Knowledge gaps in risk assessment of nanosilica in food: evaluation of the dissolution and toxicity of different forms of silica

In Vivo Toxicity of Oral Administrated Nano-SiO2: Can Food Additives Increase Apoptosis?

Nano-silicon dioxide (nano-SiO2) has a great deal of application in food packaging, as antibacterial food additives, and in drug delivery systems but this nanoparticle, despite its wide range of utilizations, can generate destructive effects on organs such as the liver, kidney, and lungs. This study is aimed at investigating the toxicological effects of nano-SiO2 through apoptotic factors. For this purpose, 40 female rats in 4 groups (n = 10) received 300, 600, and 900 mg/kg/day of nano-SiO2 at 20-30 nm size orally for 20 days. Relative expression of Caspase3, Bcl-2, and BAX genes in kidney and liver was evaluated in real time-PCR. The results indicated the overexpression of BAX and Caspase3 genes in the liver and kidney in groups receiving 300 and 900 mg/kg/day of nano-SiO2. Bcl-2 gene was up-regulated in the liver and kidney at 600 mg/kg/day compared to the control group. Overexpression of the Bcl-2 gene in the kidney in 300 and 900 mg/kg/day recipient groups was observed (P ≤ 0.05). Histopathological examination demonstrated 600 mg/kg/day hyperemia in the kidney and lungs. In addition, at 900 mg/kg/day were distinguished scattered necrosis and hyperemia in the liver. The rate of epithelialization in the lungs increased. The nano-SiO2 at 300 and 900 mg/kg/day can induce more cytotoxicity in the liver and lung after oral exposure. However, cytotoxicity of nano-SiO2 at 600 mg/kg/day in the kidney and lung was noticed. Hence, the using of nano-SiO2 as an additive and food packaging should be more considered due to their deleterious effects.

Survival, growth, behavior, hematology and serum biochemistry of mice under different concentrations of orally administered amorphous silica nanoparticle

Silica nanoparticles (SiNPs) are used extensively in consumer products and biomedical research basically due to ease of production and low cost. However, insufficient literature is reported regarding the toxicity and biocompatibility of SiNPs. The present study aimed to investigate the potential role of amorphous SiNPs on survival, growth, behavioral alterations, hematology and serum biochemistry of mice at four concentrations (control, 50, 100 and 150 mg/kg/day) of an oral supplementation for a period of 3 months. Signs of toxicity (lethargy, nausea, coma, tremors, vomiting and diarrhea, etc.) were noted at 9:00 am and 9:00 pm (twice a day) and the body weight of each of these mice was measured every week. The data were subjected to mean, standard deviation (S.D). Moreover, One-Way Analysis of Variance (ANOVA) and Dunnett's test were applied for analysis of statistical significance between groups by using SPSS software, version 20. All the mice survived with minor alterations in behavior and no significant weight changes were observed during the stipulated time period. Complete blood count (CBC) analysis indicated non-significant (P ≥ 0.05) systemic dysfunctions of organ systems. However, there was elevation in the level of AST and ALT in the analysis of serum biochemistry, while the values of all other examined parameters were not-significant (P ≥ 0.05). The study concluded that orally administered large silica nanoparticles up to the dose level of 150 mg/kg/day are nontoxic for the in vivo use in mice.

Toxicity of transition metal nanoparticles: A review of different experimental models in the gastrointestinal tract

The development of nanotechnology is becoming a major trend nowadays. Nanoparticles (NPs) have been widely used in fields including food, biomedicine, and cosmetics, endowing NPs more opportunities to enter the human body. It is well-known that the gut microbiome plays a key role in human health, and the exposure of intestines to NPs is unavoidable. Accordingly, the toxicity of NPs has attracted more attention than before. This review mainly highlights recent advances in the evaluation of NPs' toxicity in the gastrointestinal system from the existing cell-based experimental models, such as the original mono-culture models, co-culture models, three-dimensional (3D) culture models, and the models established on microfluidic chips, to those in vivo experiments, such as mice models, Caenorhabditis elegans models, zebrafish models, human volunteers, as well as computer-simulated toxicity models. Owing to these models, especially those more biomimetic models, the outcome of the toxicity of NPs acting in the gastrointestinal tract can get results closer to what happened inside the real human microenvironment.

Silicon dioxide nanoparticles induced neurobehavioral impairments by disrupting microbiota-gut-brain axis

Background

Silicon dioxide nanoparticles (SiO₂NPs) are widely used as additive in the food industry with controversial health risk. Gut microbiota is a new and hot topic in the field of nanotoxicity. It also contributes a novel and insightful view to understand the potential health risk of food-grade SiO₂NPs in children, who are susceptible to the toxic effects of nanoparticles.

Methods

In current study, the young mice were orally administrated with vehicle or SiO₂NPs solution for 28 days. The effects of SiO₂NPs on the gut microbiota were detected by 16S ribosomal RNA (rRNA) gene sequencing, and the neurobehavioral functions were evaluated by open field test and Morris water maze. The level of inflammation, tissue integrity of gut and the classical indicators involved in gut–brain, gut–liver and gut–lung axis were all assessed.

Results

Our results demonstrated that SiO₂NPs significantly caused the spatial learning and memory impairments and locomotor inhibition. Although SiO₂NPs did not trigger evident intestinal or neuronal inflammation, they remarkably damaged the tissue integrity. The microbial diversity within the gut was unexpectedly enhanced in SiO₂NPs-treated mice, mainly manifested by the increased abundances of Firmicutes and Patescibacteria. Intriguingly, we demonstrated for the first time that the neurobehavioral impairments and brain damages induced by SiO₂NPs might be distinctively associated with the disruption of gut–brain axis by specific chemical substances originated from gut, such as Vipr1 and Sstr2. Unapparent changes in liver or lung tissues further suggested the absence of gut–liver axis or gut–lung axis regulation upon oral SiO₂NPs exposure.

