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Potential Hazards of Nanoparticles

  • Hoda Jafarizadeh-Malmiri
  • Zahra Sayyar
  • Navideh Anarjan
  • Aydin Berenjian
Chapter
  • 367 Downloads

Abstract

Recent developments in the design of advanced materials have furthered interest in the commercialization of new technologies. So the increased production of nanomaterials has increased concerns about their effects on human and environmental health. The evidence for health risks of nanoparticles has been demonstrated over the last decade, yet it is unclear if metal nanoparticles cause effects directly or indirectly. This chapter gives a brief review on the toxicology pathways, recommendations and methods for screening hazard testing of nanoparticles.

8.1 Introduction

Recent developments in the design of advanced materials have furthered interest in the commercialization of new technologies. So the increased production of nanomaterials has increased concerns about their effects on human and environmental health. The evidence for health risks of nanoparticles has been demonstrated over the last decade, yet it is unclear if metal nanoparticles cause effects directly or indirectly. This chapter gives a brief review on the toxicology pathways, recommendations and methods for screening hazard testing of nanoparticles.

Nanotechnology plays an important role in the improvement of the food and drug industry in the last few years and will have an enormous impact on life sciences, including drug delivery, food, pharmacy, engineering and the production of biomaterials (Forbe et al. 2011).

The reason why nanoparticles are attractive for such purposes is based on their important and unique features, such as their small size and special surface area, and which special surface area is much larger than that of other particles and materials (Fig. 8.1). These features can cause an increase in the risk of fire and explosion compared to other particles. Therefore, nanoparticles have a large surface which might be chemically more reactive to bind, adsorb and carry other compounds such as drugs, probes and proteins compared to their fine analogues (Borm and Kreyling 2004; Oberdörster 2010).
Fig. 8.1

Properties of nanoparticles for their potential biological effects

Along with the developments in nanotechnology and new products, these materials can be harmful for human health and the environment. In nanometer scale, material properties change; along with these changes, the prediction, identification, evaluation and control of the health, safety and environmental risks of nanomaterials are also challenged (Oberdörster 2010).

Risk estimation has been supposed of as the evaluation of what can go wrong, how this is likely to occur. Risk estimation has been the guiding standard for the evaluation of environmental and product risks. In the case of chemicals and nanomaterials, risk estimation has relied on detailed, experimental data for exposure and hazard. Objective driven approaches, referred to here as top-down and bottom-up methods, rely on the achievement of information and synthesis from result makers to drive actions. Top-down methods can improve the risk estimation process by mixing technical information and expert results on an emerging technology with human values (Fadel et al. 2015).

In all studies on the effects of nanomaterials, two groups of different nanostructures should be considered:
  1. (a)

    Fixed nanoparticles, nanocomposites, nanostructured surfaces and nanoparticle components.

     
  2. (b)

    Free nanoparticles; these nanoparticles can create a complex combination of other nanoparticles from a specific element that is coated with another material.

     

Fixed nanoparticles are used in many current applications that are not naturally dispersive. New applications include coatings, textiles, ceramics, membranes, composite materials, glass products, prosthetic implants, anti-static packaging, cutting tools, industrial catalysts, a variety of electric and electronic devices including displays, batteries and fuel cells (Salata 2004; Royal Society and Royal Academy of Engineering 2004).

Other uses of nanoparticles include drugs, biodegradable materials for biomedical, personal care products, such as cosmetics, quantum dots and some pilot applications in environmental remediation (Fig. 8.2). Also potential exposure to manufacture nanoparticles may increase naturally in the future (Assa et al. 2015; Guadagnini et al. 2015; Vauthier et al. 2003).
Fig. 8.2

overview of areas of applications of nanotechnology

Researchers now focus on hazards of nanoparticles that are currently used in the production of products and on the subject of what can be done to limit the related risks. However, research on hazards of nanoparticles is still limited (Reijnders 2006).

