Something in the Fish

There is something in the fish of Madre de Dios, Peru. You wouldn’t know by looking at them—the fish look normal and they taste great—but the something may threaten the health of thousands of people.

By David Gonzalez

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Stepping into the fish market in the small city of Puerto Maldonado, the capital of Madre de Dios, a southeastern Peruvian state the size of South Carolina, the first thing I notice is the smell. It isn’t so much a cliché fishy smell as it is a pungent, earthy odor: the smell of room-temperature fish flesh, mixed with a hint of raw chicken from neighboring butchers.

The fish aren’t sitting in buckets of ice. Rather, the morning's catch rests in neat stacks on white tiled counters. Some are cut cleanly in half, and red blood mixed with water spills onto the floor. Meat cleavers clank against fish bone and cutting boards in a steady rhythm. Sellers who aren’t preparing fish or tending to customers make small talk amongst themselves.

The Amazon is home to the world’s most diverse community of freshwater fish, and, unsurprisingly, fish are a staple in local kitchens. But Madre de Dios is rich in more than just fish.

A gold rush of sorts has taken off in recent decades. Tens of thousands of small-scale miners work along rivers in the region. Most are migrants from the Andes, men with families to feed and few economic prospects. They collect sediments from near the river, washing away the big bits and putting the resulting slurry in barrels. In the slurry are flecks of gold.

To concentrate the gold together, miners have turned to a centuries-old technique. They pour in liquid mercury in the barrel, mix it with their bare hands and feet, and collect the ball of mercury-gold amalgam that settles to the bottom. Voilà. They burn the amalgam, maybe on shovels or pans over an open flame, and pour the leftover slurry into the rivers.

That’s when the fish get exposed: mercury. The toxic metal makes its way up the food chain, from water to plants to insects to fish and to larger fish, becoming more concentrated with each step. At the end of the food chain are the people who eat the fish.

A common way for people to become exposed to mercury is by eating contaminated wild caught fish. At low levels, mercury causes muscle damage, chronic headaches, mood swings, learning disabilities and sensory impairment. At high levels, mercury causes birth defects, respiratory failure, kidney damage, coma and death. Miners and the tens of thousands of people who live downstream are at risk.

That’s what brought me to Puerto Maldonado. In 2014 I worked with the Ministry of Health on a study of mercury exposure among women of childbearing age. This is a population of high concern, because mothers pass mercury onto their children in the womb or through breast milk. I found that most of the women had elevated levels of mercury, above what the World Health Organization says is safe.

I told this, in Spanish, to an auditorium full of students, researchers, policymakers, and community members at the International Forum on Mercury and Public Health, held in Puerto Maldonado in November 2014. Other researchers, both Peruvian and international, had a similar message about their work in neighboring communities.

The Forum was a watershed event for Madre de Dios. It was the first time the research community came together, under one roof, to share with one another and the community the body of work on mercury in the region.

We may also be on the verge of a watershed moment in global mercury regulation. In 2013, delegates from 91 countries traveled to Japan to sign the Minamata Convention on Mercury. Among many aims, the convention seeks to reduce or eliminate the use of mercury in small-scale gold mines. If ratified in Peru, the Minamata Convention would be an important policy tool to head off rampant mercury exposure in the human population of Madre de Dios.

Each morning, fishermen get up well before daybreak and set out on the rivers, casting nets over dark water. They plumb the Madre de Dios River while the water is calm and the fish are biting. After sunrise, boatloads of tourists will make their way up and down the river.

The fish are sensitive to things like weather and river traffic. “They don’t bite when it’s too cold out,” a local fisherman tells me, or when the water level’s too low. There seems to be a lot the fish don’t like. But the fish, as they have for generations, bite enough to provide an ample supply for local markets.

Not all fish have elevated mercury levels. Not every resident of Madre de Dios is exposed. But sweeping evidence of widespread mercury contamination presented at the Forum indicates that tens of thousands of people are at risk. Something needs to be done about the something in the fish.

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David Gonzalez is a master’s student in environmental science and global health at Yale University. He can be reached at 

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