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Screening Methods for Metal-Containing Nanoparticles in Water
Citation:
HEITHMAR, E. M. Screening Methods for Metal-Containing Nanoparticles in Water. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-11/096, 2011.
Impact/Purpose:
Engineered nanomaterials (ENMs) are increasingly being incorporated in industrial, consumer, medical, and agricultural products. This is because ENMs exhibit unique optical, electrical, and chemical properties that can impart beneficial characteristics to the product into which they are incorporated. However, these unique properties also affect the environmental behavior of ENMs. Their transport, fate, exposure potential, and effects are not predicted by those of either the corresponding bulk materials or dissolved chemicals. Most ENMs currently in production can be categorized as either metal-containing ENMs (i.e., metals, metal oxides, or semiconducting quantum dots) or carbon-based (i.e., fullerenes and their derivatives, and carbon nanotubes). ENMs containing metals have a greater potential to enter the environment than carbon-based ENMs. This is a result of the fact that the major uses of metal-containing ENMs are in dispersive applications, while carbon-based ENMs are generally incorporated into solid composites. This increased exposure potential for metal-containing ENMs has motivated intense research into their environmental processes, such as transformation, transport and fate, exposure pathways, and potential adverse effects on humans and sensitive organisms.
Description:
Screening-level analysis of water for metal-containing nanoparticles is achieved with single particle-inductively coupled plasma mass spectrometry (SP-ICPMS). This method measures both the concentration of nanoparticles containing an analyte metal and the mass of the metal in each particle. SP-ICPMS is capable of sample throughputs of over twenty samples per hour. In this report, the screening capability of SP-ICPMS is demonstrated in a study of transformations of silver nanoparticles in surface water. Test water samples were collected from two fresh water sites and two estuary sites. The effects of salinity, particle concentration, particle size, and particle surface chemistry on relative rates of transformations were studied. At high silver particle concentration (2.5x107 mL-1) shifts in the particle silver mass distribution measured by SP-ICPMS indicated increased aggregation rate at high salinity, as reported by others. However, at low silver particle concentration (2.5x105 mL-1), which is closer to expected environmental concentrations, aggregation was minimal even in highly saline estuary water. At the low concentration, a much more pronounced increase in either dissolved silver or silvercontaining nanoparticles too small to be distinguished from dissolved silver was observed. These data were operationally defined in this report as “dissolved” silver. Comparison of transformations of 50-nm and 100-nm silver indicated that rates of both aggregation and apparent dissolution are higher for the smaller particles at the same particle concentration. Transformations for citrate-capped and polyvinylpyrrolodone-capped silver nanoparticles were similar.