Regulations (Preambles to Final Rules) - Table of Contents Regulations (Preambles to Final Rules) - Table of Contents
• Record Type: Occupational Exposure to 4,4' Methylenedianiline (MDA)
• Section: 7
• Title: Section 7 - VII. Significance of Risk

VII. Significance of Risk

OSHA previously made a preliminary finding of significant risk resulting from occupational exposure to MDA in responding to EPA's referral (51 FR 6748), and in the proposed rule at 54 FR 20682. In making this determination, OSHA was guided by a number of factors that are consistent with recent court interpretations of the OSH Act and rationale, and policy formulation regarding significance of risk. As prescribed by Section 6(b)(5) of the OSH Act, the Agency examined the body of "best available evidence" on the toxic effects of MDA to determine the nature and extent of possible health consequences resulting from workplace exposure. The quantitative risk assessment found in Table 1 was used with other relevant information by OSHA to determine whether establishing a permissible exposure limit and other standard provisions would substantially reduce the risk.

For guidance in determining whether regulatory activity would substantially reduce the risk, OSHA followed general guidance given to the Agency by the Court for arriving at findings of the significance of an occupational health risk. The Court stated as follows:

It is the Agency's responsibility to determine in the first instance what it considers to be a "significant" risk. Some risks are plainly acceptable and others are plainly unacceptable. If, for example, the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. On the other hand, if the odds are one in a thousand that regular inhalation of gasoline vapors that are 2 percent benzene will be fatal, a reasonable person might well consider the risk significant and take appropriate steps to decrease or eliminate it (IUD v. API, 448 U.S. at 655).

Although the Court's example is based on a quantitative expression of the risk, the Court indicated that the significant risk determination required of OSHA is not "a mathematical straitjacket," and that "OSHA is not required to support the finding that a significant risk exists with anything approaching scientific certainty." The Court ruled that:

...a reviewing court [is] to give OSHA some leeway where its findings must be made on the frontiers of scientific knowledge [and] ....the Agency is free to use conservative assumptions in interpreting the data with respect to carcinogens, risking error on the side of over protection rather than under protection (448 U.S. at 655, 656).

OSHA largely bases its findings that a particular level of risk is "significant" on policy considerations (IUD v. API, 448 U.S. 655, 656, n. 62). As part of the significant risk determination, OSHA examined a number of factors consistent with its policy (see Arsenic, 48 FR 1864, January 14,1983; Ethylene Oxide, 48 FR 17284, April 21, 1983; Asbestos, 51 FR 22611, June 20, 1986)); and Formaldehyde, 52 FR 46167, December 4, 1987. These include the type of risk presented, the quality of the underlying data, the reasonableness of the risk assessments, and the statistical significance of risk. Table 1 was adopted by the Committee from the OSHA MDA risk assessment found in the Docket at Exhibit 1-247.


     TABLE 1 - Estimated Cancer Risks for Worker Exposure to MDA

(For Table 1, Click Here)

OSHA reviewed the toxicological and epidemiological literature and the record evidence on MDA described in the Health Effects section. The record, as summarized herein, shows that MDA exposure is associated with a number of adverse health effects. The NTP study indicates that MDA is carcinogenic in both rats and mice (Ex. 1-36). The study appears to have been conducted in accordance with good laboratory practices and is adequate for use as the basis for quantitative risk assessment. The Oak Ridge National Laboratories data also support the findings that MDA is a carcinogen in test animals (52 FR 26782). The ability of MDA to induce tumors in animals, evidence that MDA induces cancer in humans, and data indicating that MDA interacts with genetic material lead to the conclusion that this chemical is an animal carcinogen and is probably carcinogenic to humans.

In animals, MDA has also been associated with genotoxicity, retinopathy, allergic dermatitis, and hepatotoxicity. In addition, human studies strongly indicate that MDA causes a characteristic acute toxic hepatitis.

