ET&C Spotlight: Special Issue on Nanomaterials in the Environment
Compiled by Globe editors Vernon Somerset, Jane Parkin Kullmann and John Toll
Environmental Toxicology & Chemistry’s fourth decade is off to a fine start with the release of a Special Issue on Nanomaterials in the Environment (ET&C 31(1)). SETAC members have been at the forefront of nanomaterials environmental health and safety (Nano EHS) research since the early days of commercial nanotechnologies. Those early days weren’t all that long ago. In 2005 the Project on Emerging Nanotechnologies (PEN) listed 54 nanotechnology-based consumer products in its inventory. By 2010 the PEN inventory was up to 1,317 consumer products. It is projected to top 2,000 by next year. During this period of rapid technological growth, SETAC and its members are playing an important part in moving Nano EHS research and policy forward. This is readily apparent from the impressive body of work in the new ET&C Special Issue on Nanomaterials in the Environment.
If this piques your interest, then you are sure to be drawn to the Focus Article, Paradigms to Assess the Environmental Impact of Manufactured Nanomaterials. In this Focus Article authors Steve Klaine, Albert Koelmans, Nina Horne, Stephen Carley, Richard Handy, Larry Kapustka, Bernd Nowack, and Frank von der Kammer seek to answer three questions:
- Where does the science need to provide reliable data that will assist policymakers and regulators in developing strategies to manage nanomaterials and instill public confidence regarding the safety of these materials?
- What are the critical needs that will move us forward safely and intelligently in this promising field?
- Are the paradigms generally developed to assess the fate and effects of solute contaminants applicable to nanomaterials?
Along the way they explain what nanotechnology is, summarize the risks and benefits of various applications of nanomaterials, stress the responsible innovation imperative, explain “why size matters” in Nano EHS, and emphasize that our knowledge about the risks of nanotechnology advancements lags behind the pace at which those advancements are developing. From there they break into a nice overview of what it will take to develop quantitative risk assessments that regulators can use with a high degree of confidence. This overview describes the unique properties, fate, behaviors, and hazards of nanoparticles in the environment and explains the importance of teamwork to meet the rigorous technical challenges. The paper elucidates the state of Nano EHS science and exposes the knowledge gaps. The article then describes a path forward to bridge those gaps and achieve breakthroughs in detection, predicting fate and hazards, and assessing risk. The authors close the Focus article by tackling the prevailing view that uncertainty in our ability to analyze nanotechnology risks is unacceptable from the regulatory decision-making perspective. They call for an immediate and coordinated global effort to prioritize and address the most significant likely risks, and speak to the paradigm shifts that will be crucial to the success of this effort.
The impetus for the Focus article, and indeed the Special Issue as a whole, was an international, SETAC-endorsed gathering of 28 scientists that took place in Clemson, South Carolina in the summer of 2010. The results of that gathering are described in the Special Issue’s three Critical Reviews:
- Ecotoxicity Test Methods for Manufactured Nanomaterials: Practical Experiences and Recommendations from the Bench, by Richard Handy et al. talks about practical issues for working with manufactured nanomaterials (MNMs) in the ecotoxicology laboratory and suggests nano-specific protocol modifications, considering both generic practical issues and specific issues for aquatic tests, marine grazers, soil organisms, and bioaccumulation studies.
- Analysis of Engineered Nanomaterials in Complex Matrices (Environment and Biota): General Considerations and Conceptual Case Studies, by Frank von der Kammer et al. identifies factors hampering the study of environmental fate and ecotoxicological effects of MNMs at environmentally relevant concentrations in complex media, explaining why the simple act of trying to isolate, observe, and quantify MNMs may change their physicochemical properties. It identifies the development of extraction, cleanup, separation, and sample storage techniques, and techniques that can differentiate between naturally occurring and manufactured nanoparticles, as pressing research needs.
