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The Fate, Transport, Transformation, and Toxicity of Manufactured Nanomaterials in Drinking Water

Paul Westerhoff
Arizona State University, Tempe, AZ

Although the current market for nanomaterials is small and their concentration may not be high enough in the environment to cause human health or environmental problems, this market is increasing rapidly and the discharge of nanomaterials to environment in the near future could be significant as manufacturing costs decrease and new applications are discovered. The accumulation of nanomaterials in cells may have significant environmental and human impacts. However, at present, very little is known about the fate, transport, transformation, and toxicity of these man-made nanomaterials in the environment. The objectives of this project are to: (1) characterize the fundamental properties of nanomaterials in aquatic environments; (2) examine the interactions between nanomaterials and toxic organic pollutants and pathogens (viruses); (3) evaluate the removal efficiency of nanomaterials by drinking water unit processes; and (4) test the toxicity of nanomaterials in drinking water using cell culture model system of the epithelium. This study considers the physical, chemical, and biological implications of nanomaterial fate and toxicity in systems that will provide insight into the potential for nanomaterials to be present and of health concern in finished drinking water.

A multidisciplinary approach is underway that includes experiments to identify fundamental uniqueness of nine nanomaterial properties and toxicity and quite applied experiments aimed directly at understanding the fate and reactions involving nanomaterials in drinking water treatment plants. Advanced nanomaterial characterization techniques will be employed to determine the size distribution, concentration, and zeta potential of nanomaterials in buffered distilled water and model waters representative of raw drinking water supplies (anions, cations, NOM). Adsorption of dissolve pollutants (anions, metals, range of synthetic organic chemicals) and NOM are proposed to quantify the potential for nanomaterials to transport such compounds and be transformed by the compounds (e.g., aggregation, change in zeta potential). Coagulation processes will be studied by compressing the electric double layer of nanomaterials, and exposing nanomaterials to alum coagulations, using mono- and heterodisperse solutions; comparable filtration work will also be conducted. Adsorption of virus onto nanomaterials and subsequent disinfectant shielding will be studied. Toxicity screening will include toxicity of nanomaterials on several cell lines selected to mimic oral ingestion routes in drinking water.

During the first year of this project significant advances have been made. These have been incorporated in numerous invited and unsolicited presentations at national conferences. The first year focused in part on methodological advances. This included demonstrating that commercial nanoparticles do not behave as discrete nanoparticles in aqueous systems, and aggregation of these materials result in particles than 1 m. Our work has focused on metal oxide nanoparticles, and understanding how surface change (zeta potential) affects the removal of nanoparticles during simulated drinking water treatment. Coagulation and sedimentation processes remove 30 to 80 percent of the nanoparticles, meaning that many would not be removed. Second, experiments with inorganic (arsenic) and organic (MIB) chemicals or pathogen models (MS2 bacteriaphage) have concluded that surface change will affect the extent of interaction and nanoparticles can facilitate the transport of these substances. Third, conditions conducive to growing various epithelial cell layers that mimic intestinal cell linings have been developed. Using resistivity-based approaches a detrimental impact of nanoparticles has been observed, and using confocal laser microscopy we have shown that nanoparticles penetrate the cell membranes. Over the next two years this work will be expanded and investigated in greater detail.

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