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Criteria air pollutants and toxic air pollutants.

This review presents a brief overview of the health effects and exposures of two criteria pollutants--ozone and particulate matter--and two toxic air pollutants--benzene and formaldehyde. These pollutants were selected from the six criteria pollutants and from the 189 toxic air pollutants on the basis of their prevalence in the United States, their physicochemical behavior, and the magnitude of their potential health threat. The health effects data included in this review primarily include results from epidemiologic studies; however, some findings from animal studies are also discussed when no other information is available. Health effects findings for each pollutant are related in this review to corresponding information about outdoor, indoor, and personal exposures and pollutant sources.

Air Pollutants↗

[Short-term effects of exposure to urban air pollution on human health in Europe. The APHEA Projects (Air Pollution and Health: a European Approach].

During the '80s, evidence was collected that air pollutants concentrations close to, or lower than, air quality standards could negatively influence public health at short term, i.e. within a few days. The European Union financed, between 1993 and 1995, the study "Short term effects of Air Pollution on Health: a European Approach using epidemiological time-series data" (APHEA-1 project), involving more than 25 millions inhabitants in 15 cities, investigated between 1977 and 1991. In this paper, the main results, already published in various scientific journals, are reported. The health effects were studied as mortality for natural causes, cardiovascular and respiratory diseases, and as emergency hospital admissions for all respiratory diseases, bronchial asthma, and chronic obstructive pulmonary disease (COPD). The pollutants whose measures were available for the analysis are sulphur dioxide (SO2), nitrogen dioxide (NO2), particulate matter (PM) measured either as black smoke or total suspended particulate, and ozone (O3). The analysis was carried out by each participating group following a detailed protocol, defined during various workshops, through the construction of Poisson regression models, adjusted for autocorrelation and overdispersion, accounting for variables influencing the daily count of deaths, such as long time trends, season, temperature, day of the week. This paper reports the results of the meta-analysis, performed using the values of each city, as relative risk of dying or being admitted to hospital associated with increases of 50 micrograms/m3 in the 24 hours average concentrations of each pollutant. The daily number of natural deaths was associated with increases in the levels of PM, SO2, O3, and NO2. Cardiovascular and respiratory deaths were associated with increases of the levels of PM, SO2, and O3; cardiovascular deaths were associated also with increases of NO2 concentrations. Emergency hospital admissions for the whole group of respiratory disorders are less consistently associated with PM, SO2, and NO2, whereas there is evidence of association with O3. COPD admissions are related to the air pollutant levels, especially those of O3. Lastly, NO2 levels may play a role in exhacerbating asthma, and SO2 levels can have an effect on asthma in children. A second study is currently going on, involving over 40 millions residents in 34 cities. The aims of this project are: to evaluate the dose-response relationship, to investigate on synergy among pollutants, on the "harvesting" phenomenon, on the geographical differences inside Europe and with the U.S. through the collaboration with a similar American study now in progress. The existence of an association between daily variations in the levels of urban air pollution and adverse health effects was confirmed in Europe. This association is weak, but it involves the whole resident population, so it is a major cause of concern from the public health point of view.

Adolescent↗

Mercury pollution in two typical areas in Guizhou province, China and its neurotoxic effects in the brains of rats fed with local polluted rice.

