Yttrium trinitrate

Bioaccumulation: aquatic / sediment

Description of key information

A bibliographical review based on ca. 60 publications (1964-2016), containing information on the accumulation of lanthanides, yttrium and/or zirconium in aquatic organisms, was written to cover this endpoint. Because of the similarity between findings for the elements under consideration and those for (other) metals, such as the influence of environmental conditions on bioaccumulation, the observation of inverse relationships between bioaccumulation values and concentrations in water, and the evidence for the existence of internal regulatory mechanisms, the bioaccumulation thresholds (e.g. for classification) used for organic substances are considered not applicable, and the evaluation of aquatic bioaccumulation was evaluated through expert judgment. This has led to the following conclusions:

•A considerable decrease of bioaccumulation was observed when ascending the trophic levels, this being obvious when comparing data in fish to those in lower trophic levels.

•Lanthanides, yttrium and zirconium do not biomagnify through the aquatic food web.

Based on this pool of evidence, it was concluded that lanthanides, yttrium and zirconium are unlikely to biomagnify in predatory organisms or humans exposed via the environment.

Additional information

Under REACH Regulation (EC) No 1907/2006, substances need to be assessed for environmental hazard classification. Data on bioaccumulation are of key importance in this process because they are considered, together with degradation and ecotoxicity information, to assess the chronic hazard to the aquatic environment.

 

It has been often highlighted that bioaccumulation of metal and inorganic substances follows a different paradigm relative to organic substances, and this, for several reasons:

•Non-applicability of Kow concept,

•Influence of environmental conditions,

•Inverse relationship between bioaccumulation values and concentrations in water,

•Existence of internal regulatory mechanisms.

 

Nevertheless, the concept that a substance may bioaccumulate is important for metal and inorganic substances too and needs to be assessed even if the thresholds and underlying mechanisms cannot be considered in the same way as for organic substances. Evaluation should thus be performed on a case-by-case basis and expert judgment can be used to conclude that a substance is unlikely to pose a risk to predatory organisms or humans exposed via the environment either: (i) based on the absence of food web biomagnification and information showing that organisms in higher trophic levels are not more sensitive than those in lower trophic levels after long-term exposure, or (ii) because it is an essential element and internal concentrations will be well-regulated at the exposure concentrations anticipated (ECHA Guidance R7c, 2014).

 

Such an expert judgment was developed for lanthanides, yttrium and zirconium. A bibliographical review was conducted by considering all studies on bioaccumulation in aquatic organisms, resulting in a database composed of ca. 60 publications (1964-2016) reporting laboratory and field data on all elements and several trophic levels.

 

A first conclusion that can be drawn from this review is that the elements under consideration present particularities common to those of (other) metals:

- Bioaccumulation is influenced by environmental factors, resulting in substantial spatial/temporal variation.

- Relatively high bioaccumulation values can be observed at relatively low exposure concentrations, and inversely. The inverse bioaccumulation to exposure relationship indicates that internal exposure does not rise as quickly as exposure levels. This could be an indication for a significant degree of physiological control over accumulation.

- Indeed, physiological regulation has been demonstrated in several species for rare earths. While the essentiality of lanthanides, yttrium and zirconium has never been convincingly demonstrated, the data compiled in the review clearly show that mechanisms of regulation of internal concentrations exist.

 

As for (other) metals, it is clear from these findings that the mechanisms underlying bioaccumulation cannot be considered in the same way as for organic substances and that therefore, the thresholds used for organic substances are not applicable. Based on expert judgment of the pool of data available and described in the review document, the following conclusions can be drawn for lanthanides, yttrium and zirconium:

•A considerable decrease of bioaccumulation was observed when ascending the trophic levels, this being obvious when comparing data in fish to those in lower trophic levels: The bioaccumulation estimates determined for fish are fairly low with several publications reporting BAF/BCF values (well) below 500. In comparison, higher BCF/BAF ranges have been reported for aquatic plants and invertebrates than for fish. However, there are indications that adsorption on organism surface and/or exposure to very low, close to background, water concentrations play a significant role in the high values determined especially for these lower trophic levels. This makes it difficult to derive clear conclusions on the level of uptake and consequent distribution in these organisms, based on the available studies. Further, while there is no empirical proof that lanthanides and yttrium are essential, they can be involved in cationic competition: they can compete to bind at uptake sites of essential cations (e.g. Mg²⁺, Ca²⁺). This constitutes an additional hypothesis to explain the observed bioaccumulation in all trophic levels. Note that no indication of interaction between zirconium and essential cations has been found in scientific literature.

•Lanthanides, yttrium and zirconium do not biomagnify through the aquatic food web: This is evidenced from the previous point, but also from the available publications dealing with biomagnification. Most of the time, BMF values are low (i.e. ≤ 1) and the only cases where those values are higher than 1 correspond to trophic transfer in the lower levels of the food chain.

 

Based on this pool of evidence, it was concluded that lanthanides, yttrium and zirconium are unlikely to biomagnify in predatory organisms or humans exposed via the environment.

 

For further details, please find the full bibliographic review attached in IUCLID section 13 “Assessment reports”.