Int. J. Environ. Res. Public Health 2015, 12, 8971-9011; doi:10.3390/ijerph120808971 OPEN ACCESS International Journal of Environmental Research and Public Health ISSN 1660-4601 www.mdpi.com/journal/ijerph Review Integrated Assessment of Artisanal and Small-Scale Gold Mining in Ghana—Part 2: Natural Sciences Review Mozhgon Rajaee 1, Samuel Obiri 2, Allyson Green 1, Rachel Long 1, Samuel J. Cobbina 3, Vincent Nartey 4, David Buck 5, Edward Antwi 6 and Niladri Basu 1,7,* 1 Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI 48109, USA; E-Mails: [email protected] (M.R.); [email protected] (A.G.); [email protected] (R.L.) 2 Council for Scientific and Industrial Research-Water Research Institute, Tamale, Ghana; E-Mail: [email protected] 3 Faculty of Renewable Natural Resources, University for Development Studies, Nyankpala, Ghana; E-Mail: [email protected] 4 Department of Chemistry, University of Ghana, Legon, Ghana; E-Mail: [email protected] 5 Biodiversity Research Institute, Portland, ME 04103, USA; E-Mail: [email protected] 6 Centre for Energy, Environment & Sustainable Development, Kumasi, Ghana; E-Mail: [email protected] 7 Faculty of Agricultural and Environmental Sciences, McGill University, Montreal, QC H3A 0G4, Canada * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +1-514-398-8642. Academic Editors: Susan Keane and Paleah Black Moher Received: 7 May 2015 / Accepted: 22 July 2015 / Published: 31 July 2015 Abstract: This paper is one of three synthesis documents produced via an integrated assessment (IA) that aims to increase understanding of artisanal and small-scale gold mining (ASGM) in Ghana. Given the complexities surrounding ASGM, an integrated assessment (IA) framework was utilized to analyze socio-economic, health, and environmental data, and co-develop evidence-based responses with stakeholders. This paper focuses on the causes, status, trends, and consequences of ecological issues related to ASGM activity in Ghana. It reviews dozens of studies and thousands of samples to document evidence of heavy metals contamination in ecological media across Ghana. Soil and water mercury concentrations Int. J. Environ. Res. Public Health 2015, 12 8972 were generally lower than guideline values, but sediment mercury concentrations surpassed guideline values in 64% of samples. Arsenic, cadmium, and lead exceeded guideline values in 67%, 17%, and 24% of water samples, respectively. Other water quality parameters near ASGM sites show impairment, with some samples exceeding guidelines for acidity, turbidity, and nitrates. Additional ASGM-related stressors on environmental quality and ecosystem services include deforestation, land degradation, biodiversity loss, legacy contamination, and potential linkages to climate change. Though more research is needed to further elucidate the long-term impacts of ASGM on the environment, the plausible consequences of ecological damages should guide policies and actions to address the unique challenges posed by ASGM. Keywords: small-scale gold mining; Ghana integrated assessment; mercury; metals; water; public health; ecotoxicology 1. Introduction The practice of artisanal and small-scale gold mining (ASGM) is increasing in many low- and middle- income countries (LMICs), mainly due to the rising price of gold and widespread poverty. Gold from these informal mines may represent 20–30% of the world’s output [1]. It is estimated that about 15 million people work in ASGM and that perhaps 100 million people worldwide depend on the sector for their livelihood [2]. Gold has been mined in Ghana for over 1000 years [3], and in 2013 gold accounted for 34.4% of the country’s national export revenue [4]. The proportion of Ghana’s gold that is mined through ASGM has increased from 6% in 2000 to 23% in 2010 [5]. Artisanal and small-scale gold mining, like other extractive activities, raises numerous environmental concerns. Emissions of mercury (Hg) into the atmosphere as well as direct releases of mercury to soil and water are of primary concern because of the extensive use of mercury to amalgamate gold by artisanal miners. Recent estimates suggest that the ASGM sector is the primary source of mercury into the global atmosphere, accounting for approximately 37% (727 tonnes) of all global emissions [6]. While mercury has gained most attention, there exist many other direct and indirect factors that contribute to poor ecological conditions in ASGM communities (Figure 1). This necessitates that impacts on the natural system, as well as planning for interventions be viewed under a broad ecosystem lens. Int. J. Environ. Res. Public Health 2015, 12 8973 Figure 1. Framework linking key drivers and impacted natural systems. Principal domains of inquiry are highlighted. Framework is adapted from the Millennium Ecosystem Assessment [7]. 