4,4’-Methylenedianiline: Risk Assessment and Risk Management

Abstract

Risks associated with the production, use and disposal of 4,4′methylenedianiline (4,4′-MDA) have been under study by the Environmental Protection Agency (EPA). 4,4′-MDA was the first chemical to trigger section 4(f) of the Toxic Substances Control Act (TSCA), and EPA and the Occupational Safety and Health Administration (OSHA) have been working to find the most effective way to control the chemical’s risks. Limited information on dermal penetration rates and exposure levels have introduced uncertainty into the dose side of the dose-response equation. A cancer bioassay, on the other hand, has provided good data for estimating response, at least within the tested dose range.

A technique for estimating lifetime average daily doses to workers based on the limited dermal exposure data and inhalational exposure levels has been employed. This technique has been used to estimate the degree of risk reduction that protective clothing and equipment and improved industrial hygiene practices can produce.

The risk assessment information, complete with its uncertainties, is being made available to risk managers in EPA and OSHA, while additional work is planned to reduce uncertainty in the assessment. This work includes additional monitoring of workplaces and surface waters (the latter to assess possible contamination of drinking water supplies) and measurement of the chemical’s skin penetration rate. Since skin penetration rates can vary over several orders of magnitute, and since the limited data available indicate that dermal exposures in the workplace may be significant, reduction of uncertainty in this area is crucial for cost-effective risk management decisions.