Low-level mercury in children: associations with sleep duration and cytokines TNF-α and IL-6

Exposure to a mixture of metal(loid)s and sleep quality in pregnant women during early pregnancy: A cross-sectional study

Biological characteristics of pregnant women during early pregnancy make them susceptible to both poor sleep quality and metal/metalloid exposure. However, the effects of metal(loid) exposure on sleep quality in pregnant women remain unknown and unexplored. We aimed to examine the relationship between exposure to a mixture of metal(loid)s and pregnant women's sleep quality during early pregnancy. We recruited 493 pregnant women in the first trimester from prenatal clinics in Jinan, Shandong Province, China, and collected their spot urine samples. All urine specimens were assessed for eight metal(loid)s: arsenic (As), cadmium (Cd), iron (Fe), zinc (Zn), molybdenum (Mo), lead (Pb), selenium (Se), and mercury (Hg). We used the Pittsburgh Sleep Quality Index (PSQI) to assess sleep quality. Linear regression, logistic regression, generalized additive models (GAMs), quantile g-computation, and Bayesian kernel machine regression (BKMR) were applied to investigate the relationships between metal(loid) exposure and sleep quality. The results from single metal(loid) models, quantile g-computation models, and BKMR models consistently suggested that Fe was positively related to women's sleep quality. Moreover, in the quantile g-computation models, As was the most critical contributor to the negative effects of the metal(loid) mixture on sleep quality. In addition, we found significant As by Fe interaction for scores of PSQI and habitual sleep efficiency, Pb by Fe interaction for PSQI and sleep latency, and Hg by Fe interaction for PSQI, suggesting the interactive effects of As and Fe, Pb and Fe, Hg and Fe on sleep quality and specific sleep components. Our study provided the first-hand evidence of the effects of metal(loid) exposure on pregnant women's sleep quality. The underlying mechanisms need to be explored in the future.

Mercury and cadmium-induced inflammatory cytokines activation and its effect on the risk of preeclampsia: a review

During the last decade, there has been an increase in exposure to heavy metals that can affect human health and the environment, especially mercury (Hg) and cadmium (Cd). These exposures can pollute the rivers or oceans, then contaminating marine organisms. Humans as the last consumer of this food chain cycle can be a place for the bioaccumulation of Hg and Cd, especially for people living in coastal areas, including pregnant women. Exposure to heavy metals Hg and Cd can have a high risk of triggering blood vessel disorders, penetrating the blood-brain barrier (BBB) and the placental barrier, one of which can increase the risk of preeclampsia. Several immunological biomarkers such as some cytokines associated with Hg and Cd exposure are also involved in the pathophysiology of preeclampsia, which are the placental implantation process and endothelial dysfunction in pregnant women. Therefore, countries that have a high incidence of preeclampsia should be aware of the environmental factors, especially heavy metal pollution such as Hg and Cd.

Is exposure to chemical pollutants associated with sleep outcomes? A systematic review

Environmental exposures may influence sleep; however, the contributions of environmental chemical pollutants to sleep health have not been systematically investigated. We conducted a systematic review to identify, evaluate, summarize, and synthesize the existing evidence between chemical pollutants (air pollution, exposures related to the Gulf War and other conflicts, endocrine disruptors, metals, pesticides, solvents) and dimensions of sleep health (architecture, duration, quality, timing) and disorders (sleeping pill use, insomnia, sleep-disordered breathing)). Of the 204 included studies, results were mixed; however, the synthesized evidence suggested associations between particulate matter, exposures related to the Gulf War, dioxin and dioxin-like compounds, and pesticide exposure with worse sleep quality; exposures related to the Gulf War, aluminum, and mercury with insomnia and impaired sleep maintenance; and associations between tobacco smoke exposure with insomnia and sleep-disordered breathing, particularly in pediatric populations. Possible mechanisms relate to cholinergic signaling, neurotransmission, and inflammation. Chemical pollutants are likely key determinants of sleep health and disorders. Future studies should aim to evaluate environmental exposures on sleep across the lifespan, with a particular focus on developmental windows and biological mechanisms, as well as in historically marginalized or excluded populations.

