The large and increasing use of silver nanoparticles (AgNPs) constitutes a major environmental issue. In fact, they are widely used in a number of areas, especially for pharmaceuticals and textile items from which they have been released into the environment. AgNPs are employed due to their antibacterial and biocidal characteristics. Organisms are known to be poisoned by silver. There has been an increasing number of studies focused on the toxicity of AgNPs in recent decades[1]. The antibacterial activity of SNPs is much stronger than that of its metal salt in certain applications[2]. The structure and architecture of molecules changes according on the synthesis technique, from an oval, triangular, hexane shape to a nanowire form SNP[3]. Traditional ways can synthesise SNPs, as well as an alternate method known as a biogenic or green NPs Synthesis[4]. Recently, a variety of bacterial species, fungus, algae, and plants have been employed to create clean, nontoxic, biocompatible, and ecologically friendly SNPs [5–9]. Curiously, there has been an increasing concern over potential hazardous effects coming from their use or inadvertent release into the environment as a result of an interest in nano materials' potential benefits and increased production[10]. So far, atmospheric pollution and respiratory effects in mammals or in vitro experiments with mammalian cells have been subject to a number of nanotoxicological investigations [11].

NANOSILVER

For thousands of years, silver has been recognised as a favoured metal utilised by mankind. The advancement of silver nanoparticles has been propelled by recent progress in nanoscience, which involves the study and manipulation of chemical and biological materials with dimensions between 1 nanometre and 100 nanometres. The silver nanoparticle comprises several silver atoms or ions amalgamated to create a particle measuring up to 100 nm in size. These nanoparticles has the potential to infiltrate and eradicate bacteria and other microorganisms due to their diminutive size. Silver nanoparticles, or
nanosilver, are extensively integrated into various consumer products, including textiles like socks, sportswear, pants and beds, as well as vacuums, washing machines, toys, sunscreens and numerous others (Figure-1).

Figure-1: Different sizes of nanoparticles

However, the chronic effects of this new technology on human health or the environment remain unknown. Recent research indicate that penetrated fabrics, when laundering, release silver nanoparticles into the wash cycle, thus entering wastewater systems and the environment. These nanoparticles endanger the bacteria essential for ecological processes in the environment. Certain studies have shown that nanoparticles can traverse the blood-brain barrier and infiltrate the brain.  nanosilver compositions mentioned earlier have been utilised by researchers and documented in patent literature, nevertheless they persist in the market for an extended duration. In the early 20th century, the commercial distribution of therapeutic nanoscale silver colloids, referred to by many trade names like Collargol, Argyrol, and Protargol commenced, and utilisation became prevalent over a span of 50 years.

APPLICATION OF SILVER NANOPARTICLES

In the healthcare sector, silver nanoparticles (AgNPs) have been widely utilised as antibacterial agents in food preservation, textile coating, and various environmental applications. The evidence on silver toxicity remains ambiguous despite decades of utilisation. Several recognised organisations, including the US FDA, EPA, Japan's SIAA, Korea's Testing and Research Institute for Chemical Industry, and FITI testing and research institutes, were authorised to manufacture products utilising AgNPs. Furthermore, it promoted the utilisation of AgNPs in various textile materials by the textile sector. Silver nanocomposite fibres, featuring silver nanoparticles integrated into the fabric, have been developed in this context[15]. Nanoscale sensors exhibiting accelerated response times and reduced detection thresholds have been integrated with the electrochemical characteristics of AgNPs. Manno et al. electrodeposited silver nanoparticles onto alumina plates including gold micropatterned electrodes, demonstrating significant sensitivity to hydrogen peroxide. Nanoparticles have distinct catalytic behaviour compared to the chemical characteristics of larger materials. The optical characteristics of a metallic nanoparticle primarily rely on surface plasmon resonance, wherein free electron oscillations, denoted as Plasmon, transpire into the metal nanomaterial. The dimensions and morphology of the nanoparticle, the metallic species, and the surrounding medium are recognised to influence the Plasmon resonant peaks and linewidths. A novel form of optical data storage may utilise nanoclusters consisting of two to eight silver atoms. Moreover, biolabels and electroluminescent displays may utilise fluorescence emissions from clusters[17]. Nanotechnology is advancing swiftly by generating nanoproducts and nanoparticles (NPs) that exhibit unique and size-dependent physico-chemical properties, markedly distinct from those of bigger materials. The innovative features of these nanoparticles have been utilised in several applications, including pharmaceuticals, cosmetics, renewable energy, environmental remediation, and biomedical devices. Ag-NPs possess distinct physicochemical features, including strong electrical and thermal conductivity, enhanced surface Raman scattering, chemical stability, catalytic activity, and nonlinear optical behaviour. These attributes render them potentially valuable in inks, microelectronics, and medical imaging. Moreover, AgNPs have extensive bactericidal and fungicidal properties, rendering them highly sought after in numerous consumer products, including plastics, soaps, pastes, food, and textiles, hence enhancing their market value.

