OSHA had no former limit for doped bismuth telluride (Bi(2)Te(3)). The ACGIH has a TLV-TWA of 5 mg/m3 for Bi(2)Te(3) that has been doped with selenium sulfide. The proposed PEL was 5 mg/m3 as an 8-hour TWA; NIOSH (Ex. 8-47, Table N1) concurs with this limit, and the final rule establishes it. Bismuth telluride appears as gray, hexagonal platelets; it is also available as ingots or single crystals.
Wagner, Madden, Zimber, and Stokinger (1974, as cited in ACGIH 1986/Ex. 1-3, p. 59) conducted a one-year study in which rabbits, dogs, and rats were exposed for six hours/day, five days/week to doped bismuth telluride dust (containing 80.04 mol % Bi2Te3 and 0.20 mol % SnTe, plus a small stoichiometric excess of Te) of 1.04 um particle diameter at a mean concentration of 15 mg/m3. Small, granulomatous lesions without fibrosis appeared in the lungs of dogs at six months. In dogs that were sacrificed four months after an eight-month exposure, the lesions had regressed, and the affected lymph nodes were without cellular reaction. Rabbits exhibited similar histologic effects, but with decreased numbers of pulmonary macrophages, no fibrous tissue proliferation, and no cellular or fibrous tissue reaction around the dust deposits in the lymph nodes. The rats showed fewer granulomas but some areas of epithelialization of the alveolar walls. As was true for the other species, the rats showed neither fibrosis nor cellular reaction in the lymph nodes, despite accumulation of the intermetallic dust (Wagner, Madden, Zimber, and Stokinger 1974, as cited in ACGIH 1986/Ex. 1-3, p. 59). Only NIOSH commented on this substance.
In the final rule, an 8-hour PEL of 5 mg/m3 TWA is established for Se-doped bismuth telluride to prevent the occurrence of the pulmonary lesions seen in experimental animals. OSHA concludes that this limit will substantially reduce the significant risk of these pulmonary effects.