OSHA formerly had no exposure limits for the anhydrous or hydrated forms of sodium tetraborate. Based on the ACGIH-recommended TLVs for these substances, OSHA proposed a 1-mg/m3 8-hour TWA PEL for the anhydrous and pentahydrate forms of sodium tetraborate and a 5-mg/m3 TWA PEL for the decahydrate form. NIOSH (Ex. 8-47, Table N1) concurred with these proposed limits. However, during the rulemaking proceeding, OSHA received several comments on the proposed limits and obtained information on a large health survey currently being conducted by the U.S. Borax and Chemical Corporation. Based on this evidence, the Agency has determined that it is appropriate at this time to establish a 10-mg/m3 8-hour TWA limit for all forms of the sodium tetraborates. Anhydrous sodium tetraborate is a light gray, odorless solid; the pentahydrate and decahydrate forms are white, odorless, and crystalline.
OSHA's proposed limits were based on some early studies cited by the ACGIH (1986/Ex. 1-3) and on observation that the anhydrous and pentahydrate forms of sodium tetraborate present a greater irritant hazard than does the decahydrate form. These early studies reported that exposure to the tetraborates produces irritation of the skin, eyes, and upper respiratory tract and can cause shortness of breath and nosebleeds. These studies were criticized at the hearings by John Middleton, Manager of Product Safety for the U.S. Borax Research Corporation, because they did not have sufficient exposure data to define a dose-response relationship (Tr. p. 9-113).
During the rulemaking, commenters discussed two NIOSH health hazard evaluations (HHEs) relevant to the borates. The first study (HHE 75-059-496, NIOSH 1978o) was conducted at the Kerr-McGee Chemical Corporation plant in Trona, California. NIOSH performed clinical examinations of nine employees exposed to tetraborates and collected total dust samples for each employee. Clinical examination revealed symptoms of eye irritation in five employees, nose irritation with bleeding in three workers, throat irritation in three employees, and chapping of the hands in four workers. Four of the nine dust samples exceeded 10 mg/m3, with the highest being 29.9 mg/m3. In testimony before the Occupational Safety and Health Standards Board in California in 1985, Dr. Charles Hine of Kerr-McGee stated that dust exposures at the California plant were probably well above the 10-mg/m3 level because employees commented that dust from "frequent windstorms" was the main problem at the plant. Dr. Hine also noted that the NIOSH HHE reported that dust levels at the plant were excessive and that the visibility of employees was impaired (Ex. 3-744, Attachment I).
The second NIOSH HHE (conducted in 1980) reported on a walk-through survey of the U.S. Borax and Chemical Corporation's Boron, CA Operation. This HHE identified health complaints among employees, and its findings led to a larger, more comprehensive health survey in 1981 (HETA 80-109), a report of which was subsequently published in a peer-reviewed journal (Garabrant, Bernstein, Peters et al. 1985). Data on employees' respiratory symptoms were obtained by questionnaire, and total dust measurements were collected from historical data obtained between 1977 and 1981. The authors found no evidence of X-ray abnormalities or declines in pulmonary function among the 629 active employees examined. There was a dose-related and statistically significant increase in the frequency of reported symptoms, which included eye irritation, dry cough, nosebleeds, sore throat, shortness of breath, and chest tightness. Over 10 percent of employees having mean TWA exposures of 8.6 mg/m3, measured as total tetraborate dust, reported experiencing nosebleeds, dry cough, eye irritation, and dryness of the mouth, nose, or throat. At a mean exposure level of 14.6 mg/m3, between 15 and 30 percent of the employees examined reported these symptoms. The authors concluded that borax dust appears to act as a simple respiratory irritant and may cause small changes in pulmonary function among smokers who are also heavily exposed to borate dust.
U.S. Borax submitted to the record the written testimony of Dr. David Heilbron, a biostatistician (Ex. 3-744, Attachment 2), and of Dr. Ralph C. Smith, Professor of Occupational and Environmental Health, School of Public Health, University of Michigan (Ex. 3-744, Attachment 3), both of whom were of the opinion that the Garabrant et al. (1985) study's treatment of exposure data was biased. For example, Dr. Heilbron objected to the grouping of employees into three exposure categories, commenting that such aggregation "can seriously distort a dose-response relationship and particularly, the estimation of an effect threshold..." (Ex. 3-744, Attachment 2, p. 4). Dr. Heilbron also took issue with these authors' use of geometric means to describe the tetraborate exposure data; in the opinion of Dr. Heilbron, there was no statistical justification for the use of geometric means because of the heterogeneity of jobs within each exposure group.
