Environmental assessment of mercury contamination from the Rwamagasa artisanal gold mining centre, Geita District, Tanzania

Elevated total mercury (THg) levels in water sources under the influence of artisanal and small-scale gold mining (ASGM) in Tanzania

This study investigated the presence and distribution of mercury in water bodies under the influence of artisanal and small-scale mining (ASGM) activities in Tanzania, which continue to predominantly rely on mercury for gold extraction. Various water bodies available for domestic and animal use in mining communities were sampled from surface water sources in ASGM settlements during the rainy and dry seasons. Water samples were analysed using cold vapour atomic fluorescence spectrophotometer (CVAFS). The results indicate that most of water sources had THg levels above the WHO guideline of 1.0 µg/L (1000 ng/L) for safe drinking water. The levels were significantly higher during the wet season ranging from 3.4 to 96.3 µg/L, whereas the range was from 0.84 to 2.12 µg/L during the dry period. The higher THg values during the wet season are likely a result of increased lateral transport (e.g. via enhanced runoff) and physical properties of the waterways. Transportation and resuspension of matrix-bound mercury from surface soils and inflow of contaminated water from unprotected tailings were also observed to be potential means of lateral mercury transport. The lowest concentrations (0.846 µg/L) were observed in water samples from the Mabubi River, upstream of a mining village. Downstream of the mining village in the same river, higher concentrations were observed in the Nungwe Bay region of Lake Victoria. In other surveyed mining settlements where there were no nearby rivers, pool water indicated high concentrations of THg, including levels above thresholds for safe human use. Immediate stringent measures are needed in order to ensure human and animal safety at ASGM mining settlements. Future investigation is suggested to focus on the distribution of mercury in different media, assessing the prevalence of different mercury species, and investigating the influence of weather and hydrological conditions on the impacts of mercury to organisms as part of the strategies to mitigate mercury pollution.

Risks to Human Health from Mercury in Gold Mining in the Coastal Region of Ecuador

Artisanal and small-scale gold mining (ASGM) plays a crucial role in global gold production. However, the adoption of poor mining practices or the use of mercury (Hg) in gold recovery processes has generated serious environmental contamination events. The focus of this study is assessing the concentration of Hg in surface waters within the coastal region of Ecuador. The results are used to conduct a human health risk assessment applying deterministic and probabilistic methods, specifically targeting groups vulnerable to exposure in affected mining environments. Between April and June 2022, 54 water samples were collected from rivers and streams adjacent to mining areas to determine Hg levels. In the health risk assessment, exposure routes through water ingestion and dermal contact were considered for both adults and children, following the model structures outlined by the U.S. Environmental Protection Agency. The results indicate elevated Hg concentrations in two of the five provinces studied, El Oro and Esmeraldas, where at least 88% and 75% of the samples, respectively, exceeded the maximum permissible limit (MPL) set by Ecuadorian regulations for the preservation of aquatic life. Furthermore, in El Oro province, 28% of the samples exceeded the MPL established for drinking water quality. The high concentrations of Hg could be related to illegal mining activity that uses Hg for gold recovery. Regarding the human health risk assessment, risk values above the safe exposure limit were estimated. Children were identified as the most vulnerable receptor. Therefore, there is an urgent need to establish effective regulations that guarantee the protection of river users in potentially contaminated areas. Finally, it is important to continue investigating the contamination caused by human practices in the coastal region.

Increasing mercury bioaccumulation and biomagnification rates of Nile perch (Lates niloticus L.) in Winam Gulf, Lake Victoria, Kenya

The Nile perch (Lates niloticus L.) commercial fishery for Lake Victoria in East Africa is an important source of revenue and employment. We focused on shifts in food web structure and total mercury (THg) bioaccumulation and biomagnification in Nile perch, and lower food web items collected from Winam Gulf (Kenya) sampled 24 years apart (1998 and 2022). Stable isotope carbon (δ13C) values were higher in all species from 2022 compared to 1998. Stable nitrogen isotope (δ15N) values in baseline organisms were lower in 2022 compared to 1998. In Nile perch, δ15N values were correlated with total length, but the δ15N-length regressions were steeper in 1998 compared to 2022 except for one large (158 cm) Nile perch from 1998 with an uncharacteristically low δ15N value. Total Hg concentrations were lower in lower trophic species from 2022 compared to 1998. However, the THg bioaccumulation rate (as a function of fish length) in Nile perch was greater in 2022 compared to 1998 resulting in 24.2 % to 42.4 % higher wet weight dorsal THg concentrations in 2022 Nile perch for market slot size (50 to 85 cm) fish. The contrasting observations of increased THg bioaccumulation with size in 2022 against decreases in the rate of trophic increase with size and lower THg concentrations of lower food web items imply reduced fish growth and potential bioenergetic stressors on Winam Gulf Nile perch. All samples except 1 large Nile perch (139 cm total length collected in 2022) had THg concentrations below the European Union trade limit (500 ng/g wet weight). However, for more vulnerable individuals (women, children and frequent fish eaters), we recommend a decrease in maximum monthly meal consumption for 55-75 cm Nile perch from 16 meals per month calculated for 1998 to a limit of 8 meals per month calculated for 2022.

Prenatal arsenic and mercury levels among women practicing geophagy in areas with artisanal and small-scale gold mining activities, Northwestern Tanzania

BACKGROUND

Artisanal and small-scale gold mining (ASGM) areas potentially pose increased exposure to arsenic and mercury through community contamination, occupations at gold mines, and/or geophagy when soil is locally sourced. This study examined the effects of geophagy, a deliberate soil eating practice, along with community and occupational exposures in ASGM areas on urinary arsenic and blood mercury levels among pregnant women in the Mining and Health Longitudinal Cohort in northwestern Tanzania.

METHODS

Data on maternal arsenic and mercury levels were captured for 1056 pregnant women using an unprovoked morning urine samples and dried blood spots respectively. We used a step-wise generalized linear regression model to retain the most relevant covariates for the model. A generalized linear regression model with identity link function was used to predict the effect of geophagy practices on arsenic and mercury levels separately. The model was adjusted using sociodemographic correlates, including maternal age, education level, whether respondents lived in mining or non-mining area, years of residence, marital status, maternal occupation, individual partner's education, and occupational, and socioeconomic status.

RESULTS

In the adjusted regression model, eating soil during pregnancy increased arsenic concentration by almost 23% (β = 1.229, 95% CI: 1.094, 1.38, p < 0.001) and living in mining areas had a 21.2% (β = 1.212; 95% CI: 1.039,1.414, p = 0.014) increased risk. Geophagy significantly increased mercury levels by 13.3% (β = 1.133, 95% CI: 1.022, 1.257, p = 0.018). Living in areas with ASGM activities was associated with a 142% (β = 2.422, 95% CI: 2.111, 2.776, p < 0.0001) increase in blood mercury.

CONCLUSION

Geophagy practices increased urinary arsenic and blood mercury levels in pregnant women, which was especially true for arsenic when living in areas with ASGM activities. Working in mining = increased risk for blood mercury levels. Community-based environmental health policies should address reductions in occupational and community exposures, along with strategic geophagy reduction interventions.