Epidemiological evidence for the effect of environmental heavy metal exposure on the immune system in children

Heavy metals exist widely in daily life, and exposure to heavy metals caused by environmental pollution has become a serious public health problem worldwide. Due to children's age-specific behavioral characteristics and imperfect physical function, the adverse health effects of heavy metals on children are much higher than in adults. Studies have found that heavy metal exposure is associated with low immune function in children. Although there are reviews describing the evidence for the adverse effects of heavy metal exposure on the immune system in children, the summary of evidence from epidemiological studies involving the level of immune molecules is not comprehensive. Therefore, this review summarizes the current epidemiological study on the effect of heavy metal exposure on childhood immune function from multiple perspectives, emphasizing its risks to the health of children's immune systems. It focuses on the effects of six heavy metals (lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), nickel (Ni), and manganese (Mn)) on children's innate immune cells, lymphocytes and their subpopulations, cytokines, total and specific immunoglobulins, and explores the immunotoxicological effects of heavy metals. The review finds that exposure to heavy metals, particularly Pb, Cd, As, and Hg, not only reduced lymphocyte numbers and suppressed adaptive immune responses in children, but also altered the innate immune response to impair the body's ability to fight pathogens. Epidemiological evidence suggests that heavy metal exposure alters cytokine levels and is associated with the development of inflammatory responses in children. Pb, As, and Hg exposure was associated with vaccination failure and decreased antibody titers, and increased risk of immune-related diseases in children by altering specific immunoglobulin levels. Cd, Ni and Mn showed activation effects on the immune response to childhood vaccination. Exposure age, sex, nutritional status, and co-exposure may influence the effects of heavy metals on immune function in children.

Interactions between heavy metals and sleep duration among pre-and postmenopausal women: A current approach to molecular mechanisms involved

The effects of heavy metals (cadmium, lead, and mercury) and their mixtures on sleep duration in pre-and postmenopausal women, particularly the molecular mechanisms, remain unknown. Here, we assessed the interaction between heavy metals and sleep duration among pre-and postmenopausal women (n = 1134). Furthermore, molecular mechanisms related to sleep disorders induced by studied heavy metals were further analyzed to support the previous findings. We found that serum lead levels were positively related to weekend and weekday sleep duration in premenopausal women. There were interactions between serum lead and mercury and menopausal status for sleep duration. Serum lead and mercury levels were shown to be inversely related to sleep duration in postmenopausal women. Despite the lack of statistically significant associations between mixed heavy metals and sleep duration, there were increasing trends in premenopausal women's sleeping patterns and decreasing trends in postmenopausal women's sleeping patterns. In silico analysis, IL1B, hsa-21-5p, hsa-887-3p, hsa-877-3p, and NR4A1 were identified as the most relevant genes, miRNAs, and transcription factors linked with sleep disorders induced by combined heavy metals (cadmium, lead, and mercury). Furthermore, "type 1 melanocortin receptor binding," "endocrine hormone secretion," "interleukin-1 receptor antagonist activity," "altered melanocortin system," and "sleep wake disorders" were identified as the predominant molecular mechanisms involved in the pathophysiology of sleep disorders induced by the studied heavy metals. Cut off point values and miRNA sponge templates for heavy metal exposure levels relevant to sleep disorders in pre- and postmenopausal women were reported. Future research is needed to verify our findings and provide insight into the molecular processes of long-term mixed heavy metal exposure in various populations, such as children and the elderly.

Mercury exposure, neopterin profile, and tryptophan degradation in dental technicians

Amalgam has been widely used as a restorative dental material for over 150 years. Most standard dental amalgam formulations contain approximately 50% elemental mercury in a mixture of copper, tin, silver, and zinc. Mercury is a highly volatile metal, which can easily vaporize to a colorless and odorless gas. It has been demonstrated that mercury is released from dental amalgam, which is increased by chewing, eating, brushing, and drinking hot liquids. Besides this, amalgam is the main occupational exposure source of mercury for dental workers. It is known that mercury exposure causes immune modulation in humans. In this study, it was aimed to evaluate the changes in neopterin levels and tryptophan (Trp) degradation in dental technicians. It was observed that low levels of occupational mercury exposure resulted in decreased neopterin, kynurenine (Kyn), and Kyn/Trp levels. Moreover, mercury and neopterin levels had a significant positive correlation in workers. The lower neopterin levels and Kyn/Trp in dental technicians compared to an unexposed group indicates a possible immune suppression with low level of occupational mercury exposure during amalgam preparation. The relationship between urinary mercury levels as an indicator of occupational mercury exposure and neopterin reminded an effect on T-cell-mediated immune response.

