Cobalt molybdate

Epidemiological data

Administrative data

Endpoint:

epidemiological data

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well-documented epidemiological study that meets basic scientific principles.

Data source

Reference

Reference Type:

publication

Title:

Absence of Significant Genotoxicity in Lymphocytes sand Urine from Workers Exposed to Moderate Levels of Cobalt-Containing Dust: A Cross-Sectional Study

Author:

De Boeck, M., et al.

Year:

2000

Bibliographic source:

Environmental and Molecular Mutagenesis 36: 151-160

Materials and methods

Study type:

cross sectional study

Endpoint addressed:

genetic toxicity

Principles of method if other than guideline:

The major objective of this biomonitoring study was to assess genotoxic effects as a measure for carcinogenic risk in workers from cobalt refineries and hard metal plants currently exposed to the threshold limit value/time -weighted average (TLV-TWA) for cobalt-containing dust.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

cobalt-containing dust

IUPAC Name:

cobalt-containing dust

Details on test material:

- Name of test material (as cited in study report): cobalt-containing dust (not specified)
- Analytical purity: no data/not applicable

Method

Type of population:

occupational

Ethical approval:

not specified

Details on study design:

METHOD OF DATA COLLECTION
- Type: Work history / Clinical tests
- Details: urine and lymphocyte analyses (genotoxicity biomarkers)

SETTING: 35 workers exposed to cobalt dust from three refineries, 29 workers exposed to hard metal dust from two producing plants, and 35 matched control subjects recruited form the respective plants.
Genotoxicity biomarkers: DNA damage was measured in circulating lymphocytes with the alkaline comet assay, and specific detection of oxidative damage was achieved with a DNA glycosylase recognizing oxidized purines. Systemic oxidative DNA damage was monitored by measuring the urinary concentration of 8-hydroxydeoxyguanosine (8-OHdG). The induction of chromosome/genome mutations was monitored with the cytokinesis-block micronucleus test in lymphocytes which did or did not divide in the postsampling culture period allowing a possible discrimination between micronuclei induced by chronic exposure and those arisen during the last mitotic division in vitro. Vitamin E and selenium in serum were considered as possible parameters reflecting the capacity to protect against active oxygen species (AOS) damage.

DESCRIPTION OF METHODS
- Alkaline Comet Assay: The comet assay was performed in isolated lymphocytes. Six slides per donor were prepared. Detection of oxidative DNA damage was done by using the formamidopyrimidine glycosylase enzyme for 30 min at 37 °C. To visualize DNA damage after the electrophoresis, the rehydrated slides were stained with ethidium bromide. 100 randomly selected nuclei were evaluated and tail length (TL) and tail DNA (TD) and tail moment (TM) were recorded.
- Micronucleus Test: whole-blood cultures were prepared in duplicated and stored for 44 h, cytochalasin B was added and the cultures were arrested after 72 h. Cells were washed and after a light hypotonic shock, the cells were centrifuges and smears were made. the slides were stained with Giemsa and scoring of micronuclei was performed (in mononucleates and binucleates up to 1000 binucleated cytokinesis-blocked lymphocytes (MNCB) per culture. Data are presented as frequencies of micronucleated binucleates per 1000 binucleates (MNCB/1000) and of micronucleated mononnucleates per 1000 mononnucleates (MNMC/1000).
- 8-OHdG in Urine: The urinary concentration of 8-OHdG (8-OHdG-U) was measure by high-performance liquid chromatography-electrochemical detection. The results were expressed as µmol of 8-OHdG/L and normalized for urine dilution.
- Cotinine, Vitamin E and Selenium: The concentration of cotinine in urine was measured by HPLC with UV detection and the results were expressed as ng/mL. The results of Vitamin E and Selenium in serum (Vit E-S, Se-S) were presented as µg/dL
- Cobalt in Urine: The urinary concentration of cobalt (Co-U) was assayed by atomic absorption spectrometry in a spot sample obtained on Friday end-of-shift. The results were expressed as µg/g creatinine.