Guizhou province, which located in southwestern of China, is an important mercury (Hg) production center. This study was to investigate the environmental levels and ecological effects of mercury in two typical Hg polluted areas in Guizhou province. In addition, to improve the understanding of the neurotoxic effects of Hg, a rats based laboratory study was also carried out in this study. Samples of water, soil, plants, crops and animals collected from Wanshan mercury mine area, Guzhou province, were analyzed by mercury analyzer. The effects of Hg contaminated rice on the expression of c-jun mRNA in rat's brain and the expression of c-JUN protein in cortex, hippocampus were observed using reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemical methods. The results showed that the mercury contents in most environmental samples of aquatics, soil, atmosphere and the biomass of corn, plant and animals, were higher than the national standard and the corresponding data from unpolluted area. It was found mercury pollutions were significant in soil and air. In the laboratory study, the expression of c-jun mRNA and its protein was significantly induced by Hg polluted rice collected from local area. Selenium could reduce the Hg accumulation in the body and had antagonist effect on Hg in terms of the expression of c-jun mRNA and c-JUN protein. The environmental data and Hg levels in different creatures collected in this study will facilitate the environmental and ecological risk assessment of Hg in the polluted areas. It was urged to be alert of mental health problem in human beings when any kind of Hg-polluted food was taken. More efforts should be performed to protect the local ecosystem and human health in the mercury polluted area of Wanshan, Guizhou province of China.

Air Pollutants↗

An index directly indicates land-based pollutant load contributions of domestic wastewater to the water pollution and its application.

As indices directly indicate land-based pollutant load contributions to public water pollution, pollutant load per capita flowing into the water body (PLCwb) for the drainage areas of inner city rivers in Chiba City, Chiba Prefecture, Japan, was analyzed. It was reaffirmed that PLCwb was different by the drainage area. For example, the biochemical oxygen demand (BOD) load per capita flowing into the water body (PLCwb-BOD) was calculated as 0.83 g BOD person(-1) day(-1) for population served with wastewater treatment plant (WWTP). In regards to the three types of on-site domestic wastewater treatment methods in Japan: 0.4-2.1 g BOD person(-1) day(-1) for combined jokaso (CJ), 4.5-21 g BOD person(-1) day(-1) for simple jokaso (SJ) and 4.3-19 g BOD person(-1) day(-1) for night soil treatment (NST). In regards to nutrient parameters of the three on-site treatment methods, population weighted average of PLCwb was [corrected] almost the same, however, relatively small PLCwb was [corrected] observed for CJ and SJ comparing to that for NST expecially in the drainage areas with smaller reaching ratios. [corrected] Environmental accounting housekeeping (EAH) books for domestic wastewater were prepared based on the analysis results as the application of the indices. EAH books are effective tools for water pollution mitigation in public water bodies. The results of the preliminary correlation analysis of the indices showed that high-efficiency treatment methods including WWTP, agriculture village wastewater treatment facility (AVETF) and CJ are effective in reducing pollutant load flowing into the water body, and that PLCwb have second-order equation relationships with population density of the drainage area. Judging from these characteristics and the analytical results of this study, PLCwb may be useful as an index for demonstrating the benefit of wastewater treatment in reduction of water pollution in the water body.

Cities↗

Air pollution and daily mortality in a city with low levels of pollution.

The concentration-response relationship between daily ambient inhalable particle (particulate matter less than or equal to 10 micro m; PM(10)) concentrations and daily mortality typically shows no evidence of a threshold concentration below which no relationship is observed. However, the power to assess a relationship at very low concentrations of PM(10) has been limited in studies to date. The concentrations of PM(10) and other air pollutants in Vancouver, British Columbia, Canada, from January 1994 through December 1996 were very low: the 50th and 90th percentiles of daily average PM(10) concentrations were 13 and 23 micro g/m(3), respectively, and 27 and 39 ppb, respectively, for 1-hr maximum ozone. Analyses of 3 years of daily pollution (PM(10), ozone, sulfur dioxide, nitrogen dioxide, and carbon monoxide) concentrations and mortality counts showed that the dominant associations were between ozone and total mortality and respiratory and cardiovascular mortality in the summer, and between nitrogen dioxide and total mortality in the winter, although some association with PM(10) may also have been present. We conclude that increases in low concentrations of air pollution are associated with increased daily mortality. These findings may support the notion that no threshold pollutant concentrations are present, but they also raise concern that these effects may not be effects of the measured pollutants themselves, but rather of some other factor(s) present in the air pollution-meteorology mix.

Air Pollutants↗

Persistent pollutants urban rivers sediment survey: implications for pollution control.

