Effects of low levels of air pollution

Environmentlntcrnatid, Vol. 23, No. 2, pp.147-150,1997 copyright 01997 ElscviexScicoceud Printedin the USA. All righta maewed 0160-4120/97SlS.OO+.OO

Pergamon

PI1 SO160-4120(97)00001-9

EDITORIAL EFFECTS OF LOW LEVELS OF AIR POLLUTION

That air pollutants can cause diseasesand lead to The Clean Air Act of 1970 authorized the Adminfatalities has been known for centuries. The infamous istrator of the EPA to promulgate standards with an London fog of 1952 is often used as an example of “ample margin of safety”. This ample margin of safeharmful effects of air pollutants. During the winter of ty was intended to insure that the lack of knowledge 1952, the concentration of air pollutants in London did not causea delay in the promulgation of a standreached2-3 g/m’and the death rate during that period ard or standardsthat were grossly in error and thereby increased 2-3 fold. All of these happenedwithin one would not protect that segmentof the population that week. There have been several other episodesof dra- was known to be particularly sensitive to exposure to matic increasesin air pollution in several other parts air pollutants. The subsequentamendmentsto the Clean Air Act, of the world resulting in a corresponding increase in including its most recent comprehensive version enfatalities. Up to 1978, in the U.S., the Public Health Service acted in 1990, continue to include a similar language was responsible for all health-related activities inwhich initially was intendedto assistthe development of standardsat the time the scientific information was cluding environmental health. However, upon the lacking. Clearly, more than 20 years of extensive reformation the U.S. Environmental Protection Agency search has or should have changed the need for a re(EPA), most environmental health activities of the quirement that was meant to be temporary. Public Health Service were transferred to the EPA. Recently, the EPA initiated the process to revise Thus, the Clean Air Act of 1970 mandated the development of National Ambient Air Quality Standards NAAQS both for ozone and particulate matter. In ac(NAAQS) for a number of pollutants. Accordingly the cordance with the requirements of the law, the EPA’ has prepared a number of documents for both pollufirst NAAQS was published in 1971. The Clean Air Act required the preparation of a Criteria Document tants as follows: (CD) containing relevant scientific information, prior to the establishmentor revision of NAAQS, a require- Air Qualiv Criteria for Ozone and Related Photochemical Oxidants. Three volumes: EPAl6OOfP-931 ment that is valid to this date. The first CD was pre004aF,EPA/6OO/P-93/004bF and EPA/600@93/04cF. pared by the Public Health Service in anticipation of Washington, D.C.: U.S. Environmental Protection the passageof the Clean Air Act of 1970. Agency; July 1996. Discussions preceding enactment of the 1970 law showed a remarkable agreement among the staff of governmental agenciesand members of the scientific Air Quality Criteria for Particulate Matter. Three community that the neededscientific information was volumes:EPA/6OO/P-95/001aF, EPA/6OO/P-95100 1bF, either unavailable or inadequate.Therefore, the Conand EPA/600@95/001cF. Washington, D.C.: U.S. gress included in the law sufficient discretion for the Environmental Protection Agency; April 1996. Administrator of the EPA to insure that standards could be developed despite the acknowledged lack of scientific information. At the time, many scientists Review of ihe National Ambient Air Quality Stand&& within the EPA anticipated that it would take at for Particulate M&er: Policy Assessmentof Scientific least 10 years and possibly 15 years to gather the Information. OAQS Staff Paper EPA-4521 R-96-O13. Research Triangle Park, NC: U.S. Environmental neededscientific information to have a final NAAQS for major pollutants. Protection Agency; July 1996. 147

148

Review of the National Ambient Air Quality Standard for 0,. Assessmentof Scientl$c and Technical Information. OAQS Staff Paper EPA-452\R-96-007. Research Triangle Park, NC: U.S. Environmental Protection Agency; June 1996. In addition, the following relevant book was published recently that provides useful information: Particles in Our Air: Concentrations and Health Eficts. Richard W ilson and John D. Spengler, eds. Cambridge, MA: Harvard University Press; 1996. According to the Clean Air Act, the NAAQS must be based on science. Although the Administrator of the EPA must take uncertainties of scienceinto consideration and provide for an ample margin of safety, the core of the decision is basedon science.Hence,in order to insure adequacy of science,the law provides for a Clean Air Scientific Advisory Committee (CASAC). Ozone

