Ecotoxicity of, and remediation with, engineered inorganic nanoparticles in the environment

This article presents recent developments on the use of inorganic nanoparticles (NPs) for environmental remediation in polluted soil, water and gas. The number of publications on these topics has grown exponentially in recent years, especially those focused on wastewater treatment. Among these topics, removal of metals has become the most popular, although some works relate to the use of nanomaterials for the elimination of nutrients (e.g., nitrogen and some persistent organic pollutants). However, this growth has not been accompanied by knowledge about the behavior of NPs once used and released into the environment. In this article, we also comment upon the current situation with respect to NP toxicology (nanotoxicology). A remarkable number of different toxicology tests has been applied to NPs, often making it very difficult to interpret or to generalize the results. We analyze in detail the bioluminescence, Daphnia magna and other tests, and give some preliminary results obtained in our work.     

Applications of photocatalytic titanium dioxide-based nanomaterials in sustainable agriculture

Photocatalytic materials are attracting attention as emerging resources for agricultural applications. This timely review assesses the current developments in the use of biocompatible titanium dioxide (TiO₂)-based photocatalytic nanomaterials (TiO₂-PN) as models to unravel agricultural growth, harvest, and post-harvest problems. Such developments can lead to technological innovations aimed at addressing the pressing global environmental challenges faced by farming. TiO₂-PN have been used as antimicrobial, growth-regulating, and fertilizer-like agents. The promising agricultural research applications of TiO₂-PN are highlighted along with a discussion of the main challenges that will need to be overcome to fully understand the roles of TiO₂-PN in the sustainable and productive exploitation of land and water for agricultural applications under natural conditions. In particular, rhizosphere internalization, translocation, and plant bioaccumulation pathways of photocatalytic materials from environmental exposition are outlined to illustrate the effect of TiO₂ on the agricultural cycle. Nanotoxicology and regulations are also discussed to illustrate the importance of biocompatibility and green synthesis of nanomaterials for safe use in real applications. This overview is focused on motivating and intensifying our understanding of on-site agricultural studies. Complementary biological approaches and structural damage observed by biological transmission electron, scanning electron, and optical microscopies should accelerate the practical contribution of TiO₂-PN to sustainable agriculture in conjunction with plant factories and plasma nitrogen fixation technology. Loadings below 10 μg/L of TiO₂-PN with a size of 40 nm benefit seed germination and root elongation as well as partially suppressing metal root translocation. However, only approximately 5% of current studies were carried out in real agricultural settings.     

(Q)SAR modelling of nanomaterial toxicity: A critical review

There is increasing recognition that some nanomaterials may pose a risk to human health and the environment. Moreover, the industrial use of the novel engineered nanomaterials (ENMs) increases at a higher rate than data generation for hazard assessment; consequently, many of them remain untested. The large number of nanomaterials and their variants (e.g., different sizes and coatings) requiring testing and the ethical pressure towards nonanimal testing means that in a first instance, expensive animal bioassays are precluded, and the use of (quantitative) structure–activity relationships ((Q)SARs) models as an alternative source of (screening) hazard information should be explored. (Q)SAR modelling can be applied to contribute towards filling important knowledge gaps by making best use of existing data, prioritizing the physicochemical parameters driving toxicity, and providing practical solutions for the risk assessment problems caused by the diversity of ENMs. This paper covers the core components required for successful application of (Q)SAR methods to ENM toxicity prediction, summarizes the published nano-(Q)SAR studies, and outlines the challenges ahead for nano-(Q)SAR modelling. It provides a critical review of (1) the present availability of ENM characterization/toxicity data, (2) the characterization of nanostructures that meet the requirements for (Q)SAR analysis, (3) published nano-(Q)SAR studies and their limitations, (4) in silico tools for (Q)SAR screening of nanotoxicity, and (5) prospective directions for the development of nano-(Q)SAR models.     

Electrophoretic methods for separation of nanoparticles

This article reviews progress in the application of electrophoretic techniques for the separation of nanoparticles. Numerous types of nanoparticles have recently been synthesised and integrated into different products and procedures. Consequently, analytical methods for the efficient characterisation of nanoparticles are now required. Several studies have revealed that gel electrophoresis can readily be used for separating nanoparticles according to their size or shape. However, many other studies focused on separation of nanoparticles by CE. In some cases nanoparticles could be separated by CZE, simply using pure buffer as the BGE. In other studies, buffer additives (most often SDS) were used, enabling fast separations of metallic nanoparticles by size. Other CE methods also allowed for separation of nanoparticle conjugates with biomolecules. Dielectrophoresis is yet another electrophoretic technique useful in separation and characterisation of nanoparticles; particularly nanotubes. Detection methods often used after electrophoretic separation include UV/Vis absorption and fluorescence spectroscopy. Examples of recent and relevant older reports are presented here. The authors conclude that electrophoretic methods for nanoanalysis can provide inexpensive and efficient tools for quality assurance and safety control; and as a consequence, they can augment transfer of nanotechnologies from research to industry.     

