OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 7439-97-6; Chemical Formula: Hg

OSHA formerly had a TWA limit of 0.1 mg/m3 for mercury (including vapor). The ACGIH recommends a TLV-TWA of 0.05 mg/m3 for mercury vapor, measured as mercury, and a skin notation. NIOSH has a REL of 0.05 mg/m3 as an 8-hour TWA. The Agency proposed a PEL of 0.05 mg/m3 TWA for mercury and its vapor, measured as Hg, and the final rule establishes this limit, also with a skin notation. NIOSH (EX. 8-47, Table N1) concurs that this limit is appropriate. Elemental mercury is a silvery, odorless, heavy liquid.

Inhalation of high concentrations of mercury vapor for relatively brief periods can cause pneumonitis, bronchitis, chest pain, dyspnea, coughing, stomatitis, gingivitis, salivation, and diarrhea (NIOSH 1973b, as cited in ACGIH 1986/Ex. 1-3, p. 359; Ashe, Largent, Dutra et al. 1953/ Ex. 1-502). Chronic mercurialism is manifested by central nervous system effects, including tremor, a variety of neuropsychiatric disturbances, and loss of appetite (Kazantzis 1968, as cited in ACGIH 1986/Ex. 1-3, p. 359; Smith, Vorwald, Patil, and Mooney 1970/Ex. 1-373).

Severe organ damage occurred in rabbits exposed for four hours to an average vapor concentration of 28.8 mg/m3. Damage was observed in the kidneys, liver, brain, heart, lungs, and colon (Ashe, Largent, Dutra et al. 1953/Ex. 1-502). A study by Smith, Vorwald, Patil, and Mooney (1970/Ex. 1-373) of 567 male workers exposed to a mean exposure level of 0.065 mg/m3 (S.D. + 0.085) showed a significant dose-related increase in the incidence of weight loss, tremors, abnormal reflexes, nervousness, and insomnia among workers exposed to0.1 mg/m3 or higher. There were slight increases in the incidence of insomnia and loss of appetite among workers exposed to 0.1 mg/m3 or less. Smith, Vorwald, Patil, and Mooney (1970/Ex. 1-373) concluded that a limit of 0.1 mg/m3 contained little or no margin of safety. Six of 75 workers regularly exposed to 0.05 to 0.1 mg/m3 of mercury vapor in a glassware manufacturing plant reported insomnia, and one was found to have tremors (Danziger and Possick 1973/Ex. 1-504). One of 11 workers employed in a mercury mine or refining plant and exposed at vapor concentrations below 0.1 mg/m3 had sore gums, loose teeth, or excess salivation (Rentos and Seligman 1968/Ex. 1-523).

NIOSH (1973b, as cited in ACGIH 1986/Ex. 1-3, p. 358) has recommended a 10-hour TWA limit of 0.05 mg/m3 for inorganic mercury and concluded that hyperactivity, rather than tremor, may be the most typical symptom of chronic mercurialism. Two studies report no evidence of mercury vapor poisoning in industrial settings where characteristic exposures ranged between 0.05 and 0.1 mg/m3 (Danziger and Possick 1973/Ex. 1-504; McGill, Ladd, Jacobs, and Goldwater 1964/Ex. 1-520).

In workers exposed levels above 0.1 mg/m3, toxic symptoms were seen (Rentos and Seligman 1968/Ex. 1-523). Turrian, Grandjean, and Turrian (1956, as cited in ACGIH 1986/Ex. 1-3, p. 358) found that 33 percent of workers exposed to the vapor at levels above 0.05 mg/m3 exhibited hyperexcitability, while only 8 percent of those exposed below that level manifested this symptom. About 20 percent of workers in both groups exhibited tremor. The ACGIH notes that, after exposure to the vapor, “a relatively high percentage of the absorbed mercury remains in the brain,” compared with the amount deposited in the brain after exposure to the aryl and inorganic compounds (ACGIH 1986/Ex. 1-3, p. 359). The ACGIH accordingly recommends a higher TLV-TWA for aryl and inorganic mercury than for mercury vapor (see, however, the discussion of aryl and inorganic mercury above).

Robert G. Smerko, President of the Chlorine Institute (Ex. 3-828), and the Laboratory Products Association (Ex. 135) urged OSHA to retain its 0.1-mg/m3 PEL and to require urinary mercury analysis in lieu of a reduced PEL because dermal contact with mercury may contribute substantially to its toxicity (Ex. 3-828; Tr. pp. 10-171 to 10-177). Mr. Smerko cited several reports of such effects in his testimony and submission, including reports of poisoning resulting from contact with contaminated clothing. Because dermal contact is a significant route of exposure for mercury, Mr. Smerko commented:

  • There is a large probability that air measurements of mercury concentrations (aryl mercury, inorganic salts, or elemental mercury vapor) either overestimate or underestimate the extent of exposure to mercury. The extreme accuracy and precision of the urinary mercury analysis and the amount of work that has been done in correlating urinary mercury concentrations with the presence or absence of effects from exposure to mercury warrant the proposal that a biological standard, or a comprehensive standard that includes an air concentration and urinary mercury concentration, be established for aryl mercury, inorganic salts of mercury, and elemental mercury vapor (Ex. 3-828, p. 9).

Mr. Robert F. Adams, Senior Industrial Hygienist for Occidental Chemical Corporation (Ex. 3-1174), supported the position of the Chlorine Institute on this issue. Dr. James Melius of the New York State Department of Health supported both environmental and biological monitoring but agreed with the PEL proposed by OSHA. (Tr. pp. 11-105, 11-106, 11-109 to 11-111).

OSHA agrees that prevention of mercury contamination of skin and clothing, as well as the proper handling of contaminated clothing, are essential elements of a program to protect employees from the health hazards of mercury. OSHA also believes that mercury presents one of the rare instances in which a biological-monitoring-based standard may represent an effective and reasonable approach for ensuring worker protection. Margaret Seminario, Associate Director of Occupational Safety, Health, and Social Security for the AFL-CIO, also supported provisions for biological monitoring of mercury as well as supporting the OSHA proposed airborne level (Ex. 194, Appendix 1, p. 3). However, developing such a standard is beyond the scope of this rulemaking, which is being conducted solely to revise OSHA’s air contaminant limits.

Despite some of the uncertainties in the studies described above regarding the relationship between airborne exposure levels and health effects, OSHA concludes that the data suggest that the former PEL of 0.1 mg/m3 is not sufficiently protective. Given the severity of the neuropathic effects caused by mercury poisoning, OSHA finds that a reduction in the airborne limit is necessary to ensure that workers are not at significant risk of mercury-related neuropathic effects. Therefore, OSHA is revising its PEL for elemental mercury vapor to 0.05 mg/m3 as an 8-hour TWA. In addition, because skin absorption is a significant route of exposure and leads to systemic poisoning, as evidenced by Mr. Smerko’s written testimony, OSHA is including a skin notation in the final rule.

OSHA is establishing an 8-hour TWA PEL of 0.05 mg/m3 TWA for mercury vapor, with a skin notation. The Agency concludes that this limit will substantially reduce the significant risks of acute and chronic mercury poisoning (which constitute material health impairments) that have been demonstrated to occur at exposure levels above 0.05 mg/m3. The skin notation is added because the vapors of elemental mercury can be readily absorbed through the skin.

Page last reviewed: September 28, 2011