Mercury and selenium interactions in human blood in the Wanshan mercury mining area, China

Do high soil geochemical backgrounds of selenium and associated heavy metals affect human hepatic and renal health? Evidence from Enshi County, China

It is unclear whether the United States Environmental Protection Agency (US EPA) method can accurately assess heavy metal risks in high-Se areas. Herein, a black shale outcropping in Enshi County, China, was taken as the study area, and a carbonate outcropping in Lichuan County was the control area. Selenium and associated heavy metal concentrations in rock, soil, rice, human blood and urine samples and human sensitive hepatic and renal biomarkers were measured. The results showed that the contents of selenium, cadmium, molybdenum and copper in the study area were 3.68 ± 2.72 μg/g, 2.65 ± 1.42 μg/g, 16.3 ± 15.5 μg/g, and 57.3 ± 17.6 μg/g, respectively, in soil (n = 47) and 1.072 ± 0.924 μg/g, 0.252 ± 0.310 μg/g, 2.800 ± 2.167 μg/g, and 10.91 ± 27.42 μg/g, respectively, in rice (n = 47). The daily adult intake levels of selenium, cadmium and molybdenum from rice consumption in the study area (exposure group) exceed the recommended tolerance values in China. According to the US EPA method, these environmental media pose a significant risk to human health. However, in the exposure group (n = 111), the median levels of the sensitive hepatic biomarkers alanine aminotransferase (18 U/L), aspartate aminotransferase (28 U/L) and total bilirubin (10.9 μmol/L) and the sensitive renal biomarkers serum creatinine (70.1 μmol/L), urinary nitrogen (5.73 mmol/L) and uric acid (303.80 μmol/L) were within reference ranges and had values equivalent to those of the control group (P > 0.05). The elements tended to differentiate during migration from one medium to another. Due to the complex interaction between selenium and heavy metals, a survey of human health indicators is indispensable when the US EPA method is used to assess the heavy metal risks in high-Se areas. The recommended molybdenum tolerable intake in the U.S. (2000 μg/d) is reasonable based on a comparison.

Temporal changes of blood mercury concentrations in Chinese newborns and the general public from 1980s to 2020s

Mercury (Hg) is a global pollutant that threatens the environment and human health. As a major producer, emitter and consumer of Hg, China is currently taking different measures to curb mercury pollution in accordance with the requirements of the Minamata Convention on Mercury. Blood Hg can reflect the human body's recent exposure to Hg. This review summarized the temporal changes in blood Hg concentrations in newborns and the general public in China from 1980 s to 2020 s. It was shown that the blood Hg concentrations of newborns showed the downward trend, although it was not significant. The general public Hg concentrations showed a trend of first increase and then decrease trend. Most of the cord blood Hg and venous blood Hg concentrations in China were lower than the USEPA reference concentration of 5.8 µg/L. Since low-dose prenatal Hg exposure can affect fetal and neonatal development, continuous attention needs to be paid to reduce maternal and neonatal Hg exposure. The information provided in this review may lay a basis for the effectiveness evaluation on the implementation of Minamata Convention on Mercury.

Selenium Status: Its Interactions with Dietary Mercury Exposure and Implications in Human Health

Selenium is an essential trace element in humans and animals and its role in selenoprotein and enzyme antioxidant activity is well documented. Food is the principal source of selenium, and it is important that selenium status in the body is adequately maintained for physiological functions. There has been increasing attention on the role of selenium in mitigating the toxic effects of mercury exposure from dietary intake in humans. In contrast, mercury is a neurotoxin, and its continuous exposure can cause adverse health effects in humans. The interactions of selenium and mercury are multi-factorial and involve complex binding mechanisms between these elements at a molecular level. Further insights and understanding in this area may help to evaluate the health implications of dietary mercury exposure and selenium status. This review aims to summarise current information on the interplay of the interactions between selenium and mercury in the body and the protective effect of selenium on at-risk groups in a population who may experience long-term mercury exposure.

