Rats were exposed by inhalation to 5 or 50 mg/m 3 Mount St. Helens volcanic ash, to 50 mg/m 3 quartz (positive controls), or to filtered room air (sham-exposed controls), for 6 hr/ day, 5 days/week, for up to 24 months to investigate biological effects of chronic inhalation exposure to volcanic ash under controlled laboratory conditions. Exposure-related lung changes comprised accelerated respiratory frequency; alveolar macrophage accumulation; interstitial reaction; lymphoreticular reaction in peribronchiolar regions and in mediastinal lymph nodes; alveolar proteinosis in the 50-mg/m 3 ash-or quartz-exposed groups; increase in fresh lung weights; decreased body weight and increased mortality in the quartz-exposed group; and epidermoid carcinomas especially in the quartz-exposed females and, to a lesser extent, in the 50-mg/m 3 ash-exposed females. The observed changes reflect significant dose-response and agent-response relationships. © 1986 Academic Press, Inc. It soon became apparent that acute effects in healthy persons were minor and temporary (Johnson et al., 1982; Washington State Health Services Division, 1980). However, the effects of chronic exposure to volcanic ash--as experienced, for example, by loggers in the fallout area--were unknown. This uncertainty emphasized the necessity for evaluating the health hazards of chronic ash inhalation in a suitable animal model under controlled laboratory conditions. The results of our study exceed regional relevance and will be of interest to medical personnel and health authorities in nations experiencing volcanic activity, such as the Pacific rim countries which form "the ring of fire." The objectives of our study were to determine whether chronic inhalation of volcanic ash causes lung changes; type and degree of lung changes as a function of ash aerosol concentration and cumulative exposure time; and regression of ash-induced lung changes as a function of aerosol concentration, cumulative exposure, and recuperation time.
INTRODUCTION
MATERIALS AND METHODS
Volcanic AshMount St. Helens volcanic ash was collected at three undisturbed sites in Yakima, Ritzville, and Spokane in the State of Washington, 5 weeks after the May 18, 1980, eruption. These sites represented major population centers in the areas of heaviest ash deposition. The ash samples were oven-dried at 100 _+ 5°C, passed through a No.20 (850-txm) sieve to remove foreign materials, thoroughly mixed in a V-blender, and sterilized by heating in ceramic dishes in an oven at 130°C for 16 hr. After cooling to room temperature, the ash was sealed in polyethylene bags and stored in 5-gal paint buckets for the animal exposures. Ash samples of respirable size, analyzed in our laboratory, contained from 3 to 4% free crystalline silica. Slightly more than half this quantity was quartz and most of the remainder was cristobalite.Min-U-sil (5 fxm) was obtained from Pennsylvania Glass Sand Corporation for exposing a positive-control group to a-quartz, a known potent cytotoxic agent.
Aerosol Generation and Characteri...
