Epidemiologic study of workers exposed to titanium dioxide

Evaluation of Systemic Genotoxic/Oxidative and Proinflammatory Effects in Workers of a Titanium Dioxide Production Plant

This study is aimed at evaluating whether the occupational exposure to TiO₂ during the industrial production process is able to induce genotoxic, oxidative, and inflammatory effects on blood, biomonitoring the same workers that showed micronucleus induction in the exfoliated buccal cells, as previous published. The final aim was to find sensitive and suitable biomarkers to evaluate potential early toxicity of occupational exposure to TiO₂. On the same 40 workers involved in the manufacture of TiO₂ pigment, 5 office workers, and 18 controls previously studied, we used formamidopyrimidine glycosylase- (Fpg-) comet assay on lymphocytes to evaluate genotoxic/oxidative effects and detected cytokine (IL-6, IL-8, and TNFα) release by ELISA to evaluate proinflammation. Moreover, we studied the possible influence of single nucleotide polymorphisms of XRCC1 and hOGG1 DNA repair genes and of GST metabolism-related genes (GSTT1 and GSTM1) on the evaluated effects. We did not find statistically significant differences in the mean values of the analysed Fpg-comet assay parameters; only the percentage of DNA damaged cells appearing in the test as comets (% comets) resulted higher in the exposed workers compared to controls. Also, the data analysed taking into account the specific task (bagging, industrial cleaning, mobile operations, maintaining, and production) showed differences only for % comets which resulted higher in industrial cleaners compared to controls. We found variations of IL-6 and IL-8 levels in the exposed workers with concentrations that were lower for IL-6 and higher for IL-8 compared to the control group. XRCC1, hOGG1, and GSTT1 polymorphisms did not influence neither comet parameters nor cytokine release. These findings demonstrate that TiO₂ production process is able to induce slight proinflammatory effects in terms of IL-8 increased release but not significant genotoxic/oxidative effects on lymphocytes, which do not seem to be a target of TiO₂, prevalently inhalable particles, generated in the studied production site.

Health risks of titanium dioxide (TiO2) dust exposure in occupational settings - A scoping review

Titanium dioxide (TiO₂) is an inorganic compound with many applications, for example in paint, sunscreen or as food coloring. There have been concerns regarding its safety and according to IARC, the existing evidence is not substantial enough to rule them out, leading to the substance being classified as possibly carcinogenic to humans (2B). This work aims to provide a comprehensible overview about epidemiological studies on occupational health risks and methodological aspects. A literature search was conducted in two databases (MEDLINE and Web of Science). The search focused on occupational exposure since this setting provides the highest amounts of TiO₂ exposure. Of 443 unique search results, ten were included in this study, with publication dates ranging from 1988 to 2022. Seven of them are retrospective cohort studies and three have a case-control study design. Main outcomes of most studies were all-cause mortality and lung cancer mortality. For all-cause mortality, most cohort studies reported no association with TiO₂ exposure. For lung cancer mortality, a significantly increased risk was found in a study population from Europe. The analysis results of working cohorts from the US comparing exposed workers' mortality rates with those of the general population were unobtrusive. However, one US cohort found an elevated mortality risk for all causes and lung cancer based on a reference population of company workers unexposed to TiO₂. Case-control studies did not indicate an increased risk for cancer related to TiO₂. Recent publications partly questioned the validity of those earlier findings, claiming insufficient confounder analysis, most notably for smoking, as well as the presence of the healthy worker effect, masking a potential health risk. In conclusion, the associations between occupational TiO₂ exposure and mortality are unclear, but concerns regarding possible health risks recently re-emerged based on new analytical approaches, highlighting methodological difficulties that could have limited the inferential value of previously conducted studies.

Occupational Exposure to Poorly Soluble Low Toxicity Particles and Cardiac Disease: A Look at Carbon Black and Titanium Dioxide

Environmental particulate exposure and the potential risk to people with various types of cardiac diseases, most notably cardiovascular disease, have aroused scientific and regulatory interest worldwide. Epidemiological studies have shown associations between exposure to airborne environmental particulate matter (PM) and mortality from cardiovascular disease (CVD). The associations reported, however, are complex and may not involve a direct role for PM, since air pollutants are diverse and highly correlated. This study examines the potential role of occupational exposure to two types of particles, namely, manufactured carbon black (CB) and titanium dioxide (TiO₂), on the risk of cardiovascular disease. To address the risk of cardiovascular disease from exposure to carbon black and titanium dioxide, as reflective of poorly soluble low toxicity particles, we reviewed the published cohort mortality studies of occupational exposure to carbon black and titanium dioxide. Mortality studies of carbon black have been conducted in the United States, Germany, and the United Kingdom. Five mortality studies related to workers involved in the manufacture of titanium dioxide in the United States and Europe have also been conducted. In addition, a meta-analysis of the three-carbon black mortality studies was performed. In the random-effects meta-analysis, full cohort meta-SMRs were 1.01 (95% confidence interval (CI): 0.79–1.29) for heart disease; 1.02 (95% CI: 0.80–1.30) for ischemic heart disease; and 1.08 (95% CI: 0.74–1.59) for acute myocardial infarction (AMI) mortality. A small but imprecise increased AMI mortality risk was suggested for cumulative exposure by a meta-HR = 1.10 per 100 mg/m³-years (95% CI: 0.92–1.31) but not for lugged exposures, that is, for recent exposures. Results of five cohort mortality studies of titanium dioxide workers in the United States and Europe showed no excess in all heart disease or cardiovascular disease. In the most recent study in the United States, an internal analysis, that is, within the cohort itself, with no lag time, showed that the exposure group 15–35 mg/m³-years yielded a significantly increased risk for heart disease; however, there was no evidence of increasing risk with increasing exposure for any of the exposure categories. In contrast to environmental studies, the results of cohort mortality studies do not demonstrate that airborne occupational exposure to carbon black and titanium dioxide particulates increases cardiovascular disease mortality. The lack of a relationship between carbon black and titanium dioxide and CVD mortality suggests that the associations reported in air pollution studies may not be driven by the particulate component.

Dispersion of Natural Airborne TiO2 Fibres in Excavation Activity as a Potential Environmental and Human Health Risk

Titanium is the ninth most abundant element, approximately 0.7% of the Earth crust. It is used worldwide in large quantities for various applications. The IARC includes TiO2 in Group 2B as possibly carcinogenic to humans suggesting that pathological effects correlate to particle size and shape. This study case quantifies the release of natural TiO2 particles during mining activity, involving meta-basalt and shale lithologies in the Ligurian Alps, during excavation of the Terzo Valico as part of the Trans-European Transport Network. Type, width, length, aspect ratio, and concentration of TiO2 particles in needle habit were determined. The different samplings have reported that airborne concentrations in meta-basalt were 4.21 ff/L and 23.94 ff/L in shale. In both cases, the concentration never exceeds the limits established by various organizations for workers health protection. Nevertheless, TiO2 elongated particles, recognized as rutile, showed the dimensional characteristic of fibres, as reported by WHO. These fibres deserve particular attention because they can reach the alveolar space and trigger inflammation and chronic diseases. The results indicate that monitoring the TiO2 in both working environments and Ti-rich geological formations, associated with epidemiological studies, may represent a useful tool to determine the exposure risk of workers and the general population.