The impacts of diffuse urban sources of pollution on watercourses are quantified. A survey of nine urban streams in Scotland for persistent pollutants in stream sediments is described, together with sediments from SUDS ponds. Determinands reported are: PAHs, total hydrocarbons, and toxic metals (As, Zn, Ni, Pb, Cu, Cr, Cd). Results highlight hydrocarbons as a major urban pollutant, and show significant sediment contamination by toxic metals. The metals that occurred in the highest concentrations varied across the nine streams, but Pb, Cr, Ni, Zn and Cu most frequently present exceeded sediment quality standards. The pattern of contamination by PAHs suggested that pyrolytic sources were more ubiquitous and present in greater quantities than oil spill sources in these urban catchments. Exceptions were the sites below industrial estates. The findings indicate that four levels of activity will be needed to control urban diffuse sources of pollution: reductions in quantities of toxic pollutants used by manufacturers in the motor and construction industries; housekeeping measures to minimise storage and handling risks for oil and chemicals; public engagement to minimise polluting activities such as dumping oil and chemicals, and private car use; use of SUDS technology, including retro-fits in the worst affected urban areas.

Cities↗

Foraminiferal proxies for pollution monitoring in moderately polluted harbors.

Benthic foraminifera are increasingly used as environmental bio-indicators, especially in polluted environments where their sensitivity to pollutants may be expressed by a modification of the assemblages. Eighteen sediment samples were collected in September 2000 in five harbors located in moderately polluted estuaries on the coast of Vendée (France) for the study of foraminiferal assemblages. Ten heavy metals and 13 PAH have been analyzed from the sediments. The marine to continental estuarine gradient has a prevalent influence on the foraminiferal distribution. However, the results show that foraminiferal density and species richness of the assemblages decrease with an increase in heavy metal and PAH concentration, and therefore may be used as pollution indicators. Moreover, the more polluted areas are dominated by the tolerant pioneer species Haynesina germanica that may be used as bio-indicator of pollution, mainly in the uppermost areas.

Animals↗

Validity of annoyance scores for estimation of long term air pollution exposure in epidemiologic studies: the Swiss Study on Air Pollution and Lung Diseases in Adults (SAPALDIA).

In air pollution epidemiology, estimates of long term exposure are often based on measurements made at one fixed site monitor per area. This may lead to exposure misclassification. The present paper validates a questionnaire-based indicator of ambient air pollution levels and its applicability to assess their within-area variability. Within the framework of the SAPALDIA (Swiss Study on Air Pollution and Lung Diseases in Adults) cross-sectional study (1991), 9,651 participants reported their level of annoyance caused by air pollution on an 11-point scale. This subjective measure was compared with annual mean concentrations of particulate matter less than 10 microm in diameter (PM10) and nitrogen dioxide. The impact of individual factors on reported scores was evaluated. Nitrogen dioxide concentrations at home outdoors (measured in 1993), smoking, workplace dust exposure, and respiratory symptoms were found to be predictors of individual annoyance scores. Regression of population mean annoyance scores against annual mean PM10 and nitrogen dioxide concentrations (measured in 1993 and 1991, respectively) across areas showed a linear relation and strong correlations (r>0.85). Analysis within areas yielded consistent results. The observed associations between subjective and objective air pollution exposure estimates suggest that population mean scores, but not individual scores, may serve as a simple tool for grading air quality within areas. Reported annoyance due to air pollution should be considered an indicator for a complex environmental condition and thus might be used for evaluating the implementation of environmental policies.

Adolescent↗

Lung function and long term exposure to air pollutants in Switzerland. Study on Air Pollution and Lung Diseases in Adults (SAPALDIA) Team.

