Mobilisation of Hg through the activities of small-scale gold miners exerts a major influence on the global pollutant Hg budget. A Technology Development and Research (TDR) programme (R6226) funded by the UK Government Overseas Development Administration (ODA), Engineering Division seeks to address the adverse impacts of mining-related Hg contamination. The project objectives are:
Provision of a generic protocol for monitoring the sources and fates of contaminant mercury in gold mining regions.
Assessment of human and ecotoxicological impacts of mercury pollution and calculation of human/environmental risk thresholds.
Promotion of improved methods of gold recovery with applicability to the artisanal sector.
Design and implementation of practical legislation for abatement of mining-related mercury contamination.
Initial geochemical surveys carried out in the Philippines (Williams et al., 1995, 1996a, 1996b) have led to the development of protocols for monitoring the sources and fates of contaminant mercury in gold mining regions. In order to test the applicability of these protocols in other topographic, climatic and geological settings, a systematic assessment of the distribution of Hg and other contaminants in the Ponce Enriquez artisanal gold mining area of Ecuador was carried out in July 1996 in collaboration with CODIGEM, DINAPA, DINAMI and Swedish Consultants working with the World Bank funded \"Proyecto Desarrollo Minero y su Control Ambiental\" (PRODEMINCA).
A major environmental concern in the Ponce Enriquez mining district is the potential exposure of workers to mercury as a result of its use in the recovery of gold. There is also concern regarding mercury contamination of soil, stream water, stream sediment and vegetation, particularly in downstream areas hosting economically important banana plantations and shrimp farms. In addition to the Hg hazard, large volumes of gravity tailings holding high concentrations of potentially harmful elements (copper and arsenic) are stored on the steep slopes of the Bella Rica mining sector. At the time of the BGS survey, no comprehensive information existed on the level and spatial extent of degradation caused to the aquatic environment by mining and mineral processing in the Ponce Enriquez area.
Filtered water, suspended sediment, stream bottom sediment and heavy mineral (panned) concentrate samples were collected at c. 30 sites. Mercury and a range of other elements were determined in these samples by a combination of CV-AFS and ICP-AES methods. In this report, multi-element geochemical data are presented and their significance is discussed.
The Ponce Eniiquez survey has confirmed the utility of the BGS monitoring protocol established in the Philippines under this TDR project. Longer term monitoring of this area is planned under the World Bank funded PRODEMINCA project (Monitoreo de los impactos ambientales, socio-económicos y sobre la salud, relacionados con las actividades mineras) and the Fundacion CENDA-COSUDE (Proyecto Mineria Sin Contaminación) project. More detailed monitoring is required to verify the level, frequency and duration of high As and Cu fluxes in stream water and sediment. There is probably little justification for major BGS involvement in additional Hg contamination studies in the Ponce Enriquez area under the auspices of this TDR project. Data collated through the World Bank PRODEMINCA project and the Proyecto Minena Sin Contaminación should provide a comprehensive picture of the influence of Hg, As and Cu contamination on biota downstream of Ponce Enríquez. This should provide supporting information for work carried out in the Philippines directed towards the other main objectives of the current project (i.e. assessment of human and ecotoxicological impacts and the promotion of improved methods of gold recovery with applicability to the artisanal sector).
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