Troubled Waters

BY Caroline E. Moore, DVM, Ph.D.

Scientist for San Diego Zoo Wildlife Alliance

Environmental Effects of Gold Mining

Gold has fascinated people for centuries, and is considered one of the most valuable materials on Earth. Yet, methods to collect it often have destructive consequences for people, wildlife, and ecosystems.

The global price of gold remained unchanged in 2022 from a record high in 2021, demonstrating continuing worldwide demand. To give a perspective of the gold economy close to home, domestic gold mining production in the US was estimated at nearly $10 billion in 2022, yet the gold resources in the US are considered to be only a small percentage of total global gold resources.

A Global Industry—and Concern

Peru was one of the world’s top 10 gold producers in 2022. (The top 10 gold producers in 2022 were China, Australia, Russia, Canada, the US, Mexico, Kazakhstan, South Africa, Peru, and Uzbekistan.) In the Peruvian Amazon, San Diego Zoo Wildlife Alliance partners closely with local communities and nongovernmental organizations (NGOs) to better understand, mitigate, and prevent gold mining’s threats to wildlife.

A gold mining operation clears a swath of much-needed rainforest across the river from the Los Amigos Conservation Concession, leaving behind mounds of sand and rocks.

A decade ago, gold prices spiked after the great recession, and a new wave of people came into the Madre de Dios region of the southeast Peruvian Amazon with the intent to mine gold. With a few rudimentary devices and access to the rivers, anyone willing to perform hard labor can mine up to several hundred dollars’ worth of gold a day—a life-changing amount of money, for many families. As gold demand remains steady, it has created an important and continued source of income for many in the Peruvian Amazon. But this is not without environmental and social impacts.

Gold mining requires large swaths of accessible land, and the often illegal and remote nature of mining can push local and indigenous communities away, through criminal activities, human rights abuses, and contaminated food and water sources from the extensive use of mercury throughout the process.

Considering Effects

Gold in the Peruvian Amazon is not found in large nuggets, like those of the California Gold Rush. Those gold nuggets were large enough for John Sutter to pick up and show off the gold flecks in 1848, triggering crowds of miners rushing to California’s mountain rivers over the next 10 years. In contrast, the gold in the Amazon is so tiny and fine it is called gold dust, and is seemingly laid down everywhere the rivers touch.

Mercury-based gold mining techniques leave mercury behind in ecosystems, posing a threat for people and wildlife who are exposed to toxic levels through water and food sources.

The Madre de Dios River in the Amazon is not static—it moves and travels with time, creating oxbow lakes, where the river bends away but leaves a curve of water behind (a favorite haven for giant river otters and yellow-spotted river turtles). Every new path carved and old path left behind leaves a trail of gold. Deforestation—via clear cutting and wildfires—is one result when miners seek access to the gold-containing silt. Since the gold is too small to pan and sift, toxic mercury is mixed with silt in giant barrels, often stirred by hands and feet, to separate the gold dust from the silt. Mercury and gold bind together, and miners collect and burn this amalgam, vaporizing the mercury and leaving behind pure gold.

Mercury in its many forms is toxic to people, animals, and plants—aquatic and terrestrial. It is a natural component of our ecosystems, but it is usually not present in high concentrations at the earth’s surface. However, mercury-based gold mining techniques leave mercury behind, exposing people and animals to toxic levels, through water and food sources. Mercury can bioaccumulate in an individual over time, and biomagnify up food chains, so that top predators carry higher and higher amounts of mercury. High levels of exposure compromise brain function and ability to reproduce, as well as harming other organs. This can result in blindness, abnormal behavior, paralysis, and even death. People in the Peruvian Amazon have been documented carrying mercury levels above what the World Health Organization calculates as “safe,” which has compromised their health.

Old-growth forests—the preferred habitat for Peruvian spider monkeys—can act like a sponge to capture vaporized mercury, leaving all who rely on these ecosystems at risk for mercury exposure.

Our team members supported a recent study demonstrating that when intact old-growth forests are located next to mercury-based gold mining operations, they can act like a sponge to capture vaporized mercury, allowing it to integrate into the ecosystem at levels comparable to industrial mercury pollution. This is big news, as terrestrial wildlife species—including birds, bats, and carnivores—were historically thought to be at a lower risk for mercury exposure, compared to aquatic species such as giant river otters and fish. Yet, we are finding that almost all tested terrestrial animals in forests next to gold mining operations have detectable mercury levels in their hair or feathers. We do not yet know what this means for the protection and biodiversity of the Amazon. But we are working hard to find out more, and to fully understand the mercury threat to Amazonia ecosystems, where the mercury is coming from (whether mining or other sources), and how exposure changes the health of wildlife, communities, and forests within the Amazon.

Damage Control

Easily observed from satellite imagery, the scale of destruction by gold mining is massive. As the Peruvian government works to reduce illegal gold mining in one region, it pops up in other regions. Gold mining expansion up the Madre de Dios River, within the buffer region to the Manu National Park, has been devastatingly evident on each trip we make to the Wildlife Conservation Laboratory at the Los Amigos Conservation Concession.

With harpy eagles, emperor tamarins, and countless other unique species, Manu National Park is one of the most biodiverse places on Earth. Despite being a protected area, this ecosystem and the wildlife within are impacted as gold mining expands in surrounding regions.

As we travel up the river, the boat has to stick to deeper channels, and cruise around mining equipment and operations that spill across the river as the dry season exposes more silt. When we sit on the bluffs of the Estación Biológica Río Los Amigos to watch the sun set behind the Andes, we see a gaping, growing hole where a forest once stood across the Madre de Dios River, smell the forest fires, and hear the chain saws and ever-present fuel and water pumps. Behind us sits the protected 360,000-acre Los Amigos Conservation Concession, an old-growth forest that was once the site of hunting and logging operations. Today, it is home to one of the most valuable biodiversity hotspots within the Amazon region. This forest is home to at least 12 globally threatened species, 11 primate species (some found only at this site), over 550 bird species, and over 4,300 species total. Additionally, charismatic Amazonian fauna including giant otters, emperor tamarins, harpy eagles, red howler monkeys, spider monkeys, white-lipped peccaries, and jaguars—all call this region home.

Saving Tomorrow, Today

With our partners, we collect over 800 feather and hair samples annually from terrestrial and aquatic wildlife in the Madre de Dios region. We can then test these samples for the presence of mercury. By establishing a gold-standard mercury testing pipeline at the Wildlife Conservation Laboratory, we are ensuring that annual mercury measurements throughout the food chain, and soon in the environment, can be monitored by local scientists, in conjunction with mercury monitoring projects by other NGOs and laboratories throughout Peru.

By monitoring the presence of mercury throughout the food chain, we can make informed conservation decisions to protect wildlife.

Together, we hope to build one of the strongest networks of mercury data in a region impacted by mining, so that we can provide evidence to support the need for urgent changes. Mercury-free methods of gold mining can be implemented, and mining with restoration plans in place can be established. Further, changes in human behavior can reduce the demand for gold. Supporting these changes will require multidisciplinary teams—from wildlife veterinarians, to social scientists and local communities—to take on the issue of unsustainable gold mining and propose alternatives to ensure that people, wildlife, and ecosystems can thrive.

Discover more about what your support makes possible for vulnerable wildlife through our Amazonia Conservation Hub.