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Marine mammals found at the top of the trophic pyramid are excellent bioindicators of pollutants in the marine environment, the concentrations of which increase along with the trophic level of the organism. As these animals are usually protected species, their contamination has to be assessed non-invasively by analysing excrement and epidermal structures such as fur or claws. The present study involved testing the excrement and fur of the grey seal (Halichoerus grypus) from the Southern Baltic coast and the Southern elephant seal (Mirounga leonine) from Admiralty Bay, along with fish muscle (food) and the lithological background of both areas, for the presence of rare earth elements (REE). The soil on the Baltic coast is characterized by the predomination of light rare earth elements (LREE): yttrium, lanthanum and cerium (∑REE = 7.86 mg·kg -1 dw). In the soil and bedrock of Admiralty Bay all REEs were found except for terbium, thulium and lutetium (∑REE = 96.1 mg·kg -1 dw). The REE levels found in the muscles of Baltic herring (∑REE = 0.057 mg·kg -1 ww) were lower than those in the muscles of marbled rockcod (∑REE = 0.540 mg·kg -1 ww). The situation was analogous in the mammals, with the REE concentrations in grey seal fur (∑REE = 0.489 mg·kg -1 dw) and excrement (∑REE = 0.676 mg·kg -1 dw) being lower than those found in the fur (∑REE = 10.1 mg·kg -1 dw) and excrement (∑REE = 83.6 mg·kg -1 dw) of the elephant seal. The LREE/HREE partition coefficients in the grey seal excrement (3.37) and its fur (4.00), but also in the faeces of the elephant seal (2.63) and its fur (2.65), indicate that in each species the process of elimination from the body occurs in similar proportions., Competing Interests: Declaration of competing interest On behalf of the authors of the manuscript I certify that authors have no conflict of interest to declare., (Copyright © 2020 Elsevier B.V. All rights reserved.)