Review of the Evidence from Epidemiology, Toxicology, and Lung Bioavailability on the Carcinogenicity of Inhaled Iron Oxide Particulates

Inflammation related to inhalation of nano and micron sized iron oxides: a systematic review

Inhalation exposure to iron oxide occurs in many workplaces and respirable aerosols occur during thermal processes (e.g. welding, casting) or during abrasion of iron and steel products (e.g. cutting, grinding, machining, polishing, sanding) or during handling of iron oxide pigments. There is limited evidence of adverse effects in humans specifically linked to inhalation of iron oxides. This contrasts to oxides of other metals used to alloy or for coating of steel and iron of which several have been classified as being hazardous by international and national agencies. Such metal oxides are often present in the air at workplaces. In general, iron oxides might therefore be regarded as low-toxicity, low-solubility (LTLS) particles, and are often considered to be nontoxic even if very high and prolonged inhalation exposures might result in diseases. In animal studies, such exposures lead to cancer, fibrosis and other diseases. Our hypothesis was that pulmonary-workplace exposure during manufacture and handling of SPION preparations might be harmful. We therefore conducted a systematic review of the relevant literature to understand how iron oxides deposited in the lung are related to acute and subchronic pulmonary inflammation. We included one human and several in vivo animal studies published up to February 2023. We found 25 relevant studies that were useful for deriving occupational exposure limits (OEL) for iron oxides based on an inflammatory reaction. Our review of the scientific literature indicates that lowering of health-based occupational exposure limits might be considered.

MicroRaman spectroscopy detects the presence of microplastics in human urine and kidney tissue

There is a growing concern within the medical community about the potential burden of microplastics on human organs and tissues. In this study, we investigated by microRaman spectroscopy the presence of microplastics in human kidneys and urine. Moreover, an open-access software was developed and validated for the project, which enabled the comparison between the investigated spectra and a self-created spectral database, thus enhancing the ability to characterize polymers and pigments in biological matrices. Healthy portions of ten kidneys obtained from nephrectomies, as well as ten urine samples from healthy donors were analyzed: 26 particles in both kidney and urine samples were identified, with sizes ranging from 3 to 13 μm in urine and from 1 to 29 μm in kidneys. The most frequently determined polymers are polyethylene and polystyrene, while the most common pigments are hematite and Cu-phthalocyanine. This preclinical study proves the presence of microplastics in renal tissues and confirms their presence in urine, providing the first evidence of kidney microplastics deposition in humans.

Iron Load Toxicity in Medicine: From Molecular and Cellular Aspects to Clinical Implications

Iron is essential for all organisms and cells. Diseases of iron imbalance affect billions of patients, including those with iron overload and other forms of iron toxicity. Excess iron load is an adverse prognostic factor for all diseases and can cause serious organ damage and fatalities following chronic red blood cell transfusions in patients of many conditions, including hemoglobinopathies, myelodyspasia, and hematopoietic stem cell transplantation. Similar toxicity of excess body iron load but at a slower rate of disease progression is found in idiopathic haemochromatosis patients. Excess iron deposition in different regions of the brain with suspected toxicity has been identified by MRI T2* and similar methods in many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Based on its role as the major biological catalyst of free radical reactions and the Fenton reaction, iron has also been implicated in all diseases associated with free radical pathology and tissue damage. Furthermore, the recent discovery of ferroptosis, which is a cell death program based on free radical generation by iron and cell membrane lipid oxidation, sparked thousands of investigations and the association of iron with cardiac, kidney, liver, and many other diseases, including cancer and infections. The toxicity implications of iron in a labile, non-protein bound form and its complexes with dietary molecules such as vitamin C and drugs such as doxorubicin and other xenobiotic molecules in relation to carcinogenesis and other forms of toxicity are also discussed. In each case and form of iron toxicity, the mechanistic insights, diagnostic criteria, and molecular interactions are essential for the design of new and effective therapeutic interventions and of future targeted therapeutic strategies. In particular, this approach has been successful for the treatment of most iron loading conditions and especially for the transition of thalassemia from a fatal to a chronic disease due to new therapeutic protocols resulting in the complete elimination of iron overload and of iron toxicity.

