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Air Pollution and Fatal Lung Disease in Three Utah Counties Victor E. Archer M.D.

a

a

Department of Family and Preventive Medicine , University of Utah School of Medicine Rocky Mountain Center for Occupational and Environmental Health , Salt Lake City, Utah, USA Published online: 03 Aug 2010.

To cite this article: Victor E. Archer M.D. (1990) Air Pollution and Fatal Lung Disease in Three Utah Counties, Archives of Environmental Health: An International Journal, 45:6, 325-334, DOI: 10.1080/00039896.1990.10118751 To link to this article: http://dx.doi.org/10.1080/00039896.1990.10118751

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Air Pollution and Fatal Lung Disease in Three Utah Counties

VICTOR E. ARCHER, M.D. University of Utah School of Medicine Department of Family and Preventive Medicine Rocky Mountain Center for Occupational and Environmental Health Salt Lake City, Utah

ABSTRACT. A unique situation found in two Utah counties has made it possible to estimate the fraction of respiratory cancer and nonmalignant respiratory disease (NMRD) deaths, which are attributable to community air pollution (CAP) in one county. The two counties were very similar in many ways, including low smoking rates, until a steel mill constructed during WW II caused substantial CAP in one of them. Subsequent differences in mortality rates from both respiratory cancer and NMRD are striking. A third county, similar to many counties outside Utah, was included in the analysis for comparison. In one county, 30-40% of the respiratory cancer and NMRD deaths were attributable to CAP. In this county, NMRD deaths (but not respiratory cancer deaths) were slightly more frequent than in Salt lake County where smoking rates were twice as high.

SEVERE, ACUTE AIR POLLUTION episodes have long been recognized as contributing to death.’C2 Chronic exposure to relatively low levels of such pollution are only now being recognized as a cause of death,3-5 even though the personal air pollution from chronic cigarette smoke is an important cause of death from both malignant and nonmalignant lung d i ~ e a s e .The ~ , ~ implication of passive smoking as a cause of disease pushes cigarette smoking effects, in a quantitative sense, into the same arena as other chronic toxic air pollution agents.8-11 Chronic exposure to community air pollution (CAP) results in loss of pulmonary function and/or increased symptoms of respiratory disease12-17that progress with time.18-20Elevated respiratory cancer rates may result from low-level exposure.8-11All of these CAP-induced diseases may lead to death.21-2s Most urban air contains known mutagens and carcinogens, e.g., mineral fibers, polycyclic aromatic hydrocarbons, nitrosamines, and nitroaromatics.9,26-29 With many people breathing this material, it i s not surprising that some epidemiological studies November/December 1990 [Vol. 45 (No. 6)1

have shown definite associations between CAP and respiratory c a n ~ e r . ~ #Attempts ~ O - ~ ~ at quantitation for both malignant and nonmalignant disease resulting from air pollution have been plagued by a lack of special diseases to relate to it and by the confounding of cigarette smoke. The most widely accepted estimate for overall CAP-related lung cancer is a tentative 1 - 2%.33,34 However, in special situations, increases in respiratory cancer attributable to CAP are from 5 - 100%.32,35-39 The importance of CAP in lung injury and subsequent deaths from nonmalignant respiratory diseases (NMRDs) is even more tentative. Because of confounding by cigarette smoke, useful information has come primarily from children and nonsmokers. The risk of chronic obstructive pulmonary disease (not deaths) among nonsmokers was 15% higher in areas with high air pollution.20,40Other studies found that the frequency of some symptoms of chest disease or hospital admissions for respiratory disease was nearly double among children or nonsmokers who resided in high-CAP areas.12,16,17In325

Table 1.-Comparability

of Demographic Data from Utah Counties County

Item

Cache

Utah

Total population, 1950 Nonwhite, 1950, % Nonurban, 1950, %

33 536 0.2 49.8 57 176 3.0 32.7 70.5

81 912 0.4 20.7 218 106 3.1 9.6 166.3

274 895 1.4 15.1 619 066 5.7 0.9 125.2

Logan

Provo

Salt Lake

10 30 90.3 1370 2.6 9.0 43.9 15.6 2 281 1957

6 27 90.3 1380 2.5 9.2 34.3 14.9 2 221 1948

Total population, 1980 Nonwhite, 1980, % Nonurban, 1980, %

30-y population increase, % Major city Smokers over age 17 y, 1986, % Homes containing 1 smokers, % Mormon (LDS) 1971, %

