Environmental Health Effects Research Series
ASSESSMENT OF DISEASE RATES AMONG SEWER
WORKERS IN COPENHAGEN, DENMARK
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Offifie of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
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The nine series are:
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EPA-bOO/1-78-007
January 1978
ASSESSMENT OF DISEASE RATES
AMONG SEWER WORKERS IN COPENHAGEN, DENMARK
by
R.B. Dean
LunDean Environmental Company
Cincinnati, Ohio 45230
Contract No. CA-7-2761-A
Project Officer
Herbert R. Pahren
Field Studies Division
Health Effects Research Laboratory
Cincinnati, Ohio 45268
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Health Effects Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
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FOREWORD
The U.S. Environmental Protection Agency was created because of increas-
ing public and government concern about the dangers of pollution to the
health and welfare of the American people. Noxious air, foul water, and
spoiled land are tragic testimony to the deterioration of our natural envi-
ronment. The complexity of that environment and the interplay between its
components require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solu-
tion and it involves defining the problem, measuring its impact, and search-
ing for solutions. The primary mission of the Health Effects Research Lab-
oratory in Cincinnati (HERL) is to provide a sound health effects data base
in support of the regulatory activities of the EPA. To this end, HERL con-
ducts a research program to identify, characterize, and quantitate harmful
effects of pollutants that may result from exposure to chemical, physical, or
biological agents found in the environment. In addition to valuable health
information generated by these activities, new research techniques and meth-
ods are being developed that contribute to a better understanding of human
biochemical and physiological functions, and how these functions are altered
by low-level insults.
This report provides an assessment and discussion of the health of sewer
maintenance workers in Copenhagen, Denmark, and mortality statistics of such
workers. With a better understanding of the health effects, measures can
be developed to reduce exposure to potentially harmful materials.
R. J. Garner
Director
Health Effects Research Laboratory
111
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ABSTRACT
Sewer workers in Copenhagen, Denmark have a higher death rate than the
comparable male population. An alarmingly high proportion of the deaths
occur within the year that employment terminates. Attempts to correlate the
statistics with sick leave records or chemicals in the environment have so
far not been successful. Sewer workers experience a high rate of gastro-
intestinal tract disorders which they associate with chemical odors and in-
fectious agents. They have elevated levels of gamma globulins. Analytical
work has not yet identified any agents that might be responsible for the
observed death rates or the gastro-intestinal problems. Biological ex-
aminations of stool specimens have not been made.
This report was submitted in fulfillment of Contract CA-7-2761-A by
LunDean Environmental Company under the sponsorship of the U.S. Environmental
Protection Agency. This report covers a period from May 1977 to August 1977.
xv
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CONTENTS
Foreword iii
Abstract iv
1. Introduction 1
2. Conclusions 3
3. Analysis of Reports 4
References 10
TABLES
Number Page
1. Comparison of Sick Leave for Permanently Employed Sewer Workers
(1959-1973) and City Office Workers (1964) 5
2. Death Statistics for Sewer Workers,
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SECTION 1
INTRODUCTION
The health and working conditions of sewer workers in Copenhagen have
been investigated and reported in a series of documents published and dis-
cussed over the period 1975-1977. In April 1974 the union representing the
sewer workers requested the University of Copenhagen to investigate environ-
mental and health problems of Copenhagen's sewer workers. The study was
assigned to J. M{5rkholdt Andersen and Tage Egsmose MD, Associate Professors
at the University's Institute of Hygiene. Some financial assistance was
provided by the municipality from the sewer department's budget.
The preliminary report came out in December 1975 (1), and was published
with minor corrections in April 1976 (2). Additional death statistics were
presented later (4), and sick leave data were provided by the Municipal-
ity (3) as a response to the original preliminary report. In April 1977 a
second report was published based on medical consultations with sewer work"
ers (5), and a preliminary report of blood and urine chemistry was issued
about the same time (6). Personal communications (7, 8) have greatly helped
to interpret the foregoing reports.