Application of Fe-RGO for the removal of dyes by catalytic ozonation process

Due to continuous industrialization, the discharge of hazardous dyes has enormously disrupted the ecosystem causing environmental problems. Due to the stable recalcitrant nature of dyes, advanced catalytic ozonation processes with the latest catalyst are under investigation. Fe-RGO is an effective oxidation catalyst, and the metal loaded platform provides enhanced catalytic performance. This study aims to investigate the effectiveness of Fe-RGO/O3 process for the removal of dyes. In the current research, the application of iron-coated reduced graphene oxide (Fe-RGO) was studied as a catalyst in the heterogeneous catalytic ozonation process to remove dyes. Methylene blue (MB) was selected as a model pollutant. RGO was prepared using the improved Hummers method and was coated with iron (Fe) implying the impregnation method. The FTIR, SEM-EDX, XRD, and BET analyses of RG and Fe-RGO were performed to characterize the catalyst. The effect of various parameters such as pH (3-10), catalyst dose (0.01-0.04 g), and radical scavengers (NaHCO3, NaCl) on removal efficiency was elucidated. The result revealed an excellent catalytic efficiency of Fe-RGO in the ozonation process. At optimum conditions, 96% removal efficiency was achieved in catalytic ozonation at pH 7 with a catalyst dose of 0.02 g and ozone dose 0.5 mg/min, after 10 min. Interestingly, a slight decrease in removal efficiency was observed in the catalytic ozonation process in hydroxyl radical scavengers (NaCl and NaHCO3), which makes the proposed catalyst more applicable in real conditions. Therefore, it is concluded that Fe-RGO can be used as an excellent catalyst for the removal of dyes in real conditions where radical scavengers may be present in a significant amount.

Toxicity assessment and health hazard classification of stainless steels

Stainless steels are widely used iron-based alloys that contain chromium and, typically, other alloying elements. The chromium(III)-rich surface oxide of stainless steels efficiently limits the release (bioaccessibility) of their metal constituents in most physiological environments, influencing the toxicity of the alloy. Of the constituents and impurities of stainless steels, nickel and cobalt are of particular interest, primarily due to skin sensitization and repeated-dose inhalation toxicity of nickel, and (inhalation) carcinogenicity of cobalt. A review of the available toxicological data on stainless steels, and the toxicological, mechanistic, and bioaccessibility data on their constituent metals supports the low toxicity and non-carcinogenicity of stainless steels. The comparative metal release, rather than the bulk composition of stainless steels, needs to be considered when assessing their health hazard classification according to the UN Globally Harmonized System, and the corresponding EU CLP regulation. As an illustrative example, a 28-day inhalation toxicity study on stainless steel powder showed no signs of lung toxicity at exposure levels at which significant toxicity would have been expected on the basis of its bulk nickel content. This finding is associated with the low bioaccessibility of nickel from the alloy in the lungs.

Iron oxide nanoparticles exert inhibitory effects on N-Bis(2-hydroxypropyl)nitrosamine (DHPN)-induced lung tumorigenesis in rats

Iron oxide nanoparticles (magnetite) have been widely used in industry and medicine. However, the safety assessment of magnetite has not been fully completed. The present study was conducted to assess effects of magnetite on carcinogenic activity, using a medium-term bioassay protocol. A total of 100 male Fischer 344 rats, 6 weeks old, were randomly divided into 5 groups of 20 animals each, and given a basal diet and drinking water containing 0 or 0.1% of N-bis(2-hydroxypropyl)nitrosamine (DHPN) for 2 weeks. Two weeks later, the rats were intratracheally instilled magnetite 7 times at an interval of 4 weeks, at the doses of 0, 1.0 or 5.0 mg/kg body weight, and sacrificed at the end of the experimental period of 30 weeks. The multiplicities of macroscopic lung nodules and histopathologically diagnosed bronchiolo-alveolar hyperplasia, induced by DHPN, were both significantly decreased by the high dose of magnetite. The expression of minichromosome maintenance (MCM) protein 7 in non-tumoral alveolar epithelial cells, and the number of CD163-positive macrophages in tumor nodules were both significantly reduced by magnetite. It is suggested that magnetite exerts inhibitory effects against DHPN-induced lung tumorigenesis, by the reduction of alveolar epithelial proliferation and the M2 polarization of tumor-associated macrophages.

