Nitrogen dioxide is genotoxic in urban concentrations

Abstract

In the discussion on toxic and genotoxic thresholds of air pollutants such as nitrogen dioxide (NO₂), realistically low urban concentration ranges are of major interest. For NO₂, the WHO defines the annual limit value as corresponding to 0.02?ppm. In the present study, the toxicity and genotoxicity of NO₂ is set at a concentration under this limit value and examined in human nasal epithelium at different exposure durations in vitro. Nasal epithelial mucosa samples of 10 donors were harvested during nasal air passage surgery and cultured as an air–liquid interface. Exposure to 0.01?ppm NO₂ or synthetic air as a control was performed for 0.5, 1, 2 and 3?h. Analysis included the caspase-3 ELISA, the single cell microgel electrophoresis (comet) assay and the micronucleus assay. The caspase-3 activity was not influenced by NO₂ exposure, DNA strand fragmentation correlated with exposure durations to NO₂ at 0.01?ppm NO₂, and no cytotoxic effects such as apoptosis, necrosis or disturbances of cell proliferation were present. However, micronucleus induction as a sign of genotoxicity at an exposure duration of 3?h could be shown. Shorter exposures did not induce micronucleus formation. In summary, genotoxicity of NO₂ could be demonstrated at a common urban concentration in vitro, but a threshold of NO₂ genotoxicity could not be defined based on the present experiments.     

COMBINED RESPIRATORY EFFECTS OF COLD AIR WITH SO2 OR NO2 IN SINGLE 1-HOUR EXPOSURES OF HYPERVENTILATING GUINEA PIGS

The present study is a continuation of our previous experiments on repeated 10-min exposures of anesthetized, mechanically ventilated guinea pigs to clean cold dry air (Hälinen et al., 2000a), and to cold air plus gaseous air pollutants (Hälinen et al., 2000b). This time we made continuous 60-min exposures to clean cold dry air, cold air + SO₂ at 1 ppm, cold air + NO₂ at 1 ppm, and warm humid air + NO₂ at 1 ppm, and focused on responses at 10-60 min. Clean cold dry air and cold air + pollutants (n = 8-9 in each group) produced similar cooling in the guinea pig lower respiratory tract. The decreases in intratracheal temperature (T_tr) reached a plateau at 20 min with mean maximal decreases of 9.7-11.3°C from the pre-exposure control values of 36.0-37.3°C. In contrast, there were progressive decreases in esophageal temperature (T_oe) during the exposures, indicating constant conductive and evaporative heat losses from the tracheobronchial tissues. The mean maximal decreases in T_oe were 1.2-1.4°C from the preexposure control values of 37.8-38.0°C. Clean cold dry air induced 4.5-10.8% mean decreases in peak expiratory flow (PEF) at 10-60 min of exposure, which were statistically nonsignificant due to a relatively large variation between animals. Cold air + SO₂ at 1 ppm induced a mean decrease of 11.4% in PEF at 10 min (p < .05), which was spontaneously abolished during the next 10 min of exposure. Cold air + NO₂ at 1 ppm caused no decrease, but in fact small, nonsignificant increases in PEF at 30-60 min of exposure. Cold air + NO₂ at 1 ppm, and to some extent also cold air + SO₂ at 1 ppm, attenuated significantly the mechanical ventilation induced gradual decrease in tidal volume (V_T), when compared to clean cold dry air exposure. Cold air + NO₂ at 1 ppm, but not warm humid air + NO2 at 1 ppm, increased significantly the proportion of macrophages in the differential count of bronchoalveolar lavage fluid (BALF) white cells when compared to both clean warm humid air and cold dry air. None of the exposure conditions caused morphological or inflammatory changes in the respiratory tissues. In conclusion, continuous 60-min exposures to clean cold dry air, cold air + SO₂, and cold air + NO₂ produced weaker functional effects on the lower respiratory tract of guinea pigs than our previous consecutive 10-min exposures to these air conditions. After the first 10 min, there was a strong attenuation of the bronchoconstrictor responses, especially to cold air + NO₂ at 1 ppm. The small airway effects of prolonged mechanical ventilation were significantly modified by NO₂ at 1 ppm in both cold dry and warm humid breathing air. Finally, cold air + NO₂ at 1 ppm increased the proportion of macrophages in BALF white cells.     

