Health implications of engineered nanomaterials

With the development of nanotechnology, a growing number of people are expected to be exposed to its products, the engineered nanomaterials (ENMs). Some physico-chemical properties of ENMs, linked to their size in the nanoscale (1-100 nm), make them potentially more reactive, and therefore raise concern about possible adverse effects in humans. In this article, I discuss human diseases which may be predicted after exposure to ENMs, and how their pathogenetic mechanisms may be linked to exposure; in this regard, special emphasis has been given to the triad of oxidative stress/inflammation/genotoxicity and to the interaction of ENMs/proteins in different biological compartments. The analysis of possible adverse effects has been made on an organ-by-organ basis, starting from the skin, respiratory system and gastrointestinal tract. These sites are in fact not only those exposed to the highest amounts of ENMs, but are also the portals of entry to internal organs for possible systemic effects. Although the list and the relevance of possible human disorders linked to ENM exposure are at least as impressive as that of their direct or indirect beneficial effects for human health, we must be clear that ENM-linked diseases belong to the realm of possible risk (i.e. cannot be excluded, but are unlikely), whereas ENMs with proven beneficial effects are on the market. Therefore, the mandatory awareness about possible adverse effects of ENMs should in no way be interpreted as a motivation to disregard the great opportunity represented by nanotechnology.     

A living cell quartz crystal microbalance biosensor for continuous monitoring of cytotoxic responses of macrophages to single-walled carbon nanotubes

Background  

Numerous engineered nanomaterials (ENMs) exist and new ENMs are being developed. A challenge to nanotoxicology and environmental health and safety is evaluating toxicity of ENMs before they become widely utilized. Cellular assays remain the predominant test platform yet these methods are limited by using discrete time endpoints and reliance on organic dyes, vulnerable to interference from ENMs. Label-free, continuous, rapid response systems with biologically meaningful endpoints are needed. We have developed a device to detect and monitor in real time responses of living cells to ENMs. The device, a living cell quartz crystal microbalance biosensor (QCMB), uses macrophages adherent to a quartz crystal. The communal response of macrophages to treatments is monitored continuously as changes in crystal oscillation frequency (Δf). We report the ability of this QCMB to distinguish benign from toxic exposures and reveal unique kinetic information about cellular responses to varying doses of single-walled carbon nanotubes (SWCNTs).     

Ecotoxicology of carbon-based engineered nanoparticles: Effects of fullerene (C60) on aquatic organisms

To more fully assess the toxicity of water-soluble fullerene (nC₆₀), acute toxicity assays were performed on several environmentally relevant species. Included were the freshwater crustaceans Daphnia magna and Hyalella azteca, and a marine harpacticoid copepod, and two fish species, fathead minnow Pimephales promelas and Japanese medaka Oryzias latipes. The latter two species were used to assess sublethal effects of fullerene exposure by also assessing mRNA and protein expression in liver. Because prior studies found that both sonication and using tetrahydrofuran to solubilize fullerene increased the toxicity of nC₆₀, the nC₆₀ used in this study was prepared by stirring. For the invertebrate studies, nC₆₀ could not be prepared at high enough concentration levels to cause 50% mortality (LC₅₀) at 48 or 96 h. The maximum concentrations tested were 35 ppm for freshwater and 22.5 ppm for full-strength (35 ppt) seawater, since at higher concentrations the nC₆₀ precipitated out of solution. Daphnia 21-day exposures resulted in a significant delay in molting and significantly reduced offspring production at 2.5 and 5 ppm nC₆₀, which could possibly produce impacts at the population-level. For the fish, we found that neither the mRNA nor protein-expression levels of cytochrome P450 isozymes CYP1A, CYP2K1 and CYP2M1 were changed. The peroxisomal lipid transport protein PMP70 was significantly reduced in fathead minnow, but not medaka, indicating potential changes in acyl-CoA pathways.     

