Effects by inhalation of abundant fragrances in indoor air - An overview.

Odorous compounds (odors) like fragrances may cause adverse health effects. To assess their importance by inhalation, we have reviewed how the four major abundant and common airborne fragrances (α-pinene (APN), limonene (LIM), linalool (LIL), and eugenol (EUG)) impact the perceived indoor air quality as odor annoyance, sensory irritation and sensitization in the airways. Breathing and cardiovascular effects, and work performance, and the impact in the airways of ozone-initiated gas- and particle phase reactions products have also been assessed. Measured maximum indoor concentrations for APN, LIM and LIL are close to or above their odor thresholds, but far below their thresholds for sensory irritation in the eyes and upper airways; no information could be traced for EUG. Likewise, reported risk values for long-term effects are far above reported indoor concentrations. Human exposure studies with mixtures of APN and LIM and supported by animal inhalation models do not support sensitization of the airways at indoor levels by inhalation that include other selected fragrances. Human exposure studies, in general, indicate that reported lung function effects are likely due to the perception rather than toxic effects of the fragrances. In general, effects on the breathing rate and mood by exposure to the fragrances are inconclusive. The fragrances may increase the high-frequency heart rate variability, but aerosol exposure during cleaning activities may result in a reduction. Distractive effects influencing the work performance by fragrance/odor exposure are consistently reported, but their persistence over time is unknown. Mice inhalation studies indicate that LIM or its reaction mixture may possess anti-inflammatory properties. There is insufficient information that ozone-initiated reactions with APN or LIM at typical indoor levels cause airway effects in humans. Limited experimental information is available on long-term effects of ozone-initiated reaction products of APN and LIM at typical indoor levels.

Limonene and its ozone-initiated reaction products attenuate allergic lung inflammation in mice.

Inhalation of indoor air pollutants may cause airway irritation and inflammation and is suspected to worsen allergic reactions. Inflammation may be due to mucosal damage, upper (sensory) and lower (pulmonary) airway irritation due to activation of the trigeminal and vagal nerves, respectively, and to neurogenic inflammation. The terpene, d-limonene, is used as a fragrance in numerous consumer products. When limonene reacts with the pulmonary irritant ozone, a complex mixture of gas and particle phase products is formed, which causes sensory irritation. This study investigated whether limonene, ozone or the reaction mixture can exacerbate allergic lung inflammation and whether airway irritation is enhanced in allergic BALB/cJ mice. Naïve and allergic (ovalbumin sensitized) mice were exposed via inhalation for three consecutive days to clean air, ozone, limonene or an ozone-limonene reaction mixture. Sensory and pulmonary irritation was investigated in addition to ovalbumin-specific antibodies, inflammatory cells, total protein and surfactant protein D in bronchoalveolar lavage fluid and hemeoxygenase-1 and cytokines in lung tissue. Overall, airway allergy was not exacerbated by any of the exposures. In contrast, it was found that limonene and the ozone-limonene reaction mixture reduced allergic inflammation possibly due to antioxidant properties. Ozone induced sensory irritation in both naïve and allergic mice. However, allergic but not naïve mice were protected from pulmonary irritation induced by ozone. This study showed that irritation responses might be modulated by airway allergy. However, aggravation of allergic symptoms was observed by neither exposure to ozone nor exposure to ozone-initiated limonene reaction products. In contrast, anti-inflammatory properties of the tested limonene-containing pollutants might attenuate airway allergy.

Airway irritation, inflammation, and toxicity in mice following inhalation of metal oxide nanoparticles.

Metal oxide nanoparticles are used in a broad range of industrial processes and workers may be exposed to aerosols of the particles both during production and handling. Despite the widespread use of these particles, relatively few studies have been performed to investigate the toxicological effects in the airways following inhalation. In the present study, the acute (24 h) and persistent (13 weeks) effects in the airways after a single exposure to metal oxide nanoparticles were studied using a murine inhalation model. Mice were exposed 60 min to aerosols of either ZnO, TiO2, Al2O3 or CeO2 and the deposited doses in the upper and lower respiratory tracts were calculated. Endpoints were acute airway irritation, pulmonary inflammation based on analyses of bronchoalveolar lavage (BAL) cell composition, DNA damage assessed by the comet assay and pulmonary toxicity assessed by protein level in BAL fluid and histology. All studied particles reduced the tidal volume in a concentration-dependent manner accompanied with an increase in the respiratory rate. In addition, ZnO and TiO2 induced nasal irritation. BAL cell analyses revealed both neutrophilic and lymphocytic inflammation 24-h post-exposure to all particles except TiO2. The ranking of potency regarding induction of acute lung inflammation was Al2O3 = TiO2 < CeO2 ≪ ZnO. Exposure to CeO2 gave rise to a more persistent inflammation; both neutrophilic and lymphocytic inflammation was seen 13 weeks after exposure. As the only particles, ZnO caused a significant toxic effect in the airways while TiO2 gave rise to DNA-strand break as shown by the comet assay.