In utero exposure to methylmercury impairs cognitive function in adult offspring: Insights from proteomic modulation

Methylmercury (MeHg) is a hazardous substance that has unique neurodevelopmental toxic effects. However, its molecular alteration profile, sensitive response biomarkers, and mechanism of neuronal injury remain largely unknown. Here, the effects of intrauterine methylmercury chloride (low-, medium- and high-dose groups: 0.6 mg/kg/d, 1.2 mg/kg/d, 2.4 mg/ kg /d, respectively) exposure on learning and memory were assessed in offspring rats by behavioral tests, pathological analysis and hippocampal proteomic analysis. The results suggested that intrauterine MeHg exposure impairs spatial learning and memory and leads a significant reduction in the number and dispersion scattered arrangement in the hippocampus of offspring. Furthermore, in the tandem mass tag-based proteomics analysis, compared with the control group, a total of 74 differentially expressed proteins (DEPs) were found in the MeHg exposure groups; specifically, 32 down-regulated and 42 up-regulated proteins were identified. In addition, the pathways enrichment analysis indicated that these DEPs are implicated in several biological processes, such as synaptic plasticity and energy metabolism, as well as various molecular functional categories. Simultaneously, MeHg reduced the postsynaptic density, diminished the active zone, amplified the synaptic cleft and changed the synaptic interface of pyramidal cells. Western blot analysis further revealed that MeHg significantly reduced the levels of Forkhead box protein (FOXP2), Synaptophysin (SYP) and Postsynaptic density protein 95 (PSD-95), and down-regulated the N-methyl-D-aspartate receptor 1 (NMDAR1), N-methyl-D-aspartate receptor 2 A (NR2A) and N-methyl-D-aspartate receptor 2B (NR2B). In general, from a functional perspective, most overlapping proteins were related to NMDA receptor-mediated glutamatergic signaling, which is an excitotoxicity mechanism known to influence learning and memory. These discoveries contribute to our understanding of the relationship between MeHg and cognitive deficits and provide insight into the protein mediators of this relationship and possible prospective early biomarkers.

Stress response markers in the blood of São Tomé green sea turtles (Chelonia mydas) and their relation with accumulated metal levels

Metals are persistent worldwide being harmful for diverse organisms and having complex and combined effects with other contaminants in the environment. Sea turtles accumulate these contaminants being considered good bioindicator species for marine pollution. However, very little is known on how this is affecting these charismatic animals. São Tomé and Príncipe archipelago harbours important green sea turtle (Chelonia mydas) nesting and feeding grounds. The main goal of this study was to determine metal and metalloid accumulation in the blood of females C. mydas nesting in São Tomé Island, and evaluate the possible impacts of this contamination by addressing molecular stress responses. Gene expression analysis was performed in blood targeting genes involved in detoxification/sequestration and metal transport (mt, mtf and fer), and in antioxidant and oxidative stress responses (cat, sod, gr, tdx, txrd, selp and gclc). Micronuclei analysis in blood was also addressed as a biomarker of genotoxicity. Present results showed significant correlations between different gene expressions with the metals evaluated. The best GLM models and significant relationships were found for mt expression, for which 78% of the variability was attributed to metal levels (Al, Cu, Fe, Hg, Pb and Zn), followed by micronuclei count (65% - Cr, Cu, Fe, Hg, Mn and Zn), tdx expression (52% - Cd, Fe, Mn, Pb and Se), and cat expression (52% - As, Fe, Se and Cd x Hg). Overall, this study demonstrates that these green sea turtles are trying to adapt to the oxidative stress and damage produced by metals through the increased expression of antioxidants and other protectors, which raises concerns about the impacts on these endangered organisms' fitness. Furthermore, promising biomarker candidates associated to metal stress were identified in this species that may be used in future biomonitoring studies using C. mydas' blood, allowing for a temporal follow-up of the organisms.