The current standard dates back to 1987 when a thorough literature searchwas conducted.At that time, the standard was set at 0.12 ppm (120 r&/L), to be averagedover one hour. In addition, if within a threeyear period this standard is exceeded,the region is consideredto be out of compliance.EPA’s experience indicatesthat the current 0.12 ppm, if averagedover an eight-hour period, would correspondto 0.09 ppm (90 nL/L). Hence, the new rule of the EPA would reduce the standardsto 0.08 nL/L. EPA’s justification for the tightening of the standard is to “provide additional protection for children and asthmatics”. However, there are severalmajor flaws in EPA’s decision. The first and most important flaw deals with ozone exposure.The CD for ozone indicatesa variable relationship between outdoor and indoor ozone concentration. This variability is not predictable.In effect, the concentration of ozone indoors can be as high as 80% of that outdoors, or as low as 10% or below. Accordingly, any statistical associationbetweenexposure of ozone (as measured by the outdoor monitoring stations) and an effect must be attributed to chance. The second flaw relates to controlled studies. Essentially all controlled studies show no appreciable adverse effect at current standard level. Information included in the CD provides no new evidence that children or asthmaticsare any more or any less sensitive to exposure to ozone at levels of the current standard than information included in the previous

Editorial

CD which was used to develop the current standard. Therefore, EPA’s decision must have been based on criteria other than science. One approach proposed by the EPA for the ozone standard must be given particular consideration. Instead of hourly averaging, EPA appears to favor an option to permit averaging the concentration over an eight-hour period. This approach would provide an equal level of protection but would reducethe problem of non-compliance. It should be therefore seriously considered. Particulate Matter

The criticism of the ozone standard pales as compared to the apparent shortcomings of the proposed new standard for particulate matter. The initial standardwas set for total suspendedparticles (TSP) at 260 pg/m3,averagedover 24 hours, not to be exceeded by more than once per year, with an averagegeometric mean of 75 ug/m”. Recognizing the physiology of inhalation of particulate matter, the standard was changedto cover particles of 10 urn or less, known as PM,, The limit was set at 150 pg/m3, with an annual arithmetic mean of no more than 50 pg/n?, not to be exceededmore than once per year. EPA now proposesto add a new standard for particulate matter of 2.5 pm or less. The new fine particulate matter standard sets a limit of 50 urn/n? with an arithmetic annual mean of 15 ug/m3. EPA claims that these fine particles at levels permitted by the current standard are responsible for an entire set of adversehealthy effects. Although the significance of indoor air was recognized during the preparation of the previous standard, it could not be considered. Meanwhile, there is a voluminous literature indicating that the exposure to pollutants is dominated by indoor air. It is recognized that U.S. residents spend about 85% of their time indoors, about 7.5% in or near a vehicle, and only about 7.5% outdoors. The claim of the EPA to protect children becausethey spend more time outdoors than adults is unreasonable,not only becausethe CD provides no data to support it, but also becauseeven a doubling of the time spent outdoors would constitute an insignificant amount of time as compared to the time spent indoors. The book by W ilson and Spengler provides the best scientific attempt to estimatethe level of fine particle exposure indoors, based on their outdoor concentration. However, theseauthors agreethat fixed monitor-

