Interlaboratory comparison of centrifugal ultrafiltration with ICP-MS detection in a first-step towards methods to screen for nanomaterial release during certification of drinking water contact materials.

A key requirement for evaluating the safety of nano-enabled water treatment devices is measuring concentrations of insoluble nanomaterials released from devices into water that may be ingested by consumers. Therefore, there is a need for simple technique that uses commonly available commercial laboratory techniques to discriminate between nanoparticles and dissolved by-products of the nanomaterial (e.g., ionic metals). Such capabilities would enable screening for particulate or dissolved metals released into water from nanomaterial-containing drinking water contact materials (e.g., paint coatings) or devices (e.g., filters). This multi-laboratory study sought to investigate the use of relatively inexpensive centrifugal ultrafilters to separate nanoparticulate from ionic metal in combination with inductively-coupled plasma mass spectrometry (ICP-MS) detection. The accuracy, precision, and reproducibility for the proposed method were assessed using mixtures of nanoparticulate and ionic gold (Au) in a standard and widely utilized model water matrix (NSF International Standard 53/61). Concentrations for both ionic and nanoparticulate gold based upon measurements of Au mass in the initial solutions and Au permeating the centrifugal ultrafilters. Results across different solution compositions and different participating labs showed that ionic and nanoparticulate Au could be consistently discriminated with ppb concentrations typically resulting in <10 % error. A mass balance was not achieved because nanoparticles were retained on membranes embedded in plastic holders inside the centrifuge tubes, and the entire apparatus could not be acid and/or microwave digested. This was a minor limitation considering the ultrafiltration method is a screening tool, and gold concentration in the permeate indicates the presence of ionic metal rather than nanoforms. With further development, this approach could prove to be an effective tool in screening for nanomaterial release from water-system or device materials as part of third-party certification processes of drinking water compatible products.

Potential Environmental Impacts and Antimicrobial Efficacy of Silver- and Nanosilver-Containing Textiles.

For textiles containing nanosilver, we assessed benefit (antimicrobial efficacy) in parallel with potential to release nanosilver (impact) during multiple life cycle stages. The silver loading and method of silver attachment to the textile highly influenced the silver release during washing. Multiple sequential simulated household washing experiments for fabric swatches in deionized water with or without detergent showed a range of silver release. The toxicity of washing experiment supernatants to zebrafish (Danio rerio) embryos was negligible, with the exception of the very highest Ag releases (∼1 mg/L Ag). In fact, toxicity tests indicated that residual detergent exhibited greater adverse response than the released silver. Although washing the fabrics did release silver, it did not affect their antimicrobial efficacy, as demonstrated by >99.9% inhibition of E. coli growth on the textiles, even for textiles that retained as little as 2 µg/g Ag after washing. This suggests that very little nanosilver is required to control bacterial growth in textiles. Visible light irradiation of the fabrics reduced the extent of Ag release for textiles during subsequent washings. End-of-life experiments using simulated landfill conditions showed that silver remaining on the textile is likely to continue leaching from textiles after disposal in a landfill.

Nanomaterial transformation and association with fresh and freeze-dried wastewater activated sludge: implications for testing protocol and environmental fate.

Engineered nanomaterials (ENMs) are an emerging class of contaminants entering wastewater treatment plants (WWTPs), and standardized testing protocols are needed by industry and regulators to assess the potential removal of ENMs during wastewater treatment. A United States Environmental Protection Agency (USEPA) standard method (OPPTS 835.1110) for estimating soluble pollutant removal during wastewater treatment using freeze-dried, heat-treated (FDH) activated sludge (AS) has been recently proposed for predicting ENM fate in WWTPs. This study is the first to evaluate the use of FDH AS in batch experiments for quantifying ENM removal from wastewater. While soluble pollutants sorbed equally to fresh and FDH AS, fullerene, silver, gold, and polystyrene nanoparticles' removals with FDH AS were approximately 60-100% less than their removals with fresh AS. Unlike fresh AS, FDH AS had a high concentration of proteins and other soluble organics in the liquid phase, an indication of bacterial membrane disintegration due to freeze-drying and heat exposure. This cellular matter stabilized ENMs such that they were poorly removed by FDH AS. Therefore, FDH AS is not a suitable sorbent for estimating nanoparticle removal in WWTPs, whereas fresh AS has been shown to reasonably predict full-scale performance for titanium removal. This study indicates that natural or engineered processes (e.g., anaerobic digestion, biosolids decomposition in soils) that result in cellular degradation and matrices rich in surfactant-like materials (natural organic matter, proteins, phospholipids, etc.) may transform nanoparticle surfaces and significantly alter their fate in the environment.