Conclusion

This study provides a novel idea that the SiO₂NPs induced neurotoxic effects may occur through distinctive gut–brain axis, showing no significant impact on either gut–lung axis or gut–liver axis. These findings raise the exciting prospect that maintenance and coordination of gastrointestinal functions may be critical for protection against the neurotoxicity of infant foodborne SiO₂NPs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00916-2.

Issues currently complicating the risk assessment of synthetic amorphous silica (SAS) nanoparticles after oral exposure

Synthetic amorphous silica (SAS) is applied in food products as food additive E 551. It consists of constituent amorphous silicon dioxide (SiO₂) nanoparticles that form aggregates and agglomerates. We reviewed recent oral toxicity studies with SAS. Some of those report tissue concentrations of silicon (Si). The results of those studies were compared with recently determined tissue concentrations of Si (and Si-particles) in human postmortem tissues. We noticed inconsistent results of the various toxicity studies regarding toxicity and reported tissue concentrations, which hamper the risk assessment of SAS. A broad range of Si concentrations is reported in control animals in toxicity studies. The Si concentrations found in human postmortem tissues fall within this range. On the other hand, the mean concentration found in human liver is higher than the reported concentrations causing liver effects in some animal toxicity studies after oral exposure to SAS. Also higher liver concentrations are observed in other, negative animal studies. Those inconsistencies could be caused by the presence of other Si-containing chemical substances or particles (which potentially also includes background SAS) and/or different sample preparation and analytical techniques that were used. Other factors which could explain the inconsistencies in outcome between the toxicity studies are the distinct SAS used and different dosing regimes, such as way of administration (dietary, via drinking water, oral gavage), dispersion of SAS and dose. More research is needed to address these issues and to perform a proper risk assessment for SAS in food. The current review will help to progress research on the toxicity of SAS and the associated risk assessment.

Frontiers in the treatment of glioblastoma: Past, present and emerging

Glioblastoma (GBM) is one of the most aggressive cancers of the brain. Despite extensive research over the last several decades, the survival rates for GBM have not improved and prognosis remains poor. To date, only a few therapies are approved for the treatment of GBM with the main reasons being: 1) significant tumour heterogeneity which promotes the selection of resistant subpopulations 2) GBM induced immunosuppression and 3) fortified location of the tumour in the brain which hinders the delivery of therapeutics. Existing therapies for GBM such as radiotherapy, surgery and chemotherapy have been unable to reach the clinical efficacy necessary to prolong patient survival more than a few months. This comprehensive review evaluates the current and emerging therapies including those in clinical trials that may potentially improve both targeted delivery of therapeutics directly to the tumour site and the development of agents that may specifically target GBM. Particular focus has also been given to emerging delivery technologies such as focused ultrasound, cellular delivery systems nanomedicines and immunotherapy. Finally, we discuss the importance of developing novel materials for improved delivery efficacy of nanoparticles and therapeutics to reduce the suffering of GBM patients.

Too small to matter? Physicochemical transformation and toxicity of engineered nTiO2, nSiO2, nZnO, carbon nanotubes, and nAg

Engineered nanomaterials (ENMs) refer to a relatively novel class of materials that are increasingly prevalent in various consumer products and industrial applications - most notably for their superlative physicochemical properties when compared with conventional materials. However, consumer products inevitably degrade over the course of their lifetime, releasing ENMs into the environment. These ENMs undergo physicochemical transformations and subsequently accumulate in the environment, possibly leading to various toxic effects. As a result, a significant number of studies have focused on identifying the possible transformations and environmental risks of ENMs, with the objective of ensuring a safe and responsible application of ENMs in consumer products. This review aims to consolidate the results from previous studies related to each stage of the pathway of ENMs from being embodied in a product to disintegration/transformation in the environment. The scope of this work was defined to include the five most prevalent ENMs based on recent projected production market data, namely: nTiO₂, nSiO₂, nZnO, carbon nanotubes, and nAg. The review focuses on: (i) models developed to estimate environmental concentrations of ENMs; (ii) the possible physicochemical transformations; (iii) cytotoxicity and genotoxicity effects specific to each ENM selected; and (iv) a discussion to identify potential gaps in the studies conducted and recommend areas where further investigation is warranted.

Toxic effects of the food additives titanium dioxide and silica on the murine intestinal tract: Mechanisms related to intestinal barrier dysfunction involved by gut microbiota

This study aimed to compare the effects of three food-grade particles (micro-TiO₂, nano-TiO₂, and nano-SiO₂) on the murine intestinal tract and to investigate their potential mechanisms of action. A 28-day oral exposure murine model was established. Samples of blood, intestinal tissues and colon contents were collected for detection. The results showed that all three particles could cause inflammatory damage to the intestine, with nano-TiO₂ showing the strongest effects. Exposure also led to changes in gut microbiota, especially mucus-associated bacteria. Our results suggest that the toxic effects on the intestine were due to reduced intestinal mucus barrier function and an increase in metabolite lipopolysaccharides which activated the expression of inflammatory factors downstream. In mice exposed to nano-TiO₂, the intestinal PKC/TLR4/NF-κB signalling pathway was activated. These findings will raise awareness of toxicities associated with the use of food-grade TiO₂ and SiO₂.

