Rare Earth Elements and Yttrium in Seawater and Sediments of Contaminated Pula Bay

Rare earth elements and yttrium (REY) are emerging contaminants of concern due to their widespread use in modern technologies, persistence, and unknown ecological effects. This study presents the first assessment of REY in seawater and sediments of Pula Bay, Croatia, a semi-enclosed, industrialized coastal system. Surface seawater and sediment samples were analyzed using ICP-MS, following optimized preconcentration and digestion protocols. PAAS-normalized REY patterns and λ Polynomial Modelling identified natural and anthropogenic fractionation signatures. Dissolved ΣREE in seawater ranged from 17.6 to 45.9 ng L−1, with naturally elevated concentrations from continental runoff and evidence of anthropogenic Gd (up to 33%) linked to sewage outputs. Sediment ΣREE concentrations varied from 134.8 to 218.2 mg kg−1, with spatial variation reflecting terrigenous and anthropogenic inputs. Local MREEPAAS and HREEPAAS enrichment associated with industrial and municipal inputs distinguished anthropogenic contributions from the lithogenic background. While seawater remains largely unaffected, pollution and risk assessments indicate moderate to high sediment contamination by MREEs and HREEs, showing potential concern for benthic organisms near industrial and urban hotspots. These findings highlight the combined influence of natural and anthropogenic processes on REY distribution in coastal systems and underscore the need for further studies of potential REY effects in impacted coastal environments.