Illegal mining impacts on freshwater Potamonautid crab in a subtropical Austral highland biosphere reserve

The contamination of surface water by heavy metals, especially mercury, has become a global issue. This problem is particularly exacerbated in rivers and reservoirs situated in developing nations. Therefore, the objective of this study was to evaluate the potential contamination effects of illegal gold mining activities on freshwater Potamonautid crabs and to quantify the mercury levels in 49 river sites under three land use classes: communal areas, national parks and timber plantations. We used a combination of field sampling, multivariate analysis and geospatial tools to quantify mercury concentrations in relation to crab abundances. Illegal mining was prevalent throughout the three land use classes, with mercury (Hg) being detected in 35 sites (71.5 %). The mean range of Hg concentrations detected across the three-land uses was: communal areas 0-0.1 mg kg-1, national parks 0-0.3 mg kg-1 and timber plantations 0-0.06 mg kg-1. Mean Hg geo-accumulation index values showed strong to extreme contamination in the national park, with strong contamination observed for communal areas and timber plantations; furthermore, the enrichment factor for Hg concentrations in the communal and national park areas showed extremely high enrichment. Two crab species (i.e., Potamonautes mutareensis, Potamonautes unispinus) were found in the Chimanimani area, with P. mutareensis being the dominant taxon in the region across all the three land use areas. The national parks had higher total crab abundances than communal and timber plantation areas. We observed negative and significant K, Fe, Cu and B effects on total Potamonautid crab abundances, but surprisingly not for other metals such as Hg which might reflect their widespread pollution. Thus, illegal mining was observed to impact the river system, having a serious impact on the crab abundance and habitat quality. Overall, the findings of this study underscores the need to address the issue of illegal mining within the developing world as well as to establish concerted effort from all stakeholders (e.g., government, mining companies, local communities, and civil society groups) to help protect the less charismatic and understudied taxa. In addition, addressing illegal mining and protecting understudied taxa aligns with the SDGs (e.g. SDG 14/15-life below water/life on land) and contributes to global efforts to safeguard biodiversity and promote sustainable development.

A new hazard assessment workflow to assess soil contamination from large and artisanal scale gold mining

Gold mining activities are undertaken both at large and artisanal scale, often resulting in serious 'collateral' environmental issues, including environmental pollution and hazard to human and ecosystem health. Furthermore, some of these activities are poorly regulated, which can produce long-lasting damage to the environment and local livelihoods. The aim of this study was to identify a new workflow model to discriminate anthropogenic versus geogenic enrichment in soils of gold mining regions. The Kedougou region (Senegal, West Africa) was used as a case study. Ninety-four soil samples (76 topsoils and 18 bottom soils) were collected over an area of 6,742 km2 and analysed for 53 chemical elements. Robust spatial mapping, compositional and geostatistical models were employed to evaluate sources and elemental footprint associated with geology and mining activities. Multivariate approaches highlighted anomalies in arsenic (As) and mercury (Hg) distribution in several areas. However, further interpretation with enrichment factor (EFs) and index of geoaccumulation (IGeo) emphasised high contamination levels in areas approximately coinciding with the ones where artisanal and small scale mining (ASGM) activities occur, and robust compositional contamination index (RCCI) isolated potentially harmful elements (PHE) contamination levels in very specific areas of the Kedougou mining region. The study underlined the importance of complementary approaches to identify anomalies and, more significantly, contamination by hazardous material. In particular, the analyses helped to identify discrete areas that would require to be surveyed in more detail to allow a comprehensive and thorough risk assessment, to investigate potential impacts to both human and ecosystem health.

Mercury Exposure in Two Fish Trophic Guilds from Protected and ASGM-Impacted Reservoirs in Zimbabwe and Possible Risks to Human Health

Despite a surge in mercury (Hg) pollution from artisanal and small-scale gold mining (ASGM) in Zimbabwe's drainage basins, little is known about Hg trophodynamics in the country's major reservoirs. We analyzed fish tissues for total mercury (THg) and stable isotopes of nitrogen and carbon (δ¹⁵N and δ¹³C) to compare patterns of biomagnification between two trophic guilds from a protected reservoir (Chivero) and an ASGM-impacted reservoir (Mazowe) and assessed consequences for human and fish health. Mean dry weight THg concentrations were significantly higher for both piscivorous and herbivorous fishes from Mazowe reservoir compared to fishes from similar feeding guilds in Chivero. Trophic magnification slopes (TMS), inferred from linear regressions between log₁₀[THg] and δ¹⁵N, revealed significant Hg biomagnification in Mazowe (TMS = 0.28; p < 0.05) and no evidence for Hg biomagnification in Chivero (TMS = - 0.005; p > 0.05). In Mazowe's piscivorous fishes, 32% had wet weight THg concentrations that surpassed 0.2 µg/g ww, a threshold for susceptible human populations and biochemical and gene expression alterations in fish. In addition, 17% of Mazowe's piscivorous fishes surpassed the UNEP THg toxicity threshold for human consumption (0.5 µg/g ww). To reduce exposure to Hg toxicity in humans, the maximum fish consumption for piscivorous species from Mazowe reservoir should not exceed 431 g/week for both adult male and female consumers. Our findings demonstrate the importance of creating freshwater-protected areas to prevent direct Hg contamination of aquatic ecosystems and the need for health agencies to provide fish consumption advisories to vulnerable communities.

Integrated review of the nexus between toxic elements in the environment and human health

Emerging pollutants in the environment due to economic development have become a global challenge for environmental and human health management. Potentially toxic elements (PTEs), a major group of pollutants, have been detected in soil, air, water and food crops. Humans are exposed to PTEs through soil ingestion, consumption of water, uptake of food crop products originating from polluted fields, breathing of dust and fumes, and direct contact of the skin with contaminated soil and water. The dose absorbed by humans, the exposure route and the duration (i.e., acute or chronic) determine the toxicity of PTEs. Poisoning by PTEs can lead to excessive damage to health as a consequence of oxidative stress produced by the formation of free radicals and, as a consequence, to various disorders. The toxicity of certain organs includes neurotoxicity, nephrotoxicity, hepatotoxicity, skin toxicity, and cardiovascular toxicity. In the treatment of PTE toxicity, synthetic chelating agents and symptomatic supportive procedures have been conventionally used. In addition, there are new insights concerning natural products which may be a powerful option to treat several adverse consequences. Health policy implications need to include monitoring air, water, soil, food products, and individuals at risk, as well as environmental manipulation of soil, water, and sewage. The overall goal of this review is to present an integrated view of human exposure, risk assessment, clinical effects, as well as therapy, including new treatment options, related to highly toxic PTEs.

Geogenic contaminants and groundwater quality around Lake Victoria goldfields in northwestern Tanzania

Geogenic contamination of groundwater is frequently associated with gold mining activities and related to drinking water quality problems worldwide. In Tanzania, elevated levels of trace elements (TEs) have been reported in drinking water sources within the Lake Victoria Basin, posing a serious health risk to communities. The present study aims to assess the groundwater quality with a focus on the concentration levels of geogenic contaminants in groundwater around the Lake Victoria goldfields in Geita and Mara districts. The water samples were collected from community drinking water sources and were analysed for physiochemical parameters (pH, EC, Eh), major ions, and trace elements. The analysed major ions included Na⁺, K⁺, Ca²⁺, Mg²⁺, SO₄^2-, HCO₃^- and Cl^- whereas the trace elements were As, Al, Li, Ba, B, Ti, V, U, Zr, Sr, Si, Mn Mo, Fe, Ni, Zn, Cr, Pb, Cd, and V. The present study revealed that the concentration levels of the major ions were mostly within the World Health Organization (WHO) drinking water standards in the following order of their relative abundance; for cations, Ca²⁺∼Na⁺>Mg²⁺>K⁺ and for anions was HCO₃^- > SO₄^2- > NO₃^-, Cl^- > PO₄^3-. Statistical and geochemical modelling software such as 'R Studio', IBM SPSS, geochemical workbench, visual MINTEQ were used to understand the groundwater chemistry and evaluate its suitability for drinking purpose. The concentration of As in groundwater sources varies between below detection limit (bdl) and 300 μg/L, with highest levels in streams followed by shallow wells and boreholes. In approximately 48% of the analysed samples, As concentration exceeded the WHO drinking water guideline and Tanzania Bureau of Standards (TBS) guideline for drinking water value of 10 μg/L. The concentration of the analyzed TEs and mean values of physicochemical parameters were below the guideline limits based on WHO and TBS standards. The Canadian Council of Ministries of the Environment Water Quality Index (CCME WQI) shows that the overall water quality is acceptable with minimum threats of deviation from natural conditions. We recommend further geochemical exploration and the periodic risk assessment of groundwater in mining areas where high levels of As were recorded.