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+

Elevation of major city above sea level (m) Mean home radon level (pCi/l) Average annual mean temperature ("C) Mean annual precipitation (cm) Persons below poverty line, 1969, % Mean per capita income, 1969, (8) Natural gas available (first year)

Salt Lake

18 48

66.7 1 340 2.5 10.3 38.9 10.2 2 972 1929

Sources: U.S. Census Data for 1950-1980; Atlas of Utah, W. L. Walquist, editor, Brigham Young University Press, Provo, Utah, 1981; Smoking Survey, Utah Department of Health, 1986; Topographic maps, U.S. Geological Survey; and History of Mountain Fuel Supply.

creased symptoms or disease incidence cannot be translated directly into increased mortality, but the association has been demonstrated repeatedly.7,z1-25 On the assumption that CAP might contribute to death from many causes, a multiple correlation study found that 7% or more of total deaths were associated with CAP.5A reanalysis of the data resulted in a confirmation of the association between CAP and death rates, but it was felt that the indicated magnitude may be too high.41 Two counties in Utah appeared to be very similar until the 1940s, when one had a sudden increase in CAP. Subsequent changes in mortality rates detailed in the present analysis indicate a substantial contribution of CAP to mortality in one of the counties. Material and Methods

Three counties in Utah were chosen for analysis. The first two (Cache and Utah counties) were chosen because of their similarity until the 1940s, and the third, Salt Lake County, was chosen to represent a more typical American city-county for comparison. Demographic and other data for the three counties are given in Table 1. The data on cigarette smoking are from a survey performed by the Survey Research Center of the University of Utah for the Utah State Health D e ~ a r t m e n tThe . ~ ~survey ignored pipe and cigar smoking, which are rare in Utah. A random sample of 500 households from both Salt Lake and Utah counties was obtained, but two other counties were included with Cache County in the sample of 500 households. This survey, completed by telephone in 1986, had a response rate of 84.3%. Data 326

were collected on all persons in a household. The most knowledgeable adult member of the household (in terms of household health status) provided survey information for her/himself and every other household member. Age and gender distribution was in accord with the 1980 census distribution. The other two counties included with Cache County were Box Elder and Rich. Their combined population was less than that of Cache County in 1980 (35 000 vs. 57 000), so the data from Cache County dominates the result. Except for the university in Cache County, the economies, ethnic composition, and religious preferences in the three counties are similar. This was the first survey of smoking made in Utah, so we cannot be certain that it applies to earlier periods. Although smoking rates in Utah probably increased after World War II, as they did elsewhere, because of cultural similarity we expect changes in Cache and Utah counties to have been similar. There were probably greater smoking changes in Salt Lake County. The Church of Latter-Day Saints (Mormon) has strong church teachings against the smoking of tob a c c ~ so , ~only ~ the less devout and non-Mormons are likely to smoke. This accounts for the small fraction of smokers in Cache and Utah counties. When a steel mill was constructed in Utah County in the early 1940s, some of the managers came from eastern states and may have been smokers, but the bulk of the laborers were drawn from other parts of Utah and were mostly Mormons. Brigham Young University in Utah County, sponsored by the Mormon church, actively discourages smoking among i t s stuArchives of Environmental Health

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Home radon levels are from a statewide survey made in 1987-1988.46 All readings made in a basement or other than a living space were discarded. This left 15 samples in Cache County, 92 in Utah County, and 267 in Salt Lake County. The measurements were made by track-etch detectors left in place for approximately 1 y. Annual deaths by age were supplied by the Utah State Bureau of Vital Records and Statistics for International Classification of Disease Codes (9th Revision ICD) 480-496 (nonmalignant respiratory diseases or "NMRD") for 1968 through 1987. They also supplied the data on ICD 160-165 (malignant disease of the lung, bronchi, and related organs) for 19801987. Earlier data on ICD 160-165 were obtained from Riggan and There were changes in death coding in 1968 and 1979, which resulted in some changes in the classification of respiratory diseases other than cancer. Data for the years 1968-1978 on the causes of NMRD deaths were therefore not fully comparable with data from earlier or later periods. Therefore, data used in the present analysis began with 1950 for respiratory cancer and with 1968 for NMRD. The ICD 480-496 categories for the 1968-1978 period include acute and chronic bronchitis, tracheitis, emphysema, asthma, hay fever, allergic bronchitis, pneumonia, and complicated influenza. These categories for 1979 (and later) include all these items and, in addition, specifically name bronchiectasis, chronic airway obstruction, and several types of emphysema and extrinsic allergic alveolitis. Because ICD 480-496 includes most NMRDs, that term is used here for all ICD 480-496 deaths, even though some NMRDs, which rarely cause death, e.g., pneu-