Octanol-water distribution of engineered nanomaterials.

The goal of this study was to examine the effects of pH and ionic strength on octanol-water distribution of five model engineered nanomaterials. Distribution experiments resulted in a spectrum of three broadly classified scenarios: distribution in the aqueous phase, distribution in the octanol, and distribution into the octanol-water interface. Two distribution coefficients were derived to describe the distribution of nanoparticles among octanol, water and their interface. The results show that particle surface charge, surface functionalization, and composition, as well as the solvent ionic strength and presence of natural organic matter, dramatically impact this distribution. Distributions of nanoparticles into the interface were significant for nanomaterials that exhibit low surface charge in natural pH ranges. Increased ionic strengths also contributed to increased distributions of nanoparticle into the interface. Similarly to the octanol-water distribution coefficients, which represent a starting point in predicting the environmental fate, bioavailability and transport of organic pollutants, distribution coefficients such as the ones described in this study could help to easily predict the fate, bioavailability, and transport of engineered nanomaterials in the environment.

Solar photolysis kinetics of disinfection byproducts.

Disinfection byproducts (DBPs) discharged from wastewater treatment plants may impair aquatic ecosystems and downstream drinking-water quality. Sunlight photolysis, as one process by which DBPs may dissipate in the receiving surface water, was investigated. Outdoor natural sunlight experiments were conducted in water for a series of carbonaceous DBPs (trihalomethanes, haloacetic acids, halopropanones, and haloacetaldehydes) and nitrogenous DBPs (nitrosamines, halonitromethanes, and haloacetonitriles). Their pseudo-first-order rate constants for photolytic degradation were then used to calibrate quantitative structure-activity relationship (QSAR) parameters, which, in return, predicted the photolysis potentials of other DBPs or related compounds. Nitrogenous DBPs were found to be more susceptible to solar irradiation than carbonaceous DBPs, with general rankings for the functional groups as follows: N-nitroso (N-NO)>nitro (NO(2))>nitrile (CN)>carbonyl (CO)>carboxyl (COOH). Compounds containing a high degree of halogenation (e.g., three halogens) were usually less stable than less halogenated species (e.g., those with two halogens). Bromine- or iodine-substituted species were more photosensitive than chlorinated analogs. While most bromine- and chlorine-containing trihalomethanes and haloacetic acids persisted over the 6-h test, nearly complete removal (>99%) of nitrosamines occurred within 1 h of sunlight exposure. Indoor laboratory experiments using simulated sunlight demonstrated that the degradation of nitrosamines was approximately 50% slower when organic matter was present, and approximately 11% slower in non-filtered water than in filtered water.

Fate of effluent organic matter and DBP precursors in an effluent-dominated river: a case study of wastewater impact on downstream water quality.

The impact of treated wastewater discharges on downstream water quality was evaluated in an effluent-dominated stream in the Southwest USA. The fate and transport of effluent organic matter (EfOM) and disinfection by-product (DBP) precursors was studied. Nitrification and biodegradation were important mechanisms. Changes in DBP formation potential along the river appeared to correlate with dissolved organic carbon (DOC) and organic nitrogen concentrations and specific ultraviolet absorbance. The mean oxidation state of carbon (MOC) decreased in value along the river. MOC decreases paralleled decreases in the biodegradability of residual DOC (i.e., lower biodegradable DOC/DOC ratio). The EfOM was biodegradable by up to 40 percent, both in the stream and in a laboratory reactor, and many DBP precursors (e.g., haloacetonitriles, certain nitrosamines) decreased in concentration. Alternatively, the DBP yields for trihalomethanes or haloacetic acids either remained the same or increased slightly, suggesting that these precursors were part of the recalcitrant organic matter (OM).

