OSHA formerly had a PEL of 0.3 ppm TWA for phosphine. The ACGIH recommends a TLV-TWA of 0.3 ppm and a TLV-STEL of 1.0 ppm. The proposal retained the 8-hour TWA of 0.3 ppm and added a STEL of 1 ppm. NIOSH (Ex. 8-47) concurred with this proposal. These limits are established in the final rule. Phosphine is a colorless gas with a disagreeable, garlic-like odor.
Early studies reported that laboratory animals could tolerate phosphine in four-hour-daily exposures of 5 ppm for two months, but fatalities were observed from seven similar exposures at 10 ppm (Muller 1940/Ex. 1-919). In 1975, Waritz and Brown (Ex. 1-451) reported a 4-hour LC(50) of 11 ppm in rats; these lethal exposures caused effects typical of respiratory irritation.
Prior to 1958, numerous cases of phosphine-related occupational poisonings and deaths were reported, including a fatality caused by pulmonary edema that was attributed to an exposure of 8 ppm for two hours daily (Harger and Spolyar 1958/Ex. 1-327). Sublethal symptoms (without chronic effects) occurred at phosphine exposures averaging 10 ppm or less, with excursions of up to 35 ppm; recorded symptoms included diarrhea, nausea, vomiting, respiratory distress, and dizziness (Jones, Jones, and Longley 1964/Ex. 1-420). The literature contains no documented reports of chronic poisoning caused by prolonged exposure to phosphine, although several authorities have asserted that this is a possibility (Henderson and Haggard 1943e/Ex. 1-1086; Fairhall 1957h, as cited in ACGIH 1986/Ex. 1-3, p. 883; Johnstone and Miller 1960/Ex. 1-1114; Patty 1963f, as cited in ACGIH 1986/Ex. 1-3, p. 883; American Industrial Hygiene Association (AIHA) 1964/Ex. 1-407).
Joel Carr, Health and Safety Research Director for the American Federation of Grain Millers Union, testified on the toxicology of and employee exposures to phosphine in grain elevators and flour mills (Ex. 8-1; Tr. pp. 7-240 to 7-259). Mr. Carr described a report of a group of industrial hygiene studies published by NIOSH (Zaebst 1986; Zaebst, Blade, Morelli-Schroth et al. 1987; Zaebst, Blade, Burroughs et al. 1988), in which applicators of phosphine were found to be exposed above the proposed TWA PEL and STEL; nonapplicator workers also become exposed while working near fumigated grain, while loading or transferring fumigated grain, or while working in elevators and mills.
Mr. Carr also cited additional health studies, including a report of chronic neurological problems following an acute episode of phosphine poisoning (Kurzbauer and Keise 1987), animal data indicating that phosphine inhibits catalase activity (Price and Walter 1987), and studies showing phosphine to be mutagenic both in vitro and in vivo (Occupational/ Environmental Pathology Review 1988)(Tr. p. 7-246; Ex. 45A). He cited another NIOSH report (Studies of the Prevalence of Chronic, Non-Specific Lung Disease and Related Health Problems in the Grain Handling Industry, Rankin et al. 1986) that identified several symptoms associated with phosphine exposure, including headaches, dizziness, diarrhea, nausea, and dyspnea, as well as palpable abdomen (Tr. p. 7-247). Mr. Carr also mentioned the preliminary results of an NCI mortality study of grain workers in which elevated relative risks were found for non-Hodgkin's lymphoma (Tr. p. 7-254). Mr. Carr urged OSHA to adopt a short-term limit of 0.3 ppm, which is consistent with EPA's Maximum Concentration Limit for phosphine applicators (Tr. p. 7-250); in addition, he recommended that OSHA establish provisions for exposure and medical monitoring, training, and respiratory protection for phosphine.
OSHA appreciates the information supplied by Mr. Carr on phosphine toxicity and awaits completion of the ongoing studies discussed by him at the hearing. In response to Mr. Carr's request that OSHA establish other requirements in addition to the PEL, OSHA notes that the Agency is currently conducting rulemaking activities to develop generic standards for respiratory protection, medical surveillance, and exposure monitoring, but that the sole purpose of this rulemaking is to revise OSHA's outdated exposure limits.
In the final rule, OSHA is retaining the 8-hour TWA PEL for phosphine of 0.3 ppm and adding a 15-minute STEL of 1 ppm. The Agency concludes that both of these limits are required to substantially reduce the significant risk of lung damage, diarrhea, and nausea, all material health impairments associated with elevated short-term and long-term exposure to this gas.