ANTI-MICROBIAL USE OF SILVER NANOPARTICLES

Single nucleotide polymorphisms (SNPs) are extensively utilised in cosmetic and hygiene products due to their potent antibacterial effects [21,22]. Conversely, materials containing silver may be utilised for bacterial eradication. Despite their prevalent application, the mechanism of action of nanoNPs as bactericides in aqueous solutions and solid media remains poorly understood. The emission of silver ions from the nanostructured surface induces antibacterial activity. Silver nanoparticles (AgNPs) have demonstrated efficacy as a biocide against a wide range of bacteria, including both gram-negative and gram-positive species, many of which are highly hazardous. The capacity of NPs to modify cellular permeability and generate reactive oxygen species correlates with their antibacterial efficacy.[26,27]. The antibacterial efficacy of SNPs extends beyond bacteria and fungi, since they are also efficient against other species, including viruses. Silver fungicides can effectively dismantle fungal cell walls and membranes. Colloidal solutions of silver nanoparticles (SNPs) directly adhered to solid surfaces impede the proliferation of highly multidrug-resistant bacteria, including Staphylococcus aureus, Escherichia coli, Vibrio cholera, and Pseudomonas aeruginosa [33-36]. Research indicates that silver-doped titania nanoparticles are extremely efficacious against Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and E. coli bacteria. The wound dressing SNP is commercially available and is generally considered safe for human health. The antibacterial efficacy of silver nanoparticles (SNPs) against the oral pathogen Streptococcus mutans was examined and the findings were juxtaposed with those of the dental disinfectant chlorhexidine. The results indicate that the SNPs are more efficacious than chlorhexidine[40].