The Cellular and Molecular Carcinogenic Effects of Radon Exposure: A Review

Radon-222 is a naturally occurring radioactive gas that is responsible for approximately half of the human annual background radiation exposure globally. Chronic exposure to radon and its decay products is estimated to be the second leading cause of lung cancer behind smoking, and links to other forms of neoplasms have been postulated. Ionizing radiation emitted during the radioactive decay of radon and its progeny can induce a variety of cytogenetic effects that can be biologically damaging and result in an increased risk of carcinogenesis. Suggested effects produced as a result of alpha particle exposure from radon include mutations, chromosome aberrations, generation of reactive oxygen species, modification of the cell cycle, up or down regulation of cytokines and the increased production of proteins associated with cell-cycle regulation and carcinogenesis. A number of potential biomarkers of exposure, including translocations at codon 249 of TP53 in addition to HPRT mutations, have been suggested although, in conclusion, the evidence for such hotspots is insufficient. There is also substantial evidence of bystander effects, which may provide complications when calculating risk estimates as a result of exposure, particularly at low doses where cellular responses often appear to deviate from the linear, no-threshold hypothesis. At low doses, effects may also be dependent on cellular conditions as opposed to dose. The cellular and molecular carcinogenic effects of radon exposure have been observed to be both numerous and complex and the elevated chronic exposure of man may therefore pose a significant public health risk that may extend beyond the association with lung carcinogenesis.     

Biolytic Effect of Rhamnolipid Biosurfactant and Dodecyl Sulfate Against Phagotrophic Alga <Emphasis Type="Italic">Ochromonas danica</Emphasis>

Surfactants can affect biological activities and pose serious threats to the aquatic ecosystem if discharged without proper treatment. Rhamnolipid is a biosurfactant with promising agricultural, industrial and biomedical applications. It is important to assess the risks posed by rhamnolipid before it is adopted for large scale use. In this study, toxicity of rhamnolipid was estimated with the effects of motility loss, membrane permeability, and cell lysis using a phagotrophic alga Ochromonas danica. O. danica is a sensitive algal species without a protective cell wall and it represents a group of phagotrophic flagellates ecologically important in the aquatic ecosystem. A common synthetic surfactant, sodium dodecyl sulfate (SDS), was used for comparison. Results suggested that rhamnolipid is significantly less biolytic than SDS and the effects required longer exposure. Lysis of O. danica cells by rhamnolipid was serious only at concentrations over its critical micelle concentration. Motility loss was, however, significantly more sensitive; about 75% loss after 20 min exposure to 50 mg/L rhamnolipid.     

The potential risks of nanomaterials: a review carried out for ECETOC

During the last few years, research on toxicologically relevant properties of engineered nanoparticles has increased tremendously. A number of international research projects and additional activities are ongoing in the EU and the US, nourishing the expectation that more relevant technical and toxicological data will be published. Their widespread use allows for potential exposure to engineered nanoparticles during the whole lifecycle of a variety of products. When looking at possible exposure routes for manufactured Nanoparticles, inhalation, dermal and oral exposure are the most obvious, depending on the type of product in which Nanoparticles are used. This review shows that (1) Nanoparticles can deposit in the respiratory tract after inhalation. For a number of nanoparticles, oxidative stress-related inflammatory reactions have been observed. Tumour-related effects have only been observed in rats, and might be related to overload conditions. There are also a few reports that indicate uptake of nanoparticles in the brain via the olfactory epithelium. Nanoparticle translocation into the systemic circulation may occur after inhalation but conflicting evidence is present on the extent of translocation. These findings urge the need for additional studies to further elucidate these findings and to characterize the physiological impact. (2) There is currently little evidence from skin penetration studies that dermal applications of metal oxide nanoparticles used in sunscreens lead to systemic exposure. However, the question has been raised whether the usual testing with healthy, intact skin will be sufficient. (3) Uptake of nanoparticles in the gastrointestinal tract after oral uptake is a known phenomenon, of which use is intentionally made in the design of food and pharmacological components. Finally, this review indicates that only few specific nanoparticles have been investigated in a limited number of test systems and extrapolation of this data to other materials is not possible. Air pollution studies have generated indirect evidence for the role of combustion derived nanoparticles (CDNP) in driving adverse health effects in susceptible groups. Experimental studies with some bulk nanoparticles (carbon black, titanium dioxide, iron oxides) that have been used for decades suggest various adverse effects. However, engineered nanomaterials with new chemical and physical properties are being produced constantly and the toxicity of these is unknown. Therefore, despite the existing database on nanoparticles, no blanket statements about human toxicity can be given at this time. In addition, limited ecotoxicological data for nanomaterials precludes a systematic assessment of the impact of Nanoparticles on ecosystems.     

