Complex substances such as multi-constituent substances and UVCBs usually result from the industrial processing, extraction of natural materials, or from chemical reactions. Because of the nature of source materials, and the potential variability inherent to production processes, UVCBs can contain many uncharacterized constituents, in varying concentrations, affecting the ability to identify these substances. These properties affect the ability to assess properties relevant to ecological risk assessment such as physical-chemical properties, environment fate and toxicity. To address these challenges, the UVCB Committee of the Health and Environmental Sciences Institute is building an exposure-based tiered approach considering the minimum level of information required to perform a robust ecological risk assessment. The first step (Tier 0) considers basic and readily available substance characterization and exposure information. Characterization information includes substance specifications, quality assurance data, and basic chromatographic or elemental data, while exposure information includes use/importation volumes and end uses. This first tier is critical to allow the streamlined screening of UVCBs which may or may not need in-depth characterization. This framework was tested through the development of three case studies, which revealed characterization of substance complexity and biodegradation as key steps. Substance complexity, defined as the combination of variability in constituent concentrations, diversity of constituent chemistries and chemical properties, and belonging to the applicability domain of existing test models, is likely to determine the needed depth of substance characterization. Also critical is the determination of when biodegradation should be evaluated, and whether it should be measured on the whole substance or its representative structures. This approach, will be presented and discussed. Altogether this risk screening process will help ensure that efforts and resources deployed for UVCBs risk assessment match actual needs and help streamline the risk assessment process, This abstract does not necessarily represent the views or policies of the U.S.-EPA or CEFAS.