Short-term oral administration of non-porous and mesoporous silica did not induce local or systemic toxicity in mice

In this study, two sets of methyl-coated non-porous and mesoporous amorphous silica materials of two target sizes (100 and 300 nm; 10-844 m²/g) were used to investigate the potential role of specific surface area (SSA) and porosity on the oral toxicity in mice. Female Swiss mice were administered by oral gavage for 5 consecutive days. Two silica dose levels (100 and 1000 mg/kg b.w.) were tested for all four materials. All dispersions were characterized by transmission electron microscopy (TEM) and Nanoparticle tracking analysis (NTA). Batch dispersions of porous silica were rather unstable due to agglomeration. Animals were sacrificed one day after the last administration or after a three-week recovery period. No relevant toxicological effects were induced by any of the silica materials tested, as evaluated by body weight, gross pathology, relative organ weights (liver, spleen, kidneys), hematology, blood biochemistry, genotoxicity (Comet assay in jejunum cells and micronucleus test in peripheral blood erythrocytes), liver and small intestine histopathology, and intestinal inflammation. The presence of silica particles in the intestine was evaluated by a hyperspectral imaging microscopy system (CytoViva) using histological samples of jejunum tissue. Silica spectral signatures were found in jejunum samples with all the treatments, but only statistically significant in one of the treatment groups.

'All chemical substances are harmful.' public appraisal of uncertain risks of food additives and contaminants

In toxicological health risk assessment, epistemic uncertainties (e.g. about a chemical's intrinsic properties or toxicity) often remain, preventing definitive statements about whether a chemical constitues a risk. In this study, we analyzed public appraisals of uncertain risks of food additives and contaminants. We identified three major characteristics of public appraisal. First, hazard appraisals differed consistently from risk appraisals: respondents were less disturbed by a possible health risk than by the mere presence of the chemical substance in food. Second, while a majority understood that exposure determines whether a chemical constitutes a risk, many respondents thought that all chemicals are equally harmful. This suggests a mismatch between beliefs about exposure and beliefs about toxicity. Finally, the higher people valued certainty about food safety and the less they considered uncertainty about a risk acceptable, the more severe they appraised the presence of the chemical substance in food. This suggests that a mismatch between the level of uncertainty that people expect about food safety and the actual level of scientific uncertainty, affects how people evaluate the presence of chemical substances in food. Following the findings, implications for risk communication are discussed.

A Comparative Analysis of Different Grades of Silica Particles and Temperature Variants of Food-Grade Silica Nanoparticles for Their Physicochemical Properties and Effect on Trypsin

While silica particles are used extensively in food products, different grades and temperature variants of silica particles have not been compared for their physiochemical and biological properties. Different grades of silica (food-grade nanoparticles (FG-NPs), nonfood-grade nanoparticles (NFG-NPs), and food-grade micron particles (FG-MPs)) and the temperature variants generated by exposing FG-NPs to wet heating, dry heating, and refrigeration were compared for their physicochemical properties and interaction with trypsin. FG-NPs were similar to NFG-NPs and FG-MPs in their elemental composition and amorphous nature but had relatively less branched and ring siloxane groups than the latter ones. There were subtle but noticeable changes in the agglomeration behavior and relative abundance of different silica groups in FG-NPs exposed to food-handling temperatures. Secondary structure and function of trypsin were negatively impacted by FG-NPs and their temperature variants. Silica particles showed a "mixed-type inhibition" of trypsin resulting in partial digestion of bovine serum albumin. In conclusion, our studies showed differences in the surface chemistry of different grades of silica particles and temperature variants of FG-NPs and their negative impact on the structure and function of trypsin.

Chronic Oral Exposure to Synthetic Amorphous Silica (NM-200) Results in Renal and Liver Lesions in Mice

Introduction

Silicon dioxide, produced as synthetic amorphous silica (SAS), is made of nanoparticles (NPs), either present as such or as agglomerates and aggregates, and is widely used in many types of food processes and products as an additive. To assess whether repeated, long-term exposure to SAS NPs may result in adverse effects, mice were exposed for 18 months via drinking water to NM-200, one of the reference nanostructured silica used for applications related to food, at 4.8 mg NM-200/kg body weight per day, a dose relevant to the estimated dietary exposure to SAS in humans.

Methods

The experiment focused on the kidney and liver as target organs and was carried out in parallel using 3 mouse lines (wild type and transgenic) differing for the expression of α-synuclein, that is, murine and human mutated (A53T). Sensitive determination of silicon revealed higher contents in liver and kidneys of NM-200–exposed mice compared with unexposed aged-matched controls.

Results

Histological abnormalities, such as vacuolization of tubular epithelial cells, were detected in all kidneys, as well as inflammatory responses that were also detected in livers of exposed animals. Less frequent but more deleterious, amyloidosis lesions were observed in glomeruli, associated with perivascular amyloid accumulation in liver.

Conclusion

These histological findings, in conjunction with the observation of detectable deposition of silica, highlight that chronic oral intake of SAS may pose a health risk to humans and need to be examined further.

Global metabolomics approach in in vitro and in vivo models reveals hepatic glutathione depletion induced by amorphous silica nanoparticles

The present study aimed to investigate the mechanisms involved in amorphous silica nanoparticles (aSiNPs)-mediated hepatotoxicity through the evaluation of changes in global metabolomics in in vitro and in vivo systems. ¹H NMR-based non-targeted global metabolomics and biochemical approaches were conducted in an aSiNPs-treated human hepatoma cell line (HepG2) and in ICR mice liver. The non-targeted NMR-based metabolomic analysis, followed by pathway analysis, revealed the perturbation of glutathione metabolism and the depletion of the glutathione pool after aSiNPs treatment in both in vitro (HepG2 cells) and in vivo systems. The total glutathione level, glutathione-S-transferase enzyme activity, and antioxidant gene expression strongly corroborated the metabolomic analysis results. The in vitro results were further supported by the in vivo data, specifically for metabolites profiling (Pearson Correlation coefficient is 0.462 (p = 0.026)). Furthermore, the depletion of glutathione, the formation of NADPH oxidase-mediated reactive oxygen species, and oxidative stress were evident in aSiNPs-treated HepG2 cells. Overall, the suppression of glutathione metabolism and oxidative stress are among the principal causes of aSiNPs-mediated hepatotoxicity.

