United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S1 -84-008 July 1984
Project Summary
Epidemiological Study of the
Incidence of Cancer as Related to
Industrial Emissions in
Contra Costa County, California
Donald F. Austin, Verne Nelson, Bix Swain, Linda Johnson, Susan Lum, and
Peter Flessel
The purpose of this study was to
examine the relationship of lung cancer
incidence to ambient levels of air pollu-
tion in Contra Costa County. It was
suspected that the presence of heavy
industry in the county, mainly petro-
chemical plants and oil refineries, could
be a contributing factor.
Initially, an incidence analysis estab-
lished that the industrial section of the
county had an excess of lung cancer as
compared to the remaining nonindus-
trial section.
Air pollution patterns were subse-
quently determined by five permanent
air monitoring stations and 10 tempo-
rary stations which monitored the levels
of 12 air pollutants for a period of one
year.
By correlating the 1970-79 lung
cancer rates for each census tract and
tract levels of air pollution constituents,
a statistically significant relationship
between ambient air SO4 and lung
cancer in males, but not in females, was
found. However, when adjusted for the
percent of the working population cate-
gorized as blue collar, the association
was eliminated.
An interview study of 249 cases and
373 controls was then conducted.
Demographic work history, residential
history, dietary, and smoking history
questions comprised the bulk of the
data collected. Analysis indicated that
the major contribution to lung cancer in
the country was due to cigarette smok-
ing. No significant association between
lung cancer risk and measured constit-
uents of air pollution was found. Of five
broad occupational categories (indicat-
ing possible hazardous exposures) none
had any significant relationship to lung
cancer.
This Project Summary was developed
by EPA's Health Effects Research
Laboratory. Research Triangle Park, NC.
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Contra Costa County, located in the
northeastern part of the San Francisco
Bay Area, is one of 39 U.S. counties found
to have a high mortality rate for specific
cancer sites. The fact that the county also
has five major petroleum refineries and
numerous petrochemical plants, and that
68% of the total stationary air pollution in
the Bay Area originates from the county,
prompted an epidemiological study of the
incidence of cancer in Contra Costa
County. The major objective was to
determine whether industrial emissions
have a measurable effect on cancer
occurrence. The study consisted of four
parts:
1. A comparison of cancer incidence
in heavily industrialized sections of
the county to nonindustrialized
sections.
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2. Ambient air monitoring, consisting
of sampling and chemical analysis
of components of particulate pollu-
tion.
3. Correlation analysis of lung cancer
incidence rates with air pollution
constituents and census tract char-
acteristics.
4. A case-control study to identify
specific environmental factors asso-
ciated with lung cancer incidence
in the county.
Methods
Cancer Incidence
Cases included for analysis were malig-
nant, invasive, resident incidence cases
with primary sites of lung, bronchus or
trachea for the period of 1969-1978. Age
adjusted incidence rates were generated
for the industrial and nonindustrial areas.
Air Pollution Monitoring
A total of 15 hi-volume particulate
samplers were strategically sited at 13
locations in Contra Costa County and two
locations in adjacent counties.
Air particulate material was collected
every sixth day at each of the 15 sampling
sites from November 1978 to October
1979. Particulate matter was analyzed
for total suspended particulates (TSP),
benzene soluble organics (BSD), sulfate
(SO*), nitrate (N03), lead (Pb), selected
polycyclic aromatic hydrocarbons (PAH),
and mutagenic activity. Standard chem-
ical techniques were used to analyze TSP,
BSD, SO4, NO3, and Pb. Specific PAH
were separated by high performance
liquid chromatography and analyzed using
ultraviolet absorption and fluorescence.
Mutagenicity was measured using the
Ames test.
Correlation of cancer incidence data to
air pollution measurements required
interpolation of the station data to 115
census tract population centroids using a
contour mapping program called SYMAP.
Correlation Analysis
Pearson correlation coefficients for
census tract data between each air pollu-
tant constituent and the 5- and 10-year
average annual age-adjusted lung cancer
incidence rates were computed for white
males and females (two atypical tracts
were removed from the analysis). Partial
correlation coefficients for the same data
were compared using socioeconomic
variables as controls.