Critical review of the human data on short-term nitrogen dioxide (NO2) exposures: Evidence for NO2 no-effect levels

Nitrogen dioxide (NO₂) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Evidence for health effects of ambient NO₂ derives from three types of studies: observational epidemiology, human clinical exposures, and animal toxicology. Our review focuses on the human clinical studies of adverse health effects of short-term NO₂ exposures, given the substantial uncertainties and limitations in interpretation of the other lines of evidence. We examined more than 50 experimental studies of humans inhaling NO₂, finding notably that the reporting of statistically significant changes in lung function and bronchial sensitivity did not show a consistent trend with increasing NO₂ concentrations. Functional changes were generally mild and transient, the reported effects were not uniformly adverse, and they were not usually accompanied by NO₂-dependent increases in symptoms. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO₂ exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm). Our review of these data indicates that a health-protective, short-term NO₂ guideline level for susceptible (and healthy) populations would reflect a policy choice between 0.2 and 0.6 ppm.

Extended abstract

Nitrogen dioxide (NO₂) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Natural NO₂ sources include volcanic action, forest fires, lightning, and the stratosphere; man-made NO₂ emissions derive from fossil fuel combustion and incineration.

The current National Ambient Air Quality Standard (NAAQS) for NO₂, initially established in 1971, is 0.053 ppm (annual average). Ambient concentrations monitored in urban areas in the United States are ~0.015 ppm, as an annual mean, i.e., below the current NAAQS. Short-term (1-h peak) NO₂ concentrations outdoors are not likely to exceed 0.2 ppm, and even 1-h periods exceeding 0.1 ppm are infrequent. Inside homes, 1-h NO₂ peaks, typically arising from gas cooking, can range between 0.4 and 1.5 ppm.

The health effects evidence of relevance to ambient NO₂ derives from three lines of investigation: epidemiology studies, human clinical studies, and animal toxicology studies. The NO₂ epidemiology remains inconsistent and uncertain due to the potential for exposure misclassification, residual confounding, and co-pollutant effects, whereas animal toxicology findings using high levels of NO₂ exposure require extrapolation to humans exposed at low ambient NO₂ levels. Given the limitations and uncertainties in the other lines of health effects evidence, our review thus focused on clinical studies where human volunteers (including asthmatics, children, and elderly) inhaled NO₂ at levels from 0.1 to 3.5 ppm during short-term (½–6-h) exposures, often combined with exercise, and occasionally combined with co-pollutants. We examined the reported biological effects and classified them into (a) lung immune responses and inflammation, (b) lung function changes and airway hyperresponsiveness (AHR), and (c) health effects outside the lungs (extrapulmonary).

We examined more than 50 experimental studies of humans inhaling NO₂, finding that such clinical data on short-term exposure allowed discrimination of NO₂ no-effect levels versus lowest-adverse-effects levels. Our conclusions are summarized by these six points: For lung immune responses and inflammation: (1) healthy subjects exposed to NO₂ below 1 ppm do not show pulmonary inflammation; (2) at 2 ppm for 4?h, neutrophils and cytokines in lung-lavage fluid can increase, but these changes do not necessarily correlate with significant or sustained changes in lung function; (3) there is no consistent evidence that NO₂ concentrations below 2 ppm increase susceptibility to viral infection; (4) for asthmatics and individuals having chronic obstructive pulmonary disease (COPD), NO₂-induced lung inflammation is not expected below 0.6 ppm, although one research group reported enhancement of proinflammatory processes at 0.26 ppm. With regard to NO₂-induced AHR: (5) studies of responses to specific or nonspecific airway challenges (e.g., ragweed, methacholine) suggest that asthmatic individuals were not affected by NO₂ up to about 0.6 ppm, although some sensitive subsets may respond to levels as low as 0.2 ppm. And finally, for extra-pulmonary effects: (6) such effects (e.g., changes in blood chemistry) generally required NO₂ concentrations above 1–2 ppm.

