ABSTRACT
Methylene-4,4'-dianiline (MDA, CAS-No. 101-77-9) is a high production volume intermediate that is mainly processed to diisocyanates and finally polyurethanes. This review summarizes available data concerning the environmental behavior. When released into the environment, MDA distributes into water and subsequently sediment and soil compartments; the air is of little relevance, owed to the low vapor pressure and short atmospheric half-life, which renders MDA non-critical for long-range transport. Biodegradation data present a diverged picture; in some tests, MDA is not readily biodegradable or even not inherent biodegradable; in other tests, MDA turned out to be readily biodegradable (but failing the 10-d window). The history and composition of the inoculum used for testing seem to play an important role, which is underlined by good test results with adapted inoculum. In soil, initially a rapid mineralization is observed, which slows down within the first days due to competitive chemical absorption. The latter results in degradation rates comparable to that of natural organic matter. Under anaerobic conditions, mineralization is poor. Irreversible chemisorption occurs unless soils/sediments are highly reduced. Half-lives due to primary decay do not indicate MDA to be persistent according to the regulatory guidance used in then EU, Canada, or the USA; in Japan, however, due to test results in MITI degradation tests, MDA would be regarded as persistent. The identification of microbial MDA metabolites deserves further research. MDA is not bioaccumulative, but it is toxic to aquatic organisms and mammals. MDA in pore water of soils is rapidly adsorbed on the surface of plant roots. Test runs were too short to draw a final conclusion with regards to transport to stem, leaves, and fruits. Data from structurally similar compounds indicate that such transport would account for less than 1% of the root-adsorbed material.
ABSTRACT
Information from a variety of sources has been collected and summarized to facilitate an overview of the atmospheric fate and potential environmental effects of emissions of methylenediphenyl diisocyanate (MDI) or toluene diisocyanate (TDI) to the atmosphere. Atmospheric emissions of both MDI and TDI are low, both in terms of concentration and mass, because of their low volatility and the need for careful control over all aspects of their lifecycle from manufacture through disposal. Typical emission losses for TDI are 25 g/t of TDI used in slabstock foam production. MDI emission losses are lower, often less than 1 g/t of MDI used. Dispersion modeling predicts that concentrations at the fenceline or beyond are very low for typical releases. Laboratory studies show that TDI (and by analogy MDI) does not react with water in the gas phase at a significant rate. The primary degradation reaction of these aromatic diisocyanates in the atmosphere is expected to be oxidation by OH radicals with an estimated half-life of one day. Laboratory studies also show that this reaction is not expected to result in increased ground-level ozone accumulation.
