Proposal for a revised reference concentration (RfC) for mercury vapour in adults

Estimation of smokers' exposure to mercury from combustible tobacco products, based on the approach used in food consumers' exposure estimation

Smoking has been known to mankind for centuries, but it is only in recent decades that much attention has been paid to the harmfulness of this habit. Mercury inhalation is particularly dangerous in this respect and smoking creates extremely favorable conditions for the emission and targeted delivery of this element into the lungs. Despite this fact, a lack of a clear method for estimating the exposure of tobacco consumers to mercury was identified. This work shows justification to transfer the approach of estimating food product consumers' exposure to estimate the exposure of combustible tobacco product consumers to this element. In addition, it was noted that researchers' attention is mainly focused on cigarettes, while the tobacco market has a wide range of combustible products. Therefore, in this work, the mercury content of cigars (8.45 ± 0.18-41.02 ± 0.20 μg/kg), pipe tobaccos (8.03 ± 0.52-25.48 ± 0.50 μg/kg), bidis (14.93 ± 0.47-31.79 ± 0.26 μg/kg) and cigarette tobaccos (14.22 ± 0.71-34.5 ± 1.4 μg/kg) was analyzed. This study demonstrates that smoking can contribute significant total mercury exposure to consumers', although it is unlikely to cause mercury poisoning regardless of other exposure sources.

Neurotoxicity of mercury: an old issue with contemporary significance

Mercury exerts a variety of toxic effects, depending on the specific compound and route of exposure. However, neurotoxicity in virtue of its consequence to health causes the greatest concern for toxicologists. This is particularly true regarding fetal development, where neurotoxic effects are much more severe than in adults, and the toxicity threshold is lower. Here, we review the major concepts regarding the neurotoxicity of mercury compounds (mercury vapor; methylmercury and ethylmercury), from exposure routes to toxicokinetic particularities leading to brain deposition and the development of neurotoxic effects. Albeit research on the neurotoxicity of mercury compounds has significantly advanced from the second half of the twentieth century onwards, several grey areas regarding the mechanism of toxicity still exist. Thus, we emphasize research advances during the last two decades concerning the molecular interactions of mercury which cause neurotoxic effects. Highlights include the disruption of glutamate signaling and excitotoxicity resulting from exposure to mercury and the interaction with redox active residues such as cysteines and selenocysteines which are the premise accounting for the disruption of redox homeostasis caused by mercurials. We also address how immunotoxic effects at the CNS, namely microglia and astrocyte activation modulate developmental neurotoxicity, a major topic in contemporary research.

Inhalation Exposure to Gaseous and Particulate Bound Mercury Present in the Ambient Air over the Polluted Area of Southern Poland

This study concerns the concentrations of gaseous and particle-bound mercury present in ambient air of two Polish sites, differing in terms of emission structure, and the estimation of inhalation risks related to those Hg species. The measurements of total gaseous mercury (TGM) and PM_2.5-bound mercury (PBM) were performed at an urban station in Zabrze and a rural station in Złoty Potok, in 2014–2015. Both sites are located in Silesia, considered one of the European air pollution hot-spots. TGM was measured on-line (Tekran 2537). PM_2.5 samples were taken with the use of low volume samplers. Hg contents in PM were determined by the CVAAS method following thermal decomposition. The median concentrations of TGM and PBM in Zabrze were 2.48 ng m⁻³ and 37.87 pg m⁻³, respectively; meanwhile in Zloty Potok, these were 1.69 ng m⁻³ and 27.82 pg m⁻³, respectively. Clearly, seasonal variability of TGM and PBM concentrations were observed, reflecting the importance of Hg and PM emissions from coal combustion for power and heating purposes. Health risk assessment was performed using a deterministic approach by the most conservative exposure scenario. The obtained HQ ratios and the cumulative HI indexes were below the limit value (<1). This means an unlikely health hazard due mercury inhalation.