Unravelling the interactive effect of soil and atmospheric mercury influencing mercury distribution and accumulation in the soil-rice system

Mercury (Hg) accumulation in rice is an emerging health concern worldwide. However, sources and interactions responsible for Hg species accumulation in different rice tissues are still uncertain. Four experimental plots were carefully designed at an artisanal Hg mining site and a control site to evaluate the effect of atmospheric and soil Hg contents on Hg accumulation in rice. We showed that inorganic Hg (IHg) contents in rice tissues grown either in contaminated or control site soil (non-contaminated soil) were higher at Hg artisanal mining site than those at the control site. Elevated total gaseous mercury (TGM) levels in ambient air were the predominant source of IHg to rice at the Hg mining area. Methylmercury (MeHg) concentrations in rice plant tissues increased in proportionality with MeHg contents in paddy soil. Our results suggest that both atmosphere and soil Hg sources have been impacted the IHg accumulation in rice. Above ground rice tissues, grains, leaves, and stalk accumulated IHg from both atmosphere and soil to varying degrees. Nonetheless, the study also provides the first direct evidence that atmospheric Hg accumulated by above-ground rice tissues could be translocated to below-ground tissues (roots). However, the extent to which atmosphere or soil Hg contributes to IHg in rice tissues may vary with each source's concentration gradient at the given site. No evidence of in planta Hg methylation was found during the current study. Hence, paddy fields are potential MeHg production sites, whereas paddy soil is a unique MeHg accumulation source in rice plants. This study expands and clarifies the contribution of various sources involved in Hg accumulation in the soil rice system. The findings here provide the basis for future research strategies to deal with the global issue of Hg contaminated rice.

Evaluation of the Total Mercury Weight Exposure Distribution Using Tree Bark Analysis in an Artisanal and Small-Scale Gold Mining Area, North Gorontalo Regency, Gorontalo Province, Indonesia

It is well known that atmospheric mercury (Hg) contaminates air, water, soil, and living organisms, including trees. Therefore, tree bark can be used for the environmental assessment of atmospheric contamination because it absorbs heavy metals. This study aimed to establish a new biomonitoring for the assessment of atmospheric Hg pollution. Reporting on atmospheric Hg contamination in an artisanal and small-scale gold mining (ASGM) area in North Gorontalo, Indonesia, we calculated the total weight of Hg (THg) and quantitatively measured the concentrations of Hg in the tree bark of Mangifera indica, Syzygium aromaticum, Terminalia catappa, and Lansium domesticum. The THg of Hg in the M. indica tree bark samples ranged from not detected (ND) to 74.6 μg dry weight (DW) per sample. The total Hg in the tree bark of S. aromaticum, T. catappa, and L. domesticum ranged from ND to 156.8, ND to 180, and ND to 63.4 μg DW, respectively. We concluded that topography significantly influences the accumulation of Hg together with local weather conditions. A mapped distribution of the THg suggested that the distribution of THg in the tree bark was not affected by the distance to the amalgamation site. Therefore, tree bark can be used as biomonitoring of atmospheric Hg contamination for the assessment of ASGM areas.

Effects of prenatal exposure and co-exposure to metallic or metalloid elements on early infant neurodevelopmental outcomes in areas with small-scale gold mining activities in Northern Tanzania

BACKGROUND

Artisanal and small-scale gold mining (ASGM) is associated with release of neurotoxic metallic or metalloid chemical elements including lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As).

OBJECTIVE

To examine associations between prenatal exposure and co-exposure to total lead (T-Pb), total mercury (T-Hg), total cadmium (T-Cd) and total arsenic (T-As) and infant neurodevelopment at 6 to 12 months of age in areas with ASGM activities in Tanzania.

METHODS

Women in their second trimester of pregnancy who resided in ASGM areas were enrolled from 2015 to 2017 (n = 883). At 6 to 12 months of age, children were assessed with the Malawi Developmental Assessment Tool (MDAT) (n = 439). We measured T-Pb, T-Hg, and T-Cd in maternal dried blood spots and T-As in maternal urines. Poisson regression was used to examine associations between prenatal concentrations of these elements and neurodevelopmental outcomes.

RESULTS

Prenatal T-Hg concentration was associated with global neurodevelopment status (aPR 1.03, CI:1.01-1.04; p < 0.001) and language impairment (aPR 1.05, CI:1.03-1.07; p < 0.001) on the MDAT. When prenatal T-Hg and T-As values were at or above the human biomonitoring reference values (≥95%) of the German Environmental Survey for Human Biomonitoring, that is 0.80 µg/L and 15 µg/L, respectively, the prevalence ratio of global neurodevelopmental impairment was two times higher (aPR 2.1, CI:1.0-4.3; p = 0.034). There was a 40% increase in the prevalence ratio of global neurodevelopmental impairment (aPR 1.4, CI:0.90-2.10, p = 0.027), when prenatal T-Hg was at or above the reference value of 0.80 µg/L and T-Pb was at or above the reference value of 35 µg/L. When prenatal T-Hg was at or above the reference value of 0.80 µg/L and T-As was at or above the reference value of 15 µg/L, the prevalence ratio of global neurodevelopmental impairment was two times higher (aPR 2.1, CI:1.0-4.3; p < 0.034).

DISCUSSION

Infants born to women in areas with ASGM activities are at significant risk for neurodevelopmental impairment and this is associated with exposure to higher concentrations of Hg prenatally. Co-exposure to high concentrations of Hg and Pb, or Hg and As appeared to have negative potentiated effects on infants' neurodevelopment.

Transgenic merA and merB expression reduces mercury contamination in vegetables and grains grown in mercury-contaminated soil

Arabidopsis, tobacco, tomato and rice with merA/merB expressed reduced mercury concentration of leaves, fruits or grains. These mercury-breathing plants produce agricultural products with acceptable levels of mercury from contaminated soil. Mercury contamination in plant food products can cause serious health risks to consumers. Transgenic approaches to enhance mercury phytoremediation have been accomplished with expression of bacterial merA and merB genes to convert toxic organic mercury to less toxic elemental mercury. However, little is known whether these genes can be used to produce safe foods from plants grown on mercury-contaminated land. We have used Arabidopsis and tobacco as model plants for leafy vegetables, and tomato and rice as representative fruit and grain crops to investigate whether merA and merB expression allows for production of safe foods from mercury-contaminated soils. Our results show that grown on heavily contaminated land with mercury, merA and merB expressing transgenic plants can produce vegetables, fruits and grains safe for human and animal consumption, while the wild-type plants cannot. The merA and merB transgenic plants can also efficiently remove mercury from soil. With increasing mercury contamination problems for the agricultural land worldwide, the use of the merA and merB genes can help produce safe food from mercury-polluted land and also remediate contaminated soils.

Recent advances in understanding and measurement of mercury in the environment: Terrestrial Hg cycling

This review documents recent advances in terrestrial mercury cycling. Terrestrial mercury (Hg) research has matured in some areas, and is developing rapidly in others. We summarize the state of the science circa 2010 as a starting point, and then present the advances during the last decade in three areas: land use, sulfate deposition, and climate change. The advances are presented in the framework of three Hg "gateways" to the terrestrial environment: inputs from the atmosphere, uptake in food, and runoff with surface water. Among the most notable advances: These and other advances reported here are of value in evaluating the effectiveness of the Minamata Convention on reducing environmental Hg exposure to humans and wildlife.

