In some regions of the world, high levels of arsenic are naturally occurring. This happens when volcanic bedrock erodes and the arsenic it contains is released into soil and groundwater.

One of these regions is high in the Andes mountains of Argentina where people have been exposed to high levels of arsenic for thousands of years.

In new research, published in the advanced online edition of the journal Molecular Biology and Evolution, a team of Swedish researchers sought to discover how the local population managed to adapt to high levels of a normally toxic substance in their environment, according to a statement.

‘The arsenic is in the volcanic bedrock and at some places in higher concentrations. The arsenic has then been released into springs that are used for drinking water purposes. Yet the people living in this area have a relatively high arsenic exposure and a efficient and less toxic metabolism,’ Uppsala University professor Karin Broberg told the Daily Mail.

The researchers performed a genome wide survey using 124 subjects screened for the ability to metabolize arsenic, as measured by arsenic levels in urine.

The results pointed to a set of nucleotide variants in the gene AS3MT. Those variants occurred a significantly lower frequencies in control groups from Peru and Columbia.

“In the present study, the investigators found that 68.7% of SAC [San Antonio de los Cobros] Atacameños carried the arsenic-protective AS3MT haplotype, compared with 50.5% of the Peruvians and 14.3% of the HGDP [Human Genome Diversity Project] populations. Likewise, a haplotype that has not been associated with more efficient arsenic metabolism appeared in only 26% of the SAC population, compared with 67% of HGDP individuals and 40% of Peruvians,” according to Wendee Nicole of Environmental Health Perspectives. 

The team believes that the frequency of the variation occurred relatively recently, between 10,000 and 7,000 years ago. This assumption is based on mummies excavated from the region with high levels of arsenic in their hair.

In previous research it was assumed that the people whose mummified remains were analyzed, were killed by arsenic poisoning. This new research may cause researchers to take a second look.

The team has shown that the set of nucleotide variants in AS3MT are not exclusive to the Andean people but are distributed worldwide. However, the highest frequent occurrence for it was in Peru, Eastern Asia, Vietnam and among Native American people.

The researchers speculate that it was the toxic nature of arsenic itself which drove the adaptation. The effects of arsenic are most pronounced in small children and in people in their reproductive years. This means that those without the adaptation would have been much less successful at surviving to adulthood and having children of their own.

It is important to note that the high tolerance level for arsenic does not mean that the people of the Argentine Andes have an immunity to it and the degree to which they are harmed by it has yet to be studied.

“These levels do not result in acute toxicity but arsenic slowly damages cells and tissues and can result in later diseases. It is important to emphasis that the people living in this area also can get adverse effects of arsenic, as arsenic is very potent, despite having a more efficient metabolism.  Their potential degree of tolerance is something we want to look into,” said Broberg.