Developing neodymium isotope markers: can neodymium be extracted from a wide range of marine species and tissue types?

Neodymium isotope ratios have unique characteristics for tracking the movement and origins of marine animals. However, neodymium (Nd) is present in low concentrations in seawater and marine animal tissues, which can make isotopic analysis challenging. Previous research on Nd isotope ratios in marine animals has been restricted to bivalves, with limited details regarding sample preparation and variations in Nd concentrations. We tested five hot plate-based acid digestion methods on six marine animal classes (Actinopterygii, Thecostraca, Malacostraca, Cephalopoda, Bivalve, Holothuroidea) and nine tissue types (soft and hard tissue), with Nd concentrations measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Nd concentrations obtained in this study were also compared to other published data across marine taxa. Nd was successfully extracted from all animal samples except for fish otolith, bone, and muscle which had very low levels of Nd. Concentrated HNO₃, 8M HNO₃ and 50% Reverse Aqua Regia were the most effective acid treatments overall. Nd concentration varied widely among taxa, tissue types, and individuals, ranging from less than 1 ng/g to 370 ng/g in our samples, and less than 100 ng/g in the published literature. Our results suggest that Nd isotope analysis could have wide-ranging applications to many taxa but may not be feasible for some taxa or tissue types with very low Nd concentrations. We also recommend testing Nd concentrations before pursuing isotopic analyses. We hope to encourage further exploration of the use of neodymium isotopes for tracking movement, connectivity and provenance of marine animals.