Adsorption and Release of Contaminants onto Engineered NanoparticlesEPA Grant Number: R831718
Title: Adsorption and Release of Contaminants onto Engineered Nanoparticles
Investigators: Tomson, Mason B.
Institution: Rice University
EPA Project Officer: Lasat, Mitch
Project Period: August 1, 2004 through July 31, 2007
Project Amount: $333,797
RFA: Exploratory Research to Anticipate Future Environmental Issues: Impacts of Manufactured Nanomaterials on Human Health and the Environment (2003) RFA Text | Recipients Lists
Research Category: Nanotechnology , Health , Safer Chemicals , Health Effects
As nanotechnology develops into a mature industry the environmental and health effects of its core materials becomes of increasing importance. This proposal aims to evaluate the sorption and release of contaminants onto the surfaces of engineered nanoparticles. Specifically, we will test four hypotheses in this research: 1) that carbon nanostructures have a high capacity for sorption/desorption hysteresis with polynuclear aromatic hydrocarbons and other common organic contaminants; 2) that the sorption capacity of inorganic nanomaterials for heavy metals is the same as the corresponding bulk crystals, when corrected for surface area; 3) that sorption of naturally occurring humic materials and surfactants to metal oxide and carbon nanomaterials will diminish the sorption capacity of heavy metals on oxides and increase the sorption of hydrocarbons on carbon nanomaterials; and 4) that the transport of nanoparticles in soils, sediments, and porous medial will be vastly greater than the corresponding colloids or bulk materials.
This project is motivated by the interest in collecting data needed for risk assessments of nanoparticle materials. It is never too early in an emerging technology to consider issues of environmental impact; for nanotechnology, sound technical data concerning the health risks and potential exposure of nanomaterials in water will allow nanomaterials to be targeted at the most appropriate applications. Such information also will allow environmental issues to factor in early into manufacturing development, leading to a greener and ultimately more economic industry. There is no existing technical literature which speaks to the issue of the environmental impacts of nanoengineered materials. However, related areas concerning contaminant sorption to minerals and clays, as well as the importance of particle-mediated transport to exposure calculations are quite relevant and have informed our thinking about this problem.
Nanomaterials used will include fullerenes, SWNTs, anatase, magnetite, silica, and alumina. Adsorbates will include humic materials, surfactants, naphthalene, phenanthrene, chlorinated aromatic compounds, heavy metals lead, cadmium, and arsenic. The interaction of uncoated nanoparticles and humic and surfactant coated nanoparticles in the presence of soil and sediments will be determined with batch and column experiments. The sorption and desorption of common hydrophobic organic compounds and of heavy metals to both coated and uncoated nanomaterials will be measured. Contaminant/particle interactions will also be characterized using specific surface probes. This research will provide explicit fate models that can be used in exposure assessment for nanoparticles. The surface to volume ratios of engineered nanomaterials can be as large as 30% by number, and clearly the surface chemistry of these species will be essential for understanding the fate of engineered nanoparticles in the environment. Most chemists consider surface chemistry a fixed parameter when developing nanocrystals. When surfaces are intentionally derivatized, as they often are in nanochemistry, the interaction between the sorbent and the particle are often covalent and thus strong and specific. Once bound, it is unlikely that the surface capping agent will desorb from the particle surface at least on the week timescales and controlled conditions familiar to chemists, unless drastic changes are made in the solvent or the reactive solutes. With bound adsorbates a number of spectroscopic tools can be used to discern the coverage and bonding at nanocrystal surfaces.
We rely on the availability of well-characterized and controlled nanostructures in our experiments. These nanoparticles when solvated in water can be exposed to varying concentrations of contaminants, and their adsorption and desorption isotherms can be measured using standard methods developed by this group. This information provides us with information about the sorption capacity and kinetics for model contaminants (heavy metals and polyaromatic hydrocarbons) onto nanoparticle surfaces. Our aim is to model these sorption interactions so as to provide a general set of information about the capacity for engineered nanostructures to serve as mobile surfaces for contaminants.
The main approaches of this proposed research are (1) characterize the adsorption interaction of environmental contaminants with a wide range of nanomaterials, (2) characterize the desorption hysteresis properties of environmental contaminants with a wide range of nanomaterials, and (3) characterize the attachment and detachment of nanomaterials and associated contaminants to soil particles. The fate of engineered nanoparticles and of sorbed contaminants will be studied in the presence of natural sediments.
The introduction of a new class of materials into consumer products will require information about the potential behavior and risks these systems pose to the environment and people. The high surface area of nanoparticles means that even weak sorption of contaminants to surfaces can introduce a significant new pathway for exposure, or removal, of molecular contaminants in biological systems. This grant provides the information needed to assess whether this risk is substantial for nanoparticles disposed of in groundwaters. It is expected that this research would yield the necessary parameters to understand the fate of engineered nanoparticles in the environment and to yield the necessary parameters for future development of risk assessment of the engineered nanoparticles. The PI has many years of experience in developing the necessary parameters for risk model. The PI's group has done the first ground water contamination studies. Recently, a dual equilibrium desorption equation was developed and it has been considered by many consulting companies and regulatory agency for adoption into their remediation scheme and regulatory guideline.