Smelters and mortality: Pope et al. respond.

Hidy makes several useful comments regarding our analysis of the mortality effects of a copper smelter strike in the U.S. Southwest (Pope et al. 2007). Regarding issues of atmospheric chemistry, the ambiguities of [SO.sub.4] sampling, and the role of smelterrelated trace metals and carbon, Hidy is a well-respected expert, and we do not quibble with these comments. In fact, we briefly addressed the issue of accompanying metals in our discussion, and we are in general agreement that metals, in addition to sulfur oxides and other smelter-related air pollutants, might have played a role in the observed mortality reductions.

With regard to the epidemiologic evidence, one must be careful not to over interpret the small differences in state-specific estimates of strike-period reductions in mortality. A primary statistical inference illustrated in Figure 6 of our article (Pope et al. 2007) is that similar and consistent (not significantly different) mortality decreases were observed across all four Southwest states.

Available data also suggest regional strike-related reductions in [SO.sub.4] concentrations. Based on summary data (Trijonis and Yuan 1978, Table 16), the average (and percent) decrease in [SO.sub.4] concentrations for the urban monitoring sites were 2.7 [micro]g/[m.sup.3] (38%) for Salt Lake City, Utah; 2.3 [micro]g/[m.sup.3] (51%) for Las Vegas, Nevada; 3.6 [micro]g/[m.sup.3] (62%) for Phoenix, Arizona; 2.6 [micro]g/[m.sup.3] (62%) for Maricopa county (near Phoenix); 3.4 [micro]g/[m.sup.3] (67%) for Tucson, Arizona; and 0.1 [micro]g/[m.sup.3] (2%) for Albuquerque, New Mexico. Even the remote sites of White Pine Nevada, Grand Canyon National Park, Arizona, and Mesa Verde National Park, Colorado (near the four corners of Utah, Arizona, New Mexico, and Colorado), observed 1.5 [micro]g/[m.sup.3] (76%), 1.5 [micro]g/[m.sup.3] (60%), and 1.1 [micro]g/[m.sup.3] (57%) reductions in [SO.sub.4] concentrations, respectively. The only notable exception to the region-wide strike-related reductions in [SO.sub.4] concentrations is the negligible reduction in [SO.sub.4] concentrations in Albuquerque [as noted by Hidy and discussed in our article (Pope et al. 2007)]. Regarding Nevada, data from the Las Vegas and White Pine monitoring sites indicated strike-related reductions in [SO.sub.4] similar to those observed at other comparable sites in the region.

Although our analysis of the mortality effects of a copper smelter strike has clear limitations, its unique contribution relates to the relatively simple motivation and natural experimental design. A well-defined 8.5-month copper smelter strike in the 1960s resulted in abrupt, well-documented regional reductions in [SO.sub.4] concentrations and improvements in visibility (Trijonis 1979). Available mortality data indicate a significant strike-period decrease in mortality, even while statistically controlling for time trends, mortality counts in bordering states, and nationwide mortality counts for influenza/pneumonia, cardiovascular, and respiratory deaths (Pope et al 2007). The estimated reduction in mortality is consistent with what would be expected given the average reduction in ambient concentrations of [SO.sub.4] particles and estimated mortality effects from the relevant literature. For example, both the Harvard Six Cities Study (Dockery et al. 1993) and the American Cancer Society cohort studies of long-term air pollution exposure (Pope et al. 2002) reported similar mortality risks associated with fine and [SO.sub.4] particulate pollution. Also, comparable reductions in mortality were observed following the imposition of restrictions on the sulfur content of fuel in Hong Kong (Hedley et al. 2002) and the banning of coal burning in Dublin, Ireland (Clancy et al. 2002).

Finally, it is unclear how the issues addressed by Hidy are likely to confound the estimates of strike-period mortality reduction from a well-defined statistical or epidemiologic perspective. However, these issues do "confound" how we interpret the estimated strike-period reductions in a broader context and to what extent we attribute the observed mortality reductions to smelter-source [SO.sub.4] and related pollutants. We appreciate Hidy's contributions to our efforts to interpret these and related results.

The authors declare they have no competing financial interests.

REFERENCES

Clancy L, Goodman P, Sinclair H, Dockery DW. 2002. Effect of air-pollution control on death rates in Dublin, Ireland: an intervention study. Lancet. 360:1210-1214.

Dockery DW, Pope CA III, Xu X, Spengler JD, Ware JH, Fay ME, et al. 1993. An association between air pollution and mortality in six U.S. cities. N Engl J Med 329:1753-1759.

Hedley AJ, Wong CM, Thach TQ, Ma S, Lam TH, Anderson HR. 2002. Cardiorespiratory and all-cause mortality after restrictions on sulphur content of fuel in Hong Kong: an intervention study. Lancet. 360:1646-1652.

Pope CA III, Burnett RT, Thun MJ, Calle EE, Krewski D, Ito K, et al. 2002. Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. JAMA 287:1132-1141.

Pope CA III, Rodermund DL, Gee MM. 2007. Mortality effects of a copper smelter strike and reduced ambient sulfate particulate matter air pollution. Environ Health Perspect 115:679-683.

Trijonis J. 1979. Visibility in the Southwest--an exploration of the historical data base. Atmos Environ 13:833-843.

Trijonis J, Yuan K. 1978. Visibility in the Southwest: An Exploration of the Historical Data Base. EPA-600/3-78-039. Research Triangle Park, NC:U.S. Environmental Protection Agency.

doi:10.1289/ehp.10447R

C. Arden Pope III Douglas L. Rodermund Matthew M. Gee Department of Economics Brigham Young University Provo, Utah

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