dents, staff, and faculty. Universities in Salt Lake and Cache counties during the period of this study took no stand on smoking. All three of the principal cities noted in Table 1are located in broad valleys adjacent to high mountains (2 100 to 3 000 m) on the east. There are lower mountains to the west of Provo and Logan, but Salt Lake City faces the Great Salt Lake on its west side. During the fall and winter months, weather inversions occur frequently in the areas of the three principal cities. Air pollutants collect in the stagnant air during these inversions and are much more visually noticeable in Provo and Salt Lake City than in Logan. Air pollution data have been collected intermittently since 1962.@Initially limited to particulates, surveillance has been expanded to include six different measurements. Available data for the three cities of present interest, along with that from three isolated towns, are summarized in Table 2. The steel mill in Provo contributes approximately 45% of the airborne particles under 10 pm in diameter, 95% of the sulfur oxides, 98% of nitrogen oxides, 86% of hydrocarbons, and 82% of carbon monoxide emissions in the ~ o u n t y .The ~ ~ ,steel ~ ~ mill and accompanying coke plant were built in Provo in the early 1940s as part of the World War II effort. It is near the population center of the valley. Subsequently, air pollution in Provo has been very noticeable, despite efforts that commenced in the 1970s to reduce emissions from the plant. In Provo, these efforts have had an effect: the annual geometric means for particulates in 1970 and 1980-1985 were 93 pg/m3 and 63 pg/ m3,respectively.@The steel mill was closed from August 1986 to September 1987, and air pollution levels were markedly lower for that period (Table 2).17,45

Table 2.-Summary

of Air Pollutant Data on Selected Utah Cities and Towns

Isolated Towns' PolI ut ant Total suspended particles ug/m3, mean' Sulfur dioxide, highest annual 24 h, ppm, mean Ozone, h/y, that exceeded national I-h, standard, mean Nitrogen dioxide, mean of annual means, ppm Carbon monoxide, d/y that exceeded national 8 h standard mean Particulate lead, mean of annual means, mg/m3

1970-1 979

Logan (Cache Co.)

1980-1 986 1980-1 986

Provo' (Utah Co.)

1970-1 979 1980-1 985

Salt Lake City

1986

1970-1 979

1980-1986

38(5)3

38(15)

40(2)

85(10)

63(6)

52(1)

93(10)

73(7)

O.Ol(6)

O.Ol(3)

O.Ol(2)

0.04(3)

-

-

0.09(7)

0.08(7)

0.0(2)

0.5(10)

1.7(6)

0.0(1)

34(10)

127(7)

0.03(5)

0.03(6)

0.02(1)

0.04(6)

0.03(7)

11.4(10)

14.7(6)

12.5(1)

32(10)

4.9(7)

0.36(4)

0.8(1)

-

0.39(5)

-

0.0(7)

O.oo(1)

O.Ol(2)

-

0.0(4) -

-

0.0(2) -

-

'Small cities and towns of Utah sampled sporadically. This column combines data for Castle Dale, Vernal and Rey. +The mean of the most central two or three stations was used for Salt Lake City and Provo. Data from suburbs were not used. *This is the arithmetic mean of TSP data recorded as annual geometric means. For 1962-1969, this mean was 72(6)in Provo and 104(8) in Salt Lake City. $Numbers in parentheses indicate the number of years for which data was collected, except for the isolated "towns" in which the number indicates town-years.

