Cognitive performance of children prenatally exposed to "safe" levels of methylmercury

Mercury-induced toxicity: Mechanisms, molecular pathways, and gene regulation

Mercury is a well-known neurotoxicant for humans and wildlife. The epidemic of mercury poisoning in Japan has clearly demonstrated that chronic exposure to methylmercury (MeHg) results in serious neurological damage to the cerebral and cerebellar cortex, leading to the dysfunction of the central nervous system (CNS), especially in infants exposed to MeHg in utero. The occurrences of poisoning have caused a wide public concern regarding the health risk emanating from MeHg exposure; particularly those eating large amounts of fish may experience the low-level and long-term exposure. There is growing evidence that MeHg at environmentally relevant concentrations can affect the health of biota in the ecosystem. Although extensive in vivo and in vitro studies have demonstrated that the disruption of redox homeostasis and microtube assembly is mainly responsible for mercurial toxicity leading to adverse health outcomes, it is still unclear whether we could quantitively determine the occurrence of interaction between mercurial and thiols and/or selenols groups of proteins linked directly to outcomes, especially at very low levels of exposure. Furthermore, intracellular calcium homeostasis, cytoskeleton, mitochondrial function, oxidative stress, neurotransmitter release, and DNA methylation may be the targets of mercury compounds; however, the primary targets associated with the adverse outcomes remain to be elucidated. Considering these knowledge gaps, in this article, we conducted a comprehensive review of mercurial toxicity, focusing mainly on the mechanism, and genes/proteins expression. We speculated that comprehensive analyses of transcriptomics, proteomics, and metabolomics could enhance interpretation of "omics" profiles, which may reveal specific biomarkers obviously correlated with specific pathways that mediate selective neurotoxicity.

Repurposing an antimicrobial peptide for the development of a dual ion channel/molecular receptor-like platform for metal ion detection

The presence of non-essential metals in the environment as contaminants is prone to cause hazardous health problems following accumulation in the human body and the ensuing toxic effects. This calls for continuous discovery and innovation in the realm of developing easy-to-operate, cheap and sensitive sensors. Herein, we describe the proof of concept approach for designing a molecular receptor-like, chimeric sensor based on the pore-forming peptide alamethicin (Alm), tethered via a linker with an ultrashort peptide nucleic acid (PNA) moiety, capable of generating functional ion channel oligomers in planar lipid membranes. The working principle of the sensor exploits the ability of Hg2+ ions to complex mismatching thymine-thymine sequences between the PNA receptor moiety on Alm oligomers and free, thymine-based, single-stranded DNAs (ssDNAs) in solution, thus creating a stable base pair at the oligomer entrance. This generates a transducing mechanism which converts the metal ion complexation into a specific electrical signature of the self-assembled Alm oligomers, enabling selective Hg2+ ion detection. The platform is programmable, whereby the simple exchange of the PNA sequence and its ssDNA counterpart in solution rendered the system selective for Cu2+ ion detection. With further optimization, the presented solution has the potential to translate into miniaturized, cost-effective biosensors suitable for the real-time, label-free and continuous detection of metal ions or other biomolecules.

A Dicyanoisoflurone-based Near-infrared Fluorescence Probe for Highly Sensitive Detection of Hg2

Due to its high toxicity, long durability, easy absorption by aquatic organisms, and significant bioaccumulation, Hg2+ has caused substantial environmental damage and posed serious threats to human health. Therefore, effective detection of Hg2+ is of utmost importance. In this study, a turn-on fluorescent probe based on dicyanoisoflurone was developed for the detection of Hg2+. The probe exhibited near-infrared fluorescence signal at 660 nm upon excitation by 440 nm UV light in a mixture of CH3CN and HEPES buffer (4:1, v/v, 10 mM, pH = 7.5), with selective binding to Hg2+ in a molar ratio of 1:1. This binding event was accompanied by a visible color change from light yellow to orange. By utilizing the enhanced fluorescence signal change, this probe enables highly sensitive analysis and detection of Hg2+ with excellent selectivity (association constant = 1.63 × 104 M- 1), large Stokes shift (220 nm), high sensitivity (detection limit as low as 5.6 nM), short reaction time (30 s), and a physiological pH range of 7.5-9.5. The probe was successfully employed for detecting of Hg2+ in real water and living cells.

A Ratiometric Green Fluorescent Carbazole-Bis(hydrazinobenzothiazole) Probe for the Selective Detection of Toxic Hg2+ Ions in Real Water Samples

A dyad Carbazolyl-bis(hydrazinobenzothiazole) was designed to form a symmetrical structure that containing two-arm active binding sites facilitates coordination with Hg2+ ion. This sensor has imparted a colorimetric and fluorometric changes in presence of Hg2+ ions. The ligand showed a selective blue shift in presence of Hg2+even in co-existence with heavy metal ions with luminescence change from colorless to blue and colorless to green under day light. Enhanced Intramolecular charge transfer process is responsible for fluorescence transformation when ligand interacts with Hg2+ ion. The emission spectra showed a ratiometric response to increasing addition of Hg2+ ions. The sensor is capable of detecting above the lower concentration of 6.8025×10-8 M. The fluorescence efficiency of CBT-2 with Hg2+ ion is quite stable under different co-metal ions and wide range of pH 6 to 9. The sensor CBT-2 forms a 1 : 1 stoichiometric complex with Hg2+ ions and the binding nature is confirmed from the 1H-NMR, FTIR, and mass spectroscopic studies. The sensor CBT-2 and its Hg2+ complex possess good binding nature to protein in Bovine Serum Albumin which could be good in biological applications. Additionally, wedevelop a practical application in real water sample analysis and electrochemical detection via oxidation potential discrimination.