EFFECTS OF SILVER NANOPARTICLES ON HUMAN

Air, water, and soil are reacting with nanoparticles released into the environment. This alters the surface features of particles, perhaps resulting in aggregation or modifications in particle charge and other surface attributes. To comprehend particle behaviour in the environment, these effects have been examined in aquatic ecosystems and soil, revealing that the study of nanoparticles and their environments is a complicated endeavour that requires exploration at all levels. To comprehend particle behaviour in the environment, these effects have been examined in aquatic ecosystems and soil, revealing that nanoparticles and their environments constitute a complex that must be investigated at all levels. The ongoing discussion is on the potential toxicity of nanomaterials, which may act as contaminants by hitching a ride on natural organic matter in environments such as soil or water. The degree of exposure for workers involved in nanomaterial manufacturing, certain demographic groups, or the general public must be delineated for nanoparticles manufactured on a wide scale. Several nanomaterials presently belong to this category: silicon dioxide, zinc oxide, silver, titanium dioxide, carbon nanotubes, and cerium dioxide. Research indicates that to comprehend and anticipate toxicological effects at the in vivo level, it is essential to focus on coating and surface features, in addition to the inherent nanotoxicological potential of the naked particle. To ascertain the entry pathways and susceptibility, research indicates that nanoparticles can infiltrate the body through the airways, dermal contact, or ingesting routes[45,46] (refer to Figure-2). The respiratory system serves as the principal pathway for airborne particulate matter to enter the body. Extensive data on ultrafine particles (such as dust, carbon black, and other pollutants) and their impact on the airways and lungs is accessible. Endocytosis of alveolar cells is the primary route for the transport of nanoparticles. From a neurotoxicological perspective, this might be potentially detrimental, as particles would get direct access to the central nervous system through this pathway. The skin is an additional potential pathway for human exposure. Titanium dioxide nanoparticles are commonly utilised in sunscreen formulations and may be absorbed by hair follicles or skin lesions. Given the rising utilisation of nanoparticles as food additives or in food production and packaging, there is apprehension regarding their potential entry into the bloodstream through gastrointestinal absorption. Research has demonstrated that nanoparticle absorption through the gastrointestinal tract is feasible and seems to depend on size. However, further research is essential to enhance understanding of the gastrointestinal absorption of nutrients. Nonetheless, the most concerning factor is that when nanoparticles infiltrate the body and enter the bloodstream, they may gain access to additional organs.

Figure 2: Entry of Nanoparticles in to the body mainly via the airways, the skin or via ingestion.

TOXICITY OF SILVER NANOPARTICLES

Knowledge on the toxicity of these minute chemicals is limited, however their impacts are becoming evident. Certain nanoparticles have demonstrated toxicity within biological systems in multiple investigations. Consequently, it is imperative to undertake study in both the internal and external environments; external analyses may inform the inside investigations. Certain researchers have demonstrated that the majority of nanoparticles can emit reactive oxygen species, leading to oxidative stress and inflammation via the reticuloendothelial system (RES). Acute toxicity induced by nanoparticles has been examined in the oral cavities of rats. The findings indicate that nanoparticle toxicity is contingent upon their size, coating, and chemical composition. Moreover, various organs and tissues have demonstrated susceptibility to the structural effects of nanoparticles. Oxidative stress or preinflammatory cytotoxin activity in the lungs, liver, heart, and brain may correlate with impacts on inflammatory and immunological systems. Prethrombosis and paradoxical effects on cardiac activity may potentially influence the circulatory system. Nanoparticles may induce genotoxicity, carcinogenicity, and teratogenicity. Certain nanoparticles may penetrate the blood-brain barrier and induce neurotoxicity; further research is required. Occupational studies are quite few, and in a limited number of investigations, workers have been subjected to low concentrations of SNPs below the threshold limit values for brief durations[53-55]. Consequently, dependable epidemiological and ecotoxicological research is essential to address this information deficiency. Several physical parameters, like as size, chemical composition, surface area, reactivity, charge, and aggregation propensity, are linked to the toxicity of SNPCs. Smaller particles are recognised as more harmful than larger ones; however, particle size alone does not dictate nanoparticle toxicity. The presence of a substantial quantity of nanoparticles in circulation will enhance macromolecule absorption, facilitating their passage through the intestinal system. Lectin serves as an immunologic agent for coating, perhaps leading to immunosuppression, inflammatory responses, or digestive stimulation. Potential toxicity continues to be a worry with the application of Silver Nanoparticles in various clinical conditions. Hypersensitivity reactions have been seen in a minor percentage of burn victims treated with ionic silver. Silver nanoparticle wound dressings have been utilised in clinical settings for several years, with no reports of systemic toxicity reported from the FDA. The utilisation of silver nanoparticles at low concentrations seems to be safe.