A risk perception gap? Comparing expert, producer and consumer prioritization of food hazard controls

Using a survey approach, the study examined how experts (i.e. food control representatives), producers (i.e. food industry representatives) and consumers prioritized control activities for 28 hazards related to food and other everyday items. The investigated hazards encompassed a wide range of safety issues, including health risks, consumer deception and poor food hygiene behaviour. The participants included 41 experts, 138 producers and 243 consumers from the German- and French-speaking parts of Switzerland. Based on detailed descriptions of the hazards, they were asked to rank these on a score sheet in terms of the perceived importance of monitoring by food control authorities. A between-group comparison of average rankings showed that consumers and experts differed significantly in relation to 17 of the 28 hazards. While the experts assigned higher priority to hazards related to everyday items such as nitrosamine in mascara and chromium VI in leather products, producers and consumers tended to prioritize products related to plant treatment and genetic modification of food and feeds. Producer and consumer rankings of the hazards were highly correlated (r = .96, p < .001). Rankings were also similar among participants from the two cultural regions (i.e. German and French-speaking parts of Switzerland).

Toxicology of silica nanoparticles: an update

Large-scale production and use of amorphous silica nanoparticles (SiNPs) have increased the risk of human exposure to SiNPs, while their health effects remain unclear. In this review, scientific papers from 2010 to 2016 were systematically selected and sorted based on in vitro and in vivo studies: to provide an update on SiNPs toxicity and to address the knowledge gaps indicated in the review of Napierska (Part Fibre Toxicol 7:39, 2010). Toxicity of SiNPs in vitro is size, dose, and cell type dependent. SiNPs synthesized by wet route exhibited noticeably different biological effects compared to thermal route-based SiNPs. Amorphous SiNPs (particularly colloidal and stöber) induced toxicity via mechanisms similar to crystalline silica. In vivo, route of administration and physico-chemical properties of SiNPs influences the toxicokinetics. Adverse effects were mainly observed in acutely exposed animals, while no significant signs of toxicity were noted in chronically dosed animals. The correlation between in vitro and in vivo toxicity remains less well established mainly due to improper-unrealistic-dosing both in vitro and in vivo. In conclusion, notwithstanding the multiple studies published in recent years, unambiguous linking of physico-chemical properties of SiNPs types to toxicity, bioavailability, or human health effects is not yet possible.

Nanotechnology for Food Packaging and Food Quality Assessment

Nanotechnology has paved the way to innovative food packaging materials and analytical methods to provide the consumers with healthier food and to reduce the ecological footprint of the whole food chain. Combining antimicrobial and antifouling properties, thermal and mechanical protection, oxygen and moisture barrier, as well as to verify the actual quality of food, e.g., sensors to detect spoilage, bacterial growth, and to monitor incorrect storage conditions, or anticounterfeiting devices in food packages may extend the products shelf life and ensure higher quality of foods. Also the ecological footprint of food chain can be reduced by developing new completely recyclable and/or biodegradable packages from natural and eco-friendly resources. The contribution of nanotechnologies to these goals is reviewed in this chapter, together with a description of portable devices ("lab-on-chip," sensors, nanobalances, etc.) which can be used to assess the quality of food and an overview of regulations in force on food contact materials.

Advances in Nanotechnology as They Pertain to Food and Agriculture: Benefits and Risks

Nanotechnology is an emerging and rapidly developing toolbox that has novel and unique applications to food science and agriculture. Fast and impressive developments in nanotechnology for food and agriculture have led to new experimental prototype technologies and products. Developing various types of nanodelivery systems, detection tools, nanoscale modifications of bulk or surface properties, fabrication of wide-range bionanosensors, and biodegradable nanoplatforms can potentially improve consumer health and safety, product shelf life and stability, bioavailability, environmental sustainability, efficiency of processing and packaging, and real-time monitoring. Some recently developed nanotechnology techniques and potential product applications of nanotechnology are summarized in this review. Exposure to nanomaterials may be harmful to the consumer and the environment and might increase the potential of risk. For this reason, evaluation of the potential risks resulting from the interaction of nanomaterials with biological systems, humans, and the environment is also reviewed.

Probabilistic modeling of the flows and environmental risks of nano-silica

Nano-silica, the engineered nanomaterial with one of the largest production volumes, has a wide range of applications in consumer products and industry. This study aimed to quantify the exposure of nano-silica to the environment and to assess its risk to surface waters. Concentrations were calculated for four environmental (air, soil, surface water, sediments) and two technical compartments (wastewater, solid waste) for the EU and Switzerland using probabilistic material flow modeling. The corresponding median concentration in surface water is predicted to be 0.12 μg/l in the EU (0.053-3.3 μg/l, 15/85% quantiles). The concentrations in sediments in the complete sedimentation scenario were found to be the largest among all environmental compartments, with a median annual increase of 0.43 mg/kg · y in the EU (0.19-12 mg/kg · y, 15/85% quantiles). Moreover, probabilistic species sensitivity distributions (PSSD) were computed and the risk of nano-silica in surface waters was quantified by comparing the predicted environmental concentration (PEC) with the predicted no-effect concentration (PNEC) distribution, which was derived from the cumulative PSSD. This assessment suggests that nano-silica currently poses no risk to aquatic organisms in surface waters. Further investigations are needed to assess the risk of nano-silica in other environmental compartments, which is currently not possible due to a lack of ecotoxicological data.

