For millennia, residents of the Puna de Atacama plateau in northern Argentina have consumed water naturally laced with arsenic – a toxic metalloid that poses significant health risks to most populations. Recent genetic analysis suggests that natural selection has equipped a population in the region with a unique ability to metabolize arsenic more safely, offering a rare example of human adaptation to a potent environmental toxin.
The remote, high-altitude town of San Antonio de los Cobres, situated at approximately 3,775 meters (12,385 feet), experienced particularly high levels of arsenic contamination until the installation of a filtration system in 2012. Prior to this, drinking water contained roughly 200 micrograms of arsenic per liter – twenty times the World Health Organization’s recommended limit of 10 micrograms per liter. Despite this, the region has been continuously inhabited for at least 7,000 years, and potentially as long as 11,000 years.
Scientists first observed the unusual resilience of people in the Argentinian Andes to arsenic poisoning in 1995, noting a distinct pattern in the metabolites present in their urine. When arsenic enters the body, it is processed through several chemical forms. A particularly toxic intermediate, monomethylated arsenic (MMA), is typically produced. However, residents of San Antonio de los Cobres demonstrated a tendency to produce less MMA and a greater proportion of dimethylated arsenic (DMA), a form more easily excreted by the body.
To investigate the genetic basis of this adaptation, researchers from Uppsala University, led by Carina Schlebusch and Lucie Gattepaille, collected DNA samples from 124 women in San Antonio de los Cobres. They analyzed millions of genetic markers, comparing their findings to genomic data from populations in Peru and Colombia, sourced from the international 1000 Genomes Project. Their research, published in Molecular Biology and Evolution, focused on the arsenic (+3 oxidation state) methyltransferase (AS3MT) gene, previously identified as playing a key role in arsenic metabolism.
The analysis revealed a cluster of genetic variants near the AS3MT gene that were significantly more common in the population of San Antonio de los Cobres than in their counterparts in Peru and Colombia. These variants appear to enhance the body’s efficiency in converting arsenic into forms that can be safely eliminated through urine, thereby reducing the accumulation of the more toxic intermediate compounds. This finding aligns with the earlier observations of altered arsenic metabolite profiles in the region’s inhabitants.
While arsenic contamination is widespread globally, few communities have experienced such prolonged exposure to high concentrations. The extended period of exposure in San Antonio de los Cobres – spanning thousands of years – has likely driven natural selection, favoring genetic traits that mitigate the harmful effects of arsenic. Subsequent research suggests similar genetic signals may be present in other Andean populations with long-term arsenic exposure, indicating the adaptation may be more prevalent across the region.
Researchers emphasize that individuals carrying the arsenic-tolerance genetic variants may have a significant selective advantage in high-arsenic environments, given the severe health consequences associated with arsenic exposure, including cancer, skin lesions, and birth defects. However, the long-term implications of this adaptation, and the potential trade-offs associated with it, remain areas for further investigation.
Despite a 2012 court order, arsenic continues to flow from taps in parts of Argentina, according to reports from the Global Press Journal, highlighting ongoing challenges in providing safe drinking water to affected communities.
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