Ecophysiological perspectives on engineered nanomaterial toxicity in fish and crustaceans

A comprehensive assessment of the environmental risks posed by engineered nanomaterials (ENMs) entering the environment is necessary, due in part to the recent predictions of ENM release quantities and because ENMs have been identified in waste leachate. The technical complexity of measuring ENM fate and transport processes in all environments necessitates identifying trends in ENM processes. Emerging information on the environmental fate and toxicity of many ENMs was collected to provide a better understanding of their environmental implications. Little research has been conducted on the fate of ENMs in the atmosphere; however, most studies indicate that ENMs will in general have limited transport in the atmosphere due to rapid settling. Studies of ENM fate in realistic aquatic media indicates that in general, ENMs are more stable in freshwater and stormwater than in seawater or groundwater, suggesting that transport may be higher in freshwater than in seawater. ENMs in saline waters generally sediment out over the course of hours to days, leading to likely accumulation in sediments. Dissolution is significant for specific ENMs (e.g., Ag, ZnO, copper ENMs, nano zero-valent iron), which can result in their transformation from nanoparticles to ions, but the metal ions pose their own toxicity concerns. In soil, the fate of ENMs is strongly dependent on the size of the ENM aggregates, groundwater chemistry, as well as the pore size and soil particle size. Most groundwater studies have focused on unfavorable deposition conditions, but that is unlikely to be the case in many natural groundwaters with significant ionic strength due to hardness or salinity. While much still needs to be better understood, emerging patterns with regards to ENM fate, transport, and exposure combined with emerging information on toxicity indicate that risk is low for most ENMs, though current exposure estimates compared with current data on toxicity indicates that at current production and release levels, exposure to Ag, nZVI, and ZnO may cause toxicity to freshwater and marine species.

In October 2010 the National Organic Standards Board recommended that engineered nanomaterials (ENMs) be prohibited from food products bearing the U.S. Department of Agriculture’s coveted Organic label.1 If the department adopts the recommendation, ENMs will find themselves in the same officially taboo category as genetically modified organisms when it comes to organic foods—nanotechnology-enabled innovations like flavor- and texture- enhancing ingredients and shelf life– extending packaging will be off the menu. Prior to issuing its recommendation, the board received thousands of public comments and petition signatures supporting the ban and virtually none opposing it. Although an official decision could take years, supporters are confident the recommendation will be adopted, and it will go down as one of the first lines drawn in the sand when it comes to the reach of this relatively new and potentially transformative technology in the American marketplace. Nanotechnology-enabled products are quietly proliferating on U.S. store shelves, despite nagging questions about the safety of synthetic nanoparticles and the products that contain them. “[I]n our regulation of food and most consumer products, we don’t implement the precautionary principle. Things go to market before we know whether or not they’re really safe for human beings over the long term,” says Alexis Baden-Mayer, a lawyer with the Organic Consumers Association, an advocacy group, who attended the meeting and campaigned for the ban. Baden-Mayer and other observers perceive a distinct lack of public awareness about how common ENMs are becoming in the market-place, and she hopes discussion among consumers of organic products will help change that. “Consumers don’t know much about nanotechnology, and the first time they may hear about it is now when they learn that the organic regulations are going to prohibit [it],” she says. The International Organization for Standardization defines a nanomaterial as a material with any external dimension between 1 and 100 nm.2 (By comparison, a double strand of DNA is about 2 nm thick.) Nanoparticles, which have been the focus of most nanotoxicology studies to date,3 are one subset of nanomaterials. Nanoparticles include structures of various shapes, such as nanotubes, nanowires, quantum dots, and fullerenes. They also occur naturally in substances like air, smoke, and sea spray, and “incidental” nanoparticles are created during processes such as combustion and food milling, churning, freezing, and homogenization. (Naturally occurring and incidental nanoparticles were not included in the National Organic Standards Board’s recommendation to ban ENMs.) Nanotechnology—the deliberate synthesis and manipulation of nanomaterials—began in the 1980s. Today thousands of ENMs are manufactured in a kaleidoscope of substances, shapes, and sizes for use in a wide range of products and industrial processes that take advantage of their novel physical, thermal, optical, and biological properties. These properties may be determined by the ENM’s chemical composition, size or shape, crystal structure, solubility, adhesion (the force that holds the nanoparticle components together), or surface chemistry, charge, or area.3 Industry analysts have been forecasting “game-changing” advances as a result of nanotechnology in renewable energy, computers, communications, pollution cleanup, agriculture, medicine, and more.4 Clothing, sunscreens, cosmetics, sporting equipment, batteries, food packaging, dietary supplements, and electronics are just a few of the types of nanotechnology-enabled goods in use by U.S. consumers. But safety questions arise around the nanoparticles in some of these products. The novel biological and physical properties of some ENMs pose unique challenges to comprehensive safety research, and investigators are working to figure out just how hazardous they might be to people, wildlife, and the environment. Compared with larger particles, nanoparticles’ tiny size means tissues may take them up more readily. It also can give them an unusual ability to travel throughout the body, including into cells and cell nuclei, and across the placenta and the blood–brain barrier, as demonstrated in rodent studies.5,6 No cases of human illness or death have been definitively attributed to ENMs. However, a number of researchers and consumer and environmental advocates have warned that the abundant unknowns make it necessary to proceed with caution lest we repeat the history of asbestos, polychlorinated biphenyls, the insecticide DDT, and other innovations that seemed valuable when they were introduced, proceeded with little oversight, and ultimately caused major health or environmental problems.

