Toward bioinspired polymer adhesives: activation assisted via HOBt for grafting of dopamine onto poly(acrylic acid).

The design of bioinspired polymers has long been an area of intense study, however, applications to the design of concrete admixtures for improved materials performance have been relatively unexplored. In this work, we functionalized poly(acrylic acid) (PAA), a simple analogue to polycarboxylate ether admixtures in concrete, with dopamine to form a catechol-bearing polymer (PAA-g-DA). Synthetic routes using hydroxybenzotriazole (HOBt) as an activating agent were examined for their ability in grafting dopamine to the PAA backbone. Previous literature using the traditional coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) to graft dopamine to PAA were found to be inconsistent and the sensitivity of EDC coupling reactions necessitated a search for an alternative. Additionally, HOBt allowed for greater control over per cent functionalization of the backbone, is a simple, robust reaction, and showed potential for scalability. This finding also represents a novel synthetic pathway for amide bond formation between dopamine and PAA. Finally, we performed preliminary adhesion studies of our polymer on rose granite specimens and demonstrated a 56% improvement in the mean adhesion strength over unfunctionalized PAA. These results demonstrate an early study on the potential of PAA-g-DA to be used for improving the bonds within concrete.

Effect of Cellulose Nanofibrils and TEMPO-mediated Oxidized Cellulose Nanofibrils on the Physical and Mechanical Properties of Poly(vinylidene fluoride)/Cellulose Nanofibril Composites.

Cellulose nanofibrils (CNFs) are high aspect ratio, natural nanomaterials with high mechanical strength-to-weight ratio and promising reinforcing dopants in polymer nanocomposites. In this study, we used CNFs and oxidized CNFs (TOCNFs), prepared by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation process, as reinforcing agents in poly(vinylidene fluoride) (PVDF). Using high-shear mixing and doctor blade casting, we prepared free-standing composite films loaded with up to 5 wt % cellulose nanofibrils. For our processing conditions, all CNF/PVDF and TOCNF/PVDF films remain in the same crystalline phase as neat PVDF. In the as-prepared composites, the addition of CNFs on average increases crystallinity, whereas TOCNFs reduces it. Further, addition of CNFs and TOCNFs influences properties such as surface wettability, as well as thermal and mechanical behaviors of the composites. When compared to neat PVDF, the thermal stability of the composites is reduced. With regards to bulk mechanical properties, addition of CNFs or TOCNFs, generally reduces the tensile properties of the composites. However, a small increase (~18%) in the tensile modulus was observed for the 1 wt % TOCNF/PVDF composite. Surface mechanical properties, obtained from nanoindentation, show that the composites have enhanced performance. For the 5 wt % CNF/PVDF composite, the reduced modulus and hardness increased by ~52% and ~22%, whereas for the 3 wt % TOCNF/PVDF sample, the increase was ~23% and ~25% respectively.

Effects of soot by-product from the synthesis of engineered metallofullerene nanomaterials on terrestrial invertebrates.

The synthesis of carbon-based nanomaterials is often inefficient, generating large amounts of soot with metals as waste by-product. Currently, there are no specific regulations for disposal of engineered nanomaterials or the waste by-products resulting from their synthesis, so it is presumed that by-products are disposed of in the same way as the parent (bulk) materials. We studied the terrestrial toxicity of soot from gadolinium metallofullerene nanomanufacturing on earthworms (Eisenia fetida) and isopods (Porcellio scaber). The metallofullerene soot consisted of carbon particle agglomerates in the nanometer and submicrometer ranges (1-100 and 101-999 nm, respectively), with metals used during nanomanufacturing detectable on the particles. Despite high metal concentrations (>100 000 mg/kg) in the soot, only a relatively small amount of metals leached out of a spiked field soil, suggesting only moderate mobility. Seven- and 14-d exposures in field soil demonstrated that the soot was only toxic to earthworms at high concentrations (>10 000 mg/kg); however, earthworms avoided spiked soils at lower concentrations (as low as 500 mg/kg) and at lower soil pH. The presence of soot in food and soil did not cause isopod avoidance. These data demonstrate that metallofullerene soot from nanomanufacturing may only be toxic to earthworms at high concentrations representative of improper disposal or accidental spills. However, our results indicate that terrestrial invertebrates may avoid soils contaminated with soot at sublethal concentrations. Environ Toxicol Chem 2018;9999:1-12. Published 2018 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America.

