Heavy metals (Pb, Cd, As and MeHg) as risk factors for cognitive dysfunction: A general review of metal mixture mechanism in brain

The applicability of fingernail lead and cadmium levels as subchronic exposure biomarkers for preschool children

Preschool children are exposed daily to metals in their homes and at daycare centers (DCC). Metal exposure and health effects are associated even at low levels, and children comprise a group of public health concern. Nail metals have been studied for exposure biomonitoring and compared to other biological media. The aim of this study was to explore the applicability of preschool fingernail lead and cadmium as subchronic exposure biomarkers. Nail lead and cadmium levels (NLL and NCL) of 602 preschool children (age: 1-4 years) who attended 21 DCC in São Paulo, Brazil, in 2013 were analyzed. Results were compared against blood lead and cadmium levels (BLL and BCL) found in a previous study. Inductively coupled plasma mass spectrometry (ICP-MS) analyses were performed for both samples. DCC and metal contaminated sites (MCS) were georeferencing. Logistic regression tests were applied to verify associations between nail metal levels and risk factors (sex, age, maternal education, secondary smoking, DCC geographic district, vehicle flow density, relative altitude and distance between DCC and nearest MCS) (p < 0.05). BLL was stratified by exposure level (low: <5 μg.dL^-1; high: >13.9 μg.dL^-1; medium: ≥5 μg.dL^-1 and ≤13.9 μg.dL^-1) and also tested the associations in order to verify if nail lead levels are affected by exposure intensity defined by blood metals concentrations. Radius distance and relative altitude of DCC to nearest MCS were associated with high NLL and NCL. Abnormal appearance of nails was associated with high NLL and low NCL. Lead and cadmium exposure magnitude had no significant impact on NLL. NLL should only be used for initial screening, and when financial resources are scarce, especially in areas located near contaminated sites. Preschool children were co-exposed to both lead and cadmium, reinforcing the need for broader studies evaluating exposure to environmental pollutants for more than one chemical element.

Translating Neurobehavioral Toxicity Across Species From Zebrafish to Rats to Humans: Implications for Risk Assessment

There is a spectrum of approaches to neurotoxicological science from high-throughput in vitro cell-based assays, through a variety of experimental animal models to human epidemiological and clinical studies. Each level of analysis has its own advantages and limitations. Experimental animal models give essential information for neurobehavioral toxicology, providing cause-and-effect information regarding risks of neurobehavioral dysfunction caused by toxicant exposure. Human epidemiological and clinical studies give the closest information to characterizing human risk, but without randomized treatment of subjects to different toxicant doses can only give information about association between toxicant exposure and neurobehavioral impairment. In vitro methods give much needed high throughput for many chemicals and mixtures but cannot provide information about toxicant impacts on behavioral function. Crucial to the utility of experimental animal model studies is cross-species translation. This is vital for both risk assessment and mechanistic determination. Interspecies extrapolation is important to characterize from experimental animal models to humans and between different experimental animal models. This article reviews the literature concerning extrapolation of neurobehavioral toxicology from established rat models to humans and from zebrafish a newer experimental model to rats. The functions covered include locomotor activity, emotion, and cognition and the neurotoxicants covered include pesticides, metals, drugs of abuse, flame retardants and polycyclic aromatic hydrocarbons. With more complete understanding of the strengths and limitations of interspecies translation, we can better use animal models to protect humans from neurobehavioral toxicity.

Descriptive Analysis of Heavy Metals Content of Beef From Eastern Uganda and Their Safety for Public Consumption

In this study, we initiated an effort to generate information about beef safety in Uganda. Our entry point was to assess by atomic absorption spectrophotometry the levels of essential elements copper (Cu), cobalt (Co), iron (Fe) and zinc (Zn), and non-essential elements lead (Pb), chromium (Cr), nickel (Ni), and cadmium (Cd) in 40 beef samples collected from within and around Soroti (Uganda). The information was used to evaluate the safety of consuming such beef against the World Health Organization (WHO) limits. The latter was accomplished by (i) estimating the daily intake (EDI) of each metal in the study area, (ii) modeling the non-cancer health risk using the target hazard quotient (THQ) and (iii) modeling the cancer risk using the incremental lifetime cancer risk (ILCR). The study finds that the mean concentrations (±95% CI) and EDI were in the order of Fe > Zn > Cr > Ni > Pb > Co > Cu > Cd. Cancer risk was found to be due to Ni > Cr > Cd > Pb and significantly higher in children than adults. The latter particularly demonstrates the importance of Ni poisoning in the study area. Overall, while essential elements in our beef samples were below WHO limits (hence no health risks), non-essential elements had high health and cancer risks due to higher levels of Cr and Ni.

NEUROTOXICITY OF METAL MIXTURES

Environmental exposures and/or alterations in the homeostasis of essential transition metals (ETM), such as Fe, Cu, Zn or Mn, are known to contribute to neurodegenerative diseases (ND), such as Alzheimer's Disease (AD) and Parkinson's Disease (PD). Aberrant ETM homeostasis leads to altered distributions, as significant amounts may accumulate in specific brain areas, while causing metal deficiency in others. The disruption of processes reliant on the interplay between these ETM, may lead to loss of metal balance and the ensuing neurotoxicity via shared mechanisms, such as the induction of oxidative stress (OS). Both ETM imbalance and OS may play a role, via complex positive loop processes, in primary neuropathological signatures of AD, such as the accumulation of amyloid plaques and neurofibrillary tangles (NTF), and in PD, α-Syn aggregation and loss of dopamine(DA)rgic neurons. The association between ETM imbalance and ND is rarely approached under the view that metals such as Fe, Cu, Zn and Mn, can act as dangerous endogenous neurotoxic mixtures when their control mechanisms became disrupted. In fact, their presence as mixtures implies intricacies, which should be kept in mind when developing therapies for complex disorders of metal dyshomeostasis, which commonly occur in ND.

Industrial alkali lignin-derived biochar as highly efficient and low-cost adsorption material for Pb(II) from aquatic environment

Developing a cost-effective and high-efficiency biochar is critical in various environmental applications. Lignin-based materials are natural and abundant adsorbents to heavy metals benefited from their special polyphenol structure and physicochemical properties. In this study, adsorption capacities to Pb(II) by alkali lignin (AL) and its biochar derivative (ALB) were comparatively discussed, and the latter exhibited superior adsorption performance, with a maximum adsorption capacity almost twice that of the former, and a much faster absorption rate. The q_m value of ALB was significantly superior to that of other reported biochar materials. Pb(II) was mainly adsorbed into ALB in three forms: mineral precipitation, ion exchange, and surface complexation, with complexation and mineral precipitation being the dominant mechanisms of adsorption. This study demonstrates that alkali-lignin derived biochar is a promising material for the remediation of polluted by Pb(II).

Enhanced Zinc Intake Protects against Oxidative Stress and Its Consequences in the Brain: A Study in an In Vivo Rat Model of Cadmium Exposure

We examined, in a rat model of moderate environmental human exposure to cadmium (Cd), whether the enhanced intake of zinc (Zn) may protect against Cd-caused destroying the oxidative/antioxidative balance and its consequences in the brain. The intoxication with Cd (5 mg/L, 6 months) weakened the enzymatic (superoxide dismutase, glutathione peroxidase, catalase) and non-enzymatic (total thiol groups, reduced glutathione) antioxidative barrier decreasing the total antioxidative status and increased the concentrations of pro-oxidants (hydrogen peroxide, myeloperoxidase) in this organ and its total oxidative status. These resulted in the development of oxidative stress and oxidative modifications of lipids and proteins. The co-administration of Zn (30 and 60 mg/L enhancing this element intake by 79% and 151%, respectively) importantly protected against Cd accumulation in the brain tissue and this xenobiotic-induced development of oxidative stress and oxidative damage to lipids and proteins. Moreover, this bioelement also prevented Cd-mediated oxidative stress evaluated in the serum. The favorable effect of Zn was caused by its independent action and interaction with Cd. Concluding, the enhancement of Zn intake under oral exposure to Cd may prevent the oxidative/antioxidative imbalance and oxidative stress in the brain and thus protect against injury of cellular macromolecules in the nervous system.

