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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The endpoint was covered using a weight of evidence approach including ten publications that were assigned a K2 score (reliable with restrictions) (one publication was assigned a K4 score - not assignable - because the original source was not available). Overall, bioconcentration/bioaccumulation was only observed to be high in organisms from lower trophic levels in the foodchain. Cerium does not seem to accumulate further in the aquatic foodchain, as was clear from the results of four studies with fish, including one study reporting BMF factors for organisms in three different aquatic foodchains. A key BCF/BAF value of 16 L/kg ww was calculated for fish as a worst case key value for use in case exposure calculations are needed for secondary poisoning (aquatic foodchain) or man via the environment.

Key value for chemical safety assessment

BCF (aquatic species):
16 L/kg ww

Additional information

Overall, ten publications (of which one review) were identified as useful in a weight of evidence approach for aquatic bioaccumulation. Data are available for fish, aquatic invertebrates, aquatic plants, and a blue-green alga. The available data were both from field studies and laboratory experiments and for both freshwater and marine organisms. In all studies, cerium concentration in (parts of) the exposed organisms was analytically determined, as well as cerium concentration in the water column (the latter was not the case in all studies). In the laboratory studies, soluble cerium compounds such as cerium trichloride and cerium trinitrate were used or sometimes also mixtures of salts of different rare earth elements were used (i.e., mixed exposure).

For aquatic plants (algae as well as higher plants) and blue-green algae, six studies were identified as containing useful information on bioconcentration of cerium. Weltje et al. (2002) reported BCF values between 2000 and 3000 L/kg dw for Lemna minor sampled along the Rhine-Meuse estuary (corresponding to 400 and 600 L/kg ww, assuming 20% dw, which is a very conservative value for aquatic plants). In a microcosm study in which goldfish, shellfish, Daphnia and duckweed were exposed for up to 16 days to cerium (Yang et al., 1999), a BCF value of 214.3 L/kg ww (assuming 20% dw corresponding to 1071.5 L/kg dw) was calculated for duckweed for the 16-d sampling point. In the study of Kumblad and Bradshaw (2008), BCF values were reported ranging from 20 to 2800 L/kg ww (corresponding to a range of 966 to 48611 L/kg dw, using ww-dw conversion factors reported in the publication) for microalgae and macroflora sampled from locations in the Forsmark area. Zhou et al. (2004) performed a laboratory study with the blue-green alga Microcystis aeruginosa and obtained BCF values of 72000 to 86000 L/kg dw (assuming 20% dw corresponding to 14400-17200 L/kg ww). From the study of Drndarski and Golobocanin (1995) a BCF value of ca. 1000 L/kg dw was obtained for periphyton sampled in the Sava River (affected by the Chernobyl accident) (assuming 20% dw corresponding to 200 L/kg ww). Finally, Stanley and Byrne (1990) reported BCF values of 1.72 to 979.66 L/kg ww (assuming 20% dw corresponding to a range of 8.6 to 4898 L/kg dw) for Ulva lactuca obtained in a series of experiments in which either time, pCO2 or pH were varied. The overall range of BCF values obtained in these studies was 8.6 to 86000 L/kg dw (corresponding to a range of 1.72-17200 L/kg ww), indicating that cerium is bioconcentrated in aquatic plants and blue-green algae.

Seven studies contained useful information on bioconcentration/bioaccumulation of cerium in aquatic invertebrates. Carpenter and Grant (1967) reported BAF values of 60 to 1000 L/kg ww (corresponding to 300 to 5000 L/kg dw when assuming 20% dw) for Crassostrea virginica and Mya arenaria sampled from two coastal areas (Chesapeake Bay and Chincoteague Bay). Moermond et al. (2001) reported BAF/BCF values for Corophium volutator taken from the field (Dutch locations) as well as for a laboratory study with the species. The values ranged from 3390 to 17500 L/kg dw (corresponding to 678 to 3500 L/kg ww when assuming 20% dw). Sneller et al. (2000) discussed the results of Tijink and Yland (1998) and Stronkhorst and Yland (1998). The first study calculated BAF values for worms, crustaceans and bivalves taken from the Dutch Rhine estuary. The latter study calculated BAF values for amphipods (Corophium volutator) taken from a harbour in the Netherlands. The values from these studies ranged from 8000 to 120000 L/kg dw (corresponding to 1600 to 24000 L/kg ww when assuming 20% dw). For snails and molluscs sampled along the Rhine-Meuse estuary, Weltje et al. (2002) reported BAF values of 950 to 40000 and 2000 to 4000 L/kg dw, respectively (corresponding to an overall range of 190 to 8000 L/kg ww when assuming 20% dw). In the microcosm study of Yang et al. (1999) the BAF values after 16 days of exposure were 2.75 and 400 L/kg ww for shellfish and Daphnia, respectively (assuming 20% dw corresponding to 13.75 and 2000 L/kg dw). And finally, Kumblad and Bradshaw (2008) reported BAF values for aquatic invertebrates sampled from locations in the Forsmark area ranging from 640 to 11000 L/kg ww (corresponding to a range of 3837 to 349398 L/kg dw, using ww-dw conversion factors reported in the publication). Overall, the BCF/BAF values ranged from 13.75 to 349398 L/kg dw (corresponding to a range of 2.75 to 24000 L/kg ww), indicating that cerium is also bioconcentrated in aquatic invertebrates.

