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Bronchoalveolar lavage (BAL) has been performed in 22 healthy nonsmoking male volunteers after exposure to 8 ppm SO2 (20 mg/m3). The exposure level exceeds the US Short-Term Exposure Limit (STEL) of 5 ppm, but occurs as peak exposures in industrial indoor environments. Exposures were made during light work on a bicycle ergometer in an environmental exposure chamber for 20 min. BAL was performed 2 wk or more before exposure and 4, 8, 24, and 72 h after exposure in eight subjects at each time interval. Four hours after exposure significant increases were found in the numbers of lysozyme-positive macrophages, lymphocytes, and mast cells (p less than 0.02 to 0.05). Lymphocytes, lysozyme-positive macrophages, total count of alveolar macrophages, and total cell number increased to peak values 24 h after exposure (p less than 0.02 to 0.05). Seventy-two hours after exposure the cell numbers and distribution had returned to normal. The time course of the cell reactions found in BAL fluid after controlled SO2 exposure represents a new and previously not reported response to a noxious gas.

The incidence of allergic alveolitis (AA) and of febrile reactions (FR) to inhaled mold dust in those who did not meet the criteria of AA was investigated in Swedish farmers, and the findings were related to farming methods and exposure type. A questionnaire was completed by 6,702 farmers. A stratified sample of 390 farmers underwent examination comprising spirometry, a skin-prick test, blood tests for precipitating antibodies and total IgE and an interview concerning symptoms, exposure and farming methods. The yearly incidence of AA was 2–3/10,000 farmers. The incidence of FR was 30–50 times higher (1/100 farmers) and the majority of these reactions was of a toxic rather than allergic type (organic dust toxic syndrome). Among farmers with recent FR or AA there was a higher frequency of positive precipitin reactions (p < 0.05). Exposures to moldy grain, straw, wood chips and hay were associated with both AA and FR. A major difference in exposure between 17 farmers with AA and 80 with FR was that AA appeared to require repeated exposure, while FR was associated with occasional heavy exposure to mold dust.

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