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Nanotechnology & Nanomaterials Research

Environmental Fate

Environmental fate refers to the physicochemical properties, reaction pathways, and transformation rates in the environment of engineered nanomaterials (ENMs) of interest. Due to the uncertainty surrounding the unique characteristics of nanomaterials and their potential uses and effects, it is vital that the environmental fate of these particles is mapped to facilitate policy decision-making regarding nanomaterial exposure and risk assessment. EPA are currently working to establish a compendium of information that describes the relationships between key inherent properties of ENMs and their environmental fate, transport, transformation, bio-distribution, exposure, and toxicity to humans and other species.

Estimating Nanomaterial Transport in Soils

Background:

Quantifying the mobility of engineered nanoparticles in hydrologic pathways from point of release to human or ecological receptors is essential for assessing environmental exposures. However, column transport experiments are often time-consuming, labor-intensive, and of low sample throughput.

Method Description:

EPA scientists recently evaluated the use of high-throughput screening technique (from the ToxCast chemical prioritization program) for nanoparticle transport using 96 deep well plate columns packed with porous media.

Results:

Results showed that this screening technique produced highly reproducible column hydrodynamic properties and retention levels of the ENPs consistent with the existing literature. This technique obviates the need to run repetitive tracer tests and is well suited for rapidly screening the mobility of ENPs in porous media.

How this method will be used:

This technique is well suited for rapidly screening the mobility of engineered nanomaterials (ENMs) in porous media. This methodology will be useful for generating ENM retention parameters for ENM transport in soils and sediments and is readily implementable by researchers and technicians using common laboratory materials and instrumentation. This methodology will be useful to both regulators and the regulated community for PMN preparation.

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Innovative Nanomaterial Characterization Techniques

Background:

Measuring the concentration and size distribution of engineered nanoparticles (ENP) is critical for studying their environmental behavior, as well as monitoring them in the environment. Laser light scattering techniques are frequently used to measure and characterize high concentrations of ENP in simple systems. However, these methods lack sufficient sensitivity to monitor ENP in environmental samples. To address this issue, EPA scientists have developed a unique hyphenated method to assess ENPs. This method combines a size separation technique with an elemental concentration detector to provide more sensitive and selective assessments.

Action/Plan/Method description:

EPA developed a method that couples size separation by hydrodynamic chromatography (HDC), with single particle detection using inductively-coupled mass spectroscopy (ICPMS). Hydrodynamic chromatography counts and separates particles by their size in an aqueous sample.  Single particle ICPMS measures the metal content of individual nanoparticles, rather than an average   Value from an entire sample as in conventional ICP-MS.  Therefore, the hyphenated technique provides information simultaneously on nanoparticle size, number and metallic composition which was not possible with previous procedures. 

This approach to nanoparticle detection allows scientists to distinguish natural minerals or metal with natural organic matter from low concentrations of ENP. This is critical for measuring nanoparticles in environmental samples.

How this method will be used:

Single particle ICP Mass Spectrometry is a highly sensitive mode of measurement that can be used by companies that produce nanomaterials to support premanufacture protocols. It is also useful to the Office of Water and EPA region offices to monitor engineered nanoparticles (ENPs) in surface and ground water located near suspected ENP releases.

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Case Study: The Impact of Silver Nanoparticles on Municipal Solid Waste 

Case Study:

Evaluates the impact of polyvinylpyrrolidone (PVP) coated silver nanoparticles (PVP-AgNPs) on the composting of municipal solid waste.

Results:

The taxonomical analysis suggests that microbial activity can be impacted within hours of AgNPs exposure, although at low AgNPs concentrations activity can be relatively stable.

Data from this and other studies show that toxicity dynamics might be different when dealing with complex microbial communities, suggesting that data from pure culture studies may be inaccurate in predicting the impact of AgNPs on microbial communities.
It is unclear whether the bacterial response is caused by bacterial populations resistant to AgNPs, the decrease in Ag+ release, transformation of AgNPs, or reduction in bioavailability.

More research is needed to identify which concentrations of silver nanoparticles begin to have a toxicological effect on waste management systems where the microbial groups and processes responsible for waste consumption may be impacted by silver nanoparticles.

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