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Cause-specific mortality in Finnish ferrochromium and stainless steel production workers
Type of information:
other: See "Remarks"
Cohort study
Adequacy of study:
supporting study
Study period:
From 1967 to 2004.
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Externally peer-reviewed cohort study.
Reason / purpose for cross-reference:
reference to same study

Data source

Reference Type:
study report
Report date:

Materials and methods

Study type:
cohort study (retrospective)
Endpoint addressed:
other: Malignt neoplams Diabetes mellitus Dementia Alzheimer´s disease Other diseases of the nervous system Diseases of the circulatory system Diseases of the respiratory system Alcohol-related diseases and accidental posioning by alcohol
Principles of method if other than guideline:
The study cohort was made up of Finnish stainless steel production chain workers employed between 1967 and 2004,
from chromite mining to cold rolling of stainless steel. The cohort was divided into subcohorts by production units with specific
exposure patterns. Causes of death for the years 1971–2012 were obtained from Statistics
Finland. Standardized mortality ratios (SMRs) were calculated as ratios of observed and expected
numbers of deaths based on population mortality rates of the same region.
GLP compliance:
Not applicable

Test material

Specific details on test material used for the study:
Exposure to total dust in workplace air.


Type of population:
Ethical approval:
confirmed and informed consent free of coercion received
Ethical approval recieved from the National Institute for Health and Welfare.
Details on study design:
Assessing cause-specific mortality in Finnish ferrochromium and stainless steel workers with special reference to circulatory and respiratory diseases.

All persons employed at the Kemi mine and Tornio production units of Outokumpu Group (called
Tornio Works) between 1967 and 2004, who had not died or emigrated before 1971 were included in the study. The cohort
was identified from the company’s employment records. All Finnish residents have had unique personal identity codes (PICs)
since 1967, which enable reliable automatic record linkage. Through an extensive search of population registers,
correct PICs, possible emigration date and vital status for all but nine (0.1%) of the workers were traced, leaving
a cohort of 8088 consisting of 6293 men and 1795 women (See Table 1 below). No information on the number of smokers/non-smokers of the cohort members were given in the study.
Causes of death were obtained for 1971–2012 from Statistics Finland. The longitudinal cause of death register
of Statistics Finland has 53 causes of death categories. It started in 1971, and the latest year available for
the present study was 2012. Determination of cause of death is based on medical or forensic evidence, which provides
grounds for death certification. Forensic determination may be necessary if death is not due to illness, if it is accidental
or violent or is caused by a treatment procedure or occupational disease.
In the present study, causes of death were obtained from first employment or 1 January 1971, whichever was later, to emigration, death
or 31 December 2012, whichever was first. The data was further divided by time elapsed since first employment
and analysed by production department (See Table 1 below), from the date when a person had
worked for 5 years in a department. Observed deaths and person-years at risk were counted
by 5-year age groups, separately for males and females, and for seven 6-year calendar periods between 1971 and 2012.
Expected numbers of deaths and specific causes of death were calculated by multiplying person-years in each stratum
by the corresponding average mortality and cause-specific mortality in the population of the area of the Regional State Administrative
Agency for Northern Finland. As Tornio Works is at the northernmost end of the Baltic Sea
on the Swedish border, the authors assumed that selected reference rates represented typical mortality levels in that region.
Standardized mortality ratios (SMRs) forbroader age ranges were calculated by adding up age-specific observed numbers of deaths and divided by the sum of expected numbers of respective age categories.

STUDY PERIOD: 1967-2004.

Diseases causing death included the following:
Malignant neoplasms
Malignt neoplasms of stomache
Malignt neoplasm of colon
Primary malignt neoplasm of liver
Malignt neoplasm of pancreas
Malignt neoplasm of larynx, trachea and lung
Malignt neoplasm of breast
Malignt neoplasm of prostate
Malignt neoplasm of lymphoid/haematopoietic tissue
Other malignt neoplasms
Endocrine, nutritional and metabolic diseases
Diabetes mellitus
Dementia, Alzeimer´s disease
Other disease of the nervous system
Diseases of the circulatory system
Ischaemic heart disease
Other heart disease
Cerebrovascular diseases
Other diseases of the circulatory system
Diseases of the respiratory system
Bronchitis, emphysema
Other diseases excluding dementia and alcohol-related diseases
Alcohol-related diseases and accidental poisioning by alcohol
Exposure assessment:
not specified
Information on measured metals in personal workplace air was available from previous exposure studies at Outokumpu Tornio Works (The Finnish stainless steel production company).
Details on exposure:
Occupational long-term exposure to dust and aerosols with focus on chromium, Cr6+, nickel and zinc in various forms (particles, agglomerates). Personal

The exposure information below is taken from Huvinen and Pukkala (2013) in which a study on the same cohort was conducted:

Dust exposure was contionously monitored, showing a decreased rate of chromium containing dust in work place air of 17 % from 1970 to the early 1990s inthe mine, the ferrochromium works and the stainless steel melting shop. In the cold rolling mill, the concentrations were always low.
Below, exposures for each production department are described in more detail.

At the chromite mine in the 1980s, the average exposure to total dust was 1 mg/m3. The highest personal exposures
were found in the crushing plant (1.4–4.9 mg/m3). The chromium content of the dust was 1–5%, indicating that the median personal exposure
to chromium was 22 μg/m3. Cr6+ was not detected in any of the samples from the mine.

