Impacts of ingested MWCNT-Embedded nanocomposites in Japanese medaka (Oryzias latipes)

Polymer nanocomposites combine the versatile, lightweight characteristics of polymers with the properties of nanomaterials. Polyethylene terephthalate glycol (PETG) is commonly used in polymer additive manufacturing due to its controllable transparency, high modulus, and mechanical properties. Multi-walled carbon nanotubes (MWCNTs) add tensile strength, electrical conductivity, and thermal stability. The increased use of nanocomposites has led to concern over potential human health risks. We assessed morphologic alterations to determine impacts of ingested abraded nanocomposites compared to its component materials, pristine MWCNTs (1000 mg/L) and PETG. Adult transparent Japanese medaka (Oryzias latipes) were administered materials via oral gavage in 7 doses over 16 days. In vivo observations revealed altered livers and gallbladders following exposure to pristine MWCNTs and nanocomposites. Subsequent histologic sections showed fish exposed to pristine MWCNTs had highly altered biliary structures, and exposure to nanocomposites resulted in hepatocellular alteration. Thyroid follicle proliferation was also observed in fish exposed to materials containing MWCNTs. Transmission electron microscopy of livers showed that hepatocytes of fish exposed to MWCNTs had widespread swelling of rough endoplasmic reticulum, pronounced lysosomal activity, and swelling of intrahepatic biliary passageways. Fish exposed to nanocomposites had areas of degenerated hepatocytes with interspersed cellular debris. Each analysis showed that fish exposed to pristine PETG were most similar to controls. These results suggest that MWCNTs are the source of toxicity in abraded nanocomposite materials but that nanocomposites may also have some unique effects. The similarities of many teleost and mammalian tissues are such that these findings may indicate human health risks.

Separation, Sizing, and Quantitation of Engineered Nanoparticles in an Organism Model Using Inductively Coupled Plasma Mass Spectrometry and Image Analysis

For environmental studies assessing uptake of orally ingested engineered nanoparticles (ENPs), a key step in ensuring accurate quantification of ingested ENPs is efficient separation of the organism from ENPs that are either nonspecifically adsorbed to the organism and/or suspended in the dispersion following exposure. Here, we measure the uptake of 30 and 60 nm gold nanoparticles (AuNPs) by the nematode, Caenorhabditis elegans, using a sucrose density gradient centrifugation protocol to remove noningested AuNPs. Both conventional inductively coupled plasma mass spectrometry (ICP-MS) and single particle (sp)ICP-MS are utilized to measure the total mass and size distribution, respectively, of ingested AuNPs. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) imaging confirmed that traditional nematode washing procedures were ineffective at removing excess suspended and/or adsorbed AuNPs after exposure. Water rinsing procedures had AuNP removal efficiencies ranging from 57 to 97% and 22 to 83%, while the sucrose density gradient procedure had removal efficiencies of 100 and 93 to 98%, respectively, for the 30 and 60 nm AuNP exposure conditions. Quantification of total Au uptake was performed following acidic digestion of nonexposed and Au-exposed nematodes, whereas an alkaline digestion procedure was optimized for the liberation of ingested AuNPs for spICP-MS characterization. Size distributions and particle number concentrations were determined for AuNPs ingested by nematodes with corresponding confirmation of nematode uptake via high-pressure freezing/freeze substitution resin preparation and large-area SEM imaging. Methods for the separation and in vivo quantification of ENPs in multicellular organisms will facilitate robust studies of ENP uptake, biotransformation, and hazard assessment in the environment.

Detecting Carbon in Carbon: Exploiting Differential Charging to Obtain Information on the Chemical Identity and Spatial Location of Carbon Nanotube Aggregates in Composites by Imaging X-ray Photoelectron Spectroscopy

To better assess risks associated with nano-enabled products including multiwalled carbon nanotubes (MWCNT) within polymer matrices, it is important to understand how MWCNT are dispersed throughout the composite. The current study presents a method which employs imaging X-ray photoelectron spectroscopy (XPS) to chemically detect spatially segregated MWCNT rich regions at an epoxy composites surface by exploiting differential charging. MWCNT do not charge due to high conductivity and have previously been shown to energetically separate from their insulating surroundings when characterized by XPS. XPS in imaging mode revealed that these conductive regions were spatially separated due to micrometer-scale MWCNT aggregation and poor dispersion during the formation of the composite. Three MWCNT concentrations were studied; (1, 4 and 5) % by mass MWCNT within an epoxy matrix. Images acquired in periodic energy intervals were processed using custom algorithms designed to efficiently extract spectra from regions of interest. As a result, chemical and electrical information on aggregate and non-aggregate portions of the composite was extracted. Raman imaging and scanning electron microscopy were employed as orthogonal techniques for validating this XPS-based methodology. Results demonstrate that XPS imaging of differentially charging MWCNT composite samples is an effective means for assessing dispersion quality.

Detection and speciation of brominated flame retardants in high-impact polystyrene (HIPS) polymers

Polymeric materials have been suggested as possible environmental sources of persistent organic pollutants such as flame retardants. In situ, micrometre-scale characterization techniques for polymer matrix containing flame retardants may provide some insight into the dominant environmental transfer mechanism(s) of these brominated compounds. In this work, we demonstrate that micro X-ray fluorescence spectroscopy (μXRF), focused ion beam scanning electron microscopy (FIB-SEM) combined with energy dispersive X-ray spectroscopy (EDS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are promising techniques for the elemental and chemical identification of brominated fire retardant compounds (such as the deca-congener of polybrominated diphenyl ether, BDE-209) within polymeric materials (e.g. high-impact polystyrene or HIPS). Data from μXRF demonstrated that bromine (Br) inclusions were evenly distributed throughout the HIPS samples, whereas FIB SEM-EDS analysis revealed that small antimony (Sb) and Br inclusions are present, and regionally higher concentrations of Br surround the Sb inclusions (compared to the bulk material). Four prominent mass-to-charge ratio peaks (m/z 485, 487, 489 and 491) that correspond to BDE-209 were identified by ToF-SIMS and can be used to chemically distinguish this molecule on the surface of polymeric materials with respect to other brominated organic molecules. These techniques can be important in any study that investigates the route of entry to the environmental surroundings of BDE-containing materials.

Characterization of SiGe films for use as a National Institute of Standards and Technology Microanalysis Reference Material (RM 8905)

Bulk silicon-germanium (SiGe) alloys and two SiGe thick films (4 and 5 microm) on Si wafers were tested with the electron probe microanalyzer (EPMA) using wavelength dispersive spectrometers (WDS) for heterogeneity and composition for use as reference materials needed by the microelectronics industry. One alloy with a nominal composition of Si0.86Ge0.14 and the two thick films with nominal compositions of Si0.90Ge0.10 and Si0.75Ge0.25 on Si, evaluated for micro- and macroheterogeneity, will make good microanalysis reference materials with an overall expanded heterogeneity uncertainty of 1.1% relative or less for Ge. The bulk Ge composition in the Si0.86Ge0.14 alloy was determined to be 30.228% mass fraction Ge with an expanded uncertainty of the mean of 0.195% mass fraction. The thick films were quantified with WDS-EPMA using both the Si0.86Ge0.14 alloy and element wafers as reference materials. The Ge concentration was determined to be 22.80% mass fraction with an expanded uncertainty of the mean of 0.12% mass fraction for the Si0.90Ge0.10 wafer and 43.66% mass fraction for the Si0.75Ge0.25 wafer with an expanded uncertainty of the mean of 0.25% mass fraction. The two thick SiGe films will be issued as National Institute of Standards and Technology Reference Materials (RM 8905).