Artisanal and small-scale gold mining: A cross-sectional assessment of occupational mercury exposure and exposure risk factors in Kadoma and Shurugwi, Zimbabwe

In artisanal and small-scale gold mining (ASGM) the toxic metal mercury is used for gold extraction. The objective of this cross-sectional study was to assess mercury concentrations in urine and blood and mercury-related symptoms of participants identifying themselves as miners from Kadoma and Shurugwi, Zimbabwe. Moreover, we aimed to explore possible risk factors influencing mercury body burden. In 2019, urine and blood samples of 207 participants were collected and analyzed for mercury using atomic absorption spectroscopy. All participants answered questions regarding their exposure risks. The median urine mercury value was 4.75 μg/L with a maximum of 612 μg/L. Median mercury concentration in creatinine corrected urine values was 3.98 μg/g with a maximum value of 478 μg/g. The median blood mercury value was 2.70 μg/L with a maximum of 167 μg/L. Correlations between exposure risks factors such as the lack of retort use and elevated mercury values were demonstrated. ASGM is very common in Zimbabwe. Thus, mercury exposure is a major occupational health risk for miners. Moreover, this study emphasizes the impact of exposure risk factors on the mercury body burden.

Infants and mothers levels of mercury in breast milk, urine and hair, data from an artisanal and small-scale gold mining area in Kadoma / Zimbabwe

In Kadoma (Zimbabwe) gold is extracted from ore based on a simple technology using mercury. Women are exposed whilst living in an exposed area, or even more working directly with mercury. Breast fed infants are exposed via mercury contaminated milk and the general environmental mercury exposure. The aim of the study was to measure infants and mothers levels of mercury in urine and hair, as well as in breast milk. In 2006, an environmental epidemiological field study with 120 mother - child pairs was conducted. A non exposed control group (n = 42) was compared with a medium exposed group (n = 51) and a high exposed group (occupational exposure, n = 27). Urine and hair samples from mother and infants plus breast milk samples were analyzed for total mercury. 120 breast milk samples were analyzed, median (maximum) concentrations [μg Hg/l] were (i) control group < 0.50 (1.55), (ii) medium exposed group 1.10 (10.48), (iii) high exposed group 1.20 (24.80) (p < 0,001). Urine and hair results were distributed similarly for infants and mothers, with higher levels according to the exposure subgroup. All specimen results correlated very well with another, indicating there is a pathway between breast milk and infant's level of mercury. The daily uptake of mercury via breast milk was calculated. The reference dose of 0.3°[μg Hg/kg BW/d] was used to compare the burden of the infants. No infant from the control group, but 17.6% of the medium and 18.5% of the high exposed group were above the reference dose. Mercury in breast milk is generally higher in artisanal and small scale gold mining areas. Breast fed infants were burdened with toxic mercury via breast milk and via the general environment, both are important public health issues.

Polymorphisms in potential mercury transporter ABCC2 and neurotoxic symptoms in populations exposed to mercury vapor from goldmining

BACKGROUND

Artisanal small-scale gold miners have high levels of mercury in human specimens often above recommended threshold values. There are differences reported in the manifestation of neurological symptoms of individuals with a comparable level of exposure to mercury, suggesting a genetic component influencing the susceptibility to mercury neurotoxicity.

OBJECTIVE

To investigate associations between polymorphisms (rs1885301, rs717620, rs2273697) in the potential Hg-transporter ABCC2 gene and neurological effects.

METHODS

968 participants from the Philippines, Indonesia, Tanzania and Zimbabwe were included in this study (age 12-59 years). For the statistical analysis the countries were categorized into Africa (Philippines, Indonesia) and Asia (Tanzania, Zimbabwe). Study participants were from three exposure groups: without mercury exposure from goldmining (n = 129); living in mercury-contaminated areas (n = 281) and mercury working exposure (n = 558). To identify chronic inorganic mercury intoxication we applied a modified neurological score sum including eight binary coded parameters (from anamnestic, clinical and neurophysiological examinations). Associations between genotype and neurological score sum, as well as between genotype and separate neurological tests (ataxia of gait, dysdiadochokinesia, ataxia heel to shin, pencil tapping test and matchbox test) were evaluated.

RESULTS

We found that ABCC2 genotype were associated with performance on certain neurological tests: for rs1885301, A-allele carriers in the African populations showed significantly worse performance than GG carriers on the pencil tapping test; whereas for rs2273697, A-allele carriers in the African and Asian populations showed a significantly better performance than GG carriers on this test. When including an interaction term between genotype and exposure subgroup, interaction effects were also seen for the pencil tapping test and matchbox tests for rs2273697 in Asia.

CONCLUSIONS

The results suggest that certain ABCC2 polymorphisms may influence the neurotoxic effects in mercury-burdened individuals. ABCC2 alleles associated with worse neurological performance in the present study. These alleles have previously been correlated with higher levels of urinary mercury concentrations in the same cohort. Taken together, these associations between ABCC2 genotype, mercury levels, and neurological effects support the hypothesis that some ABCC2 genotypes may have a higher neurotoxic potential, although further functional studies are needed to prove causation.