November/December 1990 [Vol. 45 (No.6 ) ]

327

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moconioses, emphyema, mediastinitis, and tuberculosis, are coded elsewhere. Population and age distribution data for the three counties are from U.S. Census data. The age distribution for 3 census years i s given in Figure 1. Estimates for intercensus years were obtained by linear interpolation. Estimates for years subsequent to the last census (1980) were made for state planning purposes.* Mortality rates for respiratory cancer and all cancer except respiratory were calculated for each of the three counties by 10-y periods, starting with 1950, except for the last period where data were not available past 1987 for respiratory and not past 1979 for all the other cancers. Mortality rates for NMRDs could not readily be divided in similar fashion. The years covered by the 8th ICD revision (1968-1978) were divided into two nearly equal periods. The years covered by the 9th ICD (1979+) were divided into two unequal parts. Because the steel plant was not operating during parts of 1986 ana 1987, it was desirable to look at deaths during those 2 y separately. With these 2 y separated, the other 7 y were combined. Based on the assumption that smoking and all other respiratory disease factors, except CAP, are equal between Cache County and Utah County, ageadjusted respiratory cancer and NMRD mortality rates found in Cache County have been subtracted from those of Utah County for comparable periods to obtain mortality rates attributable to CAP. All mortality rates were age adjusted by the direct method to the 1970 U.S. standard p o p ~ l a t i o n using , ~ ~ 5-y age intervals. Confidence limits for the various data were obtained for 95% probability by the method of Armitage,49 using prevalence or mortality rates and person-years. When these confidence limits did not overlap, numbers were considered to be significantly different. Results

Similarities and differences between the three counties are given in Table 1 and Figure 1. Each of the three counties contains a single major city that contains a major university. Prior to the 1940s, the primary industries in both Cache and Utah counties were irrigated farming, raising of livestock, and catering to their central university. The economy of Salt Lake County has been much more diverse, including agriculture, light industries, copper mining, and processing of lead, copper and uranium ores. A small plant produced pig iron in Utah County from 1923 to 1959 at a site 16 km south of the present steel mills. Its capacity was about one-fifth that of the present mill, and it was about 14 km from the population center of the valley. Because of its small size and location, it probably contributed little to population exposures. The data on cigarette smoking in Table 1 indicate that the tobacco smoking rate is approximately twice as high in Salt Lake County as in Cache and Utah counties. The smoking rate in Cache County is 10% 328

251

. \ \

n

/

-C A C H E CO

W 0

a

I

V

LL

0

0-9

10-19 20-29 30-39 40-49 50-59 60-69 70-79

8Ot

YEARS OF AGE A L L R A C E S

Fig. 1. Age distribution for the population of three Utah counties as reported in three different censuses.

(7.4-12.6) vs. 6% (3.9-8.1) in Utah County, which i s not a statistically significant difference. The fraction of homes containing a smoker i s approximately the same in Cache and Utah counties, which i s considerably lower than in Salt Lake County. The fraction of nonwhite persons, passive and active tobacco smokers, former smokers, Mormons, elevation above sea level, mean annual temperatures, mean annual precipitation, radon in homes, fraction of population below poverty line, and mean annual income were very similar for Cache and Utah counties. They differed somewhat in fraction of urban population, growth rate from 1950-1980, and total populations. The ethnic composition in the two counties is very similar, i.e., mostly whites derived from United Kingdom, Germany, and Scandinavian countries.50 The ethnic distribution in Salt Lake County is much more diverse. The age distribution of the three counties at three different censuses was very similar at ages above 50 y-the age groups that are most important for the diseases under study (Fig. 1). Natural gas became available for heating and cooking more recently in Cache than in the other two counties. Although natural gas is available only in the larger cities (and small ones near the pipeline), compressed gas (propane, etc.) became availArchives of EnvimnmewtalHealth

I

Table 3.-Mortality Rates for Respiratory Cancer and NMRD with Portions Attributable to Community Air Pollution (CAP) or to a Combination of CAP and Smoking

Cache Co. Observed rate

1950-1959 1960-1969 197&1979 1980-1 987 1960-1 987

8.0 6.3 10.4 10.6 9.3

7.2 12.2 14.8 17.0 15.0

1 96&1973 1 974-1 978 1 979-1 985 1 986-1 987 1979-1987

22.0 28.6 28.6 38.6 31 .O

36.7 33.4 46.9 62.4 50.6

Year

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Utah Co.

Observed rate x 10-5

-

x

10-5

SALT L A K E CO. CACHE CO.