A Weight-of-the-Evidence Approach for Evaluating, in Lieu of Animal Studies, the Potential of a Novel Polysaccharide Polymer to Produce Lung Overload

The United States Environmental Protection Agency (EPA) is concerned about the respiratory effects caused by respirable particles of water-insoluble high molecular weight polymers. The EPA has proposed a tiered approach to evaluate polymer lung overload, a kinetic event. Kinetic polymer lung overload in itself is not necessarily adverse, however, inhalation of respirable particulate matter can have adverse effects (i.e., inflammation, fibrosis, etc.). If Tier I testing demonstrates that particles may reach the distal lung (i.e., a non-negligible amount of respirable particles/droplets ≤10 μm in diameter and lack of biosolubility), then animal inhalation testing in Tiers II-IV would be requested. In silico, in chemico, and in vitro alternatives should be considered versus in vivo testing for animal welfare purposes. An in chemico measure of biosolubility was used to demonstrate that a novel α-1,3-glucan polysaccharide, made by enzymatic polymerization of glucose from sucrose, is biosoluble and fits a simple exponential decay model with a half-life on the order of 66 days. The multiple-path particle dosimetry (MPPD) in silico model was used to predict lung burden for the novel α-1,3-glucan polysaccharide. MPPD was validated with measurements in rats exposed to a toner particulate and showed good agreement with lung burden measurements. A simulated 24 month rat exposure yielded 10-20 times less lung burden for the polysaccharide compared to the toner at equivalent exposure concentrations. The MPPD model was refined to include biosolubility data for the polysaccharide polymer. Data for amorphous silica were used to validate the clearance model, and the model incorporating dissolution predicted the amorphous silica lung burden within 20% of measured values. Human equivalent concentrations (HECs) were calculated for each toner rat exposure concentration. HECs were also determined for the polysaccharide at exposure concentrations yielding the same predicted internal doses as the toner. The in vitro, in chemico and in silico studies described here for the novel polysaccharide provide a useful weight of evidence approach in the absence of animal studies for the evaluation of polymer substances where polymer lung overload may be a concern.

Are Titania Photocatalysts and Titanium Implants Safe? Review on the Toxicity of Titanium Compounds

Titanium and its compounds are broadly used in both industrial and domestic products, including jet engines, missiles, prostheses, implants, pigments, cosmetics, food, and photocatalysts for environmental purification and solar energy conversion. Although titanium/titania-containing materials are usually safe for human, animals and environment, increasing concerns on their negative impacts have been postulated. Accordingly, this review covers current knowledge on the toxicity of titania and titanium, in which the behaviour, bioavailability, mechanisms of action, and environmental impacts have been discussed in detail, considering both light and dark conditions. Consequently, the following conclusions have been drawn: (i) titania photocatalysts rarely cause health and environmental problems; (ii) despite the lack of proof, the possible carcinogenicity of titania powders to humans is considered by some authorities; (iii) titanium alloys, commonly applied as implant materials, possess a relatively low health risk; (iv) titania microparticles are less toxic than nanoparticles, independent of the means of exposure; (v) excessive accumulation of titanium in the environment cannot be ignored; (vi) titanium/titania-containing products should be clearly marked with health warning labels, especially for pregnant women and young children; (vi) a key knowledge gap is the lack of comprehensive data about the environmental content and the influence of titania/titanium on biodiversity and the ecological functioning of terrestrial and aquatic ecosystems.

Titanium Dioxide Nanoparticles in Food and Personal Care Products-What Do We Know about Their Safety?

Titanium dioxide (TiO2) is a material of diverse applications commonly used as a food additive or cosmetic ingredient. Its prevalence in products of everyday use, especially in nanosize, raises concerns about safety. Current findings on the safety of titanium dioxide nanoparticles (TiO2 NPs) used as a food additive or a sunscreen compound are reviewed and systematized in this publication. Although some studies state that TiO2 NPs are not harmful to humans through ingestion or via dermal exposure, there is a considerable number of data that demonstrated their toxic effects in animal models. The final agreement on the safety of this nanomaterial has not yet been reached among researchers. There is also a lack of official, standardized guidelines for thorough characterization of TiO2 NPs in food and cosmetic products, provided by international authorities. Recent advances in the application of 'green-synthesized' TiO2 NPs, as well as comparative studies of the properties of 'biogenic' and 'traditional' nanoparticles, are presented. To conclude, perspectives and directions for further studies on the toxicity of TiO2 NPs are proposed.

Weight of epidemiological evidence for titanium dioxide risk assessment: current state and further needs

We address here the importance of epidemiological evidence in risk assessment and decision-making in Europe. To illustrate this, titanium dioxide (TiO₂) was used as a model compound. TiO₂ is widely used as an odorless white pigment and opacifying agent. A recent systematic review assessing the weight of evidence on the relationship between exposure to TiO₂ (all forms) and cancer in humans questions the assumptions that TiO₂ is an inert material of low toxicity. Based on this new data, France submitted a proposal to classify TiO₂ as a possible human carcinogen under the European regulation. The European Chemicals Agency Risk assessment committee concluded that TiO₂ (all forms) warrants a classification as a suspected human carcinogen via inhalation (Category-2) under the CLP regulation (for Classification, Labeling and Packaging of chemicals). No considerations was given to TiO₂ particle size, which may affect human health effects. Consequently, further epidemiological studies are needed to assess possible associations between different physical-chemical characteristics of TiO₂ exposures and their impact on human health. This would allow strengthening the evidence on which to build the most appropriate regulation and to guaranty safe use given any exposure route of any TiO₂ particle shape or size.

Mechanism of Action of TiO2: Recommendations to Reduce Uncertainties Related to Carcinogenic Potential

The Risk Assessment Committee of the European Chemicals Agency issued an opinion on classifying titanium dioxide (TiO₂) as a suspected human carcinogen upon inhalation. Recent animal studies indicate that TiO₂ may be carcinogenic through the oral route. There is considerable uncertainty on the carcinogenicity of TiO₂, which may be decreased if its mechanism of action becomes clearer. Here we consider adverse outcome pathways and present the available information on each of the key events (KEs). Inhalation exposure to TiO₂ can induce lung tumors in rats via a mechanism that is also applicable to other poorly soluble, low-toxicity particles. To reduce uncertainties regarding human relevance, we recommend gathering information on earlier KEs such as oxidative stress in humans. For oral exposure, insufficient information is available to conclude whether TiO₂ can induce intestinal tumors. An oral carcinogenicity study with well-characterized (food-grade) TiO₂ is needed, including an assessment of toxicokinetics and early KEs.

Titanium dioxide nanoparticles induce COX-2 expression through ROS generation in human periodontal ligament cells

Titanium dioxide nanoparticles (TiO₂-NPs) are used to improve the aesthetic of toothpaste. While TiO₂-NPs have been used safely in toothpaste products for a long time, there haven't been studies to determine whether absorption of TiO₂-NPs by the mucous membranes in the mouth induces pathogenic conditions. Here, we assessed whether TiO₂-NPs induce cyclooxygenase-2 (COX-2) and investigated the molecular mechanisms underlying the pro-inflammatory effect of TiO₂-NPs on human periodontal ligament (PDL) cells. Treatment of PDL cells with TiO₂-NPs led to induction of both COX-2 mRNA and protein expression. TiO₂-NPs stimulated the nuclear translocation of nuclear factor-kappaB (NF-κB) as well as its DNA binding by inducing phosphorylation and subsequent degradation of the inhibitory protein IκBα in PDL cells. TiO₂-NPs treatment resulted in rapid activation of extracellular signal-regulated kinase (ERK)1/2 and Akt, which could be upstream of NF-κB. Treatment of PDL cells with both the MEK1/2 inhibitor U0126 and the PI3K inhibitor LY294002 strongly attenuated TiO₂-NPs-induced activation of NF-κB, and also the expression of COX-2. PDL cells treated with TiO₂-NPs exhibited increased accumulation of intracellular reactive oxygen species (ROS). Pretreatment of cells with ROS scavenger N-acetyl cysteine (NAC) abrogated the stimulatory effect of TiO₂-NPs on p65, p50, and COX-2 expression. In conclusion, ROS, concomitantly overproduced by TiO₂-NPs, induce COX-2 expression through activation of NF-κB signaling, which may contribute to the inflammatory effect of PDL cells.

