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Administrative data

Endpoint:
epidemiological data
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.
Cross-reference
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
publication
Title:
A study of mortality among 14 730 male workers in 12 Norwegian ferroalloy plants: Cohort characteristics and the main causes of death.
Author:
Hobbesland, A., H. Kjuus, et al.
Year:
1996
Bibliographic source:
Occupational and Environmental Medicine.53(8): 540-546.

Materials and methods

Study type:
cohort study (retrospective)
Endpoint addressed:
repeated dose toxicity: inhalation
carcinogenicity
Principles of method if other than guideline:
The mortality pattern among employees in twelve ferroalloy plants, including ten plants, which produced silicon metal/ferrosilicon and four plants producing ferro- or silicomanganese was evaluated in a cohort study.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent

Method

Type of population:
occupational
Ethical approval:
not specified
Details on study design:
HYPOTHESIS TESTED: mortality of workers among male employees in ferroalloy plants differs from that of general population

METHOD OF DATA COLLECTION
- Type: Record review
- Details: Mortality of workers employed in Norwegian ferroalloy factories was obtained from the national registry for causes of death. Causes of mortality were compared to causes of mortality in general population

STUDY PERIOD: Each was followed up from the beginning of 1962 or if hired later from the date of first employment until death (or emigration) or to the end of the study, which was 31 December 1990.

STUDY POPULATION
- Total population (Total no. of persons in cohort from which the subjects were drawn): 18,290
- Selection criteria: women were excluded (n=1,326) and those employed before 1933 (n=1,605), 467 were lost during follow up and 162 had died between 1952 and 1961
- Total number of subjects at end of study: 14,730
- Other: median duration of employment of 5.4 years in the sector (5-95 percentiles 0.7-35.8 years) between 1933 and 1990
- In addition, subcohort of 2,517 male furnace workers in ferrosilicon and silicon metal production and a subcohort of 3,086 male furnace workers from ferromagnanese/silicomagnanese metal production was studied

COMPARISON POPULATION
- Type: National registry
- Details: Norwegian National registry for causes of death

HEALTH EFFECTS STUDIED
- Disease(s): main causes of death
Exposure assessment:
not specified
Details on exposure:
Crystalline and amorphous silica (FeSi, Si metal subcohorts), MnO2, CO, PAH's, asbestos, dusts of coke and coal, arsine, metal dusts (FeSi, Si in ferrosilicon/Si-metal subcohort and e.g. Mn in ferromagnanese subcohort), arsine, phosphine, Cr(VI), heat, electromagnetic fields, shift work.
In the case of subcohort of FeSi/Si-metal furnace workers additional information on exposure is derived from Hobbesland et al., 1997b:
TYPE OF EXPOSURE: Total dust, crystalline and amorphous silica
TYPE OF EXPOSURE MEASUREMENT: personal sampling. Measurements performed between 1974-1990. Altogether 401 personal samplings performed. EXPOSURE LEVELS: Total dust levels were on average (median) for 1974-1979: 4.8 mg/m3, 3.3 mg/m3 for 1980-1985 and 3.4 for 1986-1990. Approximately 50% of total dust exposure of furnace workers may be constituted of amorphous silica. 4-6% of the total dust was crystalline silica.
Statistical methods:
SMR's were calculated with 95% confidence intervals, as well as internal comparisons by Poisson regression; risk ratios, P values for trend analysis. Epicure program package was used both the SMR analysis and internal comparison of rates with poisson regression analysis.

Results and discussion

Results:
Results showed only slightly increased total mortality (SMR 1.08, 95 % CI 1.04-1.11) among ferroalloy workers when compared to expected number of deaths in the general population. The mortality, however, correlated negatively with the duration of employment. This suggests the effect of some lifestyle factors on total mortality. Slight, statistically significant increases in cancer mortality (SMR 1.11, CI 1.02 -1.20) from specific causes of deaths and sudden deaths were seen, but also these correlated negatively with the duration of employment. No significant increase in respiratory tract mortality was seen. Among the subcohort of 2,517 male furnace workers in ferrosilicon plants cancer mortality was not statistically significantly increased; SMRs were 1.17 for employment time <3 years and 1.10 for employment time ≥3 years with CI's of 0.85-1.56 and 0.88-1.36, respectively. When ferrosilicon/silicon metal furnace workers were separated, none of the SMR's were significantly increased for workers with an employment time of more than 3 years, whereas among workers with employment time <3 years, deaths from diseases of digestive and circulatory system as well as accidents, poisonings and acts of violence were significantly increased.
Confounding factors:
Life-style factors may have had a remarkable contribution to these figures.
Strengths and weaknesses:
Strengths: large size of the cohort, long term follow-up, low proportion of losts, almost complete information on death causes, the ability to study mortality in relation to work in separate departments
Weaknesses:
-selection bias caused by different recruiment and observation periods
-information on life-style factors lacking

Applicant's summary and conclusion

Conclusions:
Exposures at this industry sector have low/negligible effect on general mortality. In subcohorts of ferrosilicon and silicon metal manufacturing no statistically increased mortality was seen for any causes (including cancer, respiratory diseases) with >3 years of duration of work.
Executive summary:

Hobbesland et al. (1996) evaluated the mortality pattern among employees in twelve ferroalloy plants, including ten plants which produced silicon metal/ferrosilicon and four plants producing ferro- or silicomanganese. The cohort comprised 14,730 workers with median duration of employment of 5.4 years in this sector (5-95 percentiles 0.7-35.8 years) between 1933 and 1990. Results showed only slightly increased total mortality (SMR 1.08, CI 1.04-1.11) among ferroalloy workers when compared to expected number of deaths in the general population. The mortality, however, correlated negatively with the duration of employment. This suggests the effect of some lifestyle factors on total mortality. Slight, statistically significant increases in sudden deaths was seen, but also this correlated negatively with the duration of employment.

Slightly increased cancer mortality (SMR 1.11, CI 1.02-1.20) was seen in whole cohort.

Cancer mortality in the whole cohort was statistically significantly increased among the workers with employment time ≥3 years. Among the subcohort of 2,517 male furnace workers in ferrosilicon plants cancer mortality was not statistically significantly increased; SMRs were 1.17 for employment time <3 years and 1.10 for employment time ≥3 years with CI's of 0.85-1.56 and 0.88-1.36, respectively.

No significant increase in respiratory tract mortality was seen. When ferrosilicon/silicon metal furnace workers were separated, none of the SMR's were significantly increased among workers with an employment time of more than 3 years, whereas among workers with employment time <3 years, deaths from diseases of digestive and circulatory system as well as accidents, poisonings and acts of violence were significantly increased. Life-style factors may have had a remarkable contribution to these figures. In earlier studies, which evaluated mortality and cancer incidence in Norwegian ferroalloy industry (Langård et al. 1980; Langård et al. 1990; Kjuus et al. 1986), no increased total mortality was observed. According to these studies, exposures in this industry sector has a low/negligible influence on general mortality.