Mollusks are a prospective food for the world’s growing population, but the contents of toxic and essential trace elements in them have not been studied comprehensively. In this work, using inductively coupled plasma mass spectrometry, the contents of 72 elements in soft tissues of the edible mollusks Mytilus galloprovincialis, Rapana venosa, and Crassostrea gigas from the coastal area of the southwestern Crimea were estimated and compared with the maximum permissible levels. Element accumulation similarities were observed in the two bivalve species. Cluster analysis applied to the non-normalized contents allowed finding an optimal number of non-overlapping element clusters: 1 group of macroelements, 1–2 groups of trace elements, and 1–2 groups of ultratrace elements. As an outcome of this analysis, the element accumulation universality index was introduced, which demonstrated the accumulation universality decrease in the order: mussel > sea snail > oyster. An original approach to estimating the mollusk consumption rate was proposed to assess human health risks. Two possible consumption scenarios were identified for Crimean residents. From the expected consumption of all species in both scenarios, there are no health risks, but they are not excluded, within the 95% probability, from high consumption of mussels and sea snails in the pessimistic scenario.

Rare earth elements (REE) are a class of increasingly used high-tech product components and new emerging environmental pollutants, which are accumulated, in particular, in marine biota. In this study, REE contents were estimated in shells of several molluscs common in the Black Sea. The summed REE contents in mollusc shells decreased in the following order of species: Magallana gigas = Anadara kagoshimensis > Flexopecten glaber ponticus ≥ Rapana venosa > Mytilus galloprovincialis, ranging from 0.46 to 1.9 mg·kg⁻¹. Canonical analysis of principal coordinates allowed for the correct identification of species based on the REE composition in no fewer than 67% of the samples. The mollusc shells were anomalously enriched in Sc, Y, La, Eu and Tb, most likely due to anthropogenic contamination. The Y/Ho ratios in all samples were represented by two fit values: 23.2 (chondritic) and 67.6 (superchondritic, mainly associated with A. kagoshimensis). A new universal relationship linking the contents of three light and heavy REE in Black Sea mollusc shells was proposed: Ce^0.3 Er^0.7/Yb = 2.00 ± 0.46 (mean ± standard deviation).

Assessment of the interaction of marine farms with the environment in the industrial cultivation of the mussel Mytilus galloprovincialis is very important. In the mussel farm – environment system, biotic fluxes of chemical compounds through gonads, gametes (sperm and eggs), and larvae make a considerable contribution to this interaction. Since gonads play a key role in the mussel reproduction, it is interesting to study the budget of materials, that are directly involved in this process. Out of these materials, testosterone, estradiol, fatty acids, and some trace minerals, such as Se and Zn, are known to affect spawning, growth, and development. The molluscs absorb these materials from food and water. These materials are partly metabolically assimilated by mussels and partly excreted into the environment with gametes. The aim of this study was to estimate the components of the budget of steroid hormones, fatty acids, and two essential trace elements (Zn and Se) in mussel gonads, gametes, and larvae. The total testosterone and estradiol in gonads and gametes were quantified by enzyme-linked immunosorbent assay. The contents of the trace elements were found using inductively coupled plasma mass spectrometry. The fatty acid composition was determined by means of gas chromatography–mass spectrometry. The contents of Se and Zn in mussel gonads and gametes were found to depend on the stage of the reproductive cycle. In female gonads, Se and Zn concentrations were higher than in male ones. The highest concentration of Se was recorded in eggs: (14.7 ± 2.9) μg·g−1 dry weight (d. w.). In sperm, it was (14.4 ± 1.8) μg·g−1 d. w. Zn content in gonads before spawning was higher than in gametes. In male gonads and in sperm, its values were (27.5 ± 3.7) and (19.3 ± 6.4) μg·g−1 d. w., respectively. In female gonads and eggs, the contents of zinc were (53.6 ± 10.9) and (49.3 ± 8.2) μg·g−1 d. w., respectively. In spring, the mean values of Se and Zn assimilation degree (q) in gonads of the mussel were within 0.1–0.6. The limit values of the alimentary accumulation coefficient (Klim) of Se and Zn ranged 0.6 to 1.4. While spawning, mussels excrete polyunsaturated fatty acids (PUFA), which are probably used by other marine organisms. Up to 56.2 % of PUFA are excreted with sperm, and 48.1 %, with eggs, whereas in larvae this fraction does not exceed 10.2 %. The data obtained indicate that the molluscs assimilate sex hormones, fatty acids, selenium, and zinc to maintain vital processes: prostaglandins are synthesized from PUFA in the body, and testosterone esters are formed from testosterone. Se and Zn, when coupled with proteins, play a key role in the reproduction and formation of larval shells.

Among the commercial mollusks from the Black Sea, the ark clam Anadara kagoshimensis, the oyster Crassostrea gigas, the mussel Mytilus galloprovincialis, the scallop Flexopecten glaber ponticus, and the gastropod Rapana venosa hold the top positions in terms of cultivation and harvesting volumes. Mollusk shells are attracting attention due to their potential use in various biotechnological applications, including nutraceutical production. In the present study, using inductively coupled plasma mass spectrometry, concentrations of essential trace elements (Cr, Mn, Fe, Co, Cu, Zn, Se, Mo, and I) were measured in shells of the five mollusks sampled from the same biotope. The essential element concentrations in the mollusk shells differed significantly. The highest concentrations of Cr, Mn, and I were found in Anadara shells; Fe and Co in Crassostrea shells; Zn in Mytilus shells; and Cu and Se in Rapana shells. Principal component analyses demonstrated the overall accumulation of all elements as the main cause of the total data variance and the species-specific accumulation of certain elements as the second most important source of the data dispersion. Matrices of element concentration correlations showed considerable dissimilarity, which suggested species specificity in the concerted or competing element accumulation. Powdered shells of Anadara, Crassostrea, and Rapana are most suitable to fulfill the daily human requirements for many essential elements, and the consumption of these powders in amounts of less than a few tens of grams appears to be sufficient for this purpose.

Contents of the bulk and trace elements were determined in male and female gonads, gametes (sperm and oocytes), and larvae (trochophores) of black and brown morphs of the Mediterranean mussel Mytilus galloprovincialis using energy dispersive X-ray spectroscopy and inductively coupled plasma mass spectrometry. The mollusks were collected in spring 2019 on a mussel-and-oyster farm (Black Sea, Crimea, Sevastopol, Karantinnaya Bay). In male and female gonads of the black and brown morphs, no statistically significant differences were detected in the contents of the bulk structural elements (C, N, O, P, S), while in gametes and trochophores, these differences were significant. Trace elemental analysis revealed that in the female gonads of both black and brown morphs, Cu, Fe, and As were dominant. However in brown morphs, the contents of these elements were significantly lower than in black mussels. Zn and Se contents in gonads of the black morph were significantly higher than in gonads of brown mussels. Most of the statistically significant differences were found between trochophores and oocytes of black vs. brown morphs. These data show that the two M. galloprovincialis morphs differ in their elemental composition.