Health Effects of Diesel Exhaust Emissions
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Copyright #ERS Journals Ltd 2001 Eur Respir J 2001; 17: 733±746 European Respiratory Journal Printed in UK ± all rights reserved ISSN 0903-1936 Health effects of diesel exhaust emissions A. Sydbom*, A. Blomberg#, S. Parnia#,}, N. Stenfors#, T. SandstroÈm#, S-E. DahleÂn* Health effects of diesel exhaust emissions. A. Sydbom, A. Blomberg, S. Parnia, N. *Unit for Experimental Asthma & Stenfors, T. SandstroÈm, S-E. DahleÂn. #ERS Journals Ltd 2001. Allergy Research, The National Insti- ABSTRACT: Epidemiological studies have demonstrated an association between tute of Environmental Medicine, Kar- different levels of air pollution and various health outcomes including mortality, olinska Institutet, Stockholm, Sweden. #Dept of Respiratory Medicine and exacerbation of asthma, chronic bronchitis, respiratory tract infections, ischaemic heart Allergy, University Hospital, UmeaÊ, disease and stroke. Of the motor vehicle generated air pollutants, diesel exhaust Sweden. }Respiratory Cell andMole- particles account for a highly signi®cant percentage of the particles emitted in many cular Biology Research Division, towns and cities. This review is therefore focused on the health effects of diesel exhaust, Southampton General Hospital, Tre- and especially the particular matter components. mona Road, Southampton, UK. Acute effects of diesel exhaust exposure include irritation of the nose and eyes, lung function changes, respiratory changes, headache, fatigue and nausea. Chronic exposures Correspondence: S-E. DahleÂn, Unit for are associated with cough, sputum production and lung function decrements. In addition Experimental Asthma & Allergy Research, The National Institute of to symptoms, exposure studies in healthy humans have documented a number of Environmental Medicine, Karolinska profound in¯ammatory changes in the airways, notably, before changes in pulmonary Institutet, SE-171 77 Stockholm, function can be detected. It is likely that such effects may be even more detrimental in Sweden. asthmatics and other subjects with compromised pulmonary function. Fax: 46 8300619 There are also observations supporting the hypothesis that diesel exhaust is one important factor contributing to the allergy pandemic. For example, in many Keywords: Air pollution, allergy incid- experimental systems, diesel exhaust particles can be shown to act as adjuvants to ence, animal studies, asthma exacerba- allergen and hence increase the sensitization response. tion, diesel, human exposure Much of the research on adverse effects of diesel exhaust, both in vivo and in vitro, has Received: October 5 2000 however been conducted in animals. Questions remain concerning the relevance of Acceptedafter revision October 20 2000 exposure levels and whether ®ndings in such models can be extrapolated into humans. It is therefore imperative to further assess acute and chronic effects of diesel exhaust in The authors were supportedby the mechanistic studies with careful consideration of exposure levels. Whenever possible and Swedish Heart and Lung Foundation, ethically justi®ed, studies should be carried out in humans. The Medical Research Council =project Eur Respir J 2001; 17: 733±746. No 9071), the Swedish National Road Administration =VaÈgverket) andThe Foundation for Health Care and Allergy Research =VaÊrdal). There is growing international concern regarding standthe relevance of associations foundin the the adverse health effects of air pollution. Pollution is epidemiological studies. This overview is based on a becoming an important public health problem and literature search including papers published up to the political issue, due to the rapid growth in world ®rst quarter of the year 2000. Much of the research on population andthe increasing world-widemigration the adverse effects of diesel exhaust, both in vivo and in from rural to urban areas [1]. Recent UnitedNations vitro, has been conducted in animals. Such experimental estimates have indicated that 47% of the global studies are reviewed critically and the ®ndings are population is living in urban areas. This urbanization comparedwith those in human studies. has brought with it an increasedneedfor transporta- tion andhence an increase in motor vehicle generated air pollutants. However, a large number of epidemio- Diesel emission logical studies from different parts of the world have consistently identi®ed an association between ambient Of the motor vehicle generatedair pollutants, diesel levels of air particles andvarious health outcomes, exhaust particles =DEPs) account for a highly signi®- including mortality, exacerbation of asthma, chronic cant percentage of the particles emittedin many towns bronchitis, respiratory tract infections, ischaemic heart