Abstract
We describe the use of handheld X-ray fluorescence, for elephant tusk species identification. Asian (n = 72) and African (n = 85) elephant tusks were scanned and we utilized the species differences in elemental composition to develop a functional model differentiating between species with high precision. Spatially, the majority of measured elements (n = 26) exhibited a homogeneous distribution in cross-section, but a more heterologous pattern in the longitudinal direction. Twenty-one of twenty four elements differed between Asian and African samples. Data were subjected to hierarchical cluster analysis followed by a stepwise discriminant analysis, which identified elements for the functional equation. The best equation consisted of ratios of Si, S, Cl, Ti, Mn, Ag, Sb and W, with Zr as the denominator. Next, Bayesian binary regression model analysis was conducted to predict the probability that a tusk would be of African origin. A cut-off value was established to improve discrimination. This Bayesian hybrid classification model was then validated by scanning an additional 30 Asian and 41 African tusks, which showed high accuracy (94%) and precision (95%) rates. We conclude that handheld XRF is an accurate, non-invasive method to discriminate origin of elephant tusks provides rapid results applicable to use in the field.
Highlights
We describe the use of handheld X-ray fluorescence, for elephant tusk species identification
In 2015, the African elephant was placed in Appendix I of Convention on International Trade in Endangered Species (CITES), except populations in Botswana, Namibia, South Africa and Zimbabwe, which are included in Appendix II because of their large population numbers
Cd displayed a preferential accumulation in E1 and E2 (p < 0.05), whereas As and Pb were non-significantly dispersed along the length of the tusk (p > 0.05)
Summary
We describe the use of handheld X-ray fluorescence, for elephant tusk species identification. Today DNA analysis is considered the gold standard for tusk species identification, the technique requires destruction of a portion of the sample and the process of extraction is difficult, with failure of DNA to amplify being one technical problem[10,11] This approach requires considerable technical expertise and equipment, and is time-consuming. Using principal component analysis of nine elements identified by XRF in Asian (n = 12), African (n = 6) and unknown (n = 1) tusks, Kautenburger[18] identified two components that accounted for 84% of the variance in distinguishing species Together, these results suggested it is feasible to use multi-element analyses to distinguish ivory samples from different elephant populations. Prior work was based on relatively small sample sizes, so the power of XRF to identify tusk species origin has yet to be definitively established
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