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The relevance of this research is based on systematic study of the causes of geophagy from the viewpoint of the rare-earth hypothesis. It follows from the original results of comprehensive geological–hydrobiogeochemical studies carried out on Olkhon Island (Lake Baikal) that the phenomenon of geophagy in wild and domestic ungulates is due to a deficiency of light rare-earth elements (LREEs) in plant foods and natural waters. This deficiency is related to a low LREE concentration in the composition of the most common metamorphic terrigenous–carbonate rocks, talus, and soils in the island. This geochemical specificity of landscapes can be the cause of LREE imbalance in the hormonal system of the body. The hormonal stress makes animals consume regularly and periodically kaolinite clays of weathering rocks enriched in the necessary elements. [ABSTRACT FROM AUTHOR]

Geological and hydrobiogeochemical studies carried out in two areas of active geophagy among herbivorous animals in the area of Teletskoye Lake in the Altai Mountains suggest that consumption of lithogenic substances by animals is typical for mountain-taiga and mountain-steppe landscapes with high soluble REE contents in rocks. The high soluble REE contents were measured in the deluvial deposits of some magmatic and metamorphic rocks, as well as in the associated glacial deposits and in the derived soils and vegetation. The revealed geochemical specificity of landscapes similar to that previously established in the Sikhote-Alin becomes the cause of unbalance in the composition and concentration of REEs in the neuroimmunoendocrine system of the animal body. Being in a state of hormonal stress, animals try to compensate for this problem by consuming mineral sorbents, which, as we found out, can remove excess REEs from the body. [ABSTRACT FROM AUTHOR]

This paper reports the results of the experimental determination of the coefficient of sorption of rare-earth elements and yttrium (REY) under conditions of acidic pH using several strains of heterotrophic bacteria (Microbacterium sp., Curtobacterium sp., Bacillus subtilis, Pseudomonas putida, and Bacillus pumilis) that are widespread in natural and technogenic waters of the Far East (Russia). Insignificant fractionation between heavy and light rare-earth elements, negative cerium and dysprosium anomalies, and a positive europium anomaly were revealed. The selectivity of REY biosorption by gram-positive and gram-negative bacteria, as well as inertia of the biosorption process under more acidic conditions of the medium, were shown. [ABSTRACT FROM AUTHOR]