PUB - Publikationen an der Universität Bielefeld

**Background:** Mercury is used in more than 70 countries to extract gold in artisanal small-scale gold mining (ASGM). The application of mercury is simple and plays a key role in the livelihood for more than 16 million gold miners. Mercury is added to the crushed ore and builds an amalgam with the gold it contains. The amalgam is then smelted, the mercury evaporates, and gold remains. The amalgam smelting is the main source of mercury exposure in ASGM. ASGM is the largest anthropogenic source of global mercury pollution. The toxic metal poses a risk to the health of both the miners involved and the residents in the area, who do not work in ASGM. Mercury can be detected in critical quantities in the human bodies of both groups. The local threat aside, the mercury released is also of global concern due to its high transportability and persistence in the environment as well as its tendency to bioaccumulate. Mercury is neurotoxic and its harmful effects on the development of unborn children and infants are particularly alarming. Describing and reducing the health risk posed by the mercury used in ASGM are urgently needed measures, as demanded in the 2013 agreed Minamata Convention on Mercury.
Objective and research questions: The overall objective of this thesis is to apply public health measures to describe the health risk due to the use of mercury in selected ASGM areas and to test the feasibility of a mercury-free extraction procedure using borax to reduce the risk. The main research question is: How to describe and reduce the human health risk of mercury used in ASGM? Four subquestions regard (I) the relevance of addressing different subgroups when attempting to describe and reduce the human health risk of mercury used in ASGM, (II) the mercury body burden in ASGM, (III) the health burden due to mercury exposure in ASGM, and (IV) a means of reducing the health risk due to the use of mercury in ASGM. The response to the research questions is included in the present synopsis and based on five published and peer-reviewed scientific papers.
**Materials and methods:** This thesis comprises different materials and methods. The literature used was searched by applying narrative and systematic approaches (papers P1, P2, P3, P4, P5). P1 is a narrative review about children’s health and exposure to mercury. In P2 and P3, the mercury body burden was determined using human biomonitoring (HBM) data collected in Mongolia in 2008 (P2) and Zimbabwe in 2004 and 2006 (P3) and compared with the German HBM values, HBM I and II (P2, P3). Health effects attributable to mercury were analyzed for the sample from Zimbabwe using anamnestic data, neuropsychological testing, and clinical examination (P3). Cases of chronic mercury intoxication were identified and the sample prevalence determined and extrapolated to all of Zimbabwe (P3). The environmental burden of disease (EBD) was quantified in terms of disability-adjusted life years (DALYs) including primary, secondary, and modeled data (P3). Disease-specific and generic health state descriptions were developed which could be used to derive disability weights (DWs) for disease stages of the intoxication due to exposure to mercury in gold mining. Information about the health-related quality of life (HRQoL) and a comprehensive list of possible symptoms were gathered by expert elicitation. The list of symptoms was supplemented by a systematic literature search (P4). The feasibility of a mercury-free gold extraction method using borax was tested in a field project in Kadoma, Zimbabwe, in 2013 (P5).
**Results:** Children are particularly vulnerable to mercury exposure. They might be exposed directly and indirectly to it from ASGM while several subgroups (pregnant and breastfeeding women, parents working as miners, etc.) play a role in the children’s exposure (P1). In the districts Bornuur and Jargalant, Mongolia, a sample of women of child-bearing age involved in mining or living in mining areas (P2), and in Kadoma, Zimbabwe (P3), a sample of adult and child male and female miners were investigated. Both samples showed raised mercury concentrations in human specimens above health-related exposure limit values. The analyses of health data showed a higher frequency of possibly mercury-related health effects in miners in comparison to controls (P3). The EBD in male and female adult and child miners in Zimbabwe in 2004 was high (total of 95,400 DALYs, 8 DALYs/1,000 population) while subgroup analyses identified males, particularly male children and young male adult workers, as the group with the highest burden (P3). The HRQoL of individuals with chronic metallic mercury vapor intoxication (CMMVI) caused by mercury exposure from ASGM can be substantially reduced by a number of health symptoms of varying severities (P4). In field testing, the application of a mercury-free gold extraction method using borax has been considered as feasible, what could reduce the health risk posed by mercury in ASGM (P5).
**Discussion:** This thesis provides evidence to improve the understanding of the human health risk due the use of mercury in ASGM. The human health risk posed by mercury in ASGM can be described as considerable, subgroup-specific, and, indeed, reducible. The health risk is considerable given the particular risk of children (P1), the high mercury concentrations in specimens obtained from miners and not occupationally exposed residents in ASGM areas (P2, P3), the high prevalence of intoxications and EBD of miners (P3), the extensive range of possible health symptoms, and the reduced HRQoL due to mercury intoxication (P4). The health risk can be considered subgroup-specific for several reasons. These include the particular risk to children and the influence which the behavior of other subgroups has on the children’s exposure (P1), the human body burden detectable in miners and non-occupationally exposed residents in ASGM areas varying by sex and age (P2, P3), the prevalence of intoxications and EBD of intoxications in miners varying by sex and age (P3), and the extensive range of possible health symptoms which can but do not have to occur in individuals as a result of exposure to mercury (P3, P4). The health risk is reducible with regard to the fact that a mercury-free gold extraction method has been tested successfully (P5). Research of international literature reveals significant differences in mercury concentrations in human specimens of subgroups in ASGM areas. Combining HBM with health data is reasonable for identifying cases of chronic mercury intoxication, has also been done in samples of other countries. Based on the preliminary DALY estimates, chronic mercury intoxication from ASGM was integrated in the top 20 causes of the BoD in Zimbabwe in 2004 as estimated by the World Health Organization (WHO) in the GBD 2004 update. A national estimation of DALYs due the use of mercury in ASGM had not been investigated up to this point. Other DALY quantifications with focus on mercury are available, however, the research gaps for the use of mercury in ASGM (e.g., missing DWs) are mentioned in international literature. Results about the HRQoL of CMMVI enabled comparisons with the HRQoL of other health states investigated in other studies. The mercury-free gold extraction procedure using borax was identified as feasible in ASGM in Kadoma, Zimbabwe, and was also reported from other ASGM areas. However, a sustainable introduction needs follow-up implementation activi-ties. Further main limitations of this thesis are restricted literature search strategies, small sample sizes, and the reliance on assumptions and modeled data. The results of this thesis can be integrated into 8 of 9 steps of a human health risk analysis. Measures used to describe the risk should be applied in a health impact assessment (HIA) to monitor the success of a comprehensive introduction of a mercury-free extraction procedure.
**Conclusions:** It is the conclusion of this thesis that the human health risk from mercury used in ASGM is considerable, subgroup-specific, and reducible. Various materials and methods were used, while some (e.g., estimation of DALYs and determination of HRQoL) had not been applied to this topic before. The relevance of different subgroups in the effort to describe and reduce the risk due to mercury from ASGM was identified. Some subgroups require attention most urgently either due to their particularly high vulnerability (fetuses and children), their influence on the exposure of others (e.g., pregnant women), or their particularly high EBD (young male gold miners). This thesis underlines the necessity to reduce the human health risk due to mercury in ASGM. The results of this thesis should be understood as an impetus to finding solutions for the continuing threat to human health from the use of mercury in ASGM.