Silicic acid, calcium salt

Epidemiological data

Administrative data

Endpoint:

epidemiological data

Type of information:

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

Adequacy of study:

weight of evidence

Study period:

1976 and 1982

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The study was performed according to an observational design (no randomisation). In the cross sectional study an individual dose assessment was performed and adjusted for smoking habits. Furthermore, age, length and smoking habbit adjusted control group was included. In the follow up study, no information was reported on the calibration of the lungfunction equipment between 1976 and 1982, and no control group was included.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1984

Materials and methods

Study type:

cross sectional study

Endpoint addressed:

repeated dose toxicity: inhalation

Test guideline

Qualifier:

according to guideline

Guideline:

other: Standard epidemiological methodology for cross sectional studies For example : Kleinbaum and Kupper 1982 Epidemiological Research

Deviations:

not applicable

Principles of method if other than guideline:

not applicable

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

wollastonite

IUPAC Name:

wollastonite

Constituent 2

Reference substance name:

Wollastonite (Ca(SiO3))

EC Number:

237-772-5

EC Name:

Wollastonite (Ca(SiO3))

Cas Number:

13983-17-0

IUPAC Name:

calcium oxosilanediolate

Details on test material:

Wollastonite containing
- Less than 2% free silica.
- Fibrious particulates with median diameter of d=0,22 um and median length of l=2,5 um.
Note: Hazardous fibres are defined as shapes with d<3 um and l>5 um.

Method

Type of population:

occupational

Ethical approval:

not applicable

Remarks:

observational study

Details on study design:

The cross sectional study was performed in 1982 among white male workers. Exact dates (or seasonal data) of the medical examination are not given. 86 Male workers from a neary electronic component plant with a comparible age, height, smoking patern, were examined as a comparison group.

The longitudinal, follow up study enrolled employees that were examined in 1982 and also earlier in 1976. Exact dates of medical data collection are not given. Two consecutive measurements per worker with a 6 years interval were compared. No control group was used. The changes per person seem to be modeled in the same way as in the cross sectional study

Exposure assessment:

measured

Details on exposure:

Real time exposure measurements were performed by company, NIOSH MSHA between 1977-1981.
Mean total dust 8 hours exposure of 5 job categories:
- mining exept crushing 0,9 mg/m2
- administrative 2,3 mg/m3 (2 measurements only)
- milling & crushing 4,1 mg/m3
- labourer & beneficiator 8,71 mg/m3
- Mill maintenance and packers 10 mg/m3

Workers cummulative exposure (dose) is calculated by multiplying the exposure duration in years with the average estimated exposure based on the measurments per job and subsequently by summing the doses per function in his working life.

Statistical methods:

cross sectional: (1) multiple linear regression of lungfunction (independant variable) with lenght, age, smoking and dust years (dependant variables)
(2) Student-t test for comparison of unpaired and unstratified means of exposued and controls

Longitudinal:multiple linear regression of lungfunction changes (independant variable) with lenght, age, smoking and dust years (dependant variables).

Results and discussion

Results:

In the cross sectional study of the Wollastonite exposed workers, the height independant FEV1/FVC was significant associated with the amount of dust years in mg/m3/year.Normal FEV1/FVC values normaly decrease with age with about 0,2% per year from 83% (20 years) to 75% (60 years).
For the total employee population (n=108) 1 mg/m3 total dust is assiciated with an additional decrease of 0,05 %/year.
The Peak flow decrease with age (about 0,03 l/s/year) increases with an additional 0,0088 L/sec/year (total population) and 0,0052 L/sec/year (non-smoker) per mg/m3.

In the cross sectional comparison with the controls, the Wollastonite workers showed about 8% lower FEV1/FVC and Peak-flow values.

For non-smokers only, the decrease is 0,22% per mg/m3/year. However the small number (n=32 ) makes this value less reliable

Confounding factors:

Wollastonite workers do not differ much from the controls in age, smoking, participation rate and respiratory symptoms.
Within the Wollastonite workers age and respiratory symptoms did not differ for the different exposure categories

Strengths and weaknesses:

Weakness:
No infront hypothesis is tested.
The FEV1/FVC ratio has normally a much higher random variance than numerator FEV1 and denominator FVC and is therefore a weaker measure to find influence of exposure than the individual FEV1 and FVC.

Follow up study
The larger decline of the FEV1 and FVC compared to literature suggest a possible influence of equipment calibration between 1982 and 1976. No information is provided on the calibration of the lungfunction equipment between 1976 and 1982 . The exposure related differences in the peak flow in the follow up study may be caused by equipment differences

In the multiple linear regression, the same dependant variables (age, length, smoking and dust years, probably status 1982) were used as in the 1982 cross sectional analysis. Since lenght and age are considered to be linear related with the lung function outcome in the multiple linear regression, these parameters should not have been included. Aging in the follow up period is for all participants about 6 years. The individual changes in lungfunction between 1976 and 1982 should have been related only to the cummulative exposure and smoking habits in the follow up period, not to the total cummulative dose.

Strenght:
The association between dust exposure and additional decrease in FEV1/FVC and Peak flow is found in two more or less independent ways:
- in the cross sectional multiple linear regression
- in the cross sectional comparison with the control group
The follow up study cannot be considered as a strength, due to the possible equipment calibration bias.

Applicant's summary and conclusion

Conclusions:

In line with the authors the applicant concludes that Wollastonite may not be entirely innocuous and that long term high exposure (>30 mg-year/m3) may give slight systemic effects.