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For ecologic effects, numerous international experts were sent a questionnaire listing more than 100 different chemical substructures and asked to predict (based on their field of expertise related to ecologic effects and knowledge of modes of action) the potential for chemicals containing any of the substructures to cause effects to algae, aquatic invertebrates, birds, fish, mammals, microorganisms, plants, or terrestrial invertebrates. Opinions from these ecologic effects experts were converted to codes that identified chemical substructures and indicated potential of chemicals containing one or more substructures to cause effects to the previously listed organisms.

SuCCSES is a relational database with fields indexed on Chemical Abstract Service (CAS) Registry numbers. It was created using Molecular Design Limited Information Systems’ Integrated Scientific Information System. For chemicals in SuCCSES, chemical formulas, molecular weights, two-dimensional chemical structures, and simplified molecular input line entry system (SMILES) notations (Weininger 1988; Weininger et al. 1989) are provided. Features of SuCCSES promote substructure searching to identify structurally related chemical classes of chemicals and their potential ecologic or human health effects. For each record in SuCCSES, a computer screen displays fields for CAS Registry number, molecular weight, molecular formula, SMILES notation, two-dimensional chemical structure, chemical name, predicted mode of action, and potential health or ecologic effects. SuCCSES is not available to the public became it contains confidential business information.

SuCCSES is used to facilitate the ITC’s review of large groups of chemicals (Walker 1991, 1995; Walker and Brink 1989). The aldehyde substructures in SuCCSES that were associated with potential to cause acute effects to aquatic organisms were included in recent publications (Walker and Printup In press; Walker et al. In press (b)]. A forthcoming book chapter summarizes the development of SuCCSES and its applicability to the ITC’s statutory mandate to use SARs before recommending chemicals for testing in May and November reports to the U.S. EPA administrator (Walker and Gray. In press).

Other approaches to toxicity prediction. Other approaches to predict toxicity include those for predicting water quality objectives (Vighi et al. 2001). This was a multivariate QSAR approach that involved the assessment of water quality objectives for a set of 125 chemicals [derived from the European priority list in compliance with Directive 76/464/EEC (EEC 1976)]. Predictions from classification models (based on algae, Daphnia, and fish toxicity values) were shown to perform satisfactorily compared with the classifications using literature toxicity data.

EU Regulatory Use

Technical guidance documents. In Europe, data obtained from QSARs can be used according to the guidance on the use of QSARs for specific groups of substances found in Part IV of the TGD (EEC 1996). The TGD provides recommendations for the use of QSARs to predict acute toxicity to fish (96 hr L[C.sub.50]), Daphnia (48 hr E[C.sub.50]) and algae (72- to 96-hr E[C.sub.50]). In particular, QSARs are provided for chemicals acting by nonpolar narcosis and polar narcosis mechanisms of action. No QSARs have been recommended for substances that act by more specific modes of action.