Overall, our review of data from experiments with humans indicates that a health-protective, short-term-average NO₂ guideline level for susceptible populations (and healthy populations) would reflect a policy choice between 0.2 and 0.6 ppm. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO₂ exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm).     

Inflammatory response and endothelial dysfunction in the hearts of mice co‐exposed to SO2, NO2, and PM2.5

SO₂, NO₂, and PM_2.5 are typical air pollutants produced during the combustion of coal. Increasing evidence indicates that air pollution has contributed to the development and progression of heart‐related diseases over the past decades. However, little experimental data and few studies of SO₂, NO₂, and PM_2.5 co‐exposure in animals exist; therefore, the relevant mechanisms underlying this phenomenon are unclear. An important characteristic of air pollution is that co‐exposure persists at a low concentration throughout a lifetime. In the present study, we treated adult mice with SO₂, NO₂, and PM_2.5 at various concentrations (0.5 mg/m³ SO₂, 0.2 mg/m³ NO₂ 6 h/d, with intranasal instillation of 1 mg/kg PM_2.5 every other day during these exposures; or 3.5 mg/m³ SO₂, 2 mg/m³ NO₂ 6 h/d, and 10 mg/kg PM_2.5 for 28 d). Blood pressure (BP), heart rate (HR), histopathological damage, and inflammatory and endothelial cytokines in the heart were assessed. The results indicate that co‐exposure caused endothelial dysfunction by elevating endothelin‐1 (ET‐1) expression and repressing the endothelial nitric oxide synthase (eNOS) level as well as stimulating the inflammatory response by increasing the levels of cyclooxygenase‐2 (COX‐2), inducible nitric oxide synthase (iNOS), tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6). Additionally, these alterations were confirmed by histological staining. Furthermore, we observed decreased BP and increased HR after co‐exposure. Our results indicate that co‐exposure to SO₂, NO₂, and PM_2.5 may be a major risk factor for cardiac disease and may induce injury to the hearts of mammals and contribute to heart disease. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1996–2005, 2016.     

A dynamic system for single and repeated exposure of airway epithelial cells to gaseous pollutants

In vitro models are promising approaches to investigate the adverse effects and the mode of action of air pollutants on the respiratory tract. We designed a dynamic system that allows the single or repeated exposure of cultured cells to two major indoor air gaseous pollutants, formaldehyde (HCHO) and nitrogen dioxide (NO₂), alone or as a mixture. In this system, the Calu-3 human bronchial epithelial cell line was exposed at the air–liquid interface (ALI) or submerged by culture medium to synthetic air or to target concentrations of HCHO and/or NO₂ once or on 4 consecutive days before assessment of cell viability and necrosis, IL-6 and IL-8 release and trans-epithelial electrical resistance. Our data showed that whereas the ALI method can be used for single short-term exposures only, the submerged method provides the possibility to expose Calu-3 cells in a repeated manner. As well, we found that repeated exposures of the cells to HCHO and NO₂ at concentrations that can be found indoors triggered a significant decrease in cell metabolism and an increase in IL-8 release that were not evoked by a single exposure. Thus, our work highlights the fact that the development of systems and methods that allow repeated exposures of cultured cells to gaseous compounds in mixtures is of major interest to evaluate the impact of air pollution on the respiratory tract.     

Synergistic effects of exposure to concentrated ambient fine pollution particles and nitrogen dioxide in humans

Context: Exposure to single pollutants e.g. particulate matter (PM) is associated with adverse health effects, but it does not represent a real world scenario that usually involves multiple pollutants.

Objectives: Determine if simultaneous exposure to PM and NO₂ results in synergistic interactions.

Materials and methods: Healthy young volunteers were exposed to clean air, nitrogen dioxide (NO₂, 0.5 ppm), concentrated fine particles from Chapel Hill air (PM_2.5CAPs, 89.5?±?10.7 µg/m³), or NO₂+PM_2.5CAPs for 2?h. Each subject performed intermittent exercise during the exposure. Parameters of heart rate variability (HRV), changes in repolarization, peripheral blood endpoints and lung function were measured before and 1 and 18?h after exposure. Bronchoalveolar lavage (BAL) was performed 18?h after exposure.