The effect of long-term exposure to air pollutants was studied in a cross-sectional population-based sample of adults (aged 18 to 60 yr; n = 9,651) residing in eight different areas in Switzerland. Standardized medical examination included questionnaire data, lung function tests, skin-prick testing, and end-expiratory CO concentration. The impact of annual means of air pollutants on FVC and FEV1 was tested (controlling for age and age squared, sex, height, weight, educational level, nationality, and workplace exposure). Analyses were done separately for healthy never-smokers, ex-smokers (controlling for pack-yr), for current smokers (controlling for cigarettes per day and pack-yr smoked), and for the whole population. Significant and consistent effects on FVC and FEV1 were found for NO2, SO2, and particulate matter < 10 microm (PM10) in all subgroups and in the total population, with PM10 showing the most consistent effect of a 3.4% change in FVC per 10 microg/m3. Results for ozone were less consistent. Atopy did not influence this relationship. The limited number of study areas and high intercorrelation between the pollutants make it difficult to assess the effect of one single pollutant. Our conclusion is that air pollution from fossil fuel combustion, which is the main source of air pollution with SO2, NO2, and PM10 in Switzerland, is associated with decrements in lung function parameters in this study.

Adolescent↗

[A follow-up study on renal tubular dysfunction in women living in the cadmium-polluted Jinzu River basin in Toyama, Japan. Part 1. Changes in the level of exposure to cadmium after soil replacement of polluted paddy fields and the related effects on the prognosis of renal tubular dysfunction].

A follow-up study on renal tubular dysfunction was carried out on 193 female inhabitants of the cadmium (Cd)-polluted Jinzu River basin and 40 reference subjects living in an adjacent area in 1994-95. They were 54 to 70 years old when the initial examination was conducted in 1983-84. In the Cd-polluted Jinzu River basin, extensive reclamation of polluted rice fields has been conducted since 1979; as a result, the average Cd concentrations in polished rice consumed by the subjects in the 1994-95 study (0.12 ppm in 1994, 0.14 ppm in 1995) were significantly lower than those in the 1983-84 study (0.26 ppm in 1983, 0.29 ppm in 1984). The average Cd levels in urine in the follow-up study (7.5 micrograms/g Cr. in 1994, 7.7 micrograms/g Cr. in 1995) were also significantly lower than those in the initial study (13.5 micrograms/g Cr. in 1983, 13.3 micrograms/g Cr. in 1984). However, the mean values for urinary excretion of beta 2-microglobulin (beta 2-m) (3.9 mg/g Cr. in 1994, 3.7 mg/g Cr. in 1995) and glucose (203 mg/g Cr. in 1994, 251 mg/g Cr. in 1995) in the follow-up study were significantly higher than those obtained at the initial examination (2.0 mg/g Cr. and 125 mg/g Cr. in 1983 and 1.1 mg/g Cr. and 78 mg/g Cr. in 1984 for beta 2-m and glucose excretion, respectively). The magnitude of increase in urinary excretion of beta 2-m and glucose in inhabitants of the Cd-polluted area was significantly higher than that of the inhabitants of the reference area. Moreover, an increase was observed in the prevalence of renal tubular dysfunction determined by urinary beta 2-m exceeding 10 mg/g creatinine and urinary glucose exceeding 150 mg/g creatinine only among inhabitants of the Cd-polluted area; it is noteworthy that 31 new cases of renal tubular dysfunction were observed in the follow-up study. These results indicate that renal tubular dysfunction among inhabitants of the Cd-polluted Jinzu River basin is irreversible and progressive, and many new cases of renal tubular dysfunction were also noted over a period of 11 years, despite the fact that Cd exposure had decreased over the past 11 years.

Aged↗

Air pollution in asthma: effect of pollutants on airway inflammation.

