ACS Meeting News: Arsenic Link to Ancient Migration

ACS MEETING NEWS

Why the Sinagua people suddenly left Arizona's Verde Valley around 1450 may have a chemical explanation. Richard D. Foust Jr., a chemistry professor at Northern Arizona University, thinks that arsenic-laden water in the Montezuma Well, near the valley, could have helped lead to the departure.

A graduate student in Foust's lab, Jeevanthie Senanayake, presented results supporting this hypothesis at the American Chemical Society national meeting, held last week in San Diego.

The Sinagua people, who are the likely ancestors of the Hopi, lived in the Verde Valley from 700 to 1450; why they left is still a matter of debate among historians, according to Senanayake.

Historians know that the Sinagua left 20 years after irrigation from the Montezuma Well peaked. Because Montezuma Well water contains high levels of arsenic, exceeding 100 ppb, Foust suspects arsenic poisoning is behind the migration. The National Academy of Sciences recommends a safe drinking water standard of 5 ppb for arsenic.

To get a sense of how the high levels of arsenic in the water may have affected the Sinagua, Senanayake analyzed rabbit and turtle bones dated to the mid-1400s found in a cave a short distance from the well. Turtles and rabbits were part of the Sinagua diet.

Arsenic levels as high as 229 mg per kg were found in the turtle bones, compared with 2.0 mg per kg in bones from turtles not exposed to unusually high levels of arsenic. Senanayake reasons that significant elevation of arsenic levels would likely also be found in the bones of the ancient Sinagua.

Foust and Senanayake suggest that the Sinagua may have taken the symptoms of arsenic poisoning—black foot disease and goiter, which might have been manifest among the people—as a religious sign to leave the area.