A method for assessing nanomaterial dispersion quality based on principal component analysis of particle size distribution data

Seemingly contradictory findings between studies are a major issue in nanoecotoxicological research and have been explained as a result of the lack of comparability between assay methods, with dispersion of nanomaterials being identified as a key factor. Here we show the use of a multivariate method, principal component analysis (PCA), as a tool in protocol development and categorization of dispersion quality. Results show the significance of particle concentration within a protocol, and its effect on repeatability. Our results suggest that future studies should involve the use of PCA as a powerful data exploration tool to facilitate method development, comparability and integration of data across different laboratories.     

Nanotoxicology: characterizing the scientific literature, 2000–2007

Understanding the toxicity of nanomaterials and nano-enabled products is important for human and environmental health and safety as well as public acceptance. Assessing the state of knowledge about nanotoxicology is an important step in promoting comprehensive understanding of the health and environmental implications of these new materials. To this end, we employed bibliometric techniques to characterize the prevalence and distribution of the current scientific literature. We found that the nano-toxicological literature is dispersed across a range of disciplines and sub-fields; focused on in vitro testing; often does not specify an exposure pathway; and tends to emphasize acute toxicity and mortality rather than chronic exposure and morbidity. Finally, there is very little research on consumer products, particularly on their environmental fate, and most research is on the toxicity of basic nanomaterials. The implications for toxicologists, regulators and social scientists studying nanotechnology and society are discussed.

Characterization of size, surface charge, and agglomeration state of nanoparticle dispersions for toxicological studies

Characterizing the state of nanoparticles (such as size, surface charge, and degree of agglomeration) in aqueous suspensions and understanding the parameters that affect this state are imperative for toxicity investigations. In this study, the role of important factors such as solution ionic strength, pH, and particle surface chemistry that control nanoparticle dispersion was examined. The size and zeta potential of four TiO₂ and three quantum dot samples dispersed in different solutions (including one physiological medium) were characterized. For 15 nm TiO₂ dispersions, the increase of ionic strength from 0.001 M to 0.1 M led to a 50-fold increase in the hydrodynamic diameter, and the variation of pH resulted in significant change of particle surface charge and the hydrodynamic size. It was shown that both adsorbing multiply charged ions (e.g., pyrophosphate ions) onto the TiO₂ nanoparticle surface and coating quantum dot nanocrystals with polymers (e.g., polyethylene glycol) suppressed agglomeration and stabilized the dispersions. DLVO theory was used to qualitatively understand nanoparticle dispersion stability. A methodology using different ultrasonication techniques (bath and probe) was developed to distinguish agglomerates from aggregates (strong bonds), and to estimate the extent of particle agglomeration. Probe ultrasonication performed better than bath ultrasonication in dispersing TiO₂ agglomerates when the stabilizing agent sodium pyrophosphate was used. Commercially available Degussa P25 and in-house synthesized TiO₂ nanoparticles were used to demonstrate identification of aggregated and agglomerated samples.     

Strategies for quantifying C(60) fullerenes in environmental and biological samples and implications for studies in environmental health and ecotoxicology

Fullerenes are sphere-like molecules with unique physico-chemical properties, which render them of particular interest in biomedical research, consumer products and industrial applications. Human and environmental exposure to fullerenes is not a new phenomenon, due to a long history of hydrocarbon-combustion sources, and will only increase in the future, as incorporation of fullerenes into consumer products becomes more widespread for use as anti-aging, anti-bacterial or anti-apoptotic agents.An essential step in the determination of biological effects of fullerenes (and their surface-functionalized derivatives) is establishment of exposure-assessment techniques. However, in ecotoxicological studies, quantification of fullerenes is performed infrequently because robust, uniformly applicable analytical approaches have yet to be identified, due to the wide variety of sample types. Moreover, the unique physico-chemistry of fullerenes in aqueous matrices requires reassessment of conventional analytical approaches, especially in more complex biological matrices (e.g., urine, blood, plasma, milk, and tissue).Here, we present a review of current analytical approaches for the quantification of fullerenes and propose a consensus approach for determination of these nanomaterials in a variety of environmental and biological matrices.