The Chattanooga school children study: effects of community exposure to nitrogen dioxide. II. Incidence of acute respiratory illness

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 approximately 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 ((1/2)-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).

The German view: effects of nitrogen dioxide on human health--derivation of health-related short-term and long-term values

The presented overview concerning health relevant effects caused by nitrogen dioxide (NO2) resumes the current state of results from animal experiments and human studies (epidemiology and short-term chambers studies). NO2 concentrations applied in animal experiments were mostly considerably higher than in ambient air. Therefore, short- and long-term limit values were derived from human data. Experimental studies conducted with humans demonstrate effects after short-term exposure to concentrations at or above 400 microg NO2/m3. Effects on patients with light asthma could not be observed after short-term exposure to concentrations below 200 microg/m3. On basis of epidemiological long-term studies a threshold below which no effect on human health is expected could not be specified. Two short-term limit values have been proposed to protect public health: a 1-h value of 100 microg/m3 and a 24-h mean value of 50 microg/m3. Due to the limitations of epidemiological studies to disentangle effects of single pollutants, a long-term limit value cannot be easily derived. However, applying the precautionary principle, it is desirable to adopt an annual mean of 20 microg NO2/m3 as a long-term mean standard to protect public health.

Is the incidence of tonsillectomy influenced by the family medical or social history?

Previous reports have suggested that the incidence of tonsillectomy, and/or tonsillitis in children, is influenced by factors such as parental smoking, maternal health and previous parental tonsillectomy. The reports have considered single factors and have not considered the possible confounding effect of the factors upon one another. Previous studies have not investigated the influence of social class. This paper uses the background of a large case-control trial of children awaiting tonsillectomy for recurrent tonsillitis, and a normal control group to study the influence of parental smoking, parental surgical history, parental tonsillectomy, family atopy and social class upon the reported incidence of sore throats and tonsillitis. A multivariate analysis is used. The paper shows that parental smoking, previous parental surgery and social class have no effect upon the number of sore throat episodes. A history of parental tonsillectomy and a family history of atopy are both significant predictive factors for the number of reported sore throats and episodes of tonsillitis in children.

[Air pollutant burden and bronchial asthma in school children]

To examine the possibility of an effect of indoor and outdoor exposures on the prevalence of asthma in childhood we conducted a cross-sectional study in the area of Freiburg city and two communities in the Black Forest. The study group consists of 704 children aged 7 to 16 years. The children and their mothers took part in a standardized interview and a medical examination. Indoor exposures were assessed from information gathered in the interview by two different indices: (a) heating system and single room heating, and (b) the amount of indoor ventilation. The measurement of outdoor pollutants took into account weekly estimations of NO2 and combustion particles. The presence of asthma was recorded according to a previous medical diagnosis. Confounders were assessed during the interview (passive smoking, genetic predisposition to asthma etc.) or during the medical examination (cutaneous sensitization with a skin prick test). For the analysis of the data we applied logistic regression models and estimated odds-ratios. Only one of the four hypothesis variables displays a significant effect on the prevalence of asthma: Stoves as heating device carry a 4.8-fold relative risk for asthma compared to other types of heating. Among the confounding variables controlled for in the explanatory model, cutaneous reactions showed a relative risk of eight.

Indoor woodsmoke pollution causing lower respiratory disease in children

Suggested aetiological factors were evaluated in 244 consecutive children presenting with lower respiratory disease at Marondera Hospital, Zimbabwe. Data obtained from these children were compared with information obtained from 500 children seen at the local well baby clinic. There were no differences in the prevalence of malnutrition, breast feeding, overcrowding, poor housing conditions and poverty in these two groups of children. A significant association was identified between lower respiratory disease and exposure to atmospheric woodsmoke pollution in young children. Air sampling within the kitchens of 40 children revealed levels of atmospheric pollution far in excess of the WHO recommended exposure limit. Elevated carboxyhaemoglobin concentrations confirmed childhood smoke inhalation. We suggest that in many Third World communities a chemical pneumonitis resulting from the inhalation of noxious constituents of woodsmoke predisposes to lower respiratory disease in children.

