Mercury Pollution from Artisanal and Small-Scale Gold Mining in Myanmar and Other Southeast Asian Countries

Climate control on the channel morphodynamics of the Sittaung River, Myanmar

The spatio-temporal development of a meandering river is controlled by its channel morphodynamics. In regions of rapid channel evolution, understanding the driving factors of meander migration is crucial in forecasting the rate and extent of morphological change. Sediment supply and fluvial discharge are the primary influences on migration rate, however climate oscillations are also integral in indirectly regulating migration rate through their control of regional precipitation, as well as the monsoon season of sub-tropical Asia. Despite this, an in-depth investigation into the impact of climate oscillations on meander bend migration remains undocumented. This study presents a satellite-based analysis of multi-decadal climatic forcing on the migration rate of the Sittaung River in Myanmar, through interpretation of the El Niño Southern Oscillation (ENSO). The mode of ENSO exerts significant climatic control on the migration rate of the meandering channels of the Sittaung River, with low-to-average migration rates recorded during dry El Niño events and peak migration rates observed during wet La Niña events. However, this climatic signal may have been obscured by certain local environmental conditions. In cases where meanders faced geological basement, the basement rock inhibited their migration through extension, forcing more rapid migration by way of seaward translation. Consequently, these translating meanders developed to be more elongate, with lower curvatures. Meanders downstream of the approximate tidal limit were less downstream skewed, indicative of tidal modulation, potentially obscuring the impact of fluvially driven climate forcing. Additionally, downstream of a major confluence, the input of sediment and fluvial discharge may have been regulated by upstream anthropogenic activities such as mining and dam construction, leading to greater variability in migration rate downstream of this confluence and further obfuscation of the climate signal.

Poison in the nursery: Mercury contamination in the tadpole-rearing sites of an Amazonian frog

Artisanal and small-scale gold mining (ASGM) has become a major threat for Neotropical forests. This technique for obtaining gold is a substantial driver of small-scale deforestation and the largest contributor of Hg emissions to both the atmosphere and freshwater systems globally. Previous studies have demonstrated the impacts of Hg accumulation on various aquatic ecosystems and organisms. However, its consequences in other, more discrete systems such as phytotelmata (water-holding plant structures), and the organisms therein, have so far gone unnoticed. Here, we show high concentrations of Hg (mean ± SD: 1.43 ± 2.19 ppm) in phytotelmata and other small pools, the aquatic microenvironments used by the Neotropical poison frog Dendrobates tinctorius as tadpole-rearing sites. In 17 % of the cases, we detected Hg concentrations above the severe effect level (SEL = 2 ppm) for freshwater sediments. Hg concentrations varied depending on pool characteristics and tended to increase in proximity to known ASGM sites. We did not find an effect of Hg concentration on the number of D. tinctorius tadpoles in a given pool. Tadpoles were found in pools with concentrations of up to 8.68 ppm, suggesting that D. tinctorius fathers do not avoid pools with high Hg levels for tadpole deposition. While further research is needed to determine the potential effects of Hg on tadpole development, we found an intriguing tendency for tadpoles in later developmental stages to have lower body condition when occurring in pools with higher Hg concentrations. Our findings provide evidence of relevant Hg concentrations in the terrestrial water systems used by phytotelm-breeding anurans, and highlight the need of further field and experimental studies investigating the implications of Hg contamination for tadpole development and behaviour and the overall conservation of Amazonian biodiversity.