For bioconcentration/bioaccumulation in fish, four studies were identified. The laboratory study of Sun et al. (1996) reported BCF values for muscle, skeleton, gills, and internal organs of carp (Cyprinus carpio) after 43 days of exposure to a mixture of rare earth elements, among which cerium. Maximum BCF values for muscle tissue, skeleton, gills, and internal organs were 1.46, 5.94, 14.8 and 804 L/kg ww, respectively. The BCF values for internal organs were highest but are not considered as a good indication of the bioconcentration potential of cerium, since the alimentary tract reflects the normal transit of the substance. The second study (Yang et al., 1999) was a microcosm study in which goldfish, shellfish, Daphnia and duckweed were exposed for up to 16 days to cerium. The BAF value for goldfish (Carassius auratus) appeared to be around 1.25 L/kg ww, based on whole body analysis. This is in agreement with the low values for muscle and skeleton observed in the study from Sun et al. (1996). The third study (Carpenter and Grant, 1967) reported a BAF value of < 20 L/kg ww for edible portions of striped bass sampled in the field, which also confirms that bioconcentration/bioaccumulation of cerium in fish is rather low. Finally, the study of Kumblad and Bradshaw (2008) reported BAF values between 1.8 and 4.6 L/kg ww when internal organs were removed from fish sampled in the Forsmark area. BAF values varied between 110 and 2000 L/kg ww however when whole fish were analysed. This is in agreement with the results from the study of Sun et al. (1996), which obtained higher bioconcentration/bioaccumulation in internal organs.

Overall, bioconcentration/bioaccumulation in fish seemed to be substantially lower than in organisms at a lower level in the food chain. The fact that goldfish in a microcosm study (in which they could feed on other organisms present in the microcosm) showed a low bioaccumulation factor (BAF = 1.25 L/kg ww) indicates that the high bioconcentration/bioaccumulation is leveled out when ascending along the foodchain. This is confirmed by the results on biomagnification in three aquatic foodchains reported by Kumblad and Bradshaw (2008). Biomagnification factors (BMFs) were generally 0 or 1 for all organisms, except one value for zooplankton which was 374 kg/kg (dw based). For fish (whether planktivore, feeding on benthos, or carnivore), BMFs were all <= 1 kg/kg (dw based), confirming that biomagnification is not an issue for cerium.

Clearly, cerium has a limited potential to bioaccumulate through the foodchain and it definitely does not biomagnify. Similar differences in bioconcentration/bioaccumulation between different trophic levels have been observed for other metals. In case exposure assessments need to be performed, a value is needed that can be used for calculating exposure levels in prey via the generic scenario for secondary poisoning starting in the aquatic foodchain, as well as for calculating exposure levels for exposure of man via the environment. An average (geometric mean) BCF/BAF of 16 L/kg ww for fish was therefore calculated based on the results of the four available studies. Before calculating the overall mean, a study-specific mean (geometric mean) was calculated for each study. For Sun et al. (1996), all data were included, also those for internal organs. For Kumblad and Bradshaw (2008), only the results for whole fish were included (i.e., not those for samples from which the internal organs were removed). Therefore, the obtained value can be considered as a worst case value.

Finally, on the relatively high values observed for aquatic plants, blue-green algae, and aquatic invertebrates, it should be noticed that many of the studies investigated bioconcentration/bioaccumulation at a very low environmental concentration of cerium (e.g., 1 µg Ce/L or lower). What is often observed for metals is that bioconcentration/bioaccumulation is concentration dependent, showing increasing BCF/BAF values with decreasing (almost background) environmental concentrations. This may also have shifted the upper boundaries of the ranges for these trophic levels up. Overall, the results for fish clearly indicate that bioconcentration/bioaccumulation is typically high only for lower trophic levels and cerium does not further accumulate through the foodchain. Metals are typically well regulated by living organisms, especially when they are essential for their vital functions. For cerium, there is evidence available that it is either an essential element that is needed at extremely low concentrations or it can stimulate certain vital functions. The concentration dependency of the BCF/BAF values in organisms from lower trophic levels may be explained to a certain extent by this.