From lead to manganese through mercury: mythology, science, and lessons for prevention

Manganese-based advanced nanoparticles for biomedical applications: future opportunity and challenges

Nanotechnology is the most promising technology to evolve in the last decade. Recent research has shown that transition metal nanoparticles especially manganese (Mn)-based nanoparticles have great potential for various biomedical applications due to their unique fundamental properties. Therefore, globally, scientists are concentrating on the development of various new manganese-based nanoparticles (size and shape dependent) due to their indispensable utilities. Although numerous reports are available regarding the use of manganese nanoparticles, there is no comprehensive review highlighting the recent development of manganese-based nanomaterials and their potential applications in the area of biomedical sciences. The present review article provides an overall survey on the recent advancement of manganese nanomaterials in biomedical nanotechnology and other fields. Further, the future perspectives and challenges are also discussed to explore the wider application of manganese nanoparticles in the near future. Overall, this review presents a fundamental understanding and the role of manganese in various fields, which will attract a wider spectrum of the scientific community.

Urinary 1H NMR metabolomics profile of Italian citizens exposed to background levels of arsenic: a (pre)cautionary tale

Objectives: Arsenic is a toxic metal ubiquitous in the environment and in daily life items. Long-term arsenic exposure is associated with severe adverse health effects involving various target organs. It would be useful to investigate the existence of metabolic alterations associated with lifestyle and/or with the environment. For this purpose, we studied the correlation between urinary arsenic levels and urinary proton nuclear magnetic resonance spectroscopy (¹H NMR) metabolomics profiles in a non-occupationally nor environmentally arsenic exposed general population.Methods: Urine samples were collected from 86 healthy subjects. Total and non-alimentary urinary arsenic (U-naAs) levels, namely the sum of arsenite, arsenate, monomethylarsonate and dimethylarsinate, were measured and ¹H NMR analysis was performed. Orthogonal Projection to Latent Structures was applied to explore the correlation between the metabolomics profiles and U-naAs levels.Results: Despite the extremely low U-naAs levels (mean value = 6.13 ± 3.17 µg/g creatinine) of our studied population a urinary metabolomics profile related to arsenic was identified.Conclusion: The identified profile could represent a fingerprint of early arsenic biological effect and could be used in further studies as an indicator of susceptibility, also in subjects exposed to a low arsenic dose, with implications in occupational health, toxicology, and public health.

Effect of manganese on neural endocrine hormones in serum of welders and smelters

BACKGROUND

Although manganese (Mn)-induced neurotoxicity effects are well known among occupational Mn exposure, few reports have investigated the effects on endocrine systems among welders and smelters.

OBJECTIVE

To determine the effect of high level occupational manganese (Mn) exposure on neuropsychological parameters and hormonal status.

METHODS

We used a cross-sectional design with 52 welders, 48 smelters and 43 age-matched office workers from the same factory in China. We analyzed serum endocrine hormones level and airborne Mn concentrations. Erythrocyte and urine Mn levels were quantified using inductively-coupled plasma atomic emission spectroscopy.

RESULTS

The geometric mean of air Mn concentrations for the welders and smelters were 19.7 and 273.1 μg/m³, respectively. Mn concentrations in erythrocytes of smelters were markedly greater than those in controls and welders, but there was no difference between the erythrocytes Mn levels of Control and welders. We also found an increase of Mn levels in the urine of both welders and smelters vs. controls; Mn levels in urine of smelters were higher than in welders. Self-reported neurobehavioral symptoms were higher in welders and smelters than in controls. Finally, thyroid-stimulating hormone (TSH) levels of welders were significantly lower than in controls, whereas smelters had lower prolactin (PRL), testosterone (TST) and follicle-stimulating hormone (FSH) concentrations than either controls or welders.

CONCLUSIONS

These results show that smelters have higher Mn exposure than do welders, and that Mn levels in erythrocytes or urine can be a marker for exposure. Moreover, high level occupational Mn exposure increases adverse neurobehavioral effects, and also may disrupt endocrine systems.

