Environmental arsenic exposure by ancient Andeans: Measurement of As in mummy hair using LA-ICP-MS

The potable, ground and surface water in the Atacama Desert is rich in leached geogenic arsenic. Human hair can offer a unique archival record of past exposure to toxic elements including arsenic. The bulk of hair strand is made of sulfur rich protein called α- keratin. The purpose of this study was to investigate exposure to environmental As in antiquity by ancient Andeans (n = 123) from two river valleys (i.e., Azapa and Camarones) of northern Chile using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Before laser ablation, hair strands were cleaned thoroughly, dried and mounted on a mounting tape. The instrument was calibrated with a pressed pellet certified reference human hair standard (CRM GBW7601) for As measurements, and ¹³C isotope was used as an internal standard. Triplicate, 1000 µm long linear ablation scans were made along the medulla at the root, middle, and distal end of the hair. The tissue level spatial distribution of As in a select hair strand was performed. The average accuracy of the method was + 7.5%. It appears that As is mostly bioaccumulated in medulla and cortex regions. The results revealed that children and older adults as well as ancient Andeans belonging to the Late Period had elevated levels of As in hair. The results showed ancient Andeans are exposed to geogenic As likely due to the consumption of arsenic rich water especially among the populations who lived in As laden Camarones Valley (average: 30.08 μg/g; range:1.02–117.21 μg/g; n = 24) while individuals that lived in the Azapa valley had least exposed.