Results: NO₂ exposure alone increased cholesterol and HDL 18?h after exposure, decreased high frequency component of HRV one and 18?h after exposure, decreased QT variability index 1?h after exposure, and increased LDH in BAL fluid. The only significant change with PM_2.5CAPs was an increase in HDL 1?h after exposure, likely due to the low concentrations of PM_2.5CAPs in the exposure chamber. Exposure to both NO₂ and PM_2.5CAPs increased BAL α1-antitrypsin, mean t wave amplitude, the low frequency components of HRV and the LF/HF ratio. These changes were not observed following exposure to NO₂ or PM_2.5CAPs alone, suggesting possible interactions between the two pollutants.

Discussion and conclusions: NO₂ exposure may produce and enhance acute cardiovascular effects of PM_2.5CAPs. Assessment of health effects by ambient PM should consider its interactions with gaseous copollutants.     

Short-term air pollution exposure is associated with hospital length of stay and hospitalization costs among inpatients with type 2 diabetes: a hospital-based study

Air pollution is a risk factor for type 2 diabetes (T2D), exerting heavy economic burden on both individuals and societies. However, there is no apparent report regarding the influence of air pollutants such as particulate matter (PM_2.5 and PM₁₀), sulfur dioxide (SO₂), carbon monoxide (CO), nitrogen dioxide (NO₂), and ozone (O₃) on financial burden to individuals and societies suffering from T2D. This study aimed to determine whether short-term (no more than 16 d) air pollution exposure was associated with T2D-related length of stay (LOS) and hospitalization expenses incurred by patients. This investigation examined 2840 T2D patients hospitalized from December 17, 2013 to May 31, 2016 in China. Multiple linear regression analysis was applied to determine the association between short-term (no more than 16 d) ambient air pollution, LOS, and hospitalization expenses, controlling for age, gender, ethnicity, marital status, and weather conditions. Sulfur dioxide (SO₂) and carbon monoxide (CO) were significantly positively while nitrogen dioxide (NO₂) was negatively associated with presence of T2D, LOS, and expenses. A 10-μg/m³ rise in 16-d (lag 0–15) average concentrations of SO₂ and CO prior to hospitalization was correlated with a significant elevation in LOS and elevation in expenses in T2D patients. However, a 10-μg/m³ rise in 16-d average NO₂ was associated with marked negative alterations in LOS and hospital costs in T2D patients. Taken together, data demonstrate that exposure to air pollutants impacts differently on LOS and hospitalization costs for T2D patients. This is the first apparent report regarding the correlation between air pollution exposure and clinical costs of T2D in China. It is of interest that air pollutants affected T2D patients differently as evidenced by LOS and clinical expenses where SO₂ and CO exhibited a positive adverse relationship in contrast to NO₂.     

Assessment of low dose effects of acute sulphur dioxide exposure on the airways using non-invasive methods

Sulphur dioxide (SO₂) is an important environmental and workplace air pollutant. Some studies demonstrate that subjects without adaptation respond to SO₂ up to 10 ppm with irritative effects on the airways. The aim of our study was to assess irritative effects of SO₂ up to 2 ppm on the airways using non-invasive methods like exhaled breath condensate (EBC), nasal lavage fluid (NALF) and exhaled nitric oxide (FeNO). Sixteen healthy volunteers were exposed for 4 h to SO₂ in concentrations of 0 (clean air), 0.5, 1.0 and 2.0 ppm in a repeated measures cross-over design. Before and after exposure, FeNO and biomarkers of airway inflammation in NALF and EBC were measured. All EBC pH values, collected after exposure, were more alkaline than before, significant only for clean air (7.05 ± 0.4 vs. 7.27 ± 0.3, P = 0.0031) and 0.5 ppm SO₂ exposure (6.85 ± 0.53 vs. 7.08 ± 0.42, P = 0.0251). No dose-dependent differences before and after exposure were measured for LTB₄, PGE₂ and 8-isoPGF_2α. Substance P in NALF collected after exposure tended to result in higher concentrations compared to pre-samples, without clear dose effect. Further cellular and soluble parameters measured were not significantly affected. Our results show that 4 h SO₂ exposure up to 2.0 ppm did not induce significant changes in the biomarker composition of the EBC and NALF when compared with clean air or with pre-samples of the same subject. Therefore our data suggest that acute low dose SO₂ exposure in not adapted subjects did not induce airway irritation or/and inflammation measured under these conditions.     

