The groundwater in San Antonio de los Cobres in northwestern Argentina averages around 200 micrograms of arsenic per liter, 20 times the level deemed acceptable by the World Health Organization. A genetic analysis reveals that people from this region have different genes for the liver enzyme that breaks down arsenic than do people from neighboring areas where arsenic levels are not so high.
The genetic differences might help the people of San Antonio de los Cobres efficiently get rid of arsenic, though scientists still don’t know if residents are less susceptible to arsenic-caused diseases, researchers report March 3 in Molecular Biology and Evolution.
“It is the first example of human adaptation to a toxic environment,” says study coauthor Karin Broberg, a geneticist at the Karolinska Institute in Stockholm. She says that the negative effects of arsenic early in life, which make infants susceptible to diarrhea and other illnesses, could have provided the selective pressure over thousands of years that accounts for the genetic differences.