Ashes (residues), rice husk

Health surveillance data

Administrative data

Endpoint:

health surveillance data

Type of information:

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

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well documented publication which meets basic scientific principles

Data source

Reference

Reference Type:

publication

Title:

Effects of chronic amorphous silica exposure on sequential pulmonary function

Author:

Wilson, R.K. et al.

Year:

1979

Bibliographic source:

Journal of Occupational Medicine 21(6): 399-402

Materials and methods

Study type:

health record from industry

Endpoint addressed:

repeated dose toxicity: inhalation

Principles of method if other than guideline:

Review of pulmonary function testing parameters and chest radiograph findings

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Silicon dioxide

EC Number:

231-545-4

EC Name:

Silicon dioxide

Cas Number:

7631-86-9

Molecular formula:

O2Si

IUPAC Name:

dioxosilane

Details on test material:

- Name of test material (as cited in study report): amorphous silica
- Analytical purity: no data

Method

Type of population:

occupational

Ethical approval:

not specified

Details on study design:

The medical records of 165 precipitated amorphous silica (PAS) workers in two industrial facilities were reviewed with regard to their annual spirometry, chest roentgenogram, and most recent respiratory questionnaire. Subjects included in this study had at least one full year of exposure to PAS. Spirograms were performed on Collins’ (Model 5000) and Donti spirometers in one facility and a Vitalor spirometer in another. All data were calculated from the original tracings by the same experienced pulmonary technician to obtain forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC ratio, and maximum mid-expiratory flow (FEF25-75). Change per year for each variable was calculated by taking the difference between first and last test and dividing by number of years between testing. Demographic data, smoking histories, and positive responses to the most recently completed respiratory questionnaire were obtained from each worker’s medical chart. The questionnaire was modified from the standard British Medical Research form. Respiratory symptoms and their relationship to both PAS exposure and smoking history were examined. The initial and most recent chest radiographs were compared by a radiologist to evaluate radiographic change consistent with pneumoconiosis as defined by the UICC/Cincinnati criteria.
The extent of each worker’s exposure to PAS was expressed so as to reflect both the quantity and duration of exposure. The “cumulative exposure index” reflects total PAS exposure and was calculated for each worker by summing monthly dust exposure. Dust concentration was measured by personal airspace gravimetric monitoring and graded on a scale of 1 (minimal) to 4 (extensive). Technical difficulties were encountered in the actual measurement of respirable dust fractrion due to the agglomeration characteristics of the dust. However, total airborne dust values for the categories ranged from < 1.0 mg/m³ for class I up to 10 mg/m³ with occasional higher excursions for class IV. The “mean exposure index” indicates the average monthly concentration of PAS exposure for workers with variable exposure and was calculated from cumulative exposure index divided by total months of exposure. Statistical analyses were performed using Student’s t-test, Fisher’s exact test, linear and multiple regression, and analysis of variance.

Results and discussion

Results:

There was no correlation by linear regression analysis between the change per year of FVC, FEV1, or FEF25-75, and the cumulative exposure index or total years of exposure of the workers. When workers were stratified into groups of increasing magnitude of cumulative exposure index, there was no difference in the change per year of FVC, FEV1, or FEF25-75 among groups.
There were 44 workers who had spent from 11 to 35 (mean 18) years in PAS, but had serial pulmonary function data only during their last 10 years of exposure. Changes in the serial mean FVC or FEV1 for these workers were identical to a group of workers with 10 or less (mean 5.2) years of exposure.
There was no correlation between mean exposure index and clinical symptoms. While the age and smoking histories were similar in all groups of patients, sputum production was noted more frequently in patients with the lesser years of exposure as well as the lesser cumulative exposure index. Cough and dyspnea were independent of years of exposure but related best to increased pack-years of smoking.
In spite of similar CEI, smokers showed a significant 2 to 4-fold higher occurrence of cough, sputum production, and wheezing than nonsmokers.
Chest roentgenograms of 143 workers taken prior to exposure to PAS were compared to the most recent radiograph. Eleven of these workers (7.7%) had radiographic changes consistent with Grade I/I or I/O small rounded o or small irregular t type opacities. All of these workers had a previous history of working in a limestone mine or in a soda ash plant using crushed limestone. No worker with a work history of exposure only to PAS had any evidence of pneumoconiosis, including some workers exposed for up to 35 years.

Applicant's summary and conclusion

Conclusions:

No relationship was found between pulmonary function testing parameters or chest radiograph findings and either the quantity of or duration of exposure to PAS. Symptoms either have no relationship to or correlate inversely with PAS exposure – howevere, symptoms are related to cigarette smoking.