Effect of nitrogen dioxide exposure on susceptibility to influenza A virus infection in healthy adults

The effect of NO2 exposure and human susceptibility to respiratory virus infection was investigated in a placebo-controlled, randomized, double-blind trial conducted in an environmentally controlled research chamber over 3 yr. Healthy, nonsmoking, young adult volunteers who were seronegative to influenza A/Korea/82 (H3N2) virus were randomly assigned to breathe either filtered clean air (control group) or NO2 for 2 h/day for 3 consecutive days. The NO2 concentrations were 2 ppm (Year 1), 3 ppm (Year 2), and 1 or 2 ppm (Year 3). Live, attenuated cold-adapted (ca) influenza A/Korea/82 reassortant virus was administered intranasally to all subjects immediately after the second exposure. Only one of the 152 volunteers had any symptoms; this person had a low grade fever. Pulmonary function measurements and nonspecific airway reactivity to methacholine were unchanged after NO2 exposure, virus infection, or both. Infection was determined by virus recovery, a fourfold or greater increase in serum or nasal wash influenza-specific antibody titers, or both. The infection rates of the groups were 12/21 (2 ppm NO2) versus 15/23 (clean air) in Year 1, 17/22 (3 ppm NO2) versus 15/21 (clean air) in Year 2, and 20/22 (2 ppm) and 20/22 (1 ppm) versus 15/21 (clean air) in Year 3. Each group exposed to 1 or 2 ppm NO2 in the last year became infected more often (91%) than did the control group (71%), but the differences were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

The Tayside infant morbidity and mortality study: effect on health of using gas for cooking

The relation between respiratory illness and the use of gas for cooking was examined from data on 1565 infants born to mothers who were primigravidas living in Dundee in 1980. Episodes of, and admissions to hospital for, respiratory illness were recorded during the first year of life. Both admissions and episodes were more common in infants from families using gas for cooking or heating than in infants from families using any other type of cooking or heating, but the differences were not significant. Results from this and other studies show that there is probably a small relation between respiratory illness and the use of gas appliances without a flue. To show convincingly whether such a relation exists might require a survey of 18 000-23 000 subjects. Respiratory illness was, however, strongly and positively related to parental smoking, a finding that is often made even in small studies.

An epidemiological study of salt miners in diesel and nondiesel mines

A cross-sectional study of 5 NaCl mines and 259 miners addressed the following questions: 1) Is there an association of increased respiratory symptoms, radiographic findings, and reduced pulmonary function with exposure to nitrogen dioxide (NO2) and/or respirable particulate (RP) among these miners? 2) Is there increased morbidity of these miners compared to other working populations? Personal samples of NO2 and respirable particulate for jobs in each mine were used to estimate cumulative exposure. NO2 is used as a surrogate measure of diesel exposure. Cough was associated with age and smoking, dyspnea with age; neither symptom was associated with exposure (years worked, estimated cumulative NO2 or RP exposure). Phlegm was associated with age, smoking, and exposure. Reduced pulmonary function (FVC, FEV1, peak, flow, FEF50, FEF75) showed no association with exposure. There was one case of small rounded and one case of small irregular opacities; pneumoconiosis was not analyzed further. Compared to underground coal miners, above ground coal miners, potash miners, and nonmining workers, the study population after adjustment for age and smoking generally showed no increased prevalence of cough, phlegm, dyspnea, or obstruction (FEV1/FVC less than 0.7). Obstruction in younger salt miners and phlegm in older salt miners was elevated compared to nonmining workers. Mean predicted pulmonary function was reduced 2-4% for FEV1 and FVC, 7-13% for FEF50, and 18-22% for FEF75 below all comparison populations.