Amorphous silica nanoparticle-induced perturbation of cholesterol homeostasis as a function of surface area highlights safe-by-design implementation: an integrated multi-OMICS analysis

The systems toxicology approach revealed that the alterations of cholesterol biosynthesis were directly proportional with the surface area of amorphous silica nanoparticles (aSiNPs); the larger the surface area the higher the cholesterol level.

Physicochemical and toxicological evaluation of silica nanoparticles suitable for food and consumer products collected by following the EC recommendation

Specific information about the particle size distribution, agglomeration state, morphology, and chemical composition of four silica samples, used as additives in food and in personal care products, were achieved with a combination of analytical techniques. The combined use of differential centrifugal sedimentation (DCS), sedimentation field flow fractionation (SdFFF), and scanning and transmission electron microscopy (SEM and TEM) allows to classify the water dispersed samples as "nanomaterials" according to the EC definition. The mechanical stirring and the ultrasound treatment were compared as dispersion methods. The particle surface chemical composition, determined by particle-induced X-ray emission (PIXE) and X-ray photoelectron spectroscopy (XPS), assessed the different levels of purity between the pyrogenic and the precipitated silica and highlighted particle surface chemical composition modifications in the outer shell when dispersed by mechanical stirring. The potential toxic effects of silica on intestinal Caco-2 cells were investigated using MTS assay and by measuring lactate dehydrogenase (LDH) release and caspases 3/7 activity after 24 h of incubation. No or limited decrease of cell viability was observed for all particles regardless of dispersion procedure, suggesting a relative innocuity of these silica samples.

Nanomaterials in consumer products: a challenging analytical problem

Many products used in everyday life are made with the assistance of nanotechnologies. Cosmetic, pharmaceuticals, sunscreen, powdered food are only few examples of end products containing nano-sized particles (NPs), generally added to improve the product quality. To evaluate correctly benefits vs. risks of engineered nanomaterials and consequently to legislate in favor of consumer's protection, it is necessary to know the hazards connected with the exposure levels. This information implies transversal studies and a number of different competences. On analytical point of view the identification, quantification and characterization of NPs in food matrices and in cosmetic or personal care products pose significant challenges, because NPs are usually present at low concentration levels and the matrices, in which they are dispersed, are complexes and often incompatible with analytical instruments that would be required for their detection and characterization. This paper focused on some analytical techniques suitable for the detection, characterization and quantification of NPs in food and cosmetics products, reports their recent application in characterizing specific metal and metal-oxide NPs in these two important industrial and market sectors. The need of a characterization of the NPs as much as possible complete, matching complementary information about different metrics, possible achieved through validate procedures, is what clearly emerges from this research. More work should be done to produce standardized materials and to set-up methodologies to determine number-based size distributions and to get quantitative date about the NPs in such a complex matrices.

Integrated probabilistic risk assessment for nanoparticles: the case of nanosilica in food

Insight into risks of nanotechnology and the use of nanoparticles is an essential condition for the social acceptance and safe use of nanotechnology. One of the problems with which the risk assessment of nanoparticles is faced is the lack of data, resulting in uncertainty in the risk assessment. We attempt to quantify some of this uncertainty by expanding a previous deterministic study on nanosilica (5-200 nm) in food into a fully integrated probabilistic risk assessment. We use the integrated probabilistic risk assessment method in which statistical distributions and bootstrap methods are used to quantify uncertainty and variability in the risk assessment. Due to the large amount of uncertainty present, this probabilistic method, which separates variability from uncertainty, contributed to a better understandable risk assessment. We found that quantifying the uncertainties did not increase the perceived risk relative to the outcome of the deterministic study. We pinpointed particular aspects of the hazard characterization that contributed most to the total uncertainty in the risk assessment, suggesting that further research would benefit most from obtaining more reliable data on those aspects.

Review of nanomaterial aging and transformations through the life cycle of nano-enhanced products

In the context of assessing potential risks of engineered nanoparticles (ENPs), life cycle thinking can represent a holistic view on the impacts of ENPs through the entire value chain of nano-enhanced products from production, through use, and finally to disposal. Exposure to ENPs in consumer or environmental settings may either be to the original, pristine ENPs, or more likely, to ENPs that have been incorporated into products, released, aged and transformed. Here, key product-use related aging and transformation processes affecting ENPs are reviewed. The focus is on processes resulting in ENP release and on the transformation(s) the released particles undergo in the use and disposal phases of its product life cycle for several nanomaterials (Ag, ZnO, TiO2, carbon nanotubes, CeO2, SiO2 etc.). These include photochemical transformations, oxidation and reduction, dissolution, precipitation, adsorption and desorption, combustion, abrasion and biotransformation, among other biogeochemical processes. To date, few studies have tried to establish what changes the ENPs undergo when they are incorporated into, and released from, products. As a result there is major uncertainty as to the state of many ENPs following their release because much of current testing on pristine ENPs may not be fully relevant for risk assessment purposes. The goal of this present review is therefore to use knowledge on the life cycle of nano-products to derive possible transformations common ENPs in nano-products may undergo based on how these products will be used by the consumer and eventually discarded. By determining specific gaps in knowledge of the ENP transformation process, this approach should prove useful in narrowing the number of physical experiments that need to be conducted and illuminate where more focused effort can be placed.