Editorial

ing stationsare poor surrogatesfor exposureto people. Even if such a relationship could be established, the current risk assessmentby the EPA must be questioned. The CD includes some attempts to establish a relationship between the concentration of PM,, to the concentration of PM,,5. However, the EPA does not seem to have a clear position on this important issue. Hence, if there is a reasonably constant relationship betweenthese two segmentsof particulate matter, the need for a new standardmust be questioned. If such a relationship does not exist, appropriate data are necessary to establish the exposure and thus the potential benefits that may be derived from the new standard. The idea that one can perform a risk assessmentwithout having the exposuredata is equivalent to driving a car without a having steering wheel. The proposed standardfor PM,, is largely basedon epidemiological studies. The EPA relies upon both ecological and cross-sectional studies. Ecological studies attempt to relate death rates over a geographical area to air pollution in that area. In contrast to these,cohort studiescompare two groups. However, a valid epidemiological study requires not only a statistical association but also a reasonablelevel of causation. During the sixties, the requirement of causation was modified by accepting also a series of other parameters that in totality can be used to weigh the evidence. All epidemiological studiesthat lack the requirement of causationmust be used with extreme caution. There are numerous examples of incorrect conclusions that can be derived from statistical association. For example, there is a statistically significant correlation between the number of babies born and the increasein the population of storks in Germany during the fifties. Thus, the statistical association would suggest that storks are bringing babies. Similarly, there is a likely statistical associationbetweenthe consumptionof soft drinks and ice cream and drowning during the summer time around beaches. Statistical associations can be real, but also can be caused by chance or confounders not considered in the study. For example, none of the epidemiological studies includes consideration of allergens, and many microorganisms that can be present indoors. Neither ecological nor cohort studies can claim consideration of microorganisms and allergens which are likely to be the dominant factor in causing adverse effects, particularly in asthmatics and other sensitive populations.

149

Table 1. Ambient concentrationof particulatematter,mortality rate causedby COPD, and mortality causedby asthmain recentyears.

Year

Mean concentration PM,, Mm3

Mortality per 100 000 population Chronic obstructive pulmonary diseases

Asthma

1988

32.1

19.6

1.4

1989

31.9

19.6

1.4

1990

29.4

19.7

1.4

1991

29.1

20.1

1.5

1992

26.7

19.9

1.4

1993

26.0

21.4

1.4

Table 1 shows the annual mean concentration of PM,, as reported by the EPA and the occurrence of chronic obstructive pulmonary diseases(COPD) and Asthma, respectively, as reported by the Centers for Disease Control and Prevention (CDC). The correlation coefficient computedfor PM,, vs asthma is -1.9%, implying that there is a slight probability that exposure to particulate matter reducesmortality causedby asthma. In contrast to asthma, the statistical association with COPD has a correlation coefficient of -77.7%, indicating a strong probability that reducing exposure to particulate matter has a high probability to increase the mortality associatedwith COPD. Thus, these data would lead to the conclusion that decreasingthe concentration of particulate matter in air increased the death rate causedby COPD, thereby causing one to use caution in interpreting other epidemiological data. Despite the statistical association,there is no biologically plausible mechanismsuggestingthat exposure to particulate matter enhances the health of those afflicted with COPD. An unstated theoretical assumption in EPA’s risk assessment,but claimed for particles in the book by Wilson and Spengler, is that there is no threshold for adverse effects to exposure to ozone or particulate matter. There is neither a biological mechanism nor a valid experiment supporting such a hypothesis. The evidencepoints to a threshold, although that threshold may not be the same for everyone. The EPA is poorly advisedto disregardthe impact of allergens and microorganisms that may be present outdoors but are known to occur abundantly indoors. It is possible and probable that a great deal of reported

150

asthmatic attacks and the observed COPD are the consequenceof thesematerials. In most cases,the occurrence of these materials cannot be attributed to a specific industry, and thus, their mitigation is considerably more difficult. Thus, after three decadesof intense environmental research, it is becoming increasingly clear that simplistic approaches are no longer appropriate to solve problems related to the protection of human health and the environment.

Editorial

A standardthat is basedon lack of data and assesses the sciencespeculatively cannot claim that it protects people - including children. Finally, the book by W ilson and Spengler must be consideredone of the clearestdescriptionsof scientific aspects of particles in air. Although the authors represent a specific scientific point of view, they are clearly leaders in their respective fields. This book is highly recommended. A. Alan Moghissi