, yielding composites of 1,500 milliliters of water and 600 grams of sediment. Physicochemical profiling of the samples confirmed measurable burdens of nickel, cadmium, lead, mercury, and cobalt in both water and sediment, with sediment nickel reaching 5.21 milligrams per kilogram at the reference site and water nickel peaking at 1.18 milligrams per kilogram at the industrial site.

The isolation strategy relied on continuous enrichment, a technique that applies strong selective pressure to favor organisms with the desired traits. Samples were incubated aerobically for 30 days in mineral salt medium containing 1 percent Escravos light crude oil as the sole carbon and energy source, fortified with filter-sterilized solutions of nickel chloride, cadmium chloride, and lead acetate at concentrations of 0.5, 0.1, and 1.0 millimolar respectively. Flasks were shaken at 150 revolutions per minute in the dark at 27 degrees Celsius, and after three consecutive transfers onto fresh medium, pure bacterial colonies were obtained. Control flasks containing heat-killed cells confirmed that the observed changes were biological rather than abiotic.

Molecular identification using 16S rDNA Sanger sequencing and phylogenetic analysis with the Neighbor Joining algorithm revealed three standout strains. Strain OLW3 was identified as Alcaligenes aquatilis with 99.86 percent sequence similarity, strain OLW6 as Alcaligenes faecalis with 99.45 percent similarity, and strain OLW15 as Rossellomorea marisflavi with 98.28 percent similarity. The 16S rRNA sequences were deposited in GenBank under accession numbers OP626095, OP626097, and OP626099. The genus Alcaligenes, belonging to the phylum Pseudomonadota, is renowned for its metabolic versatility, with members documented in impacted sediments from Charleston Harbor in the United States to Quintero Bay in Chile, where they degrade hydrocarbons, synthetic dyes, and pharmaceutical compounds. Rossellomorea marisflavi, a Gram-positive, spore-forming, moderately halophilic bacterium formerly classified among the bacilli, contributes to organic matter decomposition and nutrient cycling in sediments.

When the three strains were grown on crude oil-heavy metal mineral salt medium over a 30-day time course, their degradation performance was striking. Strain OLW3, after a six-day lag phase likely reflecting the time needed to induce catabolic enzymes such as dioxygenases for these complex hydrophobic substrates, achieved a degradation rate of 0.056 milligrams per liter per day, a degradation rate constant of 6.43 per day, a half-life of 12.49 days, and an overall percentage degradation of 81.06 percent. Strain OLW15 proved the most efficient, with a degradation rate of 0.065 milligrams per liter per day, a rate constant of 7.16 per day, a half-life of 10.58 days, and 85.67 percent degradation. Strain OLW6, after a seven-day acclimatization period, degraded 54.27 percent of the hydrocarbons, a figure the authors suggest could be improved through optimization of growth conditions.

Gas chromatography with flame ionization detection provided molecular-level confirmation of biodegradation. Chromatograms taken at day 0, day 15, and day 30 showed progressive reductions in the peak areas of hydrocarbon fractions across all three enrichment systems. Strain OLW3 completely removed nC5 pentane and nC6 hexane by day 30 and reduced nC4 isobutane from 43.66 to 10.04 milligrams per kilogram, consistent with aerobic oxidation of straight-chain alkanes into alcohols and organic acids that feed into central metabolic pathways and beta-oxidation. Strain OLW6 cut m,p-xylene from 175.11 to 32.78 milligrams per kilogram and nC13 tridecane from 128.16 to 47.64 milligrams per kilogram, while strain OLW15 halved anthraquinone and reduced propyl-benzene from 125.47 to 36.27 milligrams per kilogram. Declining ratios of nC17 to pristane and nC18 to phytane, classic biomarkers of biodegradation, further documented preferential consumption of readily degradable aliphatics over recalcitrant isoprenoids.

Equally important was the demonstration that these bacteria tolerated the metals present in their enrichment medium. In tolerance assays on Luria Bertani media fortified with metal concentrations ranging from 0.5 to 20 millimolar, strain OLW3 tolerated up to 2.5 millimolar lead, strain OLW6 resisted cadmium concentrations in the same range, and strain OLW15 withstood 1.5 millimolar nickel. The authors note that bacteria deploy diverse detoxification strategies, including efflux pumps that expel metal ions, extracellular sequestration via exopolysaccharides, biosorption and bioprecipitation, and intracellular binding by metallothioneins. Exopolysaccharide production carries a double benefit, decreasing cell surface hydrophobicity to aid adhesion to hydrophobic hydrocarbons while simultaneously binding lead outside the cell, thereby reducing metal bioavailability and protecting the wider food web from uptake.