Historical Hg accumulation (∼65 cal kyr BP) in upland lakes of the Southeastern Brazilian Amazonia: New evidence of the extent of geogenic and diagenetic control

The historical upland lake sediments in the Brazilian Amazon witnessed significant enrichment of total mercury (Hg). However, its spatio-temporal relationships between lakes and the main factors responsible for this enrichment are still poorly constrained. Given this, we geochemically investigated 12 radiometrically dated (extending back to ∼65 cal kyr BP) sediment cores from the Carajás plateau, Brazil. The Hg level in historical sediments presented a large temporal variability (from 1 to 3200 μg/kg), with maximum accumulation peaks observed between 30 and 45 cal kyr BP in core R2, LB3, and R1. However, the lack of the Hg peak in other cores (LV2 and LTI3) during the same period despite being proximity and non-correlation of these Hg peaks with the onset of major volcanic events indicates that this source has little bearing. Hg enrichment is highly dependent on the type of sedimentary facies, with higher values were associated with detritic facies (MI) and detritic+organic facies (P/M). Principal component analysis shows that aluminosilicate minerals and organic matter are essential hosts of Hg in sediments. The positive correlation between Al, Ti, and Hg in detritic facies and their strong coherence with Hg/TOC in R1, R5, LSL, ST02, and LB3 cores indicate that Hg is primarily of lithogenic origin. This can be substantiated by the higher background threshold value of Hg (574 μg/kg) in historical lake sediments compared to those in recent lake sediments (340 μg/kg). However, the most pronounced Hg peak (3200 μg/kg) in R2 around 45 cal kyr BP, which correlates positively with TOC, S, Se, As, and Mo indicates their diagenetic enrichment in organic-rich sediments under anoxic conditions. Thus, in addition to the lithogenic effect, it can be argued that diagenesis can play a significant role in prompting Hg enrichment in the Carajás lake sediments in Amazonia.

Mining wastewater treatment technologies and resource recovery techniques: A review

Mining wastewater can have adverse effects on the ecosystem; thus, treatment before discharging into the environment is of utmost importance. This manuscript reports on the effect of mining wastewater on the environment. Moreover, the currently used, effective and commercialised mine wastewater treatment technologies such as SAVMIN®, SPARRO®, Biogenic sulphide, and DESALX® are reported in this study. These technologies integrate two or more separation processes, which have been proven to be effective for the high recovery of salts and water for reuse. Some of the technologies reported can significantly recover salts and >95% of water. Modern pilot-stage and laboratory-scale treatment systems used for the recovery and removal of metals are also reported herein. Since some treatment technologies can generate highly toxic sludge and other waste products, the management of the generated waste was also considered. Some studies have focused on the treatment of wastewater at the laboratory level using the adsorption process. Most adsorbents exhibit promising results; however, there is insufficient research on reusability, toxic sludge management, and the economic analysis of the systems. Moreover, the implementation of adsorption systems in wastewater is necessary. Furthermore, the integration of treatment systems to recover precious metals at low concentrations is desirable in addition to water reclamation to achieve circular mine water.

Mercury cyanide complexes and their relevance as environmental contaminants

This review addresses the formation and relevance of mercury cyanide complexes as environmental contaminants. Gold extraction is traditionally carried out through the process of mercury amalgamation (Hg) due to its simplicity and low cost. However, this process is inefficient, capturing only about 30% of the gold present in the processed material. Additionally, mercury is toxic, mobile, and capable of accumulating in aquatic ecosystems, leading to its prohibition in several countries. As an alternative, cyanidation has been widely used in gold extraction. However, the frequent combination of Hg amalgamation with cyanidation can result in the formation of mercury cyanide complexes, which can be released into local water bodies, potentially impacting human health and the environment. This article reviews the existing knowledge of these complexes and highlights the remaining gaps in understanding their environmental behavior. It also emphasizes the need to address concerns related to the formation of these complexes and seek solutions to minimize their negative impacts. Furthermore, the article highlights the lack of updates in the literature regarding the impacts of cyanidation and the limited availability of comprehensive information on the topic. It is essential to conduct updated research in this area to advance knowledge and promote safer and more responsible practices in the mining industry.