Gellan gum incorporating titanium dioxide nanoparticles biofilm as wound dressing: Physicochemical, mechanical, antibacterial properties and wound healing studies

In this work, the potential of titanium dioxide nanoparticles incorporated gellan gum (GG + TiO₂-NPs) biofilm as wound dressing material was investigated. The GG + TiO₂-NPs biofilm was prepared via evaporative casting technique and was characterized using FTIR, XRD, and SEM to study their physiochemical properties. The mechanical properties, swelling and water vapor transmission rate (WVTR) of biofilm was determined to comply with an ideal wound dressing material. In vitro and in vivo wound healing studies was carried out to evaluate the performance of GG + TiO₂-NPs biofilm. In vitro wound healing was studied on 3 T3 mouse fibroblast cells for cell viability, cell proliferation, and scratch assay. The acridine orange/propidium iodide (AO/PI) staining and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay were used to evaluate the viability of cell and cell proliferation. Cell migration assay was analyzed using Essen BioScience IncuCyteTM Zoom system. In vivo wound healing via open excision wounds model on Sprague Dawley rat was studied within 14 days. The FT-IR spectra of GG + TiO₂-NPs biofilm show main bands assigned to OH stretching, OH deformation, and TiO stretching modes. XRD pattern of GG + TiO₂-NPs biofilm suggesting that TiO₂-NPs was successfully incorporated in biofilm and well distributed on the surface as proved by SEM analysis. The GG + TiO₂-NPs biofilm shows higher mechanical strength and swelling (3.76 ± 0.11 MPa and 1061 ± 6%) as compared to pure GG film (3.32 ± 0.08 Mpa and 902 ± 6%), respectively. GG + TiO₂-NPs biofilm shows good antibacterial properties as 9 ± 0.25 mm and 11 ± 0.06 mm exhibition zone was observed against Staphylococcus aureus and Escherichia coli bacteria, respectively. While no exhibition zone was obtained for pure GG biofilm. GG + TiO₂-NPs biofilm also demonstrated better cell-to-cell interaction properties, as it's promoted cell proliferation and cell migration to accelerate open excision wound healing on Sprague Dawley rat. The wound treated with GG + TiO₂-NPs biofilm was healed within 14 days, on the other hand, the wound is still can be seen when it was treated with GG. However, GG and GG + TiO₂-NPs biofilm show no cytotoxicity effects on mouse fibroblast cells.

Current state of knowledge on the health effects of engineered nanomaterials in workers: a systematic review of human studies and epidemiological investigations

Objectives The widespread application of nano-enabled products and the increasing likelihood for workplace exposures make understanding engineered nanomaterial (ENM) effects in exposed workers a public and occupational health priority. The aim of this study was to report on the current state of knowledge on possible adverse effects induced by ENM in humans to determine the toxicological profile of each type of ENM and potential biomarkers for early detection of such effects in workers. Methods A systematic review of human studies and epidemiological investigations of exposed workers relative to the possible adverse effects for the most widely used ENM was performed through searches of major scientific databases including Web of Science, Scopus, and PubMed. Results Twenty-seven studies were identified. Most of the epidemiological investigations were cross-sectional. The review found limited evidence of adverse effects in workers exposed to the most commonly used ENM. However, some biological alterations are suggestive for possible adverse impacts. The primary targets of some ENM exposures were the respiratory and cardiovascular systems. Changes in biomarker levels compared with controls were also observed; however, limited exposure data and the relatively short period since the first exposure may have influenced the incidence of adverse effects found in epidemiological studies. Conclusions There is a need for longitudinal epidemiologic investigations with clear exposure characterizations for various ENM to discover potential adverse health effects and identify possible indicators of early biological alterations. In this state of uncertainty, precautionary controls for each ENM are warranted while further study of potential health effects continues.

Genotoxicity and gene expression analyses of liver and lung tissues of mice treated with titanium dioxide nanoparticles

Titanium dioxide nanoparticles (TiO₂ NPs) are used in paints, plastics, papers, inks, foods, toothpaste, pharmaceuticals and cosmetics. However, TiO₂ NPs cause inflammation, pulmonary damage, fibrosis and lung tumours in animals and are possibly carcinogenic to humans. Although there are a large number of studies on the toxicities of TiO₂ NPs, the data are inconclusive and the mechanisms underlying the toxicity are not clear. In this study, we used the Comet assay to evaluate genotoxicity and whole-genome microarray technology to analyse gene expression pattern in vivo to explore the possible mechanisms for toxicity and genotoxicity of TiO₂ NPs. Mice were treated with three daily i.p. injections of 50 mg/kg 10 nm anatase TiO₂ NPs and sacrificed 4 h after the last treatment. The livers and lungs were then isolated for the Comet assay and whole genome microarray analysis of gene expression. The NPs were heavily accumulated in liver and lung tissues. However, the treatment was positive for DNA strand breaks only in liver measured with the standard Comet assay, but positive for oxidative DNA adducts in both liver and lung as determined with the enzyme-modified Comet assay. The genotoxicity results suggest that DNA damage mainly resulted from oxidised nucleotides. Gene expression profiles and functional analyses revealed that exposure to TiO₂ NPs triggered distinct gene expression patterns in both liver and lung tissues. The gene expression results suggest that TiO₂ NPs impair DNA and cells by interrupting metabolic homeostasis in liver and by inducing oxidative stress, inflammatory responses and apoptosis in lung. These findings have broad implications when evaluating the safety of TiO₂ NPs used in numerous consumer products.

Relevance of the rat lung tumor response to particle overload for human risk assessment-Update and interpretation of new data since ILSI 2000

The relevance of particle-overload related lung tumors in rats for human risk assessment following chronic inhalation exposures to poorly soluble particulates (PSP) has been a controversial issue for more than three decades. In 1998, an ILSI (International Life Sciences) Working Group of health scientists was convened to address this issue of applicability of experimental study findings of lung neoplasms in rats for lifetime-exposed production workers to PSPs. A full consensus view was not reached by the Workshop participants, although it was generally acknowledged that the findings of lung tumors in rats following chronic inhalation, particle-overload PSP exposures occurred only in rats and no other tested species; and that there was an absence of lung cancers in PSP-exposed production workers. Since the publication of the ILSI Workshop report in 2000, there have been important new data published on the human relevance issue. A thorough and comprehensive review of the health effects literature on poorly soluble particles/lung overload was undertaken and published by an ECETOC (European Centre for Ecotoxicology and Toxicology of Chemicals) Task Force in 2013. One of the significant conclusions derived from that technical report was that the rat is unique amongst all species in developing lung tumors under chronic inhalation overload exposures to PSPs. Accordingly, the objective of this review is to provide important insights on the fundamental differences in pulmonary responses between experimentally-exposed rats, other experimental species and occupationally-exposed humans. Briefly, five central factors are described by the following issues. Focusing on these five interrelated/convergent factors clearly demonstrate an inappropriateness in concluding that the findings of lung tumors in rats exposed chronically to high concentrations of PSPs are accurate representations of the risks of lung cancer in PSP-exposed production workers. The most plausible conclusion that can be reached is that results from chronic particle-overload inhalation studies with PSPs in rats have no relevance for determining lung cancer risks in production workers exposed for a working lifetime to these poorly soluble particulate-types.