8.2 Hazard and Risk Definition

Nanotoxicology, an important subcategory of nanotechnology, has been defined as science of nanostructures that has an effect on living organisms (Borm et al. 2006). The term hazard is defined in different forms. In this chapter the term hazard is used following the definition of the United States Environmental Protection Agency (USEPA), which defines hazard as the inherent toxicity of a compound. According to this definition, if a chemical material has the toxicity property, it is hazardous. Any exposure to a hazardous material may lead to adverse health effects in humans. USEPA defines risk with respect to the above definition of hazard as a measure of the probability of damage to life, health, property and the environment. According to this definition, because the probability of exposure to a hazardous material is high and the consequences cause risk for the health or environment it is therefore important to estimate risk (Kavlock and Dix 2010; Warheit 2004). Usually known risks and potential risks are two categories of risk that are distinguished in literature. When the causal relationship between a cause and damage is established, prevention is possible. In case of potential risks, it is unclear whether there is a danger, how significant the damage can be or what is the probability of its occurrence. To evaluate the risks of hazardous agents is very important. The likelihood that a hazardous substance will cause harm is the determinant of how cautious one should be and what preventative or precautionary measures should be taken (Hristozov and Malsch 2009).

In the last few years, a number of experimental studies were done where the adverse health effects of 965 tested nanoparticles of various chemical compositions were observed (Foss Hansen et al. 2007). A lot of studies, relevant to hazard, have been done with different nanoparticles, but most of them were obviously not meant to facilitate risk evaluation; they use non-standardized tests and the lack of standardized testing results makes the univocal hazard of nanoparticles impossible (Fadel et al. 2015).

The objective of this chapter is to investigate the current state of knowledge of the hazard of nanoparticles on human health and the environment. This chapter is based on an extensive review of literature published in the past to now.

8.3 Overall Theories

The U.S. community and nanotechnology industry continue to evaluate validated and reliable science-based methods and tools to enhance approaches for risk analysis of nanomaterials. Significant global efforts by government and private sector investors to collect environmental health and safety (EHS) risk information have resulted in a large volume of data concerning nanomaterial effects. The value and application of this information to relevant policy makers have been the subject of multiple national and international efforts, including four workshops organized by the National Nanotechnology Initiative (NNI)—a strategy exposing potential nanotechnology risks—from 2009 to 2010 (Roco 2007). Various investor communities, such as industry, workers, consumers and non-government organizations, should confirm that novel nanomaterials are safe for human health and the environment. Collected EHS information by government decision makers and private sector investors have helped to create data concerning nanomaterial effects such as information about the toxicity of a compound and determining limits for exposure and uptake into the body. Such research must be followed by the modified methods for characterizing and quantifying exposure to humans and the environment. To consider the best path in 2009 for nanotechnology, NNI agencies studied the 2008 EHS Research Strategy and data in EHS. In 2008 the Nanotechnology Environmental and Health Implications (NEHI) Working Group of the NNI published a document titled Strategy for Nanotechnology-Related Environmental, Health, and Safety Research. The EHS Research Strategy document represented the conclusion of a comprehensive effort led by the Nanotechnology Environmental and Health Implications (NEHI) Working Group under the National Science, Nanoscale Science, Engineering, and Technology Subcommittee to provide guidance to the NNI Federal agencies producing scientific information for risk management (Howard 2013; Roco 2007; Schmidt 2009).

To share the latest information, newest developments and research gaps in the nanotechnology EHS field, workshops were organized. Overall, the knowledge collected from the workshops were critical to the development of the NNI EHS Research Strategy and established standards. This strategy document identified important data needed in the areas of nanomaterial measurement organization, risk valuation and management methods, human health and the environment.

The 2013 NNI workshops were designed to facilitate discussion among various investors of approaches, equipment and methods used to measure, manage and communicate the potential risks of nanomaterials and nanotechnology-based products (Fig. 8.3) (Howard 2013).
Fig. 8.3

2013 National Nanotechnology Initiative workshop objectives

Associates discussed the importance of providing sufficient information on nanomaterial products in safety in order to protect human health and the environment against damage of nanomaterials. The challenges of nanotechnology risk management suggested the creation of information that includes guidance documents to aid the small business community in making informed decisions when entering the nanotechnology market (Maynard et al. 2006).

Several requirements were discussed such as techniques to measure particles in vivo, the release of particles into the environment and the toxicity potential of nanomaterials. Particle uniformity might also influence the kinetics and toxicity of nanomaterials in unknown ways. Universal attempts have developed strategies for improving the data quality for characterizing nanomaterials, toxicological studies and validated methods for characterizing and quantifying nanomaterials in experimental media, tissues and cells. Also, attempts in the private sector have concentrated on the development of new methods to estimate ‘commercial’ risk and exposure control measures, and the scientific and regulatory information to evaluate toxicity (Schmidt 2009).