Coumarin derivative-functionalized nanoporous silica as an on-off fluorescent sensor for detecting Fe3+ and Hg2+ ions: a circuit logic gate

A highly efficient fluorescent sensor (S-DAC) was easily created by functionalizing the SBA-15 surface with N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane followed by the covalent attachment of 7-diethylamino 3-acetyl coumarin (DAC). This chemosensor (S-DAC) demonstrates selective and sensitive recognition of Fe3+ and Hg2+ in water-based solutions, with detection limits of 0.28 × 10-9 M and 0.2 × 10-9 M for Hg2+ and Fe3+, respectively. The sensor's fluorescence characteristics were examined in the presence of various metal ions, revealing a decrease in fluorescence intensity upon adding Fe3+ or Hg2+ ions at an emission wavelength of 400 nm. This sensor was also able to detect ferric and mercury ions in spinach and tuna fish. The quenching mechanism of S-DAC was investigated using UV-vis spectroscopy, which confirmed a static-type mechanism for fluorescence quenching. Moreovre, the decrease in fluorescence intensity caused by mercury and ferric ions can be reversed using trisodium citrate dihydrate and EDTA as masking agents, respectively. As a result, a circuit logic gate was designed using Hg2+, Fe3+, trisodium citrate dihydrate, and EDTA as inputs and the quenched fluorescence emission as the output.

What does scientometry tell us about mercury toxicology and its biological impairments?

Mercury is a toxic pollutant that poses risks to both human and environmental health, making it a pressing public health concern. This study aimed to summarize the knowledge on mercury toxicology and the biological impairments caused by exposure to mercury in experimental studies and/or diagnosis in humans. The research was conducted on the main collection of Web of Science, employing as a methodological tool a bibliometric analysis. The selected articles were analyzed, and extracted data such as publication year, journal, author, title, number of citations, corresponding author's country, keywords, and the knowledge mapping was performed about the type of study, chemical form of mercury, exposure period, origin of exposure, tissue/fluid of exposure measurement, mercury concentration, evaluation period (age), mercury effect, model experiments, dose, exposure pathway, and time of exposure. The selected articles were published between 1965 and 2021, with Clarkson TW being the most cited author who has also published the most articles. A total of 38% of the publications were from the USA. These studies assessed the prenatal and postnatal effects of mercury, emphasizing the impact of methylmercury on neurodevelopment, including motor and cognitive evaluations, the association between mercury and autism, and an evaluation of its protective effects against mercury toxicity. In observational studies, the blood, umbilical cord, and hair were the most frequently used for measuring mercury levels. Our data analysis reveals that mercury neurotoxicology has been extensively explored, but the association among the outcomes evaluated in experimental studies has yet to be strengthened. Providing metric evidence on what is unexplored allows for new studies that may help governmental and non-governmental organizations develop guidelines and policies.

Maternal seafood consumption is associated with improved selenium status: Implications for child health

Selenium (Se) is required for synthesis of selenocysteine (Sec), an amino acid expressed in the active sites of Se-dependent enzymes (selenoenzymes), including forms with essential functions in fetal development, brain activities, thyroid hormone metabolism, calcium regulation, and to prevent or reverse oxidative damage. Homeostatic mechanisms normally ensure the brain is preferentially supplied with Se to maintain selenoenzymes, but high methylmercury (CH3Hg) exposures irreversibly inhibit their activities and impair Sec synthesis. Due to Hg's high affinity for sulfur, CH3Hg initially binds with the cysteine (Cys) moieties of thiomolecules which are selenoenzyme substrates. These CH3Hg-Cys adducts enter selenoenzyme active sites and transfer CH3Hg to Sec, thus irreversibly inhibiting their activities. High CH3Hg exposures are uniquely able to induce a conditioned Se-deficiency that impairs synthesis of brain selenoenzymes. Since the fetal brain lacks Se reserves, it is far more vulnerable to CH3Hg exposures than adult brains. This prompted concerns that maternal exposures to CH3Hg present in seafood might impair child neurodevelopment. However, typical varieties of ocean fish contain far more Se than CH3Hg. Therefore, eating them should augment Se-status and thus prevent Hg-dependent loss of fetal selenoenzyme activities. To assess this hypothesis, umbilical cord blood and placental tissue samples were collected following delivery of a cohort of 100 babies born on Oahu, Hawaii. Dietary food frequency surveys of the mother's last month of pregnancy identified groups with no (0 g/wk), low (0-12 g/wk), or high (12 + g/wk) levels of ocean fish consumption. Maternal seafood consumption increased Hg contents in fetal tissues and resulted in ∼34% of cord blood samples exceeding the EPA Hg reference level of 5.8 ppb (0.029 µM). However, Se concentrations in these tissues were orders of magnitude higher and ocean fish consumption caused cord blood Se to increase ∼9.4 times faster than Hg. Therefore, this study supports the hypothesis that maternal consumption of typical varieties of ocean fish provides substantial amounts of Se that protect against Hg-dependent losses in Se bioavailability. Recognizing the pivotal nature of the Hg:Se relationship provides a consilient perspective of seafood benefits vs. risks and clarifies the reasons for the contrasting findings of certain early studies.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

Construction of an optical sensor for copper determination in environmental, food, and biological samples based on the covalently immobilized 2-(2-benzothiazolylazo)-3-hydroxyphenol in agarose

An optical chemical sensor has been developed for the quantitative spectrophotometric analysis of copper. The optode is dependent on covalent immobilization of 2-(2-benzothiazolylazo)-3-hydroxyphenol (BTAHP) in a transparent agarose membrane. The absorbance variation of immobilized BTAHP on agarose as a film upon the addition of 5 × 10-3 M aqueous solutions of Mn2+, Zn2+, Hg2+, Cd2+, Pb2+, Co2+, Ni2+, Fe2+, La3+, Fe3+, Cr3+, Zr4+, Se4+, Th4+, and UO22+ revealed substantially higher changes in the Cu2+ ion content compared to other ions investigated here. The effects of various experimental parameters, such as the solution pH, the reaction time, and the concentration of reagents, on the quality of Cu2+ sensing were examined. Under ideal experimental circumstances, a linear response was achieved for Cu2+ concentrations ranging from 1.0 × 10-9 to 7.5 × 10-6 M with an R2 value of 0.9988. The detection (3σ) and quantification (10σ) limits of the procedure for Cu2+ analyses were 3.0 × 10-10 and 9.8 × 10-10 M, respectively. No observable interference was recorded in the detection of Cu2+ due to other inorganic cations. With no indication of BTAHP leaching, the membrane demonstrated good durability and quick response times. The optode was effectively used to determine the presence of Cu2+ in environmental water, food, and biological samples.