- Potential Scenarios for Nanomaterial Release and Subsequent Alteration in the Environment, by Bernd Nowack et al. characterizes the processes controlling the fate of MNMs released directly into the environment, MNMs in consumer products, and MNMs released from those products. It talks about the ecotoxicological relevance of each of these three exposure pathways, and about MNM alterations and transformation processes. These issues are addressed using four hypothetical case studies covering a wide range of MNMs, their applications, and their likely fate in the environment.
Had the Special Issue contained just the Focus article and Critical Reviews, it would have been an important contribution to the public discourse on nanotechnology. It doesn’t stop there though; the Special Issue goes on to present 21 research papers from authors working in Asia, Europe, and North America on the environmental toxicology and chemistry of MNMs:
- Methodological Considerations for Testing the Ecotoxicity of Carbon Nanotubes and Fullerenes: Review, by Elijah J. Petersen and Theodore Henry is intended to serve as a next step toward developing standardized toxicity tests for carbon nanoparticles. It focuses on important elements of measuring the ecotoxicity of carbon nanoparticles and makes recommendations that should enable more rigorous interpretations of collected data and inter-laboratory comparisons.
- Impact of Carbon Nanotube Morphology on Phenanthrene Adsorption, by Onur Guven Apul et al., examines the roles of specific surface area, diameter, and length of carbon nanotubes on the adsorption of phenanthrene. The authors found that data from the manufacturer may not always represent the characteristics of carbon nanotubes in a particular batch and that accurate characterization of morphology is critical to understanding behaviors such as adsorption and transport in environmental systems.
- Adsorption Kinetics of Aromatic Compounds on Carbon Nanotubes and Activated Carbons, by Shujuan Zhang et al., examines adsorption kinetics of two organic compounds on granular and fibrous activated carbon and single- and multi-walled carbon nanotubes in aqueous solutions. The authors found that the processes controlling sorption of organic compounds onto carbon nanotubes differ from the processes controlling sorption onto activated carbons.
- Adsorption and Desorption of Bivalent Metals to Hematite Nanoparticles, by Valerie Grover et al., studies the use of commercially prepared hematite nanoparticles as an adsorbent in the removal of cadmium, copper, lead, and zinc from aqueous solutions, reporting that with further development, nanohematite could be applicable in water treatment technology for removing metals.
- Solubility of Nano-Zinc Oxide in Environmentally and Biologically Important Matrices, by Robert Reed et al., examines the relative solubilities of zinc oxide nanoparticles in matrices used for environmental fate and transport or biological toxicity studies, in order to better understand whether zinc oxide toxicity is due to the zinc oxide nanoparticles, dissolved Zn2+, or some combination thereof.
- Effect of Copper Ion on Adsorption of Chlorinated Phenols and 1-Naphthylamine to Surface-Modified Carbon Nanotubes, by Fang Wang et al., investigates how transitional metal ions with strong complexing capabilities might affect the adsorption of organic contaminants to carbon nanotubes and reports results that provide insights into the mechanism of adsorptive interactions between organic contaminants and carbon nanotubes, knowledge that they say is critical to developing environmental applications of carbon nanotubes.
- Toxicity of Copper Oxide Nanoparticle Suspensions to Aquatic Biota, by Levonas Manusadžianas et al., investigates toxicity effects of nano-copper oxide suspensions on macrophytic algae cells of Nitellopsis obtusa, microphytic algae Chlorella spp., the shrimp Thamnocephalus platyurus, and the rotifer Brachionus calyciflorus. They report that observed adverse effects on N. obtusa cells may be attributed to nanoparticles, but not to ionic copper.
- Detecting Nanoparticulate Silver Using Single-Particle Inductively Coupled Plasma–Mass Spectrometry, by Denise Mitrano et al., demonstrates the use of inductively coupled plasma–mass spectrometry, operated in a single-particle counting mode (SP-ICP-MS), to detect and quantify silver nanoparticles. Analysis of two wastewater samples demonstrated the applicability of SP-ICP-MS at nanogram per liter silver concentrations. Differentiation of dissolved and particulate silver is a feature of the technique. The method provides the ability to monitor silver and other metal and metal oxide nanoparticles in fate, transport, stability, and toxicity studies using a commonly available laboratory instrument, with rapid throughput and element specificity.