Mechanism of action of lung damage caused by a nanofilm spray product.

Inhalation of waterproofing spray products has on several occasions caused lung damage, which in some cases was fatal. The present study aims to elucidate the mechanism of action of a nanofilm spray product, which has been shown to possess unusual toxic effects, including an extremely steep concentration-effect curve. The nanofilm product is intended for application on non-absorbing flooring materials and contains perfluorosiloxane as the active film-forming component. The toxicological effects and their underlying mechanisms of this product were studied using a mouse inhalation model, by in vitro techniques and by identification of the binding interaction. Inhalation of the aerosolized product gave rise to increased airway resistance in the mice, as evident from the decreased expiratory flow rate. The toxic effect of the waterproofing spray product included interaction with the pulmonary surfactants. More specifically, the active film-forming components in the spray product, perfluorinated siloxanes, inhibited the function of the lung surfactant due to non-covalent interaction with surfactant protein B, a component which is crucial for the stability and persistence of the lung surfactant film during respiration. The active film-forming component used in the present spray product is also found in several other products on the market. Hence, it may be expected that these products may have a toxicity similar to the waterproofing product studied here. Elucidation of the toxicological mechanism and identification of toxicological targets are important to perform rational and cost-effective toxicological studies. Thus, because the pulmonary surfactant system appears to be an important toxicological target for waterproofing spray products, study of surfactant inhibition could be included in toxicological assessment of this group of consumer products.

Pulmonary toxicity of perfluorinated silane-based nanofilm spray products: solvent dependency.

A number of cases of pulmonary injury by use of aerosolized surface coating products have been reported worldwide. The aerosol from a commercial alcohol-based nanofilm product (NFP) for coating of nonabsorbing surfaces was found to induce severe lung damage in a recent mouse bioassay. The NFP contained a 1H,1H,2H,2H-perfluorooctyl trialkoxysilane (POTS) and the effects were associated with the hydrolyzed forms of the silane; increase in hydrolyzation resulted in faster induction of compromised breathing and induction of lung damage. In this study, the impact of the solvent on the toxicity of POTS has been investigated. BALB/cA mice were exposed to aerosolized water-based NFPs containing POTS, and solutions of hydrolyzed POTS in methanol, ethanol, and 2-propanol, respectively. No acute respiratory effect was observed at exposure concentrations up to 110 mg/m³ with an aqueous solution of POTS. However, exposure to POTS in methanol resulted in a decrease of the tidal volume--an effect that did not resolve within the recovery period. After 27 min of exposure, the tidal volume had decreased by 25%, indicating partial alveolar collapse. For POTS in ethanol and 2-propanol, a 25% reduction of the tidal volume was observed after 13 and 9 min, respectively; thus, the tidal volume was affected by increase of the chain length. This was confirmed in vitro by investigating lung surfactant function after addition of POTS in different solvents. The addition of vaporized methanol, 2-propanol, or acetone to aerosolized POTS in methanol further exacerbated the tidal volume reduction, demonstrating that the concentration of vaporized solvent participated in the toxicity of POTS.

Human reference values for acute airway effects of five common ozone-initiated terpene reaction products in indoor air.