Chronic exposure to sulfur dioxide enhances airway hyperresponsiveness only in ovalbumin-sensitized rats

Sulfur dioxide (SO₂) is a common air pollutant that triggers asthmatic symptoms, but its toxicological mechanisms are not fully understood. Specifically, it is unclear how airborne SO₂ affects airway hyperresponsiveness (AHR) – a hallmark feature of asthma. To this end, we investigated the effects of chronic exposure to SO₂ on AHR, airway inflammation, tissue remodeling, cell stiffness (G′) and contractility of the airway smooth muscle cell (ASMC). Newborn Sprague–Dawley (SD) rats sensitized to ovalbumin (OVA) was used as the model to mimic asthmatic symptoms. The experimental results show that exposure to SO₂: (1) significantly increased Penh (an indicator of AHR) in the OVA-sensitized rats (p < 0.01) but not in the normal rats (p > 0.05), which correlated with the increase of airway smooth muscle mass; (2) increased IL-4 production in BALF of both the normal (p < 0.05) and OVA-sensitized rats (p < 0.001), but decreased IFN-γ in BALF of only the normal rats, and in serum only increased IL-4 production of the OVA-sensitized rats (p < 0.001); (3) increased ASMC stiffness (G′) and contractility only in the OVA-sensitized rats (p < 0.001, p < 0.05, respectively). Taken together, these results demonstrate that SO₂ may be a universal airway inflammatory factor, but more importantly, specific to exacerbating AHR in asthmatics only. These findings uncover a potential mechanism of SO₂-induced health effects and may provide a basis for therapeutic targets.     

Analysis of the concentration–respiratory response among asthmatics following controlled short-term exposures to sulfur dioxide

Some of the most compelling evidence of sulfur dioxide (SO₂)-induced respiratory morbidity is derived from a large body of studies involving controlled short-term exposures among groups of asthmatic volunteers. These studies were extensively cited in the recently completed review of the primary National Ambient Air Quality Standards for SO₂. Although it is clear from these investigations that exposure to SO₂ may result in a significant increase in bronchoconstriction, there is uncertainty regarding the range of concentrations over which this respiratory response occurs. The objective of this study was to better characterize the concentration–response relationship between SO₂ and measures of bronchoconstriction using individual subject lung function response data. In reviewing studies of asthmatics exposed to SO₂ during 5- to 10-min periods of elevated ventilation, we observed clear and consistent evidence of an increase in the bronchoconstrictive response to SO₂ with increasing exposure concentrations between 0.2 and 1.0 ppm. In a subsequent analysis of individual subject data, it was found that those asthmatics experiencing SO₂-induced respiratory effects at relatively high exposure concentrations are also more likely than nonresponders to experience similar effects after exposure to lower SO₂ concentrations (≤0.4 ppm). Although the clinical significance of these effects is unsettled, the findings provide additional support to epidemiologic evidence of an association between ambient SO₂ concentration and various measures of respiratory morbidity in the general population.     