Long-chain omega-3 fatty acids, selenium, and mercury in relation to sleep duration and sleep quality: findings from the CARDIA study

PURPOSE

To examine the associations of long-chain omega-3 polyunsaturated fatty acids (LCω3PUFA) intake with sleep quality and duration in a cohort of American young adults, and to explore whether the associations of interest are modified by selenium (Se) and/or mercury (Hg) status.

METHODS

The study sample consisted of 3964 men and women from the longitudinal Coronary Artery Risk Development in Young Adults (CARDIA) study, aged 25.0 ± 3.6 at baseline. Intake of LCω3PUFA was assessed using an interviewer-administered dietary history questionnaire at baseline (1985-1986), Y7 (1992-1993), and Y20 (2005-2006). Toenail Se and Hg concentrations were quantified at Y2 (1987-1988). The outcomes were self-reported sleep quality and sleep duration measured by one question for each at Y15 (2000-2001) and Y20. Generalized estimating equation was used to examine the association between cumulative average intake of LCω3PUFA and sleep measures. Restricted cubic spline was performed to explore the potential non-linear associations of interest. Se and Hg were dichotomized by their median values to examine the potential effect modification of Se and/or Hg.

RESULTS

We did not observe any significant associations (linear or non-linear) of LCω3PUFA intake with either sleep quality or duration. Also, no significant association was observed in any subgroup classified by toenail Se and/or Hg concentrations. Similarly, sensitivity analysis indicated that the null associations between LCω3PUFA intake and sleep quality or duration persisted across subgroups classified by race, gender, obesity, or having small children.

CONCLUSION

Findings from this longitudinal analysis did not support the hypothesis that LCω3PUFA intake is associated with sleep quality or sleep duration.

Cadmium, total mercury, and lead in blood and associations with diet, sociodemographic factors, and smoking in Swedish adolescents

BACKGROUND

Despite their vulnerability to the toxic effects of certain metals, biomonitoring data on adolescents are limited. In the present study, we assessed blood concentrations of toxic metals (cadmium [Cd], total mercury [Hg], and lead [Pb] in a national representative sample of Swedish adolescents. We also examined the associations of Cd, total Hg and Pb with habitual intakes of major energy-providing food groups and other possible determinants such as age, sex, household education, Nordic or non-Nordic origin, and smoking.

METHODS

We analysed blood concentrations of Cd, total Hg, and Pb in a sample of 1099 adolescents from the Riksmaten Adolescents 2016-17 study in three age groups (mean age of 12, 15, and 18 years) using inductively coupled plasma mass spectrometry. The participants completed web-based questionnaires on food consumption frequency, sociodemographic factors and health status. Dietary data from two web-based 24-h dietary recalls were used to estimate the habitual intake of 10 major food groups.

RESULTS

Almost all participants had detectable concentrations of Cd, total Hg, and Pb in whole blood. The median blood concentrations were 0.12 μg/L for Cd, 0.72 μg/L for total Hg, and 7.1 μg/L for Pb. Higher blood concentrations of Cd were observed in girls than in boys, whereas concentrations of total Hg and Pb were higher in boys. We observed an inverse association between Cd and meat intake. Total Hg concentrations were positively associated with intakes of fish, eggs, meat, and vegetables, and Pb concentrations were inversely associated with intakes of dairy products. Furthermore, smokers had higher concentrations of Cd and Pb.

CONCLUSIONS

We found that fish was a potentially important source of exposure to total Hg in Swedish adolescents. No other food group was identified to have a strong impact on the blood levels of Cd, total Hg and Pb. Thirteen per cent of the adolescents had blood Pb concentrations above 12 μg/L, the reference point used in the risk assessment of Pb by the European Food Safety Authority (EFSA).

