World emissions of mercury from artisanal and small scale gold mining

Abstract

We estimate mercury releases from artisanal and small scale gold mining (ASGM) based on available data about mercury and gold exports and imports by country and from field reports from the countries known to have active ASGM communities. The quality of the estimates ranges from reasonable to poor across the countries. This paper aims to give a first order estimate of the amount and location of mercury being released into the environment globally by ASGM, to motivate stakeholders to improve the quality of these estimates, to illustrate the linkages between global mercury trade and its use in ASGM, and the fourth objective is to provide a practical outline of the options available for reducing mercury use in ASGM. We estimate that artisanal and small scale gold mining releases between 640 to 1350 Mg of mercury per annum into the environment, averaging 1000 Mg yr-1, from at least 70 countries. 350 Mg yr-1 of this are directly emitted to the atmosphere while the remainder (650 Mg yr-1) are released into the hydrosphere (rivers, lakes, soils, tailings). However, a significant but unknown portion of the amount released into the hydrosphere is later emitted to the atmosphere when it volatilizes (latent emissions). Considering that ASGM is growing, latent emissions conservatively amount to at least 50 Mg yr-1 bringing the total emission of mercury to the atmosphere from ASGM to 400 Mg yr-1. This estimate of emission to the atmosphere differs from the previous one provided in the 2002 UNEP Global Mercury Assessment both in terms of its magnitude (400 Mg yr-1, versus 300 Mg yr-1) and in the way the estimate has been made. The current estimate is based on a better understanding of ASGM and on a wider variety of information sources, more field evidence, better extrapolation methods, and independent testing by analysis of official trade data.