Concerns about environmental mercury toxicity: do we forget something else?

An exploratory in N-doped carbon dots as green fluorescence probes for Hg(II) ions detection

Carbon dots (CDs), as a fascinating carbon nanomaterial, have important applications in various fields due to their unique properties. The physical and chemical properties of CDs can be fine-tuned using heteroatom doping and surface functionalisation. Here, we synthesised N-doped carbon dots (N-CDs) by reacting Citric acid, which serve as the carbon core, with twenty amino acids under microwave irradiation. The fluorescence quenching of each amino acid doped CDs by Hg(II) ions was experimentally measured. Then the effect of the molecular features and chemical properties of amino acids on the fluorescence quenching of N-CDs by Hg(II) ions was investigated by using the quantitative structure-property relationship (QSPR) method. Applying different machine learning techniques including correlation-based and ReliefF algorithm feature selection approaches to choose relevant descriptors, multi-linear regression, and support vector machine to construct QSPR model, some reliable and predictive models were developed. Based on the variables used throughout the final QSPR models, hydrophobic interactions, in addition to hydrogen bonding interactions, can be considered a major factor governing the photoluminescence behaviour of different N-CDs quenched by Hg(II) ions. N-CDs derived from amino acids bearing larger hydrophobic surfaces show greater fluorescence quenching, indicating that a greater capacity to interact with Hg(II) metal ions resulting in further fluorescence quenching.

Graphitic carbon nitride derived probes for the recognition of heavy metal pollutants of environmental concern in water bodies

Graphitic carbon nitride (g-CN) has a number of valuable features that have been recognized during the studies related to its photocatalytic activity enhancement derived by visible light. Because of these characteristics, g-CN can be used as a detecting signal transducer with different transmission modalities. The latest up-to-date detection capabilities of modified g-CN nanoarchitectures are covered in this study. The structural features and synthetic methodologies have been discussed in a number of reports. Herein, employment of the g-CN as a promising probing modality for the recognition of different toxic heavy metals is the promising feature of the present study.

Synthesis, characterization and metal ions sensing applications of meta-benziporphodimethene-embedded polyacrylamide/carboxymethyl guargum polymeric hydrogels in water

We have developed a robust procedure for the visual on-site detection of zinc, cadmium and mercury metal ions in an aqueous medium using a polymeric hydrogel matrix-based colorimetric sensor. Zn²⁺, Cd²⁺and Hg²⁺, owing to their biological significant value and environmental harm, have attracted more attention. The selective detection of Zn²⁺, Cd²⁺and Hg²⁺ metal ions has always been challenging due to their closed-shell d¹⁰ electronic configuration which makes them spectroscopically silent. A polyacrylamide/carboxymethyl guargum polymeric hydrogel-based metal ion sensor was synthesized by in situ embedding 11, 16-bis (phenyl)-6, 6, 21, 21-tetramethyl-m-benzi-6,21-porphodimethene (meta-BPDM) in a host hydrogel. The meta-BPDM-embedded hydrogel shows high stability, sensitivity and selectivity when it is dipped into the aqueous solutions of Zn²⁺, Cd²⁺and Hg²⁺ metal ions. During detection, the binding of these metal ions in hydrogel causes hydrogel to change from red to bluish-green which was visually detected and confirmed by UV-visible spectroscopy. The meta-BPDM-embedded polymeric hydrogel was characterized by using solid-state UV-visible spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis and its sensing properties were studied. The meta-BPDM-embedded polymeric hydrogel was found to be an excellent colorimetric sensor for Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous medium without leaching of meta-BPDM from the hydrogel. The selectivity to sense these ions is mainly dependent on the binding constant of these metal ions with the meta-BPDM embedded in the hydrogel. The sensitivity of the hydrogel was 0.5, 1, and 2 mg/L with Hg²⁺, Zn²⁺ and Cd²⁺, respectively.