Interactive toxicity effect of combined exposure to hematite and amorphous silicon dioxide nanoparticles in human A549 cell line

The study on the health effects of combined exposure to various contaminants has been recommended by many authors. The objective of the present study was to examine the effects of the co-exposure to hematite and amorphous silicon dioxide (A-SiO₂) nanoparticles on the human lung A₅₄₉ cell line. The A₅₄₉ cell line was exposed to 10, 50, 100, and 250 µg/ml concentrations of hematite and A-SiO₂ nanoparticles both independently and in combination. Their toxicity in both circumstances was investigated by MTT, intracellular reactive oxygen species, cell glutathione content, and mitochondrial membrane potential tests, and the type of interaction was investigated by statistical analysis using Statistical Package for Social Sciences (SPSS, v. 21). Results showed that the independent exposure to either hematite or A-SiO₂ compared with the control group produced more toxic effects on the A₅₄₉ cell line. The toxicity of combined exposure of the nanoparticles was lower compared with independent exposure, and antagonistic interactive effects were detected. The findings of this study could be useful in clarifying the present debate on the health effects of combined exposure of hematite and A-SiO₂ nanoparticles. Because of the complexities of combined exposures, further studies of this kind are recommended.

Complexity of Respirable Dust Found in Mining Operations as Characterized by X-ray Diffraction and FTIR Analysis

The mineralogical complexity of mine dust complicates exposure monitoring methods for occupational, respirable hazards. Improved understanding of the variability in respirable dust characteristics, e.g., mineral phase occurrence and composition, is required to advance on-site monitoring techniques that can be applied across diverse mining sectors. Principal components analysis (PCA) models were applied separately to XRD and FTIR datasets collected on 130 respirable dust samples from seven mining commodities to explore similarities and differences among the samples. Findings from both PCA models classified limestone, iron, and granite mine samples via their analytical responses. However, the results also cautioned that respirable samples from these commodities may not always fit patterns observed within the model. For example, one unique sample collected in a limestone mine contained no carbonate minerals. Future predictive quantification models should account for unique samples. Differences between gold and copper mine dust samples were difficult to observe. Further investigation suggested that the key to their differentiation by FTIR may lie in the characterization of clays. The results presented in this study provide foundational information for guiding the development of quantification models for respirable mineral hazards in the mining industry.

Tumorigenic response in lung tumor susceptible A/J mice after sub-chronic exposure to calcium chromate or iron (III) oxide

Iron oxides are Group 3 (not classifiable as to its carcinogenicity to humans) according to the International Agency for Research on Cancer (IARC). Occupational exposures during iron and steel founding and hematite underground mining as well as other iron predominant exposures such as welding are Group 1 (carcinogenic to humans). The objective of this study was to investigate the potential of iron as iron (III) oxide (Fe2O3) to initiate lung tumors in A/J mice, a lung tumor susceptible strain. Male A/J mice were exposed by oropharyngeal aspiration to suspensions of Fe2O3 (1 mg) or calcium chromate (CaCrO4; 100 μg; positive control) for 26 weeks (once per week). Shams were exposed to 50 μL phosphate buffered saline (PBS; vehicle). Mice were euthanized 70 weeks after the first exposure and lung nodules were enumerated. Both CaCrO4 and Fe2O3 significantly increased gross-observed lung tumor multiplicity in A/J mice (9.63 ± 0.55 and 3.35 ± 0.30, respectively) compared to sham (2.31 ± 0.19). Histopathological analysis showed that bronchiolo-alveolar adenomas (BAA) and carcinomas (BAC) were the primary lung tumor types in all groups and were increased in the exposed groups compared to sham. BAC were significantly increased (146 %) in the CaCrO4 group and neared significance in the Fe2O3 group (100 % increase; p = 0.085). BAA and other histopathological indices of toxicity followed the same pattern with exposed groups increased compared to sham control. In conclusion, evidence from this study, in combination with our previous studies, demonstrate that exposure to iron alone may be a potential risk factor for lung carcinogenesis.