Risk assessment strategies for nanoscale and fine-sized titanium dioxide particles: Recognizing hazard and exposure issues

The basic tenets for assessing health risks posed by nanoparticles (NP) requires documentation of hazards and the corresponding exposures that may occur. Accordingly, this review describes the range and types of potential human exposures that may result from interactions with titanium dioxide (TiO2) particles or NP - either in the occupational/workplace environment, or in consumer products, including food materials and cosmetics. Each of those applications has a predominant route of exposure. Very little is known about the human impact potential from environmental exposures to NP - thus this particular issue will not be discussed further. In the workplace or occupational setting inhalation exposure predominates. Experimental toxicity studies demonstrate low hazards in particle-exposed rats. Only at chronic overload exposures do rats develop forms of lung pathology. These findings are not supported by multiple epidemiology studies in heavily-exposed TiO2 workers which demonstrate a lack of correlation between chronic particle exposures and adverse health outcomes including lung cancer and noncancerous chronic respiratory effects. Cosmetics and sunscreens represent the major application of dermal exposures to TiO2 particles. Experimental dermal studies indicate a lack of penetration of particles beyond the epidermis with no consequent health risks. Oral exposures to ingested TiO2 particles in food occur via passage through the gastrointestinal tract (GIT), with studies indicating negligible uptake of particles into the bloodstream of humans or rats with subsequent excretion through the feces. In addition, standardized guideline-mandated subchronic oral toxicity studies in rats demonstrate very low toxicity effects with NOAELs of >1000 mg/kg bw/day. Additional issues which are summarized in detail in this review are: 1) Methodologies for implementing the Nano Risk Framework - a process for ensuring the responsible development of products containing nanoscale materials; and 2) Safe-handling of nanomaterials in the laboratory.

Titanium dioxide exposure induces acute eosinophilic lung inflammation in rabbits

Titanium dioxide (TiO2) is increasingly widely used in industrial, commercial and home products. TiO2 aggravates respiratory symptoms by induction of pulmonary inflammation although the mechanisms have not been well investigated. We aimed to investigate lung inflammation in rabbits after intratracheal instillation of P25 TiO2. One ml of 10, 50 and 250µg of P25 TiO2 was instilled into one of the lungs of rabbits, chest computed-tomography was performed, and bronchoalveolar lavage (BAL) fluid was collected before, at 1 and 24 h after P25 TiO2 exposure. Changes in inflammatory cells in the BAL fluids were measured. Lung pathological assay was also carried out at 24 h after P25 TiO2 exposure. Ground glass opacities were noted in both lungs 1 h after P25 TiO2 and saline (control) instillation. Although the control lung showed complete resolution at 24 h, the lung exposed to P25 TiO2 showed persistent ground glass opacities at 24 h. The eosinophil counts in BAL fluid were significantly increased after P25 TiO2 exposure. P25 TiO2 induced a dose dependent increase of eosinophils in BAL fluid but no significant differences in neutrophil and lymphocyte cell counts were detected. The present findings suggest that P25 TiO2 induces lung inflammation in rabbits which is associated with eosinophilic inflammation.

Genotoxicity of titanium dioxide nanoparticles

Titanium dioxide nanoparticles (TiO₂-NPs, <100 nm) are increasingly being used in pharmaceuticals and cosmetics due to the unique properties derived from their small sizes. However, their large surface-area to mass ratio and high redox potential may negatively impact human health and the environment. TiO₂-NPs can cause inflammation, pulmonary damage, fibrosis, and lung tumors and they are possibly carcinogenic to humans. Because cancer is a disease involving mutation, there are a large number of studies on the genotoxicity of TiO₂-NPs. In this article, we review the results that have been reported in the literature, with a focus on data generated from the standard genotoxicity assays. The data include genotoxicity results from the Ames test, in vitro and in vivo Comet assay, in vitro and in vivo micronucleus assay, sister chromatid exchange assay, mammalian cell hypoxanthine-guanine phosphoribosyl transferase gene assay, the wing somatic mutation and recombination assay, and the mouse phosphatidylinositol glycan, class A gene assay. Inconsistent results have been found in these assays, with both positive and negative responses being reported. The in vitro systems for assessing the genotoxicity of TiO₂-NPs have generated a greater number of positive results than the in vivo systems, and tests for DNA and chromosome damage have produced more positive results than the assays measuring gene mutation. Nearly all tests for measuring the mutagenicity of TiO₂-NPs were negative. The current data indicate that the genotoxicity of TiO₂-NPs is mediated mainly through the generation of oxidative stress in cells.

How to measure hazards/risks following exposures to nanoscale or pigment-grade titanium dioxide particles

Due to its multifunctional applications, titanium dioxide particles have widespread use in commerce. The particle-types function as sources of pigment color, in food products, anti-bacterial components, ultraviolet radiation scavengers, catalysts, as well as in cosmetics. Because of its inherent properties in a diverse number of products, exposures may occur via any of the major point-of-entry routes, i.e., inhalation, oral or dermal. Although the majority of TiO2 applications are known to exist in the pigment-grade form, nanoscale forms of TiO2 are also common components in several products. This brief review is designed to identify relevant toxicology and risk-related issues which inform health effects assessments on the various forms of titanium dioxide particles. While there has been an abundance of hazard data generated on titanium dioxide particulates, many of the published reports have limited informational value for assessing health effects due, in large part, to shortcomings in experimental design issues, such as: (1) inadequate material characterization of test samples; (2) questionable relevance of experimental systems employed to simulate human exposures; (3) applications of generally high doses, exclusive focus on acute toxicity endpoints, and a lack of reference benchmark control materials, to afford interpretation of measured results; and/or (4) failure to recognize fundamental differences between hazard and risk concepts. Accordingly, a number of important toxicology issues are identified and integrated herein to provide a more comprehensive assessment of the health risks of different forms of pigment-grade and nanoscale titanium dioxide particles. It is important to note that particle-types of different TiO2 compositions may have variable toxicity potencies, depending upon crystal structure, particle size, particle surface characteristics and surface coatings. In order to develop a more robust health risk evaluation of TiO2 particle exposures, this review focuses on the following issues: (1) Introduction to TiO2 particle chemistry/functionality and importance of robust material characterization of test samples; (2) Implementation of meaningful hazard studies for gauging EHS safety issues – pulmonary bioassay data and development of the Nano Risk Framework for developmental nano TiO2 compounds; (3) Epidemiological study findings on titanium dioxide workers – the most heavily-exposed populations; (4) Methodologies for setting occupational exposure limits including benchmarking or bridging comparisons; and (5) The importance of particle overload data in the lungs of rats as it relates to gauging the relevance of health effects for humans. A comprehensive evaluation of the existing animal and human health data is a necessary prerequisite for facilitating accurate assessments of human health risks to TiO2 exposures.

Occupational exposure and mortality among workers at three titanium dioxide plants

BACKGROUND

A cohort of 3,607 workers employed in three DuPont titanium dioxide production facilities was followed from 1935 through 2006.

METHODS

Combined and plant-specific cohort mortality was compared with the overall US population and other DuPont employees. The relationships between selected causes of death and annual cumulative exposures to titanium dioxide and chloride were investigated using Poisson regression methods to examine trends with increasing exposure.

