Denise M. Mitrano

Are nanosized or dissolved metals more toxic in the environment? A meta‐analysis

Recently, much has been written about the extreme urgency of elaborating the regulations for engineered nanomaterials. Such regulations are needed both from lawmakers, to protect people from potentially adverse effects, and from industry representatives, to prove that nanoproducts are produced carefully and with caution to avoid possible lawsuits. However, developing regulations has proven to be a difficult task, and an ambiguous topic where errors can easily occur. In the present study, the authors present a meta-analysis of 3 different nanomaterials (nano-Ag, nano-ZnO, and nano-CuO) in which data from ecotoxicity studies and published half-maximal effective concentration (EC50) values are compared for both the nano form and the corresponding dissolved metal. A ratio equal to 1 means that the particle is as toxic as the dissolved metal ion, whereas a lower ratio signifies that the nano form is less toxic than the dissolved metal based on total metal concentrations. The results show that for 93.8% (Ag), 100% (Cu), and 81% (Zn) of the ratios considered, the nano form is less toxic than the dissolved metal in terms of total metal concentration. Very few of the studies surveyed found a ratio of EC50 values for (dissolved/nano) that was larger than 2 (Ag: 1.1%; Cu: 0%; Zn: 2.8%). Hence, a reduction in existing metal concentration thresholds by a factor of 2 in current freshwater and soil regulations for ecotoxicity may be sufficient to protect organisms and compartments from the nano form of these metals as well.

Progress towards the validation of modeled environmental concentrations of engineered nanomaterials by analytical measurements

Environmental exposure modeling has been used extensively in the last years to obtain estimates of environmental concentrations of engineered nanomaterials (ENMs). In this perspective piece, we explore the issues when aiming to validate modeled environmental concentrations and propose options for both modelers and analytical chemists on how to proceed in the future to better compliment one anothers efforts. In this context, validation means to determine the degree to which the simulation results from a model are accurate representations of the real world by comparison with analytical data. Therefore, for such a model validation procedure, analytical methods need to be available which provide information in the same subject area. Currently, a major issue with nanometrology is that a multitude of nanomaterials are present in natural systems but only some are ENMs; various other particles of natural origin are abundant in the same systems. The analytical tools available are not yet capable to distinguish the natural from engineered nanomaterials at the low ENM concentrations expected in complex environmental matrices. However, both modeling and analytical studies are able to provide an orthogonal view on nanomaterials: modeling is able to yield estimates of the presence of ENMs in various environmental compartments while analytics can provide physical characterization of ENMs in these systems with hints towards the total nanomaterial concentration. While we need to make strides to improve the two approaches separately, using the resulting data together in a mutually supportive way will advance the field of ENM risk assessment.

Textile Functionalization and Its Effects on the Release of Silver Nanoparticles into Artificial Sweat.

This study addresses the release of total silver (Ag) and silver nanoparticles (Ag-NPs) from textiles into artificial sweat, particularly considering the functionalization technology used in textile finishing. Migration experiments were conducted for four commercially available textiles and for six laboratory-prepared textiles. Two among these lab-prepared textiles represent materials in which Ag-NPs were embedded within the textile fibers (composites), whereas the other lab-prepared textiles contain Ag particles on the respective fiber surfaces (coatings). The results indicate a smaller release of total Ag from composites in comparison to surface-coated textiles. The particulate fraction determined within the artificial sweat was negligible for most textiles, meaning that the majority of the released Ag is present as dissolved Ag. It is also relevant to note that nanotextiles do not release more particulate Ag than conventional Ag textiles. The results rather indicate that the functionalization type is the most important parameter affecting the migration. Furthermore, after measuring different Ag-NP types in their pristine form with inductively coupled plasma mass spectrometry in the single particle mode, there is evidence that particle modifications, like surface coating, may also influence the dissolution behavior of the Ag-NPs in the sweat solutions. These factors are important when discussing the likelihood of consumer exposure.