Air pollution-related peak expiratory flow rates among asthmatic children in Chiang Mai,Thailand

The severity of air pollution in northern Thailand has long been recognized; in spite of that there have been no epidemiological studies regarding the associations between the air pollution and health effects in the area. The authors followed a cohort of 31 asthmatic children (4–11 years of age) residing in Muang district, Chiang Mai, Thailand, from 29 August 2005 to 30 June 2006, for 306 days. The daily air pollutants, including particulate matter with aerodynamic diameter?<?2.5?μm, particulate matter with aerodynamic diameter?<?10?μm, carbon monoxide, ozone (O₃), nitrogen dioxide, and sulfur dioxide (SO₂), and the meteorological parameters, including pressure, temperature, relative humidity, rain quantity, and sunshine duration, were recorded. The peak expiratory flow rates (PEFRs) were fitted with pollutants and meteorological covariates using general linear mixed models to account for random effects and autocorrelation. The authors found that there were inverse associations of SO₂ and evening PEFR, with a coefficient of -2.12 (95% confidence interval (CI)?=?-3.22 to -0.28); of SO₂ and daily percent deviation of PEFR, with a coefficient of -0.73 (95% CI?=?-1.33 to -0.12); and of O₃ combining with SO₂ and daily average PEFR, with a coefficient of -0.16 (95% CI?=?-0.31 to -0.00) and -1.60 (95% CI?=?-3.10 to -0.11), respectively. The associations of O₃ and SO₂ with PEFR were found even when SO₂ concentrations never exceeded the standard level.     

Sensory and pulmonary effects of acute exposure to sulfur dioxide (SO2)

Background

Exposure to sulfur dioxide (SO₂) affects large populations worldwide. Pulmonary effects have been reported at concentrations relevant in the general (<0.5 ppm) and working environment (>0.5 ppm). SO₂ is an irritant but the existing studies often emphasize only pulmonary effects and no clear dose–response relationship has yet been described.

Objectives

Using a multi-level, multi-method approach, odor annoyance, sensory irritation and pulmonary effects of SO₂ were to be investigated in an experimental exposure study.

Methods

Eye blink frequency, rhinomanometry, spirometry and symptom ratings of acute health effects were assessed before, during, and after the exposures. Each session lasted 4 h and concentrations of 0.5, 1, and 2 ppm were investigated and compared to a control condition using clean air. Sixteen human volunteers (8 females/8 males) participated and during exposure light physical exercise was simulated with bicycle ergometry.

Results

Eye blink frequency, nasal airflow, and lung function were not affected by the acute SO₂ exposure investigated. These physiological responses to moderate SO₂ exposures were not significantly affected by gender. Regarding subjectively measured chemosensory sensations, only odor annoyance ratings increased in a dose-dependent manner, but the average magnitudes were labeled weak to moderate.

Conclusions

In healthy volunteers, without hyperresponsiveness to SO₂, no dose-dependent effects of acute SO₂ exposures up to 2 ppm could be measured. Due to olfactory perceptions subjects were aware of the different SO₂ exposures but the associated annoyance was relatively low.     

Pre-exposure to sulfur dioxide attenuates most allergic reactions upon trimellitic anhydride challenge in sensitized Brown Norway rats

Irritant-induced inflammation of the airways may aggravate respiratory allergy induced by chemical respiratory allergens. Therefore, it was studied whether airway irritation by sulfur dioxide (SO₂) would enhance respiratory allergic reactions to trimellitic anhydride (TMA), using a rat model. Brown Norway (BN) rats were topically sensitized, subsequently exposed for a single time or repeatedly to 300?ppm SO₂, and challenged by inhalation to a distinctly irritating or minimally irritating concentration of TMA after the (last) SO₂ exposure. Repeated exposure to SO₂ alone reduced breathing frequency during exposure, and caused epithelial alterations including hyperplasia and squamous metaplasia, and infiltration of polymorphonuclear inflammatory cells into nasal tissues, larynx, trachea, and bronchi/bronchioli. Histopathological changes were less prominent after 1 day of SO₂ exposure. Repeated pre-exposure to SO₂ reduced the number of TMA-induced apnoeas, in an SO₂ exposure duration-dependent manner. This effect of SO₂ on TMA-induced functional allergic reactions (apnoeas) was distinct only when the TMA challenge concentration was not too irritating itself. Repeated pre-exposure to SO₂ reduced TMA-induced laryngeal ulceration, goblet-cell hyperplasia, and inflammation in the lungs in most animals, regardless of the TMA challenge concentration. The SO₂-induced replacement of normal respiratory epithelium by less sensitive, squamous epithelium may offer an explanation for the, unexpected, reduced allergic manifestation. However in a few animals, SO₂ appeared to facilitate TMA-induced irritation, probably due to incomplete protection. Overall, SO₂ exposure of TMA-sensitized rats reduced TMA-related allergic respiratory responses in most animals.     

