The chronic impact of rare earth elements on biological species within an aquatic bentho-pelagic ecosystem

Since rare earth elements (REE) are increasingly used in society, they can enter the aquaticenvironment through a variety of pathways. Their potential adverse ecotoxicological effects on the aquaticfood web have made REE a concern as emerging contaminants. The REE attached to sediments and fineorganic particle matter are considered not to be bioavailable to aquatic organisms in the water column.However, as part of benthic-pelagic coupling, REE can become bioavailable when organisms consumesediment particles, when chemical equilibria are disrupted, or when environmental conditions change.The aim of this thesis was to investigate the chronic effects of rare earth elements on the aquatic benthopelagicecosystem, to better understand the toxicity on individual aquatic invertebrates and communities.To achieve this, single-species, multi-species, and modeling tools were applied to identify the chronicecotoxicological effects of benthic-pelagic coupling of lanthanum (La) and gadolinium (Gd) on multipleaquatic organisms. The results demonstrated the significance of researching the impact of REEcontamination in both the sediment and water phase. Low concentrations of REE over a long period oftime should not be considered trivial, and contaminated sediment leads to active avoidance by pelagicinvertebrates. The results also showed that strong portioning of REE with the sediment can still causeadverse effects to multiple species in sediment-water systems. Acute and chronic exposure in both thewater and sediment phase should be taken into account, as well as the special characteristics of REE thatmake it complex to fully comprehend the mechanisms underlying the negative effects – many of whichare still unknown. This thesis presents research on the possible long-term impacts of REE concentrationson the aquatic bentho-pelagic ecosystem. It also discusses the need to consider different experimentalsystems, test species, and exposure durations in order to assess the risk of REE toxicity on the aquaticcommunity.