Identification,Phylogeny, and Comparative Expression of the Lipoxygenase Gene Family of the Aquatic Duckweed,Spirodela polyrhiza,during Growth and in Response to Methyl Jasmonate and Salt

Lipoxygenases (LOXs) (EC 1.13.11.12) catalyze the oxygenation of fatty acids and produce oxylipins, including the plant hormone jasmonic acid (JA) and its methyl ester, methyl jasmonate (MeJA). Little information is available about the LOX gene family in aquatic plants. We identified a novel LOX gene family comprising nine LOX genes in the aquatic plant Spirodela polyrhiza (greater duckweed). The reduced anatomy of S. polyrhiza did not lead to a reduction in LOX family genes. The 13-LOX subfamily, with seven genes, predominates, while the 9-LOX subfamily is reduced to two genes, an opposite trend from known LOX families of other plant species. As the 13-LOX subfamily is associated with the synthesis of JA/MeJA, its predominance in the Spirodela genome raises the possibility of a higher requirement for the hormone in the aquatic plant. JA-/MeJA-based feedback regulation during culture aging as well as the induction of LOX gene family members within 6 h of salt exposure are demonstrated.     

Inhalation of Silver Nanomaterials—Seeing the Risks

Demand for silver engineered nanomaterials (ENMs) is increasing rapidly in optoelectronic and in health and medical applications due to their antibacterial, thermal, electrical conductive, and other properties. The continued commercial up-scaling of ENM production and application needs to be accompanied by an understanding of the occupational health, public safety and environmental implications of these materials. There have been numerous in vitro studies and some in vivo studies of ENM toxicity but their results are frequently inconclusive. Some of the variability between studies has arisen due to a lack of consistency between experimental models, since small differences between test materials can markedly alter their behaviour. In addition, the propensity for the physicochemistry of silver ENMs to alter, sometimes quite radically, depending on the environment they encounter, can profoundly alter their bioreactivity. Consequently, it is important to accurately characterise the materials before use, at the point of exposure and at the nanomaterial-tissue, or “nanobio”, interface, to be able to appreciate their environmental impact. This paper reviews current literature on the pulmonary effects of silver nanomaterials. We focus our review on describing whether, and by which mechanisms, the chemistry and structure of these materials can be linked to their bioreactivity in the respiratory system. In particular, the mechanisms by which the physicochemical properties (e.g., aggregation state, morphology and chemistry) of silver nanomaterials change in various biological milieu (i.e., relevant proteins, lipids and other molecules, and biofluids, such as lung surfactant) and affect subsequent interactions with and within cells will be discussed, in the context not only of what is measured but also of what can be visualized.     