1.1. Objective This report is one of three papers [8,9] being co-published to provide a foundation for a special issue in the International Journal of Environmental Research and Public Health entitled “Integrated Assessment of Artisanal and Small-Scale Gold Mining in Ghana” (http://www.mdpi.com/journal/ ijerph/special_issues/asgm). This integrated assessment (IA) is guided by an over-arching policy- relevant question: What are the causes, consequences, and correctives of artisanal and small-scale gold mining in Ghana? More specifically, what alternatives are available in resource-limited settings in Ghana that allow for artisanal and small-scale gold-mining to occur in a manner that is safe for ecological health and human health without affecting near- and long-term economic prosperity? Given the complex and global nature of ASGM, an integrated assessment provides the framework for us to analyze economic, social, and environmental data, and co-develop evidence-based solutions with pertinent stakeholders [10]. The purpose of this report is to document and scrutinize environmental impacts that may arise from ASGM activities in Ghana. The ultimate goal of the endeavor is to identify response and policy options associated with ASGM in Ghana that would lead to improved ecological health and sustainability. Ideally, the options would be sustainable, low-tech, health-promoting, and socially acceptable, while improving the standard of living of people who currently are involved in ASGM activities. As part of the IA, here we present evidence from Ghanaian ASGM sites that document relatively high levels of metals (e.g., mercury, cadmium, arsenic, and lead) in ecological media including soil, foodstuffs, sediment, and water. Impairment of water quality (e.g., acidity, turbidity, and nitrates) was noted at many Int. J. Environ. Res. Public Health 2015, 12 8974 sites based on “snapshot” samples by several studies. We also review limited data on deforestation, agriculture, biodiversity, desertification, and ecosystem services for people dependent upon altered lands. 1.2. Limitations and Assumptions Substantial gaps in data availability, not only in Ghana but elsewhere, prevent a full assessment of ecological risks associated with ASGM. Public policy should be grounded in strong, objective, peer-reviewed science. Speculative conclusions and opinions about possible hazards based solely upon anecdotes and oversimplified chronologies are not a sufficient foundation to advance regulatory reforms or policies. Nevertheless, ecological concerns, especially those with scientific plausibility and those recurring across temporal and spatial scales, need to be taken seriously. In this report, all currently available evidence was reviewed and considered. As best as possible, all evidence from Ghana was reviewed (peer-reviewed and non-refereed; published and non-published; etc.), though studies from other regions were drawn in as appropriate. A majority of the evidence reviewed in this report was obtained from studies undertaken in Ghana. However, within the country, there exists wide variation in the types of communities and ecosystems in which mines are situated (e.g., the south is more tropical, populated, and developed than the north of Ghana). While a majority of ecological issues (e.g., mercury contamination, land use degradation) are ubiquitous across sites, it is recognized that some risks may be site-specific owing to, for example, variation in types of receptors (e.g., organisms, vegetation) present. For the purposes of this assessment, we maintain broad generalizations as the focus is on developing countrywide response options. There is a low level of research on the effects of small-scale gold mining on the natural environment in Ghana. Many studies are based in areas with varied and overlapping activities (i.e., large, small-scale, and illegal mining activities occurring simultaneously) making it difficult to specifically identify ASGM’s role in affecting ecological health. In addition, ASGM sites may cluster, making it difficult to isolate impacts associated with single sites. It is also near impossible to distinguish between legal and illegal ASGM mining operations, and thus determine if differences exist between the groups in terms of their impacts on the natural environment. In terms of operational methods, it is difficult to differentiate between the two groups of miners because they use similar methods for obtaining mineral-laden ore and for extracting the gold. This review is also limited by the available data in other studies. While a few studies provided full datasets to adequately summarize measures of central tendency, a number of studies lack information on the distribution and spread of metals concentrations, for example, or explicit information on the number of samples and subsamples collected. A few studies with inadequate information on data collection or low quality assurance and control were excluded from this review. The lack of coordination between research institutions, academia, and policy-makers; funding for issues of ASGM; the political will to implement policies; and legal and institutional frameworks concerning mining in Ghana all pose barriers to providing and exchanging information and implementing changes. Int. J. Environ. Res. Public Health 2015, 12 8975 2. An Assessment of the Ecological Health Issues Here we review and analyze natural science issues that arise because of ASGM in Ghana by discussing the causes, status and trends, and consequences of key hazards. This assessment summarizes scientific knowledge to help build consensus and guide decision-making in the selection of response options. The information is intended to be an objective description of the current conditions. Here the key consequences of ASGM towards the health of natural systems are itemized and briefly described. These consequences serve as means to prioritize, combine, and summarize the most important points identified in the previous section. Figure 2 displays the causes and consequences highlighted in this report. Figure 2. Key ecological hazards in the Ghanaian artisanal and small-scale gold mining (ASGM) sector. Silhouettes adapted from UNEP Mercury: Time to Act (2013) [11]. 