Environmental contamination and risk assessment of mercury from a historic mercury mine located in southwestern China

New Insights into MeHg Accumulation in Rice (Oryza sativa L.): Evidence from Cysteine

The intake of methylmercury (MeHg)-contaminated rice poses immense health risks to rice consumers. However, the mechanisms of MeHg accumulation in rice plants are not entirely understood. The knowledge that the MeHg-Cysteine complex was dominant in polished rice proposed a hypothesis of co-transportation of MeHg and cysteine inside rice plants. This study was therefore designed to explore the MeHg accumulation processes in rice plants by investigating biogeochemical associations between MeHg and amino acids. Rice plants and underlying soils were collected from different Hg-contaminated sites in the Wanshan Hg mining area. The concentrations of both MeHg and cysteine in polished rice were higher than those in other rice tissues. A significant positive correlation between MeHg and cysteine in rice plants was found, especially in polished rice, indicating a close geochemical association between cysteine and MeHg. The translocation factor (TF) of cysteine showed behavior similar to that of the TF of MeHg, demonstrating that these two chemical species might share a similar transportation mechanism in rice plants. The accumulation of MeHg in rice plants may vary due to differences in the molar ratios of MeHg to cysteine and the presence of specific amino acid transporters. Our results suggest that cysteine plays a vital role in MeHg accumulation and transportation inside rice plants.

Mercury pollution risks of agricultural soils and crops in mercury mining areas in Guizhou Province, China: effects of large mercury slag piles

The historical large mercury slag piles still contain high concentrations of mercury and their impact on the surrounding environment has rarely been reported. In this study, three different agricultural areas [the area with untreated piles (PUT), the area with treated piles (PT), and the background area with no piles (NP)] were selected to investigate mercury slag piles pollution in the Tongren mercury mining area. The mercury concentrations of agricultural soils ranged from 0.42 to 155.00 mg/kg, determined by atomic fluorescence spectrometry of 146 soil samples; and mercury concentrations in local crops (rice, maize, pepper, eggplant, tomato and bean) all exceeded the Chinese food safety limits. Soil and crop pollution trends in the three areas were consistent as PUT > PT > NP, indicating that mercury slag piles have exacerbated pollution. Mercury in the slag piles was adsorbed by multiple pathways of transport into soils with high organic matter, which made the ecological risk of agricultural soils appear extremely high. The total hazard quotients for residents from ingesting mercury in these crops were unacceptable in all areas, and children were more likely to be harmed than adults. Compared to the PT area, treatment of slag piles in the PUT area may decrease mercury concentrations in paddy fields and dry fields by 46.02% and 70.36%; further decreasing health risks for adults and children by 47.06% and 79.90%. This study provided a scientific basis for the necessity of treating large slag piles in mercury mining areas.

A comprehensive assessment to offer optimized remediation method for mercury contamination in Musa Bay by using hybrid Fuzzy AHP-VIKOR approach

Musa Bay, the largest wetland in Iran and one of the most important Hg-polluted media, plays a significant role in the ecosystem of the area and supports many forms of life. Mercury pollution has detrimental effects on the human body and at high levels leads to the loss of microorganisms in marine ecosystems. Hence, a comprehensive assessment for selecting an effective and sustainable remediation method is crucial to restoring the ecosystem promptly. The determination of a proper and practical treatment method not only is a case-based approach, but could be challenging due to its multi-criteria decision-making nature. Considering preferred crucial factors involved in the effectiveness of remedial actions, in this study a questionnaire is designed to assess the opinion of environmental experts, stakeholders, and some occupants of the area on remedial actions based on the importance weights of criteria. Subsequently, practical remediation and management strategies ranked by hybrid FVIKOR as a multi-criteria decision making (MCDM) method. Ranking results show that dredging and stabilization could offer a promising solution for the remediation of the case study. The results of the study demonstrate that the development of MCDM methods along with effective criteria and considering the analysis of the questionnaires, could offer the best remediation strategy for a specific contaminated site.