Environmental exposures and sleep outcomes: A review of evidence, potential mechanisms, and implications

Environmental exposures and poor sleep outcomes are known to have consequential effects on human health. This integrative review first seeks to present and synthesize existing literature investigating the relationship between exposure to various environmental factors and sleep health. We then present potential mechanisms of action as well as implications for policy and future research for each environmental exposure. Broadly, although studies are still emerging, empirical evidence has begun to show a positive association between adverse effects of heavy metal, noise pollution, light pollution, second-hand smoke, and air pollution exposures and various sleep problems. Specifically, these negative sleep outcomes range from subjective sleep manifestations, such as general sleep quality, sleep duration, daytime dysfunction, and daytime sleepiness, as well as objective sleep measures, including difficulties with sleep onset and maintenance, sleep stage or circadian rhythm interference, sleep arousal, REM activity, and sleep disordered breathing. However, the association between light exposure and sleep is less clear. Potential toxicological mechanisms are thought to include the direct effect of various environmental toxicants on the nervous, respiratory, and cardiovascular systems, oxidative stress, and inflammation. Nevertheless, future research is required to tease out the exact pathways of action to explain the associations between each environmental factor and sleep, to inform possible therapies to negate the detrimental effects, and to increase efforts in decreasing exposure to these harmful environmental factors to improve health.

A systematic review of the association between sleep health and stress biomarkers in children

Sleep is intimately linked with the stress response system. While the evidence for this connection has been systematically reviewed in the adult literature, to our knowledge no studies have examined this relationship in young children. Recent scientific interest in understanding the effects of adverse environments in early childhood, including an emphasis on understanding the role of sleep, highlights the importance of synthesizing the current evidence on the relationship between sleep and the stress response system in early childhood. The aim of this systematic review is to examine the relationship between sleep health and biomarkers of physiologic stress (neuroendocrine, immune, metabolic, cardiovascular) in healthy children ages 0-12 y. Following PRISMA guidelines, we identified 68 empirical articles and critically reviewed and synthesized the results across studies. The majority of studies included school-age children and reported sleep dimensions of duration or efficiency. Overall, evidence of associations between sleep health and stress biomarkers was strongest for neuroendocrine variables, and limited or inconsistent for studies of immune, cardiovascular, and metabolic outcomes. Gaps in the literature include prospective, longitudinal studies, inclusion of children under the age of 5 y, and studies using objective measures of sleep.

Mercury exposure in relation to sleep duration, timing, and fragmentation among adolescents in Mexico City

INTRODUCTION

Mercury intoxication is known to be associated with adverse symptoms of fatigue and sleep disturbances, but whether low-level mercury exposure could affect sleep remains unclear. In particular, children may be especially vulnerable to both mercury exposures and to poor sleep. We sought to examine associations between mercury levels and sleep disturbances in Mexican youth.

METHODS

The study sample comprised 372 youth from the Early Life Exposures to Environmental Toxicants (ELEMENT) cohort, a birth cohort from Mexico City. Sleep (via 7-day actigraphy) and concurrent urine mercury were assessed during a 2015 follow-up visit. Mercury was also assessed in mid-childhood hair, blood, and urine during an earlier study visit, and was considered a secondary analysis. We used linear regression and varying coefficient models to examine non-linear associations between Hg exposure biomarkers and sleep duration, timing, and fragmentation. Unstratified and sex-stratified analyses were adjusted for age and maternal education.

RESULTS

During the 2015 visit, participants were 13.3 ± 1.9 years, and 48% were male. There was not a cross-sectional association between urine Hg and sleep characteristics. In secondary analysis using earlier biomarkers of Hg, lower and higher blood Hg exposure was associated with longer sleep duration among girls only. In both boys and girls, Hg biomarker levels in 2008 were associated with later adolescent sleep midpoint (for Hg urine in girls, and for blood Hg in boys). For girls, each unit log Hg was associated with 0.2 h later midpoint (95% CI 0 to 0.4), and for boys each unit log Hg was associated with a 0.4 h later sleep midpoint (95% CI 0.1 to 0.8).