A weight-of-evidence approach to identify nanomaterials in consumer products: a case study of nanoparticles in commercial sunscreens.

Nanoscale ingredients in commercial products represent a point of emerging environmental concern due to recent findings that correlate toxicity with small particle size. A weight-of-evidence (WOE) approach based upon multiple lines of evidence (LOE) is developed here to assess nanomaterials as they exist in consumer product formulations, providing a qualitative assessment regarding the presence of nanomaterials, along with a baseline estimate of nanoparticle concentration if nanomaterials do exist. Electron microscopy, analytical separations, and X-ray detection methods were used to identify and characterize nanomaterials in sunscreen formulations. The WOE/LOE approach as applied to four commercial sunscreen products indicated that all four contained at least 10% dispersed primary particles having at least one dimension <100 nm in size. Analytical analyses confirmed that these constituents were comprised of zinc oxide (ZnO) or titanium dioxide (TiO2). The screening approaches developed herein offer a streamlined, facile means to identify potentially hazardous nanomaterial constituents with minimal abrasive processing of the raw material.

Efficacy of non-toxic surfaces to reduce bioadhesion in terrestrial gastropods.

BACKGROUND: Invasive species are described as the greatest threat to biodiversity, after habitat destruction and climate change, potentially imposing economic impacts and indigenous species impairment. Commonly applied chemical controls present the potential for legacy contamination and non-target organism injury. This study investigated the effects of different substrates and novel topographical surfaces on the behavioral and mechanical associations of the terrestrial gastropod Otala lactea. RESULTS: The gastropod preferentially aestivated on rough glass (61% increase, P < 0.01) relative to smooth glass but avoided a cross-patterned surface tessellation on silicone (82% reduction, P < 0.01) relative to smooth silicone. Significant deviations in turning behavior were found on the cross-patterned topographical surface and hydrophobic Teflon surfaces. The strongest correlation with gastropod adhesion strength to surfaces was found for surface elastic modulus (R = 0.88, P = 0.03), followed by hydrophobicity (R = - 0.71, P = 0.14), but no relationship with roughness (P = 0.36). CONCLUSION: Preliminary data suggest surface roughness controlled aestivation behavior while elastic modulus (surface flexibility) controlled adhesion strength. In spite of greater adhesion to high-modulus materials, surface modulus was not a statistically significant controlling factor on gastropod aestivation preference. Understanding and exploiting the behavioral and mechanistic cues that organisms use while attaching to surfaces may lead to more environmentally benign control approaches.

Desorption of nitramine and nitroaromatic explosive residues from soils detonated under controlled conditions.

Potentially toxic nitroaromatic and nitramine compounds are introduced onto soils during detonation of explosives. The present study was conducted to investigate the desorption and transformation of explosive compounds loaded onto three soils through controlled detonation. The soils were proximally detonated with Composition B, a commonly used military explosive containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). Gas-exchangeable surface areas were measured from pristine and detonated soils. Aqueous batches of detonated soils were prepared by mixing each soil with ultrapure water. Samples were collected for 141 d and concentrations of Composition B compounds and TNT transformation products 2-amino-4,6-dinitrotoluene (2ADNT), 4-amino-2,6-dinitrotoluene (4ADNT), and 1,3,5-trinitrobenzene (1,3,5-TNB) were measured. The RDX, HMX, and TNT concentrations in detonated soil batches exhibited first-order physical desorption for the first, roughly, 10 d and then reached steady state apparent equilibrium within 40 d. An aqueous batch containing powdered Composition B in water was sampled over time to quantify TNT, RDX, and HMX dissolution from undetonated Composition B particles. The TNT, RDX, and HMX concentrations in aqueous batches of pure Composition B reached equilibrium within 6, 11, and 20 d, respectively. Detonated soils exhibited lower gas-exchangeable surface areas than their pristine counterparts. This is likely due to an explosive residue coating on detonated soil surfaces, shock-induced compaction, sintering, and/or partial fusion of soil particles under the intense heat associated with detonation. Our results suggest that explosive compounds loaded to soils through detonation take longer to reach equilibrium concentrations in aqueous batches than soils loaded with explosive residues through aqueous addition. This is likely due to the heterogeneous interactions between explosive residues and soil particle surfaces.