CONCLUSION

In recent years, nanotechnology has advanced significantly and permeated all scientific disciplines, including medicine. Among several types of nanoparticles, silver nanoparticles (Ag NPs) have garnered the most interest about their prospective applications. Silver nanoparticles (AgNPs) are among the most appealing nanomaterials for commercial uses. Antimicrobials, electrical, and medicinal devices have seen extensive utilisation. AgNPs are among the most appealing nanomaterials for commercial applications. This review offers a thorough examination of AgNPs, focusing on synthesis methods, antibacterial properties, and potential toxicological implications of an AgNP. Progress in nanotechnology has enabled the utilisation of particles measuring only nanometres. In vitro toxicity assessments involving particles sized between 1 and 100 nm are predominantly conducted for SNPs. Short-term research exist within the animal population. Nevertheless, there is limited study about the impact of single nucleotide polymorphisms on human health. Subchronic dermal exposure may result in substantial buildup of SNPs in the liver and lungs. Available animal findings indicate that SNPs induce histological abnormalities in the spleen, liver, and skin. The data unequivocally indicate that the target organs of SNP poisoning include muscles. In certain tissues, colloidal SNPs seem to elicit a harmful reaction that is contingent upon the dosage frequency. Ultimately, to more accurately assess the health risks associated with SNPs, there is a scarcity of rigorously controlled human research on their potential toxicity, necessitating further long-term investigations across a broad spectrum of dosages, ideally incorporating various particle sizes. It is strongly advised to ascertain the influence of shape and particle size in this context. The toxicity profile of the SNPs will be evaluated depending on various routes of administration in future research.

REFERENCES

1.      Nowack B, and Bucheli TD. “Occurrence, behavior and effects of nanoparticles in the environment.” Environ Pollut 150 (2007): 5–22.

2.      Besinis A, De Peralta T, Handy RD. Inhibition of biofilm formation and antibacterial properties of a silver nano-coating on human dentine. Nanotoxicology 2014;8:745–54.

3.      Panigrahi S, Kundu S, Ghosh S, Nath S, Pal T. General method of synthesis for metal nanoparticles. J Nanopart Res 2004;6:411–4.

4.      Bansal V, Bharde A, Ramanathan R, Bhargava SK. Inorganic materials using ‘unusual’ microorganisms. Adv Colloid Interface Sci 2012;179–182:150–68.

5.      Bai HJ, Yang BS, Chai CJ, Yang GE, Jia WL, Yi ZB. Green synthesis of silver nanoparticles using Rhodobacter Sphaeroides. World J Microb Biotech 2011;27:2723–8.

6.      Kumar CG, Mamidyala SK. Extracellular synthesis of silver nanoparticles using culture supernatant of Pseudomonas aeruginosa. Colloids Surf B Biointerfaces 2011;84:462–6.

7.      Soni N, Prakash S. Fungal-mediated nano silver: an effective adulticide against mosquito. Parasitol Res 2012;111:2091–8.

8.      Barwal I, Ranjan P, Kateriya S, Yadav SC. Cellular oxido-reductive proteins of Chlamydomonas reinhardtii control the biosynthesis of silver nanoparticles. J Nanobiotechnology 2011;9:56.

9.      Antony JJ, Sivalingam P, Siva D, Kamalakkannan S, Anbarasu K, Sukirtha R, et al. Comparative evaluation of antibacterial activity of silver nanoparticles synthesized using Rhizophora apiculata and glucose. Colloids Surf B Biointerfaces 2011;88:134–40.

10.   Bernd Nowack, Harald F Krug, and Murray Height. “120 Years of Nanosilver History: Implications for Policy Makers.” Environ Sci Technol 45 .4 (2011): 1177–1183.