Study of the inhibition of certain trophic levels by the presence of metal cations in water

Bioassays and biological tools have been developed for the evaluation of the toxicity of water. A protocol of short-term tests allowed the examination of the influence of temperature, salinity, hardness and effect of complexation on the toxicity of Cd²⁺, Cu²⁺, Ni²⁺ and Zn²⁺ by means of a test daphnia (Daphnia magna). The development of an experimental installation functioning continuously, where the trophic level is represented by the daphnia, led to the development of a system of bio-indication. The survival of the daphnia is examined under conditions of disturbances produced by Cd²⁺, Cu²⁺, Ni²⁺ and Zn²⁺. The application of the chronic test (21 d) allowed the folow-up of the inhibition of the survival and the reproduction of D. magna by Cd²⁺, Cu²⁺ and Ni²⁺. A methodology with the help of the phototactic effect of D. magna was proposed. This one aims at developing a phototactic biosensor subjected to the toxicity of cadmium. Bioassays, using the purifying activity of the activated sludge, were considered and enabled understanding of the phenomena of inhibition and adaptation of these muds in the presence of trivalent chromium. In addition, two watery freshwater plants, Lemna minor and Salvinia natans, were exposed to Cd²⁺, Cu²⁺ and Zn²⁺ in order to test their sensitivity. We consequently carried out a histological study on leaves of S. natans contaminated by metal toxicity independently of the test.     

Ecotoxicological Assessment of Mixtures of Ether Carboxylic Derivative and Amine-Oxide-Based Non-ionic Surfactants on the Aquatic Environment

The purpose of this study was to discuss the effect of the chemical structure of anionic and non-ionic surfactants and surface activity on toxicity. Single and binary mixtures of three ether carboxylic derivative surfactants and three amine-oxide-based non-ionic surfactants were used. Toxicity was determined using three test organisms: freshwater crustaceans (Daphnia magna), luminescent bacteria (Vibrio fischeri), and microalgae (Selenastrum capricornutum). The toxicity of surfactants is related to the hydrophobic alkyl chain, the degree of ethoxylation, and the critical micelle concentration of surfactants. Relationships found agreed with the fact that the lower toxicity is shown by the shorter alkyl chain. There is a strong relation between surface activity and toxicity: the toxicity increased as the CMC of the surfactant or mixtures of surfactants decreased. Commercial products are formulated using surfactants mixtures, so it is important to know their behavior using an easily measured property: the least toxic mixtures were formed by the surfactants having lower individual toxicity. Around the CMC, our data show a synergism for the binary mixtures. The results have given rise to a classification of the different surfactants and their mixtures according to the organism test, as safe, harmful or toxic. V. fischeri was in general the most sensitive microorganism to the toxic effect of the surfactants, followed by Daphnia magna, while Selenastrum capricornutum was more tolerant. These results can be useful for selecting technically efficient surfactants and their mixtures with a lower ecotoxicity on the aquatic environment.     

New Pyrrole Derivatives as Promising Biological Agents: Design,Synthesis, Characterization,In Silico,and Cytotoxicity Evaluation

The current study describes the synthesis, physicochemical characterization and cytotoxicity evaluation of a new series of pyrrole derivatives in order to identify new bioactive molecules. The new pyrroles were obtained by reaction of benzimidazolium bromide derivatives with asymmetrical acetylenes in 1,2-epoxybutane under reflux through the Huisgen [3 + 2] cycloaddition of several ylide intermediates to the corresponding dipolarophiles. The intermediates salts were obtained from corresponding benzimidazole with bromoacetonitrile. The structures of the newly synthesized compounds were confirmed by elemental analysis, spectral techniques (i.e., IR, ¹H-NMR and ¹³C-NMR) and single-crystal X-ray analysis. The cytotoxicity of the synthesized compounds was evaluated on plant cells (i.e., Triticum aestivum L.) and animal cells using aquatic crustaceans (i.e., Artemia franciscana Kellogg and Daphnia magna Straus). The potential antitumor activity of several of the pyrrole derivatives was studied by performing in vitro cytotoxicity assays on human adenocarcinoma-derived cell lines (i.e., LoVo (colon), MCF-7 (breast), and SK-OV-3 (ovary)) and normal human umbilical vein endothelial cells (HUVECs). The obtained results of the cytotoxicity assessment indicated that the tested compounds had nontoxic activity on Triticum aestivum L., while on Artemia franciscana Kellogg nauplii, only compounds 2c and 4c had moderate toxicity. On Daphnia magna, 4b and 4c showed high toxicity; 2a, 2b, and 2c moderate to high toxicity; only 4a and 4d were nontoxic. The compound-mediated cytotoxicity assays showed that several pyrrole compounds demonstrated dose- and time-dependent cytotoxic activity against all tested tumor cell lines, the highest antitumor properties being achieved by 4a and its homologue 4d, especially against LoVo colon cells.     