I25

- 120 - 115 - I10

- 105 - 100

-

95

25 20 15

10 5 I 1960-69

I 1970-79

-

1980 8 9

YEARS

Fig. 2. Age-adjusted respiratory cancer and all other cancer mortality in three Utah counties by four time periods.

able at about the same time the pipelines were introduced and i s widely used in rural areas. Electricity became available in the major cities prior to 1900, but was uncommon in rural areas until about 1950. Natural gas is presently used for cooking in about 19% of homes in the larger Utah cities. The air pollution data summarized in Table 2 indicate that the air of Logan and of isolated Utah towns contains comparable, but minimal, amounts of the five pollutants measured over the 1970-1986 period. These amounts were substantially less than the amounts measured in the air of Provo and Salt Lake City. Prior to 1940, it i s presumed that the air of Provo November/December 1990 [Vol. 45 (No. 6 ) ]

Observed rate x 10-5

Respiratory cancer 0.0 12.3 5.9 (4.8-7.0) 17.8 4.4 (3.6-5.2) 23.0 6.4 (5.5-7.3) 23.6 5.7 (5.1-6.3) 21.7 Nonmalignant respiratory disease 14.7 (12.5-16.9) 34.8 4.8 (3.6-6.0) 32.9 18.3 (16.6-20.0) 43.5 23.8 (20.3-27.3) 48.4 19.6 (18.0-21.2) 44.6

&-----aUTAH CO.

1950-59

Salt Lake Co.

Attributable to CAP x 10-5

Attributable to CAP and extra smoking x

4.3 11.5 12.6 13.0 12.4

(3.74.9) (10.6-12.4) (11.&13.4) (12.2-13.8) (11.9-12.9)

12.8 4.3 14.9 9.8 13.6

(11.7-13.9) (3.74.9) (14.0-15.8) (8.4-11.2) (12.8-14.4)

resembled that of Logan, but the air of Salt Lake City was presumably more polluted because of size, its industries, and higher automobile traffic. As expected from the steel mill closure, the levels of all pollutants measured in Provo had a lower average in 1986 than in previous years. Respiratory cancer mortality rates for the three counties for four successive time periods are given in Table 3 and in Figure 2. The data indicate that respiratory cancer rates were nearly identical in Cache and Utah counties during the 1950-1960 period, and both had rates that were approximately 60% of the rate in Salt Lake County. During the subsequent 10-y period, the respiratory cancer rate in Utah County nearly doubled whereas that of Cache County remained approximately the same (the difference between the two was statistically significant). The respiratory cancer rates of these two counties have continued to exhibit a similar difference. The respiratory cancer rate in Salt Lake County rose steadily from 1950 onward. Respiratory cancer rates in both Cache and Salt Lake counties suggest a flattening of the curve during the 1980-1987 period, whereas the rate in Utah County continued to rise at its previous rate. The rates for all cancer, except lung, were essentially the same for Cache and Utah counties (Fig. 2) but were somewhat higher in Salt Lake County. The NMRD mortality rates for the three counties for four different time periods are given in Table 3 and Figure 3. The NMRD rates for Salt Lake and Utah counties were nearly identical from 1968 through 1985, but Utah County rates were significantly higher in 1986-1987. Both were significantly higher than Cache County rates for two of the four periods. The 1979 change in disease coding caused less change in Cache County than in the other two counties. The NMRD rates increased in all three counties in 1986-1987, but this increase was statistically significant in Utah County only. The sex ratios (M+ F) of respiratory cancers for the years studied were 2.8,3.5, and 3.8 for Cache, Utah, 329

275 T

>

0

60

- 60

CACIIECOUNIY

a 0 0

8

-.

45

-4s

30

-7 0

0

vl

r

2LLI

n

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I5

Fig. 3.

