The U.S. Environmental Protection Agency (EPA) has posted a June 17, 2010, document entitled “Interim Technical Guidance for Assessing Screening Level Environmental Fate and Transport of, and General Population, Consumer, and Environmental Exposure to Nanomaterials.” According to the Interim Guidance, EPA prepared it “to serve as a guide when developing screening level exposure and environmental fate and transport assessments for nanomaterials,” such as those submitted under the Toxic Substances Control Act (TSCA) New Chemicals Program.  The Interim Guidance is applicable for neat nanomaterials (i.e., powdered or particulate forms), as opposed to nanoscale particles embedded within composites.  At this time, according to the Interim Guidance, EPA does not have models or methods capable of predicting the fate of, or exposure to, nanoscale particulates in the environment.  This fact, combined with the limited data for nanomaterials, means that there is uncertainty in estimating removal efficiencies, degradation half-lives, partitioning, and transport of nanomaterials.  To address the uncertainty, EPA recommends using a conservative bounding “what if” scenario, which assumes that nanomaterials are not removed during wastewater treatment or incineration (i.e., 0 percent removal efficiency), are persistent (i.e., P3), are highly bioaccumulative (i.e., B3), and are highly mobile in groundwater unless measured data is available that proves otherwise.  EPA describes this conservative approach as “prudent at this time given the limited available data and lack of historical knowledge regarding the behavior of nanomaterials in the environment.”