Usefulness of myeloperoxidase as a biomarker for the ranking of pulmonary toxicity of nanomaterials

Background

In order to examine whether myeloperoxidase (MPO) can be a useful marker for evaluating the pulmonary toxicity of nanomaterials, we analyzed MPO protein in bronchoalveolar lavage fluid (BALF) samples obtained from previous examinations of a rat model. In those examinations we performed intratracheal instillation exposures (dose: 0.2–1.0 mg) and inhalation exposures (exposure concentration: 0.32–10.4 mg/m³) using 9 and 4 nanomaterials with different toxicities, respectively. Based on those previous studies, we set Nickel oxide nanoparticles (NiO), cerium dioxide nanoparticles (CeO₂), multi wall carbon nanotubes with short or long length (MWCNT (S) and MWCNT (L)), and single wall carbon nanotube (SWCNT) as chemicals with high toxicity; and titanium dioxide nanoparticles (TiO₂ (P90) and TiO₂ (Rutile)), zinc oxide nanoparticles (ZnO), and toner with external additives including nanoparticles as chemicals with low toxicity. We measured the concentration of MPO in BALF samples from rats from 3 days to 6 months following a single intratracheal instillation, and from 3 days to 3 months after the end of inhalation exposure.

Results

Intratracheal instillation of high toxicity NiO, CeO_2, MWCNT (S), MWCNT (L), and SWCNT persistently increased the concentration of MPO, and inhalation of NiO and CeO₂ increased the MPO in BALF. By contrast, intratracheal instillation of low toxicity TiO₂ (P90), TiO₂ (Rutile), ZnO, and toner increased the concentration of MPO in BALF only transiently, and inhalation of TiO₂ (Rutile) and ZnO induced almost no increase of the MPO. The concentration of MPO correlated with the number of total cells and neutrophils, the concentration of chemokines for neutrophils (cytokine-induced neutrophil chemoattractant (CINC)-1 and heme oxygenase (HO)-1), and the activity of released lactate dehydrogenase (LDH) in BALF. The results from the receiver operating characteristics (ROC) for the toxicity of chemicals by the concentration of MPO proteins in the intratracheal instillation and inhalation exposures showed that the largest areas under the curves (AUC) s in both examinations occurred at 1 month after exposure.

Conclusion

These data suggest that MPO can be a useful biomarker for the ranking of the pulmonary toxicity of nanomaterials, especially at 1 month after exposure, in both intratracheal instillation and inhalation exposure.

     

Determination of silver nanoparticle release from antibacterial fabrics into artificial sweat

Silver nanoparticles have been used in numerous commercial products, including textiles, to prevent bacterial growth. Meanwhile, there is increasing concern that exposure to these nanoparticles may cause potential adverse effects on humans as well as the environment. This study determined the quantity of silver released from commercially claimed nanosilver and laboratory-prepared silver coated fabrics into various formulations of artificial sweat, each made according to AATCC, ISO and EN standards. For each fabric sample, the initial amount of silver and the antibacterial properties against the model Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria on each fabric was investigated. The results showed that silver was not detected in some commercial fabrics. Furthermore, antibacterial properties of the fabrics varied, ranging from 0% to greater than 99%. After incubation of the fabrics in artificial sweat, silver was released from the different fabrics to varying extents, ranging from 0 mg/kg to about 322 mg/kg of fabric weight. The quantity of silver released from the different fabrics was likely to be dependent on the amount of silver coating, the fabric quality and the artificial sweat formulations including its pH. This study is the unprecedented report on the release of silver nanoparticles from antibacterial fabrics into artificial sweat. This information might be useful to evaluate the potential human risk associated with the use of textiles containing silver nanoparticles.     