OSHA believes that it is not possible to determine whether arithmetic or geometric means are appropriate without having access to the raw data. OSHA notes further that Garabrant and his co-authors (1985) both gathered and analyzed the data and that neither Dr. Heilbron nor Dr. Smith had access to these data.
Dr. Smith (Ex. 3-347, Attachment 3) believes that the exposure data in the Garabrant et al. (1985) study substantially underreported the actual exposures of the workers comprising the study group. According to Dr. Smith, when the data are reanalyzed using arithmetic means, the observed health effects would be associated with exposures to much higher dust levels than those presented in the report (Ex. 3-744, Attachment 3, p. 13).
Because the raw exposure data from the study were not available to Dr. Smith, he based his reanalysis of the exposure data on an assumption that all individuals in a job category had exposures equal to the mean exposure level for the job category as a whole. For example, according to Dr. Smith, if "four laborers in the fusing building had average exposures of 49.2 mg/m3...[it was assumed] that all four had the same exposure" (Ex. 3-744, Attachment 3, p. 8). OSHA believes that Dr. Smith's approach provides less information about the actual exposures of the members of the cohort than does Dr. Garabrant's because Dr. Garabrant took two factors (representative data by job category as well as subjective self-reporting of exposure levels by employees) into account, while Dr. Smith only considered a single factor (job category). That is, Dr. Smith assumes that all workers in a job category have the same exposure, while Dr. Garabrant's approach recognizes the impact of such factors as individual differences in work practices, differences in control effectiveness at different workstations, etc., on the exposures of individuals in the same job category. OSHA is therefore unpersuaded by Dr. Smith's reanalysis; the Agency finds Dr. Garabrant's analysis convincing and believes that it more accurately reflects the true exposures of members of this cohort.
Largely because of questions raised concerning the dose-response relationship for tetraborates, U.S. Borax has been conducting a large epidemiologic study at its facility. This study, described at the informal hearing by Mr. Middleton (Tr. pp. 9-114 to 9-115, Ex. 120), will span a three- to four-year period and will obtain about 400 measurements of workplace tetraborate dust. The test protocols have been reviewed by representatives of OSHA, the U.S. Bureau of Mines, NIOSH, the ACGIH TLV Committee, and the Mine Safety and Health Administration. The final report is expected to be released in mid-1989. At the hearing, Mr. Middleton stated the position of U.S. Borax:
OSHA commends U.S. Borax for undertaking this effort to study the relationship between exposure to tetraborates and respiratory effects. OSHA believes that such data are essential to inform employees properly about hazards present in their workplaces and to guide employers in the development of effective occupational health programs. However, OSHA does not agree that the evidence currently available is inadequate to serve as a basis for establishing a PEL for the tetraborates at the present time. The study by Garabrant et al. (1985) does demonstrate a dose-response relationship for respiratory symptoms and exposure to sodium borates. OSHA finds that employees should be protected from experiencing the symptoms that have been reported. These symptoms, which have been reported in the more recent Garabrant et al. (1985) and NIOSH (1978o; 1980b) studies, as well as in the older literature, include nosebleeds, upper respiratory tract irritation, dermatitis, and dyspnea. OSHA believes that this evidence clearly indicates that the tetraborates act as primary respiratory and skin irritants, and that a 10-mg/m3 PEL is clearly warranted. In light of the research currently being conducted by U.S. Borax, however, OSHA notes that the Agency will consider new evidence as it becomes available and will revise its limits if such action appears to be appropriate.
OSHA agrees with U.S. Borax that, at this time, there are insufficient data upon which to establish different PELs for the different hydrated forms of tetraborate. OSHA believes that current sampling and analytical procedures cannot distinguish among the various hydrated forms of tetraborate (Ex. 3-744, Attachment 3, pp. 4 - 5) and therefore that separate standards of 5 mg/m3 and 1 mg/m3 are not feasible at this time.
OSHA concludes that an 8-hour TWA of 10 mg/m3 is appropriate for the tetraborates, and the final rule establishes this limit. OSHA finds that, in the absence of any limit on exposure, employees are at significant risk of experiencing acute eye, skin, and respiratory irritation effects, and that a 10-mg/m3 PEL will substantially reduce these risks. The Agency considers the eye, skin, and upper respiratory tract irritation caused by exposure to all forms of sodium tetraborates to be material impairments of health.