Workshops displayed characterization information to modify best management performance to manage uncertain dangers. Uncertainty in the valuation process was often related to a lack of standard methods or test procedures, and the inability to predict statements of a technology in early stages of development. Finally, best management practices should be introduced to ensure worker safety (Fadel et al. 2015).

To use the potential of nanotechnology in all industries, full attention is required for safety and toxicological issues. However, for specific application, a toxicological evaluation is necessary. This is particularly true for the application of nanoparticles for drug delivery. In these applications particles are used in the human body and environment, and some of these new applications are an important enhancement of health care (Buxton et al. 2003). Toxicologists claimed that new science, methods and protocols are necessary, and this can make these evaluations cost effective, facilitating new product development (Nel et al. 2006). However, the requirement for this application is now emphasized by the following theories:
  1. 1.

    Nanomaterials are modified for their unique properties such as surface area in comparison to bulk materials. Since contact surface with the body tissue, unique properties are investigated from a toxicological viewpoint. Although current tests and procedures in drug and device evaluation may be appropriate to detect many dangerous reactions, it cannot be expected that these analyses will detect all potential risks. So additional analyses may be required that depend on the type of particles used.

     
  2. 2.

    Nanoparticles have different physico-chemical characteristics compared to micro-sized particles, which may result in changed body distribution, passage of the blood pathway and brain barrier. A basic understanding of the biological behavior of nanoparticles in distribution in vivo and body both at the organ and cellular level is useful for understanding risk potential.

     
  3. 3.

    Effects of combustion resulting nanoparticles exposure in environmental that create diseased individuals. Typical preclinical testing is almost always done in healthy animals and volunteers. It may be discussed that they do not have specific effects on health during routine testing and post marketing evaluation after clinical use but risks of particles may be detected at a very late stage. All would depend on the types of tests used in the preclinical evaluation, which should be considered. The use of nanoparticles as a drug carrier may reduce the toxicity of the incorporated drug (De Jong and Borm 2008; Nel et al. 2006).

     

8.4 Critical Information of Physico-Chemical Properties and Evidence for Nanoparticle Toxicity

After developing separate lists of critical information needs in the breakout groups, the participants produced the following consensus priority list in Fig. 8.4 (Balbus et al. 2007).
Fig. 8.4

Critical information needs for nanoparticle toxicity

The main characteristic of nanoparticles is their size in the zone between individual atoms or molecules and the corresponding bulk materials. These physicochemical properties of the material can create the opportunity for increased uptake and interaction with biological tissues (Kreyling et al. 2010). This combination of effects can produce adverse biological effects in living cells, although the extraordinary properties of nanoparticles may require a novel investigative method to evaluate their hazard potential and particle toxicology (Buzea et al. 2007; Oberdörster et al. 2005b). Inhaled or instilled ambient nanoparticles can induce pulmonary inflammation, oxidative stress, distal organ involvement, fibrosis, cytotoxicity and mediator release from lung target cells (Donaldson and Tran 2002).

Tissue and cell culture analysis show the physiological response and role of oxidative stress in the making of inflammatory cytotoxic cellular responses. Clinical and experimental studies indicate that a small size, a large surface area and an ability to generate reactive oxygen species (ROS) play an important role in the ability of nanoparticles to induce lung injury (Nel 2005).

However, particle coating, surface treatments, surface excitation by ultraviolet radiation and particle aggregation can develop the effects of particle size. It is possible, therefore, that some nanoparticles may create their toxic effects as aggregates or through the release of toxic chemicals (Liu et al. 2014).

The increase in surface area causes an increase in the potential number of reactive groups, such as ROS, on the particle surface. So the change in the physicochemical and structural properties could be responsible for a number of material interactions that could lead to toxicological effects and increase in oxidation (Oberdörster et al. 2005a, b).

