Rare earth metals are widely used in various technologies, and their environmental impact needs to be assessed. Brown algae are recognized bioindicators of xenobiotic pollution in coastal marine areas, so we studied the rare earth element contents in short-lived branchlets of the two most abundant species of Cystoseira (C. barbata and C. crinita) on Black Sea coasts. The abundance of rare earth elements including scandium (Sc), yttrium (Y), lanthanum (La) and 14 lanthanides in the algae, seawater and sediments were determined using inductively coupled plasma mass spectrometry. The average contents of the prevalent elements in the algae decreased in the following order: Sc ≥ La > Europium (Eu) > Y > Neodymium (Nd) > Cerium (Ce). The factors affecting rare earth element content were age > locality > species of the alga. Most of the rare earth metals reached their maximum levels in branchlets > 5 month old, presumably associated with biosorption processes, whereas others (Eu, Terbium (Tb), Lutetium (Lu)) were most concentrated in 2–5 month old branchlets. In contrast to existing reports on the possible use of brown seaweeds for monitoring rare earth elements in coastal waters, the suitability of Cystoseira spp. branchlets, which have a 7 month life cycle, for short-term rare earth contamination monitoring was not confirmed in this study. Highlights

In the present work, we assessed the contents of rare earth elements (REEs), including yttrium and scandium, in rhizomes and leaves of the widespread seagrass Zostera noltei Hornemann 1832 and in the nearby sediments from the Black Sea coast. The total REE content in the sediments was found to be much higher than in Z. noltei. The order of decrease in the major REE contents in the sediments and the seagrass rhizomes was identical, except for La and Y. La was the most abundant in the sediments, and Y in the rhizomes. The contents of all REEs in rhizomes of Z. noltei were 1.5–10 times higher than in the leaves. The highest difference in the REE contents was found for the minor elements (Sm–Lu). The translocation factors for Sc and the minor elements (excluding Tb) from the sediments to the rhizomes and from the rhizomes to the leaves turned out to be pairwise equal, which indicates the similarity of the REE translocation mechanisms. Comparing our results with the literature data, it is possible to conclude that the seagrass Z. noltei does not have an advantage in the REE accumulation over marine macroalgae. At the same time, large coastal deposits of this seagrass after storms allow us to consider it as a possible source of REEs in the future.

Mollusc shells serve as valuable biogeochemical archives of natural or anthropogenic processes occurring in the aquatic environment throughout the life of the molluscs. One such process is trace element pollution, which can be assessed by analyzing the elemental composition of mollusc shells. However, different mollusc species accumulate elements in their shells from the aquatic environment at varying concentrations, and specific patterns of this accumulation remain largely unknown. In the present study, we measured the concentrations of 33 elements in the shells of five commercially important Black Sea molluscs, all collected from the same site, using inductively coupled plasma mass spectrometry. The species were ranked according to the number of elements with the highest concentrations in their shells as follows: Crassostrea gigas (9) = Rapana venosa (9) = Anadara kagoshimensis (9) > Flexopecten glaber ponticus (4) > Mytilus galloprovincialis (2). Cluster analysis of Pearson’s coefficients of correlation of elemental concentrations in the molluscan shells revealed significant separation of C. gigas, F. glaber ponticus, and M. galloprovincialis. Multivariate ordination analyses allowed the accurate classification of >92.3% of shell samples using as few as four elements (Fe, As, Sr, and I). Linear discriminant analysis revealed the probability of separation of all species based on the concentrations of these elements in their shells being not lower than 79%. The applied multivariate approach based on the analysis of four base elements in shells can help not only in the taxonomic identification of molluscs, but also, upon appropriate calibration, in monitoring medium-term dynamics of trace elements in the aquatic environment.