OBJECTIVES: The objective of this review is to examine the impact of air pollutants on airway inflammation, with an emphasis on the interaction of the effect of ozone, particulate matter, and endotoxin exposure and immunoglobulin E-mediated airway inflammation. DATA SOURCES: This review examines the National Ambient Air Quality Standards and sources for different types of air pollution, as well as undertakes a review of epidemiologic and human challenge studies which address the impact of air contaminants in asthma and allergic inflammation. RESULTS: Epidemiologic and human challenge studies both demonstrate that ozone and endotoxin exposure can exacerbate allergic inflammation in the airway. Conversely, allergic processes may enhance individual response to air pollutants as well. CONCLUSIONS: Ozone and particulate matter are both important agents in inducing asthma exacerbation. However, these pollutants have not been implicated in development of immunoglobulin E responses to neoantigens. Decreased exposure to these pollutants or a better understanding of the processes by which they impact the airway may be useful in decreasing asthma severity.

Air Pollutants↗

Short-term effects of air pollution on hospital admissions of respiratory diseases in Europe: a quantitative summary of APHEA study results. Air Pollution and Health: a European Approach.

The Air Pollution and Health: a European Approach (APHEA) project is a coordinated study of the short-term effects of air pollution on mortality and hospital admissions. Five West European cities (i.e., London, Amsterdam, Rotterdam, Paris, Milano) contributed several years of hospital admissions data for all respiratory causes. In the current study, the authors describe the results obtained from the quantitative pooling (meta-analysis) of local analyses. The diagnostic group was defined by ICD 460-519. The age groups studied were 15-64 y (i.e., adults) and 65+ y (elderly). The air pollutants studied were sulfur dioxide; particles (i.e., Black Smoke or total suspended particles); ozone; and nitrogen dioxide. The pollutants were obtained from existing fixed-site monitors in a standardized manner. We used Poisson models and standardized confounder models to examine the associations between daily hospital admissions and air pollution. We conducted quantitative pooling by calculating the weighted means of local regression coefficients. We used a fixed-effects model when no heterogeneity could be detected; otherwise, we used a random-effects model. When possible, the authors investigated the factors correlated with heterogeneity. The most consistent and strong finding was a significant increase of daily admissions for respiratory diseases (adults and elderly) with elevated levels of ozone. This finding was stronger in the elderly, had a rather immediate effect (same or next day), and was homogeneous over cities. The elderly were affected more during the warm season. The Sulfur dioxide daily mean was available in all cities, and it was not associated consistently with an adverse effect. Effects were present in areas in which more than one station was used in the assessment of daily exposure. Some significant associations were observed, although no conclusion that related to an overall particle effect could be drawn. The effect of Black Smoke was significantly stronger with high nitrogen dioxide levels on the same day, but nitrogen dioxide itself was not associated with admissions. The ozone results were in good agreement with the results of similar U.S. studies. The coherence of the results of this study and other results gained under different conditions strengthens the argument for causality.

Adolescent↗

Sex ratios of births, mortality, and air pollution: can measuring the sex ratios of births help to identify health hazards from air pollution in industrial environments?

OBJECTIVES: To compare the sex ratios of births and mortality in 12 Scottish localities with residential exposure to pollution from a variety of industrial sources with those in 12 nearby and comparable localities without such exposure. METHODS: 24 localities were defined by postcode sectors. SMRs for lung cancer and for all causes of death and sex ratios of births were calculated for each locality for the years 1979-83. Log linear regression was used to assess the relation between exposure, sex ratios, and mortality. RESULTS: Mortalities from all causes were consistently and significantly higher in the residential areas exposed to air pollution than in the non-exposed areas. A similar, but less consistently significant, excess of mortality from lung cancer in the exposed areas was also found. The associations between exposure to the general air pollution and abnormal sex ratios, and between abnormal sex ratios and mortality, were negligible. CONCLUSIONS: Sex ratios were not consistently affected when the concentrations or components of the air pollution were insufficiently toxic to cause substantially increased death rates. Monitoring of the sex ratio does not provide a reliable screening measure for detecting cryptic health hazards from industrial air pollution in the general residential environment.

Air Pollutants↗

Environmental epidemiology applied to urban atmospheric pollution: a contribution from the Experimental Air Pollution Laboratory (LPAE).