The biosurfactant credentials of the isolates were assessed through hemolytic, oil spread, and cetyltrimethylammonium bromide blue agar assays, along with measurements of the emulsification index after 24 hours. Strains OLW3 and OLW6 showed complete beta-hemolysis on blood agar, a presumptive indicator of biosurfactant production, while OLW15 tested positive on the blue agar plate assay used to detect anionic biosurfactants such as rhamnolipids. Emulsification indices reached 50 to 58.9 percent on crude oil and kerosene for OLW3, and 58.3 and 50 percent on crude oil for OLW6 and OLW15 respectively, with all isolates emulsifying vegetable oil at 36 to 58 percent. Statistical analysis using one-way analysis of variance with Friedman multiple test comparison confirmed significant differences among the emulsification datasets, with post-hoc Dunn’s testing showing the greatest divergence between OLW6 and OLW15.

Perhaps most compelling from an applied perspective is the robustness of the biosurfactants under harsh conditions. Near-neutral pH favored production for all isolates, but OLW3 and OLW6 remained active at pH 10, and OLW6 continued producing biosurfactant at 80 degrees Celsius while OLW3 and OLW15 functioned at 50 degrees Celsius. All three tolerated 10 percent sodium chloride, suggesting utility in coastal and saline environments where salt stress often undermines bioremediation. These properties point toward applications ranging from in-situ cleanup in hot climates to microbial enhanced oil recovery, where biosurfactants reduce oil viscosity and improve mobility, and to refinery and petrochemical wastewater treatment. The authors propose that whole-genome sequencing, characterization of metal resistance mechanisms, and high-performance liquid chromatography profiling of the biosurfactants represent the next steps. For now, the message from Ologe Lagoon is clear: even ecosystems degraded by unchecked pollution can yield microbial resources capable of healing environments like their own home.

Subject of Research: Hydrocarbon-degrading, heavy metal-tolerant, biosurfactant-producing bacteria isolated from Ologe Lagoon water and sediments in Lagos State, Nigeria

Article Title: Hydrocarbon degradation and heavy metal tolerance of bacterial isolates from Ologe lagoon water and sediments

Article References: Ashade, A. O., Obayori, O. S., Fashola, M. O., Salam, L. B., & Oso, S. O. (2026). Hydrocarbon degradation and heavy metal tolerance of bacterial isolates from Ologe lagoon water and sediments. BMC Environmental Science, 3(1), Article 8. https://doi.org/10.1186/s44329-026-00051-z

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00051-z

Keywords: bioremediation, hydrocarbon degradation, heavy metal tolerance, biosurfactant, Ologe Lagoon, Alcaligenes, Rossellomorea marisflavi, crude oil pollution, 16S rRNA sequencing, gas chromatography, freshwater pollution, Nigeria

The technical foundation of the dispute lies in two biomarkers. Ethylene is a simple gaseous molecule that humans both produce internally and inhale from the environment, including from combustion sources and ripening fruit. Inside the body, a fraction of inhaled ethylene is converted by cytochrome P450 enzymes into ethylene oxide, a more reactive epoxide that can bind to hemoglobin and DNA. The specific biomarker used to track this chemistry is N-(2-hydroxyethyl)valine, abbreviated HEV, an adduct formed when ethylene oxide reacts with the N-terminal valine residue of hemoglobin proteins. Because red blood cells circulate for roughly four months, HEV provides an integrated record of ethylene oxide exposure over time. Lin and colleagues compiled a database of breath ethylene measurements and, using physiologically based pharmacokinetic modeling, sought to estimate how much endogenous ethylene oxide production contributes to total HEV burdens in the general population.

What Kirman and Bus highlight in their correspondence is a fundamental analytical problem embedded in that database. Breath ethylene concentrations reported across the literature are extraordinarily variable, and the variability appears to track with the measurement technology rather than with genuine differences between study populations. Studies employing laser-based photoacoustic spectrometry, a technique that detects gas absorption of laser light, reported mean ethylene concentrations of roughly 61 parts per billion with a standard deviation of 130 ppb, an enormous spread. By contrast, studies relying on gas chromatography reported a mean of approximately 20 ppb with a standard deviation of 16 ppb, far tighter and consistently lower. Even within the subset of studies that Lin and colleagues designated as high confidence, mean ethylene levels hovered around just 0.5 ppb, orders of magnitude below the values coming from the laser-based literature.

This is not a new concern, and Kirman and Bus invoke a striking historical precedent. More than two decades ago, Berkelmans and colleagues, working with online laser photoacoustic detection, observed that endogenous ethylene production rates derived from laser-based studies were significantly lower than published values based on gas chromatography, an inconsistency they attributed to fundamental differences between the two analytical approaches. When Berkelmans’s team attempted to fit a physiologically based pharmacokinetic model to their laser-derived data, they found they had to modify measured physiological and biochemical parameters to make the model work, indicating that the laser measurements were inconsistent with the well-established understanding of ethylene toxicokinetics built on gas chromatography. Kirman and Bus argue that this methodological fault line has not been resolved, and that Lin and colleagues’ database largely inherits the problem rather than correcting it.