Nanoactivated Carbon Reduces Mercury Mobility and Uptake by Oryza sativa L: Mechanistic Investigation Using Spectroscopic and Microscopic Techniques

Mercury (Hg) contamination of paddy field poses a health risk to rice consumers, and its remediation is a subject of global scientific attention. In recent years focus has been given to in situ techniques which reduce the risk of Hg entering the food chain. Here, we investigate the use of nanoactivated carbon (NAC) as a soil amendment to minimize Hg uptake by rice plants. Application of 1-3% NAC to soil (by weight) reduced Hg concentration in the pore water (by 61-76%) and its bioaccumulation in the tissues of rice plants (by 15-63%), relative to the corresponding control. Specifically, NAC reduced the Hg concentration of polished rice by 47-63% compared to the control, to a level that was 29-49% lower than the food safety value (20 ng g^-1) defined by the Chinese government. The NAC induced a change in Hg binding from organic matter to nano-HgS in the soil as a function of soil amendment. This Hg speciation transformation might be coupled to the reduction of sulfoxide to reduced sulfur species (S⁰) by NAC. The NAC amendment may be a practical and effective solution to mitigate the risk of Hg transferring from contaminated soil to rice grains at locations around the world.

Mercuric pollution of surface water, superficial sediments, Nile tilapia (Oreochromis nilotica Linnaeus 1758 [Cichlidae]) and yams (Dioscorea alata) in auriferous areas of Namukombe stream, Syanyonja, Busia, Uganda

The mercury content and the contamination characteristics of water, sediments, edible muscles of a non-piscivorous fish (Oreochromis nilotica Linnaeus 1758 [Cichlidae]) and yams (Dioscorea alata) from Namukombe stream in Busia gold district of Uganda were evaluated. Human health risk assessment from consumption of contaminated fish and yams as well as contact with contaminated sediments from the stream were performed. Forty-eight (48) samples of water (n = 12), sediments (n = 12), fish (n = 12) and yams (n = 12) were taken at intervals of 10 m from three gold recovery sites located at up, middle and down sluices of the stream and analyzed for total mercury (THg) using US EPA method 1631. Results (presented as means  ±  standard deviations) showed that water in the stream is polluted with mercury in the range of < detection limit to 1.21  ±  0.040 mg/L while sediments contain mean THg from < detection limit to 0.14  ±  0.040 ugg^-1. Mean THg content of the edible muscles of O. nilotica ranged from < detection limit to 0.11 ± 0.014 ugg^-1while D. alata contained from < detection limit to 0.30  ±  0.173 ugg^-1mean THg. The estimated daily intake ranged from 0.0049 ugg^-1day^-1 to 0.0183 ugg^-1day^-1 and 0.0200 ugg^-1day^-1 to 0.0730 ugg^-1day^-1 for fish consumed by adults and children respectively. The corresponding health risk indices ranged from 0.0123 to 0.0458 and 0.0500 to 0.1830. Estimated daily intake was from 0.0042 ugg^-1day^-1 to 0.1279 ugg^-1day^-1 and 0.0130 ugg^-1day^-1 to 0.3940 ugg^-1day^-1 for D. alata consumed by adults and children respectively. The health risk indices recorded were from 0.011 to 0.320 and 0.033 to 0.985 for adults and children respectively. The mean THg content of the sediments, edible muscles of O. nilotica and D. alata were within acceptable WHO/US EPA limits. About 91.7% of the water samples had mean THg above US EPA maximum permissible limit for mercury in drinking water. Consumption of D. alata grown within 5 m radius up sluice of Namukombe stream may pose deleterious health risks as reflected by the health risk index of 0.985 being very close to one. From the pollution and risk assessments, mercury use should be delimited in Syanyonja artisanal gold mining areas. A solution to abolish mercury-based gold mining in the area needs to be sought as soon as possible to avert the accentuating health, economic and ecological disaster arising from the continuous discharge of mercury into the surrounding areas. Other mercury-free gold recovering methods such as use of borax, sluice boxes and direct panning should be encouraged. Waste management system for contaminated wastewater, used mercury bottles and tailings should be centralized.

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.

Validation of Dried Blood Spots for Maternal Biomonitoring of Nonessential Elements in an Artisanal and Small-Scale Gold Mining Area of Tanzania

Biomonitoring studies of vulnerable populations in low- and middle-income countries are limited because traditional sampling methods are challenging to implement in low-resource settings. The present study examined the feasibility, precision, and accuracy of dried blood spots (DBS) for human biomonitoring of nonessential elements (cadmium [Cd], mercury [Hg], and lead [Pb]) in an area of northern Tanzania with artisanal and small-scale gold mining activities. Pregnant women (n = 44) were recruited in Geita during antenatal clinic visits, and DBS from capillary blood were collected on filter paper. As a gold-standard comparison, venous blood was sampled from the same participants and compared with the DBS. Venous blood, DBS, and quality control samples were analyzed for chemical elements by inductively coupled plasma mass spectrometry. Field blanks were very clean for most elements, generally only twice as high as corresponding laboratory filter blanks. No significant differences were found between duplicate DBS samples taken from the same participants, with near perfect intraclass correlation coefficients (0.99) for Cd, Hg, and Pb, indicating excellent reliability. Moreover, correlation was strong (r² > 0.9) and significant (p < 0.0001) between DBS and the quantitative venous blood, with regression line slopes close to 1.0 (0.847, 0.976, and 0.969 for Cd, Hg, and Pb, respectively), indicating high accuracy of the DBS method compared with the gold-standard approach. The DBS method is minimally invasive and was a feasible, precise, and accurate means of measuring exposure to Cd, Hg, and Pb in pregnant women in a low-resource setting. Environ Toxicol Chem 2019;38:1285-1293. © 2019 SETAC.

Maternal exposure to arsenic and mercury in small-scale gold mining areas of Northern Tanzania

Artisanal and small-scale gold mining (ASGM) in Tanzania results in occupational exposures and environmental contamination to toxic chemical elements such as arsenic and mercury. Populations living in such areas may be exposed by various routes, and prenatal exposure to arsenic and mercury has been associated with adverse birth outcomes and developmental delays. The aim of this study was to determine if levels of arsenic and mercury differed among pregnant women living in areas with and without ASGM activities in Northern Tanzania. This cross-sectional study is part of the ongoing Mining and Health prospective longitudinal study. Spot urine samples and dried blood spots were collected at the antenatal health clinics from pregnant women (n = 1056) at 16-27 weeks gestation. Urine samples were analyzed for total arsenic (T-As) and dried blood spots were analyzed for total mercury (T-Hg). Women in the ASGM cohort had median T-As levels (9.4 μg/L; IQR: 4.9-15.1) and T-Hg levels (1.2 μg/L; IQR: 0.8-1.86) that were significantly higher than the median T-As levels (6.28 μg/L; IQR: 3.7-14.1) and T-Hg levels (0.66 μg/L; IQR: 0.3-1.2) of women in the non-ASGM cohort (Mann-Whitney U test, T-As: z = -9.881, p = 0.0005; T-Hg: z = -3.502, p < 0.0001). Among pregnant women from ASGM areas, 25% had urinary T-As and 75% had blood T-Hg above the established human biomonitoring reference values of 15 and 0.80 μg/L. In the ASGM cohort, lower maternal education and low socioeconomic status increased the odds of higher T-As levels by 20% (p < 0.05) and 10% (p < 0.05), respectively. Women involved in mining activities and those of low socioeconomic status had increased odds of higher T-Hg by 70% (p < 0.001) and 10% (p < 0.05), respectively. Arsenic and mercury concentrations among women in non-ASGM areas suggest exposure sources beyond ASGM activities that need to be identified. Arsenic and mercury levels in women in Tanzania are of public health concern and their association with adverse birth and child developmental outcomes will be examined in future studies on this cohort.