Also, these properties could confirm specific surface groups that could function as reactive sites. The extent of reactive sites and their importance intensely depend on the chemical composition of the material. Surface groups can make nanoparticle hydrophilic or hydrophobic, lipophilic or lipophobic, or catalytically active or passive, which are shown in Fig. 8.5 (Nel et al. 2006).
Fig. 8.5

Possible mechanisms by which nanomaterials interact with biological tissue

Toxicities of nanoparticles can be influenced by many other factors such as shape, aggregation, surface coating, surface charges, particle surface chemistry, biodegradability, concentration, and solubility may also affect the lectured specific physicochemical and transport properties with the possibility of negating or amplifying the size effects (Nel et al. 2006).

For example, those surface properties can lead to toxicity due to the interaction of electron donor or acceptor active sites with molecular oxygen (O2). Electron capture can lead to the formation of the superoxide radical (\( {O^{.}}_2^{-} \)), which can generate additional reactive oxygen species (ROS) (Fig. 8.5). Thus, several nanoparticle characteristics can conclude in ROS generation, which is presently the developed model for nanoparticle toxicity (Table 8.1) (Shvedova et al. 2005).
Table 8.1

Nanoparticle’ effects as the basis for pathophysiology and toxicity (Nel et al. 2006)

Experimental nanoparticle effects

Possible pathophysiological outcomes

ROS generation

• Protein

• DNA and membrane injury

• Oxidative stress

Oxidative stress

• Phase II enzyme induction

• Inflammation

• Mitochondrial perturbation

Mitochondrial perturbation

• Inner membrane damage

• Permeability transition (PT) pore opening

• Energy failure

• Apoptosis

• Apo-necrosis

• Cytotoxicity

Inflammation

• Tissue infiltration with inflammatory cells

• Fibrosis

• Granulomas

• Atherogenesis

• Acute phase protein expression (e.g., C-reactive protein)

Protein denaturation, degradation

• Loss of enzyme activity

• Auto-antigenicity

Nuclear uptake

• DNA damage

• Nucleoprotein clumping

• Autoantigens

Uptake in neuronal tissue

• Brain and peripheral nervous system injury

Altered cell cycle regulation

• Proliferation

• Cell cycle arrest

• Senescence

DNA damage

• Mutagenesis

• Metaplasia

• Carcinogenesis

Comparing the results of different studies showed that the aggregation of nanoparticles may reduce their toxicity, due to a more effective macrophage clearance for larger particles compared to smaller ones (Oberdörster et al. 2005b). Thus, experiments done with high concentrations of nanoparticles may not be as toxic as lower concentrations of the same nanoparticles (Buzea et al. 2007; Gurr et al. 2005). Another critical factor is particle chemistry in determining nanoparticle toxicity. It is especially relevant from the topic of cell molecular chemistry and oxidative stress. On the other hand, depending on their chemistry, nanoparticles can show different cellular uptake and ability to catalyze the production of ROS. For example, rutile TiO2 nanoparticles were found to induce oxidative DNA damage in the absence of light, but anatase TiO2 nanoparticles of the same size did not (Wiesner and Bottero 2007). Moreover, hydroxyl radicals (.OH) associated with TiO2 nanoparticles induced cytotoxicity and oxidative DNA damage (Reeves et al. 2008).

Also, surfactants can alter the physicochemical properties of nanoparticles and affect their cytotoxicity. Finally, besides the potential hazards of nanoparticles, their occurrence in the aqueous system are also important in determining their final toxicity to the public (Ahmad et al. 2005).

The challenge to relate the physicochemical properties of colloidal nanoparticles to their cytotoxicity is an important issue. So far, there is no agreement on the dose at which nanoparticles cause a biological response. Some of them measured the dose of toxicity by total weight, some others by the number of particles per volume. Some others found that the best way to find how toxic the particles are to cells was to calculate the dose based on the total surface area of the nanomaterial. Auffan et al. (2009) indicated that chemically stable metallic nanoparticles had no significant cellular toxicity, whereas nanoparticles able to be oxidized reduced or dissolved were cytotoxic and even genotoxic to cellular organisms. It seems that different parameters play major roles under different conditions on the toxicity evaluation of nanoparticles (Liu et al. 2014).

