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•
Summary
Occupational
exposure to chromium compounds has been reported in various industries
including chromium chemicals and metallurgical production. Speciation
of chromium is essential in exposure assessment. It has been under
discussion whether there is a threshold level for hexavalent chromium
exposure, especially in relation to genotoxic effects. Technological
innovations in metallurgical industry have reduced the chromium exposure
levels during the last decades. Ideal medical examination methods
for surveillance for occupational health effects should be non-invasive
and non-radiative. They should also give early warning signals.
Magneto-pneumography provides a non-invasive method for studying lung
retention and the clearance of dust among subjects exposed to industrial
aerosols with a magnetic component. Micronucleus assay of exfoliated
cells of nasal mucosa is a method to study genotoxic effects of various
exposures. These modern methods, in addition to the conventional ones,
have been used in a research program in the Finnish ferrochromium
and stainless steel production chain. The results indicated that an
average exposure time of 23 years in ferrochromium and stainless steel
production and exposure to dusts containing low concentrations of
Cr6+ or Cr3+
does not lead to any respiratory changes detectable by lung function
tests or radiography nor to any increase in symptoms of respiratory
diseases. Nor does this exposure lead to nasal changes detectable
by clinical or cytological examination. No genotoxic effects attributable
to occupational chromium exposure could be observed in the micronucleus
analysis of exfoliated nasal cells.
•
Introduction
Occupational exposure to chromium
Exposure to chromium can occur in the production and use of chromates
and dichromates in the chemical industry, in the stainless steel industry,
in the production and use of alloys, in refractory work, in the chromium-plating
industry, in leather tanning, in the production and use of wood preservatives,
in cement manufacture and use, and in the welding of stainless steel.
There are several studies on chromium exposure in ferrochromium production.
In a Norwegian ferrochromium plant the mean level of total chromium
ranged from 10 to 290 µg/m3,
about 11% - 13% of which was water-soluble [1].
Among Swedish ferrochromium workers the exposure to Cr6+
was estimated to be 250 µg/m3
during arc furnace operations and 10 - 50 µg/m3
during transport, metal grinding, maintenance and sample preparation.
The total concentration of metallic chromium and Cr3+
at the worksites was 500 - 2500 µg/m3
[2]. In an Italian ferrochromium
plant the dust samples contained
0.9% - 3.8% chromium and the airborne levels of total chromium were
20 - 158 µg/m3. The concentration
of Cr6+ was below 1 µg/m3
[3]. In a Finnish ferrochromium smelter
the exposure to total chromium was reported to be 200 µg/m3
during ferrochromium smelting [4].
The quantitative data on chromium exposure in the production of stainless
steel are limited. In a French stainless steel plant the concentrations
of total chromium ranged from 15 to 300 µg/m3
[5]. In a Finnish stainless steel
plant the fumes and dusts contained 1.5% - 5% chromium during stainless
steel melting, 0.2% - 0.3% during continuous casting and 1.6% - 13%
during the grinding of stainless steel. The mean Cr6+
concentration was 1.5 µg/m3 [6].
The chemical solubility of metal particles present in workplace air
may vary substantially at different stages of production, which indicates
that the metals are chemically bound in different ways. The particle
structure of metallurgical fumes and dusts will depend largely on
temperature, process conditions like oxidation and reduction, slag
compounds, other metals present and mechanical handling. The speciation
of metal compounds is very important in order to understand their
biological effects.
Respiratory health effects of chromium
Ulcerations and perforations of the nasal septum among chromate workers
were described as early as 1869 [7].
Nasal chrome ulcers and perforations have been observed among ferrochromium
production workers, too [8].
Obstructive
effects on lung function have been reported in several studies. Reduced
forced vital capacity (FVC) and an increased prevalence of obstructive
lung diseases were found among electro-furnace workers in a ferrochromium
plant. According to the International Agency for Research on Cancer
(IARC) chromate production, chromate pigment manufacture and chrome
plating are causally associated with an increased risk of lung cancer [9].
The
carcinogenicity of Cr6+ may be mediated
through genotoxic mechanisms. Cr6+
has been shown to be genotoxic in various short-term tests [10].
Although there are also clearly negative studies on these end points,
many studies have reported elevated frequencies of chromosome aberrations,
sister chromatid exchanges or micronuclei in peripheral lymphocytes
of chromium electroplating workers or in other workers exposed to
Cr6+ compounds [11-17].
