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AN ASSESSMENT OF THE FATE OF METAL OXIDE NANOMATERIALS IN POROUS MEDIA
Citation:
LOUX, N. T. AND N. SAVAGE. AN ASSESSMENT OF THE FATE OF METAL OXIDE NANOMATERIALS IN POROUS MEDIA. WATER, AIR, AND SOIL POLLUTION. Springer, New York, NY, 194(1-4):227-241, (2008).
Impact/Purpose:
There are four objectives of this work: A: Updating/Assessing EPA's MINTEQA2 Geochemical Speciation Model EPA has distributed the MINTEQA2 geochemical speciation model to the professional research community for several decades. Although the model has undergone a number of improvements during this period, this effort will involve: 1) expanding the thermodynamic data base in MINTEQA2 to include components not currently in the model, and 2) assessing the error associated with applying the low ionic strength activity coefficient algorithms in MINTEQA2 to marine and hypersaline aquatic systems. B: Advancing the State-of-the-Science in Ionic Toxicant Adsorption to Natural Surfaces Modeling. There does not currently exist an accurate mechanistic model applicable to all environments for predicting the partitioning behavior of ionic contaminants to natural surfaces. The absence of accurate mechanistic models of ionic contaminant partitioning impairs EPA's efforts to apply the NRC Risk Assessment Paradigm to assess aqueous ionizable contaminant exposures. This work is designed to support current efforts to develop rigorous and defensible mechanistic adsorption models.
Description:
Developing procedures for assessing the potential environmental fate and transport of nanomaterials is an active endeavor of the environmental technical research community. Insufficient information exists for estimating the likelihood of nanomaterial deposition on natural surfaces in aquatic environments. This work develops a framework for estimating potential metal oxide nanomaterial self-aggregation through the combined application of recent developments in diffuse layer model surface complexation theory with historical DLVO procedures. Findings from the work include: 1) the surface and/or zeta potential of nanomaterials in environmental aqueous systems is likely to have an absolute value less than 25 mV, 2) only nanomaterials with a Hamaker constant as large as 1E-19 J (and an absolute surface potential ≤25 mV) will likely aggregate in most environmental aquatic media, 3) natural organic matter coatings may render metal oxide nanomaterials less likely to aggregate in aquatic media, 4) nanomaterials in aqueous suspension will likely have an absolute surface potential less than their micron-sized counterparts of the same composition, and 5) robust diffuse layer model databases of intrinsic surface site reactivity constants with multivalent aqueous environmental ions will need to be developed in order to provide accurate mechanistic estimates of the surface potential of nanoparticles suspended in aqueous environmental systems.