RESULTS

Among the 833 deaths, no causes of deaths were statistically significantly elevated either overall or plant-specific when compared to the US population. Compared to DuPont workers, statistically significantly elevated SMRs for all causes, all cancers, and lung cancers were found driven by the workers at the oldest plant. Comparing increasing exposure groups to the lowest group, disease risk did not increase with exposure.

CONCLUSIONS

There was no indication of a positive association between occupational exposure and death from all causes, all cancers, lung cancers, non-malignant respiratory disease, or all heart disease.

Differential mouse pulmonary dose and time course responses to titanium dioxide nanospheres and nanobelts

Three anatase titanium dioxide (TiO(2)) nanoparticles (NPs) were prepared; nanospheres (NSs), short nanobelts (NB1), and long nanobelts (NB2). These NPs were used to investigate the effect of NP shape and length on lung toxicity. Mice were exposed (0-30 µg per mouse) by pharyngeal aspiration and pulmonary toxicity was assessed over a 112-day time course. Whole lung lavage data indicated that NB1- and NB2-exposed mice, but not NS-exposed mice, had significant dose- and time-dependent pulmonary inflammation and damage. Histopathological analyses at 112 days postexposure determined no interstitial fibrosis in any NS-exposed mice, an increased incidence in 30 µg NB1-exposed mice, and significant interstitial fibrosis in 30 µg NB2-exposed mice. At 112 days postexposure, lung burden of NS was decreased by 96.4% and NB2 by 80.5% from initial deposition levels. At 112 days postexposure, enhanced dark field microscopy determined that alveolar macro- phages were the dominant deposition site, but a fraction of NB1 and NB2 was observed in the alveolar interstitial spaces. For the 30 µg exposure groups at 112 days postexposure, confocal micro- scopy and immunofluorescent staining demonstrated that retained NB2 but not NS were present in the interstitium subjacent to the terminal bronchiole near the normal location of the smallest lymphatic capillaries in the lung. These lymphatic capillaries play a critical role in particle clearance, and the accumulation of NB2, but not NS, suggests possible impaired lymphatic clearance by the high aspect ratio particles. In summary, our data indicate that TiO(2) NP shape alters pulmonary responses, with severity of responses being ranked as NS < NB1 < NB2.

Genotoxicity evaluation of titanium dioxide nanoparticles using the Ames test and Comet assay

Titanium dioxide nanoparticles (TiO2-NPs) are being used increasingly for various industrial and consumer products, including cosmetics and sunscreens because of their photoactive properties. Therefore, the toxicity of TiO2-NPs needs to be thoroughly understood. In the present study, the genotoxicity of 10nm uncoated sphere TiO2-NPs with an anatase crystalline structure, which has been well characterized in a previous study, was assessed using the Salmonella reverse mutation assay (Ames test) and the single-cell gel electrophoresis (Comet) assay. For the Ames test, Salmonella strains TA102, TA100, TA1537, TA98 and TA1535 were preincubated with eight different concentrations of the TiO2-NPs for 4 h at 37 °C, ranging from 0 to 4915.2 µg per plate. No mutation induction was found. Analyses with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) showed that the TiO2-NPs were not able to enter the bacterial cell. For the Comet assay, TK6 cells were treated with 0-200 µg ml(-1) TiO2-NPs for 24 h at 37 °C to detect DNA damage. Although the TK6 cells did take up TiO2-NPs, no significant induction of DNA breakage or oxidative DNA damage was observed in the treated cells using the standard alkaline Comet assay and the endonuclease III (EndoIII) and human 8-hydroxyguanine DNA-glycosylase (hOGG1)-modified Comet assay, respectively. These results suggest that TiO2-NPs are not genotoxic under the conditions of the Ames test and Comet assay.

The potential health risk of titania nanoparticles

Widespread use of titania nanoparticles (TNPs) has caused a significant release of TNPs into the environment, increasing human exposure to TNPs. The potential toxicity of TNPs has become an urgent concern. Various models have been used to evaluate the toxic effects of TNPs, but the relationship between TNPs' toxicity and physicochemical properties is largely unknown. This review summarizes relevant reports to support the development of better predictive toxicological models and the safe future application of TNPs.

Titanium dioxide in our everyday life; is it safe?

BACKGROUND

Titanium dioxide (TiO(2)) is considered as an inert and safe material and has been used in many applications for decades. However, with the development of nanotechnologies TiO(2) nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. Therefore increased human and environmental exposure can be expected, which has put TiO(2) nanoparticles under toxicological scrutiny. Mechanistic toxicological studies show that TiO(2) nanoparticles predominantly cause adverse effects via induction of oxidative stress resulting in cell damage, genotoxicity, inflammation, immune response etc. The extent and type of damage strongly depends on physical and chemical characteristics of TiO(2) nanoparticles, which govern their bioavailability and reactivity. Based on the experimental evidence from animal inhalation studies TiO(2) nanoparticles are classified as "possible carcinogenic to humans" by the International Agency for Research on Cancer and as occupational carcinogen by the National Institute for Occupational Safety and Health. The studies on dermal exposure to TiO(2) nanoparticles, which is in humans substantial through the use of sunscreens, generally indicate negligible transdermal penetration; however data are needed on long-term exposure and potential adverse effects of photo-oxidation products. Although TiO(2) is permitted as an additive (E171) in food and pharmaceutical products we do not have reliable data on its absorption, distribution, excretion and toxicity on oral exposure. TiO(2) may also enter environment, and while it exerts low acute toxicity to aquatic organisms, upon long-term exposure it induces a range of sub-lethal effects.

CONCLUSIONS

Until relevant toxicological and human exposure data that would enable reliable risk assessment are obtained, TiO(2) nanoparticles should be used with great care.

Pre-irradiation of anatase TiO2 particles with UV enhances their cytotoxic and genotoxic potential in human hepatoma HepG2 cells

Titanium dioxide (TiO(2)) is active in the UV region of the light spectra and is used as a photocatalyst in numerous applications. Photo-activated anatase TiO(2) particles promote increased production of free radicals. This is a desirable property, although the potential toxicity of such photo-activated TiO(2) particles on exposure of humans and the environment remains unknown. Therefore, we studied whether pre-irradiation of TiO(2) particles with UV influences their cytotoxic and genotoxic potential. The TiO(2) particles, as TiO(2)-A (<25 nm) and TiO(2)-B (>100 nm), were UV pre-irradiated (24h) and tested for cytotoxic and genotoxic activities in human hepatoma HepG2 cells. Non-irradiated TiO(2)-A/B at 1.0-250 μg/ml did not reduce viability of HepG2 cells, nor induce significant increases in DNA strand breaks; only TiO(2)-A induced significant increases in oxidative DNA damage. After UV pre-irradiation, both TiO(2)-A and TiO(2)-B reduced cell viability and induced significant increases in DNA strand breaks and oxidative DNA damage. This is the first study that shows that UV pre-irradiation of anatase TiO(2) particles results in increased cytotoxic and genotoxic potential. This warrants further studies as it has important implications for environmental and human health risk assessment and preventive actions to limit human exposure.