PM Origin or Exposure Duration? Health Hazards from PM-Bound Mercury and PM-Bound PAHs among Students and Lecturers

This study assessed inhalation exposure to particulate matter (PM₁)-bound mercury (Hg_p) and PM₁-bound polycyclic aromatic hydrocarbons (PAHs) among university students. For this purpose, simultaneous indoor (I) and outdoor (O) measurements were taken from two Polish technical universities (in Gliwice and Warsaw) located in distinct areas with respect to ambient concentrations and major sources of PM. The indoor geometric mean concentrations of Hg_p were found to be 1.46 pg·m⁻³ and 6.38 pg·m⁻³ in Warsaw and Gliwice, while the corresponding outdoor concentrations were slightly lower at 1.38 pg·m⁻³ and 3.03 pg·m⁻³, respectively. A distinct pattern was found with respect to PAH concentrations with estimated I/O values of 22.2 ng·m⁻³/22.5 ng·m⁻³ in Gliwice and 10.9 ng·m⁻³/11.12 ng·m⁻³ in Warsaw. Hazard quotients (HQs) as a result of exposure to Hg_p for students aged 21 ranged from 3.47 × 10⁻⁵ (Warsaw) to 1.3 × 10⁻⁴ (Gliwice) in terms of reasonable maximum exposure (RME). The non-cancer human health risk value related to Hg_p exposure was thus found to be below the acceptable risk level value of 1.0 given by the US EPA. Daily exposure values for lecture hall occupants, adjusted to the benzo(a)pyrene (BaP) toxicity equivalent (BaP_eq), were 2.9 and 1.02 ng·m⁻³ for the Gliwice and Warsaw students, respectively. The incremental lifetime cancer risk (ILCR) values with respect to exposure to PM₁-bound PAHs during the students’ time of study were 5.49 × 10⁻⁸ (Warsaw) and 1.43 × 10⁻⁷ (Gliwice). Thus, students’ exposure to indoor PAHs does not lead to increased risk of lung cancer.

Current progress on understanding the impact of mercury on human health

Mercury pollution and its impacts on human health is of global concern. The authors of this paper were members of the Plenary Panel on Human Health in the 12th International Conference on Mercury as a Global Pollutant held in Korea in June 2015. The Panel was asked by the conference organizers to address two questions: what is the current understanding of the impacts of mercury exposure on human health and what information is needed to evaluate the effectiveness of the Minamata Convention in lowering exposure and preventing adverse effects. The authors conducted a critical review of the literature published since January 2012 and discussed the current state-of-knowledge in the following areas: environmental exposure and/or risk assessment; kinetics and biomonitoring; effects on children development; effects on adult general populations; effects on artisanal and small-scale gold miners (ASGM); effects on dental workers; risk of ethylmercury in thimerosal-containing vaccines; interactions with nutrients; genetic determinants and; risk communication and management. Knowledge gaps in each area were identified and recommendations for future research were made. The Panel concluded that more knowledge synthesis efforts are needed to translate the research results into management tools for health professionals and policy makers.

Essential Indicators Identifying Chronic Inorganic Mercury Intoxication: Pooled Analysis across Multiple Cross-Sectional Studies

Background

The continuous exposure to inorganic mercury vapour in artisanal small-scale gold mining (ASGM) areas leads to chronic health problems. It is therefore essential to have a quick, but reliable risk assessing tool to diagnose chronic inorganic mercury intoxication. This study re-evaluates the state-of-the-art toolkit to diagnose chronic inorganic mercury intoxication by analysing data from multiple pooled cross-sectional studies. The primary research question aims to reduce the currently used set of indicators without affecting essentially the capability to diagnose chronic inorganic mercury intoxication. In addition, a sensitivity analysis is performed on established biomonitoring exposure limits for mercury in blood, hair, urine and urine adjusted by creatinine, where the biomonitoring exposure limits are compared to thresholds most associated with chronic inorganic mercury intoxication in artisanal small-scale gold mining.