11.   Lewinski N, Colvin V, and Drezek R. “Cytotoxicity of Nanoparticles.” Small 4 (2008): 26–49.

12.   Handy RD, Von der Kammer F, JR Lead, M Hassellov, R Owen, and M Crane. “The ecotoxicology and chemistry of manufactured nanoparticles.” Ecotoxicology 17 (2008): 287–314

13.   Lewinski N, Colvin V, and Drezek R. “Cytotoxicity of Nanoparticles.” Small 4 (2008): 26–49.

14.   Jia X, Maa X, Wei D, Dong J, and Qian W. “Direct Formation of Silver Nanoparticles in Cuttlebone Derived Organic Matrix for Catalytic Applications.” Coll Surf A Phys Cochem Aspects 330 (2008): 234.

15.   Sang Young Yeo, Hoon Joo Lee, and Sung Hoon Jeong. “Preparation of nanocomposite fibers for permanent antibacterial effect.” J Mat Sci 38.10 (2003): 2143-2147.

16.   Manno D, Filippo E, Giulio Di M, and Serra A. “Synthesis and characterization of starch- stabilized Ag nanostructures for sensors applications.” Journal of Non-Crystalline Solids 354.52–54.15 (2008): 5515–5520.

17.   Berciaud S, Cognet L, Tamarat P, and Lounis B. Observation of intrinsic size effects in the optical response of individual gold nanoparticles.” Nano Lett 5. 3 (2005):515-8.

18.   Torreggiani A, Jurasekova A, D’Angelantonio M, Tamba M, GarciaRamos JV and Sanchez-Cortes S. “Colloids and Surfaces A: Physicochemical and Engineering Aspects.” Colloids and Surfaces A Physicochemical and Engineering Aspects 3391–3 (2009): 1-246, A 339 60.

19.   Lee Y, Choi JR, Lee KJ, Stott NE, and Kim D. “Large-scale synthesis of copper nanoparticles by chemically controlled reduction for applications of inkjet-printed electronics.” Nanotechnology 1519.41 (2008): 415604.

20.   Dongjo Kim, Sunho Jeong, and Jooho Moon. “Synthesis of silver nanoparticles using the polyol process and the influence of precursor injection.” Nanotechnology 17 (2006):4019–4024.

21.   Wilkinson LJ, White RJ, Chipman JK. Silver and nanoparticles of silver in wound dressings: a review of efficacy and safety. J Wound Care 2011;20:543–9.

22.   Edwards-Jones V. The benefits of silver in hygiene, personal care and healthcare. Lett Appl Microbiol 2009;49:147–52.

23.   Hebeish A, El-Rafie MH, El-Sheikh MA, Seleem AA, El-Naggar ME. Antimicrobial wound dressing and anti-inflammatory efficacy of silver nanoparticles. Int J Biol Macromol 2014;65:509–15.

24.   Kim JS, Kuk E, Yu KN, Kim JH, Park SJ, Lee HJ, et al. Antimicrobial effects of silver nanoparticles. Nanomedicine 2007;3:95–101.

25.   Chernousova S, Epple M. Silver as antibacterial agent: ion, nanoparticle, and metal. Angew Chem Int Ed Engl 2013;52:1636–53

26.   Zhang W, Qiao X, Chen J, and Wang H. “Preparation of silver nanoparticles in water-in- oil AOT reverse micelles.” J Colloid Interface Sci Oct 1. 302. 1 (2006):370-3.

27.   Jin X, Li M, Wang J, Marambio-Jones C, Peng F, Huang X, et al. High-throughput screening of silver nanoparticle stability and bacterial inactivation in aquatic media: influence of specific ions. Environ Sci Technol 2010;44:7321–8.

28.   Zodrow K, Brunet L, Mahendra S, Li D, Zhang A, Li Q, et al. Polysulfone ultrafiltration membranes impregnated with silver nanoparticles show improved biofouling resistance and virus removal. Water Res 2009;43:715–23.

29.   Lamsal K, Kim SW, Jung JH, Kim YS, Kim KS, Lee YS. Application of silver nanoparticles for the control of colletotrichum species in vitro and pepper anthracnose disease in field. Mycobiology 2011;39:194–9.