Engineered nanomaterials (ENM) are anthropogenic materials with at least one dimension less than 100nm. Their ubiquitous employment in biomedical and industrial applications in the absence of full toxicological assessments raises significant concerns over their safety on human health. This is a significant concern, especially for metal and metal oxide ENM as they may possess the greatest potential to impair human health. A large body of literature has developed that reflects adverse systemic effects associated with exposure to these materials, but an integrated mechanistic framework for how ENM exposure influences morbidity remains elusive. This may be due in large part to the tremendous diversity of existing ENM and the rate at which novel ENM are produced. In this review, the influence of specific ENM physicochemical characteristics and hemodynamic factors on cardiovascular toxicity is discussed. Additionally, the toxicity of metallic and metal oxide ENM is presented in the context of the cardiovascular system and its discrete anatomical and functional components. Finally, future directions and understudied topics are presented. While it is clear that the nanotechnology boom has increased our interest in ENM toxicity, it is also evident that the field of cardiovascular nanotoxicology remains in its infancy and continued, expansive research is necessary in order to determine the mechanisms via which ENM exposure contributes to cardiovascular morbidity.

Increasing use of engineered nanomaterials (ENM) in consumer products and commercial applications has helped drive a rise in research related to the environmental health and safety (EHS) of these materials. Within the cacophony of information on ENM EHS to date are data indicating that these materials may be neurotoxic in adult animals. Evidence of elevated inflammatory responses, increased oxidative stress levels, alterations in neuronal function, and changes in cell morphology in adult animals suggests that ENM exposure during development could elicit developmental neurotoxicity (DNT), especially considering the greater vulnerability of the developing brain to some toxic insults. In this review, we examine current findings related to developmental neurotoxic effects of ENM in the context of identifying research gaps for future risk assessments. The basic risk assessment paradigm is presented, with an emphasis on problem formulation and assessments of exposure, hazard, and dose response for DNT. Limited evidence suggests that in utero and postpartum exposures are possible, while fewer than 10 animal studies have evaluated DNT, with results indicating changes in synaptic plasticity, gene expression, and neurobehavior. Based on the available information, we use current testing guidelines to highlight research gaps that may inform ENM research efforts to develop data for higher throughput methods and future risk assessments for DNT. Although the available evidence is not strong enough to reach conclusions about DNT risk from ENM exposure, the data indicate that consideration of ENM developmental neurotoxic potential is warranted.