The PBPK modeling itself is the second pillar of the critique. Physiologically based pharmacokinetic models are mathematical descriptions of how a chemical moves through the body, incorporating blood flow, tissue partitioning, metabolic rates, and ventilation. The model used by Lin and colleagues traces back to the foundational work of Filser and Klein, who developed a toxicokinetic model for inhaled ethylene and ethylene oxide across mouse, rat, and human species, and to earlier work by Csanády and colleagues, who modeled the formation of 2-hydroxyethyl adducts with hemoglobin and DNA from both exogenous and endogenous sources. Running the model with the breath ethylene data, Lin’s team concluded that endogenous production pathways account for less than 20 percent of total HEV in nonsmokers, leaving more than 80 percent unexplained. Kirman and Bus point out that this large unexplained fraction is itself a signal that something in the exposure reconstruction may be missing, whether it be analytical bias in breath measurements, unrecognized internal sources, or contributions from pathways not captured by the model.

Exogenous exposure, meaning ethylene and ethylene oxide inhaled from outside sources such as ambient and indoor air, is the other candidate explanation for the unaccounted adduct burden. Here, Kirman and Bus note that available air monitoring data, including large-scale studies such as Health Canada’s Windsor Exposure Assessment Study, indicate that environmental contributions to total ethylene oxide body burden are expected to be small for the general population. This conclusion aligns with their own prior publications, including a 2021 comprehensive review characterizing total ethylene oxide exposure from endogenous and exogenous pathways and a 2025 assessment of background exposures in the United States that questioned theoretical health risks for populations living near industrial sources. The implication is that the apparent gap between modeled endogenous production and measured HEV cannot simply be closed by invoking ambient air pollution, contrary to some popular narratives about ethylene oxide risk.

The broader context makes this technical disagreement consequential beyond the laboratory. Ethylene oxide is used industrially to sterilize roughly half of all medical devices in the United States, and the Environmental Protection Agency’s recent regulatory actions targeting sterilization facilities have relied on risk estimates derived from inhalation unit risk values. If a substantial fraction of the population’s hemoglobin adduct burden derives from endogenous biology rather than industrial emissions, then the margin between background internal exposure and levels associated with elevated cancer risk is narrower than many assume, and any risk assessment that fails to account for endogenous background risks mischaracterizing the true incremental danger of industrial emissions. Kirman and Bus have argued elsewhere that recognizing endogenous ethylene oxide formation is essential for a coherent risk management framework, since regulatory limits that ignore the body’s own production of the chemical cannot meaningfully protect public health in proportion to actual incremental exposure.

They also point to emerging molecular dosimetry work that helps interpret HEV data. Recent studies by Liu and colleagues on hemoglobin adduct formation in mice exposed to ethylene oxide, and Lin’s own companion work integrating PBPK modeling with tobacco biomarkers to interpret HEV levels in the U.S. population, demonstrate that smoking contributes substantially to measured adduct burdens, since tobacco smoke contains both ethylene and ethylene oxide directly. In nonsmokers, however, the origin of the remaining adduct burden remains contested. Classical biomonitoring studies from the 1990s and 2000s, including molecular dosimetry work by Walker, Fennell, Upton, and Swenberg in rodents exposed to ethylene oxide, established the dose-response framework that still underpins modern interpretation, and those studies consistently emphasized the importance of distinguishing background from incremental exposure when translating adduct measurements into cancer risk.

Neither the correspondence nor the original analysis settles the question of how much endogenous metabolism contributes to human ethylene oxide body burdens, but the exchange underscores a lesson that resonates across exposure science: the quality of a risk assessment is bounded by the quality of the exposure data fed into it. When two analytical technologies applied to the same biological matrix differ by more than an order of magnitude, as laser-based photoacoustic spectrometry and gas chromatography evidently do for breath ethylene, downstream models, no matter how sophisticated, inherit that uncertainty. Kirman and Bus contend that progress requires reconciling the methodological discrepancy, validating breath ethylene measurements against gas-chromatographic benchmarks, and ensuring that PBPK models are fit to data consistent with established toxicokinetics. Until that reconciliation occurs, estimates of how much ethylene oxide in the average person’s blood comes from industry versus biology will remain contested, and the regulatory debate over one of the world’s most widely used sterilants will continue to be fought on contested ground.

Subject of Research: Human exposure to ethylene and endogenous ethylene oxide assessed through breath biomarkers and pharmacokinetic modeling

Article Title: Regarding ethylene exposure and endogenous ethylene oxide levels in humans (Lin et al., 2025)

Article References: Regarding ethylene exposure and endogenous ethylene oxide levels in humans (Lin et al., 2025). (n.d.). https://doi.org/10.1038/s41370-026-00967-3

Image Credits: AI Generated

DOI: 10.1038/s41370-026-00967-3

Keywords: ethylene, ethylene oxide, hemoglobin adducts, PBPK modeling, breath analysis, biomonitoring, exposure science, risk assessment, photoacoustic spectrometry, gas chromatography, environmental epidemiology, Regarding