Review of the Air Quality Criteria Document for Particulate Matter

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against which changes associated with PM 10 were evaluated. In presenting data onheterogenicity, it would be of interest to include data on cigarette smoking for each city and/orregion, recognizing that cigarette smoking is the largest factor driving cardio-respiratory baselinerates.Page 6-268, lines 3-6: This statement needs expanded discussion. If the effects estimates forPM 10 hospital admissions are higher than the effects estimates (percentage-wise) for PM 10mortality, does that imply that PM is more effective (than other underlying risk factors) incausing hospital admissions as compared to mortality? If so, what is the potential explanation?Page 6-269, line 3. Useful to add a sentence "However, the statistical association of healtheffects with PM acting alone or with other pollutants should not be taken as an indicator of alack of effect of the other pollutants. Indeed, the effects of the other pollutants may be greater orless than the effects attributed to PM."Page 6-269, line 19: I suggest you omit reference to the APHEA study at this point in thedocument. While being a useful study it should not have nearly the same influence as theNMMAP study in terms of relevance to the U.S. The quality of the aerometric data was muchpoorer than that used in the NMMAP study.Page 6-270, lines 4-7: This broad statement sounds intuitively appropriate. However, I suspectit is supported by very little data and the data were not reviewed in the CD.Page 6A-2, Table 6A-1. For completeness, also present the data as rates; i.e., CVD deaths per10 6 /day. This will help in examining heterogenicity.Page 6A-11: It would be useful in the interest of completeness to include the table shown asAppendix A, Table 4 in the Staff Paper in the CD.CHAPTER 7 - DOSIMETRY – GENERAL COMMENTSThis chapter is a useful summary of what is known concerning the dosimetry of inhaledparticles. However, the chapter does not have as strong a linkage to the rest of the CD and to theissues of setting a NAAQS for PM as is needed. The chapter would be substantially improvedby providing a better linkage to aerosols characterized with PM 10 and PM 2.5 samplers at thebeginning of the chapter. At the end of the chapter, it would be useful to have a sectionsummarizing what can be predicted as the total deposition and regional deposition and retainedburden for various exposure conditions likely encountered in the ambient environment. Thisshould be done by using various PM indicators, i.e., PM 10 , PM 10-2.5 , and PM 2.5 . In doing theanalysis, it is important to recall that the indicator measurement does not describe the total PMsize distribution and mass. For example, continuous exposure to ambient air characterized ashaving either 30 :g/m 3 of PM 10 , 15 :g/m 3 of PM 10-2.5 , and 15 :g/m 3 PM 2.5 will yield the sametotal deposition irrespective of which indicator was used assuming the size distribution was thesame in all three cases. It will also be important for the normalized calculations to be done for afew key PM constituents.Throughout the chapter, care should be taken to describe deposition relative to particlesize as probabilistic phenomena. This will help in conveying the correct view that particles from0.5 to more than 10 :m can penetrate to and deposit in the nares, tracheo-bronchial region, smallairway, and alveoli—it is only the probability of doing so that changes.CHAPTER 7 - DOSIMETRY – SPECIFIC COMMENTSPage 7-2, line 28, 7.1.1 Size Characteristics of Inhaled Particles. This section needs to beexpanded to provide a linkage to measurements of PM 10 and PM 2.5 . In its present form, thissection is disconnected from the rest of the CD.A - 61
Page 7-4, Structure of the Respiratory Tract. This section would be enhanced by includingone of the well-known figures illustrating the gross structure of the respiratory tract.Page 7-9: The chapter would be enhanced by inclusion of a figure illustrating regionaldeposition in the human as a function of particle size.Page 7-24: The chapter would be enhanced by including one or more figures illustrating interspeciespatterns of total deposition and regional deposition for commonly used laboratory animalspecies and the species of interest, humans.Page 7-38: The chapter would be enhanced by including one or more figures illustrating interspeciespatterns of clearance and retained burden for commonly used laboratory animal speciesand humans.CHAPTER 8 - TOXICOLOGY – GENERAL COMMENTSThe introduction of the chapter could be strengthened with a better linkage to the epidemiologychapter. The epidemiology chapter relates findings from multiple studies showing an increase inhealth effects, primarily cardio-respiratory effects especially in susceptible populationsassociated with various PM indicators when assessed in larger populations (usually a study sizeof over 10,000 mortality or morbidity events times study days) with a relatively low prevalencerate for the adverse events of concern. Restating this at the beginning of the Toxicology chapterwill help provide a setting for consideration of the toxicological findings on PM in humans andlaboratory animals under controlled exposure conditions. In my opinion, the toxicologicalfindings have generally not been very informative, as to how PM may be pathogenic in humansor in identifying specific putative causative agents with PM. I suggest that the lack of progressrelates to the blunt “statistical” nature of current toxicological methods for tackling lowprobability of added effects when the diseases of concern have low prevalence rate outcomeseven in susceptible populations.It would also be useful if the introduction of the chapter could identify the challenge of movingbeyond characterizing whether a specific material is hazardous; i.e., capable of causing adverseeffects at any level of exposure, to the critical issue of the relevance of the findings at typicalambient concentrations of PM.The section of the chapter addressing susceptible populations should briefly consider the issue ofcigarette smoking as a risk factor. I submit that the vast majority of increased health effectsassociated with PM in adult populations are observed in smokers or former smokers. Thesepopulations contribute a disproportionate number of individuals with cardio-respiratory diseaseand, thus, are the major susceptible population at risk from PM-related disease. It is noteworthythat to date a well-defined animal model has not been found for cigarette smoking inducedcardio-respiratory disease. Smoking-related diseases develop slowly and are usually manifestedlate in life. The absence of such models is also reflected in the lack of well-developed andvalidated models of the common PM-related cardio-respiratory diseases. The minimal nature ofrespiratory disease in young rats exposed for months to heavy doses of cigarette smoke may alsohelp rationalize the relatively refractory nature of rats exposed for modest lengths of time to PMand constituents.The section of Chapter 8 on in vitro exposures lacks information that would help place the invitro studies in perspective relative to in vivo exposures of humans to ambient PM. In commentson Chapter 7, I noted the need for calculations of deposition rates and steady state burdens ofPM in humans exposed to various levels of ambient PM. Such information presented in detail inChapter 7 could be summarized in Chapter 8 and provide a metric for comparison to the levelsused in in vitro studies. A review of these in vitro studies suggests that the concentrations of PMand constituents studied are orders of magnitude in excess of any concentrations likely to beA - 62
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known, the potential causes deserve
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SCIENCE ADVISORY BOARD STAFFMr. A.
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Review of the Air Quality Criteria Document for Particulate Matter

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