- Effect of Silver Nanoparticles on Bacterial Activity in Natural Waters, by Pranab Das et al., investigates the impacts of silver nanoparticles on natural aquatic microbial activity. The authors exposed bacterioplankton collected from nine aquatic habitats to carboxy-functionalized silver nanoparticles. They report that in natural aquatic systems, silver nanoparticle concentrations in the low microgram per liter range would likely be required to negatively impact natural aquatic bacterioplankton processes.
- Influence of a Nanoparticle Mixture on an Arctic Soil Community, by Niraj Kumar et al., examines the impact of a mixture of silver, copper, and silica nanoparticles on an arctic microbial community using soil microcosms incubated for 176 days. They report that treated soil appeared to show a reduction in the ability to use carbohydrate and amino acid substrates, and demonstrated an altered pattern of major fatty acid peaks.
- Production and Consumption of Reactive Oxygen Species by Fullerenes, by Lingjun Kong and Richard Zepp, investigated the production and consumption of reactive oxygen species in aqueous systems by Buckminster fullerene and fullerenol in order to better understand the potential environmental impacts of fullerenes. Reactive oxygen species are among the most important intermediates in chemical, photochemical, and biological processes. The study reports that environmental conditions, including light exposure and oxygen concentration, have the potential to impact the generation of toxic reactive oxygen species by fullerenes.
- Interspecies Comparisons on the Uptake and Toxicity of Silver and Cerium Dioxide Nanoparticles, by Birgit Gaiser et al., compares the potential biological effects of silver and cerium dioxide nanoparticles in a range of cell (human hepatocyte and intestinal and fish hepatocyte) and animal (Daphnia magna, Cyprinus carpio) models to assess possible commonalities in toxicity across taxa. The authors employed a variety of analytical techniques to characterize the particles and investigate their biological uptake. They found commonalities in toxicity of these particle types across diverse biological systems, indicating that cross-species extrapolations may be possible for metal nanoparticle test development in the future. Their findings also suggest transport of particles through the gastrointestinal barrier, which is likely to be an important uptake route when assessing particle risk.
- Ion-Release Kinetics and Ecotoxicity Effects of Silver Nanoparticles, by Yong-Ju Lee et al., examines the ecotoxicity of silver nanoparticles in aquatic organisms, silver ion-release kinetics of silver nanoparticles, and their relationship. The authors found that dissolved EC50 values for Daphnia magna were similar for powder-type and sol-type silver nanoparticles despite differences in the total silver EC50 values.
- Effects of Chronic Nanoparticulate Silver Exposure to Adult and Juvenile Sheepshead Minnows (Cyprinodon variegatus), by Robert Griffitt et al., examines effects of silver nanoparticles on juvenile and adult sheepshead minnows (Cyprinodon variegarus). The authors present data indicating that chronic exposure to low levels of silver produced significant increases in tissue burdens in both juveniles and adults. They found alteration in gene expression, with the greatest effect in adult gonads, but no evidence of dysfunction related to silver nanoparticle exposure was found at the gonad tissue level. In contrast, the authors found significant thickening of gill tissue, yet very little evidence of effect on gill transcription profiles. They report that the results do not appear to be attributable to silver nanoparticle dissolution.
- Effects of Natural Water Chemistry on Nanosilver Behavior and Toxicity to Ceriodaphnia dubia and Pseudokirchneriella subcapitata, by Julianne McLaughlin and Jean-Claude Bonzongo, reports on a series of batch experiments that they conducted to determine the effect of natural waters with different solution chemistries on silver nanoparticle dispersion, stability, and toxicity. Differences in the chemistry of these aquatic systems will control changes in surface properties of nanoparticles and therefore could impact their environmental fate and toxicity. Toxicity assays were performed in tested natural waters as well as in traditional growth media. The findings help to establish needed correlations between water-matrix-dependent silver nanoparticle properties and toxicity implications, and indicate that the use of traditional growth media in toxicity assays concerning engineered nanoparticles might not always be appropriate.