Effects of Low-dose Mercury Exposure in Newborns on mRNA Expression Profiles

This study was designed to investigate the molecular mechanism of mercury (Hg) toxicity in the newborns by mRNA sequencing (mRNA-seq). A questionnaire survey, routine blood parameters of pregnant women, and umbilical cord blood (UCB) of newborns were collected. The median (25th percentile, 75th percentile) of total Hg (THg) concentrations in UCB of newborns was 3.63 (2.50, 6.19) µg/L. A total of 504 differentially expressed genes of mRNA were revealed between the case and control group, including 456 upregulated and 48 downregulated genes. The Gene Ontology (GO) analysis showed that differentially expressed genes were primarily involved in mitophagy, hemoglobin complex, and oxygen carrier activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the most differentially expressed genes were annotated in Huntington's disease, Parkinson's disease, and Alzheimer's disease. The qRT-PCR was used to validate the results of mRNA-seq. Low-dose Hg exposure could increase blood NE# and WBC in the pregnant women. This study provides scientific evidences on mechanism of Hg toxicity in newborns.

Levels, Spatial Distribution, and Impact Factors of Heavy Metals in the Hair of Metropolitan Residents in China and Human Health Implications

Chronic exposure to low levels of heavy metals threatens human health. However, few studies evaluated the health effects and spatial distributions of chronic exposure to heavy metals in metropolitan residents throughout mainland China using unified sampling methods and evaluation indicators at the national level. Here, the concentrations and spatial distributions of heavy metals (As, Cd, Cr, Sb, Pb, and Hg) in the hair of 1202 metropolitan residents from mainland China were analyzed, and differences in age and sex were evaluated. Most target metals exhibited higher concentrations in the hair of residents from South Central China. Generally, male hair had higher As and Se concentrations, whereas female hair had higher Cd and Pb levels (p < 0.05). A significant pairwise correlation existed between most metals in hair, especially Cd-Pb (r = 0.638, p < 0.05). The Se/heavy metal molar ratio is used as an indicator to assess the detoxification ability. The results demonstrated that protecting metropolitan residents in South Central China from heavy metals in their daily life is crucial, particularly for Hg, Pb, and Cr with Se/(Hg, Pb, or Cr) molar ratios < 1. This is the first study to comprehensively consider the antagonistic effects of Se and heavy metals using the molar ratio of Se/heavy metals to evaluate health implications and propose health management policies for metropolitan residents in China.

Prenatal exposure to legacy contaminants and visual acuity in Canadian infants: a maternal-infant research on environmental chemicals study (MIREC-ID)

BACKGROUND

Prenatal exposure to environmental contaminants can have deleterious effects on child development. While psychomotor, cognitive and behavioural outcomes have been investigated in relation to chronic exposure, the associations with visual functions remains unclear. The present study's aim was to assess the associations of prenatal exposure to legacy persistent organic pollutants and heavy metals with visual acuity in Canadian infants. The potential protective effects of selenium against mercury toxicity were also examined.

METHODS

Participants (mean corrected age = 6.6 months) were part of the Maternal-Infant Research on Environmental Chemicals (MIREC) study. Concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), lead and mercury were measured in maternal blood during pregnancy, as well as in the cord blood. The Teller acuity card test (TAC) (n = 429) and the visual evoked potentials in a sub-group (n = 63) were used to estimate behavioural and electrophysiological visual acuity, respectively. Multivariable linear regression models were used to investigate the relationship between exposure to each contaminant and visual acuity measures, while controlling for potential confounders. Breastmilk selenium, which was available for about half of the TAC and VEP samples, was also taken into account in the mercury models as exploratory analyses.

RESULTS

We observed no significant associations between exposure to any contaminants and TAC. Analyses revealed a negative trend (p values < 0.1) between cord blood lead and mercury and electrophysiological visual acuity, whereas PCB and PBDE showed no association. When adding breastmilk selenium concentration to the mercury models, this association became statistically significant for cord concentrations (β = - 3.41, 95% CI = - 5.96,-0.86), but also for blood levels at 1st and 3rd trimesters of pregnancy (β = - 3.29, 95% CI = - 5.69,-0.88). However, further regression models suggested that this change in estimates might not be due to adjustment for selenium, but instead to a change in the study sample.