The quantitative risk assessment, which is used to estimate risk in humans is based on animal studies by NTP. This correlation is achieved by reliance upon generally accepted health policies, which indicate that carcinogenicity demonstrated by a chemical in mammalian species is sufficient to conclude that carcinogenicity is possible to humans. The fit of the experimental cancer data to the model used in making the extrapolations is good and the risk assumptions are reasonable. Therefore, the resulting assessment appears appropriate.

Currently, there is no OSHA standard regulating occupational exposure to MDA. The estimates of occupational risk resulting from inhalation and dermal contact with MDA were made from data (approximately 1983) collected by NIOSH, EPA, and CMA which indicate that current ambient exposures are in the range of 50 to 70 ppb (Scenarios I(a) and I(b) of Table I). The estimates of lifetime risk resulting from these ambient exposures together with dermal deposition were approximately 6-30 per 1000. OSHA concludes that the exposure data and the data used to make risk predictions are appropriate and finds that occupational exposure to MDA constitutes a significant risk of harm to workers. These findings are consistent with OSHA determinations from other rulemakings, such as: Ethylene Oxide (April. 21, 1983; 48 FR 17284, 17295); Benzene (September 11, 1987; 52 FR 34460, 34497); and Formaldehyde (December 4, 1987; 52 FR 46168, 46223). Those estimates per 1000 employees for a working life-time exposure were 63-109 excess cancer deaths from ethylene oxide; 95 excess leukemia deaths from benzene; and .4 - 18 excess cancer deaths from formaldehyde, based on the PEL's which applied prior to the completion of new lower standards.

In evaluating significant risk a framework is provided by an examination of occupational risk rates and legislative intent. For example, in the high risk occupations of fire fighting and mining and quarrying the average risk of death from an occupational injury or an acute occupationally related illness from a lifetime of employment (45 years) is 27.45 and 20.16 per 1,000 employees respectively. Typical lifetime occupational risks of death in occupations of moderate risk are 2.7 per 1,000 for all manufacturing and 1.62 per 1,000 for all service employment. Typical lifetime occupational risks of death in occupations of relatively low risk are 0.48 per 1,000 in electric equipment and 0.07 per 1,000 in retail clothing. These rates are derived from 1979 and 1980 Bureau of Labor Statistics data from employers with 11 or more employees adjusted to 45 years of employment for 46 weeks per year.

In light of the above, OSHA concludes that the estimates of risk associated with occupational exposure to MDA (6 to 30 per 1000) fit well within the range of other risks which OSHA has previously concluded are significant. These estimates are higher than risks of fatality in occupations of average risk, and are substantially higher than the examples presented by the Supreme Court (IUD v. API, Id.).

OSHA finds that the implementation of the final standards will substantially reduce the risks associated with occupational exposure to MDA. OSHA estimates that the risks associated with the PEL of 10 ppb in conjunction with other provisions of the standard will be reduced to less than 0.8 excess cancer deaths per 1000 workers exposed over a working life-time (See Table 1, Scenario III(e)). This represents an 87 to 98 percent reduction in risk. OSHA considers such a reduction to be substantial. Although OSHA is not able to quantify the reduction in the incidence of other diseases that would occur with the implementation of the standard, OSHA finds that these would also be reduced.

OSHA believes that the presence of the additional provisions in the MDA standards act together to reduce the risks associated with occupational exposure to MDA. Provisions, such as annual training, medical surveillance, hazard communication, emergency plans, housekeeping, and exposure monitoring, work together in an inextricable manner to provide additional protection to workers both from cancer and from other toxic effects (52 FR 46234).

No evidence was provided as a result of the issuance of the NPRM which would cause OSHA to change any of the risk assessment analyses or conclusions. A more complete discussion of the significant risk of occupational exposure to MDA can be found in the NPRM (54 FR 20672, May 12, 1989) and the Committee's Recommendations (52 FR 26776, July 16, 1987).

[57 FR 35630, Aug. 10, 1992]

Regulations (Preambles to Final Rules) - Table of Contents Regulations (Preambles to Final Rules) - Table of Contents