Drinking Water and the Developing Brain

While the problem of unsafe tap water in Flint, Michigan fueled outrage and better awareness in regard to the hazards of lead in tap water, the problem has existed in city after city for years in the US and in other countries. Our author, a winner of the MacArthur Foundation "genius" grant for her work in identifying preventable causes of human disease related to environmental exposures, points out that problems extend well beyond lead. Many potentially harmful contaminants have yet to be evaluated, much less regulated. Her article examines a number of neurotoxins and related issues as they pertain to brain development.

Neurotoxicity of metals

Metals are frequently used in industry and represent a major source of toxin exposure for workers. For this reason governmental agencies regulate the amount of metal exposure permissible for worker safety. While essential metals serve physiologic roles, metals pose significant health risks upon acute and chronic exposure to high levels. The central nervous system is particularly vulnerable to metals. The brain readily accumulates metals, which under physiologic conditions are incorporated into essential metalloproteins required for neuronal health and energy homeostasis. Severe consequences can arise from circumstances of excess essential metals or exposure to toxic nonessential metal. Herein, we discuss sources of occupational metal exposure, metal homeostasis in the human body, susceptibility of the nervous system to metals, detoxification, detection of metals in biologic samples, and chelation therapeutic strategies. The neurologic pathology and physiology following aluminum, arsenic, lead, manganese, mercury, and trimethyltin exposures are highlighted as classic examples of metal-induced neurotoxicity.

Neuropsychologic evaluation and exposure to neurotoxicants

The history of neuropsychologic assessment describes the development of a psychometric approach to neuropsychologic measurement, based on the initial clinical/theoretical approach exemplified by pioneers, who also discussed different brain functions and hypotheses for clinical exploration and treatment. Early neuropsychologic assessment practices in the USA arose out of the need to screen, diagnose, and treat World War II veterans who returned with brain injuries. Clinical testing was used to determine treatment and rehabilitation potential. Clinical psychologists had previously developed educational tests to investigate students' abilities and disabilities. Using population studies, primarily in the USA, Canada and Europe, neuropsychologists developed standardized test scores, permitting comparisons of scores based on the normal curve and evolving knowledge of brain/behavior relationships. In clinical interpretations, neuropsychologists use extensive normative data based on cognitive, mood, executive, neurologic, and motor brain functions of groups with different cultural and educational backgrounds and psychiatric illnesses. Large groups of workers can be screened with a brief neuropsychologic screening test battery to assess the psychologic status of personnel. Commonly used tests by domain are described, as well as patterns of acute and chronic neurotoxicant exposures, treatment, and rehabilitation. Future developments will relate imaging studies to neuropsychologic performance.

Synthesis and structural characterization of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium halide complexes, {[Tm(MeBenz)]Cd(μ-Cl)}2 and [Tm(MeBenz)]CdI: a rare example of cadmium in a trigonal bipyramidal sulfur-rich coordination environment

The tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complexes, {[Tm(MeBenz)]Cd(μ-Cl)}2 and [Tm(MeBenz)]CdI, have been synthesized via the reactions of [Tm(MeBenz)]K with CdCl2 and CdI2, respectively. While X-ray diffraction studies demonstrate that the iodide derivative, [Tm(MeBenz)]CdI, is a monomer, the chloride derivative, {[Tm(MeBenz)]Cd(μ-Cl)}2, exists as a dimer, which is unprecedented for Group 12 [Tm(R)]MX (X = Cl, Br, I) compounds. Furthermore, the cadmium centers of {[Tm(MeBenz)]Cd(μ-Cl)}2 are trigonal bipyramidal, which is an uncommon motif for cadmium complexes with a [S3Cl2] coordination sphere.

