The growing production and utilization of ZnO nanoparticles (ZON) in numerous areas ranging from medicine and manufacturing to microelectronics and personal care products   will unavoidably lead to their introduction to the environment through accidental releases during production, transport, manufacturing and through disposal. Understanding the physicochemical properties, surface chemical reactivity, and charge properties of ZON is key for evaluating the transformations they may undergo when released to the environment and, hence in assessing their potential impacts on biogeochemical processes. Characterization data obtained with a variety of techniques including TEM, XRD, FTIR and Raman spectroscopies as well as high resolution thermogravimetric analysis (HR-TGA) indicate a critical role of the counter anion used to stabilize the nanoparticles in suspension on surface chemistry and reactivity. HR-TGA coupled with traditional chemical methods suggests the existence of multiple populations of acetate associated with the ZON (~5 nm), which affect both their structure and reactivity. Results from ZON compared to those obtained from bulk ZnO (~1 mm) suggest that the hypothesis of increased surface reactivity in the nanosize range is not supported. Future studies will focus on the potential bioavailability, toxicity, and trophic transfer of nanosized oxides.