Acute respiratory illness in families exposed to nitrogen dioxide ambient air pollution in Chattanooga, Tennessee

The incidence of acute respiratory illness in families in Chattanooga, Tennessee was studied in 1972 and 1973 to determine if residents of a formerly high nitrogen dioxide exposure community continued to experience a high incidence of illness after ambient air concentrations of the pollutant had been reduced substantially. Illness data were collected by telephone at 2-wk intervals and illness rates per 100 person weeks of observation were contrasted with air pollution concentrations measured no more than 3.2 km from the home. Data were contrasted by communities designated as high, intermediate, or low pollution exposure. In 1972, higher rates of respiratory illness continued to occur in the designated high pollution area. These were associated with current higher short-term concentrations of nitrogen dioxide even though the long-term mean concentrations of the pollutant were little higher than those in the low pollution area. It was not possible to attribute the excesses in illness to specific pollutants or to specific exposure periods. However, reduction of the illness rate in 1973 associated with a strike at the primary source industry that curtailed nitrogen dioxide pollution in the high exposure community suggested that the short-term exposure may be more important than long-term exposure.

The incidence and severity of acute respiratory illness in families exposed to different levels of air pollution, New York metropolitan area, 1971-1972

The incidence and severity of acute respiratory disease was studied in families in three New York communities with different ambient levels of SO2 and particulate air pollution. Upper, lower, and total respiratory disease rates in fathers, mothers, and school children tended to be higher in the communities with higher pollution levels. Similar higher rates, however, were not observed among preschool children. Regression analyses were used to adjust rates for socioeconomic status, parental smoking, chronic bronchitis in parents, and possible indoor pollution resulting from the use of a gas stove for cooking. After these adjustments the community differences were still significant (P less than .01), for schoolchildren. The indoor pollution related to gas stoves was a significant covariate among children. The effects of smoking were inconsistent. It was not possible to attribute the higher rates observed to any specific pollutant, since both SO2 and particulate matter levels were higher in the high pollution communities, nor was it possible to attribute the excesses to current levels of exposure or to a residual effect of previous higher exposure concentrations. The fact that young children did not follow the pattern suggests the latter. It was concluded, however, that current or previous exposures to the complexity of air pollutants in New York City was at least partially responsible for increased incidences of acute respiratory disease.

Relationship of maternal smoking to morbidity and mortality of the child up to the age of five

The effect of maternal smoking during pregnancy on the morbidity and mortality of the child up to the age of five was studied in 12068 births. The children of the smokers were compared with those of controls of similar age, parity, marital status and place of residence. Perinatal mortality was no higher among the smokers, but postneonatal mortality from 28 days to 5 years was almost significantly (p less than 0.05) higher. The children of the smokers were highly significantly (p less than 0.001) more often hospitalized in pediatric departments, the difference being clearest below the age of one. The average duration of hospital admissions was longer among the children of the smokers, and similarly the numbers of visits to the doctor and hospital admissions to any hospital under the age of one were more frequent among the children of the smokers. Respiratory diseases caused highly significantly more hospitalizations among these children.

Effects of ozone and sulfur dioxide on virus growth in mice

Inhalation of ozone and sulfur dioxide inhibited influenza virus growth in the nose of mice. Ozone inhalation caused the more pronounced inhibition of influenza virus growth: 0.6 ppm ozone for 3 hours post-virus exposure almost completely inhibited influenza virus growth in the nose, whereas sulfur dioxide (6 ppm for 7 days) causes only partial inhibition of influenza growth in the nose. Neither gas altered the propagation of influenza virus in the lungs of mice. Vesicular stomatitis virus (VSV) growth was either unaffected by exposure to ozone (0.9 ppm for 3 hours) or, when ozone exposure preceeded VSV exposure, the virus may have grown to slightly higher titer. The inhibitory effect of ozone and sulfur dioxide on influenza virus growth in nasal epithelium suggests a competitive interaction between the chemical inhalant, the virus, and host tissues, with net consequences for the pathogenesis of this disease. If the effcts of these inhalants are to be properly interpreted, they should be determined for all major regions of virus growth and inhalant deposition.