Nanoscale materials (nanomaterials) have been described as having at least one dimension on the order of approximately 1100 nanometers (nm) (NSTC, 2011). Although this size range is not universally accepted and continues to evolve, 100 nm is typically used as an upper bound, and this working definition is used as the size standard in this case study. Engineered nanomaterials are intentionally made, as opposed to being an incidental by-product of combustion or a natural process such as erosion, and often have unique or novel properties that arise from their small size. Like all technological developments, engineered nanomaterials offer the potential for both benefits and risks. The assessment of such benefits and risks relies on information, and, given the nascent state of nanotechnology, much remains to be learned about nanomaterials to support such assessments. This document is part of an endeavor to identify what is known and, more importantly, what is not yet known that could be of value in assessing the broad environmental implications of certain nanomaterials. The focus of this document is a specific application of a selected nanomaterial: the use of engineered nanoscale silver (nano-Ag)2 as an agent in disinfectant spray products. The U.S. Environmental Protection Agency (EPA) completed similar case studies of nanoscale titanium dioxide (nano-TiO2) used for drinking water treatment and for topical sunscreen (U.S. EPA, 2010d). Such case studies do not represent completed or even preliminary assessments; rather, they are intended as a starting point in a process to identify and prioritize possible research directions to support future assessments of nanomaterials.