Bibliometric study of the toxicology of nanoescale zero valent iron used in soil remediation

The application of nanoscale zero-valent iron is one of the most widely used remediation technologies; however, the potential environmental risks of this technology are largely unknown. In order to broaden the knowledge on this subject, the present work consists of a bibliometric study of all of publications related to the toxicity of zero-valent iron nanoparticles used in soil remediation available from the Scopus (Elsevier) and Web of Science (Thompson Reuters) databases. This study presents a temporal distribution of the publications, the most cited articles, the authors who have made the greatest contribution to the theme, and the institutions, countries, and scientific journals that have published the most on this subject. The use of bibliometrics has allowed for the visualization of a panorama of the publications, providing an appropriate analysis to guide new research towards an effective contribution to science by filling the existing gaps. In particular, the lack of studies in several countries reveals a promising area for the development of further research on this topic.

Inhalation of iron-abundant gas metal arc welding-mild steel fume promotes lung tumors in mice

Welding fumes were reclassified as a Group 1 carcinogen by the International Agency for Research on Cancer in 2017. Gas metal arc welding (GMAW) is a process widely used in industry. Fume generated from GMAW-mild steel (MS) is abundant in iron with some manganese, while GMAW-stainless steel (SS) fume also contains significant amounts of chromium and nickel, known carcinogenic metals. It has been shown that exposure to GMAW-SS fume in A/J mice promotes lung tumors. The objective was to determine if GMAW-MS fume, which lacks known carcinogenic metals, also promotes lung tumors in mice. Male A/J mice received a single intraperitoneal injection of corn oil or the initiator 3-methylcholanthrene (MCA; 10 μg/g) and, one week later, were exposed by whole-body inhalation to GMAW-MS aerosols for 4 hours/day x 4 days/week x 8 weeks at a mean concentration of 34.5 mg/m3. Lung nodules were enumerated by gross examination at 30 weeks post-initiation. GMAW-MS fume significantly increased lung tumor multiplicity in mice initiated with MCA (21.86 ± 1.50) compared to MCA/air-exposed mice (8.34 ± 0.59). Histopathological analysis confirmed these findings and also revealed an absence of inflammation. Bronchoalveolar lavage analysis also indicated a lack of lung inflammation and toxicity after short-term inhalation exposure to GMAW-MS fume. In conclusion, this study demonstrates that inhalation of GMAW-MS fume promotes lung tumors in vivo and aligns with epidemiologic evidence that shows MS welders, despite less exposure to carcinogenic metals, are at an increased risk for lung cancer.

Insights into the toxicity of iron oxides nanoparticles in land snails

The use of manufactured nanoparticles (NPs) is spreading rapidly across technology and medicine fields, posing concerns about their consequence on ecosystems and human health. The present study aims to assess the biological responses triggered by iron oxide NPs (IONPs) and iron oxide NPs incorporated into zeolite (IONPZ) in relation to oxidative stress on the land snail Helix aspersa in order to investigate its use as a biomarker for terrestrial environments. Morphology and structure of both NPs were characterized. Snail food was supplemented with a range of concentrations of IONPs and IONPZ and values of the hemocyte lysosomal membranes' destabilization by 50% were estimated by the neutral red retention (NRRT50) assay. Subsequently, snails were fed with NPs concentrations equal to half of the NRRT50 values, 0.05 mg L^-1 for IONPs and 1 mg L^-1 for IONPZ, for 1, 5, 10 and 20 days. Both effectors induced oxidative stress in snails' hemocytes compared to untreated animals. The latter was detected by NRRT changes, reactive oxygen species (ROS) production, lipid peroxidation estimation, DNA integrity loss, measurement of protein carbonyl content by an enzyme-linked immunoabsorbent assay (ELISA), determination of ubiquitin conjugates and cleaved caspases conjugates levels. The results showed that the simultaneous use of the parameters tested could constitute possible reliable biomarkers for the evaluation of NPs toxicity. However, more research is required in order to enlighten the disposal and toxic impact of iron oxide NPs on the environment to ensure their safe use in the future.