Case-Control Study
A case-control questionnaire study was
conducted. All cases of cancer of the
trachea, bronchus or lung among black or
white residents of Contra Costa County,
diagnosed between May 8,1980 and July
31,1981, and who were at least 35 years
of age and less than 75 years of age at
diagnosis, comprised a group of 332
eligible cases. Proxies were interviewed
where cases were too ill or were de-
ceased.
Controls were matched to cases of the
same race and sex, and 5-year age group
in each of 32 age, race, and sex strata.
Controls were selected from the general
population of Contra Costa County by
random digit dialing.
At the end of the matching and data
editing processes 19 cases and 37 con-
trols were deleted leaving 249 cases and
373 controls for analysis.
The measure of the respondent's expo-
sure to air pollution was expressed as an
estimated cumulative dose for each pollu-
tant, based on the residential history in
the county.
The respondent's smoking experience
was characterized by several parameters;
total smoking duration, total pack years
and average packs smoked per day.
The occupational exposure analysis
was based on the coding of each work
experience using occupation and industry
titles in the Census' 7950 Alphabetical
Index of Industries and Occupations.
Each blue collar job experience was
assigned to one of four broad industry
categories: construction, petrochemical,
metal, and other industries.
The duration of time worked in an
industrial category was calculated and
accumulated for each respondent.
An asbestos exposure variable was
created from various occupational cate-
gories. All shipyard occupations plus all
other jobs for which asbestos exposures
were reported were combined to form a
total duration of asbestos exposure per
respondent.
Each respondent was assigned a water
source based on the water source for
each census tract of residency at the time
of interview or, for cases, diagnosis.
Certain census tracts in Contra Costa
County contain known dumps of toxic or
chemical waste. Each respondent was
coded to indicate whether or not their
census tract of residence contained a
dump site.
To evaluate possible response variation
among controls, the number of controls
expected from each census tract was
computed and compared to the number
actually obtained. One area of the county
was overrepresented and a separate small
area of the county was underrepresented
so that these responses were appropri-
ately weighted in the analysis.
The amount of alcohol consumed per
week was determined by history and
formed an estimate of alcohol consump-
tion. A dietary questionnaire provided
estimates of weekly consumption of
certain dietary items.
Within a particular race, sex and 5-year
age group, controls were matched to
cases by age using a variable matching
ratio. Thus a case may have one or more
matched controls.
Analysis of the data was carried out
using multiple logistics regression pro-
cedures.
Conclusions
Incidence Analysis
The incidence analysis established that
when the county was divided into two
parts, the industrial section of the county
had a 40% excess of lung cancer as
compared to the nonindustrial section in
the 1975-79 time period.
Air Pollution Monitoring
The Pb map was consistent with the
fact that the largest source of Pb in the
area is the automobile and the map
conformed approximately to the paths of
freeways. Comparison of the BSO and Pb
maps suggests the contribution of the
automobile to the BSO levels may be
significant. The SO4 distribution differs
from the Pb by conforming to the indus-
trial belt. This is consistent with the fact
that SO2, the precursor of SO*, is emitted
by stationary sources, primarily chemical
industries, refineries and power plants,
all located along the industrial belt. The
patterns of the five PAH are similar to one
another and to lead.
The correlation coefficients between
pollutants for the 15 monitoring stations
show very similar relationships to those
based on the 113 census tracts which
provided validation for their use in subse-
quent correlation analyses.
Correlation Analysis
A correlation analysis of 1970-79 lung
cancer rates by census tract and various
air pollution constituents showed only
one statistically significant relationship
That relationship was between ambient
air SO* and lung cancer in males, but not
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in females. However, when controlled for
the percent of the population categorized
as blue collar workers the relationship
was eliminated.
Case-Control Study
Using multiple logistics regression anal-
ysis, all air pollution constituents were
individually reviewed for their relation-
ship with lung cancer. None of the
measured air pollutants showed a statis-
tically significant relationship. However,
because SC>4 had shown a relationship in
correlation analysis, it was included in
the study as discussed below.
