Smelters and Mortality
Environ Health Perspect 115:A439-A443 (2007). doi:10.1289/ehp.10447 available via http://dx.doi.org [Online 4 January 2007]
Referencing: Mortality Effects of a Copper Smelter Strike and Reduced Ambient Sulfate Particulate Matter Air Pollution
Pope et al. (2007) provide results for reduced mortality during the 1967–1968 smelter strike in the U.S. Southwest. They ascribed mortality reduction to a decrease in ambient sulfate from the smelters. Although I found the thesis interesting, there is confounding that should be noted involving a) inconsistencies in state mortality relationships; b) the trace metal role, and possibly carbon exposure from the plant complexes; and c) ambiguities associated with SO4 sampling.
The basis for the study by Pope et al. (2007)is a study by Trijonis and Yuan (1978), who analyzed the National Air Surveillance Network (NASN) SO4 and visibility. They attributed improved visibility across the Southwest to SO4 reduction during the strike. Ambient SO4 includes SO4 from oxidation of sulfur dioxide in air (secondary) and that emitted directly (primary). NASN data [e.g. U.S. Environmental Protection Agency (EPA) 1971, 1972, 1973] indicate a strike reduction in SO4 (0.1–3.6 µg/m3) at sites in the region (Trijonis and Yuan 1978; Table 16) and not Pope et al.'suniform 2.5 µg/m3. However, the accompanying association with non–weather-related visibility change is problematic (e.g., Hidy 1984).
If the smelter SO4 was present regionally, exposure to concentration gradients of SO4, SO2, and metals would be expected with distance from the plants (Eldred et al. 1983; Malm et al. 1990). Pope et al. (2007)did not differentiate their results by distance from the smelters, but some information in their article is relevant because mortality is associated mainly with population centers (cities).
The risk estimates for New Mexico presented by Pope et al. (2007) in their Figure 6 (dominated by Albuquerque; the nearest smelter is 300 km south southwest) show high levels of mortality reduction in spite of an increase in annual average SO4 between 1966 and 1967–1968 and a negligible reduction during the strike. The mortality reduction in Nevada is largest of the four states presented by Pope et al. 2007 (Figure 6), even though Reno and Las Vegas (population centers) are upwind of the smelters and are far distant over mountain ranges from the nearest smelter at Ely. The smallest risk change is in Arizona, but reductions in Utah are similar to those of New Mexico. However, note that the population centers in Arizona (Phoenix and Tucson) and Utah (Salt Lake City) are close to smelters.
The results of Pope et al. (2007) are further confounded by the fact that trace metals and carbon accompany the emissions from plant complexes (e.g., Leipold and Chow 1998; Small et al. 1981). Local exposure to smelter emissions involves primary SO4 as well as SO2 [the apparent SO4 concentrations are biased high by a variable SO2 filter adsorption artifact (e.g., Lee and Wagman 1966; Lipfert 1994)]. Emission reduction would reduce SO4, including the bias from SO2 adsorption; metals such as copper, lead, iron, cadmium, antimony, chromium, nickel, and arsenic; and possibly carbon. Distant exposure would be enriched in secondary SO4 up to a point, followed by decline from atmospheric dilution and deposition. Pope et al. (2007) mentioned the metal–SO4 linkage but did not explore it relative to the SO4 theory. The combined exposure in sulfur oxides and metals from the smelters preset in aerosols from many sources adds further complexity to interpreting their results, including the differences in Salt Lake City and the Arizona cities.
Recent research suggests that a combination of primary SO4 and metals from oil combustion, as well as carbon emissions from motor vehicles, may be important factors in mortality risk (e.g., Grahame and Schlesinger 2007). The smelter inferences appear inconsistent with these findings.
Pope et al. (2007) focused on the strike in the Southwest. However, they excluded the same period in Montana as a cross-check on their results. In the 1960s, a major copper production complex was located in Anaconda, Montana. NASN data from nearby Helena and Glacier National Park do not show a significant change in average SO4 concentrations during the strike years (U.S. EPA 1971, 1972, 1973). This appears inconsistent with the widespread reductions seen in the Southwest. This difference could be a valuable adjunct to their results if mortality data are available.