Studies
on the frequency of micro-nucleated exfoliated nasal epithelial cells
have suggested that the reductive capacity of the mucosa and reduction
and trapping of Cr3+ and reactive
oxygen species inside the target cells probably adequately protect
the cells from the genotoxic effects of Cr6+.
These defence mechanisms may be overcome only at high exposures, so
that a threshold has been proposed for Cr6+
carcinogenicity [18,19].
•
Medical Examination Methods in Metallurgical Industry
Ideal
medical examination methods for surveillance of occupational health
effects should be non-invasive and non-radiative. They should also
give early warning signals.
Classical
methods include lung function tests (spirometry, measurement of diffusing
capacity), radiological examinations and biological monitoring. Examples
of the more recent methods are magneto-pneumography and micronucleus
assay of exfoliated epithelial cells.
Magneto-pneumography
(MPG) provides a non-invasive method for studying lung retention and
the clearance of dust among subjects exposed to industrial aerosols
with a magnetic component. MPG measures the remanent magnetic field
(RMF) and the relaxation rate (ReR) of lung burden particles after
a short magnetization pulse.
The
minimum detectable average magnetic field is about 10 pT. The sensitivity
corresponds to a magnetic moment of 1.5 µAm2
and about 0.5 mg of magnetite. The reproducibility of the measurement
results is 5%.
Micronuclei
are small additional nuclei seen in the cytoplasm of a cell. These
micronuclei are formed of total chromosomes or particles of chromosomes
that are left over after cell division. In micronucleus assay it is
possible to identify exposures causing either structural or numerical
chromosome aberrations.
•
Finnish Research Programme
The
integrated stainless steel production chain in Finland is unique;
the chromite mine and all the ferrochromium and stainless steel production
plants are in the same region. (Figure 1)
Figure
1. From Chrome Ore to Stainless Steel
The
research programme on long-term respiratory health effects was carried
out in 1987 - 2002. There were six individual studies, which have
been published in peer-reviewed journals. The cross-sectional clinical
pulmonary studies were conducted in 1993 and 1998.
The
purpose of the research programme was to assess the exposure levels
of different chromium species throughout the consecutive stages of
stainless steel production and to study possible health effects and,
if health effects are detected, to examine the causal relationship
between specific exposure and the health effects. There were approximately
300 workers in the follow-up study of respiratory health. Their average
exposure time was 23 years in the same production department.
Exposure
to dust and chromium compounds was assessed from personal and stationary
samples. Chromium concentrations were measured in urine and blood.
The surface structure and the chemical composition of the metal particles
encountered in the workplace air were examined by electron microscopic
methods. Magneto-pneumography was used to study the retention of dust
in the lungs. Nasal health effects were studied by clinical examination,
endoscopy, cytology and an assessment of the frequency of micronucleated
exfoliated cells of the nasal mucosa. Respiratory symptoms and diseases
were studied with the aid of a questionnaire, lung function testing,
measurements of diffusing capacity and radiographic examinations.
•
Results of the Research Programme
Exposure
to chromium was observed in all the departments studied. Exposure
to hexavalent chromium was low; at the chromite mine no hexavalent
chromium was detected. The observed levels of chromium in the urine
and blood were, on average, higher than the levels among persons with
no occupational exposure to chromium.
Magneto-pneumography showed a low accumulation of dust in the lungs.
There were no significant differences in nasal symptoms, diseases,
cytology or the frequency of micro-nucleated cells between the exposed
groups. In the first cross-sectional study no significant differences
in the odds ratios of the respiratory symptoms were found
between the exposed and control groups. The smokers in the chromite
group had significantly lower forced vital capacity, forced expiratory
volume in one second and diffusing capacity. In the follow-up study
no adverse effects were observed in the group exposed to hexavalent
chromium, either in comparison with the control group in the cross-sectional
study or during the 5-year follow-up. (Tables 1 and 2) [20].