8.5 Hazard and Risk Evaluation for Nanoparticles

To determine the unique physico-chemical properties of nanoparticles, the nanotechnology community should try new ways to evaluate hazard and risk (Nel et al. 2006). These new approaches must also consider studies of chemical mixtures. The major database on the toxicity of nanoparticles has been created from inhalation and explosion toxicology, that they can be great reasons for research (Balbus et al. 2007). The toxicological profile of nanoparticles has developed during the past decade because of an increase in their consumption (Kreyling et al. 2004).

Toxicity of nanoparticles is an important discussion where adverse effects of environmental particulate air pollution comes from several sources. Particle toxicology proposes that more particle surface equals more toxicity and has adverse effects such as exacerbations of respiratory disease and deaths as well as hospitalizations and deaths from respiratory andcardiovascular disease (Brook et al. 2004). Other adverse effect of nanoparticles is pulmonary inflammation. Large surface areas which bind these adverse effects and the ability of nanoparticles together to cause inflammation can be seen as an important factor. Some nanoparticles may have the extra potential to affect cardiovascular disease directly (Mills et al. 2005). However, information of toxicity of nanoparticles in the body is limited, and all studies of nanoparticles have not shown clear information of toxicity from lung to the blood (Borm and Kreyling 2004; De Jong and Borm 2008).

One of the essentials in understanding nanoparticle toxicity is to understand the kinetics of inhaled ambient air nanoparticles. There are numerous mechanisms that are either based on the large surface area of particle core or on soluble components released by the nanoparticles whereby nanoparticles could lead to inflammatory effects. In addition, various chemicals, including those of biological origin like endotoxin—a component of the outer membrane of Gram-negative bacteria, may be adsorbed onto the nanoparticles and released in the body (Kreyling et al. 2004). In fact, a large surface area of organics and metals is characteristic of nanoparticles, so these have attracted significant toxicological attention in vitro. The aggregation of multiple chemical species, including biological compounds like endotoxin, limits the application of nanoparticles because of decreasing surface area (De Jong and Borm 2008).

As already mentioned above, nanoparticles exert some special properties that are very relevant in the further design of the development of engineered nanomaterials. Several effects are just quantitatively different from fine particles. Nanoparticles could also cause new types of effects, for example mitochondrial damage, uptake through olfactory epithelium, platelet aggregation, and cardiovascular effects where clearly new ways are a requirement for control over their toxicology. So advanced toxicological testing models should be used (De Jong and Borm 2008).

Risk characterization is defined as the final step to evaluation of risk procedure as an estimation of the incidence of the adverse effects to happen in a human or environment due to actual or predicted exposure to a substance (Hristozov and Malsch 2009). A basis of nano risk has been expanded by two organizations, namely Environmental Defense and the DuPont Company, for recognizing EHS risks. First, definition of health or environmental risks needs a realizing of both hazard and exposure based on reasonable attentions of the product lifecycle. In addition, the EHS framework could include hazard studies which provide a reasonable evaluation of the toxicity of the nanoparticles for human and environmental.

The nano risk framework contains six basic steps corresponding to stages of expanding. Briefly, these six steps are listed in Fig. 8.6.
Fig. 8.6

Steps of the nano risk framework

For the user of this nano risk framework, step 2 contains three sections, a, b, and c. Section a is about identifying and characterizing the physical and chemical properties of the nanomaterial. It characterizes the hazard profile and identifies the nanomaterial’s potential safety, health and environmental hazards in section b. Section c is planned to identify and characterize the potential for human or environmental exposures to the nanomaterial. For example, the results of base toxicity tests demonstrated that exposure to TiO2 nanoparticles in the lungs of rats produced low inflammatory potential. These findings establish confidence for EHS attentions in expanding TiO2 nanoparticles. Also the Nano Risk Framework approach shows reasonable assurances that the commercialization of this product has a very low health and environmental risk potential (Warheit et al. 2008).

Although the risks hazards of nano particles relevant to humans and the environment have been studied. A majority of the research has been done on animals which cannot be an accurate risk estimate for humans as there are fundamental differences between animals and humans against toxicity. Some of the risk of nanoparticles are as follows (Chalupa et al. 2004):

8.5.1 Risks of Inhaled Nanoparticles

The high deposition efficiency of inhaled nanoparticles in the pulmonary region increases in people with asthma or chronic obstructive lung disease. Inflammation of the lung is often seen as a response to the inhalation of nanoparticles as well (Chalupa et al. 2004). Warheit et al. (2007), by studying in vivo pulmonary toxicity in rats, showed that TiO2 nanoparticles had low inflammatory potential and lung tissue toxicity. There was also evidence that nanoparticles might act as an adjuvant for allergic sensitization (Kreyling et al. 2004; Reijnders 2006).