Triazine based fluorescent sensor for sequential detection of Hg2+ and L-Cysteine in real samples and application in logic Gate: A combination of Extensive experimental and theoretical analysis

Triazine based fluorescent sensor TBT was rationally designed and synthesized to achieve sequential detection of Hg²⁺ and L-cysteine based on the presence of sulfur moiety and suitable cavity in the molecule. Sensor TBT exhibited excellent sensing potential for the selective detection of Hg²⁺ ions and L-cysteine (Cys) in real samples. Upon addition of Hg²⁺ to sensor TBT, enhancement in emission intensity of sensor TBT was observed which was accredited to the presence of sulfur moiety and size of cavity in the sensor. Upon interaction with Hg²⁺ blockage of intramolecular charge transfer (ICT) along with chelation-enhanced fluorescence (CHEF) resulted in the increase in fluorescence emission intensity of sensor TBT. Further, TBT-Hg²⁺ complex was employed for the selective detection of Cys through fluorescence quenching mechanism. This was attributed to the significantly stronger interaction of Cys with Hg²⁺, which resulted in the formation of Cys-Hg²⁺ complex and subsequently sensor TBT was released from TBT-Hg²⁺ complex. The nature of interaction between TBT-Hg²⁺ and Cys-Hg²⁺ complex was evaluated through ¹H NMR titration experimentations. Extensive DFT studies were also carried out which include thermodynamic stability, frontier molecular orbitals (FMO), density of states (DOS), non-covalent interaction (NCI), quantum theory of atom in molecule (QTAIM), electron density differences (EDD) and natural bond orbital (NBO) analyses. All the studies supported the non-covalent type of interaction between analytes and sensor TBT. The limit of detection for Hg²⁺ ions was found to be as low as 61.9 nM. Sensor TBT was also employed for the quantitative detection of Hg²⁺ and Cys in real samples. Additionally, logic gate was fabricated by using sequential detection strategy.

Plasmonic scattering imaging of single Cu2-xSe nanoparticle for Hg2+ detection

The development of new efficient contrast nanoprobe has been greatly concerned in the field of scattering imaging for sensitive and accurate detection of trace analytes. In this work, the non-stoichiometric Cu_2-xSe nanoparticle with typical localized surface plasmon resonance (LSPR) properties originating from their copper deficiency as a plasmonic scattering imaging probe was developed for sensitive and selective detection of Hg²⁺ under dark-field microscopy. Hg²⁺ can compete with Cu(I)/Cu(II) which were sources of optically active holes coexisting in these Cu_2-xSe nanoparticles for its higher affinity with Se^2-. The plasmonic properties of Cu_2-xSe were adjusted effectively. Thus, the color scattering images of Cu_2-xSe nanoparticles was changed from blue to cyan, and the scattering intensity was obviously enhanced with the dark-field microscopy. There was a linear relationship between the scattering intensity enhancement and the Hg²⁺ concentration in the range of 10-300 nM with a low detection limit of 1.07 nM. The proposed method has good potential for Hg²⁺ detection in the actual water samples. This work provides a new perspective on applying new plasmonic imaging probe for the reliable determination of trace heavy metal substances in the environment at a single particle level.

Neurotransmitter disturbances caused by methylmercury exposure: Microbiota-gut-brain interaction

The fetal and early postnatal stages are periods of rapid brain development, during which, methylmercury (MeHg) exposure can cause lasting cognitive impairments. MeHg exposure disrupts neurotransmitter metabolites, which increased susceptibility to neurological responses. However, the neurotoxic mechanism underlying the MeHg-induced disruption of neurotransmitter metabolism requires further exploration. To this end, female Sprague-Dawley (SD) rats were administered NaCl (control group) or MeHg (0.6 mg/kg, 1.2 mg/kg and 2.4 mg/ kg body weight (bw), where the body weight refers to the dams) during the perinatal period, and then changes in neurotransmitter profiles and the gut microbiota of offspring were detected. The results showed that tryptophan (Trp) and tyrosine (Tyr) pathway neurotransmitter metabolites, including serotonin (5-HT), 5-hydroxy indole acetic acid (5-HIAA), N-acetyl-5-hydroxytryptamin (NAS), Tyr, dopamine (DA) and epinephrine (E), were significantly changed, and the Kynurenine/Tryptophan (Kyn/Trp) ratio was increased in the MeHg-treated groups. Meanwhile, acetylcholine (ACh) and neurotransmitters involved in the amino acid pathway were significantly reduced. Notably, MeHg treatment induced a significant reduction in tight junctions in the colon and hippocampal tissue. Furthermore, fecal microbiota analysis indicated that the diversity and composition characteristics were significantly altered by MeHg exposure. Mediation analysis showed that the gut microbiota mediated the effect of MeHg treatment on the neurotransmitter expression profiles. The present findings shed light on the regulatory role of the gut microbiota in MeHg-disrupted neurotransmitter metabolic pathways and the potential impact of perinatal MeHg treatment on the "cross-talk" between the gut and brain.