Hydrogen sulfide protects hippocampal CA1 neurons against lead mediated neuronal damage via reduction oxidative stress in male rats

H2S plays vital roles in modulation brain function. It is associated with antioxidant and anti-inflammatory properties. We assessed the H2S impact on spatial learning and memory deficit and cell death due to lead exposure, and probable mechanisms of action. The 36 male Wistar rats that (200-220 g), were in random assigned to 3 groups, control group (12 rats), lead acetate group (12 rats), and lead acetate +H2S groups (NaHS as a H2S donor; 5/6 mg/kg; 12 rats). Administration of lead to rats was performed through acute lead poisoning (25 mg/kg of lead acetate, IP through 3 days). Using male Morris water maze, their spatial learning and memory function were measured. We carried out ELISA method to calculate TNF-α and antioxidant enzymes level. Immunohistochemical staining was applied for evaluating the caspase-3 expression levels. Treatment with H2S improved learning and memory impairment in Pb-exposed rats (P<0.05). H2S treatment suppressed Pb-related apoptosis in the hippocampal CA1 subfield (P<0.01). Also, the TNF-α over-expression in the CA1 region of hippocampus due to lead exposure showed a significant reduction (P<0.05) after administrating H2S. Simultaneously, H2S treatment reduced the MDA levels, enhanced SOD, GSH level than the Pb-exposed group in hippocampus (P<0.05). H2S was able to significantly improve Pb-related spatial learning and memory deficit, and neuronal cell death in the CA1 region of hippocampus in the male rats at least partly by reducing oxidative stress and TNF.

Multi-omics analysis reveals that co-exposure to phthalates and metals disturbs urea cycle and choline metabolism

This study aimed to evaluate the response of HepaRG cells after co-exposure to phthalates and heavy metals, using a high-dimensional biology paradigm (HDB). Liver is the main metabolism site for the majority of xenobiotics. For this reason, the HepaRG cell line was used as an in vitro model, and cells were exposed to two characteristic mixtures of phthalates and heavy metals containing phthalates (DEHP, DiNP, BBzP) and metals (lead, methylmercury, total mercury) in a concentration-dependent manner. The applied chemical mixtures were selected as the most abundant pollutants in the REPRO_PL and PHIME cohorts, which were studied using the exposome-wide approach in the frame of the EU project HEALS. These studies investigated the environmental causation of neurodevelopmental disorders in neonates and across Europe. The INTEGRA computational platform was used for the calculation of the effective concentrations of the chemicals in the liver through extrapolation from human biomonitoring data and this dose (and a ten-times higher one) was applied to the hepatocyte model. Multi-omics analysis was performed to reveal the genes, proteins, and metabolites affected by the exposure to these chemical mixtures. By extension, we could detect the perturbed metabolic pathways. The generated data were analyzed using advanced bioinformatic tools following the HEALS connectivity paradigm for multi-omics pathway analysis. Co-mapped transcriptomics and proteomics data showed that co-exposure to phthalates and heavy metals leads to perturbations of the urea cycle due to differential expression levels of arginase-1 and -2, argininosuccinate synthase, carbamoyl-phosphate synthase, ornithine carbamoyltransferase, and argininosuccinate lyase. Joint pathway analysis of proteomics and metabolomics data revealed that the detected proteins and metabolites, choline phosphate cytidylyltransferase A, phospholipase D3, group XIIA secretory phospholipase A2, α-phosphatidylcholine, and the a 1,2-diacyl-sn-glycero-3-phosphocholine, are responsible for the homeostasis of the metabolic pathways phosphatidylcholine biosynthesis I, and phospholipases metabolism. The urea, phosphatidylcholine biosynthesis I and phospholipase metabolic pathways are of particular interest since they have been identified also in human samples from the REPRO_PL and PHIME cohorts using untargeted metabolomics analysis and have been associated with impaired psychomotor development in children at the age of two. In conclusion, this study provides the mechanistic evidence that co-exposure to phthalates and metals disturb biochemical processes related to mitochondrial respiration during critical developmental stages, which are clinically linked to neurodevelopmental perturbations.

Bi-enzymes treatments attenuate cognitive impairment associated with oxidative damage of heavy metals

Oxidative stress has been implicated in the pathogenesis of cognitive impairment. Lead (Pb) is a common environmental toxicant and plays a vital role in oxidative stress activation. In this study, a superoxide dismutase (SOD) and catalase (CAT) containing poly (lactic-co-glycolic acid) (PLGA) meso-particles (PLGA@SOD-CAT) were prepared to attenuate cognitive impairment via inhibiting oxidative stress in rats. It was prepared using a double emulsion (water/oil/water phase) technique to minimize the hazardous effects of Pb burden on cognitive impairment. The meso-particles antagonized the Pb-induced cognitive impairments. Behaviour, serum biochemical parameters and biomarkers of oxidative stress in rats were evaluated after they were subjected to intravenous injection with lead nitrate and PLGA@SOD-CAT. Moreover, the potential protective mechanism of PLGA@SOD-CAT was determined. Notably, PLGA@SOD-CAT appreciably agented memory impairment caused by lead nitrate and it could significantly inhibit Pb-induced oxidative stress in the blood. Furthermore, a remarkable reversion effect of cognitive impairments, including escape latency, crossing platform times and time per cent during the platform quadrant, after PLGA@SOD-CAT administration were noted. Therefore, these results suggested that the bi-enzymes platform was a superior product in eliminating Pb-induced cognitive impairments through reducing expression of Pb-associated oxidative stress, and it could potentially be applied in detoxifying heavy metals in blood circulation.

A comprehensive risk assessment of toxic elements in international brands of face foundation powders

Despite the COVID-19 pandemic and wearing masks in many countries, women are keen on elegance, beauty and the use of face foundations. Assessment of health risks associated with the regular use of face foundation by females is dynamic due to the emerging products. The most common international 14 brands of face foundation powders were collected and the concentrations of different elements (Ag, Al, As, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Mo, Na, P, Pb, Sb, Se, Sn, V and Zn) in each sample were determined. A combined approach merging the conventional and computational tools was used for investigating the risk of exposure to toxic elements. Monte Carlo simulations were applied to calculate risks associated with twenty elements. We attempted different probability distribution functions for concentrations because the actual distribution functions are not known, and the only data available are the mean value and standard deviation of concentrations obtained from experiment. Our results indicate that the total non-carcinogenic health risk through exposure to different elements (Hazardous Index, HI) does not strongly depend on the choice of the probability distribution function for the concentrations. We also show that taking into account probability distributions of other variables and parameters such as body weight, exposed skin area, skin adhesion, etc. does not significantly change the main result rather just slightly broadening the final Hazardous Index distribution function. We found that calculated HI is well below unity for all considered samples, i.e., the dermal exposure to toxic elements in the considered facial powders is negligible and the considered face foundation powders are quite safe to use.

The degree and position of phosphorylation determine the impact of toxic and trace metals on phosphoinositide containing model membranes

This work assessed effects of metal binding on membrane fluidity, liposome size, and lateral organization in biomimetic membranes composed of 1 mol% of selected phosphorylated phosphoinositides in each system. Representative examples of phosphoinositide phosphate, bisphosphate and triphosphate were investigated. These include phosphatidylinositol-(4,5)-bisphosphate, an important signaling lipid constituting a minor component in plasma membranes whereas phosphatidylinositol-(4,5)-bisphosphate clusters support the propagation of secondary messengers in numerous signaling pathways. The high negative charge of phosphoinositides facilitates electrostatic interactions with metals. Lipids are increasingly identified as toxicological targets for divalent metals, which potentially alter lipid packing and domain formation. Exposure to heavy metals, such as lead and cadmium or elevated levels of essential metals, like cobalt, nickel, and manganese, implicated with various toxic effects were investigated.  Phosphatidylinositol-(4)-phosphate and phosphatidylinositol-(3,4,5)-triphosphate containing membranes are rigidified by lead, cobalt, and manganese whilst cadmium and nickel enhanced fluidity of membranes containing phosphatidylinositol-(4,5)-bisphosphate. Only cobalt induced liposome aggregation. All metals enhanced lipid clustering in phosphatidylinositol-(3,4,5)-triphosphate systems, cobalt in phosphatidylinositol-(4,5)-bisphosphate systems, while all metals showed limited changes in lateral film organization in phosphatidylinositol-(4)-phosphate matrices. These observed changes are relevant from the biophysical perspective as interference with the spatiotemporal formation of intricate domains composed of important signaling lipids may contribute to metal toxicity.