| Table
1. Lung function measurements as percentage of predicted
values (smokers*) |
|
Cr6+
group |
Cr3+
group |
Chromite
group |
Control
group |
|
 |
|
|
|
| Lung |
1993 |
1998 |
1993 |
1998 |
1993 |
1998 |
1993 |
1998 |
| function |
(n=63) |
(n=63) |
(n=47) |
(n=47) |
(n=26) |
(n=26) |
(n=52) |
(n=52) |
| variable |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
|
| FVC |
93.5
(9.6) |
89.6
(11.5) |
90.7
(9.6) |
90.3
(10.6) |
87.8
(10.9) |
87.2
(10.3) |
94.9
(10.8) |
92.9
(11.5) |
| FEV1 |
91.8
(12.5) |
87.9
(14.1) |
89.1
(10.7) |
87.6
(12.2) |
85.1
(13.0) |
83.0
(12.4) |
92.6
(12.3) |
88.5
(13.6) |
| FEV% |
98.2
(8.0) |
97.8
(7.8) |
98.0
(7.1) |
97.1
(7.8) |
94.4
(8.1) |
95.2
(8.4) |
97.4
(7.2) |
95.2
(8.7) |
| TLCO |
98.5
(16.6) |
109.0
(17.5) |
92.4
(12.8) |
102.9
(14.9) |
93.1
(13.9) |
100.3
(15.7) |
94.9
(13.1) |
102.1
(11.8) |
| TLCOHb |
97.5
(15.5) |
103.8
(16.6) |
92.5
(12.6) |
96.2
(14.6) |
92.9
(13.7) |
92.9
(16.3) |
94.6
(13.6) |
95.9
(11.8) |
| TLCO/VA |
104.9
(16.56) |
92.1
(13.0) |
98.9
(15.9) |
87.3
(14.1) |
103.8
(15.9) |
90.0
(16.4) |
99.9
(14.6) |
86.3
(10.8) |
| TLCO/VAHb |
104.7
(16.4) |
101.9
(14.4) |
99.2
(15.9) |
94.8
(16.1) |
103.8
(16.3) |
96.9
(19.6) |
99.8
(15.2) |
94.1
(12.5) |
|
| *
Smokers include both current and ex-smokers. |
| P<0.05.
Cr6+, Cr3+,
and chromite groups versus the control group (differences
in 1993 not analysed). |
|
| Table
2. Lung function measurements as percentage of predicted
values (non-smokers) |
|
Cr6+
group |
Cr3+
group |
Chromite
group |
Control
group |
|
|
|
|
|
| Lung |
1993 |
1998 |
1993 |
1998 |
1993 |
1998 |
1993 |
1998 |
| function |
(n=41) |
(n=41) |
(n=21) |
(n=21) |
(n=5) |
(n=5) |
(n=27) |
(n=27) |
| variable |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
Mean
(SD) |
|
| FVC |
96.4
(11.1) |
94.2
(12.0) |
93.4
(9.1) |
93.6
(11.0) |
96.1
(11.1) |
97.0
(12.3) |
93.4
(9.7) |
92.4
(8.5) |
| FEV1 |
95.5
(11.4) |
91.9
(11.3) |
92.9
(11.2) |
91.2
(12.9) |
94.2
(10.8) |
94.3
(13.2) |
94.7
(11.6) |
92.3
(10.5) |
| FEV% |
99.8
(6.6) |
97.9
(7.2) |
99.1
(6.7) |
97.2
(7.4) |
97.7
(6.6) |
97.4
(8.4) |
101.5
(5.8) |
99.8
(5.8) |
| TLCO |
104.8
(11.8) |
112.1
(13.9) |
107.8
(15.8) |
115.5
(16.9) |
105.6
(5.9) |
109.7
(4.8) |
106.6
(14.7) |
112.1
(11.7) |
| TLCOHb |
104.1
(11.9) |
109.2
(13.9) |
107.8
(14.7) |
110.6
(19.4) |
105.9
(5.3) |
106.1
(3.4) |
106.3
(13.9) |
107.4
(13.1) |
| TLCO/VA |
108.6
(16.7) |
109.9
(14.4) |
113.2
(17.3) |
112.0
(15.8) |
111.4
(21.3) |
104.0
(12.7) |
111.5
(18.2) |
110.9
(13.9) |
| TLCO/VAHb |
108.0
(16.7) |
107.2
(13.4) |
113.3
(15.9) |
107.1
(17.2) |
111.4
(19.4) |
101.0
(13.5) |
111.4
(18.1) |
106.0
(13.8) |
|
•
Discussion on the Practical Value of Various Examination Methods
Exposure
assessment both qualitatively and quantitatively is essential in the
health surveillance of workers in metallurgical industry. Radiological
examinations seem to give minimal information, especially on early
stages of adverse health effects. At low levels of exposure biological
monitoring and measurement of diffusing capacity give fairly little
additional information. Spirometry can be recommended as non-harmful
and giving information also on non-occupational diseases.
