So Arias and dozens of other residents from the rural settlement of Río Viejo (Old River) — joining forces with members of the police and university researchers — embarked on an experiment to repair the damage. On the site, they began to grow two plant species thought capable of absorbing the mercury: the Cecropia obstusifolia tree, commonly known in the area as Guarumo, and the Jatropha curcas shrub, or Piñon.
Two years later, 50% to 60% of the mercury in the soil had been absorbed, and “other plants grew in the shade and insects returned,” says José Luis Marrugo, director of the Regional Water Institute at Colombia’s University of Cordoba, who was involved in the project. “Biodiversity was restored.”
Using trees and plants to absorb the contaminants in soil as they grow is known as phytoremediation. It’s an approach to land restoration used elsewhere in the world, says Chris Anderson, an environmental science professor at Massey University in New Zealand. Plants can clean up pollution from metals, pesticides and even oil. Anderson has been investigating uses of phytoremediation in small-scale mining in Indonesia.
Officials in Colombia hope the method is applied in other places damaged by mining, after seeing quick and dramatic results in Río Viejo and other sites. The US Embassy in Bogotá, as part of its long-standing work with Colombian police to combat international crime including illegal mining, provided funding for the project that ended in August.
Illegal gold mining is a major problem in the Andean country and many others. More than two-thirds of the gold Colombia produces is dug up in operations that aren’t certified. Skyrocketing prices for bullion encourage illegal armed groups to destroy thousands of hectares of land, cut down forests and devastate river beds in their search for more gold.
Prices have surged more than 35% in the past year to above $2,800 an ounce as central banks look to diversify their foreign reserves. Increased geopolitical friction has also added to gold’s haven appeal.
“Illegal mining is growing because international prices have risen,” says Johan Peña, who directs the environmental section of the arm of the national police in charge of rural security, known as Dicar.
Mercury is commonly used to separate gold from surrounding rock. A single gram of of it can pollute thousands of liters of water. Tremors, memory loss and headaches are common symptoms of mercury exposure, which can also cause birth defects.
Marrugo and his team had been researching the effects of mercury on human health at the start of the millennium when they began noticing that the Guarumo tree was thriving in spots where gold had been processed. After publishing their findings, the researchers caught the attention of the police’s Dicar.
That’s where the idea to use phytoremediation to clean up mercury-contaminated land originated, Marrugo says. Following an initial pilot on a plot that had been seized by the police, the project expanded to two other areas in Río Viejo and Margento near the town of Caucasia, in Colombia’s Antioquia province. The plants grew fast in the year-round hot and humid climate, soaking up the mercury quickly. The fauna also came back.
Police Superintendent Julián Amortegui has helped lead the phytoremediation project since its start, and estimates that thousands of hectares of land just in this region of northeastern Antioquia have been damaged by illegal mining. If you take a commercial flight over the area, say from Bogotá to Cartagena, chances are you’ll see some of the patches of red earth.
The success in restoring a total of 35 hectares (86 acres) can feel like just “one hair on a cat,” Amortegui acknowledges. Yet the impact goes beyond the borders of those plots, he says.
For one, it has improved the police’s relationship with local communities, according to Amortegui. “We don’t want people to feel that weapons and the use of force is the only way we achieve security,” he said.
The US Embassy and the Dicar had been looking to replicate the project this year in Choco, another province that’s been hard hit by illegal mining. Those plans are on hold, given US President Donald Trump’s order to pause foreign assistance to most countries, including Colombia.
In any case, the police have a permanent site where they take care of the plant seedlings, and project leaders have been donating plants to other affected communities in hopes the project is replicated. “Every day we go and spread the word about what we’re doing here so that the communities fall in love with the program,” Amortegui says.
Arias from Río Viejo says that with the help of the researchers, who continuously measure for mercury levels, her community has safely gone back to fishing in the marsh.
Initially, residents were paid 35,000 pesos (close to $8) for each time they worked the land. Those funds have run dry, but Arias says people still go and take care of the plants.
She likes to imagine what the land will look like in another two years: “It’ll be something you just won’t believe,” she says.
And she dreams of being able to plant fruit trees once traces of the mercury have vanished.
(By Andrea Jaramillo)