Heavy Metals and Human Health: Possible Exposure Pathways and the Competition for Protein Binding Sites

Heavy metals enter the human body through the gastrointestinal tract, skin, or via inhalation. Toxic metals have proven to be a major threat to human health, mostly because of their ability to cause membrane and DNA damage, and to perturb protein function and enzyme activity. These metals disturb native proteins’ functions by binding to free thiols or other functional groups, catalyzing the oxidation of amino acid side chains, perturbing protein folding, and/or displacing essential metal ions in enzymes. The review shows the physiological and biochemical effects of selected toxic metals interactions with proteins and enzymes. As environmental contamination by heavy metals is one of the most significant global problems, some detoxification strategies are also mentioned.

Mobility, spatial variation and human health risk assessment of mercury in soil from an informal e-waste recycling site, Lagos, Nigeria

Spatial variations and mobility of mercury (Hg) and Hg associations with other potentially toxic elements (PTEs) were studied in soil samples from Alaba, the largest e-waste recycling site in Nigeria and West Africa. Total Hg concentration was determined in surface soil samples from various locations using cold vapour atomic absorption spectrometry (CVAAS) following microwave-assisted acid extraction, while sequential extraction was used to determine operationally defined mobility. The concentrations of the PTEs arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) metals were determined using inductively coupled plasma mass spectrometry (ICP-MS) following microwave-assisted digestion with aqua regia. Total Hg concentration ranged from < 0.07 to 624 mg/kg and was largely dependent on the nature and intensity of e-waste recycling activities carried out. Mobile forms of Hg, which may be HgO (a known component of some forms of e-waste), accounted for between 3.2 and 23% of the total Hg concentration, and were observed to decrease with increasing organic matter (OM). Non-mobile forms accounted for >74% of the total Hg content. In the main recycling area, soil concentrations of Cd, Cd, Cu, Hg, Mn, Ni, Pb and Zn were above soil guideline values (Environment Agency in Science Report, 2009; Kamunda et al., 2016). Strong associations were observed between Hg and other PTEs (except for Fe and Zn) with the correlational coefficient ranging from 0.731 with Cr to 0.990 with As in April, but these correlations decreased in June except for Fe. Hazard quotient values > 1 at two locations suggest that Hg may pose health threats to people working at the e-waste recycling site. It is therefore recommended that workers should be investigated for symptoms of Hg exposure.

Improving the regulatory health risk assessment of mercury-contaminated sites

An alternative risk assessment strategy for mercury (Hg)-contaminated sites is proposed with bioaccessible fractions and soil Hg vapor (SHgV) concentrations. The new strategy avoids the conservatism of assessment rely on soil total Hg (THg) content and inaccuracy caused by predicted SHgV concentration. The exposure risk to Hg-contaminated soil associated with historical mining activities in Guizhou, China, was evaluated using the proposed strategy. The experimental results revealed that the average bioaccessibility in gastric, intestinal and lung phases was 10.39 % (2.09 % ∼ 35.28 %), 1.28 % (0.23 % ∼ 4.3 %), and 11.27 % (5.04 % ∼ 20.71 %), respectively. Via the proposed strategy, the Hg risk for the oral ingestion pathway, represented as the hazard quotient (HQ), decreased from 1.57 to an acceptable level of 0.19 (<1). The risk of SHgV inhalation sharply decreased from 1168 to 0.35 while the soil PM₁₀ inhalation pathway did not exhibit significant variations. The dominant exposure pathways turned to oral intake and inhalation of SHgV by the strategy. The results indicated that the proposed assessment strategy can greatly improve the understanding of the exposure risk level at Hg-contaminated sites and provide a reasonable decision basis for decision makers.

