The case studies are organized around the comprehensive environmental assessment (CEA) approach, which combines a product life-cycle framework with the risk assessment paradigm. Risk assessment relates exposure and effects information for a substance or stressor; CEA expands on this paradigm by including life-cycle stages and considering both indirect and direct ramifications of the substance or stressor. The organization of the document reflects the CEA approach: after Chapter 1 (Introduction), Chapter 2 highlights stages of the product life cycle (feedstocks, manufacturing, distribution, storage, use, disposal), followed by Chapter 3 on fate and transport processes, Chapter 4 on exposure-dose characterization, and Chapter 5 on ecological and health effects. Chapter 6 highlights the information that is currently available in each of these areas, and it describes information gaps and research questions identified in the case studies. It also discusses the role of the case studies in informing research planning and future assessment efforts. Appendices A through C provide supplementary information on the use of nano-TiO2 in topical sunscreens, manufacturing processes for nano-TiO2 and sunscreen formulations, and examples of laboratory and workplace exposure control practices, respectively.