Oral two-generation reproduction toxicity study with NM-200 synthetic amorphous silica in Wistar rats

Synthetic amorphous silica (SAS) like NM-200 is used in a wide variety of technological applications and consumer products. Although SAS has been widely investigated the available reproductive toxicity studies are old and do not cover all requirements of current OECD Guidelines. As part of a CEFIC-LRI project, NM-200 was tested in a two-generation reproduction toxicity study according to OECD guideline 416. Male and female rats were treated by oral gavage with NM-200 at dose levels of 0, 100, 300 and 1000mg/kg bw/day for two generations. Body weight and food consumption were measured throughout the study. Reproductive and developmental parameters were measured and at sacrifice (reproductive) organs and tissues were sampled for histopathological analysis. Oral administration of NM-200 up to 1000mg/kg bw/day had no adverse effects on the reproductive performance of rats or on the growth and development of the offspring into adulthood for two consecutive generations. The NOAEL was 1000mg/kg body weight per day.

Genotoxicity of synthetic amorphous silica nanoparticles in rats following short-term exposure. Part 1: oral route

Synthetic amorphous silica (SAS) in its nanosized form is now used in food applications although the potential risks for human health have not been evaluated. In this study, genotoxicity and oxidative DNA damage of two pyrogenic (NM-202 and 203) and two precipitated (NM-200 and -201) nanosized SAS were investigated in vivo in rats following oral exposure. Male Sprague Dawley rats were exposed to 5, 10, or 20 mg/kg b.w./day for three days by gavage. DNA strand breaks and oxidative DNA damage were investigated in seven tissues (blood, bone marrow from femur, liver, spleen, kidney, duodenum, and colon) with the alkaline and the (Fpg)-modified comet assays, respectively. Concomitantly, chromosomal damage was investigated in bone marrow and in colon with the micronucleus assay. Additionally, malondialdehyde (MDA), a lipid peroxidation marker, was measured in plasma. When required, a histopathological examination was also conducted. The results showed neither obvious DNA strand breaks nor oxidative damage with the comet assay, irrespective of the dose and the organ investigated. Similarly, no increases in chromosome damage in bone marrow or lipid peroxidation in plasma were detected. However, although the response was not dose-dependent, a weak increase in the percentage of micronucleated cells was observed in the colon of rats treated with the two pyrogenic SAS at the lowest dose (5 mg/kg b.w./day). Additional data are required to confirm this result, considering in particular, the role of agglomeration/aggregation of SAS NMs in their uptake by intestinal cells.

Uptake of bright fluorophore core-silica shell nanoparticles by biological systems

Nanoparticles are used in a variety of consumer applications. Silica nanoparticles in particular are common, including as a component of foods. There are concerns that ingested nano-silica particles can cross the intestinal epithelium, enter the circulation, and accumulate in tissues and organs. Thus, tracking these particles is of interest, and fluorescence spectroscopic methods are well-suited for this purpose. However, nanosilica is not fluorescent. In this article, we focus on core-silica shell nanoparticles, using fluorescent Rhodamine 6G, Rhodamine 800, or CdSe/CdS/ZnS quantum dots as the core. These stable fluorophore/silica nanoparticles had surface characteristics similar to those of commercial silica particles. Thus, they were used as model particles to examine internalization by cultured cells, including an epithelial cell line relevant to the gastrointestinal tract. Finally, these particles were administered to mice by gavage, and their presence in various organs, including stomach, small intestine, cecum, colon, kidney, lung, brain, and spleen, was examined. By combining confocal fluorescence microscopy with inductively coupled plasma mass spectrometry, the presence of nanoparticles, rather than their dissolved form, was established in liver tissues.

Characterization of materials released into water from paint containing nano-SiO2

In order to assess the possible risks of applications containing engineered nanomaterials, it is essential to generate more data about their release and exposure, so far largely overlooked areas of research. The aim of this work was to study the characterization of the materials released from paint containing nano-SiO2 during weathering and exposure to water. Panels coated with nano-SiO2 containing paint and a nano-free reference paint were exposed to accelerated weathering cycles in a climate chamber. The total release of 89 six-hour cycles of UV-illumination and precipitation was 2.3% of the total SiO2 contained in the paint. Additional tests with powdered and aged paint showed that the majority of the released Si was present in dissolved form and that only a small percentage was present in particulate and nano-particulate form. TEM imaging of the leachates indicated that the majority of the particulate Si was contained in composites together with Ca, representing the paint matrix, and only few single dispersed SiO2-NPs were detected. The results suggest that toxicological and ecotoxicological studies need to consider that the released particles may have been transformed or are embedded in a matrix.

Silica nanoparticles induced metabolic stress through EGR1, CCND, and E2F1 genes in human mesenchymal stem cells

The SiO2 synthesized in bulk form, adopting the conventional methods for application in food industry applications, may also contain nano-sized particles. On account of the unique physico-chemical properties, the SiO2 particulates, such as size and shape, cause metabolic toxicity in cells. Poor understanding of the molecular level nanotoxicity resulting from high-volume synthetic SiO2 exposures in humans is a serious issue, since these particles may also contribute to metabolic stress-mediated chronic diseases. In the present study, we examined the structural characteristics of these nano-sized silica particles adopting SEM and dynamic light scattering (DLS) and assessed the alterations in the cell cycle induced by these silica particles in human mesenchymal stem cells (hMSCs) adopting 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay, morphological changes in the cells adopting fluorescent microscopy, cell cycle analysis adopting flow cytometry, and the expression of genes linked to cell cycle (i.e., proliferating cell nuclear antigen (PCNA), early growth response protein (EGR1), E2F transcription factor (E2F1), cyclin D1, cyclin C, and cyclin D3) adopting qPCR. The SEM and DLS studies indicated that the commercial grade SiO2-NPs were in the nano-scale range. Alterations in the cytoplasmic organization, nuclear morphology, cell cycle progression, and expression of genes linked to cell cycle-dependent metabolic stress through EGR1, CCND, and E2F1 genes were the primary indicators of metabolic stress. Overall, the results of this study demonstrate that synthetic SiO2 acutely affects hMSC through cell cycle-dependent oxidative stress gene network. The toxicity mechanisms (both acute and chronic) of food grade silica should be investigated in greater depth with special reference to food safety.