1

-

I

I

1

1968-73

1974-78

1979-85

I

I98h-87

Age-adjusted nonmalignant respiratory disease (NMRD) mortality in three Utah counties by four time periods.

and Salt Lake counties, respectively. The NMRD sex ratios were 1.2,1.7, and 1.6, respectively. The estimates for death rates attributable to CAP or to CAP plus smoking (Table 3) are unstable for the different time periods; therefore, the values given for 1960-1987 for cancer and 1979-1987 for NMRDs are considered to provide the best data for comparisons. O f the respiratory cancer deaths since 1960 in Utah County, 5.7/100 000 (38%) are considered to be attributable to CAP. In Salt Lake County, 12.4/100 000 (5706)are attributable to a combination of CAP and a higher smoking rate. O f the NMRD deaths since I986 in Utah County, 19.6/100 000 (39%) are attributable to CAP. In Salt Lake County, 13.6/100 000 (30%) are attributable to a combination of CAP and a higher smoking rate. Discussion

Substantial differences in the 20-29-y age group of the three counties (Fig. 1) that changed over time almost certainly reflect an increasing number of college students who marry and establish residency near their university. This effect i s greater in Cache and Utah counties because the university population represents a larger fraction of the total population of these counties than of Salt Lake County. This age group contributed little to the diseases analyzed here. Because of the small age differences among older groups, it is probable that the standard age adjustment adequately compensates for the age differences. The continued rise of respiratory cancer rates noted in Figure 1 for the three counties i s consistent with national trends. The flattening of the curves in two of the counties after 1980 is also consistent with 330

- 15

A

the trend. It presumably reflects a national trend of decreasing cigarette use during the preceding decade. The failure of Utah County : o follow this trend (even though it i s not statistically significant) suggests that some factor other than smoking may be important in Utah County respiratory cancers. This suggestion is strengthened by the observation that Utah County respiratory cancer rates nearly doubled from the 1950s to the 1960s, whereas the rate in its sister county, Cache, fell slightly. This divergence of cancer rates implies that a new community-wide pulmonary carcinogen (or more of an old one) was introduced into Utah County, but not into Cache County, 10 to 20 y prior to 1960. This suggests that the new carcinogen was introduced in the 1940s-the time when the new steel mill in Provo began operating. The effluent gases from steel mills (especially the associated coke operation) often increases the respiratory cancer rates among workers54-': and of residents in nearby communiThe causative agent(s) have been considered to be polyclic aromatic h y d r o c a r b o r ~ s , ~ni~,~~,~~ troarenes, or other agent^,^^,^^ attached to dust particles in the air. The well-known, urban-rural difference in respiratory cancer rates has sometimes been attributed to differences in and sometimes to CAP difference~3'.'~0along with occupational exposure differences. But no one has felt it necessary to postulate an unknown factor t o explain the urban-rural difference in respiratory cancer rates. Since Cache County i s more rural than the other two counties, its low rate i s consistent with the known relationship, but in the present situation it must be explained by CAP or occupational differences rather than smoking differences. Archives of Environmental Health

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This urban-rural difference in respiratory cancer was present in Utah non-Mormons in one studyb1 but was not found in Utah Mormons.61There i s no satisfactory explanation for this difference. Because influenza was included with NMRDs, epidemics of this disease might increase some of the Utah rates. In all but the 1986-1987 rates, there are sufficient years included to minimize the effect of an influenza outbreak. The three Utah counties included in the study are sufficiently close and communications are frequent, so it is unlikely that one could have an influenza outbreak without the others also being affected. The introduction of antibiotics in the 1940s and 1950s had a major influence on NMRD death rates. This influence, plus the change in ICD coding, made NMRDs prior to 1968 so different from later rates than no attempt to collect them for this report was made. The introduction of new antibiotics in the 1970s may have been responsible for the drop and uniform rates of NMRD deaths in 1974-1978. A similar drop during this period is evident in other U.S. cities. Instead of preventing deaths from chronic lung conditions, e.g., chronic bronchitis and emphysema, the new antibiotics would probably just postpone the deaths, as suggested by subsequent increases. The latency period for death from NMRDs caused by environmental agents i s as long as or longer than that for ~ancer.~Although we are unable to compare NMRD mortality rates for the 1950s as we did for respiratory cancer, Figure 3 indicates that NMRD has been lower in Cache County than the other two counties since 1968. During this time period, NMRD has increased more in Utah County than the other two. The excess NMRD mortality in Utah County over that in Cache County must be attributed to its greater CAP or to occupational factors. The similar excess in Salt Lake County may result from a combination of CAP and smoking, but the fact that its NMRD rates are not higher than those of Utah County suggests that CAP and smoking do not provide proportionate contributions. These data imply that the steel mill in Utah County i s responsible for the higher NMRD and respiratory cancer rates that occur in Utah County than in Cache County. This may not be entirely true because since the early 1940s, occupational exposure and traffic density have probably been greater in Utah County. Two major north-south highways (US 89 and 91) pass through all three counties, but a third (1-15) passes through Salt Lake and Utah counties, but not Cache County. In addition, Cache County has no major east-west highways, whereas Salt Lake and Utah Counties each have one. The contribution of automobile traffic to CAP may therefore be more important in both Salt Lake and Utah counties than in Cache County. Males and females of all ages who live together are probably exposed to approximately the same indoor pollution and CAP levels, but adults differ in NovembedDecember 1990 LVol. 45 (No. 611