In addition to the documents already referred to there have been many
news media articles and discussions over the past twenty years concerning
the health of sewer workers. This report will attempt to extract the hard
data as it applies to the health of sewer workers. Conclusions based on
questionnaires will not be considered in detail.
The municipality of Copenhagen serves 600,000 permanent residents, ap-
proximately 200,000 transients and commuters and has an industrial load equi-
valent, on a BODs basis, to 1,600,000 additional persons for a total equi-
valent load of 2.4 million. The sewage is strong, of the order of 750 mg/1
BOD. At the present time sewage is screened to remove rags and large ob-
jects and discharged through two outfalls directly to the waters between
Copenhagen and Sweden. A modern treatment plant using high rate activated
sludge with the UNOX pure oxygen process is under construction and is ex-
pected to be in operation in 1979 (4). One small plant uses primary treat-
ment and digestion (8). Over the entire period covered by the reports sewer
work involved primarily cleaning and maintenance of sewers, manholes, screens
and pump stations. It did not include sewer construction or mechanical shop
work such as repairing motors and pumps. About eighty permanently employed
workers were classified as sewer workers in 1976. Management of the sewers
is a division of the City Engineers office. The sewer workers are members
of the Earth and Concrete Workers Union and the Highway Department Workers
Club.
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"The Sewer Workers Report" (2) is based on four separate studies:
1. Responses to a questionnaire to sewer workers about health and
working conditions.
2. A study of sick leave records from January 1957 through December
1973 for sewer workers and a control group of all city office
workers.
3. A study of death records compared with national mortality statis
tics (4) .
4. Assessment of reports of analyses of sewer atmospheres for toxic
substances.
The report "Sewer Work and Health" (5) is based on clinical consulta-
tions with 82 out of 97 sewer workers in 1976. The same group and two con
trol groups were subjected to a battery of tests on blood and urine (6).
The reports are considered together.
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SECTION 2
CONCLUSIONS
Mortality statistics show that sewer workers die earlier than Copen-
hagen males of comparable age, many of them soon after termination of their
employment. The sewer workers complain of nauseating odors and a high in-
cidence of gastro-intestinal tract disorders. They have elevated levels of
gamma globulin but no other significant differences from control groups.
The available evidence is insufficient to assign a specific cause for their
poor health and reduced life expectancy. It seems probable that biological
and chemical insults, caused in part by lax observance and poor enforcement
of safety regulations and discharge restrictions have all contributed to
the adverse survival expectancy of this group.
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SECTION 3
ANALYSIS OF REPORTS
QUESTIONNAIRES AND SICK LEAVE RECORDS
Responses to the questionnaires as well as the medical consultations
clearly show that sewer workers consider their job to be unhealthy and un-
safe. A detailed analysis of the responses to the questionnaires is not in-
cluded because the responses are difficult to reproduce and are liable to be
influenced by local customs and recent news items concerning the environment.
Sick leave records are also difficult to analyze because the decision to take
sick leave is made by the worker and not on the basis of a medical examina-
tion. In Denmark sick leave pay for permanently employed Municipal workers
is 100 percent of base pay but does not include extra pay for "dirty work".
Medical confirmation of short illness is seldom required.
Table 1 compares sick leave for permanently employed sewer workers over
the period 1959-1973 with male office workers of comparable ages in the year
1964. At all ages above 30 years the sewer workers take more leave than of-
fice workers. Most significant is the high percent of sick leave taken by
sewer workers over 50 years of age. Workers over 60 years of age take an
average of one day in five sick leave.
The rebuttal from the City Engineers Office (3) gives the comparative
sick leave data shown below, unfortunately without age adjustment.
Sick leave rates of unskilled wage earners in the City Engineers
Office, not adjusted for age (3) .
1973 1974
Parking meter collectors 6.12% 6.48%
Street cleaners 7.07% 7.31%
Sewer workers 7.63% 8.77%
Street repairmen 8.06% 9.42%
Garden and park workers 10.64% 10.86%
Workshop and Warehousemen 10.30% 12.17%
There are relatively few transfers between work groups (8). The high sick
leave of garden and park workers is attributed to hazardous working condi-
tions, as in trees, rather than a selection of older workers for garden and
part work. There is no evidence that sewer workers take more sick leave than
other manual workers although sewer workers certainly take more sick leave
than office workers (2,7).