Ozone-initiated monoterpene reaction products have been hypothesized to cause eye and airway complaints in office environments and some have been proposed to cause skin irritation and sensitization. The respiratory effects of 60 min exposures to five common oxidation products from abundant terpenoids (e.g. limonene), used as solvent and fragrance in common household products or present in skin lipids (e.g. squalene), were studied in a head out mouse bioassay. This allowed determination of acute upper airway (sensory) irritation, airflow limitation in the conducting airways, and pulmonary irritation in the alveolar region. Derived human reference values (RFs) for sensory irritation were 1.3, 0.16 and 0.3 ppm, respectively, for 4-acetyl-1-methylcyclohexene ( 0.2 ppm) [corrected], 3-isopropenyl-6-oxo-heptanal (IPOH), and 6-methyl-5-heptene-2-one (6-MHO). Derived RFs for airflow limitation were 0.8, 0.45, 0.03, and 0.5 ppm, respectively, for dihydrocarvone (DHC), 0.2 ppm [corrected], 4-oxo-pentanal (0.3 ppm) [corrected], and 6-MHO. Pulmonary irritation was unobserved as a critical effect. The RFs indicate that the oxidation products would not contribute substantially to sensory irritation in eyes and upper airways in office environments. Reported concentrations in offices of 6-MHO and 0.3 ppm [corrected]would not result in airflow limitation. However, based upon the RFs for IPOH and 0.3 ppm [corrected], precautionary actions should be considered that disfavor their formation in excess.

Experiences from occupational exposure limits set on aerosols containing allergenic proteins.

Occupational exposure limits (OELs) together with determined airborne exposures are used in risk assessment based managements of occupational exposures to prevent occupational diseases. In most countries, OELs have only been set for few protein-containing aerosols causing IgE-mediated allergies. They comprise aerosols of flour dust, grain dust, wood dust, natural rubber latex, and the subtilisins, which are proteolytic enzymes. These aerosols show dose-dependent effects and levels have been established, where nearly all workers may be exposed without adverse health effects, which are required for setting OELs. Our aim is to analyse prerequisites for setting OELs for the allergenic protein-containing aerosols. Opposite to the key effect of toxicological reactions, two thresholds, one for the sensitization phase and one for elicitation of IgE-mediated symptoms in sensitized individuals, are used in the OEL settings. For example, this was the case for flour dust, where OELs were based on dust levels due to linearity between flour dust and its allergen levels. The critical effects for flour and grain dust OELs were different, which indicates that conclusion by analogy (read-across) must be scientifically well founded. Except for subtilisins, no OEL have been set for other industrial enzymes, where many of which are high volume chemicals. For several of these, OELs have been proposed in the scientific literature during the last two decades. It is apparent that the scientific methodology is available for setting OELs for proteins and protein-containing aerosols where the critical effect is IgE sensitization and IgE-mediated airway diseases.

Acute airway irritation of methyl formate in mice.

Methyl formate (MF) is a volatile solvent with several industrial applications. The acute airway effects of MF were evaluated in a mouse bioassay, allowing the assessment of sensory irritation of the upper airways, airflow limitation of the conducting airways and deep lung (pulmonary) irritation. MF was studied at vapour concentrations of 202-1,168 ppm. Sensory irritation was the only effect observed, which developed slowly over the 30-min exposure period. The potency at steady state was at least 10-fold higher than expected from a hypothetically similar, but non-reactive compound. Methyl formate may be hydrolysed in vivo to formic acid, a potent sensory irritant, and methanol, a low-potent sensory irritant. Hydrolysis may be catalysed by carboxyesterases, and therefore, the role of the esterases was studied using the esterase inhibitor tri-ortho-cresyl phosphate (TOCP). TOCP pre-treatment reduced the irritation response of MF, suggesting that carboxyesterase-mediated hydrolysis plays a role in the irritative effect. However, even after administration of TOCP, MF was considerably more irritating than expected from a quantitative structure-activity relationship (QSAR) model. The slope of the concentration-effect relationship for formic acid was lower than that for the MF in the low-dose range, suggesting that different receptor activation mechanisms may occur, which may include an effect of MF itself, in addition to an effect of formic acid and potentially an effect from formaldehyde.

Airway effects of inhaled quaternary ammonium compounds in mice.

Quaternary ammonium compounds (QAC) constitute a family of widely used chemical substances. The QAC benzalkonium chloride (BAC) has caused bronchoconstriction in human beings by poorly understood mechanisms and lung damage at high concentration as shown in a single rat study. This study evaluates acute airway effects in mice after inhalation of aerosols of the QACs, BAC, hexadecyl trimethyl ammonium bromide (HTA), cetyl pyridinium chloride (CPC) and dimethyl dioctadecyl ammonium bromide (DDA). The QACs gave rise to concentration-dependent decreases in the tidal volume (VT) and a concomitant increase in respiratory rate indicating pulmonary irritation. The potencies of the QAC to induce these effects were in the order: BAC > HTA = CPC > DDA. Furthermore, inhalation of BAC and CPC aerosols gave rise to pulmonary inflammation as apparent from bronchoalveolar lavage. Stimulation of nasal trigeminal nerve endings by QAC, which may serve as a warning signal, was absent.