their exposures to tobacco and occupational agents. The differences in sex ratios for both respiratory cancer and NMRD noted above suggest that Utah County men have greater occupational exposure than do Cache County men. This i s not surprising because many Utah County men work in the steel mill and related industries. The similarity of sex ratios for Salt Lake and Utah counties suggest that the extra smoking by men in Salt Lake County may contribute to these two diseases to about the same extent that occupational exposures do in Utah County. Occupational exposures cannot be the only difference between Cache and Utah counties, however, because similar differences were found among women. Their respiratory cancer rates (2.4 and 3.0 per 100 000, respectively) were higher among Utah County females for the 1960-1987 period. A similar difference was found for 1979-1987 female NMRD rates (15 and 21 per 100 000,respectively). The 1986-1987 data in Utah County, which includes the period when the steel mill was closed, indicate a continued rise in NMRD mortality (Fig. 3). This is opposite to the effect on hospital admissions for acute respiratory disease.” Acute influences on mortality by CAP appear to be related mainly to elevated SO, Because SO, levels in Utah County have always been relatively low, they probably are not responsible for the excess NMRD death rate in Utah County or in the drop in hospital admissions during 1986-1987.17 The NMRD deaths related to chronic exposure to pollutants at levels too low to cause acute deaths are apparently a result of a combination of slow cumulative injury plus the effect of aging. If current CAP exposure contributed directly to such deaths, one would expect the NMRD death rate to fall during the 1986-1987 period when the steel mill was closed. The absence of a drop in this rate in Utah County during this period suggests that the CAP chronic lung injury is irreversible after a certain point and progresses to death, even with little added environmental insult. In Table 2, mean annual averages of pollutants have been used. However, it may be that pollution peaks are more important in lung injury than average levels, especially if average levels are below a threshold level. An examination of the times that Environmental Protection Agency (EPAbrecommended levels were exceeded followed the same pattern noted for averages in Table 2; with the exception of CO, the order was Salt Lake>Provo>Logan. More to the point, however, i s the observation from other studies that there appears to be no threshold for either acute or chronic air pollution effects on the Iung.4.5,63.61 The similarity of “all cancers except lung” (Fig. 2) suggests that ethnic, population density, and growth rate differences are not factors in the lung cancer or NMRD differences between Cache and Utah counties. The higher rate of these other cancers in Salt Lake County suggests that such differences may play a part (along with more smoking) in its higher rate of lung cancer. 331

