RADIOGRAPHIC AND SPIROMETRIC FINDINGS IN DIATOMACEOUS-EARTH WORKERS

Diatomaceous earth is a noncrystalline form of silica; in processing c alcining leads to formation of cristobalite, a form of crystalline sil ica, Four hundred ninety-two currently employed diatomaceous earth wor kers in a large mine and processing facility had chest radiographs pre formed and interpreted by the International Labour Office (ILO) system . Two hundred sixty-seven subjects underwent spirometry testing. Expos ure indices for total dust (largely diatomaceous earth) and cristobali te were reconstructed for each individual based upon personnel records . Analysis demonstrated the following prevalences of radiographic find ings: 5% had ILO scores greater than or equal to 1/0, and 25% had scor es of 0/1 or higher. Regression analyses showed that there was a relat ionship between both total cristobalite exposure and total dust (large ly diatomaceous earth) exposure and the ILO score. Radio graphic patte rns are not typical of those of classic silicosis. Linear regression a nalyses for forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC) and FEV1/FVC ratio did not demonstrate a relationship b etween cumulative exposure and lung function. Such analyses were perfo rmed using all subjects and stratified by smoking status. There were d ifferences in spirometric data according to radiographic ILO category, but the results were inconsistent and did not permit determining if p hysiologic changes are associated with radiographic change or if this is due to confounding. Overall, the study suggests that diatomaceous e arth pneumoconiosis (radiographically defined) is an entity distinct f r om silicosis, Recent exposure levels may produce radiographic abnorm alities but do not lead to demonstrable physiologic effect. The Preval ence of the disorder has diminished markedly in response to modem duet control measures. Ongoing medical surveillance is recommended in work ers with potential exposure to significant quantity of material.