Acute and subchronic airway inflammation after intratracheal instillation of quartz and titanium dioxide agglomerates in mice.

This study investigated the acute and subchronic inflammatory effects of micrometer-size (micro-size) and nanometer-size (nano-size) particles after intratracheal (i.t.) installation in mice. The role of the type of compound, polymorphism, and size of the particles was investigated. Studied compounds were the two micro-size reference quartzes, SRM1878a and DQ12, a micro- and nano-size rutile titanium dioxide (TiO2), a nano-size anatase, and an amorphous TiO2. Particles were administered by a single i.t. instillation in mice at a fixed dose of 5, 50, and 500 micrograms, respectively. Inflammation was evaluated from the bronchoalveolar lavage fluid (BALF) content of inflammatory cells, the cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6), as well as from lung histology. Evaluations were at 24 h (acute effects) and 3 months (subchronic effects) after instillations. Both types of quartz induced a dose-dependent acute increase of neutrophils, IL-6, and total protein in BALF. Limited subchronic inflammation was observed. All types of TiO2 induced a dose-dependent acute increase of neutrophils in BALF. In the acute phase, micro- and nano-size rutile and nano-size amorphous TiO2 induced elevated levels of IL-6 and total protein in BALF at the highest dose. At the nano-size rutile and amorphous TiO2, subchronic lung inflammation was apparent from a dose-dependent increase in BALF macrophages. Histology showed little inflammation overall. The two types of quartz showed virtually similar inflammatory effects. Nearly similar effects were observed for two sizes of rutile TiO2. Differences were seen between the different polymorphs of nano-size TiO2, with rutile being the most inflammogenic and amorphous being the most potent in regard to acute tissue damage.

Non-cancer effects of formaldehyde and relevance for setting an indoor air guideline.

There is considerable recent focus and concern about formaldehyde (FA). We have reviewed the literature on FA with focus on chemosensory perception in the airways and lung effects in indoor environments. Concentrations of FA, both personal and stationary, are on average in the order of 0.05 mg/m(3) or less in Europe and North America with the exception of new housing or buildings with extensive wooden surfaces, where the concentration may exceed 0.1 mg/m(3). With the eye the most sensitive organ, subjective irritation is reported at 0.3-0.5 mg/m(3), which is somewhat higher than reported odour thresholds. Objective effects in the eyes and airways occur around 0.6-1 mg/m(3). Dose-response relationships between FA and lung function effects have not been found in controlled human exposure studies below 1 mg/m(3), and epidemiological associations between FA concentrations and exacerbation of asthma in children and adults are encumbered by complex exposures. Neither experimental nor epidemiological studies point to major differences in susceptibility to FA among children, elderly, and asthmatics. People with personal trait of negative affectivity may report more symptoms. An air quality guideline of 0.1 mg/m(3) (0.08 ppm) is considered protective against both acute and chronic sensory irritation in the airways in the general population assuming a log normal distribution of nasal sensory irritation.

Time-response relationship of nano and micro particle induced lung inflammation. Quartz as reference compound.

An increasing number of engineered particles, including nanoparticles, are being manufactured, increasing the need for simple low-dose toxicological screening methods. This study aimed to investigate the kinetics of biomarkers related to acute and sub-chronic particle-induced lung inflammation of quartz. Mice were intratracheal instilled with 50 µg of microsized or nanosized quartz. Acute inflammation was assessed 1, 2, 4, 8, 16 or 48 hours post exposure, whereas sub-chronic inflammation was investigated 3 months after exposure. Markers of acute inflammation in the bronchoalveolar lavage fluid (BALF) were neutrophils (PMN), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1ß, macrophage inflammatory protein-2 (MIP-2), keratinocyte derived chemokine (KC) and total protein, which were all close to maximum 16 hours post instillation. No major differences were seen in the time-response profiles of nano- and micro-sized particles. The potency of the two samples cannot be compared; during the milling process, a substantial part of the quartz was converted to amorphous silica and contaminated with corundum. For screening, BALF PMN, either TNF-α or IL-1ß at 16 hours post instillation may be useful. At 3 months post instillation, KC, PMN and macrophages were elevated. Histology showed no interstitial inflammation three months post instillation. For screening of sub-chronic effects, KC, PMN, macrophages and histopathology is considered sufficient.