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TABLE 1. COMPARISON OF SICK LEAVE FOR PERMANENTLY EMPLOYED SEWER WORKERS (1959-1973) AND CITY
OFFICE WORKERS (1964) (2, 7)
Sewer Workers
Sick days Year days* %Sick days
Office Workers
Sick days Year days*
%Sick days
24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65+
6
65
564
1536
1954
1408
1382
1044
496
127
1032
9288
19608
33024
31992
27520
15480
10664
2408
688
0.6
0.7
2.9
4.7
6.1
5.1
8.9
9.8
20.6
18.5
345
510
840
915
1560
3107
3640
4116
6880
3072
23736
35088
48160
62952
89440
82216
96320
101136
118336
66048
1.5
1.5
1.7
1.5
1.7
3.8
3.8
4.1
5.8
4.7
AYear days equals number of working days per year times number of employees in age groups,
i.e. days worked plus sick days. Three weeks vacation not included.
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The second study (5) was recommended by the authors of the first report
(2), and was financed by the municipality to investigate health problems
among sewer workers. Matched control groups from the city gardeners and
from office workers were chosen by the Municipal personnel office and their
blood and urine chemistry were determined (6); however not enough money was
supplied for a medical examination of the controls. This report confirmed
the questionnaires of the first report (2) and concluded that sewer workers
have a higher than normal incidence of acute symptoms of gastro-intestinal
disorders including nausea, vomiting and diarrhea. It further concluded
that the disorders are directly related to the intensity of exposure to sew-
er odors and splash. Half of the workers have had diarrhea in the past year
and 10% say they have experienced it one or more times a week. The fre-
quency of the disorders is related to current exposure and not to years of
experience. Few workers go to their doctors for treatment for gastro-intes-
tinal disorders but seem to consider them to be a part of the job. No ex-
aminations of stool specimens were made.
The doctors making the 81 examinations found 21 cases of occupational
disease which were reported to the Health Service doctor. An additional 25
cases were not reported because the workers did not wish it.
Many workers consider that odors rather than infectious agents cause
their gastro-intestinal disorders, e.g, one told the doctor, "suddenly you
get this stench in the face and then you know you will have stomach trouble
for the next few days" (5).
In a publication from the Occupational Health Office a steward said,
"longer vacations are necessary because we have a very special problem get-
ting accustomed (to the sewer environment). After a vacation of a week or
more one is almost always sick the first two or three work days with vomit-
ing, nausea, headaches and smarting of the eyes. We don't know what we owe
it to but it is most likely the chemicals in the sewer" (10).
ANALYTICAL DATA
The chemical analyses reviewed (2) provide no evidence for toxic chemi-
cals that might be related to acute gastro-intestinal problems. Solvent va-
pors occasionally exceeded hygienic standards for one hour's exposure and
hydrogen sulfide once reached 13 ppm versus a standard of 10 ppm. There is
little doubt that industrial discharges frequently contribute high levels of
organic vapors to the sewer contrary to regulations. Many of these dis-
charges are of short duration and are therefore difficult to identify. The
effect of these vapors on the health of sewer workers is at present only
conjecture. One station was found to have three times the allowable level
of benzene when a sick worker was replaced (5). There was, however, no di-
agnosis of benzene toxicity in the sick man, who is now dead (8). One case
of high lead in the blood was found in a worker who had been cleaning heat-
ing coils in a sludge digester (5, 8). The job was very dusty and the dried
sludge had a lead content over 100 mg/kg. The worker was transferred to
another job and his blood Pb levels returned to the normal range. Masks are
specified for workers in dust or spray but the worker may not have been us-
ing his mask effectively. The second study (5) includes photographs of a
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worker who was using a high pressure spray to clean screens but was not using
a mask, and of a worker who was not using his gloves to handle a wooden ball
used to clean the sewer, again contrary to regulations.