30.   Hwang IS, Lee J, Hwang JH, Kim KJ, Lee DG. Silver nanoparticles induce apoptotic cell death in Candida albicans through the increase of hydroxyl radicals. FEBS J 2012;279:1327–38.

31.   Kim SW, Jung JH, Lamsal K, Kim YS, Min JS, Lee YS. Antifungal Effects of Silver Nanoparticles (AgNPs) against Various Plant Pathogenic Fungi. Mycobiology 2012;40:53–8.

32.   Nam KY, Lee CH, Lee CJ. Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles. Gerodontology 2012;29:e413–9.

33.   Morones JR, Elechiguerra JL, Camacho A, Holt K, Kouri JB, Ramírez JT, et al. The bactericidal effect of silver nanoparticles. Nanotechnology 2005;16:2346–53.

34.   Mukha Iu P, Eremenko AM, Smirnova NP, Mikhienkova AI, Korchak GI, Gorchev VF, et al. Antimicrobial activity of stable silver nanoparticles of a certain size. Prikl Biokhim Mikrobiol 2013;49:215–23

35.   Pokrowiecki R, Zareba T, Mielczarek A, Opalińska A, Wojnarowicz J, Majkowski M, et al. Evaluation of biocidal properties of silver nanoparticles against cariogenic bacteria. Med Dosw Mikrobiol 2013;65:197–206.

36.   Priester JH, Singhal A, Wu B, Stucky GD, Holden PA. Integrated approach to evaluating the toxicity of novel cysteine-capped silver nanoparticles to Escherichia coli and Pseudomonas aeruginosa. Analyst 2014;139:954–63.

37.   Shahverdi AR, Fakhimi A, Shahverdi HR, Minaian S. Synthesis and effect of silver nanoparticles on the antibacterial activity of different antibiotics against Staphylococcus aureus and Escherichia coli. Nanomedicine 2007;3:168–71.

38.   Thiel J, Pakstis L, Buzby S, Raffi M, Ni C, Pochan DJ, et al. Antibacterial properties of silver-doped titania. Small 2007;3:799–803.

39.   Wilkinson LJ, White RJ, Chipman JK. Silver and nanoparticles of silver in wound dressings: a review of efficacy and safety. J Wound Care 2011;20:543–9.

40.   Besinis A, De Peralta T, Handy RD. The antibacterial effects of silver, titanium dioxide and silica dioxide nanoparticles compared to the dental disinfectant chlorhexidine on Streptococcus mutans using a suite of bioassays. Nanotoxicology 2014;8:1–16.

41.   Yacob NR, Malmstadt N, Fazlollahi F, DeMaio L, Marchelletta R, Hamm-Alvarez SF, Borok Z, Kim KJ, and Crandall ED. “Mechanisms of alveolar epithelial translocation of a defined population of nanoparticles.” Am J Respir Cell Mol Biol 42 (2010): 604–614.

42.   Aitken RJ, Chaudhry MQ, Boxall AB, and Hull M. “Manufacture and use of nanomaterials: current status in the UK and global trends.” Occup Med (Lond) 56 (2006): 300–306.

43.   Aitken RJ, Chaudhry MQ, Boxall AB, and Hull M. “Manufacture and use of nanomaterials: current status in the UK and global trends.” Occup Med (Lond) 56 (2006): 300–306.

44.   Oberdorster G. “Safety Assessment for Nanotechnology and Nanomedicine: concepts of Nanotoxicology.” Intern Med 267 (2010): 89–105.

45.   Stern ST, and McNeil SE. “Nanotechnology safety concerns revisited.” Toxicol Sci 101 (2008): 4–21.

46.   Sperling RA, Rivera Gil P, Zhang F, Zanella M, and Parak WJ. “Biological applications of gold nanoparticles.” Chem Soc Rev 37 (2008): 1896–1908.

47.   Bennett WD. “Rapid translocation of nanoparticles from the lung to the bloodstream?” Am J Respir Crit Care Med 165 (2002): 1671–1672.

