Traceability of fluorescent engineered nanomaterials and their fate in complex liquid waste matrices

Assessing the Environmental Effects Related to Quantum Dot Structure, Function, Synthesis and Exposure

Quantum dots (QDs) are engineered semiconductor nanocrystals with unique fluorescent, quantum confinement, and quantum yield properties, making them valuable in a range of commercial and consumer imaging, display, and lighting technologies. Production and usage of QDs are increasing, which increases the probability of these nanoparticles entering the environment at various phases of their life cycle. This review discusses the major types and applications of QDs, their potential environmental exposures, fates, and adverse effects on organisms. For most applications, release to the environment is mainly expected to occur during QD synthesis and end-product manufacturing since encapsulation of QDs in these devices prevents release during normal use or landfilling. In natural waters, the fate of QDs is controlled by water chemistry, light intensity, and the physicochemical properties of QDs. Research on the adverse effects of QDs primarily focuses on sublethal endpoints rather than acute toxicity, and the differences in toxicity between pristine and weathered nanoparticles are highlighted. A proposed oxidative stress adverse outcome pathway framework demonstrates the similarities among metallic and carbon-based QDs that induce reactive oxygen species formation leading to DNA damage, reduced growth, and impaired reproduction in several organisms. To accurately evaluate environmental risk, this review identifies critical data gaps in QD exposure and ecological effects, and provides recommendations for future research. Future QD regulation should emphasize exposure and sublethal effects of metal ions released as the nanoparticles weather under environmental conditions. To date, human exposure to QDs from the environment and resulting adverse effects has not been reported.

A European nano-registry as a reliable database for quantitative risk assessment of nanomaterials? A comparison of national approaches

Despite the fact that nanomaterials have been in use for decades and chemicals legislation is largely harmonised within the EU, quantitative and safety-relevant information on nanomaterials is still scarce. In particular, information about production volumes, their unique physicochemical properties (size, specific surface area, etc.) and nanomaterial exposure, which may lead to adverse effects on human health and the environment, is still lacking. While the latest amendments of the REACH Annexes have led to certain improvements, a harmonised EU-wide nano-registry would provide additional quantitative data for risk assessment but is not foreseeable for the near future. Since the European Commission, the European Parliament and some member states take contrasting approaches to the regulation of nanomaterials, France, Belgium, Denmark, Sweden and Norway (as a country of the European Economic Area), launched national mandatory reporting systems to collect quantitative information, thus fostering early risk assessment of nanomaterials. In this study, we compare national registries - based on a literature review and expert interviews - and show differences between the regulations under the respective national laws and REACH regulation. These include, for instance, thresholds for notification and level of detail on the specification of the nanomaterial, mixture and/or product, the definition of exceptions for the requirement to register and the timing of registration. As this heterogenous regulatory framework hinders comparability and potentially creates trade barriers, we argue that a harmonised EU-wide nano-registry would substantially improve the current situation by promoting the safe and sustainable handling of nanomaterials, increasing transparency and trust, and consequently nurturing innovation. Such an EU-wide nano-registry should both cover nanomaterials as substances or mixtures, such as in REACH registration, and the semi-/finished products they will be used in, since the exposure, and thus the hazardous potential of released nanomaterials during their life cycle, depends largely on the scope of application.

Mobility and fate of ligand stabilized semiconductor nanoparticles in landfill leachates

Semiconductor quantum dots (QDs) are nanocrystals used in diverse optoelectronics. At the end of their useful life they are likely to end up in landfills, where they could be mobilzed by infiltrating rain water. In this work, spectroscopic and light scattering techniques were employed to investigate the environmental fate of QDs exposed to leachates from Austrian landfill sites containing municipal solid and bulky wastes. Brij-58-coated CdSe QDs, a model for surfactant stabilized hydrophobic nanoparticles, primarily sedimented before being degraded on a slower timescale in the course of 6 months. In contrast, N-acetyl-l-cystein-coated CdTe QDs, which represent electrostatically stabilized nanoparticles with a small covalently linked stabilizing molecule, mainly underwent a degradation mechanism that was accelerated by temperature. 71-95 % of this QD type was still dispersed in all leachates after 6 months at low temperature. Leachate temperature and composition, such as the DOC, as well as the used particle coating determined the mechanistic route of clearance of sedimentation versus degradation. Our study shows, that mechanistic investigations are necessary to determine the persistence of nanoparticles depending on their coatings in waste matrices which can be further used to assess hazardous risks of such nanowastes.

