S17 (I) Mercury in artisanal and small-scale gold mining

Mercury releases from the incineration of amalgam in artisanal and small-scale gold mines (ASGM) pose serious environmental problems in Bolivia. In the National Area of Apolobamba Integrated Management (ANMIN Apolobamba), located in the Andean region of La Paz province, there are many high elevation artisanal and small-scale gold mines (ASGM) in where intense mining activities are carry out, and the mercury is still being used in the amalgamation processes that involv the use of incineration facilities to vaporize Hg to separate Au from the amalgam. Facilities at these incinerators (or burning areas) range from crude open flame burners in the yard or inside the house of individual miners to common small places for use by group (or cooperative) of miners. The vaporized Hg is known to condense and settle on plant leaves, soils and water bodies and impact on the the main food sources - meats from llama, alpaca and sheep. Our objetive is evaluate the anomalously high Hg contents in soils and native plants around the incineration areas. We collected surface soil and plant samples and total Hg were determinated. Mean contents of Hg in soils were between 0.5 and 48.6 mg Hg kg^-1 soil and were at least 5 to 60 times more compared to Hg in control sites and exceeded the soil Hg threshold levels in some European countries. Also our data revealed that Hg in all plant samples have > 0.1 mg Hg kg^-1 plant limit for any desirable animal feed established by the European Community. The high level of plant Hg may elevate the risk to the accumulation of Hg into the food chain because the camelids that are entirely dependent on limited forage with high Hg are the major providers of meat - the main food source for the miners in these high altitude areas. In addition, erosion of soils with high total Hg from many ASGM point sources is significant potential Hg contributor to the contamination of the lower reaches of the Amazon basin. In this overall context, the first actions could be trying to organize and manage its practice, offering cleaner technical alternatives and making local people aware of mining contamination and its risks.

Artisanal and small-scale gold mining remains the largest use of mercury globally, and the source of the greatest releases to the environment on a global basis. While considerable attention has focused on releases from artisanal and small-scale field operations, the second-stage processing of the miners’ ore is a less well-known source of significant mercury release and exposure. This presentation will discuss the magnitude of the problem as well as technical approaches to controlling mercury vapor releases from small-scale gold processing, which takes place in gold shops and buying agencies throughout the world. The presentation will include a detailed explanation of the USEPA/ANL Mercury Capture System.

Artisanal and small scale gold mining (ASGM) is responsible for large releases of mercury to the atmosphere. Small scale retail gold buying and refining facilities (commonly referred to as “Gold Shops”) are responsible for a significant part of these airborne releases, and are considered to be the single most important source of urban and semi-urban mercury emissions in regions with small scale gold production. Detailed quantitative data on the character of these gold shop emissions have been lacking. This paper provides a comprehensive characterization of airborne mercury emissions from ASGM gold shops in major gold producing regions in Brazil and Peru. The results of a suite of studies examining the mercury aerosol and vapor releases of gold shops in nine Amazonian and Andean gold producing communities are presented. Ambient airborne mercury concentrations, which indicate high levels of exposure to the general public in these communities are also presented.

Artisanal and small scale miners (ASM) use mercury to extract gold in developing nations worldwide, contributing an estimated 25% of global gold production and 30% of global Mercury emissions annually. About 350 Mg/a of this mercury is released directly to the atmosphere during amalgam burning and gold refining, but the behaviour of these emissions is poorly understood.

This study uses high-resolution roving measurements of atmospheric mercury emissions in urban areas of Colombia, Peru, Suriname, Brazil, Ecuador and Chile to show that the human health risk from airborne mercury is acute in these areas. These data can be used to map mercury distributions, emissions frequencies, human exposures, and dispersion. Rovers consist of a mercury vapour analyzer and GPS, and low speed transects are designed such that they cover the greatest area of the affected urban landscape in one hour. Repetitions over many days produce a dataset that highlights hot spots and estimate exposures of the area’s inhabitants. High frequency meteorological measurements further enhance these data, enabling comparison of atmospheric models to observations, and allowing study of urban pollution dispersion. Calibration of mercury observations is essential, and methods are presented that reliably quantify the local background concentration, as well as remove instrument drift and lag effects.

This is the first study to both measure mercury emission rates and map the resulting urban vapour distributions. The results clearly show that airborne mercury contamination in South American mining towns is acute. For example, in the urban core of Segovia, Colombia, the average mercury vapour concentration is 1264 ng/m³, which is hazardous according to the World Health Organization. Instantaneous street concentrations in all countries visited regularly exceed the WHO lowest observed effect level of 20000 ng/m³. As mercury is colourless and odorless, people are often unaware or skeptical about the magnitude of the problem. The results of these surveys can help convince people and governments that change is necessary, and show them where hazards are highest.

Artisanal and small scale gold mining (ASGM) has been carried out in Tanzania since the colonial days. It is estimated that nearly 49 % of the ASGM activities which comprise about one million people, involve in gold mining. Their combined economic and social impacts are substantial for the economy of Tanzania as they make a significant contribution to the livelihoods of a large proportion of rural communities and country’s export earnings. ASGM originally worked in mineral deposits that now host large-scale mining projects in Tanzania.

Despite the positive contributions, however, ASGM activities have negative impacts. Due to lack of technical know-how by the operators and adequate support, most activities are carried out in an uncontrolled manner. The uncontrolled use of mercury through amalgamation causes environmental effects.

Studies in Tanzania show that ASGM wash gold bearing silt or mix powder produced by pounding gold-bearing rocks with water to produce concentrated liquid containing suspended particle of gold. This is mixed with mercury to form an amalgam, which is heated in open air to burn off the mercury leaving the gold around 80% purity.

Extensive awareness raising and training campaigns within gold mining areas in the country should be conducted for mining communities in order to demonstrate the environmental and economic benefits of the improved gold extraction techniques.

The Government of Tanzania is closely following up the research on borax use as an alternative to extract Au which was conducted in some districts. Since the mercury use in ASGM has significant environmental and public health impacts there necessitate an introduction of a simple alternative and safer methods for process Au within ASGM communities.