Landscape REE anomalies and the cause of geophagy in wild animals at kudurs (mineral salt licks) in the Sikhote-Alin (Primorsky Krai, Russia)

To test the "rare earth" hypothesis of geophagy, geological and hydrogeochemical studies unparalleled anywhere in the world were carried out at kudurs (salt licks) in two districts in the Primorsky Krai, Russia. The mineral and chemical compositions of geophagic earth consumed by animals, the chemical composition of surface waters and vegetation, and the chemical composition of biological tissues of red deer (Cervus elaphus) were studied in this research. It was found that ultra-fresh surface and fontinal waters in the studied areas contain anomalously high concentrations of rare earth elements (REE), the sums of which exceeded the average values in the Primorsky Krai and worldwide by tenfold, and more. The presence of landscape REE anomalies is confirmed by elevated concentrations of these elements in vegetation. Using electron microscopy, it was determined that the sources of REE in landscape components are rocks containing secondary, readily soluble, REE minerals (hydrophosphates and fluorocarbonates). The study of the chemical composition of animal tissues showed the presence of significant concentrations of heavy REE (HREE) in the blood and brain, which indirectly indicates a high probability of animals developing stress reactions against the background REE-elementosis. Eaten earthy substances in both areas are represented by mixtures of smectite clays and zeolites with high ion-exchange properties. In the digestive tract of animals, such sorbents actively interact with the biological electrolyte, saturating it with sodium ions and absorbing HREE. The main meaning of geophagy is regulation of the concentration and proportion of REE in the body. Sometimes it manifests itself in intake of significant amounts of Na.