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: 101-14-4; Chemical Formula: CH2(C6H4ClNH2)2

Previously, OSHA had no limit for 4,4-methylene bis (2-chloroaniline), or MBOCA, although in 1974, OSHA did issue a standard for MBOCA as part of the Agency’s “14 Carcinogens” rulemaking; however, the reviewing court set the MBOCA standard aside on procedural grounds. The ACGIH has a limit of 0.02 ppm (0.22 mg/m3) TWA, with a skin notation, and classifies MBOCA as a suspected human carcinogen (A2). NIOSH recommends a TWA limit of 3 ug/m3 for MBOCA, which NIOSH considers a potential occupational carcinogen. OSHA proposed an 8-hour TWA of 0.02 ppm TWA for MBOCA, with a skin notation; the final rule establishes these limits. MBOCA is a tan-colored solid.

MBOCA is highly toxic, causing cyanosis, kidney irritation, methemoglobinemia, and cancer. It is similar in effect to the other aromatic amines (Hosein and van Roosmalen 1978/ Ex. 1-1054; Mastromatteo 1965/Ex. 1-146).

Steinhoff and Grundmann (1969/Ex. 1-762) demonstrated that feeding MBOCA at unspecified levels to rats on a protein-deficient diet caused a high incidence of liver cancer. Russfield, Homburger, Boger and associates (1975/Ex. 1-929) reported liver and lung tumors in rats fed MBOCA while on a standard diet. Dogs fed MBOCA at a dose of 100 mg/day, five days/week showed no hepatic cancer, but malignant nodules in the bladder occurred in a dog fed MBOCA for nine years (Stula et al. 1977, as cited in ACGIH 1986/Ex. 1-3, p. 392.4).

In industry, reversible hematuria has been reported among MBOCA-exposed workers, but precise concentration data are lacking (Mastromatteo 1965/Ex. 1-146). An early study of workers exposed for as long as 18 years to MBOCA showed no adverse effects, although the substance and its metabolites were detected in the urine of these subjects (Linch, O’Connor, Barnes et al. 1971/Ex. 1-791). Hosein and van Roosmalen (1978/Ex. 1-1054) reported an industrial accident in which molten MBOCA was splashed in a worker’s face; urinary levels of 3.6 mg/L MBOCA, as well as protein, were detected in the urine, and the subject experienced nausea. However, this worker recovered quickly.

A recent NIOSH retrospective study involving 370 workers employed in a MBOCA-manufacturing plant evaluated the carcinogenicity of this substance, which is structurally similar to benzidine. This study found two cases of bladder cancers in very young workers (less than 30 years of age), both of whom were nonsmokers.

The Polyurethane Manufacturers Association (PMA) expressed its support for establishing a 0.02-ppm TWA for MBOCA, stating that the proposal “will significantly assist in assuring that any exposure to the chemical is appropriately controlled while imposing a regulation which can be feasibly complied with by employers” (Ex. 3-683, p. 4). In addition, the PMA indicated that, with currently applied engineering and work practice controls, MBOCA “can be used with no or very limited employee exposure” (Ex. 3-683, p. 5). The PMA also supported establishment of a PEL for MBOCA “to provide OSHA with a chemical-specific enforcement capability to deal with any isolated instances where a user of the chemical also disregards recognized industry practices and fails to reasonably control employee exposure to the chemical” (Ex. 3-683, p. 7). The PMA supported the addition of a skin notation for MBOCA, identifying dermal contact as a “principal potential route for employee exposure” (Ex. 3-683, p. 7).

NIOSH (Ex. 8-47, Table N6B) did not concur with OSHA’s proposed PEL and recommended instead that the Agency undertake a separate 6(b) rulemaking for MBOCA. OSHA is aware of the two bladder cancer cases reported by NIOSH, and will continue to monitor the toxicologic evidence on MBOCA in the future to determine whether the evidence warrants a further reduction in the exposure limit. The AFL-CIO (Ex. 194) urged OSHA to promulgate ancillary limits for MBOCA; however, as discussed in Section IV.D., the Agency is not at this time promulgating such provisions because of the size and scope of this rulemaking.

In the final rule, OSHA is establishing an 8-hour TWA limit of 0.02 ppm for MBOCA, with a skin notation. The Agency concludes that this limit will protect workers against the significant risks of cyanosis, methemoglobinemia, kidney irritation, and bladder cancer, all material health impairments potentially associated with exposure to this substance. A skin notation is established to protect against the percutaneous absorption and systemic toxicity demonstrated by this substance in industrial accidents.

Page last reviewed: September 28, 2011