- Nanotechnology and in situ remediation: a review of the benefits and potential risks.
- Nano zero valent iron pdf printer
- Zero Valent Iron (ZVI) Applications: Nano, Powder or Aggregate? Which to use?
- Magnetic immobilization of bacteria using iron oxide nanoparticles
- Innovative materials for environmental application
- Journal of Hazardous Materials
- Nanotechnology and the environment - Hazard potentials and risks
Nanoremediation, which is the use of nanoparticles and nanomaterials for environmental remediation, is widely explored and proposed for preservation of ecosystems that suffer from the increase in human population, pollution, and urbanization.
We herein report a critical analysis of nanotechnologies for water remediation by assessing their sustainability in terms of efficient removal of pollutants, appropriate methods for monitoring their effectiveness, and protocols for the evaluation of any potential environmental risks.
Our purpose is to furnish fruitful guidelines for sustainable water management, able to promote nanoremediation also at European level. In this context, we describe new nanostructured polysaccharide-based materials obtained from renewable resources as alternative efficient and ecosafe solutions for water nano-treatment.
We also provide eco-design indications to improve the sustainability of the production of these materials, based on life-cycle assessment methodology. The increasing and rapid deterioration and degradation of the water quality is one of the most challenging issues facing the 21st century. It can be ascribed to a variety of factors such as population growth, the effects of climate change on the hydrologic cycle and increasing pollution. Globally, extensive research has been performed to address such urgent environmental issues and new technologies have been developed to remediate water pollution by both organic and inorganic contaminants.
However, the cost and challenge associated with the treatment of both groundwater and wastewater and the increasing awareness of environmental risks calls for continued improvement and innovation.
Nanotechnology and in situ remediation: a review of the benefits and potential risks.
Nanotechnology has significantly contributed to remarkable industrial and societal changes over recent decades. Compared to conventional in situ remediation techniques, such as thermal treatment, air sparging, chemical oxidation and bioremediation, often coupled with on-site pump-and-treat processes [ 2 ], which are known to be expensive, partially effective and time-consuming, nanoremediation has emerged as a new clean-up method that is less costly, more effective as well as environmentally, socially, and economically sustainable [ 3 , 4 ].
Indeed, nanotechnologies allow treatment of contaminated media in situ and minimize the addition of further chemicals in the clean-up process [ 5 ].
ENMs, due to their nanometric size, present a very high and reactive surface area, compared to the same volume of bulk material. They can also be tuned with desired properties by tailoring the synthetic processes to meet case-specific needs and overcome applicative limitations stemming from the complexity of environmental matrices to be treated.
Additionally, the far-reaching mobility of ENMs in aquatic media maximizes their potential for treating large volumes of contaminated environmental matrices [ 8 ]. According to the Project of Environmental Nanotechnology web site and United States Environmental Protection Agency USEPA , in the last ten years, almost 70 sites have been successfully treated worldwide at field scale, by using nanoremediation techniques.
These approaches have significantly reduced time frame days vs. It has been estimated that there are more than 2.
Nano zero valent iron pdf printer
Moreover, a remediation technology must attend to cost-benefit approaches considering practical immediate issues and long-term expectancies. Despite such promising expectations, environmental and human risk assessment associated with the use of ENMs is still a matter of debate and nanoremediation is seen still as an emerging technology [ 6 ].
Zero Valent Iron (ZVI) Applications: Nano, Powder or Aggregate? Which to use?
It has been slowly applied in Europe [ 11 ] probably because of the emerging societal worries on nanotechnology and the current lack of regulatory and proper legislative supports [ 12 , 13 , 14 ]. We herein report a critical analysis on the use of the ENMs for water remediation, with the aim of sharing the strategy developed within the NanoBonD project Nanomaterials for Remediation of Environmental Matrices associated to Dewatering , funded in the framework POR CReO FESR Tuscany —, whose objective is the development of innovative, ecofriendly and ecosafe polysaccharide-based nanotechnologies for the remediation of contaminated sediments and waters.
The particularly desirable ENMs characteristics, which make them suitable for environmental remediation, can negatively rebound of the safety of application of such materials in water remediation [ 15 ]. The current debate relies on the balance between known benefits of nanoremediation and potential risks associated to the use of ENMs in natural environments mainly due to their mobility, transformations and ultimately potential ecotoxicity [ 16 ].