- Effect of Titanium Dioxide Nanomaterials and Ultraviolet Light Coexposure on African Clawed Frogs (Xenopus laevis), by Junling Zhang et al., investigates the influence of particle size and interaction with ultraviolet light on the toxicity of titanium dioxide nanomaterials (nano-TiO2) to African clawed frogs (Xenopus laevis). Nano-TiO2 materials exhibit stronger photochemical oxidation/reduction capacity than their bulk counterparts, but that capacity strongly depends on particle size. The authors report significant effects on tadpole growth and developmental stage for all three particle sizes tested, whether alone or with ultraviolet light.
- Reproductive and Behavioral Responses of Earthworms Exposed to Nano-Sized Titanium Dioxide in Soil, by Heather McShane et al., investigates the responses of two species of earthworms to three types of commercially available, uncoated TiO2 nanomaterials characterized for particle size, agglomeration, surface charge, chemical composition, and purity. They report that in their experiments, exposure to field and artificial soil did not significantly affect juvenile survival and growth, adult earthworm survival, cocoon production, cocoon viability, or total number of juveniles hatched from these cocoons, but that earthworms avoided artificial soils amended with nano-TiO2. They also found that earthworms differentiated between soils amended with nano-TiO2 and micrometer-sized TiO2.
- Interactions of Gold Nanoparticles with Freshwater Aquatic Macrophytes are Size and Species Dependent, by J. Brad Glenn et al., investigates the in vivo partitioning to two species of submerged aquatic vascular plants and a free-floating aquatic fern of 4- and 18-nm gold nanoparticles suspended in well water. The authors hypothesize that because aquatic plants absorb the majority of their nutrients from the water column, they may absorb nanomaterials in suspension. They report size- and species-dependent root uptake of gold nanoparticles, and suggest that absorption of gold nanoparticles by plants may be a function of the salinity tolerance of each species.
- Influences of Multi-walled Carbon Nanotubes and Plant Residue Chars on Bioaccumulation of Polycyclic Aromatic Hydrocarbons by Chironomus plumosus Larvae in Sediment, by Mohai Shen et al., investigates the effects of multi-walled carbon nanotubes, char-stalk and char-wood on the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs), including phenanthrene, pyrene, and chrysene, in Chironomus plumosus larvae. Carbonaceous materials including carbon nanotubes and black carbon have been suggested as potential remediation materials for hydrophobic organic contaminants in sediments. The investigation indicates that multi-walled carbon nanotube-associated PAHs may be absorbed through particle ingestion, suggesting that some carbon nanotubes might not be suitable for the remediation of HOC-contaminated sediments.
- Aqueous Suspension Methods of Carbon-Based Nanomaterials and Biological Effects on Model Aquatic Organisms, by Jie Gao et al., assesses the biological effects of a number of commonly used dispersing agents on Pseudokirchneriella subcapitata and Ceriodaphnia dubia. The preparation of aqueous suspensions of carbon-based nanomaterials requires the use of dispersing agents to overcome their hydrophobic character. The results show that exposure studies should take into account the effects of used dispersing fluids. For a given organism, nanomaterial toxicity can be mitigated by use of nontoxic surfactants. The authors suggest that a multispecies testing approach is warranted to account for the sensitivity of different organisms.
- Toxicity of Aqueous C70-Gallic Acid Suspension in Daphnia magna, by Brandon Seda et al., assesses the toxic effects of stable aqueous colloidal suspensions of a fullerene (C70-gallic acid) on Daphnia magna. The authors quantified whole-organism responses and changes in antioxidative processes. They observed 50% acute toxicity at a 96-hour exposure to 0.4 ± 0.1 mg/L C70; significantly reduced fecundity in 21-day bioassays at C70-gallic acid concentrations below quantifiable limits; and evidence that exposed organisms experienced oxidative stress. Microscopic techniques used to determine cellular toxicity via apoptosis proved unsuccessful.
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