Heavy metal associated health hazards: An interplay of oxidative stress and signal transduction

Heavy metal-induced cellular and organismal toxicity have become a major health concern in biomedical science. Indiscriminate use of heavy metals in different sectors, such as, industrial-, agricultural-, healthcare-, cosmetics-, and domestic-sectors has contaminated environment matrices and poses a severe health concern. Xenobiotics mediated effect is a ubiquitous cellular response. Oxidative stress is one such prime cellular response, which is the result of an imbalance in the redox system. Further, oxidative stress is associated with macromolecular damages and activation of several cell survival and cell death pathways. Epidemiological as well as laboratory data suggest that oxidative stress-induced cellular response following heavy metal exposure is linked with an increased risk of neoplasm, neurological disorders, diabetes, infertility, developmental disorders, renal failure, and cardiovascular disease. During the recent past, a relation among heavy metal exposure, oxidative stress, and signaling pathways have been explored to understand the heavy metal-induced toxicity. Heavy metal-induced oxidative stress and its connection with different signaling pathways are complicated; therefore, the systemic summary is essential. Herein, an effort has been made to decipher the interplay among heavy metals/metalloids (Arsenic, Chromium, Cadmium, and Lead) exposures, oxidative stress, and signal transduction, which are essential to mount the cellular and organismal response. The signaling pathways involved in this interplay include NF-κB, NRF2, JAK-STAT, JNK, FOXO, and HIF.

Naturally growing grimmiaceae family mosses as passive biomonitors of heavy metals pollution in urban-industrial atmospheres from the Bilbao Metropolitan area

In analytical chemistry, biomonitoring is known as the methodology, which consider the use of living organisms to monitor and assess the impact of different contaminants in a known area. This type of monitoring is a relatively inexpensive method and easy to implement, being a viable alternative to be developed in sites where there is no infrastructure/instruments for a convenctional air quality monitoring. These organisms, having the capability to monitor the pollution, are also known as passive biomonitors (PBs), since they are able to identify possible contamination sources without the need of any additional tool. In this work, a multianalytical methodology was applied to verify the usefulness of naturally growing Grimmia genus mosses as PBs of atmospheric heavy metals pollution. Once mosses were identified according to their morphology and taxonomy, thei ability to accumulate particulate matter (PM) was determined by SEM. EDS coupled to SEM also allowed to identify the main metallic particles deposited and finally, an acid digestion of the mosses and a subsequent ICP-MS study define more precisely the levels of metals accumulated on each collected moss. The study was focused on six sampling locations from the Bilbao Metropolitan area (Biscay, Basque Country, north of Spain). The experimental evidences obtained allowed to propose naturally growing Grimmia genus as PB of atmospheric heavy metals pollution and to identify the anthropogenic sources that contribute to the emission of the airborne particulate matter rich in metals, evaluating in this sense the atmospheric heavy metals pollution of the selected locations.

(Ascorb)ing Pb Neurotoxicity in the Developing Brain

Lead (Pb) neurotoxicity is a major concern, particularly in children. Developmental exposure to Pb can alter neurodevelopmental trajectory and has permanent neuropathological consequences, including an increased vulnerability to further stressors. Ascorbic acid is among most researched antioxidant nutrients and has a special role in maintaining redox homeostasis in physiological and physio-pathological brain states. Furthermore, because of its capacity to chelate metal ions, ascorbic acid may particularly serve as a potent therapeutic agent in Pb poisoning. The present review first discusses the major consequences of Pb exposure in children and then proceeds to present evidence from human and animal studies for ascorbic acid as an efficient ameliorative supplemental nutrient in Pb poisoning, with a particular focus on developmental Pb neurotoxicity. In doing so, it is hoped that there is a revitalization for further research on understanding the brain functions of this essential, safe, and readily available vitamin in physiological states, as well to justify and establish it as an effective neuroprotective and modulatory factor in the pathologies of the nervous system, including developmental neuropathologies.

Sources of individual variation in problem-solving performance in urban great tits (Parus major): Exploring effects of metal pollution, urban disturbance and personality

Despite growing research effort, we have a limited understanding of how urban disturbance factors affect cognitive traits, such as innovative problem-solving. We performed an initial assessment of how metal pollution and urbanization levels on territories are related to problem-solving performance in urban great tits (Parus major), by presenting an obstacle removal test at nest boxes in three urban nest box populations that are exposed to different levels of metal pollution. We predicted that problem-solving capacity might be reduced within the most polluted population due to pollution-related neurological impairments. On the other hand, we predicted that problem-solving might positively correlate with urban disturbance levels on territories, because some past research suggests that problem-solving promotes persistence in urbanized habitats. We also assessed relationships between exploratory personality type, behavioral patterns during tests, and problem-solving performance, and examined the repeatability and fitness correlates of problem-solving. We found no evidence that behavioral patterns or problem-solving performance were related to metal exposure or exploratory personality, or that problem-solving promotes reproductive success. However, birds on territories exposed to more urban disturbance, as quantified by proximity to paths and roads, were more likely to problem-solve. Moreover, an aggressive problem-solving approach negatively predicted problem-solving success, and behavioral patterns during tests and problem-solving success were repeatable. Thus, rather than indicating negative effects of pollution or urban disturbance on problem-solving performance, our study provides preliminary support for the hypothesis that urbanization favors innovative problem-solving, and suggests that problem-solving could be associated with a personality dimension independent of exploratory personality.

Burn to kill: Wood ash a silent killer in Africa

Aside the emissions, burning of wood in traditional cookstoves (TCs) also generates substantial amount of ash containing hazardous pollutants such as polycyclic aromatic hydrocarbons (PAHs) and toxic metals. But, their concentrations in the ash, particularly in Africa where over 70% of the population utilize TCs, remain unknown. Here, we determined concentrations of sixteen PAHs and eleven heavy metals in ashes from twelve different African TCs, comprising six three-stone fires (TSFs) and six built-in-place cookstoves (BIPCs), burning common African wood species under real world situation. For each TC, ash samples were collected for six consecutive days (Monday-Saturday), and a total of seventy-two daily samples were collected from January-June 2019. Ash yields were measured gravimetrically, and concentrations of the pollutants were determined following standard analytical protocols. The results were used alongside secondary data (annual fuelwood consumption, African fuelwood densities, population proportion using fuelwood and surface human population density) to estimate annual tonnage, exposure potential and risk to health in Africa, using Monte Carlo simulation technique. The ash yields from all TCs studied exceeded 1% on dry weight basis, indicating that ash is a major waste by-product of wood combustion in TCs. TSFs produced more ash (5.7 ± 0.7%) than BIPCs (3.4 ± 1.0%). Concentrations of As, Cd, Hg and Pb in ashes were significantly higher (α = 0.05) for TSFs than BIPCs. In contrast, concentrations of PAHs were higher in ashes from BIPCs than TSFs. Assuming ash consumption rates range from 250 to 500 mg/day for young children weighing 10 to 30 kg, the upper dose (μg/kg-day) of Pb (0.2-3.9) or Σ₁₆PAHs (0.02-0.34), for instance, surpasses the 0.3 μg/kg-day of Pb or PAH recognized as causing adverse effects in children, indicating a concern. The top five countries with the highest annual tonnage or exposure potential to toxic pollutants are Nigeria>Ethiopia>DR-Congo>Tanzania>Uganda, or Rwanda>Burundi>Uganda>Nigeria>Guinea-Bissau, respectively.

Epigenetic influence of environmentally neurotoxic metals

Continuous globalization and industrialization have ensured metals are an increasing aspect of daily life. Their usefulness in manufacturing has made them vital to national commerce, security and global economy. However, excess exposure to metals, particularly as a result of environmental contamination or occupational exposures, has been detrimental to overall health. Excess exposure to several metals is considered environmental risk in the aetiology of several neurological and neurodegenerative diseases. Metal-induced neurotoxicity has been a major health concern globally with intensive research to unravel the mechanisms associated with it. Recently, greater focus has been directed at epigenetics to better characterize the underlying mechanisms of metal-induced neurotoxicity. Epigenetic changes are those modifications on the DNA that can turn genes on or off without altering the DNA sequence. This review discusses how epigenetic changes such as DNA methylation, post translational histone modification and noncoding RNA-mediated gene silencing mediate the neurotoxic effects of several metals, focusing on manganese, arsenic, nickel, cadmium, lead, and mercury.

Emerging risk of environmental factors: insight mechanisms of Alzheimer's diseases

Neurodegenerative disorders are typically sporadic in nature in addition to usually influenced through an extensive range of environmental factors, lifestyle, and genetic elements. Latest observations have hypothesized that exposure of environmental factors may increase the prospective risk of Alzheimer's diseases (AD). However, the role of environmental factors as a possible dangerous issue has extended importance concerned in AD pathology, although actual etiology of the disorder is still not yet clear. Thus, the aim of this review is to highlight the possible correlation between environmental factors and AD, based on the present literature view. Environmental risk factors might play an important role in decelerating or accelerating AD progression. Among well-known environmental risk factors, prolonged exposure to several heavy metals, for example, aluminum, arsenic, cadmium, lead, and mercury; particulate air, and some pesticides as well as metal-containing nanoparticles have been participated to cause AD. These heavy metals have the capacity to enhance amyloid β (Aβ) peptide along with tau phosphorylation, initiating amyloid/senile plaques, as well as neurofibrillary tangle formation; therefore, neuronal cell death has been observed. Furthermore, particulate air, pesticides, and heavy metal exposure have been recommended to lead AD susceptibility and phenotypic diversity though epigenetic mechanisms. Therefore, this review deliberates recent findings detailing the mechanisms for a better understanding the relationship between AD and environmental risk factors along with their mechanisms of action on the brain functions.