8.5.2 Risks of Contacted Nanoparticles

Dermal penetration of nanoparticles is a material of interest for use in humans. Currently the most important use of ultrafine metal oxide particles, such as TiO2 and ZnO in personal care products like sunscreens, highlights the dermal penetration of nanoparticles. TiO2 and ZnO nanoparticles can show photocatalytic activity upon exposure to sunlight (Liu et al. 2014). Menzel et al. (2004) established in experiments that TiO2 and ZnO may penetrate deep into the rat and rabbit skin. ZnO and TiO2 nanoparticles may also become involved in damaging nucleic acids and other cell components by photocatalytic reactions on exposure to sunlight due to penetration into the granular layer. Nanoparticles may also cause allergic reactions (Reijnders 2006).

8.5.3 Risks of Nanoparticles in the Aquatic Environment

The toxicity of nanoparticles can be greatly affected by various factors in the aquatic environment. Bilberg et al. (2012) investigated critical toxicity of nanosilver on the body of a zebrafish in a 48-h static renewal study and compared their results with the toxicity of silver ions (AgNO3). Results confirmed that silver nanoparticles were fatal compared to silver ions. Zhu et al. (2010) found that TiO2 created minimal toxicity to daphnia within the traditional 48-h contact time, but caused high toxicity when the contact time was increased to 72 h. Their results demonstrated that contact duration may be an important factor in nanoparticle toxicity. A considerable amount of TiO2 was also another effective factor that accumulated in daphnia, and these daphnia displayed difficulty in eliminating TiO2 from their body.

8.6 Toxicity Pathways

In this section toxicity pathways will be discussed, which is relevant to environmental exposure to nanoparticles. Particle toxicology has been the subject of a number of reviews, considering the suitable approach for exposure, in vitro versus in vivo dose evaluations and its historical improvement (Driscoll et al. 2002). Five expressions have to be taken into account for the interpretation of inhaled particle properties: dose, deposition, dimension, durability and defense. First, the dose at a specific site of the body assesses the potential toxicity. This deposited dose is dependent on the concentration and size of the particle. In the respiratory system, the deposition probability of nanoparticles increases with decreasing particle size (Bailey and Roy 1994). If a particle is neither soluble nor degradable in the lung, it has a high durability and will accumulate. However, the lung has extensive defense systems, such as mucociliary clearance and macrophage clearance, to remove deposited nanoparticles. In addition, particle transport by macrophages from the alveolar region towards the larynx is slow in humans, even under normal conditions, thus eliminating only about a third of the deposited particles in the lung periphery. So the other two thirds, which accumulate in the lungs, are biodegradable and cleared by other mechanisms (Gehr and Heyder 2000). If particles are reactive or present sufficient dose, macrophages and epithelial cells can be damaged, leading to inflammation (Borm and Kreyling 2004). Nanoparticles can also translocate through the circulatory, lymphatic and nervous systems to many tissues and organs, including the brain (Buzea et al. 2007).

A main hazard study is to research human health and the so-called ‘toxicokinetics’ of nanoparticles related to exposure via the lung, skin and intestine (Fig. 8.7). Toxicokinetics investigates how a particle may get into the body, how it is circulated and dispersed within it, and how it may be metabolized and excreted. Understanding about toxicokinetics is important as it permits attention to the important target organs that may or may not be affected and how the body responds to nanoparticle exposure of metabolism and excretion (Khan 2014).
Fig. 8.7

Assumptive toxicokinetic pathway for nanoparticles

Studies have shown that patients with existing vascular disease have an increased risk of death. Figure 8.8 shows that effects can be classified into direct effects and indirect effects of nanoparticles on the heart and vessels. Among indirect effects, inflammation can be affected on target organs by mediators that are always available. A number of mechanisms have been assumed which are listed in Fig. 8.9.
Fig. 8.8.