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Because natural gas for space heating was used later in Cache County, its residents have used wood and coal extensively u p until a more recent date than did Salt Lake or Utah counties residents. In one study of NMRD mortality i n a low-cigarette usage group, wood smoke appeared to be the major etiological factor.21-6s The few non-Mormons i n both Cache and Utah counties is consistent with the low frequency of tobacco smoking in those two counties. The slightly lower percentage of smokers in Utah County may simply reflect the absence of smokers at Brigham Young University, a Mormon-sponsored school. A suspicion that Mormons might under report their smoking habits has been shown to be unfounded when interviewees knew that the information was to be used for research purposes only.66 Many of the deaths included in ICD 480-486 have had pneumonia as a terminal event. Identification of underlying causes for this group on death certificates is i n ~ o m p l e t e ~because , ~ ~ , ~ ~some physicians will simply certify a death as due to pneumonia, whereas others will conscientiously record the underlying diseases such as chronic bronchitis, which led to the pneumonia. Chronic obstructive lung disease, especially, has been under rep ~ r t e d . This ~ ~ , reporting ~ has undoubtedly varied by area and over time. By lumping the NMRD deaths together, as done here, the variability of reporting by specific underlying cause i s avoided. There is, of course, some loss of sensitivity as it is unlikely that CAP contributes t o all the diseases included in ICD 480 -486. Two case-control studies investigated lung cancer frequency among residents who lived near the steel mill in Utah C ~ u n t y . They ~ ~ - used ~ ~ other cancers for control purposes. Questionnaire data were used in one study to control for occupational exposures, smoking, age, sex, and location of residences. Smoking was more frequent among the cases, and there was some suggestion that persons who worked i n the steel mill or who lived near it had higher lung cancer rates than controls, but these findings were not statistically significant. This methodology necessarily assumed that exposure varied inversely with distance from the mill and that the other cancers used would control for differences in smoking, age and social class distribution of the population at different distances from the mill. These assumptions are not necessarily correct. The authors provided no evidence to support their assumption that exposure varied inversely with distance. Because the mill emissions are released through stacks 40 to 100 ft high, one would expect that only the larger particles would be deposited near the mill. The high temperature of emitted smoke would increase the effective height of the stacks. It is likely that smaller particles (especially those of respirable size, i.e., less than 10 pn in size) would spread out within the valley and give fairly uniform exposure to most valley occupants on all but windy days. This would be especially true during 332

periods of temperature inversions when concentrations of toxic agents were highest. Inversions occur on as many as 200 d per year in Utah valleys. For plant emissions within a confined area, such as a valley, and for diseases attributed t o fine particulates it is likely that the case-control methodology used in these two studies was inappropriate. There are many factors that have a potential to cause an underestimate of the respiratory disease attributed to CAP in Utah County. These are as follows: 1. Age distribution. O f the three counties, Utah County has had the lowest fraction of persons over age 40. 2. Smoking. Although the greater percentage of cigarette smokers in Cache County was not statistically significantly different from that in Utah County, it was a little higher. This might mean that there were more cigarette-related cancers in Cache than in Utah County. 3. Indoor pollution. The slightly warmer weather in Utah County than in Cache County probably means that Cache County residents keep their windows and doors shut more days per year. This temperature difference also means that swamp coolers (the most common type in Utah) are more prevalent i n Utah County than i n Cache County. Both factors imply greater ventilation of Utah County homes. 4. Cooking and heating sources. Coal and wood burning for cooking and space heating were employed u p to a more recent date i n Cache than in Utah County, which implies more CAP from these sources.

Although no attempt is made here to estimate the magnitude of the cigarette smoke effect on respiratory cancer or NMRD mortality in any of the three counties, this can be done by use of background levels, such as given in reports by Enstrom7’ and Hamman et aI.’2 for nonsmoking populations. By using such background rates with the known smoking and air pollution indices of the three counties, it is possible to estimate the separate contributions of cigarette smoking and CAP in these three counties. The excess respiratory cancer and NMRD mortality i n Utah County, in the absence of other significant differences, i s evidence of a large component (i.e., 30-40%) being attributable to CAP. These percentages translate into 11-14 extra lung cancer deaths and 39-46 extra NMRD deaths per year in Utah County. A smaller fraction appears to be attributable to CAP in Salt Lake County. These data are comparable to a Chinese study in which 10-20% of lung cancer was attributed to air pollution in an area where smoking rates were relatively high.39The excess NMRD mortality demonstrated here for Utah County i s strong evidence that the excess acute respiratory disease i n Utah County, previously reported by Pope,17 i s a harbinger of later excess respiratory disease mortality. Archives of Environmental Health

* * * * * * * * * * The author i s grateful for the stimulation provided by Kimberly Warner; for the financial support of Professional Contracts, Inc. of Provo, Utah; and for valuable assistance from the Division of Environmental Health, the Statewide Risk Reduction Program, and the Bureau of Vital Records of the Utah Department of Health. Submitted for publication June 28, 1989; revised; accepted for publication June27, 1990. Requests for reprints should be sent to: Victor E. Archer, M.D., University of Utah School of Medicine, Department of Family and Preventive Medicine, Rocky Mountain Center for Occupational and Environmental Health, Bldg. 512,50 North Medical Drive, Salt Lake City, UT 84112.

* * * * * * * * * *

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