Developmental exposure to mercury chloride impairs social behavior in male offspring dependent on genetic background and maternal autoimmune environment

To date, the connection between inorganic mercury (Hg) and social behavior remains incompletely understood. The aim of this study was to investigate the influence of maternal autoimmunity by inorganic Hg (Hg²⁺) exposure on social behavior of offspring. Wild-type (WT) and immunoglobulin deficient (Ig^-/-) B10.S dams fertilized by male WT B10.S or SJL mice were treated with 50 μM Hg chloride (HgCl₂). Non-pregnant female WT B10.S mice were used to investigate factors regulating HgCl₂-induced autoimmunity to brain. HgCl₂ selectively impaired social behavior in male offspring, but not female offspring from WT B10.S dams × male SJL, in that only male offspring displayed reduced time distribution with the stranger mouse, decreased sniffing to the stranger mouse and increased self-grooming. HgCl₂ did not disrupt social behavior of male or female offspring from WT B10.S dams × male WT B10.S or Ig^-/- B10.S dams × male SJL. The offspring from WT and Ig^-/- B10.S dams × male SJL had equivalent autoimmunity to brain antigens during HgCl₂ exposure, indicating that maternal, but not offspring-derived anti-brain antibodies (Ab) impaired social behavior of the offspring. Non-pregnant WT B10.S mice treated with HgCl₂ had increased anti-brain Ab dependent on increase in CD4 T cell activation and IFNγ signaling to macrophages. IFNγ interaction with macrophages drove B cells and plasma cells to produce IgG. Therefore, HgCl₂ selectively impaired social behavior in males with certain genetic background via maternally derived anti-brain Ab production, thus providing a novel insight into our current understanding of Hg toxicity.

Status, progress and challenges of phytoremediation - An African scenario

Environmental pollution occasioned by artisanal activities and technical failures at exploration sites has affected mostly oil producing and other mineral resources mining regions in developed and developing nations. As conventional techniques of remediation seem to be progressively unreliable and inefficient, contaminated land management experts have adopted a plant-based technology described as 'phytoremediation' for effective detoxification and removal of contaminants in substrate environmental media (soil and sediment). This technique, has gained public acceptance because of its aesthetic, eco-friendly, solar energy driven and low cost attributes. With complexity of environmental pollution in Africa, identification of appropriate remediation approach that deliver net environmental benefit and economic profit to the society is vital, while also focusing on the exploitation of plants genetic tools for more clarity on phyto tolerance, uptake and translocation of pollutants. In this article, we reviewed the status, progress and challenges of phytoremediation in selected African countries (South Africa, Nigeria, Tanzania, Zambia, Egypt and Ghana), the ecological impact of the pollutants, phytoremediation strategies and the possible plants of choice. Besides highlighting the support roles played by soil fauna and flora, the fate of harvested biomass/dieback and its future prospects are also discussed. We further explored the factors challenging phytoremediation progress in Africa, amidst its promising potentials and applicability for sustainable ecosystem management paradigm.

Bioaccumulation and trophic transfer of total mercury in the subtropical Olifants River Basin, South Africa

The present study describes total mercury (THg) levels in surface water, sediment and biota from the Olifants River Basin (ORB) (South Africa) and investigates the trophic transfer of THg by means of trophic magnification factors (TMFs) in the subtropical ORB food web. Although levels in surface water, sediment and invertebrates were low, elevated levels of THg were measured in fish species of higher trophic levels (0.10-6.1 μg/g dw). This finding supports the biomagnificative character of mercury. THg concentrations in fish from the present study were find to be higher than most values reported in fish from other African aquatic ecosystems and comparable or lower compared to more industrialized regions. Fish length, trophic level, sediment THg levels and TOC in sediment were determining factors for THg levels in fish tissue. Concentrations were found to be higher in larger (and older) fish. Mercury has a high affinity for organic matter and will bind with the TOC in sediment, thus reducing the bioavailability of THg for aquatic biota which is reflected in the significant negative correlation between THg and TOC in sediment. A significant positive relationship between relative trophic level and THg concentrations was observed and also TMFs indicate biomagnification in the ORB food web. However, the trend of lower TMFs in tropical areas compared to temperate and arctic regions was not supported by the results. The consumption of fish from higher trophic levels at the average South African consumption rate is expected to pose a significant health risk.

Distribution and bioaccumulation of POPs and mercury in the Ga-Selati River (South Africa) and the rivers Gudbrandsdalslågen and Rena (Norway)

Biomagnification of Hg and persistent organic pollutants (POPs: polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs)) in aquatic food chains can lead to high pollutant concentrations in top predators, including humans. Despite this threat to human health, research concerning bioaccumulation is still underrepresented in the southern hemisphere and in (sub)arctic and (sub)tropical areas, emphasizing the need for research in these locations. In this study, samples of water, sediment and aquatic biota were analyzed to determine concentrations of POPs and total mercury (THg) in the Ga-Selati river (South Africa) and two rivers Rena and Gudbrandsdalslågen in Norway. Trophic magnification factors (TMFs) were determined to evaluate and compare the biomagnification and the threat to human health due to consumption of the fish was assessed. Concentrations of POPs in sediment and biota samples were generally low except for relatively high concentrations of ∑DDX (dichlorodiphenyltrichloroethane and metabolites) in aquatic biota from the Ga-Selati river (ranging from 1.9 to 133 ng/g ww in invertebrates and 1.9 to 5643 ng/g ww in fish). Dissolved THg concentrations were high in the Ga-Selati river (ranging from 0.009 to 0.036 μg/l) but THg concentrations in sediment and biota were low in studied rivers compared to other studies. Biomagnification occurred for THg, several DDT-metabolites and PCB compounds, TN and CN. Biomagnification of p,p'-DDT and THg differed significantly between the two countries, supporting existing patterns found in literature, although more data is needed to attribute these differences to climatic or other factors. Concentrations in fish from the rivers Ga-Selati and Rena were under the threshold levels reported for THg and POPs, but caution should be taken when consuming Northern pike (Esox Lucius) from the subarctic river Gudbrandsdalslågen, to avoid harmful effects due to both elevated THg and PBDE exposure.

A systematic review on the management and treatment of mercury in artisanal gold mining

Artisanal gold mining (AGM) continues to be a pervasive global health issue. While there are various problems associated with AGM, mercury exposure is the primary hazard contributing to adverse health effects in exposed human populations. Over the last several decades, many interventions have been developed and implemented to curb mercury emissions and releases, notwithstanding a comprehensive review of context specific effectiveness. A systematic review was conducted in order to specifically assess the impact of current mercury interventions within the AGM sector worldwide. To aid in this review, a resource pool of information on AGM and mercury, treatment and management of emissions and releases, and interventions was assembled through a search conducted via multiple search engines. This search determined that there have been many strategies used to reduce or eliminate mercury, through interventions or programs focusing on education, processing centers, or mercury alternative techniques. Education has focused on environment or health awareness or more specifically on cleaner or alternative techniques. Processing centers offered artisanal miners rudimentary equipment for grinding and amalgamation that extract less than 30% of the gold as an exchange for their tailings. Some techniques reduced mercury releases including retorts, mill leaching, vat-leaching, and others replaced mercury from the process such as magnets, direct smelting, sluices, and borax. There are both positive and negative outcomes associated with every intervention. Novel and comprehensive strategies-including mercury removal technology, miner education on mercury hazards, economic gains, and policy-are needed to address mercury public health issues associated with AGM.