Sediment toxicity and bioaccumulation of nano and micron-sized aluminum oxide.

Nano-aluminum oxide (Al(2)O(3)) is used commercially in coatings and abrasives. Nano-Al(2)O(3) can also be generated through the oxidation of nano-aluminum in military propellants and energetics. The purpose of the present study was to assess toxicity and bioaccumulation of nano-Al(2)O(3) to a variety of sediment organisms (Tubifex tubifex, Hyalella azteca, Lumbriculus variegatus, and Corbicula fluminea). The bioaccumulation and toxicity of nano-Al(2)O(3) was compared with that of micron-sized Al(2)O(3) to investigate potential size-related effects. Results of the present study show species-specific differences in relative bioaccumulation of nano and micron-sized Al(2)O(3). Significant toxic effects (survival and growth) were observed in H. azteca testing, but only at high concentrations unlikely to be found in the environment. Nano-Al(2)O(3) was found to be more toxic than micron-sized Al(2)O(3) to H. azteca survival in a 14-d study in which organisms were in direct contact with a thin layer of 625 or 2,500 mg of Al(2)O(3) dispersed on the surface of either sediment or sand. A significant growth effect was also observed for nano but not micron-sized Al(2)O(3) at the highest treatment level tested (100 g/kg Al(2)O(3)) in a 10-d H. azteca bioassay in which Al(2)O(3) was homogenized with sediment. However, differences in measured sediment Al concentrations (micron-sized = 55.1 [+/-0.6] g/kg Al; nano-sized = 66.2 [+/-0.6] g/kg Al) in the nano and micron-sized Al(2)O(3) preclude direct comparison of the toxicity of these two treatments based on particle size.

Assessing the fate and effects of nano aluminum oxide in the terrestrial earthworm, Eisenia fetida.

Nano-sized aluminum is currently being used by the military and commercial industries in many applications including coatings, thermites, and propellants. Due to the potential for wide dispersal in soil systems, we chose to investigate the fate and effects of nano-sized aluminum oxide (Al2O3), the oxidized form of nano aluminum, in a terrestrial organism. The toxicity and bioaccumulation potential of micron-sized (50-200 microm, nominal) and nano-sized (11 nm, nominal) Al2O3 was comparatively assessed through acute and subchronic bioassays using the terrestrial earthworm, Eisenia fetida. Subchronic (28-d) studies were performed exposing E. fetida to nano- and micron-sized Al2O3-spiked soils to assess the effects of long-term exposure. No mortality occurred in subchronic exposures, although reproduction decreased at >or=3,000 mg/kg nano-sized Al2O3 treatments, with higher aluminum body burdens observed at 100 and 300 mg/kg; no reproductive effects were observed in the micron-sized Al2O3 treatments. In addition to toxicity and bioaccumulation bioassays, an acute (48-h) behavioral bioassay was conducted utilizing a soil avoidance wheel in which E. fetida were given a choice of habitat between control, nano-, or micron-sized Al2O3 amended soils. In the soil avoidance bioassays, E. fetida exhibited avoidance behavior toward the highest concentrations of micron- and nano-sized Al2O3 (>5,000 mg/kg) relative to control soils. Results of the present study indicate that nano-sized Al2O3 may impact reproduction and behavior of E. fetida, although at high levels unlikely to be found in the environment.

Investigating the fate of nitroaromatic (TNT) and nitramine (RDX and HMX) explosives in fractured and pristine soils.