CONCLUSIONS

There were mostly null associations between Hg exposure and sleep characteristics among Mexican children. Yet, in both boys and girls, higher Hg exposure in mid-childhood (measured in urine and blood, respectively) was related to later sleep timing in adolescence.

The Relationship between Cytokine Profile and Hypertension among the Mercury-Exposed Residents of Temirtau Region in Central Kazakhstan

Background:

Mercury is a common environmental contaminant and it is also harmful to human health. Among reported toxicities, its harmful effect on hypertension is poorly documented. In Kazakhstan, Temirtau city has been reported to have a high level of mercury contamination from an acetaldehyde production factory. Therefore, we aimed to investigate the association between serum profile of cytokines and the development of hypertension among the exposed citizens.

Methods:

We selected 81 individuals for study, out of them, 41 exposed ones suffered hypertension and 40 – unexposed healthy controls in villages Chkalovo, Samarkand, Gagarinskoye, Tegiszhol, Rostovka in 2016. Mercury content in urine was studied by inversion voltammetry. Cytokine levels of IL-2, IL-6, IL-10 and TNF-α were determined by ELISA.

Results:

Mercury-exposed citizens, especially those with hypertension, had significantly higher concentrations of inflammatory cytokines TNF-α, IL-2, IL-6 and anti-inflammatory cytokine IL-10 as compared to the unexposed population. The dependence of the mercury level in urine on IL-2 content was also detected. Therefore, chronic low doses of exposure to mercury were associated with an increase in serum levels of immune markers and with the increased risk of hypertension.

Conclusion:

The presence of mercury in the body probably affected the expression of interleukin-2, one of the main cytokines that coordinate immune response.

Air pollution exposure and adverse sleep health across the life course: A systematic review

An increasing number of epidemiological studies have examined air pollution as a possible contributor to adverse sleep health, but results are mixed. The aims of this systematic review are to investigate and summarize the associations between exposures to air pollutants and various sleep measures across the lifespan. PubMed, CINAHL, Cochrane, Scopus, Web of Science, and PsycInfo were searched through October 2019 to identify original data-based research examining direct epidemiological associations between ambient and indoor air pollution exposures and various sleep health measures, including sleep quality, sleep duration, sleep disturbances, and daytime sleepiness. Twenty-two articles from 2010 to 2019 were selected for inclusion in this review, including a wide range of study populations (from early childhood to elderly) and locations (10 Asian, 4 North American, 3 European, 5 other). Due to variation in both exposure and outcome assessments, conducting a meta-analysis was not plausible. Twenty-one studies reported a generally positive association between exposure and poor sleep quality. While most studies focused on ambient air pollutants, five assessed the specific effect of indoor exposure. In children and adolescents, increased exposure to both ambient and indoor pollutants is associated with increased respiratory sleep problems and a variety of additional adverse sleep outcomes. In adults, air pollution exposure was most notably related to sleep disordered breathing. Existing literature generally shows a negative relationship between exposures to air pollution and sleep health in populations across different age groups, countries, and measures. While many associations between air pollution and sleep outcomes have been investigated, the mixed study methods and use of subjective air pollution and sleep measures result in a wide range of specific associations. Plausible toxicological mechanisms remain inconclusive. Future studies utilizing objective sleep measures and controlling for all air pollution exposures and individual encounters may help ameliorate variability in the results reported by current published literature.

Dietary contributions to increased background lead, mercury, and cadmium in 9-11 Year old children: Accounting for racial differences

BACKGROUND

Initial interest in the adverse consequences of exposure to lead (Pb), mercury (Hg), and cadmium (Cd) focused on relatively high exposures through environmental or occupational sources; however, recent evidence suggests even low-level background exposure to non-essential metals might be detrimental, particularly for children's health and development. One potentially important source of increased background levels of non-essential toxic metals is diet.

OBJECTIVES

We considered whether differences in diet are associated with levels of non-essential metals in blood and whether racial differences in metals are mediated by dietary differences.