Heavy metal pollution in soil associated with a large-scale cyanidation gold mining region in southeast of Jilin, China

Different gold mining and smelting processes can lead to distinctive heavy metal contamination patterns and results. This work examined heavy metal pollution from a large-scale cyanidation gold mining operation, which is distinguished from artisanal and small-scale amalgamation gold mining, in Jilin Province, China. A total of 20 samples including one background sample were collected from the surface of the mining area and the tailings pond in June 2013. These samples were analyzed for heavy metal concentrations and degree of pollution as well as sources of Cr, Cu, Zn, Pb, Ni, Cd, As, and Hg. The mean concentrations of Pb, Hg, and Cu (819.67, 0.12, and 46.92 mg kg^-1, respectively) in soil samples from the gold mine area exceeded local background values. The mean Hg content was less than the first-class standard of the Environmental Quality for Soils, which suggested that the cyanidation method is helpful for reducing Hg pollution. The geochemical accumulation index and enrichment factor results indicated clear signs that enrichment was present for Pb, Cu, and Hg, with the presence of serious Pb pollution and moderate presence to none of Hg and Cu pollution. Multivariate statistical analysis showed that there were three metal sources: (1) Pb, Cd, Cu, and As came from anthropogenic sources; (2) Cr and Zn were naturally occurring; whereas (3) Hg and Ni had a mix of anthropogenic and natural sources. Moreover, the tailings dam plays an important role in intercepting the tailings. Furthermore, the potential ecological risk assessment results showed that the study area poses a potentially strong risk to the ecological health. Furthermore, Pb and Hg (due to high concentration and high toxicity, respectively) are major pollutants on the risk index, and both Pb and Hg pollution should be of great concern at the Haigou gold mines in Jilin, China.

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.

Mercury Exposure Assessment and Spatial Distribution in A Ghanaian Small-Scale Gold Mining Community

Mercury is utilized worldwide in artisanal and small-scale gold mining (ASGM) and may pose a risk for miners and mining communities. While a number of studies have characterized mercury in ASGM communities, most have focused on a single media and few have taken a holistic approach. Here, a multiple media exposure assessment and cross-sectional study of mercury was conducted in 2010 through 2012 in northeast Ghana with a small-scale gold mining community, Kejetia, a subsistence farming community, Gorogo, and an urban ASGM gold refinery in Bolgatanga. The objective was to assess mercury in a range of human (urine and hair) and ecological (household soil, sediment, fish, and ore) samples to increase understanding of mercury exposure pathways. All participants were interviewed on demographics, occupational and medical histories, and household characteristics. Participants included 90 women of childbearing age and 97 adults from Kejetia and 75 adults from Gorogo. Median total specific gravity-adjusted urinary, hair, and household soil mercury were significantly higher in Kejetia miners (5.18 µg/L, 0.967 µg/g, and 3.77 µg/g, respectively) than Kejetia non-miners (1.18 µg/L, 0.419 µg/g, and 2.00 µg/g, respectively) and Gorogo participants (0.154 µg/L, 0.181 µg/g, and 0.039 µg/g) in 2011. Sediment, fish, and ore Hg concentrations were below guideline values. Median soil mercury from the Bolgatanga refinery was very high (54.6 µg/g). Estimated mean mercury ingestion for Kejetia adults from soil and dust exceeded the U.S. Environmental Protection Agency reference dose (0.3 µg Hg/kg·day) for pica (0.409 µg Hg/kg·day) and geophagy (20.5 µg Hg/kg·day) scenarios. Most participants with elevated urinary and household soil mercury were miners, but some non-miners approached and exceeded guideline values, suggesting a health risk for non-mining residents living within these communities.

Mercury in sediment, water, and fish in a managed tropical wetland-lake ecosystem

Mercury pollution has not been well documented in the inland lakes or fishes of Mexico, despite the importance of freshwater fish as a source of protein in local diets. Total mercury and methylmercury in waters, sediments, and the commercial fish catch were investigated in Lake Zapotlán, Mexico. Concentrations of total and methylmercury were very high in runoff and wastewater inputs, but very low in sediments and surface waters of the open water area of the lake. Concentrations of total mercury in tilapia and carp were very low, consistent with the low concentrations in lake water and sediments. Particle settling, sorption, the biogeochemical environment, and/or bloom dilution are all plausible explanations for the significant reductions in both total mercury and methylmercury. Despite very high loading of mercury, this shallow tropical lake was not a mercury-impaired ecosystem, and these findings may translate across other shallow, alkaline tropical lakes. Importantly, the ecosystem services that seemed to be provided by peripheral wetlands in reducing mercury inputs highlight the potential for wetland conservation or restoration in Mexico.

Integrated Health Risk Assessment of Heavy Metals in Suxian County, South China

The purpose of this study was to assess soil heavy metal contamination and the potential risk for local residents in Suxian county of Hunan Province, southern China. Soil, rice and vegetable samples from the areas near the mining industrial districts were sampled and analyzed. The results indicate that the anthropogenic mining activities have caused local agricultural soil contamination with As, Pb, Cu and Cd in the ranges of 8.47-341.33 mg/kg, 19.91-837.52 mg/kg, 8.41-148.73 mg/kg and 0.35-6.47 mg/kg, respectively. GIS-based mapping shows that soil heavy metal concentrations abruptly diminish with increasing distance from the polluting source. The concentrations of As, Pb, Cu and Cd found in rice were in the ranges of 0.02-1.48 mg/kg, 0.66-5.78 mg/kg, 0.09-6.75 mg/kg, and up to 1.39 mg/kg, respectively. Most of these concentrations exceed their maximum permissible levels for contaminants in foods in China. Heavy metals accumulate to significantly different levels between leafy vegetables and non-leafy vegetables. Food consumption and soil ingestion exposure are the two routes that contribute to the average daily intake dose of heavy metals for local adults. Moreover, the total hazard indices of As, Pb and Cd are greater than or close to the safety threshold of 1. Long-term As, Pb and Cd exposure through the regular consumption of the soil, rice and vegetables in the investigated area poses potential health problems to residents in the vicinity of the mining industry.

Predicted no-effect concentrations for mercury species and ecological risk assessment for mercury pollution in aquatic environment

Mercury (Hg) exists in different chemical forms presenting varied toxic potentials. It is necessary to explore an ecological risk assessment method for different mercury species in aquatic environment. The predicted no-effect concentrations (PNECs) for Hg(II) and methyl mercury (MeHg) in the aqueous phase, calculated using the species sensitivity distribution method and the assessment factor method, were 0.39 and 6.5×10(-3)μg/L, respectively. The partition theory of Hg between sediment and aqueous phases was considered, along with PNECs for the aqueous phase to conduct an ecological risk assessment for Hg in the sediment phase. Two case studies, one in China and one in the Western Black Sea, were conducted using these PNECs. The toxicity of mercury is heavily dependent on their forms, and their potential ecological risk should be respectively evaluated on the basis of mercury species.

Retrospective study of methylmercury and other metal(loid)s in Madagascar unpolished rice (Oryza sativa L.)

The rice ingestion rate in Madagascar is among the highest globally; however studies concerning metal(loid) concentrations in Madagascar rice are lacking. For Madagascar unpolished rice (n = 51 landraces), levels of toxic elements (e.g., total mercury, methylmercury, arsenic and cadmium) as well as essential micronutrients (e.g., zinc and selenium) were uniformly low, indicating potentially both positive and negative health effects. Aside from manganese (Wilcoxon rank sum, p < 0.01), no significant differences in concentrations for all trace elements were observed between rice with red bran (n = 20)and brown bran (n = 31) (Wilcoxon rank sum, p = 0.06-0.91). Compared to all elements in rice,rubidium (i.e., tracer for phloem transport) was most positively correlated with methylmercury (Pearson'sr = 0.33, p < 0.05) and total mercury (r = 0.44, p < 0.05), while strontium (i.e., tracer for xylemtransport) was least correlated with total mercury and methylmercury (r < 0.01 for both), suggesting inorganic mercury and methylmercury were possibly more mobile in phloem compared to xylem.