Systematic investigation on the effects of human exposure to environmental pollution using scientific methodology only began in the 20th century as a consequence of several environmental accidents followed by an unexpected mortality increase above expected mortality and as a result of observational epidemiological and toxicological studies conducted on animals in developed countries. This article reports the experience of the Experimental Air Pollution Laboratory at the School of Medicine, University of São Paulo, concerning the respiratory system and pathophysiological mechanisms involved in responses to exposure to pollution using toxicological and experimental procedures, complemented by observational epidemiological studies conducted in the city of São Paulo. It also describes these epidemiological studies, pointing out that air pollution is harmful to public health, not only among susceptible groups but also in the general population, even when the concentration of pollutants is below the limits set by environmental legislation. The study provides valuable information to support the political and economic decision-making processes aimed at preserving the environment and enhancing quality of life.

Air Pollutants↗

Noninvasive assessment of liver detoxification capacity of children, observed in children from heavily polluted industrial and clean control areas, together with assessments of air pollution and chloro-organic body burden.

The liver is an important target organ in exposure to foreign substances or their metabolites. Early changes in the metabolic capacity of the liver may be a first sign of the effect of an exposure and an indication of an early (pre)pathological process. For the noninvasive testing of this metabolic capacity, a special diagnostic tool has been developed and demonstrated under real exposure conditions. The main questions investigated were (1) whether the liver detoxification capacity of children is affected by long-term low exposure in a highly polluted area and (2) to what extent redevelopment in once heavily polluted industrial areas contributes to improvement in the health measured in the children from the changed detoxification capacity. Kindergarten children from a heavily polluted industrial area and a control area were observed over a prolonged period during redevelopment of the industrial area. The liver's detoxification capacity was assessed with a stable-isotope-based diagnostic test, the [(15)N]methacetin test. In addition, the region-specific external exposure (indicator components were chlorinated compounds) and internal load were measured. The difference in the children's internal load between the exposed and control groups reflected the differences in exposure (exposed children had an internal load 2.3 times greater than that of the control children). The exposed children showed a 6% lower liver detoxification capacity. A reduction in pollution by about 70% as a result of remediation was reflected in improved liver detoxification capacity, and the difference between the polluted and control areas was no longer significant. Prolonged exposure to low concentrations of xenobiotics can disturb hepatic functioning. The proposed test can be used as a tool to determine the effects of multicomponent exposure and is well suited for bioeffect monitoring.

Acetamides↗

Seasonal variation of trace metal concentrations in the digestive gland of the Mediterranean mussel Mytilus galloprovincialis: comparison between a polluted and a non-polluted site.

Seasonal changes in metal (Cu, Fe, Mn, Pb, and Zn) concentrations were observed in the digestive gland of the Mediterranean mussel, Mytilus galloprovincialis, from both a polluted and a non-polluted population. Digestive gland of mussels from the polluted site showed metal concentrations appreciably higher than in non-polluted organisms, especially for Pb (up to 160 micrograms/g d.w.), Mn (up to 300 micrograms/g d.w.), and Fe (up to 8,500 micrograms/g d.w.), whereas the two populations showed maximum mean values, respectively, of 34 and 20 micrograms/g d.w. for Cu and 170 and 120 micrograms/g d.w. for Zn. Over 1 year (1991), differences between maximum and minimum values were moderate only in the unpolluted organisms. During gametogenesis, while the metal concentrations (expressed as microgram/g dry weight) decreased in the digestive gland, the tissue burden (as microgram) in that organ remained nearly constant or increased slightly. The apparent decrease in metal concentrations was probably due to the penetration of gonadic tissues into the digestive gland during gametogenesis, which biologically diluted metal concentrations in mussels from both the polluted and unpolluted populations. The effect of mussel size on trace metal concentrations in the digestive gland was demonstrated during different stages of the reproductive cycle. Higher concentrations were found in smaller organisms; however, during the spawning period, due to the fact that this is not a synchronous process within a population, the organisms exhibit a high variability in digestive gland weight which can mask this relationship when digestive gland weight is used as a size-index and as a parameter of the trace metal digestive gland burden.