METHODS

We assessed blood levels of Pb, Hg, and Cd in a sample of 9-11 year-old children (N = 295) comprised of 42% European Americans (EAs), 58% African American (AAs), and 47% female. Diet was assessed using 24-h dietary recalls during phone interviews administered to parents on two consecutive days (Friday and Saturday). The Healthy Eating Index-2105 (HEI-2015) was calculated to assess diet quality.

RESULTS

The current study identified significant dietary sources of non-essential metal exposure - namely total fruit for Pb, total protein for Hg, and greens and beans for Cd. Moreover, AAs were found to have significantly higher blood levels of Pb and Hg than EAs and these racial differences were significantly mediated by these dietary differences.

DISCUSSION

This study is one of very few to consider total diet in children and exposure to the non-essential metals Pb, Hg, and Cd, and the first to demonstrate that racial differences in increased background blood levels of non-essential toxic metals can be accounted for by racial differences in diet. Given regional differences in food consumption patterns and specific farm and store sources for the foods, the generalizability of the current findings has yet to be determined; however, commonly consumed foods appear to be a significant source of low-level non-essential metals.

Plasma DHA Is Related to Sleep Timing and Duration in a Cohort of Mexican Adolescents

BACKGROUND

Delayed sleep timing and short sleep duration represent a significant public health burden in adolescents. Whether intake of nutrients affects the pineal gland, where sleep/wake cycles are regulated, remains unclear.

OBJECTIVES

In a cross-sectional analysis, we investigated whether plasma concentrations of DHA and arachidonic acid (AA), long-chain fatty acids that can be obtained through diet, were related to sleep timing and duration in adolescents.

METHODS

The study population included 405 Mexico City adolescents (mean age ± SD = 14.2 ± 2.1 y; 48% males) who took part in a 2015-2016 follow-up visit as a part of an ongoing cohort study. Fatty acid concentrations were measured in plasma using GLC, as a percentage of total fatty acids. Sleep midpoint and duration were assessed with 7-d wrist actigraphy. We categorized DHA and AA plasma concentrations into quartiles (Q1-Q4; Q4 = highest fatty acids). We conducted cross-sectional linear regression analysis with sleep characteristics as separate outcomes and quartiles of DHA and AA as exposures, adjusting for sex, age, and BMI z-scores.

RESULTS

Mean ± SD plasma DHA (as percentage of total fatty acids) was 1.2 ± 0.4%, whereas mean ± SD plasma AA was 6.2 ± 1.5%. In adjusted analysis, higher plasma DHA was linearly associated with longer sleep duration on the weekends; to illustrate, those in Q4 compared with Q1 had 32 min longer duration (95% CI: 7, 57; P trend = 0.005). Higher DHA was also associated with earlier sleep timing during weekdays and weekends, although in a nonlinear fashion. The largest difference was a 0.75-h (45-min) later sleep midpoint in Q2 compared with Q4 (95% CI: 0.36, 1.14).

CONCLUSIONS

Plasma DHA was associated with earlier sleep timing and longer weekend sleep duration in Mexican adolescents. Whether DHA supplementation improves sleep in adolescent populations deserves consideration in randomized trials.

Guarana improves behavior and inflammatory alterations triggered by methylmercury exposure: an in vivo fruit fly and in vitro neural cells study

Methylmercury (MeHg) is a well-known environmental pollutant associated with neurological and developmental deficits in animals and humans. However, epidemiological data showed that people living in the Amazon region although exposed to MeHg do not present these effects probably due to the protective effect of certain foods. We hypothesized here if guarana, a highly caffeinated fruit and consumed on a daily basis by Amazon people, could have some protective effect against MeHg toxicity using two complementary approaches. To assess locomotor impairment and sleep disruption, we used fruit fly (Drosophila melanogaster) model, and to evaluate neuroinflammation, we used human SH-SY5Y neural cells by measuring inflammatory cytokines levels. Results showed that guarana had a protective effect on the locomotor activity of male fruit flies reducing the excessive sleepiness caused by MeHg and increasing daily activity. Also, guarana increased the viability of flies and attenuated neural cells mortality. In addition, guarana reduced all pro-inflammatory cytokines levels increased by MeHg, along with caspase-1, caspase -3, caspase-8, and 8-dOHG levels, whereas increased the anti-inflammatory (IL-10) cytokine levels, which was decreased by MeHg. Our study provides new insights on the protective effects of guarana on the viability, locomotor activity, sleep, and activity patterns in vivo and the in vitro neuronal anti-inflammatory effect against MeHg toxicity.