STUDY POPULATION
- Total population (Total no. of persons in cohort from which the subjects were drawn): 99
- Selection criteria: age, duration of employment, Cobalt exposure, smoking and drinking behaviour
- Sex/age: male/40
- Smoker (%): 41.4 - 50.0
- Total number of subjects at end of study: 80
- Matching criteria: age, employment at same plant, smoking and drinking behaviour

Exposure assessment:

measured

Details on exposure:

TYPE OF EXPOSURE: exposure to cobalt-containing dust in plants

TYPE OF EXPOSURE MEASUREMENT: Biomonitoring (urine) / Biomonitoring blood

EXPOSURE LEVELS: A urinary concentration of 20 µg of cobalt per gram of creatinine was targetetd (normally determined at the end of shift on friday), which is equivalent to an airborne exposure level of 20 µg/m³, the current ACGIH TLV-TWA

POSTEXPOSURE PERIOD: samples were taken after a weekend off

DESCRIPTION / DELINEATION OF EXPOSURE GROUPS / CATEGORIES:
An attempt was made to match both test groups for age, smoking habits, and cobalt exposure as assessed by cobalt in urine. A third group of matched control subjects compressed workers with similar socioeconomic status, not exposed to cobalt or WC-Co, who were recruited from the five respective plants.

Statistical methods:

- All individual values (entered in an Excel file): statistical analysis with the NCSS and SAS packages (When appropriate an attempt was made to normalize distributions by using logarithmic transformations (geometric means and standard deviations.)).
- Possible associations between genotoxicity parameters: simple linear correlation analysis
(mean controls versus exposed, and cobalt versus WC-Co; K Students' t-tests two-sided)
- Possible influence of several independent variables (smoking, type of plant, type of exposure, Vit E-S, Se-S, etc.) on the genotoxicity parameters (comet, micronuclei, and 8-OHdG: multiple regression analyses (stepwise multivariate regression)

Results and discussion

Results:

EXPOSURE
- Geometric mean (µg/g creatinine ± SD, friday): exposed workers (Co): 21.5 ± 2.1; exposed workers (Hard metals): 19.9 ± 2.4; total exposed workers: 20.6 ± 2.3 (controls: 1.7 ± 1.6)

FINDING
- no statistically significant difference in the group mean of urinary 8-OHdG (control vs. exposed; cobalt vs. hard metal workers)
- alkaline comet assay: no statistically significant differences (control vs. exposed; cobalt vs. hard metal workers) for the three parameters measuring DNA damage (TL, TD, and TM)
- no statistically significant increase of DNA migration in any of the worker groups when the comet assay was combined with the Fpg enzyme to detect oxidative DNA damage
- frequency of MNCB: no statistically significant difference between control and exposed workers; statistically significant higher in cobalt compared to hard metal workers.
- frequency of MNMC: no differences
- Vit E-S and Se-S: no differences
No influence of the intensity of recent exposure (as assessed by the urinary cobalt concentration) or of parameters reflecting protection capacity against oxidative stress (Vit E or Se-S) was found.
The multivariate analysis conducted in exposed workers indicated that smoking workers exposed to hard metal particles had a higher genotoxic risk.

Confounding factors:

Age of workers from plant 2 was much higher, thus, these workers were excluded from the final population, as it was considered a potential bias.

Strengths and weaknesses:

- strength: good matching between control and exposed groups; several plants involved; simultaneous determination of several genotoxicity endpoints
- weakness: cross-sectional design (sensitive to so-called healthy worker effects), limited number of subjects, some evaluated genotoxic changes possibly induced by exposure could have been repaired at the time of sampling

Applicant's summary and conclusion

Conclusions:

The aim of this biomonitoring study was to determine wether the TLV-TWA for cobalt-containing dusts (established in 1996), which did not take carcinogenicity into consideration, is still acceptable when genotoxic effects are assessed as measuers for carcinogenic risk in workers from cobalt refineries and hard metal production plants. The second objective was to compare the genotoxic responses in relation to lung cancer in the hard metal industry. No statistically significant increase in any genotoxicity biomarker was found.