Mercury level in biological samples of dentists in Iran: a systematic review and meta-analysis

Exposure to mercury is an important risk to dentists health. The aim of the present study was to assess the pooled mean mercury level (MML) in the urine, blood, nail, and hair of Iranian dentists (IDs) through the meta-analysis technique. Comprehensive and systematic searches were performed in main local databases including SID, Magiran, Iran medex, and ISC as well as internationally available databases including Embase, PubMed and Scopus for all the relevant studies up to 2018. In order to prevent bias in this study and identify eligible studies, various steps of the study was performed independently by two researchers. Out of 13 studies in the meta-analysis process which included 1499 IDs, the mean of the mercury level in the urine, nail, and blood was estimated to be 6.29 (95% CI: 2.61-9.97, I-square: 62.7%, P: 0.006), 3.54 (95% CI: 2.81-4.28, I-square: 0.0%, P: 0.968), 11.20 (95% CI: 2.28-20.13, I-square: 59.9%, P: 0.082), respectively. The mean mercury level (MML) in the biological samples of IDs was higher than the standard of World Health Organization (WHO). So, in accordance with Article 10 of the European Union Regulations (EUR), in the context of the Minamata Convention (MC) on Dental Amalgam (DA), in order to avoid the dangers of mercury exposure in dentists, it is necessary for Iran and other countries to approve laws and to implement a national plan to reduce mercury levels and replace the appropriate materials.

Phenothiazine-chitosan based eco-adsorbents: A special design for mercury removal and fast naked eye detection

The aim of the paper was to investigate the ability of an eco-friendly luminescent xerogel prepared by chitosan crosslinking with a phenothiazine luminogen to detect and remove heavy metals. Its ability to give a divergent morphological and optical response towards fifteen environmental relevant metals was investigated by naked eye and UV lamp, fluorescence spectroscopy and scanning electron microscopy. A distinct response was noted for mercury, consisting in the transformation of the xerogel into a rubber-like material accompanied by the red shifting of the color of emitted light from yellow-green to greenish-yellow domain. The particularities of the metals anchoring into the xerogel were analyzed by FTIR spectroscopy and X-ray diffraction. The morphological changes and the metal uptake were analyzed by SEM-EDAX, swelling and gravimetric methods. It was concluded that mercury has a superior affinity towards this heteroatoms rich system, leading to a secondary crosslinking. This directed a great absorption capacity of 1673 mg/g and a specific morphological response for mercury ion concentrations up to 0.001 ppm.

Mercury Exposure Assessment in Mother-Infant Pairs from Continental and Coastal Croatia

The main source of mercury (Hg) exposure in the general population is fish. Another possible source is dental amalgam. Here, we compare the levels of Hg and selenium (Se) in samples of maternal and fetal origin collected shortly after childbirth of healthy postpartum women in the coastal (n = 96) and continental (n = 185) areas of Croatia related to maternal seafood/fish consumption. We also evaluated Hg concentrations and maternal serum metallothionein (MT2) concentrations in relation to the number of dental amalgam fillings, and MT2A-5A/G (rs28366003) polymorphism. The levels of Hg and Se in maternal hair and blood/serum, placenta and cord blood/serum increased in relation to increasing fish consumption with the highest values in subjects from the coast. The concentrations of each element and between elements correlated across the matrices. Increasing amalgam number correlated linearly with increased Hg levels in maternal and cord serum and was not associated with serum MT2. No association of MT2A-5A/G polymorphism and Hg or Se levels were found. The results confirmed higher fish consumption in coastal vs. continental Croatia and increases of both Hg and Se related to fish consumption in all analyzed samples. Increased blood Hg reflected the predominant MeHg share from seafood, while increased serum Hg matched exposure from dental amalgams.

Instant Mercury Ion Detection in Industrial Waste Water with a Microchip Using Extended Gate Field-Effect Transistors and a Portable Device

