Many materials properties are controlled by surface reactions, including those associated with cracking, dissolution, and corrosion. In each of these cases surface reactions alter the functional properties of the materials. Detailed analysis of surface reactions in relation to the material environment has been required to understand the mechanisms involved in these processes. Many of the analysis approaches used to understand dissolution, cracking corrosion and other complex material-environment interactions are relevant to the study of some types of nanoparticles. The objective of our current research is to obtain fundamental information about the physical and chemical transformations that occur on and within mineral oxide nanoparticulates due to electron transfer reactions and other interactions with their local environment, including solution contaminants such as chlorinated hydrocarbons. The nature of the reactive surfaces, the accessibility of reactive sites, and the structures of the surface and interface layers often change significantly as particles respond to and react with their local environment (e.g. surface structure alterations, phase changes, passive layer formation …). Although geochemically induced changes occur for bulk materials, the nature and rate of these changes can be more dramatic for nano-sized mineral phases. Our research focuses on obtaining information about these geochemically mediated transformations and how they alter particle reactivity, electron availability and particle mobility. Our research includes 1) synthesis of well-defined nanoparticles (NPs), 2) characterization of their surface and bulk composition as well as physical and electronic structure (prior to and following reaction measurements), and 3) in situ real-time and batch measurements of NP properties and reactivity in vacuum and solution. We will report on studies showing the impact of natural organic material (NOM) coatings on the through soil transport and reactivity of iron nanoparticles as well as the role of metal dopants on reactivity and solution aging. We have found that NOM can enhance the transport of iron metal-core oxide-shell nanoparticles through a soil column, decreasing the numbers of particles retained in the soil. We have followed up these observations and examined the impact of NOM coatings on the particle aging. Additional studies are examining the impact of S doping on particle reactivity and aging. These studies involve application of a variety of analysis methods to the particles, including XPS, XRD and TEM as well as batch and in situ measures of chemical reactivity and measurements of particle transport through soil columns.