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Concentrations of heavy metals in live and dead leaves, stems, rhizomes and roots of the seagrass Zostera marina Linnaeus, 1753 are analyzed in the study. On the basis of the concentration, the metals are arranged in the following order: Fe > Mn > Zn > Cu > Pb > Ni >Cd. Differences in Fe, Pb, Ni, and Cd for live and dead leaves are revealed. The factor of sediment enrichment in heavy metals from dead leaves is calculated. The enrichment factor for the studied metals changed in the order Cu > Pb > Zn > Ni > Mn, and the value of solubility product [–log(SP)] for sulfides of the above-listed metals changed in the same order. [ABSTRACT FROM AUTHOR]

The content of 237Np, 239,240Pu, and 241Am in seawater, suspended matter, and bottom sediment cores of the Ussuri and Amur Bays, sampled in July 2021 and August 2022, was analyzed. The activity concentrations of 237Np, 239,240Pu, and 241Am in the water of Peter the Great Bay were determined for the first time and were found to be equal to (19–105) × 10–3, 2.0–5.3, and 24.1–33.5 mBq/m3, respectively. The activity concentrations as well as the 239Pu/240Pu isotope ratio (⁓0.18) in the bottom sediments definitely indicate that global fallout is the main source of plutonium in the investigated territory. The sedimentation rates were determined for the Amur Bay (in the Razdolnaya River estuary), 0.9 mm/year, and for the Ussuri Bay, 4.1 mm/year. Actinide transfer coefficients were determined for Peter the Great Bay in the system dissolved forms (including colloids)–suspended matter–bottom sediment. [ABSTRACT FROM AUTHOR]