An overview of worldwide and regional time trends in total mercury levels in human blood and breast milk from 1966 to 2015 and their associations with health effects

BACKGROUND

Mercury is a pollutant of global concern. To protect human health and environment from mercury pollution, the Minamata Convention on mercury entered into force in 2017.

OBJECTIVES

To support a future effectiveness evaluation of the convention, this study assesses worldwide and regional time trends of total mercury levels in human blood and breast milk across different population sub-groups in the last half-century prior to entry-into-force of the Minamata Convention. This study also provides an overview of the epidemiological literature showing evidence of associations between mercury exposure (in terms of total mercury levels in whole blood, cord blood, and breast milk) and human health.

METHODS

We searched electronic databases to identify articles published prior to June 14, 2017 and reported total mercury levels in any of three biological matrices (whole blood, cord blood, or breast milk) and/or associations with human health. Temporal trends of total mercury levels in the selected biological matrices across different population sub-groups were estimated using a linear fit of the log-transformed data. In parallel, statistical methods were employed to assess any possible effect of sources of inhomogeneity (i.e. study and population characteristics such as age, sex, ethnicity, source of exposure, sampling period, and geographical region) in the collected studies. Furthermore, a summary of significant and relevant associations between mercury exposure and human health conditions in children and adults was prepared.

FINDINGS

We found significant declines in total mercury levels in whole blood, cord blood, and breast milk between 1966 and 2015. A regional overview of total mercury levels in whole blood, cord blood, and breast milk suggests the highest levels in South America, followed by Africa or Asia whereas the population groups from Europe or North America displayed the lowest levels of total mercury in the selected biological matrices. We observed conclusive consistent associations of mercury exposure with selected health conditions, especially neurodevelopment and neurotoxicity in children and adults. For several other health conditions, reported findings in the collected studies do not support conclusive associations. We also found that several studies demonstrated significant associations between mercury exposure below the USEPA reference level and various health conditions.

CONCLUSIONS

This study provides a worldwide and regional overview of trends in total mercury levels in human blood and breast milk and associated health risks prior to entry-into-force of the Minamata Convention and calls for further epidemiological investigations from across the globe to fully understand the health implications of mercury exposure.

The impact of environmental pollution on the quality of mother's milk

Breastfeeding is a gold standard of neonate nutrition because human milk contains a lot of essential compounds crucial for proper development of a child. However, milk is also a biofluid which can contain environmental pollution, which can have effects on immune system and consequently on the various body organs. Polychlorinated biphenyls are organic pollutants which have been detected in human milk. They have lipophilic properties, so they can penetrate to fatty milk and ultimately to neonate digestive track. Another problem of interest is the presence in milk of heavy metals-arsenic, lead, cadmium, and mercury-as these compounds can lead to disorders in production of cytokines, which are important immunomodulators. The toxicants cause stimulation or suppression of this compounds. This can lead to health problems in children as allergy, disorders in the endocrine system, end even neurodevelopment delay and disorder. Consequently, correlations between pollutants and bioactive components in milk should be investigated. This article provides an overview of environmental pollutants found in human milk as well as of the consequences of cytokine disorder correlated with presence of heavy metals. Graphical abstract.