The effect of titanium dioxide on the biochemical constituents of the brain of Zebrafish (Danio rerio): an FT-IR study

During recent years, the use of nanoparticles (NPs) in commercial products and industrial applications has increased greatly. One of the most widely used nanoparticles is titanium dioxide (nTiO(2)). It is a very versatile compound that has many uses, depending on its particle size. In the present paper an attempt is made to study the effect of TiO(2) nanoparticles and its bulk material on the biochemical constituents of the brain of Zebrafish (Danio rerio) by using FT-IR technique. FT-IR spectra reveals significant differences in absorbance intensities between the control and TiO(2) exposed brain tissues, reflecting alterations on the major biochemical constituents such as proteins, lipids and nucleic acids in the brain tissues of D. rerio due to TiO(2) exposure. The results further reveal that TiO(2) nanoparticles are more toxic than their bulk counterparts. The higher ratio of integrated area of carbonyl-to-CH(2) peaks (1743 cm(-1):1458 cm(-1)) observed in the present study in the nTiO(2) exposed brain tissues suggests that lipids are being oxidized. Since oxidation can cause an increase in carbonyls and a degradation of lipids, both of these changes could be contributed to the elevated ratio. Further, the observed decreasing ratio of integrated areas of both 1458 cm(-1):1542 cm(-1) and 1743 cm(-1):1542 cm(-1) in the TiO(2) exposed tissues suggests that lipid degradation predominates over carbonyl formation. The observed changes in the biochemical constituents in the brain tissues of D. rerio could be due to the overproduction of ROS.

Distinct biological effects of different nanoparticles commonly used in cosmetics and medicine coatings

BACKGROUND

Metal oxides in nanoparticle form such as zinc oxide and titanium dioxide now appear on the ingredient lists of household products as common and diverse as cosmetics, sunscreens, toothpaste, and medicine. Previous studies of zinc oxide and titanium dioxide in non-nanoparticle format using animals have found few adverse effects. This has led the FDA to classify zinc oxide as GRAS (generally recognized as safe) for use as a food additive. However, there is no regulation specific for the use of these chemicals in nanoparticle format. Recent studies, however, have begun to raise concerns over the pervasive use of these compounds in nanoparticle forms. Unfortunately, there is a lack of easily-adaptable screening methods that would allow for the detection of their biological effects.

RESULTS

We adapted two image-based assays, a fluorescence resonance energy transfer-based caspase activation assay and a green fluorescent protein coupled-LC3 assay, to test for the biological effects of different nanoparticles in a high-throughput format. We show that zinc oxide nanoparticles are cytotoxic. We also show that titanium dioxide nanoparticles are highly effective in inducing autophagy, a cellular disposal mechanism that is often activated when the cell is under stress.

CONCLUSION

We suggest that these image-based assays provide a method of screening for the biological effects of similar compounds that is both efficient and sensitive as well as do not involve the use of animals.

Toxicological effects of titanium dioxide nanoparticles: a review of in vitro mammalian studies

BACKGROUND AND OBJECTIVE

Recent rapid advances in nanotechnology raise concerns about development, production route, and diffusion in industrial and consumer products of titanium dioxide nanoparticles (TiO2-NPs). In fact, compared to recent increase in applications of this nanomaterial, the health effects of human exposure have not been systematically investigated. The aim of this review was to provide a comprehensive overview on the current knowledge regarding the effects of TiO2-NPs on mammalian cells.

EVIDENCE AND INFORMATION SOURCES

This review is based on an analysis of the current literature on this topic.

STATE OF THE ART

Fine TiO2 particles have been considered as safe and to pose little risk to humans, suggesting that exposure to this material is relatively harmless. However, available data in the literature showed that TiO2-NPs can cause several adverse effects on mammalian cells such as increase of reactive oxygen species (ROS) production and cytokines levels, reduction of cell viability and proliferation, induction of apoptosis and genotoxicity.

PERSPECTIVES AND CONCLUSIONS

Additional research is needed to obtain up-to-date knowledge on health effects of TiO2-NPs and to avoid any potential risk correlated to their exposure. Consequently, future studies need to: (1) use an homogeneous and rigorous exposure classification to clarify how the physicochemical properties of TiO2-NPs correlate with their toxicological effects; (2) assess the potential adverse effects of low level exposures to TiO2-NPs, as most of the information currently available originates from studies in which exposure levels were excessively and unrealistically high; (3) identify the possible roles of TiO2-NPs in genotoxicity and carcinogenicity (4) carry out epidemiologic studies of exposed workers to provide an assessment of possible risks correlated to the occupational exposure to TiO2-NPs.

Binding of human serum proteins to titanium dioxide particles in vitro

OBJECTIVES

To determine the capacity of human serum proteins to bind to titanium dioxide (TiO(2)) particles of different polymorphs and sizes.

METHODS

TiO(2) particles were mixed with diluted human serum, purified human serum albumin (HSA) or purified human serum gamma-globulin (HGG) solutions. After incubation at 37°C for 1 h, the particles were sedimented by centrifugation, and proteins in the supernatant, as well as those bound to the particles, were analyzed.

RESULTS

The total protein concentration in the supernatant was lowered by TiO(2), whereas the albumin/globulin ratio was elevated by the particles. Incubation with TiO(2) also lowered the immunoglobulin, pre-albumin, beta2-microglobulin, ceruloplasmin and retinol-binding protein levels, but not ferritin levels, in the supernatant. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), proteins in the supernatant, especially HGG, were observed to decrease, while those released from the particles (after adding 1% SDS and heating) increased, depending on the dose of TiO(2). Purified HGG and HSA were also bound to TiO(2), although the former appeared to have a higher affinity. All the proteins tested showed the highest binding potency to the amorphous particles (<50 nm) and the lowest to the rutile particles (<5,000 nm), while binding to anatase particles was intermediate. The affinity to the larger anatase was higher than that to smaller anatase particles in most cases.

CONCLUSIONS

Human serum proteins, including the two major components, HSA and HGG, are bound by TiO(2) particles. The polymorph of the particles seems to be important for determining the binding capacity of the particles and it may affect distribution of the particles in the body.

The carcinogenic potential of nanomaterials, their release from products and options for regulating them

A summary of a critical review by a working group of the German Federal Environment Agency and the German Federal Institute for Risk Assessment on the carcinogenic potential of nanomaterials is presented. After a critical review of the available data, we conclude that the potential carcinogenic risk of nanomaterials can currently be assessed only on a case-by-case basis. There is certain evidence that different forms of CNTs (carbon nanotubes) and nanoscale TiO(2) particles may induce tumours in sensitive animal models. It is assumed that the mode of action of the inhalation toxicity of asbestos-like fibres and of inhalable fractions of biopersistent fine dusts of low toxicity (nano-TiO(2)) is linked to chronic inflammatory processes. Existing epidemiological studies on carcinogenicity for these manufactured nanomaterials are not sufficiently conclusive. Generally speaking, the database is not adequate for an assessment of the carcinogenic potential of nanomaterials. Whereas a number of studies provide evidence of a nano-specific potential to induce tumours, other studies did not. This is possibly due to insufficient characterisation of the test material, difference in the experimental design, the use of different animal models and species and/or differences in dosimetry (both with regard to the appropriate dose metric and the estimated effective dose quantities). An assessment of the carcinogenic potential and its relevance for humans are currently fraught with uncertainty. Furthermore, the nano-specificity of the carcinogenic effects observed cannot be conclusively evaluated. Specific carcinogenic effects of nanomaterials may be both quantitative and qualitative. In quantitative terms, the carcinogenic effects of nanoparticles are thought to be simply more pronounced compared to the corresponding bulk material (due, for example, to the considerably larger surface area and higher number of particles relative to the mass concentration). On the other hand, certain nano-properties such as small size, shape and reactivity, retention time and distribution in the body after overcoming biological barriers, as well as subcellular and molecular interactions may play a role in determining the toxicity in qualitative terms, i.e. the carcinogenic potential of the nanomaterial and the non-nanoscale comparison substance may be fundamentally different. All of these factors leave no doubt about the fact that there is a great need for research in this area and that new standardised test methods need to be developed or existing ones adapted at the very least to achieve valid answers regarding the carcinogenic potential of nanomaterials. Global production of nanomaterials is set to increase in the years to come, and new materials with new properties will be developed, so that greater human exposure to them must be anticipated. No reliable conclusions can currently be drawn about exposure to nanoparticles and their release from products. Firstly, there are substantial deficits in information about the processing of nanomaterials in products and preparations. Secondly, there are only a small number of studies on nanoparticle release, and reliable techniques for measuring and monitoring nanomaterials in different environmental media are still being developed which is both complex and costly. Despite the uncertainties, the findings to date on the carcinogenic potential of nanomaterials must be taken seriously, and precautionary measures to minimise exposure should go hand in hand with the development of a comprehensive and conclusive toxicological methodology and testing procedure for nanostructured materials that includes all possible exposure routes. With regard to possible legal classification of nanomaterials and the transferability of classifications of their non-nanomaterial counterparts, we believe it is necessary to have separate procedures for nano and non-nano forms. Furthermore, criteria for evaluating nano-specific carcinogenic properties should be constantly updated and adapted to the state of knowledge. There is a need here for amendments to be made to EU legislation, as currently nanoforms do not represent a separate category of substance in their own right.

