Humans have historically used mercury for a variety of purposes, however, the massive use of mercury since the modern period has caused global biological and environmental pollution. For this reason, an international treaty, "the Minamata Convention on Mercury", entered into force in 2017, which strictly restricts the development and use of mercury. However, mercury continues to be released into the environment through human activities. The largest source of mercury is "Artisanal and Small-Scale Gold Mining (ASGM)", which uses mercury to adsorb and accumulate (amalgamate) gold. The gold is recovered by heating and vaporizing the mercury from the amalgamate.
In Indonesia, which is rich in various subsurface resources, ASGM has been practiced on several islands and the country is one of the world's largest mercury emitters. Our research project (JSPS No. 19H04334) has studied the present situation of ASGM in the western part of Sumbawa Island and its effects on workers and the surrounding environment. In the process, we found that ASGM on Lombok Island has different characteristics from that on Sumbawa Island, so we conducted a new survey on Lombok Island as well.
In December 2022, we visited ASGM-related sites in the central and southern parts of Lombok Island, observed the local conditions, interviewed people engaged in ASGM, and collected samples. Samples were collected from tailings and wastewater produced by ASGM, and water that is used for ASGM as background.
In the study area, many ASGM practitioners engaged in it on a very small scale as a side job, and these workers had generally started ASGM within 10 years. It was found that a regional network has been formed among ASGM practitioners and a division of labor was established among them. Many of the very small-scale ASGM practitioners purchased rocks from those who were in charge of the process from procurement of raw stones to crushing and milling. Some of them also sold the tailings produced by ASGM to larger-scale ASGM operators. The spatial scale of such a network exceeded approximately 40 km in linear distance.
From the viewpoint of environmental pollution, such a regional network implies that the pollution source is moving and spreading over a wide area. Therefore, it concerns that pollution is occurring over a wide area. Even if the scale of contamination at each site is not large, groundwater contamination is likely to be occurring in many areas, as many of the ASGM effluents infiltrate into the ground. In addition, in a coastal area, wastewater is discharged directly into the sea, which may lead to marine environment pollution, as in the case of Minamata Bay.
On the other hand, some ASGM practitioners have introduced the Borax method. Although the Borax method used in the study area is not sophisticated, it does not use mercury and can recover the gold of higher purity. Therefore, they have expectations for the Borax method.