2.1. Mercury Contamination 2.1.1. Causes Mercury is a naturally occurring metal that exists in three primary forms in nature: elemental (Hg0), inorganic mercurial salts (e.g., HgS, HgCl , Hg+, Hg2+), and organic mercury (e.g., CH Hg, or 2 3 methylmercury). Elemental mercury is used in ASGM because of its ability to isolate gold from other non-target minerals. Mercury creates a bond with gold, called an amalgam. Because of the low vapor pressure of mercury, burning the gold-mercury amalgam leaves the valuable gold behind. Mercury emitted during amalgam burning can have significant impacts at the local scale in villages and towns where mercury vapor is emitted, and globally when that mercury vapor enters the global atmospheric pool and is transported large distances before being redeposited as inorganic mercury on the landscape [12]. Inorganic mercury can be methylated (bound to carbon) by microorganisms mainly in aquatic ecosystems. Methylmercury is often found in fish at higher concentrations since it is able to bioaccumulate and biomagnify in organisms [12–15]. ASGM with mercury can result in atmospheric emissions as well as direct releases to soil and water, accounting for an estimated 37% of total global anthropogenic mercury emissions annually [6]. It has now been estimated by the United National Environment Programme (UNEP) that ASGM has surpassed fossil fuel combustion as the largest Int. J. Environ. Res. Public Health 2015, 12 8976 contributor to global anthropogenic mercury in the atmosphere [6]. The largest regional consumers of mercury for ASGM are East and Southeast Asia, South America, and Sub-Saharan Africa [16]. The use of mercury was banned in Ghana between 1932 and 1989, but is now in use [17]. Registered ASGM operators and licensed traders can purchase and trade mercury legally through authorized dealers (Ghana Government 1989, PNDCL 217 S.96) [18], such as the Precious Minerals Marketing Corporation (PMMC) Ltd. [19]. Mercury use, however, appears to be greater than what is officially available, according to the Ghana Minerals Commission and the PMMC, suggesting a significant “black market” for mercury. Recent upsurges in the demand for mercury may be in response to market conditions, as both the rising price of gold and falling demand for diamonds has driven an increase in ASGM activity [8,19]. Figure 3. Mercury (Hg) cycle in a typical artisanal and small-scale gold mining (ASGM) process. Numbers represent key steps in the ASGM process: 1—excavation, 2—crushing and grinding, 3—sifting/shanking, 4—washing/sluicing, 5—amalgamation, and 6— burning. Letters represent key steps in the mercury cycle: A—residual mercury from amalgamation may be discarded in local soil and water, B—volatilization of elemental mercury into the atmosphere, C—oxidation of elemental mercury, D—deposition onto local terrestrial systems, E—deposition onto local aquatic systems, F—methylation of inorganic mercury to methylmercury. Mercury is generally used in ASGM without any type of capture system to reduce chemical releases into the environment (Figure 3). Many miners have rejected retorts and complain of a slower process Int. J. Environ. Res. Public Health 2015, 12 8977 and an inability to see the gold [12,20]. Even transparent retorts, such as the ThermEx® retort promoted by the Ghanaian government, have been underutilized because of their low capacity and fragility [20]. For example, a survey of 44 licensed and 77 unlicensed miners in the Denkyira corridor showed only 27% of respondents using a retort while 68% used open flame [21]. A life cycle analysis of ASGM in Peru by Valdivia and Ugaya [22] examined ASGM mining impacts and mercury use from gold ore. Using an alluvial mining case that most closely resembles ASGM in Ghana, they estimated that 2 kg of mercury is used to produce 1 kg of concentrated gold ore (99.5% gold) [22]. The authors of this paper visited two ASGM sites in Tarkwa, Ghana to estimate Hg use in the ASGM process. At one small-scale mine, after processing and concentration using sluices, approximately 210 grams of elemental mercury was added to the concentrate ore. Miners then combusted the amalgam ball, leaving behind sponge gold weighing 211.3 g. This material was then smelted using borax to remove any remaining impurities. Assuming impurities between 2–5%, the final amount of gold produced would be ~200g. Figure 4. Regional map of Ghana. Key mining areas (Obuasi, Tarkwa) and the capital (Accra) are indicated. Int. J. Environ. Res. Public Health 2015, 12 8978 2.1.2. Status and Trends Concern about mercury contamination in ecological media near ASGM