Polyester Textiles as a Source of Microplastics from Households: A Mechanistic Study to Understand Microfiber Release During Washing

Microplastic fibers make up a large proportion of microplastics found in the environment, especially in urban areas. There is good reason to consider synthetic textiles a major source of microplastic fibers, and it will not diminish since the use of synthetic fabrics, especially polyester, continues to increase. In this study we provide quantitative data regarding the size and mass of microplastic fibers released from synthetic (polyester) textiles during simulated home washing under controlled laboratory conditions. Consideration of fabric structure and washing conditions (use of detergents, temperature, wash duration, and sequential washings) allowed us to study the propensity of fiber shedding in a mechanistic way. Thousands of individual fibers were measured (number, length) from each wash solution to provide a robust data set on which to draw conclusions. Among all the variables tested, the use of detergent appeared to affect the total mass of fibers released the most, yet the detergent composition (liquid or powder) or overdosing of detergent did not significantly influence microplastic release. Despite different release quantities due to the addition of a surfactant (approximately 0.025 and 0.1 mg fibers/g textile washed, without and with detergent, respectively), the overall microplastic fiber length profile remained similar regardless of wash condition or fabric structure, with the vast majority of fibers ranging between 100 and 800 μm in length irrespective of wash cycle number. This indicates that the fiber staple length and/or debris encapsulated inside the fabric from the yarn spinning could be directly responsible for releasing stray fibers. This study serves as a first look toward understanding the physical properties of the textile itself to better understand the mechanisms of fiber shedding in the context of microplastic fiber release into laundry wash water.

Unraveling the Complexity in the Aging of Nanoenhanced Textiles: A Comprehensive Sequential Study on the Effects of Sunlight and Washing on Silver Nanoparticles

The scientific understanding of nanoparticle (NP) release and transformations they undergo during the product life cycle is hampered by the narrow scope of many research endeavors in terms of both breadth of variables and completeness of analytical characterization. We conducted a comprehensive suite of studies to reveal overarching mechanisms and parameters for nanosilver transformations either still adhered to the fabric or when released after washing. Laboratory prepared nanoenhanced fabrics were investigated: three Ag variants and one Au used as an unreactive reference to separate mechanical from chemical releases. Sequential combinations of sunlight irradiation and/or washing in seven different detergent formulations was followed by NP characterization divided into two groups: (1) dissolved and particulate matter in the wash solutions and (2) the fraction that remained on the fabric. Analytical techniques included spICP-MS, XANES, TEM, SEM, and total metals analysis of fabric digests and wash water filtrates. Sunlight irradiation stabilizes metallic Ag upon washing. Detergents containing oxidizing agents assisted with Ag particle release but not Au NPs, inferring additional chemical mechanisms. While particle size played some role, the NP capping agent/fabric binder combination was a key factor in release. When particles were released, little alteration in size was observed. The use of well-controlled fabrics, unreactive reference materials, and a life-cycle based experimental regime are paramount to understanding changes in Ag speciation and release upon use of nanoenhanced textiles.

The need for a life-cycle based aging paradigm for nanomaterials: importance of real-world test systems to identify realistic particle transformations

Assessing the risks of manufactured nanomaterials (MNM) has been almost exclusively focused on the pristine, as-produced materials with far fewer studies delving into more complex, real world scenarios. However, when considering a life-cycle perspective, it is clear that MNM released from commercial products during manufacturing, use and disposal are far more relevant both in terms of more realistic environmental fate and transport as well as environmental risk. The quantity in which the particles are released and their (altered) physical and chemical form should be identified and it is these metrics that should be used to assess the exposure and hazard the materials pose. The goal of this review is to (1) provide a rationale for using a life-cycle based approach when dealing with MNM transformations, (2) to elucidate the different chemical and physical forces which age and transform MNM and (3) assess the pros and cons of current analytical techniques as they pertain to the measurement of aged and transformed MNM in these complex release scenarios. Specifically, we will describe the possible transformations common MNM may undergo during the use or disposal of nano-products based on how these products will be used by the consumer by taking stock of the current nano-enabled products on the market. Understanding the impact of these transformations may help forecast the benefits and/or risks associated with the use of products containing MNM.

Mobility of metallic (nano)particles in leachates from landfills containing waste incineration residues