BackgroundNanosilver is one of the most commonly used engineered nanomaterials (ENMs). In our study we focused on assessing the size-dependence of the toxicity of nanosilver (Ag ENMs), utilising materials of three sizes (50, 80 and 200 nm) synthesized by the same method, with the same chemical composition, charge and coating.MethodsUptake and localisation (by Transmission Electron Microscopy), cell proliferation (Relative growth activity) and cytotoxic effects (Plating efficiency), inflammatory response (induction of IL-8 and MCP-1 by Enzyme linked immune sorbent assay), DNA damage (strand breaks and oxidised DNA lesions by the Comet assay) were all assessed in human lung carcinoma epithelial cells (A549), and the mutagenic potential of ENMs (Mammalian hprt gene mutation test) was assessed in V79-4 cells as per the OECD protocol. Detailed physico-chemical characterization of the ENMs was performed in water and in biological media as a prerequisite to assessment of their impacts on cells. To study the relationship between the surface area of the ENMs and the number of ENMs with the biological response observed, Ag ENMs concentrations were recalculated from μg/cm2 to ENMs cm2/cm2 and ENMs/cm2.ResultsStudied Ag ENMs are cytotoxic and cytostatic, and induced strand breaks, DNA oxidation, inflammation and gene mutations. Results expressed in mass unit [μg/cm2] suggested that the toxicity of Ag ENMs is size dependent with 50 nm being most toxic. However, re-calculation of Ag ENMs concentrations from mass unit to surface area and number of ENMs per cm2 highlighted that 200 nm Ag ENMs, are the most toxic. Results from hprt gene mutation assay showed that Ag ENMs 200 nm are the most mutagenic irrespective of the concentration unit expressed.ConclusionWe found that the toxicity of Ag ENMs is not always size dependent. Strong cytotoxic and genotoxic effects were observed in cells exposed to Ag ENMs 50 nm, but Ag ENMs 200 nm had the most mutagenic potential. Additionally, we showed that expression of concentrations of ENMs in mass units is not representative. Number of ENMs or surface area of ENMs (per cm2) seem more precise units with which to compare the toxicity of different ENMs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-014-0065-1) contains supplementary material, which is available to authorized users.

Aquatic toxicity of transformed and product-released engineered nanomaterials: An overview of the current state of knowledge

Nano GO Consortium—A Team Science Approach to Assess Engineered Nanomaterials: Reliable Assays and Methods

The majority of exposures to engineered nanomaterials (ENM) are unintentional through occupational or domestic use; however ENM biomedical platforms are being developed for use in individualized and/or tissue‐targeted treatments. The placenta has been described as a barrier organ, yet maternal treatments are limited during pregnancy to diminish untoward fetal effects and direct fetal therapies are rare. While negative maternal and fetal effects have been described after ENM exposure during gestation, it is unclear if these are due to direct ENM transfer into the fetal compartment or if the placental barrier protects the fetus from direct particle exposure. Therefore, the purpose of this study was to identify ENM translocation after maternal pulmonary exposure to the fetal compartment.Sprague‐Dawley rats were exposed to 2974 μg (2.4 × 1013 particles; calculated deposition of 952 ug/dose) of Rhodamine‐labeled 20nm polystyrene (NANOCS) in 300μL or saline control via intratracheal instillation every other day from GD 5 to GD 19. An acute group was also included, with a single ENM exposure on GD19. Animals were exposed to many optical imaging techniques (CT, FX‐Pro optical imaging, and ultrasound), in either the whole animal or dissected tissues on GD 20. Litter health was affected as evidenced by significantly higher rates of reabsorption sites in the exposed dams (18‐fold, chronic; 7‐fold, acute) compared to control. Overall, we were able to identify significantly higher optical intensity measurements in many secondary organs of the exposed animals, indicative of particle translocation from the lung. These included significantly increased optical imaging intensities in the chronic group vs the controls in the placenta (142% ± 78), whole fetal pup (144% ± 17), and in situ fetal liver (146% ± 13). Interestingly even those acutely exposed (24h prior) were also significantly different than control. These were identified as the mother's heart (156% ± 8), spleen (158% ± 6), placenta (142% ± 78), fetal heart (177% ± 37), fetal liver (both excised (190% ± 14) and within body (164% ± 10)), and whole pup (157% ± 13). Using novel placental perfusion methodology, where a placental unit is isolated, dissected, cannulated and perfused (80 mmHg maternal artery and 50 mmHg fetal umbilical artery), ENM introduced in the maternal artery can be quantified within 102 ± 13 minutes from the fetal umbilical vein effluent.Using molecular imaging techniques, we were able to conclusively identify ENM translocation from the maternal lungs to the fetal compartment. These findings may be both beneficial and toxicological depending on the purpose of the ENM exposure. ENM transfer to the fetal compartment may allow for direct fetal treatment with the use of ENM‐based biomedical devices; in contrast the placenta may not be considered a barrier to ENM, with direct fetal contact also occurring after unintentional maternal ENM exposures.Support or Funding InformationNIH‐R00‐ES024783 (PAS); P30‐ES005022This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Engineered nanomaterials for plant growth and development: A perspective analysis