sites in Ghana has prompted a number of studies assessing the extent of contamination. In total, 47 studies were found in nine regions of Ghana that documented mercury levels in soil, foodstuffs, sediment, water, tailings, and fish (Tables S1–S6, S19). Of the 47 studies, 20 sampled in the Western Region, 11 sampled in the Ashanti Region, nine sampled in the Central Region, and eight sampled in the Greater Accra Region. Only two studies sampled in the Eastern and Upper East Regions, respectively, and one study sampled in each the Northern, Volta, and Brong-Ahafo Regions. Research has focused in the southeast (Western, Ashanti, and Central Regions), where ASGM has historically been most common, but ASGM also occurs in the Upper East and Upper West Regions. Figure 4 displays a regional map of Ghana for reference. Below we provide a brief review of these studies with key results emphasized. International guideline values were used to evaluate mercury concentrations in various media when available, otherwise selected U.S. guidelines were used (Table 1). Figures 5–9 show results synthesized from all relevant peer- reviewed data we could find. Table 2 summarizes the number of studies and samples reviewed for mercury and other heavy metals in various media, as well as reported mean concentration ranges. District boundaries have changed significantly in the past five years, but since boundary maps are not yet available and many studies reviewed refer to older districts, we have used the district names referred to in each respective study or older districts where geographic boundaries are available. Study sites referred to as “reference” sites in each respective study were designated as “non-mining” in this review. Since ASGM often occurs in areas with large-scale gold mining (LSGM), many sites reviewed include areas with ASGM and LSGM, and in areas near LSGM. These sites were designated as “mining” areas in this review. When detection limits were provided, a standard protocol of dividing the detection limit by √2 was followed for values below the detection limit. Values were reported as provided in each respective study when detection limits were not provided (i.e., as zero or not detectable [ND]). Mercury concentrations in soil were reviewed in 11 studies including 727 samples (565 from ASGM and LSGM areas and 54 from non-mining areas) from the Western, Central, Ashanti, and Upper East Regions (Table 2, Figure 5). Mean total mercury concentration in soil (range across studies: not detectable–185.9 µg/g) were above the U.S. Environmental Protection Agency (U.S. EPA) Ecological Soil Screening level of 0.1 µg/g mercury in 88.0% of sampling sites reviewed at ASGM and LSGM sites (n = 25) [23,24]. Samples were generally below the Canadian Environmental Quality Guidelines (6.6 µg/g or residential soil; and 50 µg/g for industrial soil [25]). Some individual soil samples greatly exceeded guidelines (e.g., 185.9 µg/g Hg, abandoned Tarkwa mine site; 330.0 µg/g, ASGM community in the Upper East Region) [26,27] in certain cases. Mercury concentrations did not follow any obvious trend by season or temporally. Most sites in southern Ghana have mean mercury concentrations below those observed in northeast Ghana, with a couple exceptions in the Wassa West District near Tawkwa, Western Region [26]. Concentrations were highest from samples taken on-site of ASGM activities (n = 8 sites; mean range: 0.792 to 185.9 µg/g), followed by studies in ASGM and LSGM areas (n = 17 sites; mean range: 0.020 to 2.40 µg/g), and non-mining areas (n = 6 sites; mean range: not detectable to 0.170 µg/g). Samples from edible plants were highest from sites closest to ASGM and LSGM activities (Figure 6, Table S2). One out of six sites measuring mercury in cassava (n = 3 studies) and one out of two sites Int. J. Environ. Res. Public Health 2015, 12 8979 measuring mercury in plantains (n = 2 studies) were found to exceed the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) guideline of 0.5 µg/g [28]. Figure 5. Metals in soil samples in southwest (bottom panel) and northeast (upper panel) Ghana. Each symbol represents the mean metals value (µg/g, ppm) from a single study in that region, and for illustrative convenience the symbols are scattered randomly within the district where the sampling took place. Political regions are distinguished by different shades of grey. Mean total mercury (Hg), lead (Pb), cadmium (Cd), or arsenic (As) above or below guidelines are indicated. Int. J. Environ. Res. Public Health 2015, 12 8980 Figure 6. Metals in edible plant parts in southwest Ghana (bottom panel). Each symbol represents the mean metals value (µg/g or ppm) from a single study in that region, and for illustrative convenience the symbols are scattered randomly within the district where the sampling took place. Political regions are distinguished by different shades of grey. Mean total mercury (Hg), lead (Pb), cadmium (Cd), or arsenic (As) above or below guidelines are indicated. Plants sampled include cassava (Manihot esculenta), cocoyam (Xanthosoma sagittifolium), water cocoyam (Colocasia esculenta), plantain (Musa paradisiacal), and water fern (Ceratopteris cornuta) grown in or around current or former ASGM sites.