Toxicity identification of effluent from a semiconductor lead frame manufacturing factory

The acute toxicity of lead frame effluent to Daphnia magna was found to be 22.62 TU, which far exceeded the toxicity discharge limit in Korea (<1 TU). TIE phases I and II result suggest that the mixture of Ag, Cu and CN were likely responsible for the observed toxicity, and this was confirmed by mass balance approach (TIE phase III). In addition, the Visual MINTEQ simulation suggested the presence of [Ag(CN)₂]⁻ and [Cu(CN)₃]²⁻ complexes in the effluent. Therefore, TIE procedures with chemical speciation modeling were effective for identifying the cause of acute toxicity in industrial effluents.     

Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy

The rapid proliferation of many different engineered nanomaterials (defined as materials designed and produced to have structural features with at least one dimension of 100 nanometers or less) presents a dilemma to regulators regarding hazard identification. The International Life Sciences Institute Research Foundation/Risk Science Institute convened an expert working group to develop a screening strategy for the hazard identification of engineered nanomaterials. The working group report presents the elements of a screening strategy rather than a detailed testing protocol. Based on an evaluation of the limited data currently available, the report presents a broad data gathering strategy applicable to this early stage in the development of a risk assessment process for nanomaterials. Oral, dermal, inhalation, and injection routes of exposure are included recognizing that, depending on use patterns, exposure to nanomaterials may occur by any of these routes. The three key elements of the toxicity screening strategy are: Physicochemical Characteristics, In Vitro Assays (cellular and non-cellular), and In Vivo Assays. There is a strong likelihood that biological activity of nanoparticles will depend on physicochemical parameters not routinely considered in toxicity screening studies. Physicochemical properties that may be important in understanding the toxic effects of test materials include particle size and size distribution, agglomeration state, shape, crystal structure, chemical composition, surface area, surface chemistry, surface charge, and porosity. In vitro techniques allow specific biological and mechanistic pathways to be isolated and tested under controlled conditions, in ways that are not feasible in in vivo tests. Tests are suggested for portal-of-entry toxicity for lungs, skin, and the mucosal membranes, and target organ toxicity for endothelium, blood, spleen, liver, nervous system, heart, and kidney. Non-cellular assessment of nanoparticle durability, protein interactions, complement activation, and pro-oxidant activity is also considered. Tier 1 in vivo assays are proposed for pulmonary, oral, skin and injection exposures, and Tier 2 evaluations for pulmonary exposures are also proposed. Tier 1 evaluations include markers of inflammation, oxidant stress, and cell proliferation in portal-of-entry and selected remote organs and tissues. Tier 2 evaluations for pulmonary exposures could include deposition, translocation, and toxicokinetics and biopersistence studies; effects of multiple exposures; potential effects on the reproductive system, placenta, and fetus; alternative animal models; and mechanistic studies.     

The Origin and Ecological Function of an Ion Inducing Anti-Predator Behavior in <Emphasis Type="Italic">Lithobates</Emphasis> Tadpoles

In aquatic environments, chemical cues are believed to be associated with prey response to predation risk, yet few basic cue compositions are known despite the pronounced ecological and evolutionary significance of such cues. Previous work indicated that negatively-charged ions of m/z 501 are possibly a kairomone that induces anti-predator responses in amphibian tadpoles. However, work described here confirms that this specific ion species m/z 501.2886 is produced by injured tadpoles, exhibits increased spectral intensity with higher tadpole biomass, and is not produced by starved predators. These results indicate the anion is an alarm cue released from tadpoles. High resolution mass spectrometry (HR-MS) revealed a unique elemental composition for [M-H]^?, m/z 501.2886, of C₂₆H₄₅O₇S^? which could not be determined in previous studies using low resolution instruments. Collision induced dissociation of m/z 501 ions formed product ions of m/z 97 and m/z 80, HSO₄^? and SO₃^?, respectively, showing the presence of sulfate. Green frog tadpoles, Lithobates clamitans, exposed to the m/z 501 anion or sodium dodecyl sulfate exhibited similar anti-predator responses, suggesting organic sulfate is a tadpole behavior modifier.     