Mercury ion selective membrane (Hg-ISM) coated extended gate Field Effect transistors (ISM-FET) were used to manifest a novel methodology for ion-selective sensors based on FET’s, creating ultra-high sensitivity (−36 mV/log [Hg²⁺]) and outweighing ideal Nernst sensitivity limit (−29.58 mV/log [Hg²⁺]) for mercury ion. This highly enhanced sensitivity compared with the ion-selective electrode (ISE) (10⁻⁷ M) has reduced the limit of detection (10⁻¹³ M) of Hg²⁺ concentration’s magnitude to considerable orders irrespective of the pH of the test solution. Systematical investigation was carried out by modulating sensor design and bias voltage, revealing that higher sensitivity and a lower detection limit can be attained in an adequately stronger electric field. Our sensor has a limit of detection of 10⁻¹³ M which is two orders lower than Inductively Coupled Plasma Mass Spectrometry (ICP-MS), having a limit of detection of 10⁻¹¹ M. The sensitivity and detection limit do not have axiomatic changes under the presence of high concentrations of interfering ions. The technology offers economic and consumer friendly water quality monitoring options intended for homes, offices and industries.

Developmental exposure to mercury chloride impairs social behavior in male offspring dependent on genetic background and maternal autoimmune environment

To date, the connection between inorganic mercury (Hg) and social behavior remains incompletely understood. The aim of this study was to investigate the influence of maternal autoimmunity by inorganic Hg (Hg²⁺) exposure on social behavior of offspring. Wild-type (WT) and immunoglobulin deficient (Ig^-/-) B10.S dams fertilized by male WT B10.S or SJL mice were treated with 50 μM Hg chloride (HgCl₂). Non-pregnant female WT B10.S mice were used to investigate factors regulating HgCl₂-induced autoimmunity to brain. HgCl₂ selectively impaired social behavior in male offspring, but not female offspring from WT B10.S dams × male SJL, in that only male offspring displayed reduced time distribution with the stranger mouse, decreased sniffing to the stranger mouse and increased self-grooming. HgCl₂ did not disrupt social behavior of male or female offspring from WT B10.S dams × male WT B10.S or Ig^-/- B10.S dams × male SJL. The offspring from WT and Ig^-/- B10.S dams × male SJL had equivalent autoimmunity to brain antigens during HgCl₂ exposure, indicating that maternal, but not offspring-derived anti-brain antibodies (Ab) impaired social behavior of the offspring. Non-pregnant WT B10.S mice treated with HgCl₂ had increased anti-brain Ab dependent on increase in CD4 T cell activation and IFNγ signaling to macrophages. IFNγ interaction with macrophages drove B cells and plasma cells to produce IgG. Therefore, HgCl₂ selectively impaired social behavior in males with certain genetic background via maternally derived anti-brain Ab production, thus providing a novel insight into our current understanding of Hg toxicity.

Insights into the Potential Role of Mercury in Alzheimer's Disease

Mercury (Hg), which is a non-essential element, is considered a highly toxic pollutant for biological systems even when present at trace levels. Elevated Hg exposure with the growing release of atmospheric pollutant Hg and rising accumulations of mono-methylmercury (highly neurotoxic) in seafood products have increased its toxic potential for humans. This review aims to highlight the potential relationship between Hg exposure and Alzheimer's disease (AD), based on the existing literature in the field. Recent reports have hypothesized that Hg exposure could increase the potential risk of developing AD. Also, AD is known as a complex neurological disorder with increased amounts of both extracellular neuritic plaques and intracellular neurofibrillary tangles, which may also be related to lifestyle and genetic variables. Research reports on AD and relationships between Hg and AD indicate that neurotransmitters such as serotonin, acetylcholine, dopamine, norepinephrine, and glutamate are dysregulated in patients with AD. Many researchers have suggested that AD patients should be evaluated for Hg exposure and toxicity. Some authors suggest further exploration of the Hg concentrations in AD patients. Dysfunctional signaling pathways in AD and Hg exposure appear to be interlinked with some driving factors such as arachidonic acid, homocysteine, dehydroepiandrosterone (DHEA) sulfate, hydrogen peroxide, glucosamine glycans, glutathione, acetyl-L carnitine, melatonin, and HDL. This evidence suggests the need for a better understanding of the relationship between AD and Hg exposure, and potential mechanisms underlying the effects of Hg exposure on regional brain functions. Also, further studies evaluating brain functions are needed to explore the long-term effects of subclinical and untreated Hg toxicity on the brain function of AD patients.