Developmental Methylmercury Exposure Induced and Age-Dependent Glutamatergic Neurotoxicity in Caenorhabditis elegans

Developmental methylmercury (MeHg) exposures cause latent neurotoxic effects in adults; however, the mechanisms underlying the latent neurotoxicity are not fully understood. In the current study, we used C. elegans as an animal model to investigate the latent neurotoxic effects of developmental MeHg exposures on glutamatergic neurons. The young larvae stage 1 worms were exposed to MeHg (0.05 ~ 5 µM) for 48 h. The morphological and behavioral endpoints of glutamatergic neurons were compared when worms reached to adult stages including the young adult stage (day 1 adult) and the old adult stage (day 10 adult). Here, we showed that C. elegans glutamatergic neurons were morphologically intact following low or medium MeHg exposures (0.05 ~ 0.5 µM). The morphological damage of glutamatergic neurons appeared to be pronounced in day 10 adults developmentally exposed to 5 µM MeHg. Behavioral assays also showed an age-dependent latent effect of MeHg. In the nose touch response assay, only day 10 adult worms exhibited a functional decline following prior 5 µM MeHg exposure. Moreover, the disruption of NaCl memory appeared only in day 1 adults following MeHg exposures but not in day 10 adults. The expression of C. elegans homologs of mammalian vesicular glutamate transporter (eat-4) was repressed in day 1 adults, while the glutamate receptor homolog (glr-1) was upregulated in day 10 adults with 5 µM MeHg. In the comparison of age-dependent changes in the insulin-like pathway (daf-2/age-1/daf-16) following MeHg exposures, we showed that the daf-2/age-1/daf-16 pathway was mobilized in day 1 adults but repressed in day 10 adults. Collectively, our data supports a conclusion that MeHg-induced glutamatergic neurotoxicity exhibits an age-dependent pattern, possibly related to the prominent changes in age-dependent modulation in the glutamatergic neurotransmission and metabolic pathways.

Ln Based Metal-organic Framework for Fluorescence "Turn Off-On" Sensing of Hg2

A highly luminescent Ln-MOF [La₃(NDC)₄(DMF)₃(H₂O)₄]_n, (NDC = 2, 6 naphthalen dicarboxylic acid) was designed and synthesized. The structure was characterized by x-ray single structure determination, TGA, IR spectra and PXRD and fluorescence spectroscopy. The structure shows high fluorescence intensity based on the presence of lanthanide metal and ligand. In the presence of I^-, the emission can be effectively quenched introducing turn off system. Furthermore, the synthesized Ln-MOF can recognize Hg (II) by showing fluorescence turn-on signal because of the high affinity between Hg (II) and I^-. Moreover, the high selectivity and sensitivity of the synthesized Ln-MOF makes it quit qualified for determination of the low concentration of mercury (2.00 nM).

Lead, mercury, and cadmium levels in breast milk and infant hair in the late period of lactation in Ankara, Turkey

Lead (Pb), mercury (Hg), and cadmium (Cd) have known harmful effects on children's well-being. The object of this study was to measure the levels of heavy metals (Pb, Hg, and Cd) in breast milk and infant hair, connected environmental factors, and the impact on infant growth and development at 8 months. Seventy-four breast milk samples and 46 infant hair samples were analyzed. Cd, Pb, and Hg were detected in 99%, 91%, and 87% of breast milk samples, respectively. Cd levels were higher in the hair of infants in extended families, living in older houses and when there was a maternal history of anemia and postpartum anemia. Hg levels in breast milk were higher in Denver II suspicious/abnormal infants than in Denver II normal infants. Further biomonitoring studies and preventive measures should be conducted to minimize exposure to toxic metals in early childhood period.

Impacts of Neonatal Methylmercury on Behavioral Flexibility and Learning in Spatial Discrimination Reversal and Visual Signal Detection Tasks

Early postnatal development in rodents is sensitive to neurotoxic effects of the environmental contaminant, methylmercury. While juvenile and adolescent exposure also produce long-term impairments in behavior, the outcome of neonatal exposure is less understood. Neural development during the neonatal period in rodents is akin to that seen in humans during the third trimester of pregnancy but methylmercury exposure occurring during the neonatal period has not been modeled, partly because breast milk is a poor source of bioavailable methylmercury. To examine this developmental period, male Long-Evans rats were exposed to 0, 80, or 350µg/kg/day methylmercuric chloride from postnatal days 1 to 10, the rodent neonatal period. As adults, behavioral flexibility, attention, memory, and expression of the dopamine transporter in these rats was assessed. Rats exhibited changes in behavioral flexibility assessed in a spatial discrimination reversal procedure. Those rats exposed to the highest dose of methylmercury displayed subtly altered patterns of perseveration compared to control animals. During acquisition of the attention/memory procedure, rats exposed to this dose also had slower acquisition, and achieved lower overall accuracy during training, compared to controls despite neither attention nor memory being affected once the task was acquired. Finally, dopamine transporter expression in the striatum, prefrontal cortex, and hippocampus was unchanged in these adult rats. The results of this study replicate the trend of findings seen with exposure during gestation or during adolescence.

Umbilical cord serum elementomics of 52 trace elements and early childhood neurodevelopment: Evidence from a prospective birth cohort in rural Bangladesh

BACKGROUND

Prenatal exposures to neurotoxic metals and trace elements are associated with early childhood neurodevelopmental outcomes. However, consequences of simultaneous exposure to mixtures of elements remain unclear.

OBJECTIVE

To examine individual and joint effects of prenatal trace element exposure on early childhood neurodevelopment.

METHODS

Using a well-established Bangladesh prospective birth cohort (2008-2011), we measured concentrations of 52 trace elements in umbilical cord serum of 569 mother-infant pairs using inductively coupled plasma mass spectrometry. Neurodevelopment was evaluated at 20-40 months of age using Bayley Scales of Infant and Toddler Development, Third Edition. Stability elastic net (ENET) was used to screen elements individually associated with the outcome; candidate exposures were combined by weighted linear combination to form a risk score representing their mixture effect on early childhood neurodevelopment.