Toxicological Assessment of Inhaled Nanoparticles: Role of in Vivo,ex Vivo,in Vitro,and in Silico Studies

The alveolar epithelium of the lung is by far the most permeable epithelial barrier of the human body. The risk for adverse effects by inhaled nanoparticles (NPs) depends on their hazard (negative action on cells and organism) and on exposure (concentration in the inhaled air and pattern of deposition in the lung). With the development of advanced in vitro models, not only in vivo, but also cellular studies can be used for toxicological testing. Advanced in vitro studies use combinations of cells cultured in the air-liquid interface. These cultures are useful for particle uptake and mechanistic studies. Whole-body, nose-only, and lung-only exposures of animals could help to determine retention of NPs in the body. Both approaches also have their limitations; cellular studies cannot mimic the entire organism and data obtained by inhalation exposure of rodents have limitations due to differences in the respiratory system from that of humans. Simulation programs for lung deposition in humans could help to determine the relevance of the biological findings. Combination of biological data generated in different biological models and in silico modeling appears suitable for a realistic estimation of potential risks by inhalation exposure to NPs.     

All that is silver is not toxic: silver ion and particle kinetics reveals the role of silver ion aging and dosimetry on the toxicity of silver nanoparticles

Background

When suspended in cell culture medium, nano-objects composed of soluble metals such as silver can dissolve resulting in ion formation, altered particle properties (e.g. mass, morphology, etc.), and modulated cellular dose. Cultured cells are exposed not just to nanoparticles but to a complex, dynamic mixture of altered nanoparticles, unbound ions, and ion-ligand complexes. Here, three different cell types (RAW 264.7 macrophages and bone marrow derived macrophages from wild-type C57BL/6?J mice and Scavenger Receptor A deficient (SR-A^(?/?)) mice) were exposed to 20 and 110?nm silver nanoparticles, and RAW 264.7 cells were exposed to freshly mixed silver ions, aged silver ions (ions incubated in cell culture medium), and ions formed from nanoparticle dissolution. The In Vitro Sedimentation, Diffusion, Dissolution, and Dosimetry Model (ISD3) was used to predict dose metrics for each exposure scenario.

Results

Silver nanoparticles, freshly mixed ions, and ions from nanoparticle dissolution were toxic, while aged ions were not toxic. Macrophages from SR-A^(?/?) mice did not take up 20?nm silver nanoparticles as well as wild-types but demonstrated no differences in silver levels after exposure to 110?nm nanoparticles. Dose response modeling with ISD3 predicted dose metrics suggest that amount of ions in cells and area under the curve (AUC) of ion amount in cells are the most predictive of cell viability after nanoparticle and combined nanoparticle/dissolution-formed-ions exposures, respectively.

Conclusions

Results of this study suggest that the unbound silver cation is the ultimate toxicant, and ions formed extracellularly drive toxicity after exposure to nanoparticles. Applying computational modeling (ISD3) to better understand dose metrics for soluble nanoparticles allows for better interpretation of in vitro hazard assessments.

     

Combustion products of polymeric materials. IV—testing of toxicity hazard

A method based on exposure of mice in the CAB 4.5 smoke chamber for the evaluation of the biological toxicity of the products of flame and smoldering combustion of polumeric materials has been developed. A toxicity index, characterizing the danger from the products of combustion of the test polymer under the given conditions, was proposed on the basis of values of the concentration of carboxyhaemoglobin in the blood of the test animals, attaining charateristic critical limits (lethal limit) and LC₅₀ values.