<strong>for</strong>mation <strong>of</strong> secondary particles, which are <strong>the</strong> actual toxic agents. NO 2 concentration (or itssources) might be considered as a “surrogate” <strong>for</strong> <strong>the</strong> proximal causal agent, PM.The third transparency provides diagrams <strong>for</strong> confounding and modification. As alreadymentioned, NO 2 is an unlikely confounder, given <strong>the</strong> lack <strong>of</strong> evidence <strong>of</strong> <strong>the</strong> increase in mortalitywith rising NO 2 concentrations. However, assuming that it were a risk factor <strong>for</strong> increasedmortality, <strong>the</strong> diagram represents <strong>the</strong> relationships <strong>for</strong> confounding. If NO 2 level modified <strong>the</strong>effect <strong>of</strong> PM, <strong>the</strong>n a set <strong>of</strong> relative risks describing <strong>the</strong> association <strong>of</strong> PM with mortality wouldbe derived, corresponding to <strong>the</strong> strata <strong>of</strong> NO 2 .There are a number <strong>of</strong> o<strong>the</strong>r epidemiological concepts to be considered in <strong>the</strong> <strong>Criteria</strong><strong>Document</strong>:· Confounding versus potential confounding: Throughout <strong>the</strong> document <strong>the</strong>re shouldbe careful attention to whe<strong>the</strong>r conditions <strong>for</strong> confounding are met. As noted,raising <strong>the</strong> possibility <strong>of</strong> confounding does not mean that confounding is actuallypresent.· Interaction: In places, <strong>the</strong> term “interaction” is used, generally in place <strong>of</strong> effectmodification. Interaction properly refers to <strong>the</strong> statistical terms used in a model to assesseffect modification.· The mixture problem: Admittedly, ambient air pollution is a complex mixture, <strong>of</strong>which PM is one component. None<strong>the</strong>less, <strong>the</strong> Clean <strong>Air</strong> Act has designated PM ando<strong>the</strong>r “criteria” pollutants <strong>for</strong> regulation. Study designs and data analysis are directed atattempting to characterize <strong>the</strong> effects <strong>of</strong> PM and <strong>the</strong>se o<strong>the</strong>r pollutants, and not that <strong>of</strong> <strong>the</strong>mixture itself. The criteria pollutants provide some indication <strong>of</strong> <strong>the</strong> characteristics <strong>of</strong><strong>the</strong>se mixtures and consideration <strong>of</strong> effect modification represents an indirect approach tounderstanding <strong>the</strong> toxicity <strong>of</strong> mixtures. The <strong>Criteria</strong> <strong>Document</strong> should acknowledge <strong>the</strong>mixture issue and <strong>the</strong> related requirements <strong>of</strong> <strong>the</strong> Clean <strong>Air</strong> Act specifically.· Measurement Error: This is a key issue that should be addressed in Chapters 5 and 6.Throughout <strong>the</strong> document, <strong>the</strong> concept <strong>of</strong> measurement error is considered but <strong>the</strong>underlining <strong>for</strong>mulations are variable and not necessarily accurate. The document shouldbe made uni<strong>for</strong>m <strong>for</strong> this key issue. The consequences <strong>of</strong> measurement error arecomplex and its potential consequences should be listed, at least in a general fashion.· Heterogeneity : The <strong>Criteria</strong> <strong>Document</strong> considers <strong>the</strong> heterogeneity <strong>of</strong> risk estimatesacross <strong>the</strong> United States. This heterogeneity cannot be completely explained byavailable, but crude, indicators. Heterogeneity does need to be explained, but itspresence is not a barrier to interpreting <strong>the</strong> findings on particulate matter. Additionally,summary estimates at a national level can be made in <strong>the</strong> face <strong>of</strong> heterogeneity as <strong>the</strong>yintrinsically weight <strong>the</strong> U.S. population’s exposure by <strong>the</strong> underlying distributionalmodifying factors.Interpretation <strong>of</strong> epidemiological data: Chapter 6 <strong>of</strong>fers a relatively literal interpretation <strong>of</strong> <strong>the</strong>epidemiological evidence, absent a clear biological framework. In interpreting epidemiologicaldata, <strong>the</strong> need <strong>for</strong> a foundation in biological understanding is evident. However, Chapter 6 aspresently authored, makes little connection to <strong>the</strong> substantial literature that is reviewed in o<strong>the</strong>rchapters. These connections should be made in Chapter 6 and <strong>the</strong>n rein<strong>for</strong>ced in Chapter 9.A - 77