RESULTS

Stability ENET identified 15 trace elements associated with cognitive composite score and 14 associated with motor composite score, which were linearly combined to form the element risk score (ERS). Children with higher ERScognitive had lower probability of cognitive developmental delay (ORhighest vs lowest: 0.21; 95 %CI: 0.10, 0.40; P < 0.001; Ptrend < 0.001). Children with ERSmotor in the top quintile had a significantly lower risk of motor developmental delay (OR: 0.16; 95 %CI: 0.09, 0.31; P < 0.001; Ptrend < 0.001) versus the lowest quintile. In Bayesian kernel machine regression analyses, lithium [conditional posterior inclusion probability (cPIP) = 0.68], aluminum (cPIP = 0.83) and iron (cPIP = 1.00) contributed most to the lower cognitive composite score; zinc (cPIP = 1.00), silver (cPIP = 0.81), and antimony (cPIP = 0.65) mainly contributed to the change of motor composite score.

CONCLUSION

Co-exposure to lithium/aluminum/iron or zinc/silver/antimony appears to impact children's neurodevelopment. ERS score reflecting maternal exposure could indicate children's risk of neurodevelopmental delay, warranting further studies to explore the underlying mechanism.

Adolescence as a sensitive period for neurotoxicity: Lifespan developmental effects of methylmercury

Neurotoxicity resulting from the environmental contaminant, methylmercury (MeHg), is a source of concern for many human populations that rely heavily on the consumption of fish and rice as stable ingredients in the diet. The developmental period of exposure is important both to the qualitative effects of MeHg and to the dose required to produce those effects. MeHg exposure during the sensitive prenatal period causes deleterious and long-lasting changes in neurodevelopment at particularly low doses. The effects include a wide host of cognitive and behavioral outcomes expressed in adulthood and sometimes not until aging. However, neurotoxic outcomes of methylmercury when exposure occurs during adolescence are only recently revealing impacts on human populations and animal models. This review examines the current body of work and showcases the sensitivity of adolescence, a period that straddles early development and adulthood, to methylmercury neurotoxicity and the implications such toxicity has in our understanding of methylmercury's effects in human populations and animal models.

Associations between developmental exposure to environmental contaminants and spatial navigation in late adolescence

Inuit communities in Northern Quebec (Canada) are exposed to environmental contaminants, particularly to mercury, lead and polychlorinated biphenyls (PCBs). Previous studies reported adverse associations between these neurotoxicants and memory performance. Here we aimed to determine the associations of pre- and postnatal exposures to mercury, lead and PCB-153 on spatial navigation memory in 212 Inuit adolescents (mean age = 18.5 years) using a computer task which requires learning the location of a hidden platform based on allocentric spatial representation. Contaminant concentrations were measured in cord blood at birth and blood samples at 11 years of age and at time of testing. Multivariate regression models showed that adolescent mercury and prenatal PCB-153 exposures were associated with poorer spatial learning, whereas current exposure to PCB-153 was associated with altered spatial memory retrieval at the probe test trial. These findings suggest that contaminants might be linked to different aspects of spatial navigation processing at different stages.

A NIR fluorescent sensor based on thiazoline-isophorone with low cytotoxicity in living cells for Hg2+ detection through ICT associated hydrogen bonding effect

Mercury (Hg) is a toxic pollutant and may cause serious health and environmental threats even at low concentrations. Thus, sensitive, efficient, and accurate techniques for the detection of Hg²⁺ ions in biological systems are in particular demand. In the current paper, a new, red emitting fluorescence probe (THI) based on electron deficient dicyanovinyl, electron-rich diethylamino, and receptor thiazoline toward Hg²⁺ has been developed. It has been determined that the recognition behavior of the probe toward Hg²⁺ is reversible with S^2-. The probe not only shows perfect selectivity toward Hg²⁺ with a low detection limit over a series of metal ions, but it also displays positive solvato-chromism among the tested solvents via modulation of intramolecular energy transfer from the diethylamino to a dicyanovinyl moiety. Furthermore, it has been shown that the probe can be applied as a fluorescent probe for visualizing Hg²⁺ in living HeLa cells through a confocal laser scanning microscope. Also, the probe THI has not shown any toxic effect in cervical cancer and epithelial cells. Thus, the probe demonstrates high promise for Hg²⁺ detection in biomarker screening, disease diagnosis, and clinical medicine with low cytotoxicity.

Electrospun Nanofiber Membranes from 1,8-Naphthimide-Based Polymer/Poly(vinyl alcohol) for pH Fluorescence Sensing

Accurately and sensitively sensing and monitoring the pH in the environment is a key fundamental issue for human health. Nanomaterial and nanotechnology combined with fluorescent materials can be emerged as excellent possible methods to develop high-performance sensing membranes and help monitor pH. Herein, a series of fluorescent nanofiber membranes (NFMs) containing poly-1,8-naphthimide derivative-3-[dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azaniumyl]propane-1-sulfonate (PNI-SBMA) are fabricated by electrospinning the solution of PNI-SBMA blended with poly(vinyl alcohol) (PVA). The surfactant-like functionalities in side chains of PNI-SBMA endow the NFMs with outstanding hydrophilicity, and the naphthimide derivatives are sensitive to pH by photoinduced electron transfer effect, which contribute to highly efficient pH fluorescence sensing applications of NFMs. Specifically, the PNI-SBMA/PVA NFM with a ratio of 1:9 (NFM2) shows high sensitivity and good cyclability to pH. This work demonstrates an effective strategy to realize a fluorescent sensor NFM that has a fast and sensitive response to pH, which will benefit its application of pH sensor monitoring in the water treatment process.

The need for "gentle medicine" in a post Covid-19 world

As it has historically been the case with many pandemics, the Covid-19 experience will induce many philosophers to reconsider the value of medical practice. This should be a good opportunity to critically scrutinize the way medical research and medical interventions are carried out. For much of its history, medicine has been very inefficient. But, even in its contemporary forms, a review of common protocols in medical research and medical interventions reveal many shortcomings, especially related to methodological flaws, and more importantly, conflicts of interests due to profit incentives. In the face of these problems, we propose a program of "gentle medicine". This term, originally formulated by philosopher Jacob Stegenga, describes a form of medicine in which physicians intervene less than they currently do. As part of this general program, we advance a series of reform recommendations that could be enacted both by medical staff in their everyday practice, but also by public health officials and policymakers.