Lung damage in mice after inhalation of nanofilm spray products: the role of perfluorination and free hydroxyl groups.

Exposures to two commercial nanofilm spray products (NFPs), a floor sealant (NFP 1) and a coating product for tiles (NFP 2), were investigated for airway irritation, airway inflammation, and lung damage in a mouse inhalation model. The particle exposure was characterized by particle number, particle size distribution, and gravimetric analysis. BALB/cJ mice were exposed for 60 min to the aerosolized products at 3.3-60 mg/m(3) (10(5)-10(6) fine particles/cm(3)) measured in the breathing zone of the mice. Lung inflammation and lung damage were assessed by study of bronchoalveolar lavage fluid (BALF) cytology, protein in BALF, and histology. Mass spectral analysis showed that NFP 1 and NFP 2 contained hydrolysates and condensates of a perfluorosilane and alkylsilane, respectively. NFP 1 induced a concentration-dependent decrease of the tidal volume lasting for at least 1 day. Exposure concentrations above 16.1 mg/m(3) (2.1 x 10(6) fine particles/cm(3)) gave rise to significant increases of protein level in BALF and reduced body weight, and histological examination showed atelectasis, emphysema, and hemorrhages. A narrow interval between the no-effect level (16.1 mg/m(3)) and the lethal concentrations (18.4 mg/m(3)) was observed. The alkylsilane-based product (NFP 2) had no effect at the concentrations studied. Experiments with different types of perfluorinated silanes and alkylsiloxanes showed that the toxic effects did not arise solely from the perfluorination. The number of free hydroxyl groups in the silanes/alkylsiloxanes was also critical for the toxicity.

Nano titanium dioxide particles promote allergic sensitization and lung inflammation in mice.

The purpose of this study was to investigate whether photocatalytic TiO(2) nanoparticles have adjuvant effect, when administered in combination with ovalbumin (OVA) in mice. Mice were immunized via intraperitoneal injections of OVA, OVA + TiO(2) or OVA + Al(OH)(3) and challenged with aerosols of OVA. At the end of the study, serum was analysed for content of OVA-specific IgE, IgG1 and IgG2a antibodies, and the bronchoalveolar lavage fluid (BALF) was analysed for content of inflammatory cells and levels of interleukin (IL)-4, IL-5, IL-10 and interferon-gamma. The TiO(2) particles promoted a Th2 dominant immune response with high levels of OVA-specific IgE and IgG1 in serum and influx of eosinophils, neutrophils and lymphocytes in BALF. The TiO(2) particles induced a significantly higher level of OVA-specific IgE than the standard adjuvant Al(OH)(3). However, the two substances were comparable regarding the level of eosinophilic inflammation and interleukins present in BALF.

Desensitization of ovalbumin-sensitized mice by repeated co-administrations of di-(2-ethylhexyl) phthalate and ovalbumin.

BACKGROUND: The plasticizer di-(2-ethylhexyl) phthalate (DEHP) has been shown to stimulate a non-allergy related immune response with increased levels of IgG1 and IgG2a, but not IgE, after co-administration with the model allergen ovalbumin (OVA) in mice. In mice, decreased IgG1 and increased IgG2a have been associated with the development of mucosal tolerance towards inhaled allergens. As DEHP selectively promote formations of IgG1 and IgG2a without stimulating the IgE response, it was hypothesized that DEHP may suppress an established IgE mediated allergic response. Mice pre-sensitised to OVA were repeatedly co-exposed to DEHP and OVA and the effects were evaluated on the levels of OVA-specific antibodies, ex vivo cytokine levels and the degree of lung inflammation after challenge with an OVA aerosol. FINDINGS: Compared to the OVA-sensitised control mice, multiple co-exposures to DEHP+OVA reduced the IgG1 level and reduced the IgE/IgG2a ratio. This suggests that DEHP may attenuate allergic sensitisation, as the IgE/IgG2a ratio has been shown to correlate with the degree of anaphylaxis. Nevertheless, no effect of DEHP exposures was seen on inflammatory cells in bronchoalveolar lavage fluid and on cytokine levels in spleen cell culture. CONCLUSION: Data from humane and murine studies suggest that DEHP may attenuate the allergic response. More studies are necessary in order to assess the size of this effect and to rule out the underlying mechanism.