Parental and preimaginal exposure to methylmercury disrupts locomotor activity and circadian rhythm of adult Drosophila melanogaster

Methylmercury (MeHg) is a well-known toxic pollutant. However, little is known about the effects of this toxic agent in an adult as a consequence of a parental or preimaginal exposure. This study used Drosophila melanogaster to investigate whether a parental or a preimaginal (eggs-larvae-pupae stages) exposure could impact parameters as viability, locomotor activity, and sleep patterns of fruit flies. Thus, we performed two exposure protocols. One where just parents were exposed to MeHg (0-12 µM) during 24 h, then flies were transferred to lay eggs in a healthy medium (without MeHg). In the other, flies were set to lay eggs in a MeHg medium, same concentrations, and discarded after this (preimaginal exposure). Viability was evaluated from egg to adult flies. F1 progeny was collected within 24 h and transferred to a fresh healthy medium. Sleep behavior analysis was performed using Drosophila Active Monitoring System (DAMS), and the locomotor activity was evaluated by climbing assay. Results have shown that the parental exposure had a significant impact on F1 progeny reducing viability and locomotor activity performance, but no significant circadian rhythm alterations. Whereas the preimaginal exposure had a stronger effect decreasing viability and locomotor activity, it also disrupted sleep patterns. MeHg preimaginal exposure showed a longer sleep duration and lower daily activity. Results corroborate the hypothesis that low MeHg exposure could trigger subclinical symptoms related to a 'neurotoxicological development effect'. Complementary investigations could clarify the underlying mechanisms of MeHg effects in neural functions due to parental and early development exposure to this toxicant.

Metals and Circadian Rhythms

Circadian rhythms describe the behavioral and physiological changes that occur in living organisms in order to attune to a 24 hour cycle of day and night. The most striking aspect of circadian function is the sleep-wake cycle, however many other physiological processes are regulated in 24 hour oscillations, including blood pressure, body temperature, appetite, urine production, and the transcription and translation of thousands of circadian dependent genes. Circadian disruption and sleep disorders are strongly connected to neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and Huntington's disease as well as others. Metal exposures have been implicated in neurodegenerative diseases, in some cases involving metals that are essential micronutrients but are toxic at high levels of exposure (such as manganese, copper, and zinc), and in other cases involving metals that have no biological role but are toxic to living systems (such as lead, mercury, and aluminum). In this review, we examine the evidence for circadian and sleep disorders with exposures to these metals and review the literature for possible mechanisms. We suggest that giving the aging population, the prevalence of environmental exposures to metals, and the increasing prevalence of neurodegenerative disease in the aged, more research into the mechanisms of circadian disruption subsequent to metal exposures is warranted.

Immunotoxicity of mercury: Pathological and toxicological effects

Mercury (Hg) is toxic and hazardous metal that causes natural disasters in the earth's crust. Exposure to Hg occurs via various routes; like oral (fish), inhalation, dental amalgams, and skin from cosmetics. In this review, we have discussed the sources of Hg and its potential for causing toxicity in humans. In addition, we also review its bio-chemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences; as well as the important considerations in risk assessment and management of Hg poisoning have been discussed in detail. Many harmful outcomes have been reported, which will provide more awareness.

Impact of fetal and childhood mercury exposure on immune status in children

BACKGROUND

Mercury exposure have been shown to affect immune status in animals as reflected by cytokine expression. It is unclear whether low levels of exposure during fetal and/or childhood periods could impact on immune status in humans.

OBJECTIVES

To test the hypothesis that fetal and childhood mercury exposure is associated with childhood cytokine profiles and to investigate whether childhood selenium levels interact with any of the associations found.

METHODS

Children were recruited from a previously established birth cohort between the ages of 6-9 years for assessment and measurement of blood mercury, selenium and cytokine profile (interleukin (IL)-4, IL-6, IL-8, IL-10, IL-13 and TNF-alpha). Multivariable linear regression models were used to assess the adjusted association of cord blood mercury concentration and current mercury concentrations with levels of the cytokine levels. We tested whether the association with current mercury level varied by current selenium level and cord blood mercury level.

RESULTS

IL-10 was negatively associated with current blood mercury concentration. The effect was greatest in cases with low cord blood mercury and low current selenium concentrations. None of the other cytokine levels were associated with either cord blood or current blood mercury concentrations, except that cord blood mercury was negatively associated with IL-6.

CONCLUSIONS

Childhood mercury exposure was negatively associated with childhood IL-10 levels. It is postulated that while selenium is protective, low levels of fetal mercury exposure may increase the degree of this negative association during childhood. Further studies into the clinical significance of these findings are required.