48.   Greulich C, Diendorf J, Simon T, Eggeler G, Epple M, and Koller M. “Uptake and intracellular distribution of silver nanoparticles in human mesenchymal stem cells.”Acta Biomater 7 (2011): 347–354.

49.   Crosera M, Bovenzi M, Maina G, Adami G, Zanette C, Florio C, and Filon Larese F. “Nanoparticle dermal absorption and toxicity: a review of the literature.” Int Arch Occup Environ Health 82 (2009): 1043–1055.

50.   Hagens WI, Oomen AG, de Jong WH, Cassee FR, and Sips AJAM. “What do we (need to) know about the kinetic properties of nanoparticles in the body?.” Regul Toxicol Pharmacol 49 (2007): 217– 229.

51.   Tse C, Zohdy MJ, Ye JY, O'Donnell M, Lesniak W, and Balogh L. “Enhanced optical breakdown in KB cells labeled with folatetargeted silver-dendrimer composite nanodevices. Nanomedicine.” Nanotechnology Biology and Medicine 7.1 (2011): 97-

106.

52.   Unrine JM, Tsyusko OV, Hunyadi SE, Judy JD and Bertsch PM “Effect of particle size on chemical speciation and bioavailability of copper to earthworms (Eisenia fetida) exposed to copper nanoparticles.” J Env Qual 39 (2010): 1942–53.

53.   Lee JH, Mun J, Park JD, Yu IJ. A health surveillance case study on workers who manufacture silver nanomaterials. Nanotoxicology 2012;6:667–9.

54.   Drake PL, Hazelwood KJ. Exposure-related health effects of silver and silver compounds: a review. Ann Occup Hyg 2005;49:575–85.

55.   Lamberti M, Zappavigna S, Sannolo N, Porto S, Caraglia M. Advantages and risks of nanotechnologies in cancer patients and occupationally exposed workers. Expert Opin Drug Deliv 2014;11:1087–101.

56.   Brown DM, Wilson MR, MacNee W, Stone V, Donaldson K. Size-dependent proinflammatory effects of ultrafine polystyrene particles: a role for surface area and oxidative stress in the enhanced activity of ultrafines. Toxicol Appl Pharmacol 2001;175:191–9.

57.   Duffin R, Tran L, Brown D, Stone V, Donaldson K. Proinflammogenic effects of low- toxicity and metal nanoparticles in vivo and in vitro: highlighting the role of particle surface area and surface reactivity. Inhal Toxicol 2007;19:849–56.

58.   Xiong Y, Brunson M, Huh J, Huang A, Coster A, Wendt K, et al. The role of surface chemistry on the toxicity of Ag nanoparticles. Small 2013;9:2628–38.

59.   Wang X, Ji Z, Chang CH, Zhang H, Wang M, Wang M, et al. Use of coated silver nanoparticles to understand the relationship of particle dissolution and bioavailability to cell and lung toxicological potential. Small 2014;10:385–98.

60.   Hill G T, Mitkowski NA, Aldrich-Wolfe L, Emele LR and Jurkonie DD. “Methods for assessing the composition and diversity of soil microbial communities.” Appl Soil Ecol 15 (2000): 25–36.

61.   Muhlfeld C, Gehr P, and Rothen-Rutishauser B. “Translocation and cellular entering mechanisms of nanoparticles in the respiratory tract.” Swiss Med Wkly 138 (2008):387– 39.

62.   Rutishauser R, Muhlfeld C, Blank F, Musso C, and Gehr P. “Translocation of particles and inflammatory responses after exposure to ine particles and nanoparticles in an epithelial air-way model.” Part Fibre Toxicol 4 (2007):9–15.

63.   Nel A, Xia T, Madler L, and Li N. “Toxic Potential of Materials at the Nano level.” Sci 311 (2006):622–627