Predictions of environmental concentrations of engineered nanomaterials (ENM) are needed for their environmental risk assessment. Because analytical data on ENM-concentrations in the environment are not yet available, exposure modeling represents the only source of information on ENM exposure in the environment. This work provides material flow data and environmental concentrations of nine ENM in Denmark. It represents the first study that distinguishes between photostable TiO2 (as used in sunscreens) and photocatalytic TiO2 (as used in self-cleaning surfaces). It also provides first exposure estimates for quantum dots, carbon black and CuCO3. Other ENM that are covered are ZnO, Ag, CNT and CeO2. The modeling is based for all ENM on probability distributions of production, use, environmental release and transfer between compartments, always considering the complete life-cycle of products containing the ENM. The magnitude of flows and concentrations of the various ENM depends on the one hand on the production volume but also on the type of products they are used in and the life-cycles of these products and their potential for release. The results reveal that in aquatic systems the highest concentrations are expected for carbon black and photostable TiO2, followed by CuCO3 (under the assumption that the use as wood preservative becomes important). In sludge-treated soil highest concentrations are expected for CeO2 and TiO2. Transformation during water treatments results in extremely low concentrations of ZnO and Ag in the environment. The results of this study provide valuable environmental exposure information for future risk assessments of these ENM.

Over the last decade or so, one question about engineered nanomaterials (ENMs) has been constantly asked: Are nanomaterials inherently toxic? It is because characteristics such as “nano” scale size, surface charge, surface plasmon resonance, greater surface area, and propensity to ligand with (in)organic and/or polymeric molecules set ENMs physicochemically apart from their bulk/parent analogs. Related to unique properties, which enable greater functionality in a wide range of consumer applications, is the uncertainty about whether unique risk is posed to the environment, health, and safety (EHS) as ENMs are anthropogenically released into the environment. Recognized as the major sinks, soil, water, and air contamination of ENMs, including their leachable or modified by-products, is inevitable. Understanding of potential impacts on terrestrial plant species has remained unclear as anomalies in morphological, anatomical, and physiological endpoints, which have potential for impairing later development in life, are not routinely screened for, however. In this chapter, we report valuable information synthesized via thorough literature review of the current understanding of potential implications of ENM release and exposure to plants via soil, water, and atmospheric deposition. In particular, we report potential fate, biouptake, site of translocation/associated mechanisms, in vivo transformation, and toxicity (germination rate, growth and development, anatomical and physiological anomalies, and yield) of metal-based ENMs. Additionally, potential mechanisms and factors influencing ENMs’ toxicity are explained. Such information is critical to direct future research aimed at uncovering better understanding of nanotoxicology in plants, and to determine whether risk to public health exists from exposure to ENMs through the dietary route.

Nanotechnology is a broad and rapidly developing field resulting in the inclusion of engineered nanomaterials (ENMs) into a number of products, applications, and processes. Due to the increased usage and production of ENMs, they represent an emerging exposure of toxicological concern among workers during ENM manufacturing and handling. The major routes of ENM exposure in occupational settings include inhalation, dermal contact, and potential ingestion. To date, a limited number of exposure assessments have been performed in industrial settings and few specific regulatory guidelines have been established. An increasing number of toxicology evaluations have suggested the potential for various adverse effects following ENM exposure. For example, in industrial settings, workers with longer exposures to ENMs have higher incidences of lung diseases, gastrointestinal tract alteration, hepatic injuries, reproductive failure, and neurological disorders. This chapter specifically focuses on ENMs that are currently or projected to be highly utilized in industrial settings including carbon nanotubes, graphene, fullerene, zinc oxide, silver, titanium oxide, cerium oxide, gold, and iron oxide. For each of these ENMs current suggested regulatory standards are provided. Further, findings from exposure assessment studies are described to determine exposure risks related to distinct ENMs and specific duties in the workplace. Toxicity data from human and animal studies are included to identify biological responses and adverse health effects potentially related to distinct ENM exposures. Throughout the chapter, critical gaps in our knowledge in regard to workplace ENM exposures and risk are highlighted.

Nanotechnologies, engineered nanomaterials and occupational health and safety – A review