In the report of medical consultations with sewer workers (5), the doc-
tors conclude that the working environment is responsible for a high level
of acute disorders of the gastro-intestinal tract. They also conclude that
sewer workers have a high level of chronic problems including fatigue, dif-
ficulty in concentrating, headaches, dizziness as well as psychic problems.
The preliminary report of clinical laboratory analyses (6) showed little
essential difference over a wide range of chemical parameters between sewer
workers and the control groups chosen by the personnel office. In many
cases the sewer workers, as a group, fell between office workers and garden
workers. The only significant difference was an elevated level of gamma
globulins among sewer workers, suggesting that they have had more infections
than the other groups. The biochemical examinations have not yet been com-
pleted.
DEATH RATES AMONG SEWER WORKERS
The initial study (1) showed 24 deaths among 142 sewer workers who had
been employed for at least one year in the period 1957-1973. This is sig-
nificantly greater than the death rate for all Copenhagen men of comparable
ages. An updated report (4) added 9 additional deaths that had not been
supplied to the authors at the time of the original study. Table 2 groups
the workers by years of employment and shows the comparable death rates for
Copenhagen males based on the 1975 statistical yearbook. Death rates in
Copenhagen do not change very much from year to year.
Workers who have spent 1 to 8 years in sewer work in the 15 year study
period have a death rate indistinguishable from the city rate. For the next
8 years of employment the rate is more than twice the expected rate. A
statistical analysis of the data shows the following: The chi-squared test
on the two groups 1-8 years and 9-16 years is highly significant. Individ-
ual groups were tested against the Poisson distribution. Death rates for
workers with 9-12, 11-12, 15-16+ and 13-16+ years of employment were all
significant at the 5% level or better. Therefore one can conclude that work-
ers who have spent more than 8 years in Copenhagen sewers have about twice
the death rate of all Copenhagen males. The normal death rate during the
first 8 years of employment also reflects an adverse environment since sewer
workers are selected from healthy able-bodied males who should have a death
rate significantly below the city average (11).
When the causes of death of the original 24 cases were examined (2),
the only outstanding difference from the national average was for cancer of
the pancreas. Of 9 cases of cancer recorded on the death certificates there
were 3 cases of cancer of the pancreas, 2 cases of lung cancer and 1 each
of four other cancers. The expected rate of pancreatic cancer was only 0.3
among 24 deaths of men over 25, therefore 3 deaths are highly significant.
There were no additional cases of pancreatic cancer among the 9 additional
deaths reported (4,7). A recalculation based on an expected 0.414 deaths out
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TABLE 2. DEATH STATISTICS FOR SEWER WORKERS (4)*
Years of
sewer work
1-2
3-4
5-6
7-8
1-8
9-10
11-12
9-12
13-14
15-16+
13-16+
9-16+
Number
of deaths
N
1
2
3
2
8
6
8
14
4
7
11
25
Expected Chi squared Poisson Cumulative
deaths (N-E) ^/E Probability for N or
E more deaths in %
2.0
2.3
2.6
2.7
9.6 0.27
3.0 8.2
2.8 0.75f
5.8 0.25tf
2.5 24.
3.1 3.7f
5.6 2.6f
11.4 16.22
1-16+
33
21.0
16.49
tt
Statistical calculations by R.B. Dean
Significant at the 5% level
tt,,.
Significant at the 0.5% level
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of 33 shows a Poisson probability of 0.8% for 3 or more deaths. The death
certificates are currently being studied for other possible correlations (7) .
Over 40% of dead former sewer workers died within the calendar year in
which they stopped working (2). The calculation is based on 210 sewer work-
ers of whom 111 left the work force in the years 1959-1973. Thirty-two of
these had died by the end of 1976, 13 of them in the year that employment
terminated. The ages at death of 12 of the 13 men who died in the year that
employment terminated were evenly distributed between 51 and 58 years. Some
of these men were ill when they stopped working. Put another way, 12% of the
former workers died in the calendar year in which they terminated work. For
comparison only 1% of Copenhagen males aged 55 and 3% of those aged 65 will
die within the twelve months following their respective birthdays. Compara-
tive data for other occupations in Copenhagen is not available.