Detection criteria and preventive measures for occupational disease in the mines of Almaden (Spain)

This research focuses on the metallurgy and underground mining job positions in the historic mines of Almaden (Spain). We introduce a preventive methodology for hydrargyrism in work environments known by the name of Methodology for Operational Units Action Levels for Health Indicators (MUONAIS). The methodology allows critical levels to be established using environmental and clinical-biological indicators. The prevention plan concentrated on 15 job positions in the metallurgy department that employed more than 100 workers between the years 1986 and 1997. The development of this preventive methodology managed to keep workers' mercury levels below 60 μg/l in blood and 200 μg/l in urine, values that present no negative effects on human health. MUONAIS has proven very effective in protecting workers' health. During this period, some cases of micro-mercurialism were detected, yet were completely reversible, allowing us to affirm that the terrible disease of hydrargyrism was totally eradicated.

Neurobehavioral deficits and parkinsonism in occupations with manganese exposure: a review of methodological issues in the epidemiological literature

Exposure to manganese (Mn) is associated with neurobehavioral effects. There is disagreement on whether commonly occurring exposures in welding, ferroalloy, and other industrial processes produce neurologically significant neurobehavioral changes representing parkinsonism. A review of methodological issues in the human epidemiological literature on Mn identified: (1) studies focused on idiopathic Parkinson disease without considering manganism, a parkinsonian syndrome; (2) studies with healthy worker effect bias; (3) studies with problematic statistical modeling; and (4) studies arising from case series derived from litigation. Investigations with adequate study design and exposure assessment revealed consistent neurobehavioral effects and attributable subclinical and clinical signs and symptoms of impairment. Twenty-eight studies show an exposure-response relationship between Mn and neurobehavioral effects, including 11 with continuous exposure metrics and six with three or four levels of contrasted exposure. The effects of sustained low-concentration exposures to Mn are consistent with the manifestations of early manganism, i.e., consistent with parkinsonism. This is compelling evidence that Mn is a neurotoxic chemical and there is good evidence that Mn exposures far below the current US standard of 5.0 mg/m³ are causing impairment.

2-Seleno-1-alkylbenzimidazoles and their Diselenides: Synthesis and Structural Characterization of a 2-Seleno-1-methylbenzimidazole Complex of Mercury

2-Seleno-1-methylbenzimidazole, H(sebenzimMe), can be synthesized from 1-methylbenzimidazole by sequential treatment with (i) BunLi, (ii) elemental selenium and (iii) HCl(aq). This method is also applicable to the synthesis of 2-seleno-1-t-butylbenzimidazole, H(sebenzimBut ). Single crystal X-ray diffraction and NMR spectroscopic data demonstrate that H(sebenzimMe) and H(sebenzimBut ) exist as the selone rather than the selenol tautomers, which is in accord with the results of density functional theory (B3LYP) calculations. The data also indicate that the selone is best represented as a C+-Se- zwitterion rather than as a C=Se doubly bonded species. Aerobic oxidation of H(sebenzimMe) and H(sebenzimBut ) in the presence of Et3N yields the diselenides, (sebenzimMe)2 and (sebenzimBut )2. In addition, H(sebenzimMe) reacts with HgCl2 to give [H(sebenzimMe)]2HgCl2, the first structurally characterized example of a 2-seleno-1-alkylimidazole mercury complex.

Characterization of bacterial communities exposed to Cr(III) and Pb(II) in submerged fixed-bed biofilms for groundwater treatment

Two pilot-scale submerged-bed microbial biofilms were set up for the removal of Cr(III) and Pb(II) from groundwater, and the biological activities and structure of the bacterial communities developed in the presence of the heavy metals were analyzed. Artesian groundwater was polluted with Cr(III) or Pb(II) (15 mg/l) and amended with sucrose (250 mg/l) as carbon source. While Pb(II) was over 99% removed from groundwater during long-term operation (130 days), the efficiency of the removal of Cr(III) significantly decreased in time (95-73% after 60 days). Cr(III)-amended biofilms displayed significant lower sucrose consumption, ATP cell contents and alkaline phosphatase activity, compared to biofilms formed in the presence of Pb(II), while analysis of exopolymers demonstrated significant differences in their composition (content of carbohydrates and acetyl groups) in response to each heavy metal. According to transmission electron microscopy (TEM) and electron-dispersive X-ray analysis (EDX), Cr(III) bioaccumulated in the exopolymeric matrix without entering bacterial cells, while Pb(II) was detected both extra and intracellularly, associated to P and Si. Temperature-gradient gel electrophoresis (TGGE) profiling based on partial amplification of 16S rRNA genes was used to analyze the differences in the structure of the biofilm bacterial communities developed under exposure to each heavy metal. Prevalent populations in the biofilms were further identified by reamplification and sequencing of isolated TGGE bands. 75% of the sequences in the Pb(II) biofilter were evolutively close to the Rhodobacterales, while in the Cr(III) biofilter 43% of the sequences were found affiliated to the Rhizobiales and Sphingomonadales, and 57% to Betaproteobacteria.