Methods

Health data from miners and community members in Indonesia, Tanzania and Zimbabwe were obtained as part of the Global Mercury Project and pooled into one dataset together with their biomarkers mercury in urine, blood and hair. The individual prognostic impact of the indicators on the diagnosis of mercury intoxication is quantified using logistic regression models. The selection is performed by a stepwise forward/backward selection. Different models are compared based on the Bayesian information criterion (BIC) and Cohen`s kappa is used to evaluate the level of agreement between the diagnosis of mercury intoxication based on the currently used set of indicators and the result based on our reduced set of indicators. The sensitivity analysis of biomarker exposure limits of mercury is based on a sequence of chi square tests.

Results

The variable selection in logistic regression reduced the number of medical indicators from thirteen to ten in addition to the biomarkers. The estimated level of agreement using ten of thirteen medical indicators and all four biomarkers to diagnose chronic inorganic mercury intoxication yields a Cohen`s Kappa of 0.87. While in an additional stepwise selection the biomarker blood was not selected, the level of agreement based on ten medical indicators and only the three biomarkers urine, urine/creatinine and hair reduced Cohen`s Kappa to 0.46. The optimal cut-point for the biomarkers blood, hair, urine and urine/creatinine were estimated at 11. 6 μg/l, 3.84 μg/g, 24.4 μg/l and 4.26 μg/g, respectively.

Conclusion

The results show that a reduction down to only ten indicators still allows a reliable diagnosis of chronic inorganic mercury intoxication. This reduction of indicators will simplify health assessments in artisanal small-scale gold mining areas.

Polymorphisms in genes encoding potential mercury transporters and urine mercury concentrations in populations exposed to mercury vapor from gold mining

BACKGROUND

Elemental mercury (Hg0) is widely used in small-scale gold mining. Persons working or living in mining areas have high urinary concentrations of Hg (U-Hg). Differences in genes encoding potential Hg-transporters may affect uptake and elimination of Hg.

OBJECTIVE

We aimed to identify single nucleotide polymorphisms (SNPs) in Hg-transporter genes that modify U-Hg.

METHODS

Men and women (1,017) from Indonesia, the Philippines, Tanzania, and Zimbabwe were classified either as controls (no Hg exposure from gold mining) or as having low (living in a gold-mining area) or high exposure (working as gold miners). U-Hg was analyzed by cold-vapor atomic absorption spectrometry. Eighteen SNPs in eight Hg-transporter genes were analyzed.

RESULTS

U-Hg concentrations were higher among ABCC2/MRP2 rs1885301 A-allele carriers than among GG homozygotes in all populations, though differences were not statistically significant in most cases. MRP2 SNPs showed particularly strong associations with U-Hg in the subgroup with highest exposure (miners in Zimbabwe), whereas rs1885301 A-allele carriers had higher U-Hg than GG homozygotes [geometric mean (GM): 36.4 µg/g creatinine vs. 21.9; p = 0.027], rs2273697 GG homozygotes had higher U-Hg than A-allele carriers (GM: 37.4 vs. 16.7; p = 0.001), and rs717620 A-allele carriers had higher U-Hg than GG homozygotes (GM: 83 vs. 28; p = 0.084). The SLC7A5/LAT1 rs33916661 GG genotype was associated with higher U-Hg in all populations (statistically significant for all Tanzanians combined). SNPs in SLC22A6/OAT1 (rs4149170) and SLC22A8/OAT3 (rs4149182) were associated with U-Hg mainly in the Tanzanian study groups.

CONCLUSIONS

SNPs in putative Hg-transporter genes may influence U-Hg concentrations.

Estimating human indoor exposure to elemental mercury from broken compact fluorescent lamps (CFLs)

The 2008 EU regulation, which prohibits conventional incandescent light bulbs, is to be implemented in phases, completing in 2012. One of the possible substitutes is the compact fluorescent lamp (CFL), which, however, does contain up to 5 mg of mercury in its elemental or amalgamated form. The question arises as to the possible exposure of individuals to mercury as a result of lamp breakage during operation or when disconnected from the power supply. Therefore, an apparatus was built to shatter CFLs and drop the shards onto glycol-modified polyethylene terephthalate, a carpeted floor, or laminate floor under defined climatic parameters and operating conditions. Six CFLs of different types and mercury content were studied. After the breakage of a common CFL containing liquid mercury, concentrations up to 8000 ng/m(3) were reached in the chamber. Much lower peak values were obtained with amalgam-type lamps (414 ng/m(3)) or with lamps with a shatter-proof coating (60 ng/m(3)). It was found that ventilation can considerably reduce the indoor air concentration within 20 min. Acute health effects would only be expected if the mercury is not removed immediately. Careful collection and disposal of the lamp fragments would also prevent dwellers from the risk of long-term exposure.