Inhalation exposure of nano-scaled titanium dioxide (TiO2) particles alters the inflammatory responses in asthmatic mice

Abstract

Context: Titanium dioxide (TiO₂) nanoparticles (NPs) are regarded as relatively non-toxic in concentrations occurring in occupational environments. Nevertheless, it is conceivable that adverse health effects may develop in sensitive populations such as individuals with respiratory diseases.

Objective: We investigated whether single or repeated exposure to TiO₂ could aggravate inflammatory responses in naïve mice and mice with ovalbumin (OVA)-induced airway inflammation.

Methods: Exposure to aerosolized TiO₂ was performed during OVA sensitization, before, or during the OVA challenge period. The effects on respiratory physiology, inflammatory cells in bronchoalveolar lavage (BAL) and inflammatory mediators in BAL and serum were assessed 24?h after the last OVA challenge or TiO₂ exposure.

Results: A single exposure of TiO₂ had a marked effect on responses in peripheral airways and increasing infiltration of neutrophils in airways of naïve animals. Marked aggravation of airway responses was also observed in animals with allergic disease provided that the single dose TiO₂ was given before allergen challenge. Repeated exposures to TiO₂ during sensitization diminished the OVA-induced airway eosinophilia and airway hyperresponsiveness but concomitant exposure to TiO₂ during the OVA challenge period resulted in neutrophilic airway inflammation and a decline in general health condition as indicated by the loss of body weight.

Conclusion: We conclude that inhalation of TiO₂ may aggravate respiratory diseases and that the adverse health effects are highly dependent on dose and timing of exposure. Our data imply that inhalation of NPs may increase the risk for individuals with allergic airway disease to develop symptoms of severe asthma.     

Effect of NO2 and SO2 inhalation on benzo(a)pyrene metabolism in rat lung

Male Wistar rats were continuously exposed to NO₂ (14.4 ppm), SO₂ (46.5 ppm) and to a mixture of both gases and their effect on lung microsomal aryl hydrocarbon (benzo(a)pyrene) hydroxylase (AHH) activity was determined. The pre-exposed animals were administered methylcholanthrene (MC) to investigate the exposure effect on enzyme inducibility and pattern of B(a)P metabolites. NO₂ significantly increased AHH activity but no marked change was noted with SO₂. Induction of AHH by MC was markedly inhibited by SO₂, only slightly by mixture of NO₂-SO₂ but not with NO₂ alone.     

Analysis of EPA’s endocrine screening battery and recommendations for further review

To establish primary National Ambient Air Quality Standards (NAAQS) for criteria air pollutants such as nitrogen dioxide (NO₂), ozone (O₃), and sulfur dioxide (SO₂), US EPA relies in part on controlled human exposure studies. It has been suggested that evaluating average responses for all participants in these studies may not reflect the responses of sensitive participants in these studies. To evaluate this, we identified controlled exposure studies with multiple exposure concentrations or durations that provided individual-level lung function data. Based on individual lung function responses at specific exposure concentrations and the slope of individual concentration–response curves, we identified 12 participants out of a total of 208 participants in 12 studies who were potentially sensitive to O₃, SO₂, or sulfuric acid (H₂SO₄). We did not identify any participants sensitive to NO₂. All of these participants were found to be potentially sensitive only at concentrations that were well above the NAAQS (SO₂), above likely ambient concentrations (H₂SO₄), or at concentrations at which the study reported significant lung function effects for all participants (O₃). Based on our analysis, average responses for all participants combined adequately reflect lung function responses for potentially sensitive study participants at concentrations in the range of the current NAAQS.     