Removal of arsenate and 17alpha-ethinyl estradiol (EE2) by iron (hydr)oxide modified activated carbon fibers.

Activated carbon fibers (ACF) were modified with iron (hydr)oxide and studied to determine their suitability to remove arsenate and 17alpha -ethinyl estradiol (EE2) from water. Two synthesis methods, one involving aqueous KMnO(4) pretreatment followed by Fe(II) treatment, and the other involving reaction with Fe(III) in an organic solvent followed by NaOH treatment, were used to produce modified ACF media containing 5.9% and 8.4% iron by dry weight, respectively. Scanning electron microscopy (SEM) and Electron dispersion X-ray (EDX) techniques indicated slightly higher iron content near the outer edges of the fibers. Pseudo-equilibrium batch test experimental data at pH = 7.0 +/- 0.1 in 5 mM NaHCO(3) buffered ultrapure water containing approximately 100 micro g(As)/L and approximately 500 micro gEE2/L were fitted with the Freundlich isotherm model (q = K x C(E)(1/n)). The adsorption capacity parameters (K) were approximately 2586 (micro gAs/gFe)(L/micro gAs)(1/n) and approximately 425 (micro gAs/gFe)(L/micro gAs)(1/n)), respectively, for the KMnO(4)/Fe(II) and Fe(III)/NaOH treated media. The KMnO(4)/Fe(II) media exhibited a lower adsorption capacity at 99% EE2 removal than did the Fe(III)/NaOH treated media (1.3 mgEE2/g -dry -media vs. 1.8 mgEE2/g -dry -media). The arsenate adsorption intensity parameters (1/n) for both modified ACF media were < 0.29, implying very favorable adsorption, which suggests that this type of media may be suitable for single point -of -use applications in which arsenic and organic co-contaminants require simultaneous removal and the depth of the packed bed is the key factor.

Arsenate removal by nanostructured ZrO2 spheres.

A new zirconium oxide-based media for arsenate removal from water was fabricated and evaluated in batch and continuous flow experiments. Highly porous (epsilonp approximately 0.9) nanostructured zirconium oxide spheres were fabricated by the impregnation of macroporous ion-exchange media (CalRes 2103, Calgon) with zirconium salt; the media was then ashed at T > 750 +/- 50 degrees C to remove the organic polymer resin and obtain ZrO2 spheres. The spheres generally ranged from 200 to 800 microm in diameter, and consisted of ZrO2 nanoastructures generally ranging between 20 and 100 nm. They also exhibited monoclinic and tetragonal crystalline structures, and had an isoelectric point of 5.6. Equilibrium batch experiments were conducted in 10 mM NaHCO3 buffered nanopure water at three pH values (6.4,7.3, and 8.3) with 120 microg/L As(V). Data were fit with the Freundlich isotherm equation (q(e) = Kx CE(1/n)), resulting in an intensity parameter (1/n) of approximately 0.33 and capacity parameters (K) ranging from 115 to 400 (microg As(V) g(-1) dry media)(L microg(-1))1/n. The pore diffusion coefficient and toruosity were estimated to be 6.4 x 10(-6) cm2 s(-1) and 1.3, respectively. For a packed bed adsorbent operating at a loading rate of 11.5 m3 m(-2) hr(-1) in a realistic continuous flow experiment, the external mass transport coefficient was estimated to be kf approximately 6.3 x 10(-3) cm s(-1). The pore diffusion coefficient and the external mass transport coefficient were used with the pore surface diffusion model (PSDM) to predict the arsenate breakthrough curve. A short bed adsorbent (SBA) test was conducted under the same conditions to validate the model. In this study, surface diffusion was ignored because the particles have a very high porosity. The validated model was used to predict arsenate breakthrough in a simulated full-scale system. The overall combined use of modeling, material characterization, equilibria, and kinetics tests determined the suitability of the media for arsenate treatment cheaper, easier, faster, and with less media than a long duration pilot test would have. Although the fabricated zirconium oxide spheres exhibited adsorption capacity comparable to some commercially available media such as iron based (hydr)oxides, the high cost of fabrication may render the media not feasible for wide use in commercial applications. However, the very high porosity of this media provides for improved pore diffusion and faster overall mass transport, which may be critical for applications where mass transport is the limiting factor.