Toxic metal(loid)-based pollutants and their possible role in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social interaction, verbal and non-verbal communication, and stereotypic behaviors. Many studies support a significant relationship between many different environmental factors in ASD etiology. These factors include increased daily exposure to various toxic metal-based environmental pollutants, which represent a cause for concern in public health. This article reviews the most relevant toxic metals, commonly found, environmental pollutants, i.e., lead (Pb), mercury (Hg), aluminum (Al), and the metalloid arsenic (As). Additionally, it discusses how pollutants can be a possible pathogenetic cause of ASD through various mechanisms including neuroinflammation in different regions of the brain, fundamentally occurring through elevation of the proinflammatory profile of cytokines and aberrant expression of nuclear factor kappa B (NF-κB). Due to the worldwide increase in toxic environmental pollution, studies on the role of pollutants in neurodevelopmental disorders, including direct effects on the developing brain and the subjects' genetic susceptibility and polymorphism, are of utmost importance to achieve the best therapeutic approach and preventive strategies.

Mercury exposure and health impacts in dental personnel

Based on toxicological, clinical, and epidemiological knowledge, the present paper reviews the status regarding possible deleterious health effects from occupational exposure to metallic mercury (Hg) in dental practice. Symptoms from the central nervous system are among the health problems that most often are attributed to Hg exposure in dentists and dental nurses working with amalgam. Uncharacteristic symptoms of chronic low-level Hg vapor exposure including weakness, fatigue, and anorexia have been observed in numerous studies of dental personnel. It is crucial to protect both human health and the environment against negative effects of Hg. In line with this, the use of dental amalgam in industrial countries is about to be phased out. In Norway and Sweden, the use of the filling material is banned.

Delayed-type hypersensitivity to metals in connective tissue diseases and fibromyalgia

Rheumatic diseases include a group of autoimmune disorders with environmental and genetic etiology that are characterized as a subgroup of connective tissue diseases (CTD). Rheumatoid arthritis (RA) often involves the small joints of the hands in a symmetrical fashion that can lead to loss of joint function, and RA, as well as Sjögren's syndrome (SS) and other rheumatic diseases, are often accompanied by sensitivity to metals. Numerous investigations on metal sensitivity were evaluated in this review. A detailed metal exposure history was collected by different evaluation of studies. In all subjects, the main source of metal exposure was nickel, mercury, gold, palladium, titanium, and chromium. All of SLE (systemic lupus erythematosus), RA and SS patients appeared to have an increased frequency of metal delayed-type hypersensitivity (DTH) (Type IV allergy). As dental restorative materials release minor amounts of their metals (including mercury, gold, and nickel), many adults are commonly exposed to these metal ions by vapor or corrosion into saliva. Metal-related DTH in these patients will induce an inflammatory response. Such inflammations are important factors in CTD progress. It is hypothesized that metal-specific T cell reactivity can act as an etiological agent in the propagation and chronification of rheumatic inflammation. The key responses of metal delayed-type hypersensitivity in autoimmunity are precipitating as an appealing challenge for further investigations.

Relationship between selenium, lead, and mercury in red blood cells of Saudi autistic children

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that can cause significant social, communication and behavioral challenges. Environmental contribution to ASD is due in large part to the sensitivity of the developing brain to external exposures such as lead (Pb), and mercury (Hg) as toxic heavy metals or due to a poor detoxification ability as the phenotype of this disorder. Selenium (Se) as an antioxidant element that counteracts the neurotoxicity of Hg, and Pb, presumably through the formation of nontoxic complexes. In the present study, Pb, Hg, and Se were measured in red blood cells (RBCs) of 35 children with ASD and 30 age- and gender-matched healthy control children using atomic absorption spectrometry. Receiver Operating Characteristics (ROC) analysis of the obtained data was performed to measure the predictive value of their absolute and relative concentrations. The obtained data demonstrates a significant elevation of Hg and Pb together with a significant decrease in the Se levels in RBCs of patients with ASD when compared to the healthy controls. The ratios of Se to both Pb and Hg were remarkably altered, being indicative of heavy metal neurotoxicity in patients with ASD. In conclusion, the present study indicates the importance of Se for prevention and/or therapy of heavy metal neurotoxicity.