EXPOSURE TO TREMOLITE FIBERS OF NATURAL ORIGIN IN THE EL DORADO HILLS AREA, CALIFORNIA: A CASE STUDY OF IN VIVO ALTERATION

The town of Ed Dorado Hills California is located on a Mesozoic volcanic and volcanoclastic complex composed largely of arc derived meta-basaltic rocks and detritus that are intersected by intermittent lens of ultramafic rock. Slip-fiber and cross fiber veins of tremolite are common. Some crack intersections contain tubular, straight, rope-like masses of tremolite that are also common in the overlying soil. Previously, in the process of doing a day's fieldwork in the El Dorado Hills one of the authors (MG), a geologist and physician, documented his exposure to tremolite fibers. Tremolite, rock, and soil samples were collected at several sites with minimal visible dust. Tremolite fibers were recovered in purulent sputum the next morning in the setting of a brief and mild dust-induced bronchitis. A laryngeal washing of 400 cc, taken 3 months later, showed retained tremolite fibers in the process of oxidation and splitting, with a fiber concentration too high to measure without diluting the sample. The tremolite in samples from several field sites was analyzed by PLM, SEM, and TEM. Sputum and washings were analyzed by PLM and by SEM and TEM, respectively. Crystallographic data indicate an oxidation/cleavage mechanism of fine fiber formation, resulting from progressive splitting along cleavage traces in massive to coarsely fibrous tremolite. High resolution TEM showed continuous double chains between conjoined fibers prior to splitting. Longitudinal tremolite fiber surfaces from weathered samples, from the laryngeal washing, and fibers treated with hydrogen peroxide, were eroded irregularly by oxidation that cuts across cleavage planes producing an amorphous oxidation product. Fiberization, emergence of flexibility, and spontaneous inter-fiber rotation were observed with progressive fiber splitting. The oxidized tremolite is itself highly oxidizing, suggesting mechanisms for induction of purulent response and oxidative carcinogenesis. We conclude that the potential health risk is heightened by a combination of a considerable retention of tremolite despite brief exposure under minimal dust conditions, in vivo production of fine fibers out of massive to coarsely fibrous tremolite, and in vivo production of amorphous oxidized tremolite surfaces that may increase carcinogenesis.