A suspected bronchial carcinoma

A 68-year-old male patient, who was an ex-smoker of 20 cigarettes a day and a retired welder, presented to his general practitioner with a 4-day history of sweats, significant weight loss of almost 13 kg, no appetite and feeling tired, with a productive cough, phlegm and significant haemoptysis. His past medical history included an 8-year history of chronic obstructive pulmonary disease (COPD), 60 years of asthma, tuberculosis (TB) diagnosed and treated in 1974, a 15-year history of anxiety, a 16-year history of herpes zoster, and excision of a lesion from the facial bone in 2002 for a suspected melanoma. His medications included a salmeterol inhaler (Seretide 500BD; GlaxoSmithKline, Brentford, UK), tiotropium, amiodarone, carbocisteine, omeprazole and simvastatin, and due to his recurrent chest infections, he was treated with appropriate courses of antibiotics.

The cause of this patient’s symptoms is not what it seems. Can you diagnose him?
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Potential Toxicity and Underlying Mechanisms Associated with Pulmonary Exposure to Iron Oxide Nanoparticles: Conflicting Literature and Unclear Risk

Fine/micron-sized iron oxide particulates are incidentally released from a number of industrial processes, including iron ore mining, steel processing, welding, and pyrite production. Some research suggests that occupational exposure to these particulates is linked to an increased risk of adverse respiratory outcomes, whereas other studies suggest that iron oxide is biologically benign. Iron oxide nanoparticles (IONPs), which are less than 100 nm in diameter, have recently surged in use as components of novel drug delivery systems, unique imaging protocols, as environmental catalysts, and for incorporation into thermoplastics. However, the adverse outcomes associated with occupational exposure to IONPs remain relatively unknown. Relevant in vivo studies suggest that pulmonary exposure to IONPs may induce inflammation, pulmonary fibrosis, genotoxicity, and extra-pulmonary effects. This correlates well with in vitro studies that utilize relevant dose, cell type(s), and meaningful end points. A majority of these adverse outcomes are attributed to increased oxidative stress, most likely caused by particle internalization, dissolution, release of free iron ions, and disruption of iron homeostasis. However, because the overall toxicity profile of IONPs is not well understood, it is difficult to set safe exposure limit recommendations that would be adequate for the protection of at-risk workers. This review article will focus on known risks following IONPs exposure supported by human, animal, and cell culture-based studies, the potential challenges intrinsic to IONPs toxicity assessment, and how these may contribute to the poorly characterized IONPs toxicity profile.

Strategies and knowledge gaps for improving nanomaterial biocompatibility

With rapid development of nanotechnology and nanomaterials, nanosafety has attracted wide attention in all fields related to nanotechnology. As well known, a grand challenge in nanomaterial applications is their biocompatibility. It is urgent to explore effective strategies to control the unintentional effects. Although many novel methods for the synthesis of biocompatible and biodegradable nanomaterials are reported, the control strategy of nanotoxicity remains in its infancy. It is urgent to review the archived strategies for improving nanomaterial biocompatibility to clarify what we have done and where we should be. In this review, the achievements and challenges in nanomaterial structure/surface modifications and size/shape controls were analyzed. Moreover, the chemical and biological strategies to make nanomaterial more biocompatible and biodegradable were compared. Finally, the concerns that have not been studied well were prospected, involving unintended releases, life-cycle, occupational exposure and methodology.

Oxidative stress and early DNA damage in workers exposed to iron-rich metal fumes

Occupational exposure to metal fumes occurs routinely in many occupational settings. The inflammatory response to fumes and metals after exposure could lead to an increase in reactive oxygen species and level of DNA damage. In this study, the level of early DNA damage and oxidative stress was evaluated in a group of steel company (n = 30) and compared to the non-exposed (n = 28) subjects. All DNA damage markers in workers were significantly higher in exposed group in comparison with controls (p < 0.001). Stratified analysis based on smoking showed no significant differences between smoking and comet assay parameters. There was no significant difference between workers and controls in terms of HCT, TIBC, iron, and ferreting. However, HB in controls was significantly lower than exposed group (p < 0.001). A significant increase in catalase activity and MDA serum levels were observed in workers in comparison with controls. These findings suggest for the potential genotoxic effect of iron reach dust. Due to recent findings on the predictive potential of comet assay for cancer development, further, researches should be conducted to investigate the possible biochemical mechanism of such finding.