Exposure to
diatomaceous earth with low crystalline
silica content (< 1%) is rarely reported to cause pneumoconiotic disease, whereas
airway obstruction and
bronchitis are more frequently reported. We investigated the occurrence of
pneumoconiosis and airflow limitation in 172 male workers from 5 potato sorting plants (55 controls, 29 salesmen, 72 currently exposed, and 16 retired exposed) exposed to inorganic dust from former sea terraces (7.7-15.4 mg/m3), high in
diatomaceous earth. The presence of
fibrosis was evaluated by chest radiographs (exposed only) and serum levels of
type III procollagen (
P-III-P) were measured as an estimate of fibrogenetic activity. Lung function was assessed by flow volume curves and impedance measurements. A validated questionnaire was used to record respiratory symptoms. No pneumoconiotic abnormalities were demonstrated by chest radiographs. In line with this finding, serum
P-III-P levels were not elevated in exposed workers as compared to controls, suggesting no differences in fibrogenetic activity. In fact, serum
P-III-P levels decreased significantly (P < 0.03) with increasing cumulative exposure. Flow volume parameters indicated airflow obstruction, dose-related to (cumulative) dust exposure; the annual decline in forced expiratory flow volume (FEV1) was estimated at 10.5 ml/year (P < 0.05).
Airway obstruction was confirmed by impedance analysis: In the retired group impedance changes were compatible with
airway obstruction extending into the peripheral airways. We conclude that this exposure to
quartz during potato sorting does not result in an increased risk for
pneumoconiosis, but that (prolonged) surveillance in this group is desirable in order to detect early indications of airflow obstruction.