Multi-pathway mercury health risk assessment, categorization and prioritization in an abandoned mercury mining area: A pilot study for implementation of the Minamata Convention

This is a systematic study of human health risk assessment (HHRA) and risk categorization for inorganic mercury (IHg) and methylmercury (MeHg) in Hg mining areas. A multi-pathway exposure model coupled with Monte Carlo simulation was constructed for the Wanshan Hg mining area (WSMM), Southwestern China, with consideration of oral ingestion (foodstuffs, water and soil), dermal contact (water and soil), and inhalation (gaseous Hg and particulate Hg). The results show that dietary intake (food and water), gaseous Hg inhalation, oral ingestion of soil particles, dermal contact, and particulate Hg inhalation comprised 88.3-96.3%, 3.49-6.14%, 0.14-5.3%, 0.02%, and <0.01% of total IHg ingestion, respectively. As expected, rice consumption contributed the highest proportion (86.3-92.7%) of MeHg. The study shows that the elevated MeHg exposure risk is the most significant issue in Hg mining areas. In addition, Hg risk categorization and prioritization in the WSMM are established for the first time based on rice-based exposure doses of IHg and MeHg. Target areas for future treatment and/or remediation are characterized according to thresholds of reference dose and provisional tolerable weekly intake for exposure doses, as well as risk screening values and risk control values for contaminated soil. The proposed multi-pathway exposure model is strongly recommended for the HHRA of Hg-contaminated sites worldwide and helps facilitate the implementation of the Minamata Convention on Mercury.

Risk Assessment Methods in Mining Industry—A Systematic Review

Recently, there has been a growing interest in the mining industry in issues related to risk assessment and management, which is confirmed by a significant number of publications and reports devoted to these problems. However, theoretical and application studies have indicated that risk in mining should be analyzed not only in the human factor aspect, but also in strategic (environmental impact) and operational ones. However, there is a lack of research on systematic literature reviews and surveys of studies that would focus on these identified risk aspects simultaneously. Therefore, the purpose of this article is to develop a literature review in the area of analysis, assessment and risk management in the mining sector, published in the last decade and based on the concept of a human engineering system. Following this, a systematic search was performed with the use of Primo multi-search tool following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The main inclusion criteria were: (a) not older than 10 years, (b) article written in English, (c) publication type (scientific article, book, book chapter), (d) published in chosen electronic collections (Springer, Taylor and Francis, Elsevier, Science Direct, JSTOR). This resulted in the selection of the 94 most relevant papers in the area. First, the general bibliometric analysis was conducted. Later, the selected papers in this review were categorized into four groups and the critical review was developed. One of the main advantages of this study is that the results are obtained from different scientific sources/databases thanks to using a multi-search tool. Moreover, the authors identified the main research gaps in the area of the implementation of risk management in the mining industry.

Endoplasmic reticulum stress participates in the pathophysiology of mercury-caused acute kidney injury

Acute exposure to mercury chloride (HgCl₂) causes acute kidney injury (AKI). Some metals interfere with protein folding, leading to endoplasmic reticulum stress (ERS), and the activation of cell death mechanisms, but in the case of mercury, there is no knowledge about whether the ERS mediates tubular damage. This study aimed to determinate if HgCl₂ causes an AKI course with temporary activation of ERS and if this mechanism is involved in kidney cell death. Male mice were intoxicated with 5 mg/kg HgCl₂ and sacrificed after 24, 48, 72, and 96 h of mercury administration. The kidneys of euthanized mice were used to assess the renal function, oxidative stress, redox environment, antioxidant enzymatic system, cell death, and reticulum stress markers (PERK, ATF-6, and IRE1α pathways). The results indicate temporary-dependent renal dysfunction, oxidative stress, and an increase of glutathione-dependent enzymes involved in the bioaccumulation process of mercury, as well as the enhancement of caspase 3 activity along with IRE1a, GADD-153, and caspase 12 expressions. Mercury activates the PERK/eIF2α branch during the first 48 h. Meanwhile, the activation of PERK/ATF-4 branch allowed for ATF-4, ATF-6, and IRE1α pathways to enhance GADD-153. It led to the activation of caspases 12 and 3, which mediated the deaths of the tubular and glomerular cells. This study revealed temporary-dependent ERS present during AKI caused by HgCl₂, as well as how it plays a pivotal role in kidney cell damage.