Schematic of presentation of mechanisms and their sequence suggested through lung permeability

Fig. 8.9

Three mechanisms have been assumed for indirect effects of nanoparticles

The natural environment is made up of many complex ecosystems including atmospheric, terrestrial, fresh water, ground waters, soils and aquatic compartments. Unlike human exposure, the number of species potentially at risk from nanoparticles is extremely large. Hazards related to nanoparticle exposure can potentially act at individual or population level and might also impact on the structure and function of the ecosystem as a whole (Khan 2014; Leite et al. 2015).

8.7 Screening Hazards Test of Nanoparticle Applications

Since one of the new applications of nanoparticles is in novel drug delivery methods, nanoparticles are used to specific tissues and to increase drugs biological half-life. Also, a number of nanoparticles are used for imaging purposes for extravasation or tumor vascularization (De Jong and Borm 2008). A successful nanoparticle for drug conjugation and delivery must be able to have its pharmacokinetics developed at the organ and cellular level to promote increased delivery or efficiency and avoiding toxic effects of the nanoparticles. In fact, the lung as a barrier is bypassed in most applications and these nanoparticles should be considered to reach all target cells of the cardiovascular system, hepatic system and kidney, as well as interact with the pool of immune competent cells. Several cells and/or receptors on these organs have been found sensitive to nanoparticle, and nanoparticles can disturb normal cell function in various ways. An overview of test methods that can be used to explore potential hazards of nanoparticles before their use as drug delivery tools can be found in Table 8.2 (Borm and Kreyling 2004).
Table 8.2

Overview of test methods to explore potential hazards of nanoparticles (Borm and Kreyling 2004)

Hazard

Test system

Biomarker

Acute damage and responses after iv administration

• Red blood cells

• Hemoglobin in supernatant

• Whole blood system

• Release of inflammatory markers

Acute phase response

• Hepatocytes

• Lung cells

• Liver perfusion

• Fibrinogen

• C-reactive protein, factor VII

• Heat shock proteins

Increased permeability

• Endothelial or epithelial cell layers

• Permeability of H2O or DTPA (probe to measure permeability)

Destabilization of atheromatous plaques

• Watanabe-rabbit

• Apo-E (AplolipoproteinE)

• Plaque morphology

• CRP serum (C-reactive protein)

Effects of autonomic nervous system

• Langendorff heart vascular strips

• Altered response to endogenous mediators

Adjuvant activity

• Rat Ovalbumin sensitization

• IgE formation

Immune effects

• PLN assay (Poplithal Lymph Node assay)

• T-cells and cytokine profiles

Surface activity

• EPR (Electron Paramagnetic Resonance)

• DCFH (Dichlorofluorescine)

• Radical formation (OH, O2, H2O2)

Oxidative stress

• Alveolar macrophage

• Epithelial cell

• Isoprostane

• Radical formation (O2, H2O2)

Toxicity

• Various cell types

• Primary and lines

• LDH (lactate dehydrogenase) release

• MTT conversion dye-exclusion (dimethylthiazol-diphenyltetrazolium bromide)

Also, the ecotoxicity data on the effects of nanoparticles are essential for the suitable environmental risk evaluation. Different documents already exist which deal with emerging and newly identified health risks (Hristozov and Malsch 2009). The critical and important step in characterizing the potential safety of nanoparticles and the associated health and environmental hazards is development of a hazard outline. So a base set of hazard data has been suggested as a reference for characterization (Borm and Kreyling 2004). To characterize nanoparticles, its potential hazards and toxicity information on human health and the environment should be evaluated (Drobne et al. 2009). However, in vivo testing is required to rapidly identify hazardous substances with no available toxicity data. The TiO2 nanoparticles has a number of applications such as in water treatment, food, sensors, additive pharmaceuticals and cosmetics (Masciangioli and Zhang 2003). It had been considered biologically inert prior to studies with nanoparticles which showed that TiO2 nanoparticles activated an inflammatory response in laboratory test organisms (Drobne et al. 2009).

The extensive use of the nanoparticles brings the risk of chronic exposure to increasing levels of these compounds. Furthermore, their small size enables them to reach intracellular structures, such as under special circumstances the nucleus that are inaccessible for larger sized materials. Particle dissolution plays a critical role in hazard generation by metal and metal oxide nanoparticles and can have common effects on cell physiology with reactive oxygen species (ROS) (Soenen et al. 2015).