Spatial distribution of mercury and arsenic levels in water, soil and cassava plants in a community with long history of gold mining in Tanzania

This study examined the spatial distribution of total mercury (THg) and total arsenic (TAs) in water, soil and cassava (Manihot esculenta) (leaves and roots) samples taken from areas in Rwamagasa village in northwestern Tanzania where daily living activities occur in close proximity to extensive artisanal and small scale gold mining. Results indicated that 33.3 % of the water sources had THg levels above the WHO guideline of 1.0 µg/L for safe drinking water, and 12.5 % had TAs levels above 10 µg/L. Cassava leaves were found to have higher THg (ranging from 8.3 to 167 µg/kg) and TAs (ranging from 60 to 1,120 µg/kg) levels than cassava roots, which ranged between 1.2-8.3 µg/kg for THg and 25-310 µg/kg for TAs. Concentrations of THg and TAs in soil samples ranged between 5.8-1,759 and 183-20,298 µg/kg, respectively. Both THg and TAs were found to be distributed throughout Rwamagasa village.

Mercury contamination in Khramulia (Capoeta capoeta) from the Cheshme Kile and Zarrin Gol Rivers in Iran and human health risk assessment

Total mercury concentrations were determined in muscle tissue of Khramulia (Capoeta capoeta) captured in the Cheshme Kile and Zarrin Gol Rivers, Iran. In Cheshme Kile River, 49 fish samples were collected. The mean total mercury concentration in the muscles of C. capoeta from this area was 249 ng g(-1) dw. In Zarrin Gol River, where 62 fish samples were collected, the total mercury in muscles averaged 164 ng g(-1) dw. A significant difference was found between means of mercury in the rivers (p < 0.001). All samples from the two rivers had mean mercury concentrations below the maximum allowable limits for mercury set by the Food and Agriculture Organization, World Health Organization, Standardization Administration of China and Environmental Protection Agency. The results of this study indicate that the values of hazard target quotient and estimated weekly intake are low and represent a negligible risk for human health.

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.

Geophagy practices and the content of chemical elements in the soil eaten by pregnant women in artisanal and small scale gold mining communities in Tanzania

BACKGROUND

Geophagy, a form of pica, is the deliberate consumption of soil and is relatively common across Sub-Saharan Africa. In Tanzania, pregnant women commonly eat soil sticks sold in the market (pemba), soil from walls of houses, termite mounds, and ground soil (kichuguu). The present study examined geophagy practices of pregnant women in a gold mining area of Geita District in northwestern Tanzania, and also examined the potential for exposure to chemical elements by testing soil samples.

METHOD

We conducted a cross sectional study using a convenience sample of 340 pregnant women, ranging in age from 15-49 years, who attended six government antenatal clinics in the Geita District, Tanzania. Structured interviews were conducted in June-August, 2012, to understand geophagy practices. In addition, soil samples taken from sources identified by pregnant women practicing geophagy were analysed for mineral element content.

RESULTS

Geophagy was reported by 155 (45.6%) pregnant women with 85 (54.8%) initiating the practice in the first trimester. A total of 101 (65%) pregnant women reported eating soil 2 to 3 times per day while 20 (13%) ate soil more than 3 times per day. Of 155 pregnant women 107 (69%) bought pemba from local shops, while 48 (31%) consumed ground soil kichuguu. The estimated mean quantity of soil consumed from pemba was 62.5 grams/day. Arsenic, chromium, copper, iron, manganese, nickel and zinc levels were found in both pemba and kichuguu samples. Cadmium and mercury were found only in the kichuguu samples. Based on daily intake estimates, arsenic, copper and manganese for kichuguu and copper and manganese for pemba samples exceed the oral Minimum Risk Levels designated by the U.S. Agency for Toxic Substance and Disease Registry.

CONCLUSION

Almost 50% of participants practiced geophagy in Geita District consistent with other reports from Africa. Both pemba and kichuguu contained chemical elements at varying concentration, mostly above MRLs. As such, pregnant women who eat soil in Geita District are exposed to potentially high levels of chemical elements, depending upon frequency of consumption, daily amount consumed and the source location of soil eaten.

Rapid assessment of environmental health risks posed by mining operations in low- and middle-income countries: selected case studies

Previous studies have evaluated associated health risks and human exposure pathways at mining sites. Others have provided estimates of the scale of the issue based in part on surveys. However, a global census of mining-related hazardous waste sites has been lacking. The Toxic Sites Identification Program (TSIP) implemented by Blacksmith Institute (New York, NY, USA) since 2009 is an ongoing effort to catalogue a wide range of chemically contaminated sites with a potential human health risk (Ericson et al., Environ Monit Assess doi:10.1007/s 10661-012-2665-2, 2012). The TSIP utilizes a rapid assessment instrument, the Initial Site Screening (ISS), to quickly and affordably identify key site criteria including human exposure pathways, estimated populations at risk, and sampling information. The resulting ISS allows for comparison between sites exhibiting different contaminants and pollution sources. This paper explores the results of a subset of ISSs completed at 131 artisanal and small-scale gold mining areas and 275 industrial mining and ore processing sites in 45 countries. The authors show that the ISS captures key data points, allowing for prioritization of sites for further investigation or remedial activity.

Assessment of heavy metals in water samples and tissues of edible fish species from Awassa and Koka Rift Valley Lakes, Ethiopia

The Ethiopian Rift Valley Lakes host populations of edible fish species including Oreochromis niloticus, Labeobarbus intermedius and Clarias gariepinus, which are harvested also in other tropical countries. We investigated the occurrence of six heavy metals in tissues of these fish species as well as in the waters of Lake Koka and Lake Awassa. Both lakes are affected by industrial effluents in their catchments, making them ideal study sites. Mercury concentrations were very low in the water samples, but concentrations in the fish samples were relatively high, suggesting a particularly high bioaccumulation tendency as compared with the other investigated metals. Mercury was preferentially accumulated in the fish liver or muscle. It was the only metal with species-specific accumulation with highest levels found in the predatory species L. intermedius. Lower mercury concentrations in O. niloticus could be attributed to the lower trophic level, whereas mercury values in the predatory C. gariepinus were unexpectedly low. This probably relates to the high growth rate of this species resulting in biodilution of mercury. Accumulation of lead, selenium, chromium, arsenic and cadmium did not differ between species, indicating that these elements are not biomagnified in the food chain. Values of cadmium, selenium and arsenic were highest in fish livers, while lead and chromium levels were highest in the gills, which could be related to the uptake pathway. A significant impact of the industrial discharges on the occurrence of metals in the lakes could not be detected, and the respective concentrations in fish do not pose a public health hazard.

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

A field survey of mercury pollution in environmental media and human hair samples obtained from residents living in the area surrounding the Chatian mercury mine (CMM) of southwestern China was conducted to evaluate the health risks of mercury to local residents. The results showed that mine waste, and tailings in particular, contained high levels of mercury and that the maximum mercury concentration was 88.50 μg g(-1). Elevated mercury levels were also found in local surface water, paddy soil, and paddy grain, which may cause severe health problems. The mercury concentration of hair samples from the inhabitants of the CMM exceeded 1.0 μg g(-1), which is the limit recommended by the US EPA. Mercury concentrations in paddy soil were positively correlated with mercury concentrations in paddy roots, stalks, and paddy grains, which suggested that paddy soil was the major source of mercury in paddy plant tissue. The average daily dose (ADD) of mercury for local adults and preschool children via oral exposure reached 0.241 and 0.624 μg kg(-1) body weight per day, respectively, which is approaching or exceeds the provisional tolerable daily intake. Among the three oral exposure routes, the greatest contributor to the ADD of mercury was the ingestion of rice grain. Open-stacked mine tailings have resulted in heavy mercury contamination in the surrounding soil, and the depth of appreciable soil mercury concentrations exceeded 100 cm.