On the chalcogenophilicity of mercury: evidence for a strong Hg-Se bond in [Tm(Bu(t))]HgSePh and its relevance to the toxicity of mercury

One of the reasons for the toxic effects of mercury has been attributed to its influence on the biochemical roles of selenium. For this reason, it is important to understand details pertaining to the nature of Hg-Se interactions and this has been achieved by comparison of a series of mercury chalcogenolate complexes that are supported by tris(2-mercapto-1-t-butyl-imidazolyl)hydroborato ligation, namely [Tm(Bu(t))]HgEPh (E = S, Se, Te). In particular, X-ray diffraction studies on [Tm(Bu(t))]HgEPh demonstrate that although the Hg-S bonds involving the [Tm(Bu(t))] ligand are longer than the corresponding Cd-S bonds of [Tm(Bu(t))]CdEPh, the Hg-EPh bonds are actually shorter than the corresponding Cd-EPh bonds, an observation which indicates that the apparent covalent radii of the metals in these compounds are dependent on the nature of the bonds. Furthermore, the difference in Hg-EPh and Cd-EPh bond lengths is a function of the chalcogen and increases in the sequence S (0.010 A) < Se (0.035 A) < Te (0.057 A). This trend indicates that the chalcogenophilicity of mercury increases in the sequence S < Se < Te. Thus, while mercury is often described as being thiophilic, it is evident that it actually has a greater selenophilicity, a notion that is supported by the observation of facile selenolate transfer from zinc to mercury upon treatment of [Tm(Bu(t))]HgSCH(2)C(O)N(H)Ph with [Tm(Bu(t))]ZnSePh. The significant selenophilicity of mercury is in accord with the aforementioned proposal that one reason for the toxicity of mercury is associated with it reducing the bioavailability of selenium.

Synthesis, structure, and reactivity of two-coordinate mercury alkyl compounds with sulfur ligands: relevance to mercury detoxification

The susceptibility of two-coordinate mercury alkyl compounds of the type X-Hg-R (where X is a monodentate sulfur donor) towards protolytic cleavage has been investigated as part of ongoing efforts to obtain information relevant to understanding the mechanism of action of the organomercurial lyase, MerB. Specifically, the reactivity of the two-coordinate mercury alkyl compounds PhSHgR, [mim(Bu(t))]HgR and {[Hmim(Bu(t))]HgR}(+) (Hmim(Bu(t)) = 2-mercapto-1-t-butylimidazole; R = Me, Et) towards PhSH was investigated, thereby demonstrating that the ability to cleave the Hg-C bond is very dependent on the nature of the system. For example, whereas the reaction of PhSHgMe with PhSH requires heating at 145 degrees C for several weeks to liberate CH(4), the analogous reaction of PhSHgEt with PhSH leads to evolution of C(2)H(6) over the course of 2 days at 100 degrees C. Furthermore, protolytic cleavage of the Hg-C bond by PhSH is promoted by Hmim(Bu(t)). For example, whereas the reaction of {[Hmim(Bu(t))]HgEt}(+) with PhSH eliminates C(2)H(6) at elevated temperatures, the protolytic cleavage occurs over a period of 2 days at room temperature in the presence of Hmim(Bu(t)). The ability of Hmim(Bu(t)) to promote the protolytic cleavage is interpreted in terms of the formation of a higher coordinate species {[Hmim(Bu(t))](n)HgR}(+) that is more susceptible to Hg-C bond cleavage than is two-coordinate {[Hmim(Bu(t))]HgR}(+). These observations support the notion that access to a species with a coordination number greater than two is essential for efficient activity of MerB.

