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The extent to which bioaccumulation may occur depends on the bioavailability of cerium for uptake. Bioavailability is affected by the substance’s water solubility as well as by the characteristics of the receiving environmental compartment, determining cerium speciation. Because cerium speciation and bioavailability are expected to be similar after release of water soluble cerium compounds (e.g., cerium trichloride, cerium trinitrate) to the environment, data from laboratory studies using soluble cerium compounds were lumped for covering the endpoint. Similarly, data from field studies, in which cerium distribution between environment and biota was studied, were added to the lumped dataset for covering this endpoint.

The available information on bioaccumulation of cerium in the aquatic and terrestrial foodchain was thoroughly studied, yielding the following conclusions:

- In the aquatic foodchain, cerium has clearly the potential to bioconcentrate/bioaccumulate in organisms from lower trophic levels, such as aquatic plants and invertebrates. However, the available information on fish, including valuable information from a microcosm experiment and trophic transfer factors for organisms in several foodchains calculated based on field data, indicate that bioaccumulation of cerium decreases when ascending the foodchain. The values obtained for fish were very low and indicate that cerium does certainly not biomagnify and has a limited potential for bioaccumulation at higher levels in the foodchain. There is evidence that cerium promotes certain processes in living organisms. As for many other metals (even non-essential metals), organisms are able to regulate metal uptake and retainment, and bioaccumulation is expected to be limited. Also, a concentration dependency may exist for bioaccumulation of cerium in aquatic organisms, showing increasing BCF/BAF values with decreasing environmental concentrations (down to background levels). Indeed, for several field studies in which cerium exposure was very low, quite high BCF/BAF values were observed for aquatic plants or invertebrates.

- Based on a selection of reviews on the transfer of cerium and other rare earths from soil to plants, it could further be concluded that there is no potential for bioaccumulation of cerium in the terrestrial foodchain, as all BSAF values were < 1. BSAF values for a sediment dwelling amphipod and water spinach rooted in sediment were also consistently below 1.

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