Molecular mechanism of zinc neurotoxicity in Alzheimer's disease

Zinc (Zn) is an essential trace element for most organisms, including human beings. It plays a crucial role in several physiological processes such as catalytic reaction of enzymes, cellular growth, differentiation and metabolism, intracellular signaling, and modulation of nucleic acid structure. Zn containing above 50 metalloenzymes is responsible for proteins, receptors, and hormones synthesis and has a critical role in neurodevelopment. Zn also regulates excitatory and inhibitory neurotransmitters such as glutamate and GABA and is found in high concentration in the synaptic terminals of hippocampal mossy fibers that maintains cognitive function. It regulates LTP and LTD by regulation of AMPA and NMDA receptors. But an excess or deficiency of Zn becomes neurotoxic or cause impairment in growth or sexual maturation. There is mounting evidence that supports this idea of Zn becoming neurotoxic and being involved in the pathogenesis of AD. Zn dyshomeostasis in AD is an area that needs attention as moderate concentration of Zn is involved in the memory regulation via regulation of amyloid plaque. Dyshomeostasis of Zn is involved in the pathogenesis of diseases like AD, ALS, depression, PD, and schizophrenia.

Comparison of Plasma Concentrations of Mercury, Cadmium, and Arsenic among Women in 2005 and 2012 in a Historically Contaminated Area in China

Mercury (Hg), cadmium (Cd), and arsenic (As) concentrations in women were measured and compared to evaluate the effects of environmental heavy-metal pollution control on internal exposure levels. In 2005 and 2012, 200 and 182 women, respectively, were enrolled in the study. Demographic and diet information were collected using a questionnaire. Fasting venous blood samples were collected, and plasma concentrations of Hg, Cd, and As were measured using inductive coupled plasma mass spectrometry. The median concentrations (P₂₅-P₇₅) of Hg, Cd, and As decreased from 0.56 (0.46-0.75) ng/mL, 0.14 (0.09-0.21) ng/mL, and 0.83 (0.66-1.09) ng/mL in 2005 to 0.39 (0.19-0.66) ng/mL, 0.09 (0.05-0.13) ng/mL, and 0.48 (0.29-0.72) ng/mL in 2012, respectively. The difference in plasma metal concentrations between measurements in 2005 and 2012 remained statistically significant after we adjusted for confounders. The adjusted ORs were 0.31 (0.16-0.60), 0.24 (0.12-0.48), and 0.25 (0.13-0.50) for Hg, Cd, and As concentrations, respectively, in 2012, relative to those in 2005. The levels of Hg, Cd, and As were 30% to 40% lower in 2012 than in 2005, indicative of lower human internal exposure to these contaminants due to the implementation of environmental pollution control. Engagement with agriculture and high-frequency water product consumption were associated with high Hg levels, and a high frequency of consumption of fresh fruit and eggs was negatively associated with lower levels of Cd in plasma.

A Cross-Sectional Study of Dairy Cattle Metagenomes Reveals Increased Antimicrobial Resistance in Animals Farmed in a Heavy Metal Contaminated Environment

The use of heavy metals in economic and social development can create an accumulation of toxic waste in the environment. High concentrations of heavy metals can damage human and animal health, lead to the development of antibiotic resistance, and possibly change in bovine microbiota. It is important to investigate the influence of heavy metals in food systems to determine potential harmful effects environmental heavy metal contamination on human health. Because of a mining dam rupture, 43 million cubic meters of iron ore waste flowed into the Doce river basin surrounding Mariana City, Brazil, in 2015. Following this environmental disaster, we investigated the consequences of long-term exposure to contaminated drinking water on the microbiome and resistome of dairy cattle. We identified bacterial antimicrobial resistance (AMR) genes in the feces, rumen fluid, and nasopharynx of 16 dairy cattle 4 years after the environmental disaster. Cattle had been continuously exposed to heavy metal contaminated water until sample collection (A) and compared them to analogous samples from 16 dairy cattle in an unaffected farm, 356 km away (B). The microbiome and resistome of farm A and farm B differed in many aspects. The distribution of genes present in the cattle's nasopharynx, rumen, and feces conferring AMR was highly heterogeneous, and most genes were present in only a few samples. The relative abundance and prevalence (presence/absence) of AMR genes were higher in farm A than in farm B. Samples from farm A had a higher prevalence (presence) of genes conferring resistance to multiple drugs, metals, biocides, and multi-compound resistance. Fecal samples had a higher relative abundance of AMR genes, followed by rumen fluid samples, and the nasopharynx had the lowest relative abundance of AMR genes detected. Metagenome functional annotation suggested that selective pressures of heavy metal exposure potentially skewed pathway diversity toward fewer, more specialized functions. This is the first study that evaluates the consequences of a Brazilian environmental accident with mining ore dam failure in the microbiome of dairy cows. Our findings suggest that the long-term persistence of heavy metals in the environment may result in differences in the microbiota and enrichment of antimicrobial-resistant bacteria. Our results also suggest that AMR genes are most readily detected in fecal samples compared to rumen and nasopharyngeal samples which had relatively lower bacterial read counts. Since heavy metal contamination has an effect on the animal microbiome, environmental management is warranted to protect the food system from hazardous consequences.

Microplastics in the environment: Interactions with microbes and chemical contaminants

Microplastics (MPs) are contaminants of emerging concern that have gained considerable attention during the last few decades due to their adverse impact on living organisms and the environment. Recent studies have shown their ubiquitous presence in the environment including the atmosphere, soil, and water. Though several reviews have focused on the occurrence of microplastics in different habitats, little attention has been paid to their interaction with biological and chemical pollutants in the environment. This review therefore presents the state of knowledge on the interaction of MPs with chemicals and microbes in different environments. The distribution of MPs, the association of toxic chemicals with MPs, microbial association with MPs and the microbial-induced fate of MPs in the environment are discussed. The biodegradation and bioaccumulation of MPs by and in microbes and its potential impact on the food chain are also reviewed. The mechanisms driving these interactions and how these, in turn, affect living organisms however are not yet fully understood and require further attention.

Heavy metal and pesticide levels in dairy products: Evaluation of human health risk

Cattle milk's health benefits can be compromised by the presence of contaminants. The levels of cadmium, copper, lead and zinc, and residues of dichlorodiphenyldichloroethylene (DDE), dichlorodiphenyldichloroethane (DDD), dichlorodiphenyltrichloroethane (DDT) were determined in soil, milk and cheese samples collected from cow farms from 3 Romanian areas with industrial and agriculture tradition. A new methodology was applied for the determination of the corrected estimated daily intake (cEDI) corresponding to the aggregate dietary exposure. For the risk assessment, we calculated the source hazard quotient (HQs) for each contaminant and the adversity specific hazard index (HIA). Cadmium, copper, lead and zinc, and the sum of DDT levels in soil samples were below maximum residue levels (MRLs). The MRLs of lead and DDD were exceeded in milk and cheese samples from all the 3 areas. The MRLs of copper and zinc were exceeded in cheese samples from area 2 and 3. HQs >10 for lead indicates increased risk, while HQ > 1 for copper and sum of DDT indicates moderate risk for both milk and cheese. By calculating the HI_A, we identified a moderate and increase risk for nephrotoxicity, hepatotoxicity, hematotoxicity, cardiotoxicity and reproduction toxicity after consumption of the dairy products from the 3 areas.

Redox and essential metal status in the brain of Wistar rats acutely exposed to a cadmium and lead mixture

Most Pb and Cd neurotoxicity studies investigate exposure to either of the toxic metals alone, while data on co-exposure are scarce. The aim of our study was to fill that gap by investigating acute combined effects of Pb and Cd on redox and essential metal status in the brain of Wistar rats. Animals were randomised in four groups of six to eight rats, which received 15 or 30 mg/kg of Cd, 150 mg/kg of Pb, or 150 mg/kg of Pb + 15 mg/kg of Cd by gavage. The fifth, control, group received distilled water only. Co-treatment with Pb and Cd induced significant increase in malondialdehyde (MDA) and thiobarbituric acid-reactive substances (TBARS) compared to control and groups receiving either metal alone. This is of special importance, as MDA presence in the brain has been implicated in many neurodegenerative disorders. The groups did not significantly differ in Zn, Cu, Mn, and Fe brain levels. Our findings highlight the importance of metal mixture studies. Neurotoxicity assessments of single chemicals do not provide a real insight into exposure to mixtures in real life. Further research should look into interactions between these metals to reveal complex molecular mechanisms of their neurotoxicity.