Water-soluble mercury induced by organic amendments affected microbial community assemblage in mercury-polluted paddy soil

Mercury (Hg) pollution or organic amendments (OA) may individually induce changes in the microbial community of paddy soils. However, little is known regarding the interaction of Hg and OA and the effect of different OA applications on the microbial community assemblage in Hg-polluted paddy soil. A soil incubation experiment was performed by applying three organic amendments (OA), namely a food-waste compost (FC), and its HA and FA, into an Hg-polluted paddy soil to examine the changes in the microbial community and merA/merB gene abundance. The results showed that the OA treatments promoted total (SOC) and dissolved organic carbon (DOC) in soils, which may harbor copiotrophic bacteria. The HA and FA treatments decreased microbial diversity and richness along with an increase of water-soluble Hg (WHg) through the complexation of DOC to Hg, which may be mainly attributed to the enhanced Hg biotoxicity to soil microbiome induced by the increased WHg under these two treatments. Additionally, the WHg enhancement also contributed to the increase of Hg-resistant bacteria and merA/merB gene abundance, and consequently, induced changes in the microbial community. These results indicated the interaction of Hg and different OA induced the variation of WHg fraction in paddy soil, which played a fundamental role in the distinct responses of the microbial community assemblage. Collectively, the application of FA and HA to Hg-polluted soil should be limited considering Hg risk to microbiome, and FC can be an alternative.

Indicative and complementary effects of human biological indicators for heavy metal exposure assessment

Although human biological indicators have been widely utilized for biomonitoring environmental pollutants in health exposure assessment, the relationship between internal and external exposure has not yet been adequately established. In this study, we collected and analyzed 61 rice, 56 pepper, and 58 soil samples, together with 107 hair, 107 blood, and 107 urine samples from residents living in selected intensive mining areas in China. Concentrations of most of the four elements considered (Pb, Cd, Hg, and Se) exceeded national standards, implying high exposure risk in the study areas. Regression analysis also revealed a correlation (0.33, P < 0.001) between the concentration of Pb in soil and that in human hair (as well as in human blood); to some extent, Pb content in hair and blood could therefore be used to characterize external Pb exposure. The correlation between Hg in rice and in human hair (up to 0.5, P < 0.001) further confirmed a significant indicative effect of human hair for Hg exposure. A significant correlation was also noted between concentrations of some elements in different human samples, for example, between Hg in hair and blood (0.641, P < 0.01) and between Cd in urine and blood (0.339, P < 0.01). To some extent, there could thus be mutual reflectance of the same heavy metal in different samples, with the possibility for complementary use in assessing heavy metal exposure.

Water Consumption as Source of Arsenic, Chromium, and Mercury in Children Living in Rural Yucatan, Mexico: Blood and Urine Levels

Studies investigating the correlation between metal content in water and metal levels in children are scarce worldwide, but especially in developing nations. Therefore, this study investigates the correlation between arsenic, chromium, and mercury concentrations in drinking and cooking water and in blood and urine samples collected from healthy and supposedly non-exposed children from a rural area in Yucatan, Mexico. Mercury in water shows concentrations above the recommended World Health Organization (WHO) value for drinking and cooking water. Also, 25% of the children show mercury in urine above the WHO recommended value. Multivariate analyses show a significant role for drinking and cooking water as a vector of exposure in children. Also, the factor analysis shows chronic exposure in the case of arsenic, as well as an ongoing detoxification process through urine in the case of mercury. Further studies should be done in order to determine other potential metal exposure pathways among children.