Mercury, arsenic and selenium concentrations in water and fish from sub-Saharan semi-arid freshwater reservoirs (Burkina Faso)

Despite intensive mining activities in Burkina Faso, little is known on the environmental impacts of metals and metalloids potentially released from these activities. Water samples and 334 fish from 10 reservoirs were taken in order to evaluate the extent of mercury (Hg), selenium (Se) and arsenic (As) contamination in aquatic systems and their potential health risk for humans and wildlife, taking into account their antagonistic interactions. Water and fish levels of these elements were relatively low and did not reveal an important impact of gold mining activities. Water temperature and conductivity were the key factors associated with higher levels of MeHg. Higher sulfate content was reported in sites with more particulate Hg, As and Se, suggesting anthropogenic origin of metal(loid) inputs in water reservoirs. Metal(loid) concentrations in fish were low and ranged from 0.002 to 0.607 μg/g wet weight (w.w.) for Hg, 0.023 to 0.672 for Se and 0.039 to 0.42 for As. These levels are similar or slightly higher than those reported in many other studies from Africa. Nevertheless, more than 70% of piscivore fish exceeded the threshold for wildlife protection for MeHg. Further, a traditional risk analysis performed ignoring Se antagonism indicated that these piscivores should be consumed by humans with caution. However, when taking into account the antagonistic effect of Se on Hg toxicity, up to 99% of all fish could be protected from Hg toxicity by their Se content. When considering both As/Se and Se/Hg antagonism, 83% instead the 99% of fish should be considered safe for consumption. Fish Se and As concentrations did not pose potential risk for both animals and humans. Overall, these reservoirs were relatively unaffected by As, Se and Hg contamination despite the rising gold mining activities. Further, considering antagonistic effects of As, Se and Hg may help refine consumption advisories.

A cross-sectional survey on knowledge and perceptions of health risks associated with arsenic and mercury contamination from artisanal gold mining in Tanzania

BACKGROUND

An estimated 0.5 to 1.5 million informal miners, of whom 30-50% are women, rely on artisanal mining for their livelihood in Tanzania. Mercury, used in the processing gold ore, and arsenic, which is a constituent of some ores, are common occupational exposures that frequently result in widespread environmental contamination. Frequently, the mining activities are conducted haphazardly without regard for environmental, occupational, or community exposure. The primary objective of this study was to assess community risk knowledge and perception of potential mercury and arsenic toxicity and/or exposure from artisanal gold mining in Rwamagasa in northwestern Tanzania.

METHODS

A cross-sectional survey of respondents in five sub-villages in the Rwamagasa Village located in Geita District in northwestern Tanzania near Lake Victoria was conducted. This area has a history of artisanal gold mining and many of the population continue to work as miners. Using a clustered random selection approach for recruitment, a total of 160 individuals over 18 years of age completed a structured interview.

RESULTS

The interviews revealed wide variations in knowledge and risk perceptions concerning mercury and arsenic exposure, with 40.6% (n=65) and 89.4% (n=143) not aware of the health effects of mercury and arsenic exposure respectively. Males were significantly more knowledgeable (n=59, 36.9%) than females (n=36, 22.5%) with regard to mercury (x²=3.99, p<0.05). An individual's occupation category was associated with level of knowledge (x²=22.82, p=<0.001). Individuals involved in mining (n=63, 73.2%) were more knowledgeable about the negative health effects of mercury than individuals in other occupations. Of the few individuals (n=17, 10.6%) who knew about arsenic toxicity, the majority (n=10, 58.8%) were miners.

CONCLUSIONS

The knowledge of individuals living in Rwamagasa, Tanzania, an area with a history of artisanal gold mining, varied widely with regard to the health hazards of mercury and arsenic. In these communities there was limited awareness of the threats to health associated with exposure to mercury and arsenic. This lack of knowledge, combined with minimal environmental monitoring and controlled waste management practices, highlights the need for health education, surveillance, and policy changes.

Strong positive associations between seafood, vegetables, and alcohol with blood mercury and urinary arsenic levels in the Korean adult population

Blood mercury and urinary arsenic levels are more than fivefold greater in the Korean population compared with those of the United States. This may be related to the foods people consumed. Therefore, we examined the associations between food categories and mercury and arsenic exposure in the Korean adult population. Data regarding nutritional, biochemical, and health-related parameters were obtained from a cross-sectional study, the 2008-2009 Korean National Health and Nutrition Examination Survey (3,404 men and women age ≥ 20 years). The log-transformed blood mercury and urinary arsenic levels were regressed against the frequency tertiles of each food group after covariate adjustment for sex, age, residence area, education level, smoking status, and drinking status using food-frequency data. Blood mercury levels in the high consumption groups compared to the low consumption groups were elevated by about 20 percents with salted fish, shellfish, whitefish, bluefish, and alcohol, and by about 9-14 percents with seaweeds, green vegetables, fruits and tea, whereas rice did not affect blood mercury levels. Urinary arsenic levels were markedly increased with consumption of rice, bluefish, salted fish, shellfish, whitefish, and seaweed, whereas they were moderately increased with consumption of grains, green and white vegetables, fruits, coffee, and alcohol. The remaining food categories tended to lower these levels only minimally. In conclusion, the typical Asian diet, which is high in rice, salted fish, shellfish, vegetables, alcoholic beverages, and tea, may be associated with greater blood mercury and urinary arsenic levels. This study suggests that mercury and arsenic contents should be monitored and controlled in soil and water used for agriculture to decrease health risks from heavy-metal contamination.

Lead levels in breast milk, blood plasma and intelligence quotient: a health hazard for women and infants

Lead levels in human breast milk and blood plasma or serum were analyzed and qualitatively their intelligence quotient (I.Q.) studied. Samples at different stages of lactation, from 5 days to 51 weeks post partum, were collected from 25 healthy breast-feeding mothers in Ranipet Industrial area of Vellore district of Tamil Nadu and from 25 lactating mothers in the non-industrial areas of the same district. The samples from mothers in non-industrial area showed lower lead levels ranging from 5 to 25 μg/L whereas samples from mothers in industrial area showed higher lead levels ranging between 15 and 44.5 μg/L. It was generally noticed that the lactating mothers from industrial area have lower I.Q. levels compared to mothers from non-industrial area.

Mercury concentrations in water resources potentially impacted by coal-fired power stations and artisanal gold mining in Mpumalanga, South Africa

Total mercury (TotHg) and methylmercury (MeHg) concentrations were determined in various environmental compartments collected from water resources of three Water Management Areas (WMAs) - viz. Olifants, Upper Vaal and Inkomati WMAs, potentially impacted by major anthropogenic mercury (Hg) sources (i.e coal-fired power stations and artisanal gold mining activities). Aqueous TotHg concentrations were found to be elevated above the global average (5.0 ng/L) in 38% of all aqueous samples, while aqueous MeHg concentrations ranged from below the detection limit (0.02 ng/L) to 2.73 +/- 0.10 ng/L. Total Hg concentrations in surface sediment (0-4 cm) ranged from 0.75 +/- 0.01 to 358.23 +/- 76.83 ng/g wet weight (ww). Methylmercury accounted for, on average, 24% of TotHg concentrations in sediment. Methylmercury concentrations were not correlated with TotHg concentrations or organic content in sediment. The concentration of MeHg in invertebrates and fish were highest in the Inkomati WMA and, furthermore, measured just below the US EPA guideline for MeHg in fish.