Labeling milk along its production chain with DNA encapsulated in silica

The capability of tracing a food product along its production chain is important to ensure food safety and product authenticity. For this purpose and as an application example, recently developed Silica Particles with Encapsulated DNA (SPED) were added to milk at concentrations ranging from 0.1 to 100 ppb (μg per kg milk). Thereby the milk, as well as the milk-derived products yoghurt and cheese, could be uniquely labeled with a DNA tag. Procedures for the extraction of the DNA tags from the food matrixes were elaborated and allowed identification and quantification of previously marked products by quantitative polymerase chain reaction (qPCR) with detection limits below 1 ppb of added particles. The applicability of synthetic as well as naturally occurring DNA sequences was shown. The usage of approved food additives as DNA carrier (silica = E551) and the low cost of the technology (<0.1 USD per ton of milk labeled with 10 ppb of SPED) display the technical applicability of this food labeling technology.

Effects of SiO₂, ZrO₂, and BaSO₄ nanomaterials with or without surface functionalization upon 28-day oral exposure to rats

The effects of seven nanomaterials (four amorphous silicon dioxides with or without surface functionalization, two surface-functionalized zirconium dioxides, and barium sulfate) upon 28-day oral exposure to male or female rats were investigated. The studies were performed as limit tests in accordance with OECD Test Guideline 407 applying 1,000 mg test substance/kg body weight/day. Additionally, the acute phase proteins haptoglobin and α2-macroglobulin as well as cardiac troponin I were determined, and metabolome analysis was performed in plasma samples. There were no test substance-related adverse effects for any of the seven nanomaterials. Moreover, metabolomics changes were below the threshold of effects. Since test substance organ burden was not analyzed, it was not possible to establish whether the lack of findings related to the absence of systemic exposure of the tested nanomaterials or if the substances are devoid of any potential for toxicity. The few published subacute oral or short-term inhalation studies investigating comparable nanomaterials (SiO₂, ZrO₂, and BaSO₄) also do not report the occurrence of pronounced treatment-related findings. Overall, the results of the present survey provide a first indication that the tested nanomaterials neither cause local nor systemic effects upon subacute oral administration under the selected experimental conditions. Further investigations should aim at elucidating the extent of gastrointestinal absorption of surface-functionalized nanomaterials.

The protein corona protects against size- and dose-dependent toxicity of amorphous silica nanoparticles

Besides the lung and skin, the gastrointestinal (GI) tract is one of the main targets for accidental exposure or biomedical applications of nanoparticles (NP). Biological responses to NP, including nanotoxicology, are caused by the interaction of the NP with cellular membranes and/or cellular entry. Here, the physico-chemical characteristics of NP are widely discussed as critical determinants, albeit the exact mechanisms remain to be resolved. Moreover, proteins associate with NP in physiological fluids, forming the protein corona potentially transforming the biological identity of the particle and thus, adding an additional level of complexity for the bio-nano responses. Here, we employed amorphous silica nanoparticles (ASP) and epithelial GI tract Caco-2 cells as a model to study the biological impact of particle size as well as of the protein corona. Caco-2 or mucus-producing HT-29 cells were exposed to thoroughly characterized, negatively charged ASP of different size in the absence or presence of proteins. Comprehensive experimental approaches, such as quantifying cellular metabolic activity, microscopic observation of cell morphology, and high-throughput cell analysis revealed a dose- and time-dependent toxicity primarily upon exposure with ASP30 (Ø = 30 nm). Albeit smaller (ASP20, Ø = 20 nm) or larger particles (ASP100; Ø = 100 nm) showed a similar zeta potential, they both displayed only low toxicity. Importantly, the adverse effects triggered by ASP30/ASP30L were significantly ameliorated upon formation of the protein corona, which we found was efficiently established on all ASP studied. As a potential explanation, corona formation reduced ASP30 cellular uptake, which was however not significantly affected by ASP surface charge in our model. Collectively, our study uncovers an impact of ASP size as well as of the protein corona on cellular toxicity, which might be relevant for processes at the nano-bio interface in general.

Novel insights into the risk assessment of the nanomaterial synthetic amorphous silica, additive E551, in food

This study presents novel insights in the risk assessment of synthetic amorphous silica (SAS) in food. SAS is a nanostructured material consisting of aggregates and agglomerates of primary particles in the nanorange (<100 nm). Depending on the production process, SAS exists in four main forms, and each form comprises various types with different physicochemical characteristics. SAS is widely used in foods as additive E551. The novel insights from other studies relate to low gastrointestinal absorption of SAS that decreases with increasing dose, and the potential for accumulation in tissues with daily consumption. To accommodate these insights, we focused our risk assessment on internal exposure in the target organ (liver). Based on blood and tissue concentrations in time of two different SAS types that were orally and intravenously administered, a kinetic model is developed to estimate the silicon concentration in liver in (1) humans for average-to-worst-case dietary exposure at steady state and (2) rats and mice in key toxicity studies. The estimated liver concentration in humans is at a similar level as the measured or estimated liver concentrations in animal studies in which adverse effects were found. Hence, this assessment suggests that SAS in food may pose a health risk. Yet, for this risk assessment, we had to make assumptions and deal with several sources of uncertainty that make it difficult to draw firm conclusions. Recommendations to fill in the remaining data gaps are discussed. More insight in the health risk of SAS in food is warranted considering the wide applications and these findings.