Urinary profiles of selected metals and arsenic and their exposure pathway analysis in four large floodplains of Pakistan

In context of fragile geological conditions and rapid urbanization, element exposure via dietary (food, water) and non-dietary (dust, soil) routes into human population at different land use settings is a major concern in the Indus floodplains (FPs) of Pakistan. In current study, several important trace elements including arsenic (As), chromium (Cr), manganese (Mn), cobalt (Co), cadmium (Cd), nickel (Ni), copper (Cu) and lead (Pb) were analyzed in the paired human urine, food, water and dust samples collected from main FPs of Pakistan. Daily intake estimation and regression analysis were used to evaluate the relationships between internal exposure, exposure routes of studied trace elements and different land use settings. High concentrations of urinary As, Cr, Cu, Mn, and Cd were detected in the general male population of the studied floodplains (FPs). Moreover, the levels (μg/L) of urinary As increased gradually from FP1 (12.8), FP2 (18), FP3 (61) to FP4 (71). Regression analysis showed that As contaminated water was correlated with elevated urinary As concentrations in FP3 and FP4, and water Cr and Mn was significantly associated with urinary Cr and Mn concentrations in FP2. Moreover, the associations of food Mn and urinary Mn were found in FP1. Over all, cumulative estimated daily intake (EDI) values from water, dust and food from all the flood plains showed that Mn had the highest values (6.6, 9.2, 14.4 μg/kg/day) followed by water As (1.98 μg/kg/day), dust Cu (1.5 μg/kg/day) and Pb (1.7 μg/kg/day). Studied floodplains were moderately to highly polluted in terms of studied trace elements (As, Cr, Cu, Mn, and Cd) contamination especially in FP3 and FP4. The results will contribute to improve the knowledge and information on current exposure of Pakistani male adults to the different contaminants.

Metal brain bioaccumulation and neurobehavioral effects on the wild rodent Liomys irroratus inhabiting mine tailing areas

Ecotoxicological studies are necessary in order to evaluate the effects of environmental exposure of chemicals on wild animals and their ecological consequences. Particularly, neurobehavioral effects of heavy metal elements on wild rodents have been scarcely investigated. In the present study, we analyzed the effect of metal bioaccumulation (Pb, As, Mg, Ni, and Zn) in the brain and in the liver on exploratory activity, learning, memory, and on some dopaminergic markers in the wild rodent Liomys irroratus living inside mine tailings, at Huautla, Morelos, Mexico. We found higher Pb concentration but lower Zn in striatum, nucleus accumbens, midbrain, and hippocampus in exposed animals in comparison to rodents from the reference site. Exposed rodents exhibited anxious behavior evaluated in the open field, while no alterations in learning were found. However, they displayed slight changes in the memory test in comparison to reference group. The neurochemical evaluation showed higher levels of dopamine and 5-hydroxyindolacetic acid in midbrain, while lower levels of metabolites dihydroxyphenyl acetic acid and homovanillic acid in striatum of exposed rodents. In addition, mRNA expression levels of dopaminergic D2 receptors in nucleus accumbens were lower in animals from the mining zone than in animals from the reference zone. This is the first study that shows that chronic environmental exposure to metals results in behavioral and neurochemical alterations in the wild rodent L. irroratus, a fact that may comprise the survival of the individuals resulting in long-term effects at the population level. Finally, we suggest the use of L. irroratus as a sentinel species for environmental biomonitoring of mining sites.

Analysis of search strategies for evaluating low-dose heavy metal mixture induced cognitive deficits in rats: An early sensitive toxicological approach

Heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg) are representative neurotoxicological contaminants that can evoke cognitive dysfunctions. Low levels of these contaminants can be detected simultaneously in the human blood. In our previous study, behavioral performances were markedly impaired by exposure to these heavy metal mixtures (MM) at low levels. However, the aspects of cognitive functions involved are not well understood. Here, we further analyzed search strategies using a new algorithm named Morris water maze-unbiased strategy classification (MUST-C). Rat pups were co-exposed to low doses of Pb, Cd, and Hg during the embryonic and lactation stage. MM exposure at low doses, similar to those found in the general population, impaired search strategies even though their latency and path length were not affected in the Morris water maze task. MM-exposed rats preferred to use more directionless repetition strategies and less target orientation strategies than did vehicle-exposed animals in a dose-dependent manner. In addition, thionine staining and electron microscopy further revealed that MM exposure induced dose-dependent search strategy related place cell injures in the hippocampal CA1 and CA3 regions. These results demonstrate that the use of suboptimal search strategies underlies the early cognitive deficits in rats exposed to low doses of MM. The current study determined that search strategy analysis might be a novel sensitive assessment method for evaluating in the neurobehavioral toxicity.

Chemical mixtures and neurobehavior: a review of epidemiologic findings and future directions

Background Epidemiological studies have historically focused on single toxicants, or toxic chemicals, and neurodevelopment, even though the interactions of chemicals and nutrients may result in additive, synergistic, antagonistic, or potentiating effects on neurological endpoints. Investigating the impact of environmentally-relevant chemical mixtures, including heavy metals and endocrine disrupting chemicals (EDCs), is more reflective of human exposures and may result in more refined environmental policies to protect the public. Objective In this review, we provide a summary of epidemiological studies that have analyzed chemical mixtures of heavy metals and EDCs and neurobehavior utilizing multi-chemical models, including frequentist and Bayesian methods. Content Studies investigating chemicals and neurobehavior have the opportunity to not only examine the impact of chemical mixtures, but they can also identify chemicals from a mixture that may play a key role in neurotoxicity, investigate interactive effects, estimate non-linear dose response, and identify potential windows of susceptibility. The examination of neurobehavioral domains is particularly challenging given that traits emerge and change over time and subclinical nuances of neurobehavior are often unrecognized. To date, only a handful of epidemiological studies examining neurodevelopment have utilized multi-pollutant models in the investigation of heavy metals and EDCs. However, these studies were successful in identifying contaminants of importance from the exposure mixtures. Summary and Outlook Investigators are encouraged to broaden their focus to include more environmentally relevant mixtures of chemicals using advanced statistical approaches, particularly to aid in identifying potential mechanisms underlying associations.

Acid mine drainage (AMD) treatment by neutralization: Evaluation of physical-chemical performance and ecotoxicological effects on zebrafish (Danio rerio) development

Acid mine drainage (AMD) represents a major problem in the mining industry worldwide due to the risk of water and soil pollution. Its active treatment involves the addition of alkaline reagents such as NaOH or Ca(OH)₂ to increase the pH and precipitate the dissolved metals, although substantial amounts of dissolved ions might persists. Under a remediation approach, the aim of this work was to assess the chemical and physical characteristics of treated effluent and to evaluate its ecotoxicological effects on zebrafish (Danio rerio) embryonic and larval stages, through developmental, functional, morphological, and behavioral end-points. The studied AMD sample, highly associated with pyrite, presented high sulfate and dissolved metal ions content and was submitted to the following treatment conditions: NaOH - pH 7.0 and 8.7, and Ca(OH)₂ - pH 7.0 and 8.7. All neutralizing treatments resulted in a satisfactory reduction of the metals concentration, with best results achieved using Ca(OH)₂ at pH 8.7; although Mn and As still remained above or very near the discharge maximum limits according to Brazilian legislation. Therefore, an additional step was employed to Mn and As adsorption by algal biomass. Regarding in-vivo toxicological assays, no significant lethality was recorded in all treated AMD groups, although adverse effects were observed in all endpoints analyzed. Ca(OH)₂ groups performed closer to control than NaOH-treated groups. The additional polishing stage treatment with the algae Scenesmus sp. allowed tenuous improvements in terms of removal of residual amounts of As and Mn but not in the toxicological characteristics of treated AMD.