Characteristics and Risk Assessments of Mercury Pollution Levels at Domestic Garbage Collection Points Distributed within the Main Urban Areas of Changchun City

The mercury that is released from the centralized treatment of municipal solid waste is an important source of atmospheric mercury. We chose the main urban area of Changchun as a representative area. Environmental factors such as total mercury content, temperature, wind speed, and other factors were measured in samples from the trash cans of two types of collection points (trash cans and garbage stations), the topsoil under the selected trash cans, and the ambient air above the selected trash cans. The potential ecological risks of mercury pollution were evaluated. The results showed that the mercury content levels of all sample types in the refuse transfer station were higher than the garbage cans and there were no significant differences observed between soil surface mercury and garbage cans. The mercury content levels in the atmosphere and the surface soil at the garbage collection points were found to increase along the cascade relationship of the garbage collection. However, there were no correlations observed between the atmospheric mercury content levels and the surface soil mercury content levels with the attachments and the sum of the former two. There were no correlations observed between surface soil and the attachments, or among the attachments, surface soil, and the atmospheric mercury content levels. The mercury content levels in the attachments, surface soil, and atmosphere of the garbage collection points in the study area were negatively correlated with the loop lines. Meanwhile, the potential ecological risk indexes of the garbage cans and garbage stations were found to be high. The chronic non-carcinogenic risks of mercury to children and adults were determined to be very low. The risks of mercury to children were higher when compared with adults. The highest non-carcinogenic risks of mercury pollution were determined to be within the central area of Changchun.

Developmental Exposure to Low Concentrations of Methylmercury Causes Increase in Anxiety-Related Behaviour and Locomotor Impairments in Zebrafish

Methylmercury (MeHg) is a ubiquitous pollutant shown to cause developmental neurotoxicity, even at low levels. However, there is still a large gap in our understanding of the mechanisms linking early-life exposure to life-long behavioural impairments. Our aim was to characterise the short- and long-term effects of developmental exposure to low doses of MeHg on anxiety-related behaviours in zebrafish, and to test the involvement of neurological pathways related to stress-response. Zebrafish embryos were exposed to sub-acute doses of MeHg (0, 5, 10, 15, 30 nM) throughout embryo-development, and tested for anxiety-related behaviours and locomotor activity at larval (light/dark locomotor activity) and adult (novel tank and tap assays) life-stages. Exposure to all doses of MeHg caused increased anxiety-related responses; heightened response to the transition from light to dark in larvae, and a stronger dive response in adults. In addition, impairment in locomotor activity was observed in the higher doses in both larvae and adults. Finally, the expressions of several neural stress-response genes from the HPI-axis and dopaminergic system were found to be disrupted in both life-stages. Our results provide important insights into dose-dependent differences in exposure outcomes, the development of delayed effects over the life-time of exposed individuals and the potential mechanisms underlying these effects.

Sex-specific neurotoxic effects of heavy metal pollutants: Epidemiological, experimental evidence and candidate mechanisms

The heavy metals lead (Pb), mercury (Hg), and cadmium (Cd) are ubiquitous environmental pollutants and are known to exert severe adverse impacts on the nervous system even at low concentrations. In contrast, the heavy metal manganese (Mn) is first and foremost an essential nutrient, but it becomes neurotoxic at high levels. Neurotoxic metals also include the less prevalent metalloid arsenic (As) which is found in excessive concentrations in drinking water and food sources in many regions of the world. Males and females often differ in how they respond to environmental exposures and adverse effects on their nervous systems are no exception. Here, we review the different types of sex-specific neurotoxic effects, such as cognitive and motor impairments, that have been attributed to Pb, Hg, Mn, Cd, and As exposure throughout the life course in epidemiological as well as in experimental toxicological studies. We also discuss differential vulnerability to these metals such as distinctions in behaviors and occupations across the sexes. Finally, we explore the different mechanisms hypothesized to account for sex-based differential susceptibility including hormonal, genetic, metabolic, anatomical, neurochemical, and epigenetic perturbations. An understanding of the sex-specific effects of environmental heavy metal neurotoxicity can aid in the development of more efficient systematic approaches in risk assessment and better exposure mitigation strategies with regard to sex-linked susceptibilities and vulnerabilities.

Mercury accumulation in reef fishes: a comparison among red grouper, scamp, and gag of the Atlantic southeastern US and evaluation of "grouper" consumption guidelines

In fish consumption advisories pertaining to Hg, grouper species in the family Serranidae are often lumped together and labeled generically as Grouper. However, grouper species vary considerably in growth rate, maximum age, and maximum size. This study examined the variability of Hg concentrations and bioaccumulation rates (increase of Hg concentrations in relation to age) for populations of three long-lived, slow-growing, protogynous hermaphrodite grouper species, gag Mycteroperca microlepis, scamp M. phenax, and red grouper Epinephelus morio, which are commercially and recreationally important in the offshore waters of the US southeastern region. A total of 268 samples from the three grouper species were processed for Hg analysis from 2013-2015. Concentrations of Hg ranged from 0.03 to 0.87 ppm wet weight, with a mean of 0.30 ppm. Gag accumulated Hg at a faster rate (as measured by the increase of Hg with fish age) than the other two species. Size, age, and δ¹⁵N were significant predictors for Hg in the two Mycteroperca species, while size and age were significant predictors for Hg in red grouper. Two of the three species had mean Hg concentrations within the one meal per week "Good Choices" consumption category (red grouper and scamp), and one species (gag) had a mean Hg level within the two meals per week "Good Choices" consumption category as advised by the US EPA and US FDA. These results support the separation of grouper species in advisories.