Engineered nanomaterials (ENMs) are a new class of environmental pollutants. Researchers are beginning to debate whether new modeling paradigms and experimental tests to obtain model parameters are required for ENMs or if approaches for existing pollutants are robust enough to predict ENM distribution between environmental compartments. This Account outlines how experimental research can yield quantitative data for use in ENM fate and exposure models. We first review experimental testing approaches that are employed with ENMs. Then we compare and contrast ENMs against other pollutants. Finally, we summarize the findings and identify research needs that may yield global descriptors for ENMs that are suitable for use in fate and transport modeling. Over the past decade, researchers have made significant progress in understanding factors that influence the fate and transport of ENMs. In some cases, researchers have developed approaches toward global descriptor models (experimental, conceptual, and quantitative). We suggest the following global descriptors for ENMs: octanol-water partition coefficients, solid-water partition coefficients, attachment coefficients, and rate constants describing reactions such as dissolution, sedimentation, and degradation. ENMs appear to accumulate at the octanol-water interface and readily interact with other interfaces, such as lipid-water interfaces. Batch experiments to investigate factors that influence retention of ENMs on solid phases are very promising. However, ENMs probably do not behave in the same way as dissolved chemicals, and therefore, researchers need to use measurement techniques and concepts more commonly associated with colloids. Despite several years of research with ENMs in column studies, available summaries tend to discuss the effects of ionic strength, pH, organic matter, ENM type, packing media, or other parameters qualitatively rather than reporting quantitative values, such as attachment efficiencies, that would facilitate comparison across studies. Only a few structure-activity relationships have been developed for ENMs so far, but such evaluations will facilitate the understanding of the reactivities of different forms of a single ENM. The establishment of predictive capabilities for ENMs in the environment would enable accurate exposure assessments that would assist in ENM risk management. Such information is also critical for understanding the ultimate disposition of ENMs and may provide a framework for improved engineering of nanomaterials that are more environmentally benign.

The potential applications associated with engineered nanomaterials (ENMs) are seemingly limitless, particularly in the broad disciplines of biomedical therapeutics and diagnostics, or ‘theranostics’ [1]. The National Nanotechnology Initiative has invested a considerable amount of resources, research and infrastructure for material development at dimensions less than 100 nm [2]. Materials manufactured at the nanoscale express unique properties and characteristics that differ from those of their larger counterparts of the same chemical composition. Furthermore, the toxicities and physiochemical properties of these ENMs are distinctly different, and thus are not well understood [3]. Moreover, novel ENMs and ENM properties are generated faster than their toxicities can be determined. Federal resources have been allocated to generate research and development of commercial products and medical technologies within the fields of drug delivery and imaging. To a lesser extent, these resources also support investigations into the toxicokinetics of these novel materials [2,4]. For good reason, most early nanotoxicology research has focused almost exclusively on pulmonary exposures within a young, healthy, male model. Our studies on micro-vascular dysfunction subsequent to ENM inhalation is of no exception. While this approach has yielded important descriptive and mechanistic information, the increased use of ENMs in novel biomedical and consumer products inevitably leads to increased occupational, environmental and domestic exposures to a variety of ENMs that are both intentional and unintentional. Perhaps some of the applications with the greatest potential to improve human health are those that require the intentional introduction of ENMs to the body. Such ENM exposure routes would no longer be limited to the lungs and would include ingestion, transdermal and injections (intravenous or other). Potential applications under development include drug delivery, high-resolution imaging, preventative measures (antioxidants) and implantable devices. The shear breadth of these applications mandates that we considerably widen our exposure models. The fetomaternal relationship during gestation is a unique, dynamic and complex physiological system. The term ‘milieu’, coined by Claude Bernard, or homeostatic environment is often used to describe different compartments, conditions and components associated with a given physiological function. At the outset, maternal health and homeostasis is paramount for a successful gestational outcome; therefore, uterine adaptation to pregnancy (e.g., growth and pressure regulation) or the uterine milieu must be first considered. Incorporated in the gestational uterine milieu is placental development, a transient organ with significant influence over fetal development. In addition to exchange of nutrients and wastes, the placenta serves as an endocrine organ to both the maternal and fetal circulations [5]. Lastly, the intrauterine environment where the fetus develops, or the fetal milieu, must be established and maintained to promote appropriate growth and development. Any dysfunction within the coordinated exchange of hormones, nutrients and wastes during gestation may lead to devastating fetal consequences. Therefore, regulation of maternal homeostasis and the fetal milieu are highly susceptible to a variety of external influences or exposures. Currently, our understanding of ENM exposure in these regards is quite poor. To date, few studies have explored the consequences of maternal ENM exposure during pregnancy [6–8]. Failure to recognize the consequences of ENM exposure during gestation may lead to untoward outcomes for generations. While it would be easy to label nanomaterial theranostics as contraindicated during pregnancy, the potential benefits within the field of obstetric theranostics may be immense. For example, applications of immediate interest to human health may include: fetal imaging, assessment of high-risk pregnancies and early pharmacological interventions. These promising advancements, while exciting and novel, can only reach their full potential if the toxicity of a given ENM, and its terms are first properly understood in all regards.