Acute airway effects of diacetyl in mice.

Occupational exposures to the butter flavouring agent diacetyl (2,3-butanedione) have caused lung inflammation and severe airflow limitation due to bronchiolitis obliterans. Diacetyl is naturally present in butter, beer, white wine, etc., and its pleasant odour is easily recognized by consumers. However, this pleasant odour may induce a false sense of safety when higher airborne concentrations are encountered in industrial use. In this study, the acute warning properties, in terms of sensory irritation, that could be useful to prevent workers from exposures to a high concentration were first investigated in a mouse bioassay. Then at higher exposure concentrations, the possibility of airflow limitation and pulmonary irritation were studied with the same mouse bioassay. Diacetyl induces concentration-dependent irritation in all parts of the respiratory tract during a 2-h exposure period. The no-observed-effect levels for each effect in the mice were above 100 ppm and initiation of sensory irritation in humans was estimated to occur above 20 ppm. No acute warning signal from the airways is expected at diacetyl levels that have caused bronchiolitis obliterans and other toxic effects. The sensory irritation effect, which occurred rapidly upon initiation of exposure, faded rapidly. Furthermore, high-level diacetyl exposures decreased the sensory irritation warning signal in mice upon repeated exposure, which suggests that the compound is especially insidious.

Structure-activity relationship of immunostimulatory effects of phthalates.

BACKGROUND: Some chemicals, including some phthalate plasticizers, have been shown to have an adjuvant effect in mice. However, an adjuvant effect, defined as an inherent ability to stimulate the humoral immune response, was only observed after exposure to a limited number of the phthalates. An adjuvant effect may be due to the structure or physicochemical characteristics of the molecule. The scope of this study was to investigate which molecular characteristics that determine the observed adjuvant effect of the most widely used phthalate plasticizer, the di-(2-ethylhexyl) phthalate (DEHP), which is documented as having a strong adjuvant effect. To do so, a series of nine lipophilic compounds with structural and physicochemical relations to DEHP were investigated. RESULTS: Adjuvant effect of phthalates and related compounds were restricted to the IgG1 antibody formation. No effect was seen on IgE. It appears that lipophilicity plays a crucial role, but lipophilicity does not per se cause an adjuvant effect. In addition to lipophilicity, a phthalate must also possess specific stereochemical characteristics in order for it to have adjuvant effect. CONCLUSION: The adjuvant effect of phthalates are highly influenced by both stereochemical and physico-chemical properties. This knowledge may be used in the rational development of plasticizers without adjuvant effect as well as in the design of new immunological adjuvants.

Acute airway effects of ozone-initiated d-limonene chemistry: importance of gaseous products.

There are concerns about ozone-initiated chemistry, because the formation of gaseous oxidation products and ultrafine particles may increase complaints, morbidity and mortality. Here we address the question whether the gaseous products or the ultrafine particles from the ozone-initiated chemistry of limonene, a common and abundant indoor pollutant, cause acute airway effects. The effects on the airways by d-limonene, a ca. 16s old ozone/d-limonene mixture, and clean air were evaluated by a mice bioassay, from which sensory irritation of the upper airways, airflow limitation, and pulmonary irritation can be obtained. A denuder was inserted to separate the ultrafine particles from the gaseous products prior to the exposure chamber. Reduction of mean respiratory frequency (>30%) and 230% increase of time of brake were observed without denuder, during 30min exposure, to the ozonolyzed d-limonene mixture, which are indicative of prominent sensory effects. The initial concentrations (ppm) were 40 d-limonene and 4 ozone. The exposure concentrations (ppm) were about 35 d-limonene and 0.05 ozone. Formaldehyde and residual d-limonene, the salient sensory irritants, accounted for up to three-fourth of the sensory irritation. The upper airway effects reversed to baseline upon cessation of exposure. An effect on the conducting airways was also significant, which did not reverse completely upon cessation. Airway effects were absent with the denuder inserted, which did not alter the size distribution of ultrafine particles ( approximately 10mg/m(3)), significantly. The result was statistically indistinguishable from clean dry air. It is concluded that ultrafine particles that are generated from ozone-initiated d-limonene chemistry and denuded are not causative of sensory effects in the airways.