CONCLUSIONS

Our results suggest that subtle, but detectable alterations of infant electrophysiological visual acuity can be identified in a population prenatally exposed to low mercury concentrations. Compared to behavioural visual acuity testing, electrophysiological assessment may more sensitive in detecting visual neurotoxicity in relation with prenatal exposure to mercury.

Maternal inorganic mercury exposure and renal effects in the Wanshan mercury mining area, southwest China

This study evaluated the relationship between urine mercury (UHg) concentrations and renal function (serum creatinine (SCr) and blood urea nitrogen (BUN)) in delivery women in the Wanshan mercury (Hg) mining area. Leishan County was selected as the control area. 165 and 65 maternal samples were collected from the Wanshan and Leishan area, respectively. The geometric means of UHg concentrations were 1.09 and 0.29 μg/L in Wanshan and Leishan subjects, respectively. Significant differences (p < 0.01) of UHg were observed between the two populations, indicating the potential risks of inorganic Hg exposure in the Wanshan population. The median (interquartile range) values of SCr were 69.1 (12.5) μmol/L and 46.0 (11.0) μmol/L for the Wanshan and Leishan populations, respectively, indicating significant differences (p < 0.01) between the two groups. However, no significant differences among BUN values for the two groups were observed. A significant positive correlation (r = 0.385, p < 0.001) was observed between UHg concentration and SCr in the study population. The odds ratio (OR) value of UHg in Wanshan area was 9.29 times higher than that in Leishan area (95% confidence interval (CI): 3.58-24.1). The OR value of SCr decrease in patients with low UHg was 0.32 times higher than that in patients with high UHg (95% CI: 0.19-0.55). The OR value of SCr decrease in the population with fish consumption was 0.71 times higher than that of the population without fish consumption (95% CI: 0.58-0.88). In conclusion, maternal IHg exposure caused impaired renal function and fish consumption may play a role in preventing Hg-induced nephrotoxicity.

Total mercury, chromium, nickel and other trace chemical element contents in soils at an old cinnabar mine site (Merník, Slovakia): anthropogenic versus natural sources of soil contamination

The aims of this study were to investigate the occurrence and distribution of total mercury (Hg) and other trace elements of environmental concern, such as arsenic (As), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), lead (Pb), zinc (Zn) and vanadium (V), in soils from the abandoned Merník cinnabar mine in eastern Slovakia. For this purpose, thirty soil samples from two depth intervals within the mine area (n = 60 soil samples) and additional sixteen soil samples from adjacent areas (n = 25 soil samples) were collected. Total Hg was measured by atomic absorption spectrometry, while As and other metals were analyzed using inductively coupled plasma atomic emission spectrometry. High mercury concentrations (> 100 mg/kg with a maximum of 951 mg/kg) were observed only in surface soils close to mine waste heaps and adits. Otherwise, Hg concentrations in the majority of surface soils were lower (0.14-19.7 mg/kg), however, higher than Hg in soils collected from sites outside the mine area (0.19-6.92 mg/kg) and even considerably higher than Hg in soils at sites not influenced by the Merník mine. Elevated Cr and Ni concentrations in soils regardless of their sampling sites (mean of 276 mg/kg and median of 132 mg/kg for Cr and 168 mg/kg and 81 mg/kg for Ni, respectively) were attributed to the lithology of the area; the soils are underlain by the sediments of the Central Carpathian Palaeogene, containing a detritus of ultrabasic rocks. As our geochemical data are compositional in nature, they were further treated by compositional data analysis (CoDA). Robust principal component analysis (RPCA) applied on centred (clr) log-ratio-transformed data and correlation analysis of compositional parts based on symmetric balances distinguished very well different sources of origin for the chemical elements. The following three element associations were identified: Hg association with the main source in mining/roasting, Cr-Ni association derived from bedrock and As-Cu-Mn-Pb-Zn-V association (natural background and minor sulphides/sulfosalts in mineralized rocks). The values of geoaccumulation index and enrichment factor suggested that concentrations of Hg in the soils were influenced by human industrial activities.

