EPA-Expo-Box (A Toolbox for Exposure Assessors)
Due to the wide range of nanomaterial compositions and applications, it is theoretically possible for nanomaterials to be found in any environmental media, including indoor and outdoor air, surface water and drinking water, soil, sediment, and indoor dust.
Research questions laid out by the National Nanotechnology Initiative Workshop on Human and Environmental Exposure Assessment (2009) and Workshop on Nanomaterials & the Environment and Instrumentation, Metrology, and Analytical Techniques (2009) regarding behavior of nanomaterials in various environmental media include:
- Will nanomaterials in air follow conventional particle dispersion models? How do the small particle size and aggregation properties of specific nanomaterials affect particle behavior?
- Will nanomaterials in water aggregate and settle like many non-nanoscale-sized suspended solids, or will they remain dispersed in the water column? How do the water qualities, such as pH or presence of natural organic matter, impact aggregation of nanomaterials in water?
- Are detection/characterization methods that exist for non-nanoscale-sized materials, which typically are mass-based, appropriate for nanomaterials which are unique for their qualities at small mass?
Additionally, the NNI Workshop Reports outlined many challenges that currently exist for detecting, characterizing, and quantifying nanomaterials in environmental media, including:
- The physical-chemical properties of an engineered nanomaterial can be altered or modified by the environment (e.g., surface chemistry of carbon nanotubes can be altered following UV exposure; physical abrasion can result in shortening of nanofibers), making characterization difficult.
- Little data are available regarding the effect of variables such as sample preparation techniques, storage temperatures, and solvent interactions on detection/quantification methods; therefore, comparing results across studies with different protocols is difficult.
- Many methods for quantification and analysis have not been validated, meaning issues of quality control, sensitivity, reliability, and reproducibility exist around most current studies measuring environmental concentrations of nanomaterials (or predicting based on behavior in controlled laboratory settings).