Distribution and health risk assessment to heavy metals near smelting and mining areas of Hezhang, China

Mining and smelting areas in Hezhang have generated a large amount of heavy metals into the environment. For that cause, an evaluative study on human exposure to heavy metals including Co, Ni, Cu, Zn, Cr, As, Cd, Pb, Sb, Bi, Be, and Hg in hair and urine was conducted for their concentrations and correlations. Daily exposure and non-carcinogenic and carcinogenic risk were estimated. Sixty-eight scalp hair and 66 urine samples were taken from participants of different ages (6-17, 18-40, 41-60, and ≥ 65 years) living in the vicinity of an agricultural soil near mine and smelting areas. The results compared to the earlier studies showed an elevated concentration of Pb, Be, Bi, Co, Cr, Ni, Sb, and Zn in hair and urine. These heavy metals were more elevated in mining than in smelting. Considering gender differences, females were likely to be more affected than male. By investigating age differences in this area, high heavy metal concentrations in male's hair and urine existed in age of 18-40 and ≥ 66, respectively. However, females did not present homogeneous age distribution. Hair and urine showed a different distribution of heavy metals in different age and gender. In some cases, significant correlation was found between heavy metals in hair and urine (P > 0.05 and P > 0.01) in mining area. The estimated average daily intake of heavy metals in vegetables showed a great contribution compared to the soil and water. Non-carcinogenic and carcinogenic risk values of total pathways in mining and smelting areas were higher than 1 and exceeded the acceptable levels. Thus, the obtained data might be useful for further studies. They can serve as a basis of comparison and assessing the effect of simultaneous exposure from heavy metals in mining and smelting areas, and potential health risks from exposure to heavy metals in vegetables need more consideration.

Low-level prenatal mercury exposure in north China: an exploratory study of anthropometric effects

In order to investigate anthropometric effects of mercury (Hg) exposure, we examined the status of human prenatal exposure to Hg species, including total mercury (THg), methylmercury (MeHg) and inorganic mercury (IHg), in North China, as well as their potential effects on fetal and infant growth. Hg concentrations in various bioindicators were measured from 50 Chinese women and newborns in 2011. The participants were followed for 12 months to collect anthropometric information. Linear and two-level regression analyses were performed to determine the associations between Hg levels and body growth. The geometric mean levels of THg in the placenta, cord blood, fetal hair, and maternal blood, hair, and urine were 25.88 μg/kg dry wt, 2.73 μg/L, 572.98 μg/kg, 2.29 μg/L, 576.54 μg/kg, and 0.58 μg/g creatinine, respectively. Nearly 100% of Hg presented as IHg in urine, and the percentage of IHg in other bioindicators was 14.86-48.73%. We observed significantly negative associations between Hg levels in some matrixes and anthropometry of neonates (weight and height) and infants (height) (p < 0.05). THg levels in maternal hair were also negatively associated with infant growth rate of weight during 12 months after delivery (p = 0.017). This study suggests that low-level prenatal Hg exposure could play a role in attenuating fetal and infant growth, and the effects of MeHg and IHg are different.

Speciation and bioaccessibility of mercury in adobe bricks and dirt floors in Huancavelica, Peru

Huancavelica, Peru, a historic cinnabar refining site, is one of the most mercury (Hg)-contaminated urban areas in the world. Exposure is amplified because residents build their adobe brick homes from contaminated soil. The objectives of this study were to compare two Hg-leaching procedures, and their application as risk-assessment screening tools in Hg-contaminated adobe brick homes in Huancavelica. The purpose was to evaluate potential health implications, particularly for children, after ingestion of Hg-contaminated particles. Hg was measured in adobe brick and dirt floor samples from 60 households by total Hg extraction, simulated gastric fluid (GF) extraction, and sequential selective extraction (SSE), which provides more detailed data but is resource-intensive. Most of the Hg present in samples was relatively insoluble, although in some households soluble Hg species were present at concentrations that may be of concern after ingestion. A strong correlation was identified between results from simulated GF extraction of adobe bricks and dirt floors and the more soluble fractions of Hg from SSE. Simulated GF extraction data were combined with ingestion and body mass characteristics for small children to compare potential risk of ingestion of Hg-contaminated soil with current health standards. Simulated GF extraction can be used as a risk assessment screening tool for effective allocation of time and resources to households that have measurable concentrations of bioaccessible Hg. Combining simulated GF extraction data with health standards enables intervention strategies targeted at households with the greatest potential health threat from ingestion of Hg-contaminated particles.

