EXISTING CHEMICAL-TESTING FOR ENVIRONMENTAL FATE AND EFFECTS UNDER TSCA SECTION-4 - A CASE-STUDY WITH OCTAMETHYLCYCLOTETRASILOXANE (OMCTS)

Octamethylcyclotetrasiloxane (OMCTS, or D4) is a highly volatile, cyclic silicone that is an important intermediate in the synthesis of polydimethylsiloxanes and other higher-molecular-weight silicones. As a category of chemicals, silicones have generated substantial scientific and regulatory interest over the last few years. OMCTS, one of the first silicones considered for regulatory review, was recommended for testing in the 15th Report of the Interagency Testing Committee (ITC) in 1984 based on its high volume of production, alleged presence in aquatic environments, and the general lack of environmental fate and effects information for this type of compound. As a result, the environmental effects and fate of OMCTS have been extensively evaluated in a series of laboratory toxicity and environmental fate studies, fate modeling studies, and field monitoring studies. Most of these studies were conducted as parr of a negotiated consent order (CO) under Section 4 of the Toxic Substances Control Act (TSCA). Applying the principles of ecological risk assessment (ERA) to the OMCTS program, the current paper presents the problem-formulation phase of the ERA process including stressor characteristics, identification of the ecosystem potentially at risk, and development of a conceptual model. In addition, the planning phase with interactions among the industry representatives, the risk assessors, and the risk managers are discussed. OMCTS was one of the first chemicals to reach the RM1 (risk management) level of regulatory analysis under TSCA, which resulted in a determination that no additional data was needed. Application of ERA principles in this program were instrumental in this favorable determination.