Explosives compounds, known toxins, are loaded to soils on military training ranges predominantly during explosives detonation events that likely fracture soil particles. This study was conducted to investigate the fate of explosives compounds in aqueous slurries containing fractured and pristine soil particles. Three soils were crushed with a piston to emulate detonation-induced fracturing. X-ray diffraction, energy-dispersive X-ray spectrometry, gas adsorption surface area measurements, and scanning electron microscopy were used to quantify and image pristine and fractured soil particles. Aqueous batches were prepared by spiking soils with solutions containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 2,4-dinitrotoluene (2,4-DNT). Samples were collected over 92 d and the concentrations of the spiked explosives compounds and TNT transformation products 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT) were measured. Our results suggest soil mineralogical and geochemical compositions were not changed during piston-induced fracturing but morphological differences were evident with fractured soils exhibiting more angular surfaces, more fine grained particles, and some microfracturing that is not visible in the pristine samples. TNT, 2,4-DNT, RDX, and HMX exhibited greater analyte loss over time in batch solutions containing fractured soil particles compared to their pristine counterparts. 2ADNT and 4ADNT exhibited greater concentrations in slurries containing pristine soils than in slurries containing fractured soils. Explosives compound transformation is greater in the presence of fractured soil particles than in the presence of pristine soil particles. Our results imply fractured soil particles promote explosive compound transformation and/or explosives compounds have a greater affinity for adsorption to fractured soil particle surfaces.

Release of metal impurities from carbon nanomaterials influences aquatic toxicity.

Few studies have considered the environmental impacts of impurities and byproducts associated with low-efficiency nanomanufacturing processes. Here, we study the composition and aquatic toxicity of low-purity, as-produced fullerenes (C60) and metallofullerene waste solids, both of which were generated via arc-discharge synthesis. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and inductively coupled plasma mass spectroscopy (ICP-MS) were used to characterize the metals composition of the solid test materials and of aqueous leachates prepared by mixing test materials with waters of varying pH, hardness, and salinity. The aquatic toxicity of the leachates was determined using U.S. Environmental Protection Agency recommended aquatic bioassay protocols with two standard test organisms-Pimephales promelas and Ceriodaphnia dubia. Results indicated that metals associated with the solid test materials became mobilized in our test system upon interaction with waters of circumneutral pH and reached concentrations sufficient to induce toxicity in both test species. Acute (48 h) LC50 values for P. promelas and C. dubia exposed to leachates prepared from metallofullerene waste solids were 54 and 5% (as % leachate in diluent), respectively. Toxicity was eliminated after adding the chelator EDTA to the leachates, implicating divalent transition metals as the toxicity source. Our results demonstrate the aquatic toxicity of metals mobilized from products and byproducts of nanomanufacturing, and they emphasize the need for a global review of nanomanufacturing wastes and low-purity products.

Factors influencing the partitioning and toxicity of nanotubes in the aquatic environment.

Carbon nanotubes (NTs) may be among the most useful engineered nanomaterials for structural applications but could be difficult to study in ecotoxicological evaluations using existing tools relative to nanomaterials with a lower aspect ratio. Whereas the hydrophobicity and van der Waals interactions of NTs may suggest aggregation and sedimentation in aquatic systems, consideration regarding how engineered surface modifications influence their environmental fate and toxicology is needed. Surface modifications (e.g., functional groups and coatings) are intended to create conditions to make NTs dispersible in aqueous suspension, as required for some applications. In the present study, column stability and settling experiments indicated that raw, multiwalled NTs (MWNTs) settled more rapidly than carbon black and activated carbon particles, suggesting sediment as the ultimate repository. The presence of functional groups, however, slowed the settling of MWNTs (increasing order of stability: hydroxyl > carboxyl > raw), especially in combination with natural organic matter (NOM). Stabilized MWNTs in high concentrations of NOM provided relevance for water transport and toxicity studies. Aqueous exposures to raw MWNTs decreased Ceriodaphnia dubia viability, but such effects were not observed during exposure to functionalized MWNTs (> 80 mg/L). Sediment exposures of the amphipods Leptocheirus plumulosus and Hyalella azteca to different sizes of sediment-borne carbon particles at high concentration indicated mortality increased as particle size decreased, although raw MWNTs induced lower mortality (median lethal concentration [LC50], 50 to >264 g/kg) than carbon black (LC50, 18-40 g/kg) and activated carbon (LC50, 12-29 g/kg). Our findings stress that it may be inappropriate to classify all NTs into one category in terms of their environmental regulation.