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REFERENCES
1. Andersen, J.M., L. Egsmose and T. Egsmose. "Unders^gelse af arbejdsfor-
hold for kloakarbejdere ansat ved K^benhavns kommune" (Study of working
conditions of sewer workers employed by the municipality of Copenhagen).
University of Copenhagen Institute of Hygiene, Dec. 1975.
2. Andersen, J.M., L. Egsmose and T. Egsmose. "Kloakarbejder rapporten"
(The Sewer Workers Report). FADL's Forlag, Copenhagen, April 1976.
3. Gulstad, E. Unpublished communication. City Engineers Office, Copen-
hagen, Feb. 1976.
4. Egsmose, T., and J. Nyboe. "Verdr^rende d^delighedsunders^gelsen i Klo-
akarbejder rapporten" (Concerning studies of death in the sewer workers
report). University of Copenhagen Institute of Hygiene, Jan. 1976.
5. Jansson, P., and H. Klausen. "Kloakarbejde og Helbred" (Sewer Work and
Health). Eks-skolens Trykkeri ApS., Copenhagen, April 1977.
6. Lous, P., "Forel^big rapport til Stadslaegen" (Provisional report to
the Public Health Office). Bispebjerg Hospital, Copenhagen, May 1977.
7. Egsmose, T., Personal communication. Institute of Hygiene, University
of Copenhagen, 1977.
8. Malchow-M«5ller, 0. Personal communication. City Engineers Office,
Dept. of Sewage, Copenhagen, 1977.
9. "Sewage Treatment Plant Lynetten, City of Copenhagen". City Engineers
Office, Copenhagen, 1976.
10. "Psykisk arbejdsmilj«$: Trivsel i kloakr«5r og kontorlandskaber" (Psych-
ic working conditions: Thriving in sewer pipes and office landscapes).
Arbejdstilsynet, Annual Publication of the Office of Occupational Health,
p. 45-51, Copenhagen, 1976.
11. Fox, A.E. and P.F. Collier. "Low mortality rates in industrial cohort
studies due to selection for work and survival in the industry". J.
Prev. Soc. Med. 30, 225-30, 1976.
10
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TECHNICAL REPORT DATA
(Please read Instructions on tlic rci-crsc before completing)
1. REPORT NO.
EPA-600/1-78-007
4. TITLE AND SUBTITLE
ASSESSMENT OF DISEASE RATES AMONG SEWER WORKERS
IN COPENHAGEN, DENMARK
3. RECIPIENT'S ACCESSI Of* NO.
5. REPORT DATE
January 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R. B. Dean
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
LunDean Environmental Company
Cincinnati, Ohio 45230
10. PROGRAM ELEMENT NO.
1BA607
11. CONTRACT/GRANT NO.
CA-7-2761-A
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory, Cin-OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA/600/10
15. SUPPLEMENTARY NOTES
Project Officer: Herbert R. Pahren (513)684-7217
16. ABSTRACT Sewer workers in Copenhagen, Denmark have a higher death rate than the
comparable male population. An alarmingly high proportion of the deaths occur within
the year that employment terminates. Attempts to correlate the statistics with sick
leave records or chemicals in the environment have so far not been successful. Sewer
workers experience a high rate of gastro-intestinal tract disorders which they as-
sociate with chemical odors and infectious agents. They have elevated levels of gamma
globulins. Analytical xrork has not yet identified any agents that might be responsi-
ble for the observed death rates or the gastro-intestinal problems. Biological ex-
aminations of stool specimens have not been made.
This report was submitted in fulfillment of Contract CA-7-2761-A by LunDean
Environmental Company under the sponsorship of the U.S. Environmental Protection
Agency. This report covers a period from May 1977 to August 1977.
h.IDENTIFIERS/OPEN ENDED TERMS C. COSATi rieki/Ooup
Sewage Treatment", Diseases*, Health,
Waste Treatment, Mortality, Morbidity,
Sewers, Epidemiology
Denmark,
Copenhagen,
Sewer Workers
Occupational Diseases
57 U
94 D
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RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
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UNCLASSIFIED
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