Rice methylmercury exposure and mitigation: a comprehensive review

Rice cultivation practices from field preparation to post-harvest transform rice paddies into hot spots for microbial mercury methylation, converting less-toxic inorganic mercury to more-toxic methylmercury, which is likely translocated to rice grain. This review includes 51 studies reporting rice total mercury and/or methylmercury concentrations, based on rice (Orzya sativa) cultivated or purchased in 15 countries. Not surprisingly, both rice total mercury and methylmercury levels were significantly higher in polluted sites compared to non-polluted sites (Wilcoxon rank sum, p<0.001). However, rice percent methylmercury (of total mercury) did not differ statistically between polluted and non-polluted sites (Wilcoxon rank sum, p=0.35), suggesting comparable mercury methylation rates in paddy soil across these sites and/or similar accumulation of mercury species for these rice cultivars. Studies characterizing the effects of rice cultivation under more aerobic conditions were reviewed to determine the mitigation potential of this practice. Rice management practices utilizing alternating wetting and drying (instead of continuous flooding) caused soil methylmercury levels to spike, resulting in a strong methylmercury pulse after fields were dried and reflooded; however, it is uncertain whether this led to increased translocation of methylmercury from paddy soil to rice grain. Due to the potential health risks, it is advisable to investigate this issue further, and to develop separate water management strategies for mercury polluted and non-polluted sites, in order to minimize methylmercury exposure through rice ingestion.

Hair mercury concentrations and associated factors in an electronic waste recycling area, Guiyu, China

OBJECTIVE

Toxic heavy metals are released to the environment constantly from unregulated electronic waste (e-waste) recycling in Guiyu, China, and thus may contribute to the elevation of mercury (Hg) and other heavy metals levels in human hair. We aimed to investigate concentrations of mercury in hair from Guiyu and potential risk factors and compared them with those from a control area where no e-waste processing occurs.

METHODS

A total of 285 human hair samples were collected from three villages (including Beilin, Xianma, and Huamei) of Guiyu (n=205) and the control area, Jinping district of Shantou city (n=80). All the volunteers were administered a questionnaire regarding socio-demographic characteristics and other possible factors contributed to hair mercury concentration. Hair mercury concentration was analyzed by hydride generation atomic fluorescence spectrometry (AFS).

RESULTS

Our results suggested that hair mercury concentrations in volunteers of Guiyu (median, 0.99; range, 0.18-3.98μg/g) were significantly higher than those of Jinping (median, 0.59; range, 0.12-1.63μg/g). We also observed a higher over-limit ratio (>1μg/g according to USEPA) in Guiyu than in Jinping (48.29% vs. 11.25%, P<0.001). Logistic regression model showed that the variables of living house also served as an e-waste workshop, work related to e-waste, family income, time of residence in Guiyu, the distance between home and waste incineration, and fish intake were associated with hair mercury concentration. After multiple stepwise regression analysis, in the Guiyu samples, hair mercury concentration was found positively associated with the time residence in Guiyu (β=0.299, P<0.001), and frequency of shellfish intake (β=0.184, P=0.016); and negatively associated with the distance between home and waste incineration (β=-0.190, P=0.015) and whether house also served as e-waste workshop (β=-0.278, P=0.001).

CONCLUSIONS

This study investigated human mercury exposure and suggested elevated hair mercury concentrations in an e-waste recycling area, Guiyu, China. Living in Guiyu for a long time and work related to e-waste may primarily contribute to the high hair mercury concentrations.