Enzymatic recognition of DNA damage induced by UVB-photosensitized titanium dioxide and biological consequences in Saccharomyces cerevisiae: evidence for oxidatively DNA damage generation

Although titanium dioxide (TiO(2)) has been considered to be biologically inert, finding use in cosmetics, paints and food colorants, recent reports have demonstrated that when TiO(2) is attained by UVA radiation oxidative genotoxic and cytotoxic effects are observed in living cells. However, data concerning TiO(2)-UVB association is poor, even if UVB radiation represents a major environmental carcinogen. Herein, we investigated DNA damage, repair and mutagenesis induced by TiO(2) associated with UVB irradiation in vitro and in vivo using Saccharomyces cerevisiae model. It was found that TiO(2) plus UVB treatment in plasmid pUC18 generated, in addition to cyclobutane pyrimidine dimers (CPDs), specific damage to guanine residues, such as 8-oxo-7,8-dihydroguanine (8-oxoG) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG), which are characteristic oxidatively generated lesions. In vivo experiments showed that, although the presence of TiO(2) protects yeast cells from UVB cytotoxicity, high mutation frequencies are observed in the wild-type (WT) and in an ogg1 strain (deficient in 8-oxoG and FapyG repair). Indeed, after TiO(2) plus UVB treatment, induced mutagenesis was drastically enhanced in ogg1 cells, indicating that mutagenic DNA lesions are repaired by the Ogg1 protein. This effect could be attenuated by the presence of metallic ion chelators: neocuproine or dipyridyl, which partially block oxidatively generated damage occurring via Fenton reactions. Altogether, the results indicate that TiO(2) plus UVB potentates UVB oxidatively generated damage to DNA, possibly via Fenton reactions involving the production of DNA base damage, such as 8-oxo-7,8-dihydroguanine.

Disturbed mitotic progression and genome segregation are involved in cell transformation mediated by nano-TiO2 long-term exposure

Titanium dioxide (TiO2) nano-particles (<100 nm in diameter) have been of interest in a wide range of applications, such as in cosmetics and pharmaceuticals because of their low toxicity. However, recent studies have shown that TiO2 nano-particles (nano-TiO2) induce cytotoxicity and genotoxicity in various lines of cultured cells as well as tumorigenesis in animal models. The biological roles of nano-TiO2 are shown to be controversial and no comprehensive study paradigm has been developed to investigate their molecular mechanisms. In this study, we showed that short-term exposure to nano-TiO2 enhanced cell proliferation, survival, ERK signaling activation and ROS production in cultured fibroblast cells. Moreover, long-term exposure to nano-TiO2 not only increased cell survival and growth on soft agar but also the numbers of multinucleated cells and micronucleus (MN) as suggested in confocal microscopy analysis. Cell cycle phase analysis showed G2/M delay and slower cell division in long-term exposed cells. Most importantly, long-term TiO2 exposure remarkably affected mitotic progression at anaphase and telophase leading to aberrant multipolar spindles and chromatin alignment/segregation. Moreover, PLK1 was demonstrated as the target for nano-TiO2 in the regulation of mitotic progression and exit. Notably, a higher fraction of sub-G1 phase population appeared in TiO2-exposed cells after releasing from G2/M synchronization. Our results demonstrate that long-term exposure to nano-TiO2 disturbs cell cycle progression and duplicated genome segregation, leading to chromosomal instability and cell transformation.

Nano titanium dioxide particles promote allergic sensitization and lung inflammation in mice

The purpose of this study was to investigate whether photocatalytic TiO₂ nanoparticles have adjuvant effect, when administered in combination with ovalbumin (OVA) in mice. Mice were immunized via intraperitoneal injections of OVA, OVA + TiO₂ or OVA + Al(OH)₃ and challenged with aerosols of OVA. At the end of the study, serum was analysed for content of OVA-specific IgE, IgG1 and IgG2a antibodies, and the bronchoalveolar lavage fluid (BALF) was analysed for content of inflammatory cells and levels of interleukin (IL)-4, IL-5, IL-10 and interferon-γ. The TiO₂ particles promoted a Th2 dominant immune response with high levels of OVA-specific IgE and IgG1 in serum and influx of eosinophils, neutrophils and lymphocytes in BALF. The TiO₂ particles induced a significantly higher level of OVA-specific IgE than the standard adjuvant Al(OH)₃. However, the two substances were comparable regarding the level of eosinophilic inflammation and interleukins present in BALF.

Nano-scaled particles of titanium dioxide convert benign mouse fibrosarcoma cells into aggressive tumor cells

Nanoparticles are prevalent in both commercial and medicinal products; however, the contribution of nanomaterials to carcinogenesis remains unclear. We therefore examined the effects of nano-sized titanium dioxide (TiO(2)) on poorly tumorigenic and nonmetastatic QR-32 fibrosarcoma cells. We found that mice that were cotransplanted subcutaneously with QR-32 cells and nano-sized TiO(2), either uncoated (TiO(2)-1, hydrophilic) or coated with stearic acid (TiO(2)-2, hydrophobic), did not form tumors. However, QR-32 cells became tumorigenic after injection into sites previously implanted with TiO(2)-1, but not TiO(2)-2, and these developing tumors acquired metastatic phenotypes. No differences were observed either histologically or in inflammatory cytokine mRNA expression between TiO(2)-1 and TiO(2)-2 treatments. However, TiO(2)-2, but not TiO(2)-1, generated high levels of reactive oxygen species (ROS) in cell-free conditions. Although both TiO(2)-1 and TiO(2)-2 resulted in intracellular ROS formation, TiO(2)-2 elicited a stronger response, resulting in cytotoxicity to the QR-32 cells. Moreover, TiO(2)-2, but not TiO(2)-1, led to the development of nuclear interstices and multinucleate cells. Cells that survived the TiO(2) toxicity acquired a tumorigenic phenotype. TiO(2)-induced ROS formation and its related cell injury were inhibited by the addition of antioxidant N-acetyl-l-cysteine. These results indicate that nano-sized TiO(2) has the potential to convert benign tumor cells into malignant ones through the generation of ROS in the target cells.