In the furnace department of the ferrochromium smelter, the median personal dust exposure was 1.5 mg/m3.
The median chromium concentration was 143 μg/m3. The median personal workplace air concentration of Cr6+ was
below the detection limit of the method (0.5 μg/m3, maximum 2.4 μg/m3). The highest concentrations were
detected during tapping in the vicinity of the tap hole, where the proportion of Cr6+ was 10-fold that of other areas.

The average exposure to total dust in the stainless steel melting shop was 1.8 mg/m3. The dust contained
2–4% chromium. The median content of total chromium in the personal samples collected from the
breathing zone was 30 μg/m3. The median Cr6+ level was 0.5 μg/m3. The highest figures of Cr6+ among personal
samples were detected in the handling of molten metal by the arc furnace (6.6 μg/m3).

In the grinding shop, the average exposure to total dust was 0.8 mg/m3. The median chromium content was
66 μg/m3. The median Cr6+ level was below 0.5 μg/m3 (maximum 0.6 μg/m3).

The total dust content was low throughout the cold rolling mill, averaging 0.3–0.5 mg/m3, and the highest
measured single concentration was 1.8 mg/m3. In general, the content of chromium in the air in the cold
rolling mill was lower than the detection limit of the measurement method. Cr6+ was found only in the
annealing and pickling line, in the neutralisation and acid regeneration shop and near some automatic
welding machines. The median Cr6+ concentration was below 0.5 μg/m3 (maximum 6.6 μg/m3).
Statistical methods:
Calculation of the 95% confidence intervals for the standardized mortality ratios was based on the assumtion that the number of observed deaths followed a Poisson distribution.

Results and discussion

In total 6293 men (158 642 person-years) and 1795 women (41 118 person-years) were followed-up in the cohort..
Mean individual follow-up was 24.7 years. 451 deaths caused by diseases were observed. The expected number was 586.4
and the SMR was 0.77 (95% CI 0.70–0.84). Overall mortality, mortality from diseases of the circulatory
system, and in particular from ischaemic heart disease, was significantly decreased. The SMR for all malignant
neoplasms combined was 0.88 (95% CI 0.73–1.03) and for lung cancer 0.80 (95% CI 0.55–1.12). In
those who had worked in the same department for >5 years, the SMR for lung cancer was 0.60 (95% CI 0.33–1.01). In department-specific analyses, there were significant decreases in circulatory disease mortality in chromite mine workers, in the stainless steel melting shop, in the metallurgical laboratory and
in the offices. The SMR for accidents was 0.84 (95% CI 0.67–1.0) and for suicides 0.72 (95% CI 0.56–0.91).
There were no significant differences between the SMRs according to age, period or sex. For example,
the SMR for all diseases among male and female employees combined was 0.53 (95% CI 0.39–0.70) in
the 30–44 age group, 0.77 (95% CI 0.65–0.88) aged 45–59, 0.89 (95% CI 0.76–1.02) aged 60–74 and 0.74
(95 % CI 0.56–0.96) aged ≥75. The SMR among male employees was 0.79 (95% CI 0.71–0.86) for all diseases,
0.64 (95% CI 0.53–0.77) for ischaemic heart diseases and 0.69 (95% CI 0.52–0.91) for suicides.
The respective ratios for female employees were 0.63 (95% CI 0.45–0.84), 0.68 (95% CI 0.31–1.29) and 0.74 (95% CI 0.15–2.15).

Confounding factors:
Smoking is the most important confounder. According to the authors, confounding due to smoking is small and the smoking figures rather point towards a negative confounding.
Strengths and weaknesses:
The use of non-selected national registers with good data accuracy and coverage, long follow-up time and complete information on causes of death.
One of the authors has been employed by Outokumpu Group since 1975 (competing interests).

Applicant's summary and conclusion

The ferrous slags are produced in steelworks as essential by-products of iron and steel manufacturing. In terms of ferrous slags, inhalation is considered to represent the main route of exposure to human/workers.
The cohort study by Huvinen and Pukkala (2015) is thus of high relevance given the approach to assess occupational long-term exposures to dust in the Finnish ferrochromium and stainless steel industry and whether this
could be associated with increased mortaliity. Measurements of workplace air reported in the study of the same cohort (Huvinen and Pukkala, 2013)
showed concentrations of chromium, Cr6+, zinc and nickel. The highest concentration was found in the crushing plant with a chromium content of the
dust of 1-5 %. Continous measurements furthermore showed decreasing chromium concentrations in dust in workplace air between 1970 to the early 1990s.

Overall, this study shows that occupational long-term exposure to dust in ferrochromium and stainless steel industry does not appear to be associated with increased mortality from any cause of death including various cancer forms and respiratory diseases. No increase in mortality from respiratory and circulatory diseases or lung cancer was seen, nor was an increase in mortality seen for other diseases, accidents and violence.
Executive summary:

The study aimed at describing cause-specific mortality in Finnish ferrochromium and stainless steel workers employed between 1967 and 2004. The workers were divided into sub-cohorts by production units with specific exposure patterns. Causes of death were obtained for the years 1971–2012 from Statistics Finland. The cohort consited of 8088 workers. Mortality from respiratory and circulatory diseases in Finnish ferrochromium and stainless steel industry workers was not increased as might have been expected on the basis of earlier publication. The occupational exposures or working conditions in the Finnish ferrochromium and stainless steel industry appear not to be associated with

increased mortality from any cause of death.