•
Summary and Conclusions
The
observed levels of chromium in the urine and blood were, on average,
higher than the levels among persons with no occupational exposure
to chromium. None of the specimens showed the urinary chromium concentration
to exceed the national Finnish action limit, and no correlation was
observed between the chromium concentrations in the workplace air
and in urine. No significant differences were found in the blood chromium
contents in the specimens collected before or after the workweek.
The
RMF in the lungs was slightly elevated among the workers in the ferrochromium
smelter and the steel melting shop. Workers at the mine, in the sintering
plant and in the cold rolling mill exhibited RMFs comparable with
those of the controls.
There
were no significant differences between the exposure groups and the
controls regarding previous nasal diseases and nasal symptoms. None
of the subjects had chronic ulceration, septal perforation or a nasal
tumour.
No dysplasia or malignancy was observed cytologically. No statistically
significant difference in the mean frequency of nasal cells with micronuclei
(formed by chromosome breakage or mis-segregation) was observed between
the exposed groups and the control group.
No
significant differences in the frequency of the symptoms were found
between the exposed and control groups. Age and smoking significantly
explained the occurrence of most of the respiratory symptoms.
In
1998 no adverse effects (i.e., increase in symptom prevalence, deterioration
of lung function or progression of radiographic lung findings) were
observed in the group exposed to Cr6+,
either in comparison with the control group in the cross-sectional
study or during the 5-year follow-up.
The
exposure study showed that there is certainly exposure to chromium
throughout the production chain, and to Cr6+
at certain stages, but the observed health effects were minimal. This
finding can be explained partly by low exposure levels and partly
by the low bioavailability of potentially harmful chromium species.
The low bioavailability can be explained by the surface properties
and chemical composition of the metal particles in the workplace air.
An
average exposure time of 23 years in ferrochromium and stainless steel
production and exposure to dusts containing low concentrations of
Cr6+ or Cr3+
does not lead to any respiratory changes detectable by lung function
tests or radiography nor to any increase in symptoms of respiratory
diseases. Nor does this exposure lead to nasal changes detectable
by clinical or cytological examination. No genotoxic effects attributable
to occupational chromium exposure could be observed in the micronucleus
analysis of exfoliated nasal cells.
The
results of this research project indicate that it is technically and
economically possible to achieve low exposure levels in the stainless
steel production chain with no adverse health effects. This approach
should be applied in the stainless steel industry in general.
•
Recommendations for Occupational Health Measures
The
following recommendations are based on the results of the study programme
used in the Finnish research project, and they focus on the health
effects of dusts and fumes containing chromium and chromium compounds
in the stainless steel production chain.
There
are, however, several other reasons (i.e. ergonomic problems and other
exposures like noise) for monitoring health aspects of the workplace
and the workers.
•
When process conditions are stable, annual exposure assessment is
recommended. Stationary samples from typical work areas are sufficient
for the analysis of total dust, total chromium and Cr6+.
In chromite ore mining operations the type of waste rock must be
monitored with special attention to fibrous minerals.
•
Some examination methods prove to give very little, if any, additional
information on health effects in the modern stainless steel industry
with low exposure levels to chromium compounds. Therefore MPG, biological
monitoring, chest X-ray examinations, measurement of diffusing capacity,
and oto-rhino-laryngological examinations, including nasal cytology,
are not recommended as routine methods, nor is skin testing for
chromium allergy recommended or regarded as appropriate.
•
Although there are no specific occupational health needs based on
chromium exposure, periodic health examinations are justified because
of certain public and occupational health reasons, like the early
detection of chronic obstructive pulmonary disease (COPD) and the
benefits from monitoring the work capacity of workers. Periodic
health examinations are recommended to be carried out at intervals
of 3 - 5 years. They should include:
-
spirometry
- a survey of respiratory symptoms as part of the surveillance
of health and general work capacity
•
The pre-employment medical examination should include:
-
an adequate occupational and health history
- a physical examination with special attention to the respiratory
organs and skin
- spirometry
- a chest X-ray
•
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