Urinary 4,4′-Methylenebis (2-Chloroaniline) (MBOCA): A Case for Biological Monitoring

Abstract

4,4-Methylenebis (2-chloroaniline), also known as MBOCA (or MOCA®), is an aromatic amine that is absorbed primarily through the skin. MBOCA is used as a curing agent in the castable polyurethane industry. It has also been identified as a suspect human carcinogen. Because of concerns that airborne monitoring would not truly assess the degree of worker absorption of MBOCA, the Polyurethane Manufacturers Association, an association of MBOCA users, implemented a voluntary biological monitoring program 15 years ago to assess and reduce worker exposure to MBOCA. Review of biological monitoring data, generated during the past 6 years using high performance liquid chromatography methods, has shown trends in reduced urinary MBOCA concentrations and thus reduced worker exposure. In addition, the results of the biological monitoring program, indicating worker exposure, have prompted the industry to initiate programs to reduce MBOCA exposure by engineering controls. The design of closed transfer systems in 1983 and production of a fused, hardened MBOCA pellet in 1986 were examples of actions taken to reduce worker exposures. Following implementation of these engineering controls, the percentage of urine specimens below 25 μg/L increased from 77 percent in 1985 before introduction of the fused hardened pellet to 86 percent in 1990. During this time, the percentage of samples above 50 μg/L decreased from 12 percent in 1985 to 8 percent in 1990. The use of urinary MBOCA as a performance-based guideline has contributed to reduced exposure of workers, while allowing the continued use of this polyurethane curing agent.