Many people are interested in small-scale artisanal gold mining (ASGM) because it is one of the most environmentally destructive economic activities out there. It is also an occupation pursued by tens of not hundreds of thousands of Indonesians who—rightly or wrongly—perceive it to be one viable way to earn a living. And ASGM also happens to be the world’s single largest source of environmental mercury emissions, making it extraordinarily toxic to the individual miners, to the communities and ecosystems in which they live, and more broadly to all of us.

I recently had the opportunity to travel to Kalimantan, the Indonesian part of Borneo, to observe ASGM as it is actually practiced. I was able to learn how this process works, and here is what I learned.

Gold is found in trace amounts in the soil in this part of Indonesia. To extract it in economically significant quantities, one needs to find a way to collect it in amounts that are large enough to see. What this means is processing tons and tons of soil, separating out the sediment by size to identify the particulate in which it is found. Here is what that looks like.

You can see here that the miners have dug a giant pit in the earth, and are processing all of the dirt and sand by passing it across a series of inclines that separate the sediment according to size. Most of what is produced is waste, which the miners deposit into large piles. The miners keep the desired particulate and save it for further processing.

If this were the only step in the process, this would still be an extraordinarily destructive activity. It destroys the soil and removes all vegetation from it. Traveling to this site we passed miles and miles of what looked like sandy beach that was once a rich ecosystem covered in plant and animal life. It will take dozens and dozens of years to reestablish plant life on that land. Even longer for it to revert to its former natural state.

The next step, though, makes this not just environmentally destructive on a local scale but also of concern to the regional, national, and global environment. Mercury can be added to a slurry of particulate and water to entice the gold particles to “clump together” so that the miners can find them.

Here the miner is standing in a pool of water, sediment, and mercury. He is panning for the gold-and-mercury amalgam. What remains after this process is a slurry of particulate, water, and mercury that is either dumped into the river or just left there (where it eventually will make its way into the river).

When the miners find the clumps of gold and mercury, they then go through a final process of heating the amalgam.

This miner is using a blow torch to heat the amalgam. Because mercury is liquid at room temperature, the heating process makes the mercury evaporate, leaving nearly pure gold as the remainder. The miners can then sell this to gold traders in the nearest city.

As a vapor or gas, the mercury that was used in the mining process travels through the air and beyond this particular site. There are many things that can happen to it. It can condense back to liquid form and “rain down” locally onto land and into the river. In this case, it enters the food web—through bacteria and archaea that produce methylmercury, later consumed by phytoplankton, then zooplankton, and so forth on up to fish, birds, and humans. Methylmercury concentrations increase exponentially (literally—by one order of magnitude) at each step in this process.

It is also possible that mercury gas remains in that state for some time, and travels via winds and weather far beyond any particular site. It is thus a global environmental problem, as ASGM contributes to the global stock of environmental mercury. The tuna that you catch off the coast of New England has elevated mercury levels as a direct result of the mining done in Indonesia.

There is lots more to say about ASGM and its socioeconomic context, and much has already been written about it. A good place to start would be this recent issue of Inside Indonesia on mining, and in particular, this essay by Semiarto Purwanto that describes more about the region that I visited. One might want to know the social context of gold mining, and who participates—the indigenous Dayaks, or migrants from other parts of Indonesia? About the consequences—not just for miners exposed to mercury vapor but to the ecosystems in which mercury inevitably passes. One might want to know where the mercury comes from—who produces it, and how is it distributed to the miners? One might also want to understand the international political economy of both gold and mercury—global treaties such as the Minamata Convention (of which Indonesia is a party) that aim to eliminate the release of mercury into the environment, and the global market for gold and how ASGM fits into it. Here is an area in which the social, environmental, and natural sciences might fruitfully collaborate.