Influence of the Levels of Arsenic, Cadmium, Mercury and Lead on Overall Survival in Lung Cancer

The effects of heavy metals on cancer risk have been widely studied in recent decades, but there is limited data on the effects of these elements on cancer survival. In this research, we examined whether blood concentrations of the heavy metals arsenic, cadmium, mercury and lead were associated with the overall survival of lung cancer patients. The study group consisted of 336 patients with lung cancer who were prospectively observed. Blood concentrations of heavy metals were measured to study the relationship between their levels and overall survival using Cox proportional hazards analysis. The hazard ratio of death from all causes was 0.99 (p = 0.94) for arsenic, 1.37 (p = 0.15) for cadmium, 1.55 (p = 0.04) for mercury, and 1.18 (p = 0.47) for lead in patients from the lowest concentration quartile, compared with those in the highest quartile. Among the patients with stage IA disease, this relationship was statistically significant (HR = 7.36; p < 0.01) for cadmium levels in the highest quartile (>1.97–7.77 µg/L) compared to quartile I (0.23–0.57 µg/L, reference). This study revealed that low blood cadmium levels <1.47 µg/L are probably associated with improved overall survival in treated patients with stage IA disease.

RNA sequencing and proteomic profiling reveal different alterations by dietary methylmercury in the hippocampal transcriptome and proteome in BALB/c mice

Methylmercury (MeHg) is a highly neurotoxic form of mercury (Hg) present in seafood. Here, we recorded and compared proteomic and transcriptomic changes in hippocampus of male BALB/c mice exposed to two doses of MeHg. Mice were fed diets spiked with 0.28 mg MeHg kg-1, 5 mg MeHg kg-1, or an unspiked control diet for 77 days. Total mercury content was significantly (P < 0.05) increased in brain tissue of both MeHg-exposed groups (18 ± 2 mg Hg kg-1 and 0.56 ± 0.06 mg Hg kg-1). Hippocampal protein and ribonucleic acid (RNA) expression levels were significantly altered both in tissues from mice receiving a low dose MeHg (20 proteins/294 RNA transcripts) and a high dose MeHg (61 proteins/876 RNA transcripts). The majority but not all the differentially expressed features in hippocampus were dose dependent. The combined use of transcriptomic and proteomic profiling data provided insight on the influence of MeHg on neurotoxicity, energy metabolism, and oxidative stress through several regulated features and pathways, including RXR function and superoxide radical degradation.

Seafood and health: What you need to know?

Seafood, including fish and shellfish, provides an ideal package of nutrients and is an important part of a healthy diet. Strong evidence has shown that eating fish and other seafoods improve brain, eye, and heart health. The new 2020-2025 Dietary Guidelines for Americans (DGA) recommend that Americans of all ages should eat more seafood-at least twice a week-particularly pregnant women and young children. However, less than one in five Americans heed that advice. About one-third of Americans eat seafood once a week, while nearly half eat fish only occasionally or not at all. This calls for a drastic shift in the American diet to vary protein sources and include more seafood products in order to receive the most health benefits. This chapter covers (1) seafood nutrition and health benefits, (2) seafood's protective effects against mercury toxicity, (3) selenium health benefit values (HBVs), and (4) challenges and opportunities for seafood production, demand and sustainability. This chapter aims to convey recent advances in science-based information to increase public awareness of seafood safety, nutrition and health benefits of seafood as part of a healthy diet, and to advocate healthy eating with smart food choices by promoting two servings of seafood per week. This will support the healthy eating patterns and promotes a minimum two to three servings of seafood recommended by the current DGA.

Simple and sensitive colorimetric sensors for the selective detection of Cu(ii)

A simple, sensitive colorimetric probe for detecting Cu(ii) ions with fast response has been established with a detection limit of 2.82 μM. UV-Vis spectroscopy along with metal ion response, selectivity, stoichiometry, competition was investigated. In the presence of copper(ii), the UV-Vis spectrum data showed significant changes and the colorimetric detection showed a color change from colorless to yellow. After the selective binding of receptor L with Cu(ii), the UV-visible absorption at 355 nm decreased dramatically, a new absorbance band appeared at 398 nm and its intensity enhanced with the increase in the amount of Cu(ii). Moreover, it exhibited highly selective and sensitive recognition towards Cu(ii) ions in the presence of other cations over the pH range of 7-11. The complex structure was verified by FT-IR spectroscopy, elemental analysis and quantum mechanical calculations using B3LYP/6-31G(d) to illustrate the complex formation between L and Cu(ii). According to the Job plot and the quantum mechanical calculations, the stoichiometric ratio for the complex formation was proposed to be 1 : 1.

Exposure to total and methylmercury among pregnant women in Suriname: sources and public health implications

Previous research has found that women and children living in rural, interior communities in Suriname have high concentrations of mercury in hair. Freshwater fish from these areas also have high concentrations of mercury. Artisanal and small-scale gold mining operations in parts of the country use elemental mercury to extract gold from soils and sediments. Total mercury and methylmercury concentrations have been determined in hair and blood from pregnant women across the country. Pregnant women from interior communities have significantly higher concentrations of both total and methylmercury in hair (median total mercury in hair 3.64 µg/g) compared with pregnant women from two urban coastal cities, Paramaribo (0.63 µg/g) and Nickerie (0.74 µg/g). Total and methylmercury concentrations in blood and hair are highly correlated (r = 0.986, r = 0.974) with methylmercury making up 86% of the total in blood and 97% of the total in hair. Most women in the interior regions rely heavily on local fish as part of their regular diet, and many live outsides of areas with active ASGM operations. This study demonstrates that diet and fish consumption largely govern mercury exposures in pregnant women in Suriname.