Species and correlations between selenium and mercury in fishpond ecosystems

The chemical species and contents of selenium and mercury in water, sediments, and crucian carps collected from three wild and three aquaculture fishponds in Tianjin, China, were determined, and the interaction between selenium and mercury in water was also investigated by the calorimetry method. The results revealed that the average contents of total selenium (TSe) and total mercury (THg) in each item of the wild areas were higher than in those of the aquaculture areas, and significant differences (95% confidence) were presented for THg both in the sediments and crucian carps. The molar ratios between TSe and THg in all investigated fishponds were far higher than 1, indicating good protective effects of selenium on mercury toxicity. Obviously, negative correlations (r > 0.9993) were found between TSe and THg in water. The antagonism of selenium on mercury in water was confirmed to mainly result from the reaction between selenate and Hg²⁺ to form an insoluble selenium-mercury oxygenated compound, by which the addition of selenate into the water of fishponds would reduce the environmental risk of mercury. PRACTITIONER POINTS: Se and Hg in different fishpond ecosystems were investigated and compared. Direct evidence was provided for the interaction between Se and Hg in water. The addition of Se(VI) into fishpond ecosystems would reduce the environmental risk of Hg.

Soil dissolved organic matter affects mercury immobilization by biogenic selenium nanoparticles

Molecular weight (MW) heterogeneity is a fundamental property of dissolved organic matter (DOM) in soil, which has been demonstrated to influence the binding behaviour between DOM and engineered nanoparticles. In the present study, DOM, extracted from black soil, was dialyzed into four fractions: above 10,000 Da, 3500-10,000 Da, 1000-3500 Da and 100-1000 Da. Homoaggregation and fluorescence quenching titration of selenium nanoparticles (SeNPs) was examined in the presence of the different DOM fractions, as well as the consequences for immobilization of elemental mercury. It was found that the intermediate MW fraction (3500-10,000 Da) rather than the high MW DOM fraction was likely to adsorb to SeNPs. Generally, low MW DOM was expected to adsorb initially due to faster diffusion and these compounds would be displaced by high MW DOM over longer time period. However, the electrostatic barrier imparted by adsorbed DOM limited such displacement, leading to preferential adsorption of the intermediate MW fraction over the high MW fraction. Adsorbed DOM fractions, especially that of intermediate MW, enhanced the stability of SeNPs which favoured immobilization of elemental mercury. These findings show that MW exerts an important impact on DOM binding with SeNPs which, in consequence, governs the fate of SeNPs and mercury bioremediation performance.

The Development Path of the Lighting Industry in Mainland China: Execution of Energy Conservation and Management on Mercury Emission

The development path of the lighting industry in mainland China was studied in this work. Lighting electricity accounts for about 12% of social electricity consumption in mainland China, while only approximately 15% of electricity is conversed into light when incandescent light bulbs are used. To reduce electrical energy consumption and mercury emission from coal burning in the lighting industry, China worked out a roadmap to replace incandescent light bulbs with energy-saving fluorescent lamps (FLs). However, FL products utilize mercury to give out light and release mercury in their production, consumption and disposal processes. Therefore, the challenges of the lighting industry that mainland China are facing are controlling mercury pollution through the environmentally-friendly producing of fluorescent lamps, effective collecting and treating of spent fluorescent lamps. It was proposed that to effectively reduce energy consumption and mercury pollution, a good way to do this is developing energy-saving and mercury-free light emitting diode lighting industry. The mainland China Government's strategies to develop lighting industry are worthy of consideration and emulation by other countries.