Animals↗

Prevalence of asthma and mean levels of air pollution: results from the French PAARC survey. Pollution Atomosphérique et Affections Respiratoires Chroniques.

Among the possible explanations for the recent increase in the prevalence of asthma in several countries, air pollution is one of the foremost public health concerns. Data from the "Pollution Atmosphérique et Affections Respiratoires Chroniques" (PAARC) survey collected in 24 areas of seven French towns during 1974-1976 were reanalysed to assess the relationship between the prevalence of asthma and the following air pollutants: sulphur dioxide (specific (SO2) and acidimetric methods), total suspended particles (TSP), black smoke (BS), nitrogen dioxide and nitric oxide. Correlation coefficients between annual mean levels of pollution and prevalence of asthma in the different areas were first calculated. Random-effects models were then estimated. Of the 20,310 adults aged 25-59 yrs, 1,291 (6.4%) were found to be asthmatics as well as 195 (6.1%) of the 3,193 children aged 5-9 yrs. A geographical correlation between asthma and annual mean level of SO2 (ranging 17-85 microg x m(-3)) was found (r=0.45, p=0.01) in adults. No relationship was found in children. After controlling for age, educational level, smoking, and geographical clustering with a multivariate random-effects model, the relationship remained significant in adults for SO2 (odds ratio for a 50 microg x m(-3) increase=1.24, confidence interval 1.08-1.44, p=0.0035). It also remained significant when taking into account only the people reporting their last asthma attack occurring after settling in the study area. These results are consistent with the known short-term effects of SO2 in asthma and demonstrate the necessity for further studies on delayed effects of air pollution in respiratory diseases.

Adult↗

Combined effects of aerobiological pollutants, chemical pollutants and meteorological conditions on asthma admissions and A & E attendances in Derbyshire UK, 1993-96.

BACKGROUND: The effect of outdoor aeroallergen exposure in asthma may be enhanced by air pollutants, including ozone, nitrogen dioxide and particulates, and by certain weather conditions. It is not yet established whether these interactions are important in determining asthma morbidity at the population level. OBJECTIVE: We have investigated the joint effects of aeroallergens, rainfall, thunderstorms and outdoor air pollutants on daily asthma admissions and Accident and Emergency (A & E) attendance using routinely collected data between 1993 and 1996 from Derby in central England. METHODS: Daily counts during the aeroallergen season of grass and birch pollen, basidiospores, Didymella, Alternaria and Cladosporium, maximum 1 hour ozone and nitrogen dioxide and daily average black smoke measurements, all made in the vicinity of the city centre, were categorized in tertiles. Rainfall was classified as dry, light (</= 2 mm) or heavy (> 2 mm). The modifying effect of outdoor pollutant levels, and rainfall or the occurrence of a thunderstorm, upon the effects of individual aeroallergens on asthma admissions and A & E attendance were investigated by fitting appropriate interactions in log linear autoregression models with adjustment for potential confounders. RESULTS: We found a significant interaction between the effects of grass pollen and weather conditions upon A & E attendance, such that the increase with grass pollen count was most marked on days of light rainfall (adjusted rate ratio for >/= 50 vs < 10 grains/m3 at lag 2 days = 2.1, 95% CI 1.4, 3.3). Asthma admissions increased with Cladosporium count. We found no statistically significant interactions between effects of any individual aeroallergen and outdoor air pollutant upon either measure of asthma morbidity. CONCLUSIONS: Rainfall and thunderstorms are important effect modifiers in the relation between grass pollen and measures of acute asthma morbidity. Interactions between ambient levels of aeroallergens and chemical pollutants in the Derby area do not play a major role in determining asthma admissions and A & E attendance.

Air Microbiology↗