Engineered nanomaterials in food: implications for food safety and consumer health

From the current state-of-the-art, it is clear that nanotechnology applications are expected to bring a range of benefits to the food sector aiming at providing better quality and conservation. In the meantime, a growing number of studies indicate that the exposure to certain engineered nanomaterials (ENMs) has a potential to lead to health complications and that there is a need for further investigations in order to unravel the biological outcomes of nanofood consumption. In the current review, we summarize the existing data on the (potential) use of ENMs in the food industry, information on the toxicity profiles of the commonly applied ENMs, such as metal (oxide) nanoparticles (NPs), address the potential food safety implications and health hazards connected with the consumption of nanofood. A number of health complications connected with the human exposure to ENMs are discussed, demonstrating that there is a real basis for the arisen concern not only connected with the gut health, but also with the potency to lead to systemic toxicity. The toxicological nature of hazard, exposure levels and risk to consumers from nanotechnology-derived food are on the earliest stage of investigation and this review also highlights the major gaps that need further research and regulation.

Concern-driven integrated approaches to nanomaterial testing and assessment--report of the NanoSafety Cluster Working Group 10

Bringing together topic-related European Union (EU)-funded projects, the so-called "NanoSafety Cluster" aims at identifying key areas for further research on risk assessment procedures for nanomaterials (NM). The outcome of NanoSafety Cluster Working Group 10, this commentary presents a vision for concern-driven integrated approaches for the (eco-)toxicological testing and assessment (IATA) of NM. Such approaches should start out by determining concerns, i.e., specific information needs for a given NM based on realistic exposure scenarios. Recognised concerns can be addressed in a set of tiers using standardised protocols for NM preparation and testing. Tier 1 includes determining physico-chemical properties, non-testing (e.g., structure-activity relationships) and evaluating existing data. In tier 2, a limited set of in vitro and in vivo tests are performed that can either indicate that the risk of the specific concern is sufficiently known or indicate the need for further testing, including details for such testing. Ecotoxicological testing begins with representative test organisms followed by complex test systems. After each tier, it is evaluated whether the information gained permits assessing the safety of the NM so that further testing can be waived. By effectively exploiting all available information, IATA allow accelerating the risk assessment process and reducing testing costs and animal use (in line with the 3Rs principle implemented in EU Directive 2010/63/EU). Combining material properties, exposure, biokinetics and hazard data, information gained with IATA can be used to recognise groups of NM based upon similar modes of action. Grouping of substances in return should form integral part of the IATA themselves.

Sub-chronic toxicity study in rats orally exposed to nanostructured silica

Background

Synthetic Amorphous Silica (SAS) is commonly used in food and drugs. Recently, a consumer intake of silica from food was estimated at 9.4 mg/kg bw/day, of which 1.8 mg/kg bw/day was estimated to be in the nano-size range. Food products containing SAS have been shown to contain silica in the nanometer size range (i.e. 5 – 200 nm) up to 43% of the total silica content. Concerns have been raised about the possible adverse effects of chronic exposure to nanostructured silica.

Methods

Rats were orally exposed to 100, 1000 or 2500 mg/kg bw/day of SAS, or to 100, 500 or 1000 mg/kg bw/day of NM-202 (a representative nanostructured silica for OECD testing) for 28 days, or to the highest dose of SAS or NM-202 for 84 days.

Results

SAS and NM-202 were extensively characterized as pristine materials, but also in the feed matrix and gut content of the animals, and after in vitro digestion. The latter indicated that the intestinal content of the mid/high-dose groups had stronger gel-like properties than the low-dose groups, implying low gelation and high bioaccessibility of silica in the human intestine at realistic consumer exposure levels. Exposure to SAS or NM-202 did not result in clearly elevated tissue silica levels after 28-days of exposure. However, after 84-days of exposure to SAS, but not to NM-202, silica accumulated in the spleen. Biochemical and immunological markers in blood and isolated cells did not indicate toxicity, but histopathological analysis, showed an increased incidence of liver fibrosis after 84-days of exposure, which only reached significance in the NM-202 treated animals. This observation was accompanied by a moderate, but significant increase in the expression of fibrosis-related genes in liver samples.

Conclusions

Although only few adverse effects were observed, additional studies are warranted to further evaluate the biological relevance of observed fibrosis in liver and possible accumulation of silica in the spleen in the NM-202 and SAS exposed animals respectively. In these studies, dose-effect relations should be studied at lower dosages, more representative of the current exposure of consumers, since only the highest dosages were used for the present 84-day exposure study.

Nanoparticle toxicity by the gastrointestinal route: evidence and knowledge gaps

The increasing interest in nanoparticles for advanced technologies, consumer products, and biomedical applications has led to great excitement about potential benefits but also concern over the potential for adverse human health effects. The gastrointestinal tract represents a likely route of entry for many nanomaterials, both directly through intentional ingestion or indirectly via nanoparticle dissolution from food containers or by secondary ingestion of inhaled particles. Additionally, increased utilisation of nanoparticles may lead to increased environmental contamination and unintentional ingestion via water, food animals, or fish. The gastrointestinal tract is a site of complex, symbiotic interactions between host cells and the resident microbiome. Accordingly, evaluation of nanoparticles must take into consideration not only absorption and extraintestinal organ accumulation but also the potential for altered gut microbes and the effects of this perturbation on the host. The existing literature was evaluated for evidence of toxicity based on these considerations. Focus was placed on three categories of nanomaterials: nanometals and metal oxides, carbon-based nanoparticles, and polymer/dendrimers with emphasis on those particles of greatest relevance to gastrointestinal exposures.