A Meta-Analysis of Stressors from the Total Environment Associated with Children's General Cognitive Ability

General cognitive ability, often referred to as ‘general intelligence’, comprises a variety of correlated abilities. Childhood general cognitive ability is a well-studied area of research and can be used to predict social outcomes and perceived success. Early life stage (e.g., prenatal, postnatal, toddler) exposures to stressors (i.e., chemical and non-chemical stressors from the total (built, natural, social) environment) can impact the development of childhood cognitive ability. Building from our systematic scoping review (Ruiz et al., 2016), we conducted a meta-analysis to evaluate more than 100 stressors related to cognitive development. Our meta-analysis identified 23 stressors with a significant increase in their likelihood to influence childhood cognitive ability by 10% or more, and 80 stressors were observed to have a statistically significant effect on cognitive ability. Stressors most impactful to cognition during the prenatal period were related to maternal health and the mother’s ability to access information relevant to a healthy pregnancy (e.g., diet, lifestyle). Stressors most impactful to cognition during the early childhood period were dietary nutrients (infancy), quality of social interaction (toddler), and exposure to toxic substances (throughout early childhood). In conducting this analysis, we examined the relative impact of real-world exposures on cognitive development to attempt to understand the inter-relationships between exposures to both chemical and non-chemical stressors and early developmental life stages. Our findings suggest that the stressors observed to be the most influential to childhood cognitive ability are not permanent and can be broadly categorized as activities/behaviors which can be modified to improve childhood cognition. This meta-analysis supports the idea that there are complex relationships between a child’s total environment and early cognitive development.

One-step electrochemical sensor based on an integrated probe toward sub-ppt level Pb2+ detection by fast scan voltammetry

Herein, a one-step electrochemical sensor for selective and sensitive detection of lead ion Pb²⁺ was developed based on an integrated probe meso-tetra(4-carboxyphenyl) porphine (TCPP)-multi-walled carbon nanotubes (MWCNTs)@Fe₃O₄, which is TCPP-modified magnetic multi-walled carbon nanotubes. In the integrated probe, TCPP is a porphyrin with a specific cavity structure which could selectively chelate with Pb²⁺, MWCNTs with good electric conductivity provide a place to load TCPP and form a specific adsorption state of Pb²⁺ on the electrode surface, and Fe₃O₄ enables the rapid separation and one-step fabrication of the electrochemical sensor. Based on it, the sample pre-enrichment, separation and determination can be integrated, making the whole process very fast and simple. In addition, fast scan voltammetry (FSV) with a scan rate up to 200 V/s could be used to improve the detection sensitivity greatly, benefitting from the specific adsorption state formed. Under the optimal conditions obtained through orthogonal experiments including adsorption time, integrated probe dosage and solution pH, there was a good linear relationship between the peak current and Pb²⁺ concentration ranging from 2.0 × 10^-4 μg L^-1 to 2.0 × 10^-3 μg L^-1, with the limit of detection (LOD) being 6.7 × 10^-5 μg L^-1 (S/N = 3) i.e. 0.067 ppt. Analysis of actual water samples was successful. Therefore, being simple, fast, selective and sensitive, the one-step electrochemical sensor proposed has a good potential in practical applications.

Human Risk from Exposure to Heavy Metals and Arsenic in Water from Rivers with Mining Influence in the Central Andes of Peru

Water pollution by heavy metals is one of the leading environmental concerns as a result of intense anthropogenic pressure on the aquatic environment. This constitutes a significant limitation to the human right of access to drinking water. In this context, the risk to humans from exposure to heavy metals and arsenic in water from rivers subject to mining influence in the Central Andes of Peru was assessed. Water samples were collected from seven rivers at 63 sampling sites, and concentrations of Cu, Fe, Pb, Zn, and As were determined using flame atomic absorption spectrophotometry. Cluster analysis was used to group 21 sampling sites into four groups with similar chemical characteristics, and principal component analysis was used to simplify the complex relationship between the toxic elements by generating two main components with a total percentage of variation of 86%. Fe, Zn, and As had higher percentages of contribution in the Mantaro, Cunas, and Chia rivers. The hazard quotient was highest for children and adults. The hazard index for ingestion of all the studied heavy metals and As was higher than the threshold value (HIing > 1). HIing in 43% of the rivers indicated that the adult population is at risk of non-carcinogenic effects, and HIing in 14% of the rivers revealed a very high health risk. The risk of cancer by ingestion for children varied from medium to high risk and for adults from low to high risk.

Integrated probabilistic risk assessment in sites contaminated with arsenic and lead by long-term mining liabilities in San Luis Potosi, Mexico

Mining environmental liabilities (MEL) in San Luis Potosi are the result of more than 450 years of mining activity, which has contaminated the soil mainly with arsenic (As) and lead (Pb) in several areas. Risk assessments are used to estimate the possibility of the occurrence of adverse effects on human health or on ecological receptors; and the most accessible way of performing them is through probabilistic estimates such as the Latin Hypercube Sampling (LHS) model. Therefore, the aim of this study was to carry out an Integrated Probabilistic Environmental Risk Assessment (IPERA) for the estimation of health risks in infants and rodents. The mean concentrations of As and Pb in soil were significantly higher (p<0.05) in all contaminated sites than in their respective reference sites. Villa de la Paz was the site with the highest mean concentration of As (1374 mg/kg), while Charcas was the one with the highest level of Pb (12,929 mg/kg). The Hazard Quotient (HQ) was calculated and Villa de la Paz had the highest values of As in both rodents (11.994) and children (39.32), and Charcas showed the highest values of Pb in both (24.971 and 31.668 for rodents and children respectively). The cumulative hazard Index (HI) reveals there is a very significant health risk due to As and Pb exposure for both rodents and children in contaminated areas of these mining communities.

Consumption of Raw Herbal Medicines Is Associated with Major Public Health Risks amongst Ugandans

Background

Community consumption of herbal plants in developing countries is a common practice, however, scarcity of information on their physiochemical composition is a major public health concern. In Uganda, Vernonia amygdalina is of interest in rural communities due to its therapeutical action on both bacterial and protozoal parasites, however no studies have been conducted to assess the heavy metal concentrations in traditional plants used in alternative medicine. The aim of the study was to establish concentrations of heavy metals in Vernonia amygdalina, model the estimated daily intake (EDI), and assess both the non-cancer-related health risk using the target hazard quotient (THQ), and the risk related to cancer through the incremental lifetime cancer risk (ILCR) for the Ugandan population.

Methods

Leaves of Vernonia amygdalina were collected from 20 georeferenced villages and processed into powder in the laboratory using standard methods. These were then analyzed in the laboratory using an atomic absorption spectrometer for lead (Pb), chromium (Cr), copper (Cu), zinc (Zn), cobalt (Co), iron (Fe), cadmium (Cd), and nickel (Ni). Concentrations were compared against the World Health Organization (WHO) limits. The EDI, THQ, and ILCR were modelled and significance was measured at 95% confidence.

Results

The study showed that mean ± SEM concentrations of heavy metals were highest in the order of Cr, 121.8 ± 4.291 ppm > Ni, 84.09 ± 2.725 ppm > Zn, 53.87 ± 2.277 ppm > Pb, 40.61 ± 3.891 ppm > Cu, 28.75 ± 2.202 ppm > Fe, 14.15 ± 0.7271 ppm > Co, 7.923 ± 0.7674 ppm > Cd, 0.1163 ± 0.005714 ppm. Concentrations of Pb, Cr, Zn, Co, and Ni were significantly higher than the WHO limits. The EDI was significantly higher in children than in adults, demonstrating an increased risk of toxicity in children. The THQ and ILCR were over 1000 times higher in all Ugandans, demonstrating the undesirable health risks following oral consumption of Vernonia amygdalina due to very high Cr and Ni toxicities, respectively.

Conclusion

Consumption of raw Vernonia amygdalina was associated with a high carcinogenic risk, demonstrating a need to enact policies to promote physiochemical screening of herbal medicines used in developing countries against toxic compounds.

Prenatal exposure to mixture of heavy metals, pesticides and phenols and IQ in children at 7 years of age: The SMBCS study

OBJECTIVE

Prenatal exposure to heavy metals, pesticides and phenols has been suggested to interfere with neurodevelopment, but the neurotoxicity of their mixtures is still unclear. We aimed to elucidate the associations of maternal urinary concentrations of selected chemical mixtures with intelligence quotient (IQ) in children.

METHODS

Maternal urinary concentrations of selected heavy metals, pesticide metabolites, and phenols were quantified in pregnant women who participated in the Sheyang Mini Birth Cohort Study (SMBCS) from June 2009 to January 2010. At age 7 years, child's IQ score was assessed using the Chinese version of Wechsler Intelligence Scale for Children (C-WISC) by trained pediatricians. Generalized linear regression models (GLM), Bayesian kernel machine regression (BKMR) models and elastic net regression (ENR) models were used to assess the associations of urinary concentrations individual chemicals and their mixtures with IQ scores of the 7-year-old children.