Human Health Risk Assessment from Mercury-Contaminated Soil and Water in Abu Hamad Mining Market, Sudan

Artisanal and small-scale gold mining (ASGM) poses a significant global threat due to mercury emissions and resulting health hazards. This study focuses on assessing these risks in the Abu Hamad ASGM community in Sudan. Utilizing the Mercury Analyzer 3000 (NIC), analyses of twelve soil samples (including one tailings sample) and seven water samples revealed the highest concentrations near amalgam burning locations: 34.8 mg/kg in soil (S06) and 3.26 µg/L in water (W03). Concentrations decrease with distance, with soil near burning exceeding tailings (S05 = 19.0 mg/kg). Hazard quotients indicate mercury vapor inhalation as the primary exposure route from soil, with the Hazard Index reaching 5.34 for adults and 33.4 for children close to amalgam burning sites. Water samples generally pose little risk except for W03, where children face potential danger via ingestion (HI = 1.74). These findings emphasize the urgent need for adopting retorts and eco-friendly practices to reduce mercury emissions and protect ASGM communities.

An analysis of the foremost issues with artisanal and small-scale gold mining from Ghana's perspective

Ghana has abundant mineral reserves in many of its regions, and gold mining remains one of the country's main sources of revenue. Given Ghana's current position in the global gold market, this review provides insight into the ASGM sector to give an understanding of the pertinent issues in the sector and its role in the socio-economic development of the country. This review assesses the effects of ASGM operations in economic, social, health, and environmental contexts to raise awareness of issues related to ASGM. It evaluates the measures taken to lessen the consequences of ASGM and maintain the sector's long-term viability. This review considers the foremost issues, including continued Hg use in ASGM, recent use of cyanide in ASGM, pollution of water bodies, and toxic metal contamination. It takes into account sustainable measures and remedial techniques that Ghana has implemented to alleviate the negative effects and support best mining practices. The primary factors influencing people to participate in ASGM are the need for quick sources of income, the scarcity of jobs in rural areas, the economic hardship, the need to supplement earnings from other activities like trading, and the comparatively meager profits from agricultural activities. Findings indicated that to gain more traction in addressing the challenges in the ASGM sector, the involvement of the community and direct stakeholders is essential to promoting responsible mining and environmentally sustainable practices. This review will increase awareness and pressure on decision-makers, researchers, and ASGM communities about the relevance of environmental conservation and sustainability.

Environment Degradation, Health Threats, and Legality at the Artisanal Small-Scale Gold Mining Sites in Indonesia

Artisanal Small-scale Gold Mining (ASGM) activities, despite offering numerous economic incentives, inflict negative impacts on the environment and public health due to the use of mercury or cyanide. This study aims to compare three ASGM locations in Indonesia in terms of environmental impacts and potential health problems in the community. As part of this research, field surveys at three ASGM illegal locations with different conditions, observations, literature studies, and interviews with the community and stakeholders were conducted. At each of the survey sites, the potential threat to public health due to the use of mercury was determined to be high. Additionally, many of the environmental impacts detected were deemed to have reached a high-alert stage, in some cases even posing a level of extreme danger. Based on these results, it has become clear that a form of mining management which reduces the negative impacts on the surrounding environment and community health is needed. The suggestions put forward in this paper, including the call for greater control of ASGM, may also be applied in other developing countries which suffer from similar problems and conditions.

Environmental contamination and health risk assessment of potentially toxic trace metal elements in soils near gold mines - A global meta-analysis

Gold mining is the most important anthropogenic source of heavy metal emissions into the environment. Researchers have been aware of the environmental impacts of gold mining activities and have conducted studies in recent years, but they have only selected one gold mining site and collected soil samples in its vicinity for analysis, which does not reflect the combined impact of all gold mining activities on the concentration of potentially toxic trace elements (PTES) in nearby soils at a global scale. In this study, 77 research papers from 24 countries were collected from 2001 to 2022, and a new dataset was developed to provide a comprehensive study of the distribution characteristics, contamination characteristics, and risk assessment of 10 PTEs (As, Cd, Cr, Co, Cu, Hg, Mn, Ni, Pb, and Zn) in soils near the deposits. The results show that the average levels of all 10 elements are higher than the global background values and are at different levels of contamination, with As, Cd, and Hg at strong contamination levels and serious ecological risks. As and Hg contribute to a greater non-carcinogenic risk to both children and adults in the vicinity of the gold mine, and the carcinogenic risks of As, Cd, and Cu are beyond the acceptable range. Gold mining on a global scale has already caused serious impacts on nearby soils and should be given adequate attention. Timely heavy metal treatment and landscape restoration of extracted gold mines and environmentally friendly approaches such as bio-mining of unexplored gold mines where adequate protection is available are of great significance.

