Some indigenous groups in the Andes of northern Argentina have developed increased resistance to arsenic, Swedish researchers found.

Researchers at the Karolinska Institute and Uppsala University in Sweden have identified the gene that underlies the altered metabolism of these populations and protects against exposure to arsenic. The study is the first in showing that some humans have genetically adapted to a polluted environment, according to a statement from the Karolinska Institute.

Karin Broberg, a researcher at the Institute of Environmental Medicine at Karolinska, said: "There are not only extra-susceptible individuals, but also individuals who are particularly tolerant to environmental toxicants. This phenomenon is probably not unique to arsenic, but also applies to other toxicants in food and the environment, to which humans have been exposed for a long time."

Broberg said the results highlighted that health risk assessments need not be based on chemical data as there are people who could have a strong genetic tolerance to the particular chemical.

Carina Schlebusch, a researcher at the department of ecology and genetics at Uppsala University, added: "Only a few other studies have found evidence of local adaptation in humans. For instance, adaptation to high altitude conditions and the malaria parasite. This study adds another example of how humans have adapted, in a relatively short time, to tolerate an environmental stressor that they encountered when they settled in a new area."

Arsenic occurs naturally in the bedrock in many locations throughout the world and is one of the most potent carcinogens in the environment. People are exposed to arsenic mainly through drinking water and food, especially rice. People living in the Argentinean Andes have likely been exposed to high levels of arsenic in drinking water for thousands of years, the study found.

The Swedish researchers will go on to study whether other populations with historical arsenic exposure show the same type of adaptation. They also plan to examine if other toxic substances in the environment can result in an increased frequency of genetic variants that provide resistance in humans.