Air Pollution and Hospital Admissions for Congestive Heart Failure in a Tropical City: Kaohsiung,Taiwan

This study was undertaken to determine whether there was an association between air pollutant levels and hospital admissions for congestive heart failure (CHF) in Kaohsiung, Taiwan. Hospital admissions for CHF and ambient air pollution data for Kaohsiung were obtained for the period 1996–2004. The relative risk of hospital admission was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. In the single-pollutant models, on warm days (> 25°C) statistically significant positive associations were found in all pollutants except sulfur dioxide (SO₂). On cool days (< 25°C), all pollutants were significantly associated with CHF admissions. For the two-pollutant model, CO and O₃ were significant in combination with each of the other four pollutants on warm days. On cool days, NO₂ remained statistically significant in all the two-pollutant models. This study provides evidence that higher levels of ambient air pollutants increase the risk of hospital admissions for CHF and that the effects of air pollutants on hospital admissions for CHF were temperature dependent.     

Comparative Simulation of Gas Transport in Airway Models of Rat,Dog, and Human

Although a number of animal studies have been conducted to investigate the toxic effects of gaseous pollutants on human airways, the anatomical and physiological differences between animals and humans represent a challenge in extrapolating the animal data to humans. The aim of this study was to examine how interspecies anatomical and physiological differences influence the transport of the inhaled gases throughout the airways and alveoli. We designed mathematical airway models of three mammalian species, rats, dogs, and humans, in which interspecies differences in airway dimensions and respiratory patterns were taken into account. We then simulated the bulk flow of three gases (ozone [O₃], nitrogen dioxide [NO₂], and sulfur dioxide [SO₂]) and obtained the intra-airway concentrations of the gases and the amount absorbed using these models. For all three gases, both real-time and mean concentrations in the upper and lower airways were higher in humans when compared with rats and dogs. For example, the mean concentration of O₃ in the 5th bronchi of humans was 3 and 12 times higher than in rats and dogs, respectively. Similarly, the amount of absorbed gases corrected for airway surface area was again higher in the upper and lower airways of humans than the other two species. Sensitivity analysis indicated that tidal volume, respiratory rate, and surface area of the upper and lower airways had significant impact on the results. In conclusion, kinetics of inhaled gaseous substances vary substantially among animals and humans, and such variations are, at least partially, the result of anatomical and physiological differences in their airways.     

Morning NO2 exposure sensitizes hypertensive rats to the cardiovascular effects of same day O3 exposure in the afternoon

Context: Within urban air sheds, specific ambient air pollutants typically peak at predictable times throughout the day. For example, in environments dominated by mobile sources, peak nitrogen dioxide (NO₂) levels coincide with morning and afternoon rush hours, while peak levels of ozone (O₃), occur in the afternoon.

Objective: Given that exposure to a single pollutant might sensitize the cardiopulmonary system to the effects of a subsequent exposure to a second pollutant, we hypothesized that a morning exposure to NO₂ will exaggerate the cardiovascular effects of an afternoon O₃ exposure in rats.

Materials and methods: Rats were divided into four groups that were each exposed for 3?h in the morning (m) and 3?h in the afternoon (a) on the same day: (1) m-Air/a-Air, (2) m-Air/a-O₃ (0.3?ppm), (3) m-NO₂ (0.5?ppm)/a-Air and (4) m-NO₂/a-O₃. Implanted telemetry devices recorded blood pressure and electrocardiographic data. Sensitivity to the arrhythmogenic agent aconitine was measured in a separate cohort.

Results: Only m-NO₂/a-O₃-exposed rats had significant changes in electrophysiological, mechanical and autonomic parameters. These included decreased heart rate and increased PR and QT_c intervals and increased heart rate variability, suggesting increased parasympathetic tone. In addition, only m-NO₂/a-O₃ exposure decreased systolic and diastolic blood pressures and increased pulse pressure and QA interval, suggesting decreased cardiac contractility.

Discussion and conclusion: The findings indicate that initial exposure to NO₂ sensitized rats to the cardiovascular effects of O₃ and may provide insight into the epidemiological data linking adverse cardiovascular outcomes with exposures to low concentrations of O₃.