In vivo acute toxicity of titanium dioxide nanoparticles to mice after intraperitioneal injection

Because of its excellent optical performance and electrical properties, TiO2 has a wide range of applications in many fields. It is often considered to be physiologically inert to humans. However, some recent studies have reported that nano-sized TiO2 may generate potential harm to the environment and humans. In this paper the in vivo acute toxicity of nano-sized TiO2 particles to adult mice was investigated. Mice were injected with different dosages of nano-sized TiO2 (0, 324, 648, 972, 1296, 1944 or 2592 mg kg(-1)). The effects of particles on serum biochemical levels were evaluated at various time points (24 h, 48 h, 7 days and 14 days). Tissues (spleen, heart, lung, kidney and liver) were collected for titanium content analysis and histopathological examination. Treated mice showed signs of acute toxicity such as passive behavior, loss of appetite, tremor and lethargy. Slightly elevated levels of the enzymes alanine aminotransferase and aspartate aminotransferase were found from the biochemical tests of serum whereas blood urea nitrogen was not significantly affected (P < 0.05). The accumulation of TiO2 was highest in spleen (P < 0.05). TiO2 was also deposited in liver, kidney and lung. Histopathological examinations showed that some TiO2 particles had entered the spleen and caused the lesion of spleen. Thrombosis was found in the pulmonary vascular system, which could be induced by the blocking of blood vessels with TiO2 particles. Moreover, hepatocellular necrosis and apoptosis, hepatic fibrosis, renal glomerulus swelling and interstitial pneumonia associated with alveolar septal thickening were also observed in high-dose groups.

Exposure to titanium dioxide and other metallic oxide nanoparticles induces cytotoxicity on human neural cells and fibroblasts

The use of titanium dioxide (TiO₂) in various industrial applications (eg, production of paper, plastics, cosmetics, and paints) has been expanding thereby increasing the occupational and other environmental exposure of these nanoparticles to humans and other species. However, the health effects of exposure to TiO₂ nanoparticles have not been systematically assessed even though recent studies suggest that such exposure induces inflammatory responses in lung tissue and cells. Because the effects of such nanoparticles on human neural cells are unknown, we have determined the putative cytotoxic effects of these nanoparticles on human astrocytes-like astrocytoma U87 cells and compared their effects on normal human fibroblasts. We found that TiO₂ micro- and nanoparticles induced cell death on both human cell types in a concentration-related manner. We further noted that zinc oxide (ZnO) nanoparticles were the most effective, TiO₂ nanoparticles the second most effective, and magnesium oxide (MgO) nanoparticles the least effective in inducing cell death in U87 cells. The cell death mechanisms underlying the effects of TiO₂ micro- and nanoparticles on U87 cells include apoptosis, necrosis, and possibly apoptosis-like and necrosis-like cell death types. Thus, our findings may have toxicological and other pathophysiological implications on exposure of humans and other mammalian species to metallic oxide nanoparticles.

Adverse effects of titanium dioxide nanoparticles on human dermal fibroblasts and how to protect cells

The effects of exposure of human dermal fibroblasts to rutile and anatase TiO(2) nanoparticles are reported. These particles can impair cell function, with the latter being more potent at producing damage. The exposure to nanoparticles decreases cell area, cell proliferation, mobility, and ability to contract collagen. Individual particles are shown to penetrate easily through the cell membrane in the absence of endocytosis, while some endocytosis is observed for larger particle clusters. Once inside, the particles are sequestered in vesicles, which continue to fill up with increasing incubation time till they rupture. Particles coated with a dense grafted polymer brush are also tested, and, using flow cytometry, are shown to prevent adherence to the cell membrane and hence penetration of the cell, which effectively decreases reactive oxygen species (ROS) formation and protects cells, even in the absence of light exposure. Considering the broad applications of these nanoparticles in personal health care products, the functionalized polymer coating can potentially play an important role in protecting cells and tissue from damage.

Assessing the airborne titanium dioxide nanoparticle-related exposure hazard at workplace

The purpose of this study was to investigate the effects of size and phase composition on human exposure to airborne titanium dioxide (TiO(2)) nanoparticles (NPs) at workplaces. We reanalyzed published data of particle size distribution of airborne TiO(2) NPs during manufacturing activities and linked a physiologically based lung model to estimate size- and phase-specific TiO(2) NP burdens in target lung cells. We also adopted a cell model to simulate the exposure time-dependent size/phase-specific cell uptake of TiO(2) NPs in human dermal and lung cells. Combining laboratory, field, and modeling results, we proposed two major findings: (i) the estimated median effective anatase TiO(2) NP concentration (EC50) for cytotoxicity response on human dermal fibroblasts was estimated to be 24.84 (95% CI: 7.3-70.2) nmolmL(-1) and EC50 estimate for inflammatory response on human lung epithelial cells was 5414 (95% CI: 3370-7479) nmolmL(-1) and (ii) packers and surface treatment workers at the TiO(2) NP production workplaces are unlikely to pose substantial risk on lung inflammatory response. Nevertheless, our findings point out that TiO(2) NP production workers have significant risk on cytotoxicity response at relatively high airborne anatase TiO(2) NP concentrations at size range 10-30nm.

Lung cancer and exposure to metals: the epidemiological evidence

Exposure to metallic compounds is ubiquitous, with its widespread use in industry and its presence, mostly in trace amounts, in the environment. This paper reviews the epidemiologic evidence of the relation between lung cancer and exposure to metallic compounds by building on and updating the corresponding International Agency for Research on Cancer (IARC) assessments. Given that most of the well-identified human populations with given metal exposure are in occupational settings, this review is mostly based on results in occupational epidemiology. The epidemiological evidence is shortly reviewed for accepted carcinogens: chromium, nickel, beryllium, cadmium, arsenic, and silicon, highlighting what is still unclear. We then review in more detail metals for which the evidence is less clear: lead, titanium, iron, and cobalt. There is scarce evidence for the human carcinogenicity of titanium. Exposure to titanium dioxide is associated with lung cancer excesses in one large study, but this excess may be due to confounders. The evidence for lead is contradictory. The lung cancer risk is presented as a function of a post hoc exposure ranking but no dose-response relationship is found. A weak but consistent lung cancer excess in many populations exposed to iron oxides but it is not possible to state on causality. Finally the evidence in the hard metal industry is presented, which suggests a possible carcinogenic effect of cobalt in presence of tungsten carbide. A short discussion presents the limitations of epidemiology in assessing the carcinogenicity of metals.

Antimicrobial nanomaterials for water disinfection and microbial control: potential applications and implications

The challenge to achieve appropriate disinfection without forming harmful disinfection byproducts by conventional chemical disinfectants, as well as the growing demand for decentralized or point-of-use water treatment and recycling systems calls for new technologies for efficient disinfection and microbial control. Several natural and engineered nanomaterials have demonstrated strong antimicrobial properties through diverse mechanisms including photocatalytic production of reactive oxygen species that damage cell components and viruses (e.g. TiO2, ZnO and fullerol), compromising the bacterial cell envelope (e.g. peptides, chitosan, carboxyfullerene, carbon nanotubes, ZnO and silver nanoparticles (nAg)), interruption of energy transduction (e.g. nAg and aqueous fullerene nanoparticles (nC(60))), and inhibition of enzyme activity and DNA synthesis (e.g. chitosan). Although some nanomaterials have been used as antimicrobial agents in consumer products including home purification systems as antimicrobial agents, their potential for disinfection or microbial control in system level water treatment has not been carefully evaluated. This paper reviews the antimicrobial mechanisms of several nanoparticles, discusses their merits, limitations and applicability for water disinfection and biofouling control, and highlights research needs to utilize novel nanomaterials for water treatment applications.