Refining Stable Oxygen and Hydrogen Isoscapes for the Identification of Human Remains in Mississippi.

Isoscape refinement is an essential component for accurately predicting region-of-origin in forensic investigations involving isotope analysis of unidentified human remains. Stable oxygen (δ18 O) and hydrogen (δ2 H) isotopes were measured from 57 tap water samples collected across Mississippi to model refined isoscapes for the state. A tap water conversion equation, δ18 Otw =1.64 δ18 Op-31.35, was developed for the southeastern USA to test the prediction accuracy of the δ18 Otw isoscape using individuals with known residential histories. A local Mississippi resident (USAFA-134) was assigned with 90% probability to the correct region-of-origin reported by the participant. Assignments for Georgia residents (USAFA-118 and USAFA-205) had variable results, predicting USAFA-118 from Mississippi and USAFA-205 as a nonlocal resident. Stable isotope values often overlap geographically and a multi-isotope approach should be used when narrowing region(s)-of-origin(s). This study demonstrates the utility of refining isoscapes and the importance of tissue calibration in prediction assignments of human remains.