Biochemistry and biomedicine of quantum dots: from biodetection to bioimaging, drug discovery, diagnostics, and therapy

According to recent research, nanotechnology based on quantum dots (QDs) has been widely applied in the field of bioimaging, drug delivery, and drug analysis. Therefore, it has become one of the major forces driving basic and applied research. The application of nanotechnology in bioimaging has been of concern. Through in vitro labeling, it was found that luminescent QDs possess many properties such as narrow emission, broad UV excitation, bright fluorescence, and high photostability. The QDs also show great potential in whole-body imaging. The QDs can be combined with biomolecules, and hence, they can be used for targeted drug delivery and diagnosis. The characteristics of QDs make them useful for application in pharmacy and pharmacology. This review focuses on various applications of QDs, especially in imaging, drug delivery, pharmaceutical analysis, photothermal therapy, biochips, and targeted surgery. Finally, conclusions are made by providing some critical challenges and a perspective of how this field can be expected to develop in the future.

STATEMENT OF SIGNIFICANCE

Quantum dots (QDs) is an emerging field of interdisciplinary subject that involves physics, chemistry, materialogy, biology, medicine, and so on. In addition, nanotechnology based on QDs has been applied in depth in biochemistry and biomedicine. Some forward-looking fields emphatically reflected in some extremely vital areas that possess inspiring potential applicable prospects, such as immunoassay, DNA analysis, biological monitoring, drug discovery, in vitro labelling, in vivo imaging, and tumor target are closely connected to human life and health and has been the top and forefront in science and technology to date. Furthermore, this review has not only involved the traditional biochemical detection but also particularly emphasized its potential applications in life science and biomedicine.

A review of the fate of engineered nanomaterials in municipal solid waste streams

Significant knowledge and data gaps associated with the fate of product-embedded engineered nanomaterials (ENMs) in waste management processes exist that limit our current ability to develop appropriate end-of-life management strategies. This review paper was developed as part of the activities of the IWWG ENMs in Waste Task Group. The specific objectives of this review paper are to assess the current knowledge associated with the fate of ENMs in commonly used waste management processes, including key processes and mechanisms associated with ENM fate and transport in each waste management process, and to use that information to identify the data gaps and research needs in this area. Literature associated with the fate of ENMs in wastes was reviewed and summarized. Overall, results from this literature review indicate a need for continued research in this area. No work has been conducted to quantify ENMs present in discarded materials and an understanding of ENM release from consumer products under conditions representative of those found in relevant waste management process is needed. Results also indicate that significant knowledge gaps associated with ENM behaviour exist for each waste management process investigated. There is a need for additional research investigating the fate of different types of ENMs at larger concentration ranges with different surface chemistries. Understanding how changes in treatment process operation may influence ENM fate is also needed. A series of specific research questions associated with the fate of ENMs during the management of ENM-containing wastes have been identified and used to direct future research in this area.

Effect of water chemistry on the aggregation and photoluminescence behavior of carbon dots

Carbon dots are rapidly emerging carbon-based nanomaterials that, due to their growing applications, will inevitable find their way to natural waters; however, their environmental fate is mostly unknown. Carbon dots with different surface functionality were fabricated and characterized by TEM and FT-IR. Their surface charge, given by the zeta potential, and their hydrodynamic diameter in suspension were investigated under a variety of environmentally relevant conditions. The effect of ionic strength was studied in the presence of monovalent (NaCl) and divalent (CaCl₂) cations, for pH levels from 3 to 11; humic acid was used as a model for dissolved natural organic matter. Total potential energies of interactions were modeled by classical DLVO theory. The experimental results showed that water chemistry altered the surface charge of the nanomaterials, but their hydrodynamic size could not be correlated to those changes. Evidence of specific interactions was found for the amino functionalized particles in most cases, as well as the plain carbon dots in the presence of Ca²⁺ and humic acid. Nanoparticles remained largely stable in suspension, with some exception at the highest ionic strength considered. DLVO theory did not adequately capture the aggregation behavior of the system. Moreover, cation and/or humic acid adsorption negatively affected the emission intensity of the particles, suggesting limitations to their use in natural water sensing applications. The particular stability shown by the carbon dots results in exposure to organisms in the water column and the possibility of contamination transported to significant distances from their source.

"Use of acidophilic bacteria of the genus Acidithiobacillus to biosynthesize CdS fluorescent nanoparticles (quantum dots) with high tolerance to acidic pH"

The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd²⁺ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360nm and a broad emission spectra between 450 and 650nm when excited at 370nm, both characteristic of CdS QDs. Average sizes of 6 and 10nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H₂S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5-5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms.