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Comments Regarding
Chapter 6. "Epidemiology of Human Health Effects from
Ambient Particulate Matter"
Of the External Review Draft of the Air Quality Criteria Document for
Particulate Matter (PM)

By Henry Gong, Jr., M.D.
Professor of Medicine and Preventive Medicine
Keck School of Medicine
University of Southern California

A. GENERAL COMMENTS

In general, Chapter 6 represents a fairly complete and up-to-date summary with detailed information about the available epidemiological reports on PM-associated health effects. The numerous tables are very detailed and contain the majority of the scientific information. The text is very selective, apparently emphasizing certain study data sets and/or concepts. Overall, I do not detect any obvious or major errors in scientific content, although some people might argue that the resulting interpretation or emphasis about certain issues or topics could be re-oriented (e.g., Dr. David Bates, 6/01 review).

Chapter 6 was reviewed from the specific perspective of pediatric environmental health, taking into consideration the toxicologic, developmental, physiologic, and public health content summarized in this scientific document (as requested). [”Pediatric” in this context is inclusively used by me to include intrauterine, neonatal, postnatal, infant, childhood, and adolescent periods.] Studies with “adult” subjects or about non-pediatric issues were not specifically reviewed or commented.

B. REVIEW BY SECTION

6.1 INTRODUCTION.

There is no mention about pediatric aspects. It would have been of interest to indicate a gross figure about the increase in the overall number of pediatric reports since the 1996 PM Criteria Document.

6.2 MORTALITY EFFECTS OF PARTICULATE MATTER EXPOSURE.

6.2.2 Mortality Effects of Short-Term PM Exposure.

Not surprisingly, this and the subsequent long-term mortality section (6.2.3) report primarily total mortality, cardiovascular and respiratory mortality in adults (> 50 yr) since aging and aging with chronic cardiovascular disease are consistently reported risk factors for PM-related health effects. Age ranges are not mentioned in many studies in Table 6-1 and, when present, may designate a “< 65 yr-category” which severely masks any pediatric effects. The emphasis is clearly directed on adult health effects in very large, multi-city studies with large data bases. In addition, there are very few specific pediatric mortality studies reported to date. The reported studies (Table 6-1, pages 6-35 and 6-38) are by Loomis (1999) and Cropper (1997) regarding infant mortality and Pereira (1998) regarding intrauterine mortality. Of note is that all three studies are from outside the US, in sites which would have different chemical types of PM pollution than found in the US.

6.2.3 Mortality Effects of Long-Term Exposure to Ambient PM.

Section 6.2.3.4 (pages 6-101 to 6-104) is dedicated to population-based mortality studies in children. The discussion about six primary studies on intrauterine and early post neonatal mortality and intrauterine morbidity seems appropriate, although only one study (Woodruff, 1997) is from the US. The subsequent section (6.2.3.5) on shortening-of-life associated with long-term PM exposure (Brunekreef, 1997) is based on life table calculations on the population aged > 25 yr only. Yet, it is acknowledged that infant/childhood mortality can significantly increase the overall population life shortening over and above that estimated for adults > 25 yr. Formal calculations about the effects of PM-associated pediatric deaths on overall lifespan should be conducted based on previous and new pediatric mortality data.

6.3 MORBIDITY EFFECTS OF PARTICULATE MATTER EXPOSURE.

6.3.1 Cardiovascular Effects Associated with Acute PM Exposure.

There are no data regarding pediatric cardiovascular effects related to PM exposure, based on numerous epidemiological studies (primarily focusing on adults > 65 yr) and a limited number of individual-level studies of cardiovascular physiology. It seems plausible that changes in cardiac electrophysiology and blood viscosity or inflammation could be observed in PM-susceptible children. Thus, these outcomes are feasible to measure in children.

6.3.2 Effects of Short-Term PM Exposure on the Incidence of Respiratory Hospital Admissions and Medical Visits.

Table 6-17 is “massive” in its number of studies which predominantly include “all ages.” There are notable studies about pediatric asthma from Washington State (Norris, 1999, 2000) and Atlanta, GA (Tolbert, 2000), as well as a handful of studies from abroad. The text is surprisingly brief about children and seems relegated to the sub-section on potential susceptible subpopulations (pages 6-177 to 6-178). This sub-section acknowledges the limited number of children studies and clinical importance, in particular, for infants (<1 yr).

6.3.3 Effects of PM Exposure on Lung Function and Respiratory Symptoms.

This is the strongest section for pediatric effects: 12 studies summarized for pulmonary function and 9 for symptoms (Tables 6-19 and 6-20). Of interest is the finding that the respiratory symptoms in non-asthmatics are similar to those in the asthmatic children (approx. 7 studies in Table 6-22), whereas the lung function changes are more inconsistent (approx. 13 studies in Table 6-21). Also see table 6-23 for different effects of long-term PM exposure in asthmatic and non-asthmatic children (approx. 18 studies), including symptoms and changes in lung function, lung growth, and immune function. In total, section 6.3 appears to have the strongest, most coherent and consistent evidence for pediatric respiratory effects related to PM exposure. This is not emphasized by the Criteria Document. Whether these studies indicate greater sensitivity to PM exposure in pediatric patients than in adults remains unclear.

6.4 INTERPRETATIVE ASSESSMENT OF EPIDEMIOLOGIC DATABASE ON HEALTH EFFECTS OF AMBIENT PM.

6.5 KEY FINDINGS AND CONCLUSIONS DERIVED FROM PM EPIDEMIOLOGY STUDIES.

These are two disappointing sections for children's health effects despite their titles. Although section 6.4 initially indicates that new studies show “infants and children as a potentially susceptible population” (page 6-216), there is no subsequent mention of children's health until page 6-236. The latter refers to PM associations with asthma-related admissions. There is a final acknowledgment (page 6-270) that relatively little is known about the PM relationship to serious health endpoints, e.g., low birth weight, preterm birth, neonatal and infant mortality, emergency hospital admissions, and mortality in older children. The overall health impact of pediatric effects of PM exposure are unknown but appear to significantly underestimate impacts on total life span and well being.

C. SUMMARY

It is clear that Chapter 6 was not developed to emphasize or necessarily categorize children's health as a unique or different category, e.g., as compared to adult health. Although many epidemiological issues (e.g., confounding, pollutant colinearity, statistics, exposure monitoring) apply to both adults and children, there remains a significant paucity of important information about PM-related children's health in this draft (despite a probably substantial increase in pediatric studies since 1996). Why is this? There appears to be a major emphasis on adult health, in particular, in the elderly with chronic cardiorespiratory disease. The number of pediatric studies is limited, perhaps as a result of a lack of sufficient funding, investigators, resources, etc. Special issues related to intrauterine and neonatal mortality and morbidity have only recently been recognized. In fact, this area appears to have great potential and sensitivity for obtaining new information about the very early effects of PM exposure. More such studies in the US are needed.

The Chapter does not strongly convince the reader that children are a susceptible subgroup to PM health effects. This is perhaps because the Chapter is focusing on epidemiologic studies with relatively limited pediatric subjects. Nevertheless, if children are considered a sensitive subgroup, then there needs to be more recognition and written effort in the Criteria Document, e.g., in a separate chapter or as a distinct subsection. I strongly believe that ongoing and future pediatric PM research will help “fill in” the gaps of knowledge, resulting not only in more articles (to review) but also a demand for greater attention and consideration in the Criterion Document.