ABSTRACT
Polymers are a very large class of chemicals comprising often complex molecules with multiple functions used in everyday products. The EU Commission is seeking to develop environmental and human health standard information requirements (SIRs) for man-made polymers requiring registration (PRR) under a revised Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) Regulation. Conventional risk assessment approaches currently used for small molecules may not apply to most polymers. Therefore, we propose a conceptual three-tiered regulatory approach for data generation to assess individual and groups of polymers requiring registration (PRR). A key element is the grouping of polymers according to chemistry, physico-chemical properties and hazard similarity. The limited bioavailability of many polymers is a prominent difference to many small molecules and is a key consideration of the proposed approach. Methods assessing potential for systemic bioavailability are integral to Tier 1. Decisions for further studies are based on considerations of properties and effects, combined with systemic bioavailability and use and exposure considerations. For many PRRs, Tier 1 data on hazard, use and exposure will likely be sufficient for achieving the protection goals of REACH. Vertebrate animal studies in Tiers 2 and 3 can be limited to targeted testing. The outlined approach aims to make use of current best scientific evidence and to reduce animal testing whilst providing data for an adequate level of protection.
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.
