The Grapevine

High Levels Of Arsenic In Drinking Water Fostered Genetic Tolerance In Andean People

Andean Peoples
Some populations living high up in the Andes Mountains have developed resistance to the toxic chemical arsenic, as it's prevalent in a lot of their drinking water. Photo courtesy of Shutterstock

Arsenic has been used as a poison since at least the Middle Ages; its lack of color, odor, and taste made it the perfect agent for adding to a person’s food — soon after, they’d be dead. The metallic element’s reputation has carried over through the years through its portrayal in films and TV shows. And while all of us drink it in miniscule doses regulated by the Environmental Protection Agency (EPA), we might want to leave the higher doses for a population of Argentinians living high up in the Andes Mountains. That’s because they’ve actually adapted to its toxic effects.

Those were the findings of a new study published in the journal Molecular Biology and Evolution, and conducted by scientists at the Karolinska Institute and Uppsala University in Sweden. It found that, over thousands of years, they were able to genetically adapt to exposure to higher levels of the toxic element.

“The people live in the Puna region of the northern Argentinian Andes Mountains, an arid region with little industrial or traffic pollution,” Karin Broberg, of the Institute for Environmental Medicine at the Karolinska Insitute, told Medical Daily in an email. “In some areas of this region, arsenic in the volcanic bedrock is released into the groundwater that is used for drinking purposes by the people living in the area.”

It’s common all over the world for arsenic to appear in drinking water. In the U.S., major sources of arsenic include erosion from natural deposits, such as sediment, mineral ores, and coal; runoff from orchards; and runoff from glass and electronics production waste, according to the EPA. However, water treatment plants are required to remove arsenic to levels that are 0.010 micrograms per liter or less, which is called a maximum contaminant level (MCL). Anything higher than that and, over time, the person drinking it risks skin damage, such as lesions, as well as digestive problems, nerve damage, high blood pressure, shock, and eventually death. Some studies have shown it can also raise a person’s risk of developing lung cancer.

Broberg said the Andean peoples’ exposure to arsenic was about 20 times higher than than the EPA’s MCL. For their study, however, they found these people could tolerate such high levels of exposure because their very DNA adapted to accommodate it. Specifically, after studying the genome of a group of 124 Andean women with the ability to metabolize arsenic — screened for through urine samples — they found variants in the gene AS3MT, which plays a role its metabolism. When these variants were compared to the AS3MT genes among control populations in Colombia and Peru, the researchers found they appeared less often.

The researchers suspect these variants began to spread throughout the population sometime between 10,000 and 7,000 years ago, as that’s about the time from which a recently excavated mummy, whose hair contained high levels of arsenic, came. They also said in a press release that these adaptations could have developed out of a need to protect the lives of those most vulnerable to the toxic effects: children and those in their reproductive prime. “We know that many genes that metabolize toxins in the body show gene sequence variation when comparing populations from different parts of the world, suggesting that they have locally adapted to cope with different toxins,” Broberg said.   

Source: Broberg K, et al. Molecular Biology and Evolution. 2015. 

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