Manganese and its role in Parkinson's disease: from transport to neuropathology

The purpose of this review is to highlight recent advances in the neuropathology associated with Mn exposures. We commence with a discussion on occupational manganism and clinical aspects of the disorder. This is followed by novel considerations on Mn transport (see also chapter by Yokel, this volume), advancing new hypotheses on the involvement of several transporters in Mn entry into the brain. This is followed by a brief description of the effects of Mn on neurotransmitter systems that are putative modulators of dopamine (DA) biology (the primary target of Mn neurotoxicity), as well as its effects on mitochondrial dysfunction and disruption of cellular energy metabolism. Next, we discuss inflammatory activation of glia in neuronal injury and how disruption of synaptic transmission and glial-neuronal communication may serve as underlying mechanisms of Mn-induced neurodegeneration commensurate with the cross-talk between glia and neurons. We conclude with a discussion on therapeutic aspects of Mn exposure. Emphasis is directed at treatment modalities and the utility of chelators in attenuating the neurodegenerative sequelae of exposure to Mn. For additional reading on several topics inherent to this review as well as others, the reader may wish to consult Aschner and Dorman (Toxicological Review 25:147-154, 2007) and Bowman et al. (Metals and neurodegeneration, 2009).

Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study

Background

Considerable research has been directed towards the roles of metal ions in nutrition with metal ion toxicity attracting particular attention. The aim of this study is to measure the levels of metal ions found in selected beverages (red wine, stout and apple juice) and to determine their potential detrimental effects via calculation of the Target Hazard Quotients (THQ) for 250 mL daily consumption.

Results

The levels (mean ± SEM) and diversity of metals determined by ICP-MS were highest for red wine samples (30 metals totalling 5620.54 ± 123.86 ppb) followed by apple juice (15 metals totalling 1339.87 ± 10.84 ppb) and stout (14 metals totalling 464.85 ± 46.74 ppb). The combined THQ values were determined based upon levels of V, Cr, Mn, Ni, Cu, Zn and Pb which gave red wine samples the highest value (5100.96 ± 118.93 ppb) followed by apple juice (666.44 ± 7.67 ppb) and stout (328.41 ± 42.36 ppb). The THQ values were as follows: apple juice (male 3.11, female 3.87), stout (male 1.84, female 2.19), red wine (male 126.52, female 157.22) and ultra-filtered red wine (male 110.48, female 137.29).

Conclusion

This study reports relatively high levels of metal ions in red wine, which give a very high THQ value suggesting potential hazardous exposure over a lifetime for those who consume at least 250 mL daily. In addition to the known hazardous metals (e.g. Pb), many metals (e.g. Rb) have not had their biological effects systematically investigated and hence the impact of sustained ingestion is not known.

Background, approaches and recent trends for setting health-based occupational exposure limits: a minireview

The setting of occupational exposure limits (OELs) are founded in occupational medicine and the predictive toxicological testing, resulting in exposure-response relationships. For compounds where a No-Observed-Adverse-Effect-Level (NOAEL) can be established, health-based OELs are set by dividing the NOAEL of the critical effect by an overall uncertainty factor. Possibly, the approach may also be used for carcinogens if the mechanism is epigenetic or the genetic effect is secondary to effect from reactions with proteins such as topoisomerase inhibitors, and mitotic and meiotic spindle poisons. Additionally, the NOAEL approach may also be used for compounds with weak genotoxic effect, playing no or only a minor role in the development of tumours. No health-based OEL can be set for direct-acting genotoxic compounds where the life-time risks may be estimated from the low-dose linear non-threshold extrapolation, allowing a politically based exposure level to be set. OELs are set by several agencies in the US and Europe, but also in-house in major chemical and pharmaceutical companies. The benchmark dose approach may in the future be used where it has advantage over the NOAEL approach. Also, more attention should be devoted to sensitive groups, toxicological mechanisms and interactions as most workplace exposures are mixtures.