Previously, OSHA did not regulate the hydrogenated terphenyls. The ACGIH has a TLV-TWA of 0.5 ppm (approximately 5 mg/m3) TWA for these complex mixtures of ortho-, meta-, and para-terphenyls in various stages of hydrogenation. The proposed PEL was 0.5 ppm as an 8-hour TWA; NIOSH (Ex. 8-47) concurred with the proposed limit, and the final rule establishes that limit.
Acute exposure to the hydrogenated terphenyls poses a risk of potential lung, eye, and skin damage. Chronic exposure presents a risk of systemic toxicity involving injury to the liver, kidneys, and blood-forming organs, as well as possible metabolic disturbances and cancer (ACGIH 1986/Ex. 1-3, p. 311).
Early studies of unhydrogenated terphenyl isomers determined that the LD(50) in rats is low, i.e., 1900 mg/kg for the ortho isomer, 2400 mg/kg for the meta isomer, and 10,000 mg/kg for the para isomer (Cornish, Bahor, and Ryan 1962/Ex. 1-410). Thirty-day oral administration of 500 mg/kg/day in the diet of rats indicated possible liver and kidney damage, which was suggested by increases in the liver and kidney-to-body-weight ratios and decreases in the rate of weight gain (Cornish, Bahor, and Ryan 1962/Ex. 1-410). Other studies have demonstrated nephrotoxicity and liver damage in rats fed 33 mg/kg or more of unirradiated terphenyl isomers (Petkau and Hoogstraaten 1965/Ex. 1-432; Young, Petkau, and Hoogstraaten 1969/Ex. 1-459). Inhalation studies showed that bronchopneumonia is associated with exposure at 88 to 356 ppm to the ortho and meta isomers, but not to the para isomer at 103 ppm (Haley, Detrick, Komesu et al. 1959/Ex. 1-326). The work of Cornish, Bahor, and Ryan (1962/Ex. 1-410) showed that none of the isomers caused skin irritation in rabbits following a 24-hour dermal application. For terphenyls that are approximately 40-percent hydrogenated, the acute oral LD(50) in rats is reported as 17,500 mg/kg; in mice, it is 12,500 mg/kg (Adamson and Weeks 1973/Ex. 1-295). This study also demonstrated that an irradiated hydrogenated terphenyl mixture is three times more acutely toxic by ingestion than is a nonirradiated mixture. This finding was confirmed in 16-week chronic ingestion studies (Adamson, Bowden, and Wyatt 1969/Ex. 1-293); these authors found that 1200 mg/kg of an irradiated mixture was lethal to mice, while the same dose in nonirradiated form produced only an irreversible interstitial nephritis. In the same study, no effects were observed for either mixture at a dose level of 250 mg/kg.
Eight-day inhalation studies in mice showed some pathologic changes in lung tissue after 500 mg/m3 (50 ppm) exposures to nonirradiated hydrogenated terphenyls; eight-week exposures at 2000 mg/m3 (200 ppm) resulted in the same lung damage, as well as in some proliferation of the smooth endoplastic reticulum in the liver (Adamson, Bowden, and Wyatt 1969/Ex. 1-293; Adamson and Weeks 1973/Ex. 1-295). Carcinogenesis in mice has been reported from 8-week skin exposures to the irradiated mixture (Henderson and Weeks 1973/Ex. 1-784). The significance of the changes observed by Adamson and Furlong (1974/Ex. 1-294) in the mouse lung after eight weeks of inhalation exposure to the irradiated mixture is difficult to interpret in terms of the potential of the hydrogenated terphenyls to cause pulmonary cancer; particles were found to clear the lungs rapidly but to accumulate and clear more slowly in the intestine, kidney, and liver. No comments other than those of NIOSH (Ex. 8-47) were received on this substance.
In the final rule, OSHA is establishing a 0.5-ppm 8-hour TWA for the complex mixtures of ortho-, meta-, and paraterphenyls (either irradiated or nonirradiated) in various stages of hydrogenation. The Agency concludes that this limit will protect workers from the significant risks of eye, skin, and lung damage and of systemic toxicity to the liver, kidneys, and blood-forming organs, all material health impairments that are potentially associated with exposure to these substances at levels above the new PEL.