Because of the relevance of smoking to
lung cancer, two statistically significant
smoking variables for males (p<.01),
average packs smoked per day and total
smoking duration, were analyzed in con-
junction with any other single variable. In
this series of analyses only one additional
variable emerged as a statistically signifi-
cant factor in reducing the risk of lung
cancer, but only for males. This was an
indirect measure of dietary intake of
vitamin A: the consumption of green
vegetables (p<0.01). A similar but not
statistically significant effect was found
for females (p<0.16).
Although no other variables suggested
a significant effect on the risk of lung
cancer, further analyses were done adding
more variables in different combinations,
to identify possibly significant relation-
ships obscured in simpler models. In
more complex analytical models the effect
of S04 dose, TSPdose, and other pollutant
doses were analyzed separately control-
ling for the effects of smoking, drinking,
diet, occupation and asbestos exposure.
Again, no variables for males, other than
green vegetables and the smoking vari-
ables emerged as statistically significant.
For females, one smoking variable, aver-
age packs smoked per day, was signifi-
cant.
The most complex analysis contained
all variables which, in simpler models,
had shown a statistically significant rela-
tionship to lung cancer, or was a known
causal factor, or was of particular interest
because of previous analyses. This anal-
ysis contained a total of 1 3 variables and
represents a "saturated" model. The
model included variables related to smok-
ing, diet, alcohol, asbestos, S04 dose,
occupation, and water source.
No additional statistically significant
relationships with lung cancer risk ap-
peared. Other than smoking, and the one
dietary factor for males, no other relation-
ships approached statistical significance.
Discussion
This analysis of case-control data sug-
gests that the major contributor to lung
cancer in Contra Costa County is smoking.
Further, smoking accounts for most of the
previously identified difference in lung
cancer incidence between the industrial
and nonindustrial areas.
There was no identified effect on lung
cancer risk contributed from any meas-
ured constituent of air pollution. The one
air pollutant (S04) significantly correlated
with male lung cancer incidence in the
indirect correlational analysis, had a
positive but not statistically significant
relationship with lung cancer risk in the
case-control analysis only when S04 level
at the current address was used as the
measurement. When a measure of total
lifetime dose of S04 from Contra Costa
County was used, no elevated risk was
apparent.
One dietary factor had a significant
(p<0.01) protective effect for males and a
similar but not statistically significant
(p<0.16) effect for females. This factor,
weekly servings of green vegetables, is a
crude measure for several dietary consti-
tuents believed to reduce the risk of
cancer of several types. Both vitamin A
and cruciferous vegetables would be
included in this dietary mea'sure. The
dietary measure, weekly servings of
yellow vegetables, did not discriminate
between cases and controls.
None of the occupational categories
had any significant relationship to lung
cancer risk in males. The occupational
categories are very broad and undoubtedly
contain specific occupations that are of
higher and lower risk. The occupational
analysis therefore likely explains less lung
cancer than potentially it could. This
supposition is supported by the fact that a
higher proportion of lung cancer among
females is explained in the analytical
models than among males. Males would
be expected to have a higher proportion of
their numbers in occupations with car-
cinogenic hazards. A more detailed anal-
ysis of the effect of various occupations
on lung cancer risk is planned.
The effect of asbestos exposure, as
measured, did not bear a statistically
significant relationship to lung cancer in
this analysis. In any subsequent analysis
a more quantitative measure of asbestos
exposure would be desirable.
There was no apparent effect of source
of drinking water or proximity to known
toxic waste dumps on the risk of lung
cancer.
These data confirm the known causal
relationship between smoking and lung
cancer. They provide some reassurance
that constituents of particulate air pollu-
tion do not contribute measurably to the
risk of lung cancer. This is consistent with
the findings of several other studies.
These data provide supportive evidence
for the protective effect of dietary factors
on cancer risk, a finding consistent with
other epidemiologic and laboratory stu-
dies. The need for a more detailed analysis
of occupation and lung cancer risk is
apparent.
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D. F. Austin, V. Nelson, B. Swain, L Johnson, S. Lum, and P. Flesselare with the
Department of Health Services, Emeryville, CA 94608.
Wilson B. Riggan is the EPA Project Officer (see below).
The complete report, entitled "Epidemiological Study of the Incidence of Cancer
as Related to Industrial Emissions in Contra Costa County, California," (Order
No. PB84-199 785; Cost: $11.50, subject to change) will be a vailable only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
•it U S GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7743
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