particle shape, aspect ratio, chemical composition, hydrophilicity and hydrophobicity, surface coating, surface roughness, aggregation and concentration, degradability
Figure 1.3 Consequences of environmental contact of nanoparticles.
Nanoecotoxicology is a subdiscipline of ecotoxicology that is primarily designed to define and forecast the impact of nano‐sized materials on ecosystems. The quantitative risk assessment of NPs is inadequate owing to unsatisfactory research on the toxicity of nanomaterials to environmentally important organisms. It is indistinct that the structure, aspect ratio, morphology, and various other physicochemical properties have a greater impact on toxicity (Klaine et al. 2008). It must be mandatory to evaluate the NPs for their possible hazard to the environment before their use in products (Oberdörster et al. 2009; Viswanath and Kim 2016; Gaur et al. 2020). To accomplish this aim, to identify exposure, nanoecotoxicology requires taking into account the entry routes and consequences of environmental contact of NPs as shown in Figure 1.3.
Numerous critical toxic characteristics are closely associated with the nano‐size/surface area of the nanomaterials. These include surface properties, physical absorption potential, chemical reactivity, and so on, all of which strongly dominate in vivo nanotoxicological behavior (Fubini et al. 2010). NPs and their biologics, such as proteins, peptides, antibody fragments, and nucleic acids, can act as bases of antigens that can induce an immune response. Its immunogenicity can be influenced by the physicochemical properties of NPs, such as size, surface area, surface charge, hydrophobicity, and solubility. An exceptional type of toxicity owing to surface modification is of distinct apprehension. The capacity for inflammatory activity and oxidative stress is shown to be largely dependent on NPs’ surface chemistry and surface modifications (Azarnezhad et al. 2020). NPs’ toxicity also strongly depends on their shape and chemical composition. Spherical NPs are more susceptible to endocytosis than nanotubes and nanofibers. The calcium channels are commendably blocked by single‐walled carbon nanotubes than spherical fullerenes. The degradation of NPs has been shown to occur, and its magnitude depends on the conditions of the environment, such as pH or ionic strength. The toxicity also relies on the composition of the NPs’ core. Leaking metal ions from the NPs’ core is the most common source of the toxic impact of NPs reacting with cells. Indeed, the toxicity of NPs is determined to a large degree by their chemical composition (Gatoo et al. 2014; Viswanath and Kim 2016).
It has been reported that AuNPs possibly move through a mother's placenta to the fetus. During the neonatal phase, these NPs can act as allergens, activating the immune system. NPs can communicate with diverse immune cell networks found inside and under epithelial surfaces. The proficient gastrointestinal tract uptake of NPs also been well recorded in oral feeding and forced feeding studies. Despite the clinical approval, the dermal toxicity of nanosilver‐based surgical dressings and sutures is yet a matter of concern (El‐Ansary and Al‐Daihan 2009). While beneficial control of wound infection is accomplished, their dermal toxicity is even of concern. In epidemiological trials, adverse cardiovascular effects attributable to exposure to NPs have been identified (De Jong and Borm 2008). Oxidative damage to DNA is exhibited by the titanium dioxide and zinc oxide NPs in in vitro tests and cultured human fibroblasts. Nano‐sized particles inhaled can increase bloodstream access and can then be spread to other organs. There is a good likelihood that, via the lungs, skin, and gastrointestinal tract, NPs may be assimilated into the bloodstream. Besides, fluids representing the liver, blood, and airway environment are exploited to conduct experiments concerning the dissolution of NPs in artificial body fluids and classify harmful influences. NPs also have access to the brain, exhibiting toxic effects on BBB, especially high concentrations of anionic and cationic NPs, although, neutral NPs and low concentrations of anionic NPs were found not to affect the integrity of BBB (Teleanu et al. 2019). The development of reactive oxygen species and oxidative stress are caused by NPs. Further, these have shown to be involved in the development of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases (Armstead and Li 2016).
The dominant role of protein–nanoparticle interactions has begun to appear in nanomedicine and nanotoxicity. The “corona” nanoparticle protein is a dynamic coating of proteins and other biomolecules that adsorbs to the surfaces of the nanoparticle (Dickinson et al. 2019). Protein corona is a nanoparticle's biological identity since it is what the cell “sees and communicates.” At any given time, the structure of the corona protein can be determined by the concentrations of over 3700 plasma proteins. When exposed to a biological fluid, this corona may not achieve equilibrium automatically. The nanoparticle surface would initially be dominated by proteins with high concentrations and elevated interaction rate constants. They can also easily dissociate to be swapped by reduced concentration, leisurely exchange, and greater affinity proteins. Small NPs may cause protein malfunction, with their wide surface area as a binding interface, which may lead to pathogenesis and adverse health effects (Sukhanova et al. 2018; Singh et al. 2019).
There are two standard approaches adopted to study NPs’ toxic effects on human health: in vitro studies on model cell lines and in vivo experiments on experimental animals. There are unique benefits and drawbacks of both cell culture and animal laboratory models for testing NP toxicity (Osman et al. 2020). The former offers a deeper insight into the molecular processes of toxicity and describes the key targets of NPs; however, it does not take into account the patterns of the delivery of NPs in the body and their transfer to various tissues and cells (Guadagnini et al. 2015). The study of NP toxicity in animal laboratories makes it possible to predict the delayed effects of in vivo NPs action. The general pattern of manifestations of toxicity, however, is so complex that it is difficult to establish which of them is the major cause of the result observed and which are the effects thereof. The long‐term consequences of prolonged exposure to these NPs in humans must be analyzed. For all of the therapeutic NPs, methods must be built for detecting NPs in situ. Biotransformation of therapeutic NPs in the human body, their association with biological processes, and adsorption, delivery, digestion, transformation, degradation, and excretion in living systems should be studied by the characterization of NPs in terms of distribution of size, surface properties, persistence, and stabilization of initial and modified NPs (Zhao and Castranova 2011; Dickinson et al. 2019).
The latest toxicological approaches utilized for the detection of NP hazards are based on conventional toxicology approaches or complementary techniques. These tools for safety assessment of the rapidly budding list of nanomaterials have innate restrictions. There is a rising demand for strategies that could be adopted for screening by industries during the advancement of nanoproducts. These products may have to be handled on a case‐by‐case basis and require costly evaluations. Usually, acute and chronic toxicity is assessed in the pharmaceutical industry. The acute toxicity incorporates mitochondrial activity hemolysis, oxidative stress, inflammation, or complement activation. The chronic toxicity investigation is arduous, and it is more perplexing to scrutinize the results (Zhao