andcities [3, 4]. Complete combustion of diesel fuel disease and stroke [2]. Indeed, the United Nations En- produces water and carbon dioxide, but use of diesel in vironment Programme has identi®ed particulate matter motor vehicles normally results in incomplete combus- pollution as the most serious air pollution problem tion andthe formation of various gases, liquidsand facedby many cities [3]. It is therefore important to solidparticles. Comparedwith petrol engines, diesel evaluate the health effects of motor vehicle generated engines produce far less carbon monoxide, but give rise pollutants in mechanistic studies, in order to under- to a greater amount of nitrogen oxides and aldehydes, 734 A. SYDBOM ET AL. which are particularly prone to cause irritation of the sensitizedindividuals in urban areas, patients with upper respiratory tract. Diesel engines also produce airway diseases such as asthma have been found more submicron soot particles that are believedto mediate adversely affected than the normal population to several of the observedadverse effects. It has been inhalation of air pollution components [17, 18] andin estimatedthat the particulate emission from diesel particular acidaerosols [19]. Various studies have engines per travelleddistance is over 10 times higher shown that overall lung deposition is increased in than the emission from petrol engines of equivalent patients with obstructedairways [20±22]. For example, power running on unleaded petrol, and over 100 times a 30% reduction in airway cross-sectional area results higher than that from petrol engines ®ttedwith catalytic in a deposition increase in the bifurcating airways of converters [5, 6]. w100% [2, 23]. There is also an interesting case-report The dose of particle deposited in the lung depends on of DEPs alone causing asthma [24]; three nonsmok- their concentration in the inhaledair andtheir size. ing railroadworkers, without any previous history of Particles with a diameter <5 mm [7, 8] reach the alveoli asthma, developed persistent asthma after acute expo- andare depositedthere, whereas particles larger than 5 sure to excessive levels of DE. This was registeredin a mm only reach the proximal airways andare eliminated situation where two locomotive units were coupled by mucociliary clearance. Previous human studies using together andthe crew riding in the secondlocomotive radioactive particles have demonstrated that 83% of unit were exposedfor 2±5 h to signi®cant levels of DE. particles with a mass median diameter of 2.5 mmare All three subjects developed asthma, which persisted deposited in the lung, whereas only 31% of particles of 1±3 yrs after exposure. Although the actual levels were 11.5 mm are deposited [9]. Recent electron microscopy never measured, it is likely that such excessive exposure studies suggest that over 80% of DEPs have a size ¡0.1 rarely occurs even in occupational situations. mm; DEPs consist of a carbonaceous core similar to carbon black, onto which an estimated18,000 different high-molecular-weight organic compounds are adsor- Experimental studies of diesel emissions bed[2]. Diesel exhaust =DE), in addition to DEPs, contains a complex mixture of gases such as carbon Human subjects monoxide =CO), nitric oxides =NO, NO2), sulphur dioxide =SO2), hydrocarbons, formaldehyde, transition Exposure challenge studies. Experimental human expo- metals andcarbon particles [10]. Regarding the health sure studies have mainly been carried out using expo- effects, recent focus has been on ultra®ne particles sure chamber set-ups with controlledDE challenges. =diameter <0.05±0.10 mm). They are highly reactive and It is critical to ensure that the methodis designedso are present in large numbers in the urban environment. as to maintain a certain relationship between the parti- They are able to penetrate the epithelium andvascular culate andgaseous components andto obtain particles walls andenter the bloodstream. It has been hypothe- of the same size andchemical properties throughout sizedthat ultra®ne particles account for the systemic the exposure series. A unique andcarefully validated effects of DEPs, such as increasedcarcinogenicity [11], system for exposures has been particularly useful [25, potentiation of autoimmune disorders [12], alterations 26]. The effects of such diesel exposures have been in bloodcoagulability andincreasedcardiovascular evaluatedin humans using symptom questionnaires, disorders [13, 14]. lung function measurements andbronchoscopy with biopsy sampling andairway lavage. Air pollution as a cause of increased In one study, healthy volunteers were exposed to DE, asthma and allergy? with a NO2 concentration of 1.5 parts per million =ppm). Bronchoalveolar lavage =BAL) 18 h after DE Parallel to the increase in air pollution, there has also exposure revealeda