Another general observation is that toxicity is closely related to size and crystal structure, where nanoparticles are generally found to be more toxic than micrometer-sized materials (Beyerle et al. 2009; Soenen et al. 2015). In some cases, nanoparticles can be degraded totally by the biological processes in the environment, so their physical or chemical properties change. The mechanisms and potential for biodegradation is strongly dependent on the material properties that are still not fully understood. Most of the nanoparticles, such as ceramics and metal oxides, are not easily biodegradable (Hristozov and Malsch 2009).

The purpose of this section is to examine traditional toxicology tests. The term ‘traditional’ refers to those toxicology tests with well-established protocols that have been used in risk evaluation settings for many years. The term ‘apical’ refers to the fact that the end points evaluated in these tests may be the ultimate manifestation of a variety of different pathways of toxicity. Some participants suggested that the use of molecular technologies, including toxic genomics, may be more efficient at identifying novel mechanisms of toxicity. An additional, absorption-distribution-metabolism and excretion (ADME) method is developed. The general framework for ADME should be the same for nanoparticles, but the analytical challenges of detecting nanoparticles, as well as their by-products if they are transformed or metabolized, are significant. Some nanoparticles have special properties that make their real-time in vivo imaging straightforward. However, such imaging is not quantitative and must be confirmed by tissue analysis tests. Additionally, heavy reliance on imaging may not capture the dissolution or transformation of particles or their coatings. Nanoparticles that do not have intrinsic fluorescence or other properties that aid visualization present a greater challenge to accurately determine their ADME characteristics (Balbus et al. 2007).

8.8 Adverse Outcome Pathways (AOP)

Recently, a pathway-based view has been promoted for use in both human health and environmental toxicological risk evaluation. This approach aims to incorporate the information generated by non-traditional toxicity testing and high screening technologies based on small organism systems into the process of chemical hazard evaluation. The theory of adverse outcome pathways (AOPs) has been suggested as a framework to organize the existing knowledge on the toxicity mechanisms and outcomes across levels of biological organization for support of mechanism-based risk evaluation (Lee et al. 2015).

An AOP is an analytical, sequentially progressive pathway that links a molecular-initiating event to an adverse outcome. Recently, AOPs have been recognized as a potential informational tool by which the implications of molecular biomarkers in environmental risk assessments can be better understood (Reijnders 2006).

The AOP framework has also been suggested as a way to show how human-focused analyses can be useful in identifying key predicting effects in animal species. Effects of some of the nanoparticles could eventually lead to death, particularly in a natural environment. They are also involved in muscle contraction, memory, heart, and central neuronal activities. As mentioned earlier, ROS can lead to oxidative stress, which could result in cytotoxicity, pericardial edema, or apoptosis at the organ level. These effects could potentially lead to death of the organism (Garcia-Reyero et al. 2014). It is appropriate that research focuses on the life cycle of nanomaterials to reduce hazards. One of the ways is limiting exposure to manufactured nanoparticles resulting from production such as using precipitators for smaller particles and using magnetic filters to precipitate magnetic nanoparticles. Also in case of biodegradation, degradation products display very low toxicity (Reijnders 2006).

Toxicology of ultrafine particles has adverse health effects with the exposure to ambient. The potential advantages of nanomaterials are enormous, but they may possess potential hazards. Therefore, more attention on the risk assessment with nanomaterials is required. Nevertheless, knowledge about occurrence and toxicity of nanoparticles is still lacking. In this chapter, we have indicated what effects of nanoparticles have been found by toxicologists. We have focused on the important issue of hazard and risk evaluation for nanoparticles, which are critical conditions for studying health and the environmental impacts of nanomaterials.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Hoda Jafarizadeh-Malmiri
    • 1
  • Zahra Sayyar
    • 1
  • Navideh Anarjan
    • 2
  • Aydin Berenjian
    • 3
  1. 1.Faculty of Chemical Engineering, East AzarbaijanSahand University of TechnologyTabrizIran
  2. 2.Faculty of Chemical Engineering, East AzarbaijanIslamic Azad University Tabriz BranchTabrizIran
  3. 3.Faculty of EngineeringThe University of WaikatoHamiltonNew Zealand

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