Pope et al. (2007) provided a "natural" experiment in regional sulfur oxide (and metals) reduction. Their results should be examined further to insure that their interpretation is robust.
I thank T. Grahame, J. Watson, J. Chow, R. Henry, and P. Mueller for their assistance, and the Bay Area Air Quality Management District for loan of the NASN reports.
The author declares he has no competing financial interests.
George M. Hidy
Envair/Aerochem
Placitas, New Mexico
References
Eldred R, Ashbaugh L, Cahill T, Flocchini R, Pitchford M. 1983. Sulfate levels in the Southwest during the 1980 copper smelter strike. J Air Poll Contr Assoc 33: 110–113.
Grahame T, Schlesinger R. 2007. Health effects of airborne particulate matter: do we know enough to consider regulating specific particle types or sources? Inhal Toxicol 19:457–481.
Hidy GM. 1984. Aerosols: An Industrial and Environmental Science. New York:Academic Press.
Lee RE Jr, Wagman J. 1966. A sampling anomaly in the determination of atmospheric sulfate concentration. Am Ind Hyg Assoc J 27:266–271.
Leipold W, Chow J.1998. Preliminary results from a study of the impact of a nearby copper smelter on ambient levels of PM2.5. In: PM2.5: Fine Particle Standard, VIP-81. (Chow J, Koutrakis P, eds). Pittsburgh:Air and Waste Management Association, 177–190.
Lipfert F. 1994. Filter artifacts associated with particulate measurements: recent evidence and effects on statistical relationships. Atmos Environ 28: 3233–3250.
Malm W, Gebhart K, Henry R.1990. An investigation of the dominant source regions of fine sulfur in the western United States and their areas of influence. Atmos Environ 24A:3047–3060.
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; doi: 10.1289/ehp/9762 [Online 4 January 2007].
Small M, Germani M, Small A, Zoller W. 1981. Airborne plume study of emissions from the processing of copper ores in southeastern Arizona. Environ Sci Technol 15: 293–298.
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.
U.S. EPA. 1971. Air Quality Data for 1966 from the National Air Surveillance Networks. Report APTD-0741. Research Triangle Park, NC:U.S. Environmental Protection Agency.
U.S. EPA. 1972. Air Quality Data for 1967 from the National Air Surveillance Networks. Report APTD-0978. Research Triangle Park, NC:U.S. Environmental Protection Agency.
U.S. EPA. 1973. Air Quality Data for 1968 from the National Air Surveillance Networks. Reports APTD-1467. Research Triangle Park, NC:U.S. Environmental Protection Agency.
Smelters and Mortality: Pope et al. Respond
Environ Health Perspect 115:A439-A443 (2007). doi:10.1289/ehp.10447R available via http://dx.doi.org [Online 4 January 2007]
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 SO4 sampling, and the role of smelter-related 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 SO4 concentrations. Based on summary data (Trijonis and Yuan 1978, Table 16), the average (and percent) decrease in SO4 concentrations for the urban monitoring sites were 2.7 µg/m3 (38%) for Salt Lake City, Utah; 2.3 µg/m3 (51%) for Las Vegas, Nevada; 3.6 µg/m3 (62%) for Phoenix, Arizona; 2.6 µg/m3 (62%) for Maricopa county (near Phoenix); 3.4 µg/m3 (67%) for Tucson, Arizona; and 0.1 µg/m3 (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 µg/m3 (76%), 1.5 µg/m3 (60%), and 1.1 µg/m3 (57%) reductions in SO4 concentrations, respectively. The only notable exception to the region-wide strike-related reductions in SO4 concentrations is the negligible reduction in SO4 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 SO4 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 SO4 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 SO4 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 SO4 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 SO4 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.
C. Arden Pope III
Douglas L. Rodermund
Matthew M. Gee
Department of Economics
Brigham Young University
Provo, Utah
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.