RESULTS

Of 326 mother-child pairs, single-chemical models indicated that prenatal urinary concentrations of lead (Pb) and bisphenol A (BPA) were significantly negatively associated with full intelligence quotient (FIQ) among children aged 7 years [β = -2.31, 95% confidence interval (CI): -4.13, -0.48; p = 0.013, sex interaction p-value = 0.076; β = -1.18, 95% CI: -2.21, -0.15; p = 0.025; sex interaction p-value = 0.296, for Pb and BPA, respectively]. Stratified analysis by sex indicated that the associations were only statistically significant in boys. In multi-chemical BKMR and ENR models, statistically significant inverse association was found between prenatal urinary Pb level and boy's FIQ scores at 7 years. Furthermore, BKMR analysis indicated that the overall mixture was associated with decreases in boy's IQ when all the chemicals' concentrations were at their 75th percentiles or higher, compared to at their 50th percentiles. ENR models revealed that maternal urinary Pb levels were statistically significantly associated with lower FIQ scores (β = -2.20, 95% CI: -4.20, -0.20; p = 0.031).

CONCLUSIONS

Prenatal exposure to selected chemical mixtures may affect intellectual performance at 7 years of age, particularly in boys. Pb and BPA were suspected as primary chemicals associated with child neurodevelopment.

Data on the concentration of heavy metals and metalloids in lotic water of the Mantaro river watershed and human risk assessment, Peru

This article contains data on the concentration of heavy metals and metalloids in the water of seven rivers in the Mantaro river watershed in the central Andes of Peru, collected during the autumn of 2019. The concentrations of Cu, Fe, Pb, Zn and As were determined by flame atomic absorption spectrophotometry to assess human risk. The concentration of heavy metals and arsenic varied according to the sector of the rivers evaluated. The cluster analysis identified four different groups among the observation sectors. The risk assessment for humans was conducted on the basis of exposure doses to heavy metals and arsenic in water by ingestion and dermal pathways, using standard methods established by USEPA. These data can be reused as a basis for estimating the cancer risk or as a comparison group for future risk studies. They can also be useful to public health policy makers when proposing surveillance and control programmes using remedial technologies.

Renal bioaccumulation of trace elements in urban and rural Sri Lankan populations: A preliminary study based on post mortem tissue analysis

INTRODUCTION

Environmental pollution, especially by toxic trace elements, is a global health concern. Heavy metals such as Cadmium (Cd), Arsenic (As) and Lead (Pb) are associated with numerous disorders and are considered by some as an aetiological factor for the Chronic Kidney Disease (CKDu1) epidemic in Sri Lanka. This study explores patterns of bioaccumulation of six trace elements in kidneys obtained during forensic autopsies from urban and rural regions in Sri Lanka.

METHODS

Kidney samples obtained from one urban district (n = 13) and three rural districts (n = 18) were lyophilized, microwave digested and profiled by ICP-MS techniques.

RESULTS AND DISCUSSION

The mean age of the sampled population was 47.9 ± 11.3 yrs. Median (IQR) for Cd, As, Pb, Cr, Zn and Se were, 14.67(8.04-22.47) μg/g, 0.44(0.29-0.56) μg/g, 0.11(0.07-0.30) μg/g, 0.15(0.1096-0.3274), 25.55(17.24-39.35) μg/g and 0.52(0.37-0.84) μg/g, respectively. Cd, Zn and Se levels were significantly higher (p < 0.05) among the urban samples compared to that of the rural group. Zn and Se levels were higher among younger age groups. As, Pb and Cr did not show any significant differences between the two cohorts nor any correlations with age.

CONCLUSION

This population-specific baseline study provides an insight into the differences in exposure to toxic trace elements and essential elements between urban and rural populations. Residents in CKDu affected rural districts did not appear to be at risk of toxic heavy metal exposure, however their renal bioaccumulation of nephroprotective essential elements was lower than urban residents.

Concentrations of toxic metals and essential trace elements vary among individual neurons in the human locus ceruleus

Objective

Damage to locus ceruleus neurons could play a part in the pathogenesis of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis because of impairment of the blood-brain barrier and enhanced neuroinflammation. The locus ceruleus has connections throughout the brain and spinal cord, so the characteristic widespread multifocal pathology in these disorders could be due to damage to different subsets of locus ceruleus neurons. Previous studies have shown that only certain locus ceruleus neurons accumulate the neurotoxic metal mercury. To find out if concentrations of other toxic metals or of essential trace elements also vary between individual locus ceruleus neurons, we used synchrotron X-ray fluorescence microscopy on frozen sections of locus ceruleus neurons taken from people with multiple sclerosis, in whom the locus ceruleus is structurally intact.

Materials and methods

Paraffin embedded sections containing the locus ceruleus from seven people with multiple sclerosis were stained with autometallography that demonstrates accumulations of mercury, silver and bismuth. These were compared to maps of multiple elements obtained from frozen sections of locus ceruleus neurons from the same people using X-ray fluorescence microscopy. Neurons in the anterior pons from three of these donors were used as internal controls.

Results

Autometallography staining was observed in scattered locus ceruleus neurons from three of the seven donors. X-ray fluorescence microscopy showed variations among individual locus ceruleus neurons in levels of mercury, selenium, iron, copper, lead, bromine, and rubidium. Variations between donors of locus ceruleus neuronal average levels of mercury, iron, copper, and bromine were also detected. Anterior pons neurons contained no mercury, had varied levels of iron, and had lower copper levels than locus ceruleus neurons.

Conclusions

Individual human locus ceruleus neurons contain varying levels of toxic metals and essential trace elements. In contrast, most toxic metals are absent or at low levels in nearby anterior pons neurons. The locus ceruleus plays a role in numerous central nervous system functions, including maintaining the blood-brain-barrier and limiting neuroinflammation. Toxic metals, or alterations in essential trace metals within individual locus ceruleus neurons, could be one factor determining the non-random destruction of locus ceruleus neurons in normal aging and neurodegenerative diseases, and subsequently the sites of the widespread multifocal central nervous system pathology in these disorders.

Surface Modification of Magnetic Nanoparticles by Carbon-Coating Can Increase Its Biosafety: Evidences from Biochemical and Neurobehavioral Tests in Zebrafish

Recently, magnetic nanoparticles (MNPs) have gained much attention in the field of biomedical engineering for therapeutic as well as diagnostic purposes. Carbon magnetic nanoparticles (C-MNPs) are a class of MNPs categorized as organic nanoparticles. C-MNPs have been under considerable interest in studying in various applications such as magnetic resonance imaging, photothermal therapy, and intracellular transportof drugs. Research work is still largely in progress for testing the efficacy of C-MNPs on the theranostics platform in cellular studies and animal models. In this study, we evaluated the neurobehavioral toxicity parameters on the adult zebrafish (Danio rerio) at either low (1 ppm) or high (10 ppm) concentration level of C-MNPs over a period of two weeks by waterborne exposure. The physical properties of the synthesized C-MNPs were characterized by transmission electron microscopy, Raman, and XRD spectrum characterization. Multiple behavior tests for the novel tank, mirror biting, predator avoidance, conspecific social interaction, shoaling, and analysis of biochemical markers were also conducted to elucidate the corresponding mechanism. Our data demonstrate the waterborne exposure of C-MNPs is less toxic than the uncoated MNPs since neither low nor high concentration C-MNPs elicit toxicity response in behavioral and biochemical tests in adult zebrafish. The approach combining biochemical and neurobehavioral approaches would be helpful for understanding C-MNPs association affecting the bioavailability, biosafety, interaction, and uptake of these C-MNPs in the living organism.

Cadmium sulfide-induced toxicity in the cortex and cerebellum: In vitro and in vivo studies

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CdS NPs were synthesized using living organisms Viridibacillus arenosi K64.

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Morphology and size of NP were evaluated by XRD and SEM.

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In vitro studies revealed that CdS toxicity in cerebellum neuron is concentration dependent.

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In vivo study showed that CdS easily crosses blood brain barrier.

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CdS in high doses induces toxicity in both neuron and purkinje cells in rats.

Living organisms have an innate ability to regulate the synthesis of inorganic materials, such as bones and teeth in humans. Cadmium sulfide (CdS) can be utilized as a quantum dot that functions as a unique light-emitting semiconductor nanocrystal. The increased use in CdS has led to an increased inhalation and ingestion rate of CdS by humans which requires a broader appreciation for the acute and chronic toxicity of CdS. We investigated the toxic effects of CdS on cerebellar cell cultures and rat brain. We employed a ‘green synthesis’ biosynthesis process to obtain biocompatible material that can be used in living organisms, such as Viridibacillus arenosi K64. Nanocrystal formation was initiated by adding CdCl₂ (1 mM) to the cell cultures. Our in vitro results established that increased concentrations of CdS (0.1 μg/mL) lead to decreased cell viability as assessed using 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT), total antioxidant capacity (TAC), and total oxidant status (TOS). The in vivo studies showed that exposure to CdS (1 mg/kg) glial fibrillary acidic protein (GFAP) and 8-hydroxy-2' -deoxyguanosine (8-OHdG) were increased. Collectively, we describe a model system that addresses the process from the synthesis to the neurotoxicity assessment for CdS both in vitro and in vivo. These data will be beneficial in establishing a more comprehensive pathway for the understanding of quantum dot-induced neurotoxicity.