George Taylor, PhD<strong>Air</strong> <strong>Quality</strong> <strong>Criteria</strong> <strong>for</strong> <strong>Particulate</strong> <strong>Matter</strong>: Chapter 4 (Environmental Effects)General CommentsThere are eight overarching comments on <strong>the</strong> issue <strong>of</strong> PM and ecological effects.1. The consequences <strong>of</strong> particulate matter (PM) <strong>for</strong> welfare issues are largely relegated tovisibility. The effects on vegetation and ecosystems <strong>of</strong> ambient levels <strong>of</strong> PM are regarded asbeing trivial and do not require substantive discussion. In contrast, <strong>the</strong> consequences <strong>of</strong> PM onhuman health are highly significant, well characterized and easily quantifiable in economic andhuman health dimensions. This (human health) is where <strong>the</strong> emphasis needs to be directed.2. In light <strong>of</strong> <strong>the</strong> above, <strong>the</strong> CD is VERY excessive in its discussion <strong>of</strong> PM effects. Theexcessiveness can be traced to several issues. The first is inclusion <strong>of</strong> topics that simply are notrelevant or are trivial. The second is <strong>the</strong> depth <strong>of</strong> discussion <strong>of</strong> issues that probably could besuccinctly presented in 50% or less space. The third is <strong>the</strong> “handle” applied to <strong>the</strong> issue <strong>of</strong> sulfurand nitrogen inputs. This is a PM CD and sulfur and nitrogen are small contributors to <strong>the</strong>nitrogen and sulfur inputs to landscapes. The breadth and depth <strong>of</strong> attention to nitrogen andsulfur far exceeds <strong>the</strong> environmental concern as it is related to PM.3. One <strong>of</strong> <strong>the</strong> major ecosystems affected by PM deposition and <strong>for</strong> which EPA has heavilyinvested in R&D is deposition <strong>of</strong> particles to surface waters. The most notable studies are onesfrom <strong>the</strong> Great Lakes and to a lesser degree <strong>the</strong> Chesapeake. It is important that <strong>the</strong>se systemsbe included.4. By length alone, one might conclude that <strong>the</strong> nitrogen or sulfur issue is driven by PM.This misin<strong>for</strong>mation might be translated by policy makers into thinking that changes in PM willaffect significantly such issues as nitrification, etc. Since most (>80%) <strong>of</strong> <strong>the</strong> nitrogen and sulfurthat enters continental landscapes comes through processes o<strong>the</strong>r than PM, it is not appropriateto present <strong>the</strong> in<strong>for</strong>mation as currently presented in <strong>the</strong> CD.5. The human health chapters do a creditable job <strong>of</strong> linking <strong>the</strong> sections on atmosphericchemistry with <strong>the</strong> effects on human health. In <strong>the</strong> sense <strong>of</strong> a risk assessment, <strong>the</strong>re is a tidylinkage between exposure and effects. This linkage is missing altoge<strong>the</strong>r in <strong>the</strong> section onenvironmental effects. There is no ef<strong>for</strong>t to relate <strong>the</strong> PM in <strong>the</strong> atmosphere to effects interrestrial or aquatic landscapes. The consequence is that <strong>the</strong> chapter fails one <strong>of</strong> <strong>the</strong> basicpremises <strong>of</strong> risk assessment. It is strongly recommended that <strong>the</strong> chapter better establish alinkage between exposure and effects. Or, <strong>the</strong> o<strong>the</strong>r option is to simply delete <strong>the</strong> nitrogen andsulfur topics from <strong>the</strong> PM CD.In looking over <strong>the</strong> chapters on <strong>the</strong> atmospheric chemistry <strong>of</strong> PM, <strong>the</strong>re is little quantitativediscussion <strong>of</strong> <strong>the</strong> magnitude <strong>of</strong> sulfur and nitrogen in PM. Although both are discussed, it isdifficult to see how <strong>the</strong> environmental chapter could be so “loaded” with nitrogen and sulfurwhen <strong>the</strong> atmospheric chapter does not heavily present <strong>the</strong> same in<strong>for</strong>mation.6. The final overarching issue is a derivative <strong>of</strong> <strong>the</strong> above. The conclusions portray <strong>the</strong>potential <strong>for</strong> PM to be a major stress on continental landscapes in <strong>the</strong> US. This is largely drivenby <strong>the</strong> obsessive discussion <strong>of</strong> nitrogen and sulfur and by <strong>the</strong> failure to effectively link exposurein <strong>the</strong> atmosphere to effects. The conclusion is more alarmists than needs to be portrayed and<strong>the</strong> data simply do not reflect that degree <strong>of</strong> concern. More realism is needed in <strong>the</strong> assessment.7. Deposition is missing from this CD. For ecosystems, <strong>the</strong>re is a critical linkage betweenatmosphere concentration and effects and <strong>the</strong> vector is deposition. It is important to have asection devoted to deposition so <strong>the</strong>re is a frame <strong>of</strong> reference <strong>for</strong> know what <strong>the</strong> inputs toA - 78
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known, the potential causes deserve
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SCIENCE ADVISORY BOARD STAFFMr. A.
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