Costs and benefits are not always easy to handle especially for emerging materials, at least at the beginning when unexplored aspects are still present and contradictory results exist considering both human health and environmental effects.
The mobility, small size, and overall reactivity of ENMs can therefore dramatically improve the transport of ENMs in water compartments, as they could potentially reach undesired targets and lead to hazardous effects. Additionally, a typical nanoremediation process entails that ENMs are dispersed in environmental compartments, such as ground or surface waters, which are defined by peculiar levels of ionic strength, dissolved oxygen and dissolved organic matter DOM contents, and other physico-chemical parameters.
As an example, silver [ 18 , 19 , 20 ] and copper [ 21 ] nanoparticles are converted into the corresponding sulfides species via sulfidation processes, once dispersed in natural waters. The dispersion quality of ENMs can be equally affected, often leading either to homo- and hetero-aggregation phenomena or to an improved colloidal stability in natural waters [ 22 ], thus significantly influencing their mobility and determining their association with different environmental compartments.
The former case can result in faster sedimentation phenomena [ 23 ], with ENMs likely ending up in the sediment-associated fractions. Such distinct behavior stems from the complex interplay between different water chemistries, such as multivalent cations, natural colloids, and DOM, and ENMs properties, governing their environmental partition, which rebounds on exposure and hazard levels and ultimately ecotoxicity [ 17 , 26 , 27 ].
Therefore, ENMs behavior pose questions regarding their environmental fate and impact after release in the environment, beyond the envisaged benefits in terms of contaminant removal or degradation, with consequent environmental costs [ 28 ]. This is to some extent possible with magnetic ENMs, such as magnetite nanoparticles, which can be recovered with the application of weak electromagnetic fields once the remediation process is over [ 29 ].
Nevertheless, major challenges are experienced with the vast majority of non-magnetic ENMs, as an effective removal from remediated environmental media is often limited or completely impractical. To this end, efforts to assess and model the fate of different ENMs in a wide range of environmental matrices, and to track relevant physico-chemical transformations, are much needed to anticipate potential endpoints [ 28 , 30 , 31 , 32 , 33 ].
Additionally, the complexity of environmental matrices requires novel and tailored detection and characterization technologies and strategies [ 34 ]. Potential ENMs bioaccumulation due to ingestion, dermal contact, and inhalation in wildlife is still unknown as well as their potential role to act as a Trojan horse by increasing the uptake of contaminants to be remediated in exposed organisms [ 35 , 36 , 37 , 38 ].
Far more important, the current technical limitations in ENMs detection in environmental matrices as well as a proper risk assessment procedure are still challenging and limiting its development worldwide [ 39 ]. It is hence wise to foresee possible scenarios of ENMs interactions with natural ecosystems and to screen for their potential ecotoxicity toward different levels of biological organization [ 17 , 40 , 41 , 42 ].
In this light, adaptations of existing ecotoxicity tests, together with ad hoc testing strategies for nanomaterials, have been recently developed and recommended [ 43 , 44 , 45 , 46 , 47 ]. A recent body of literature has been produced over the past few years concerning the hazard posed by ENMs and different nanoformulations actually employed for nanoremediation purposes, as reported in Table 1.
Indeed, for most of the applied nanoscale materials in nanoremediation, several adverse effects in both terrestrial and aquatic organisms have been reported, thus certainly increasing governmental as well as public concerns related to their in situ application [ 48 , 49 ] see Table 1.
Among the tested ENMs, nZVI and iron oxides-based formulations received much attention, compared to other ENMs types, due to their consistent usage in ground- and surface water remediation [ 50 ]. Keller et al. Similarly, in a more recent study from Nguyen et al. Other phytoplankton functional endpoints were affected by Fe ENMs exposure, such as the photosystem II quantum yield, Chlorophyll a content, cell growth rate and cell membrane damage, with the nZVI being more toxic compared to the other tested ENMs.
The author linked such toxicity trends to the content of Fe 0 that caused high release of Fe II and Fe III , which could be in turn be taken up by cells causing oxidative stress [ 52 , 53 ]. On the other hand, such mechanism was to some extent limited concerning the other tested material, due to surface passivation or absence of zerovalent iron in the formulation [ 49 ].