Pollution assessment of mercury and other potentially toxic elements in the marine sediments of Mambulao Bay, Jose Panganiban, Camarines Norte, Philippines

In Jose Panganiban, Camarines Norte, small-scale gold miners dispose of untreated tailings into nearby rivers, which eventually flow into Mambulao Bay. In this study, nine (9) marine sediments were collected and analyzed to assess the pollution of potentially toxic elements (PTEs) in Mambulao Bay. Au concentrations in the sediments were also determined. The results showed that the Mambulao Bay sediments have high concentrations of Hg and other PTEs. The average concentrations of potentially toxic elements in the marine sediments were observed in the following order: Zn (638 mg/kg) > Pb (297 mg/kg) > Cr (283 mg/kg) > Cu (209 mg/kg) > Ni (146 mg/kg) > As (35 mg/kg) > Hg (4.4 mg/kg) > Cd (1.4 mg/kg). Geoaccumulation index values suggest that Mambulao Bay sediments close to the Danao River estuary are strongly to extremely polluted by Hg, strongly polluted by Pb, moderately to strongly polluted by Zn, and moderately polluted by Cd, Cu, Cr, Ni, and As. A high average Au concentration (0.42 mg/kg) was also reported in the sediments. The enrichment values suggest that the PTE pollution has an anthropogenic origin, most likely from the artisanal gold mine tailings of Jose Panganiban. Most of the marine sediments have Hg, Pb, Zn, and Cu concentrations above the probable effect levels for PTEs, which can result in occasional adverse biological effects on the aquatic biota of Mambulao Bay. The average Hg content of Mambulao Bay sediments is higher than those of Honda and Agusan Bays, while the average Pb and Zn contents are higher than those of Honda and Butuan Bays, Boac River estuary, and Tañon Strait. These results can help the government address marine pollution in Mambulao Bay for sustainable aquatic resources and coastal management and can serve as a baseline for future monitoring and assessment of the water body.

In utero and lactational exposure to methylmercury elicits physical-chemical and morphological damages in the alveolar bone of offspring rats: The first toxicological findings

Methylmercury (MeHg) is the most common organic form of mercury (Hg) that humans are exposed and is considered an environmental pollutant. Several populations that live in endemic regions of MeHg exposure are subject to the toxicant for long periods, including pregnant women and children, causing damage to several organs during early periods of development. Alveolar bone is an essential structure for the oral cavity, responsible for supporting teeth and masticatory forces. However, evidence on the effects of MeHg on alveolar bone and the intrauterine and lactation period is lacking. Thus, this study aimed to investigate the effects of MeHg exposure during gestation and lactation on the developing alveolar bone of offspring rats after maternal exposure. Dams were exposed during 41 days of pregnancy and lactation, and the mandibles of the offspring were collected. The alveolar bone was analyzed by Fourier Transform Infrared Spectroscopy to evaluate the physicochemical composition; by Scanning Electron Microscopy for ultrastructural evaluation; by histopathological, histochemical, and morphometric for tissue analyses. In addition, bone quality was assessed by X-ray microtomography. MeHg exposure altered the mineral composition and caused histological damage associated with a lower quantity and thickness of bone trabeculae, as well as reduced osteocyte density and collagen fiber content. A reduction in trabecular thickness and bone volume and an increase in trabecular spaces were observed and were associated with anatomical compromise of the vertical bone dimensions. Thus, the results suggest that the developing alveolar bone is susceptible to the toxic effects of MeHg when organisms are exposed during intrauterine and lactation periods. From a translational perspective, these changes in the alveolar bone can help us understand possible abnormalities induced by toxic metals and highlight the need for care for structures other than those already seen as targets for damage triggered by environmental MeHg exposure.