Arsenic and benzo[a]pyrene co-exposure acts synergistically in inducing cancer stem cell-like property and tumorigenesis by epigenetically down-regulating SOCS3 expression

Arsenic and benzo[a]pyrene (BaP) are among the most common environmental carcinogens causing lung cancer. Millions of people are exposed to arsenic through consuming arsenic-contaminated drinking water. High levels of BaP are found in well-done barbecued meat and other food in addition to cigarette smoke. Hence, arsenic and BaP co-exposure in humans is common. However, the combined health effect and the underlying mechanism of arsenic and BaP co-exposure have not been well-understood. In this study we investigate the combined tumorigenic effect of arsenic and BaP co-exposure and the mechanism using both cell culture and mouse models. It was found that arsenic (sodium arsenite, 1.0 µM) and BaP (2.5 µM) co-exposure for 30 weeks synergizes in inducing malignant transformation of immortalized non-tumorigenic human bronchial epithelial cells and cancer stem cell (CSC)-like property to enhance their tumorigenicity. In animal studies, A/J mice were exposed to arsenic in drinking water (sodium arsenite, 20 ppm) starting from gestation day 18. After birth, the dams continuously received arsenic water throughout lactation. At weaning (3 weeks of age), male offspring were exposed to either arsenic alone via drinking the same arsenic water or exposed to arsenic plus BaP. BaP was administered via oral gavage (3 µmol per mouse per week) once a week starting from 3 weeks of age for 8 weeks. All mice were euthanized 34-weeks after the first BaP exposure. It was found that mice in control and arsenic exposure alone group did not develop lung tumors. All mice in BaP exposure alone group developed lung adenomas. However, arsenic and BaP co-exposure synergized in increasing lung tumor multiplicity and tumor burden. Furthermore, 30% of mice in arsenic and BaP co-exposure group also developed lung adenocarcinomas. Mechanistic studies revealed that arsenic and BaP co-exposure does not produce more BPDE-DNA adducts than BaP exposure alone; but acts synergistically in activating aryl hydrocarbon receptor (AhR) to up-regulate the expression of a histone H3 lysine 9 methyltransferase SUV39H1 and increase the level of suppressive H3 lysine 9 dimethylation (H3K9me2), which down-regulates the expression of tumor suppressive SOCS3 leading to enhanced activation of Akt and Erk1/2 to promote cell transformation, CSC-like property and tumorigenesis. Together, these findings suggest that arsenic and BaP co-exposure synergizes in causing epigenetic dysregulation to enhance cell transformation, CSC-like property and tumorigenesis.

Neurotoxicity of e-cigarettes

It appears that electronic cigarettes (EC) are a less harmful alternative to conventional cigarette (CC) smoking, as they generate substantially lower levels of harmful carcinogens and other toxic compounds. Thus, switching from CC to EC may be beneficial for smokers. However, recent accounts of EC- or vaping-associated lung injury (EVALI) has raised concerns regarding their adverse health effects. Additionally, the increasing popularity of EC among vulnerable populations, such as adolescents and pregnant women, calls for further EC safety evaluation. In this state-of-the-art review, we provide an update on recent findings regarding the neurological effects induced by EC exposure. Moreover, we discuss possible neurotoxic effects of nicotine and numerous other chemicals which are inherent both to e-liquids and EC aerosols. We conclude that in recognizing pertinent issues associated with EC usage, both government and scientific researchers must address this public health issue with utmost urgency.

Genetic and Epigenetic Etiology Underlying Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a pervasive neurodevelopmental disorder characterized by difficulties in social interaction, language development delays, repeated body movements, and markedly deteriorated activities and interests. Environmental factors, such as viral infection, parental age, and zinc deficiency, can be plausible contributors to ASD susceptibility. As ASD is highly heritable, genetic risk factors involved in neurodevelopment, neural communication, and social interaction provide important clues in explaining the etiology of ASD. Accumulated evidence also shows an important role of epigenetic factors, such as DNA methylation, histone modification, and noncoding RNA, in ASD etiology. In this review, we compiled the research published to date and described the genetic and epigenetic epidemiology together with environmental risk factors underlying the etiology of the different phenotypes of ASD.

A systems toxicology approach to compare the heavy metal mixtures (Pb, As, MeHg) impact in neurodegenerative diseases

Conventional toxicological risk assessment methods mainly working on single chemicals that fail to adequately address the simultaneous exposure and their potential toxicity in humans. We herein investigated the toxic heavy metals lead (Pb), arsenic (As), and methylmercury (MeHg) and their binary mixtures role in neurodegenerative diseases. To characterize the toxicity of metal mixtures at the molecular level, we established a non-animal omics-based organ relevant cell model system. The obtained experimental data was refined by using the statistical and downstream functional analysis. The protein expression information substantiates the previous findings of single metal (Pb, As, and MeHg) induced alterations to mitochondrial dysfunction, oxidative stress, mRNA splicing, and ubiquitin system dysfunction relation to neurodegenerative diseases. The functional downstream analysis of single and binary mixtures protein data is presented in a comparative manner. The heavy metals mixtures' outcome showed significant differences in the protein expression compared to single metals that indicate metal mixtures exposure is more hazardous than single metal exposure. These results suggest that more comprehensive strategies are needed to improve the mixtures risk assessment in the future.

Meconium identifies high levels of metals in newborns from a mining community in the U.S

BACKGROUND

This pilot study was conducted to determine if we could identify intrauterine exposure to metals in meconium, as a measure of exposure for mother-child pairs living in proximity to a mining operation.

OBJECTIVES

We used meconium as a means to measure metal exposure in utero. We set out to quantify the exposure to selected metals that are currently being mined and also are found in the Superfund site in Butte, Montana, and to compare it to that of Columbia, South Carolina, US, where mining is not occurring.

METHODS

This cross-sectional study was conducted between May and November 2018. We received Institutional Review Board approval and we consented women following the birth of their newborns, and collected meconium within 24 h of birth, without any identifiers. Each laboratory used the same protocol for collection, transport, and storage; and the same laboratory protocol was used for the analysis of all samples. Samples were digested using standard acid/peroxide digestion methods and measured by inductively coupled plasma mass spectroscopy.

RESULTS

We collected meconium specimens from 17 infants in Columbia, South Carolina and 15 infants in Butte, Montana. The concentrations found in Columbia were in the low μg kg^-1 range (or less) and were similar to the low levels that have been identified in other studies of meconium. The magnitude of the differences in concentrations found in Butte compared to Columbia was 1792 times higher for Cu, 1650 times higher for Mn, and 1883 times higher for Zn.

CONCLUSION

Using meconium to measure exposure of newborns has implications for risk assessment in a mining-exposed population. This approach was inexpensive and thorough. The magnitude of the differences in the metal levels identified from the two study sites suggests there is an urgent need for further research to learn if there are health consequences to these highly exposed infants.

Corticosterone mediates telomere length in raptor chicks exposed to chemical mixture

Stressors experience early in life by animals may have carry over impacts on life-traits over the life cycle. Accelerated telomere attrition induced by stress during development and growth could play a role in such delayed effects. Among stressors, exposure to chemicals may modify telomere dynamic but, to date, the trends evidenced between exposure and telomere shortening remains inconsistent. Moreover, the role of corticosterone as a possible mediator of chemical impact on telomere is not yet clearly established. Here, we investigated in wild populations of Red kite whether nestling exposure to metals and pesticides was related to corticosterone concentrations in feathers and telomere length measured in 47 individuals. Lead and mercury concentrations in blood ranged from 2.3 to 59.0 µg L^-1 and to 1.4 to 115.7 µg L^-1, respectively, and were below the toxicity thresholds proposed for wildlife. Rodenticides were detected in 30% of the chicks. Corticosterone increased with mercury and lead in interaction, showing a synergistic effect of these 2 non-essential metals on this stress hormone. Telomere length was not linked to metals and/or rodenticide exposure while it was related negatively to corticosterone. The relationship between telomere and corticosterone was modulated by nestling's age, which suggests that the rate of telomere shortening is higher when corticosterone increases. Our findings propose an effect of low exposure of Red Kite nestlings to mercury and lead mixture to raise baseline corticosterone in feathers. The relationships established suggest the hypothesis that telomere attrition could be an indirect consequence of metal exposure mediated by corticosterone.