Oxidative stress and ROS generation has been recognized as the main cause of toxicity induced by titanium oxides ENMs as well [ 54 ]. TiO 2 nanomaterials are popular photocatalysts employed in the remediation of polluted surface- or groundwaters and for wastewater treatments, by enhancing the photodegradation of organic contaminants and promoting water disinfection [ 55 ].
Miller et al. This was due to an overall increase in ROS production in seawater contaminated with TiO 2 NPs, which can deeply affect phytoplankton primary producers and compromise ecosystem functionality. Loss of membrane integrity and decrease in cell viability were identified by Mathur et al.
Magnetic immobilization of bacteria using iron oxide nanoparticles
However, the authors demonstrated that TiO 2 NPs can interact with bacterial biofilms, pointing out that ENMs trapping by exopolymeric substances could, to some extent, decrease their mobility and potentially play a role in modulating their toxicity. In a review, Callaghan and MacCormack [ 58 ] gathered abundant data regarding the lack of acute mortality of common TiO 2 nanoformulations toward different fish species exposed under environmentally realistic conditions. However, the authors highlighted how, under chronic exposure, TiO 2 ENMs promoted diverse physiological alterations, ranging from gill histopathology and brain dysfunctions to swimming impairment.
Similarly, zinc oxide ZnO ENMs are excellent photocatalysts that hold promises in nanoremediation of polluted water bodies via degradation of organic pollutants, such as endocrine disrupting compounds [ 59 , 60 ].
However, differently from TiO 2 NP, ZnO-based nanoformulation are soluble in water, and since nanoparticles have higher surface area to volume ratios than bulk counterparts they often display faster dissolution, making the release of zinc ions and zinc hydroxides [ 62 ] a primary concern for ecotoxicology [ 63 ]. Indeed, Miller et al.
Carbon nanotubes CNT , either single- or multi-walled, have been successfully exploited in many technological fields, including wastewater treatment [ 67 ].
Therefore, this class of carbon-based ENMs are currently being released in the environment.
Concerns have been raised about their environmental behavior and impacts on living organisms [ 68 ] and some ecotoxicological evidences have been produced regarding their effects toward different organisms. Hanna and co-workers [ 69 ] showed that CNT can be accumulated in the tissues of exposed marine mussels and can decrease phytoplankton clearance rate at low concentrations, while higher concentration can elicit toxic responses.
Moreover, to date, there is no shortage of data regarding the toxic effects of CNT on both fish and crustacean species, as highlighted in a recent review from Callaghan and MacCormack [ 58 ].
Indeed, Boncel et al.
Innovative materials for environmental application
Moreover, such effects have been described over different level of biological organizations, ranging from plants [ 71 ] and algae [ 49 ] to aquatic invertebrate and vertebrate species [ 48 , 72 ], identifying diverse toxicological endpoints. Such evidences highlight the necessity to move toward different nanoformulations and usage strategies when applying ENMs and ENMs-based products to natural waters.
It is based on avoiding those undesirable properties of ENMs, which turn to be hazardous for environment and human health, in the process of ENMs design.
Only those properties which will maintain ENMs efficacy and safety should be incorporated as a design parameter during product development. Environmental risk assessment of ENMs should provide suitable ecotoxicity data in terms of exposure and effects to non-target organisms which will help to recognize those ENMs properties as for instance behavior and transformations in environmental media which could affect interaction with living organisms and consequently toxicity.
Such knowledge should be used to select only those properties of ENMs which will guarantee their ecofriendly and sustainable application also for environmental remediation [ 32 ]. Therefore, an eco-design of ENMs for environmental application obtained from an ecotoxicological testing strategy will allow the selection of the best ecofriendly and ecological sustainable ENMs and will significantly limit any potential side effects in term of no toxicological risk for natural ecosystems.
Upon observed ecotoxicity, ENMs should be modified up to become ecosafe, also by defining their behavior and transformation once released into the natural environment Figure 1. Standardized methodologies able to assess ENMs effectiveness, environmental safety, and economic sustainability within the context of existing environmental regulations are thus urgently needed.