PRACTICAL IMPLICATIONS

After accidental breakage of a compact fluorescent lamp (CFL) indoors, dwellers could be exposed to high mercury concentrations. From the results of our studies in test chambers and real rooms using different lamp types and scenarios, it was possible to estimate the possible human uptake of mercury by inhalation. Immediate action is important to reduce indoor mercury concentrations to a minimum level. The first step is to maximize ventilation followed by careful collection of spilled mercury.

Mercury exposure and risks from dental amalgam in the US population, post-2000

Dental amalgam is 50% metallic mercury (Hg) by weight and Hg vapour continuously evolves from in-place dental amalgam, causing increased Hg content with increasing amalgam load in urine, faeces, exhaled breath, saliva, blood, and various organs and tissues including the kidney, pituitary gland, liver, and brain. The Hg content also increases with maternal amalgam load in amniotic fluid, placenta, cord blood, meconium, various foetal tissues including liver, kidney and brain, in colostrum and breast milk. Based on 2001 to 2004 population statistics, 181.1 million Americans carry a grand total of 1.46 billion restored teeth. Children as young as 26 months were recorded as having restored teeth. Past dental practice and recently available data indicate that the majority of these restorations are composed of dental amalgam. Employing recent US population-based statistics on body weight and the frequency of dentally restored tooth surfaces, and recent research on the incremental increase in urinary Hg concentration per amalgam-filled tooth surface, estimates of Hg exposure from amalgam fillings were determined for 5 age groups of the US population. Three specific exposure scenarios were considered, each scenario incrementally reducing the number of tooth surfaces assumed to be restored with amalgam. Based on the least conservative of the scenarios evaluated, it was estimated that some 67.2 million Americans would exceed the Hg dose associated with the reference exposure level (REL) of 0.3 μg/m(3) established by the US Environmental Protection Agency; and 122.3 million Americans would exceed the dose associated with the REL of 0.03 μg/m(3) established by the California Environmental Protection Agency. Exposure estimates are consistent with previous estimates presented by Health Canada in 1995, and amount to 0.2 to 0.4 μg/day per amalgam-filled tooth surface, or 0.5 to 1 μg/day/amalgam-filled tooth, depending on age and other factors.

Air mercury contamination in the gold mining town of Portovelo, Ecuador

Portovelo is one of the oldest gold mining towns in Ecuador. Artisanal gold mining still uses mercury in the process of gold recovery. In this study, mercury concentrations in the air of Portovelo were evaluated. High mercury levels in the ambient were found in El Pache sector, where most gold mining processing plants are located. These varied between 2,356.7 ± 1,807.6 and 3,699.5 ± 1,225.3 ng/m(3) during the rainy and dry seasons, respectively. Lower levels were detected in the urban (central) area of Portovelo, with 214.6 ± 43.7 ng/m(3) in the rainy season and 574.2 ± 72.8 ng/m(3) in the dry season, exceeding the Agency for Toxic Substances and Disease Registry minimum risk level of 200 ng/m(3). Average mercury concentrations in exhaled air from miners, measured before and after amalgam burning ranged between 179-1,352 and 2,007-3,389 ng/m(3), respectively. These data suggest Portovelo air is polluted with mercury and humans are being dangerously exposed. Therefore, strong actions must be undertaken to protect human and environmental health, including changing gold recovery systems.

Mercury exposure and children's health

Acute or chronic mercury exposure can cause adverse effects during any period of development. Mercury is a highly toxic element; there is no known safe level of exposure. Ideally, neither children nor adults should have any mercury in their bodies because it provides no physiological benefit. Prenatal and postnatal mercury exposures occur frequently in many different ways. Pediatricians, nurses, and other health care providers should understand the scope of mercury exposures and health problems among children and be prepared to handle mercury exposures in medical practice. Prevention is the key to reducing mercury poisoning. Mercury exists in different chemical forms: elemental (or metallic), inorganic, and organic (methylmercury and ethyl mercury). Mercury exposure can cause acute and chronic intoxication at low levels of exposure. Mercury is neuro-, nephro-, and immunotoxic. The development of the child in utero and early in life is at particular risk. Mercury is ubiquitous and persistent. Mercury is a global pollutant, bio-accumulating, mainly through the aquatic food chain, resulting in a serious health hazard for children. This article provides an extensive review of mercury exposure and children's health.