Incineration of municipal waste and sewage sludge is becoming an increasingly popular option for the disposal of waste materials and energy generation. The incineration process can concentrate metals in the incineration slags deposited in landfills. Emitted leachates contain a myriad of salts and metals; some of them in (nano)particulate form. In this study we collected the leachate from a Swiss landfill for municipal solid waste incineration (MSWI) residues along with the slags deposited at this site (waste incineration bottom ashes and fly ash, sewage sludge incineration bottom ash) from which simulated leachates were prepared. Basic water quality analysis (pH, DOC, TSS, major ions) and natural, incidental or engineered particles suspended in the leachate were characterized by NanoSight (for general size range), serial filtration with ICP-MS analysis for element specific particle size quantification and TEM/EDX to visualize particle morphology and composition. Special priority was given to those elements that have engineered nanoparticulate counterparts (Ti, Zn, Ag, Cu, Fe and Ce) to give an indication of 1) the current concentration and form of these particles emitted from the landfill, 2) the potential presence of engineered nanoparticles already in the samples, and 3) trends in particle size (change) in the leachate from different slags to provide an indication on particle mobility. Zn, Ag, and Cu had appreciable concentrations associated with small particulate matter (nano and 0.1–0.45 μm size fractions) in natural and laboratory prepared leachates, while Ti (nano)particles were most abundant in the landfill leachate. Multiple sampling dates suggested relatively steady particulate matter in the leachate for most elements, but analysis of differently aged bottom ash slags from municipal waste revealed differences with age, indicating the influence of slag weathering in metal mobilization. MSWI residues are inherently a complex mixture of stable and unstable materials that are subject to continuous and dynamic changes over time. Therefore, in this manuscript we placed an emphasis on understanding the geochemical processes that are associated with MSWI residue weathering and how this may dictate the likelihood of particulate metals leaching into groundwater.

Durability of nano-enhanced textiles through the life cycle: releases from landfilling after washing

By taking a life cycle approach to study the potential for silver nanoparticle (AgNP) release from functionalized textiles, we can estimate the relative importance of different phases to the release of Ag over time. Alongside the fastness of the AgNPs during the use phase (e.g. washing), we further explored the release potential of NPs from fabrics disposed of in a landfill (i.e. the end of life stage). Three different laboratory-prepared nano-enhanced fabrics (60 nm and 100 nm citrate-capped Ag as reactive particles; 60 nm citrate-capped Au as a non-reactive control) were subjected to 1 or 10 washing cycles under different laundering conditions (detergents with and without oxidants). The total metal released varied significantly depending on NP incorporation and the washing pattern variant. Au served to contrast the mechanical release of NPs with the (additional) chemical release the detergents induced to the Ag textiles, where the Ag : Au ratio released from the fabric was as high as 3, suggesting more predominant chemical mechanisms for silver release in those cases. Textile disposal was simulated by the Toxicity Characteristic Leaching Procedure (TCLP), where pre-laundered fabrics were subjected to this sequential exposure. The results show that the active landfill environment cannot readily mobilize the NPs from the fabric surface as easily after washing compared to unwashed textiles. Without washing, simulated landfilling released between 35–45% of the total Ag incorporated into the fabric (and only 20% of Au), but after laundering, most variants released less than 0.5%. Therefore, larger releases of NPs from textiles were observed during the use phase of the life cycle rather than the disposal phase, where an important portion of the released NP was in the dissolved phase. Large variations in releases at the end of life stage are determined under pre-washing conditions, which proves the necessity of life-cycle aging sequences to properly assess the likelihood and characteristics of materials released from nano-enhanced textiles.

Improvements in Nanoparticle Tracking Analysis To Measure Particle Aggregation and Mass Distribution: A Case Study on Engineered Nanomaterial Stability in Incineration Landfill Leachates

Numerous nanometrology techniques have been developed in recent years to determine the size, concentration, and a number of other characteristics of engineered nanomaterials (ENM) in environmental matrices. Among the many available techniques, nanoparticle tracking analysis (NTA) can measure individual particles to create a size distribution and measure the particle number. Therefore, we explore the possibility to use these data to calculate the particle mass distribution. Additionally, we further developed the NTA methodology to explore its suitability for analysis of ENM in complex matrices by measuring ENM agglomeration and sedimentation in municipal solid waste incineration landfill leachates over time. 100 nm Au ENM were spiked into DI H2O and synthetic and natural leachates. We present the possibility of measuring ENM in the presence of natural particles based on differences in particle refractivity indices, delineate the necessity of creating a calibration curve to adjust the given NTA particle number concentration, and determine the instruments linear range under different conditions. By measuring the particle size and the particle number distribution, we were able to calculate the ENM mass remaining in suspension. By combining these metrics together with transmission electron microscopy (TEM) analyses, we could assess the extent of both homo- and heteroagglomeration as well as particle sedimentation. Reporting both size and mass based metrics is common in atmospheric particle measurements, but now, the NTA can give us the possibility of applying the same approach also to aqueous samples.