Temporal variation of total mercury levels in the hair of pregnant women from the Maternal-Infant Research on Environmental Chemicals (MIREC) study

Prenatal exposure to total mercury (T-Hg) comes from both natural and anthropogenic sources. T-Hg can cross the blood-brain and placental barriers, and may be associated with future neurological and physiological dysfunctions. Scalp hair is an optimal and non-invasive indicator of chronic T-Hg exposure. As part of the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, hair samples from 350 women were collected within weeks after giving birth, to determine temporal variations in T-Hg levels from preconception to delivery, and to compare these levels to corresponding levels measured in other matrices (maternal and umbilical cord blood, and infant's meconium). A maximum of 12 one-cm hair segments were cut starting at the scalp; segments closer to the scalp reflected recent exposure (within the last month). For proper comparison, the hair segments were matched with the collection dates for other matrices. GM hair T-Hg levels greatly decreased during pregnancy, from 0.26 μg g^-1 (preconception or full-length hair) to 0.18 μg g^-1 (at delivery or segments closer to the scalp). A similar decreasing trend was found for T-Hg in maternal blood: 1st trimester (0.60 μg L^-1) to 3rd trimester (0.47 μg L^-1). The median hair-to-blood ratios of T-Hg levels varied from 364 (1st trimester), to 408 (3rd trimester), to 229 (cord blood). Very low T-Hg levels were detected in meconium. Mercury levels in blood and hair correlated with consumption of large predatory fish.

Effects of low-level mercury exposure on brain-derived neurotrophic factor in preschool children

OBJECTIVES

Mercury (Hg), a ubiquitous heavy metal, could affect the neurodevelopment of the children, however, these associations are still equivocal. Brain derived neurotrophic factor (BDNF) plays an essential role in the central nervous system development in children. This study aimed to investigate the effects of low-level mercury exposure on serum BDNF levels and the influence of sex and dietary intake on these relationships in children.

METHODS

In this cross-sectional study, a total of 541 pre-school children were recruited, the blood mercury concentrations and serum BDNF levels were measured. The background information on demographic characteristics and dietary habits of the children was collected through questionnaires. Multivariable linear models after adjustment for potential confounders were used to evaluate the associations between mercury exposure and levels of BDNF in children.

RESULTS

The GMs of blood mercury concentrations and serum BDNF levels were 1.06 μg/L, 20.4 ng/mL, respectively. A significant positive association between blood mercury concentrations and serum BDNF levels was found. After stratification by sex, the blood mercury concentrations in children were positive associated with serum BDNF levels in girls but not in boys. However, these associations were attenuated when we further adjusted the children's dietary intake variables.

CONCLUSIONS

Our findings suggest that low-levels of mercury exposure may have sex-specific effects on BDNF levels in young children and that dietary intake may be potential confounders in these relationships. However, further studies are warranted to investigate the role of BDNF in the effects of mercury on neurodevelopment.

Fluorescent chemosensors for Hg2+ ions based on a pyridine-attached phenanthridine probe

The sensor probe detects selectively Hg2+ ions in semi-aqueous medium. Probe showed ratiometric response with low detection limit. We observed that 1 : 1 binding mode between probe and Hg2+ ions. Additionally, this probe was utilized for various practical applications.

Autoantibodies in outbred Swiss Webster mice following exposure to gold and mercury

Exposure to heavy metals may have toxic effects on several human organs causing morbidity and mortality. Metals may trigger or exacerbate autoimmunity in humans. Inbred mouse strains with certain H-2 haplotypes are susceptible to xenobiotic-induced autoimmunity; and their immune response to metals such as mercury, gold, and silver have been explored. Serum antinuclear antibodies (ANA), polyclonal B-cell activation, hypergammaglobulinemia and tissue immune complex deposition are the main features of metal-induced autoimmunity in inbred mice. However, inbred mouse strains do not represent the genetic heterogeneity in humans. In this study, outbred Swiss Webster (SW) mice exposed to gold or mercury salts showed immune and autoimmune responses. Intramuscular injection of 22.5 mg/kg.bw aurothiomalate (AuTM) induced IgG ANA in SW mice starting after 5 weeks that persisted until week 15 although with a lower intensity. This was accompanied by elevated serum levels of total IgG antibodies against chromatin and total histones. Exposure to gold led to development of serum IgG autoantibodies corresponding to H1 and H2A histones, and dsDNA. Both gold and mercury induced polyclonal B-cell activation. Eight mg/L mercuric chloride (HgCl₂) in drinking water, caused IgG antinucleolar antibodies (ANoA) after 5 weeks in SW mice accompanied by immune complex deposition in kidneys and spleen. Serum IgG antibodies corresponding to anti-fibrillarin, and anti-PM/Scl-100 antibodies, were observed in mercury-exposed SW mice. Gold and mercury trigger systemic autoimmune response in genetically heterogeneous outbred SW mice and suggest them as an appropriate model to study xenobiotic-induced autoimmunity.

A novel isatin-based probe for ratiometric and selective detection of Hg2+ and Cu2+ ions present in aqueous and environmental samples

A novel isatin derivative (1) is UV-Visible active and displays about 90 nm bathochromic shift upon interaction with only Hg²⁺ and Cu²⁺, but not with other common metal ions. Also, the colorless probe 1 turns to brick-red and yellow in the presence of Hg²⁺ and Cu²⁺, respectively. Addition of increasing amounts of Hg²⁺ or Cu²⁺ to 1 leads to the emergence of a new absorption at ~470 nm (due to LMCT), with a concomitant decrease in the intensity of absorption of 1 at ~380 nm, and thereby provides a ratiometric response. Common metal ions and anions do not interfere with the interactions of 1 with Hg²⁺or Cu²⁺ ions. Probe 1 shows very high sensitivity and selectivity towards Hg²⁺ and Cu²⁺ as revealed by their very low detection limits 0.95 × 10^-9 M and 1.5 × 10^-9 M, respectively. Formation of 1:1 complex with Hg²⁺ and 2:1 complex with Cu²⁺ is confirmed using NMR, ESI-MS and FT-IR techniques, Job plot and DFT calculations. Selective detection of Hg²⁺ from Cu²⁺ is established from the ratiometric response caused by β-mercaptoethanol. Advantages of the probe 1 in terms of high sensitivity, stability in the physiological pH and suitability for dual detection are presented. Probe impregnated silica plates for onsite detection of Hg²⁺ and Cu²⁺ present in environmental samples is also demonstrated.