All these aspects will certainly support patenting and pilot applications of new ENMs developed based on ecosafety by design approach. Schematic description of role of ecotoxicology in defining eco-design along ENM synthesis and development.
The progressive diffusion of ENMs in many fields, including nanoremediation, and the global consensus that their release into the environment will increase, has led not only to the urge of a sound evaluation of their toxicity effects on human health and on the environment, but also to the need for the evaluation of their environmental sustainability.
Life-cycle assessment LCA is a well-established tool, nowadays largely used to evaluate the potential environmental impacts of a product system product or service over its whole life cycle, from the extraction and acquisition of raw materials, to the core production process, use and end of life treatment, either recovery or final disposal [ 79 , 80 ].
LCA is considered a holistic method since it provides the assessment of the potential environmental impacts on several environmental categories, mainly on global and regional scale, such as global warming potential, ozone depletion potential, acidification potential, resource depletion etc.
Moreover, LCA permits to define the environmental hotspots of a product system, to analyze alternative solutions that provide performance improvement and to make comparison of different scenarios, therefore proving to be a powerful tool for supporting eco-design and decision-making. LCA is deemed to be the suitable tool to assess the environmental impacts of emerging technologies such as nanotechnologies and nano-enabled products, also in comparison to conventional technologies [ 81 , 82 , 83 ].
Journal of Hazardous Materials
This application is largely debated in the scientific literature and at the same time is present also in policy documents [ 84 , 85 ]. Although LCA is strongly recommended as tool to assess the sustainability of ENMs throughout their life cycle, the scientific community currently agrees on the several information gaps, which hamper the proper application of LCA in the field [ 86 , 87 ].
These gaps regard mainly two broad issues, namely the difficulty of including the whole life cycle of ENMs and to fully assess their impacts on human toxicity and ecotoxicity.
The first issue stems from the lack, in the life-cycle inventory, of specific features and properties of the new nanomaterials that differentiate them from the corresponding bulk material and of the quantification of their release into the environment across their life-cycle [ 84 ].
The second issue, instead, regards the application of the impact assessment methods, which currently do not allow consideration of the nanospecific impacts on human health and ecotoxicity. In fact, on the one hand the fate of ENMs in the environment is poorly modeled and quantitatively assessed and on the other hand, current impact assessment tools e. Several review articles on the application of LCA to nanotechnologies and ENMs have been published that show the main gaps that prevent the majority of the LCA studies to be considered fully comprehensive [ 81 , 84 , 85 , 86 , 87 , 88 ].
The main conclusions of these reviews can be summarized as follows. Studies regarding LCA and ENMs are not very abundant, although increasing in the recent years, as to show the growing interest in the issue. However most of them mention the barriers and the challenges in the application of LCA on ENMs, but do not provide concrete solutions to overcome them. For instance, many studies focus only on the production stage, from cradle to gate, leaving out the use and end of life stages, mostly due to scarce availability of data regarding the potential release and fate of ENMs to and into the environment during these stages [ 81 , 84 , 88 ].
Nanotechnology and the environment - Hazard potentials and risks
Consequently, the choice of the functional unit is often weight-based e. This approach prevents the valorization of the augmented functionalities typical of ENMs that improve their performance in the use stage.
This can be particularly significant in case of comparison with bulk materials, since the inclusion of the use stage would allow mitigation of the large impacts often found in the production stage of nanomaterials [ 68 , 81 ]. Therefore, to perform cradle-to-grave analyses, scholars agree on the urge of populating the inventory data of ENMs, regarding the release to environment compartments in the different life-cycle stages: in the production stage release in the environment, workers exposure , in the use stage planned release or unintentional release to the different environmental matrices , and in the end of life stage e.
As long as the assessment of such emissions release is not established by the scientific community, data regarding physico-chemical features of ENMs should be included in the inventory e. In particular, information regarding shape, dimension, properties, and surface chemistry, which are known to affect the interaction with the environment, are required to distinguish material flows of nanoproducts from bulk materials [ 68 , 88 ]. Since the definition of this information is very challenging, some authors suggest that, if scalability exists, it is then possible to apply traditional characterization approach, using the corresponding bulk emissions in the Life Cycle Inventory LCI and the same toxicity assessment approaches to determine the characterization factors [ 81 ].