A new study has revealed that the people of San Antonio de los Cobres are have arsenic tolerance. The study indicates that around a quarter of this population has a genetic mutation which enables them to process this poisonous metal into a less toxic form.

San Antonio de los Cobres is a remote Andean town, 4000 meters above sea level and built above volcanic rock. Research shows that the level of arsenic present in the water in the area is twenty times higher than the level declared safe by the World Health Organization.

Traditionally the go-to poison for murder, arsenic poisoning is not pretty.  At low, chronic exposure, the metal causes skin lesions, liver damage, and cancer, where as high-level exposure leads to cardiac arrest, coma, and eventually death.

People vary in their ability to metabolize arsenic and remove it from their bodies, and it appears that the residents of this Andean town are able to do this much faster than average.

In their study, Broberg and her team tested the DNA or 124 women from this isolated village, comparing their genetic fingerprints with those of people from areas in South America with a much lower frequency of arsenic. The results also showed that this genetic mutation goes back a long way; high levels of arsenic were detected in analyses of the hair of mummies from 400 to 7000 years ago. Arsenic is particularly deadly to children, and therefore interferes with reproduction. The scientists explain that those immune to the arsenic were much more likely to survive and pass on the gene to their offspring.

Broberg explains that, although these people have a higher tolerance to arsenic, they have not yet tested the effects of the metal on the population of San Antonio and therefore do not know if they are harmed by it or not.

Nevertheless, this is pretty exciting news. As Broberg says in the article, “this is the first evidence of human adaptation to toxic material”. Although more than 100 million people are exposed to arsenic in their drinking water and many populations must therefore be tolerant to its effects to a certain extent, Oxford University Press explains that this is the first study to show “evidence of a population uniquely adapted to tolerate the toxic chemical.”