Review of the Air Quality Criteria Document for Particulate Matter

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formation of secondary particles, which are the actual toxic agents. NO 2 concentration (or itssources) might be considered as a “surrogate” for the proximal causal agent, PM.The third transparency provides diagrams for confounding and modification. As alreadymentioned, NO 2 is an unlikely confounder, given the lack of evidence of the increase in mortalitywith rising NO 2 concentrations. However, assuming that it were a risk factor for increasedmortality, the diagram represents the relationships for confounding. If NO 2 level modified theeffect of PM, then a set of relative risks describing the association of PM with mortality wouldbe derived, corresponding to the strata of NO 2 .There are a number of other epidemiological concepts to be considered in the CriteriaDocument:· Confounding versus potential confounding: Throughout the document there shouldbe careful attention to whether conditions for confounding are met. As noted,raising the possibility of confounding does not mean that confounding is actuallypresent.· Interaction: In places, the term “interaction” is used, generally in place of effectmodification. Interaction properly refers to the statistical terms used in a model to assesseffect modification.· The mixture problem: Admittedly, ambient air pollution is a complex mixture, ofwhich PM is one component. Nonetheless, the Clean Air Act has designated PM andother “criteria” pollutants for regulation. Study designs and data analysis are directed atattempting to characterize the effects of PM and these other pollutants, and not that of themixture itself. The criteria pollutants provide some indication of the characteristics ofthese mixtures and consideration of effect modification represents an indirect approach tounderstanding the toxicity of mixtures. The Criteria Document should acknowledge themixture issue and the related requirements of the Clean Air Act specifically.· Measurement Error: This is a key issue that should be addressed in Chapters 5 and 6.Throughout the document, the concept of measurement error is considered but theunderlining formulations are variable and not necessarily accurate. The document shouldbe made uniform for this key issue. The consequences of measurement error arecomplex and its potential consequences should be listed, at least in a general fashion.· Heterogeneity : The Criteria Document considers the heterogeneity of risk estimatesacross the 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 the findings on particulate matter. Additionally,summary estimates at a national level can be made in the face of heterogeneity as theyintrinsically weight the U.S. population’s exposure by the underlying distributionalmodifying factors.Interpretation of epidemiological data: Chapter 6 offers a relatively literal interpretation of theepidemiological evidence, absent a clear biological framework. In interpreting epidemiologicaldata, the need for a foundation in biological understanding is evident. However, Chapter 6 aspresently authored, makes little connection to the substantial literature that is reviewed in otherchapters. These connections should be made in Chapter 6 and then reinforced in Chapter 9.A - 77
George Taylor, PhDAir Quality Criteria for Particulate Matter: Chapter 4 (Environmental Effects)General CommentsThere are eight overarching comments on the issue of PM and ecological effects.1. The consequences of particulate matter (PM) for welfare issues are largely relegated tovisibility. The effects on vegetation and ecosystems of ambient levels of PM are regarded asbeing trivial and do not require substantive discussion. In contrast, the consequences of PM onhuman health are highly significant, well characterized and easily quantifiable in economic andhuman health dimensions. This (human health) is where the emphasis needs to be directed.2. In light of the above, the CD is VERY excessive in its discussion of PM effects. Theexcessiveness can be traced to several issues. The first is inclusion of topics that simply are notrelevant or are trivial. The second is the depth of discussion of issues that probably could besuccinctly presented in 50% or less space. The third is the “handle” applied to the issue of sulfurand nitrogen inputs. This is a PM CD and sulfur and nitrogen are small contributors to thenitrogen and sulfur inputs to landscapes. The breadth and depth of attention to nitrogen andsulfur far exceeds the environmental concern as it is related to PM.3. One of the major ecosystems affected by PM deposition and for which EPA has heavilyinvested in R&D is deposition of particles to surface waters. The most notable studies are onesfrom the Great Lakes and to a lesser degree the Chesapeake. It is important that these systemsbe included.4. By length alone, one might conclude that the nitrogen or sulfur issue is driven by PM.This misinformation might be translated by policy makers into thinking that changes in PM willaffect significantly such issues as nitrification, etc. Since most (>80%) of the nitrogen and sulfurthat enters continental landscapes comes through processes other than PM, it is not appropriateto present the information as currently presented in the CD.5. The human health chapters do a creditable job of linking the sections on atmosphericchemistry with the effects on human health. In the sense of a risk assessment, there is a tidylinkage between exposure and effects. This linkage is missing altogether in the section onenvironmental effects. There is no effort to relate the PM in the atmosphere to effects interrestrial or aquatic landscapes. The consequence is that the chapter fails one of the basicpremises of risk assessment. It is strongly recommended that the chapter better establish alinkage between exposure and effects. Or, the other option is to simply delete the nitrogen andsulfur topics from the PM CD.In looking over the chapters on the atmospheric chemistry of PM, there is little quantitativediscussion of the magnitude of sulfur and nitrogen in PM. Although both are discussed, it isdifficult to see how the environmental chapter could be so “loaded” with nitrogen and sulfurwhen the atmospheric chapter does not heavily present the same information.6. The final overarching issue is a derivative of the above. The conclusions portray thepotential for PM to be a major stress on continental landscapes in the US. This is largely drivenby the obsessive discussion of nitrogen and sulfur and by the failure to effectively link exposurein the atmosphere to effects. The conclusion is more alarmists than needs to be portrayed andthe data simply do not reflect that degree of concern. More realism is needed in the assessment.7. Deposition is missing from this CD. For ecosystems, there is a critical linkage betweenatmosphere concentration and effects and the vector is deposition. It is important to have asection devoted to deposition so there is a frame of reference for know what the inputs toA - 78
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