Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
no hazard identified

Marine water

Hazard assessment conclusion:
no data: aquatic toxicity unlikely

STP

Hazard assessment conclusion:
no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:
insufficient hazard data available (further information necessary)

Sediment (marine water)

Hazard assessment conclusion:
insufficient hazard data available (further information necessary)

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

Micrometric cerium dioxide

All the justifications given above for no PNEC derivation applied to the bulk form of cerium dioxide.

 

Nanometric cerium dioxide

For the nanoparticulate cerium dioxide, the reasoning is nearly the same:

 

PNEC aquatic: for the nanometric form, acute data are available on the three trophic levels and chronic results exist on daphnids and algae:

* The Klimisch 2 study on fish does not reveal any adverse effect to Brachydanio rerio embryos up to the highest concentration tested; resulting in a 72h-EC50 > 200 mg/L.

* A similar conclusion can be drawn from acute tests on aquatic invertebrates (Daphnia magna and Thamnocephalus platyurus) which give 48h-EC50 > 1000 mg/L or > 100% saturated solution and 24h- LC50 > 5000 mg/L on both species, respectively.

* By contrast, chronic experiment on daphnids report toxicity with significant impacts appearing in the range 10 to 100 mg/L. However, due to the complexation of nutritive algal cells with nanoparticles, it cannot be excluded these effects were linked to food deprivation rather than impacts of nanoparticulate cerium dioxide. Several observations supported this hypothesis:

- The cerium dioxide nanoparticles aggregates clustered together with algal cells.

- The daphnids exposed to cerium dioxide nanoparticles were smaller than control individuals.

- Algae were absent from the gut of cerium dioxide nanoparticles-exposed organisms.

These observations suggest that decreased reproduction and eventual mortality was due to the inability to take up sufficient food. Such hypothesis is supported by the results of the algal cell density measurements which showed that when agglomerates of nanoparticulate cerium dioxide were mixed with the algal cells, both clustered together and sedimented.

* In the algal test using Pseudokirchneriella subcapitata, toxicity was also observed with 72h-EC50 and 72h-NOEC ranging from 10 to 100 mg/L and from 1 to 10 mg/L, respectively. To explain the observed toxicity, the authors tested several hypotheses: toxicity was due to: (1) an artefact of measurement, (2) adsorption to the algal cell walls, (3) dissolved cerium, (4) nutriment depletion, (5) shading. However, none of these hypotheses can be unambiguously considered as valid. Nevertheless, it should be kept in mind that clustering between algal cells and nanoparticles and indirect effect of phosphate depletion cannot be completely ruled out due to weight of evidence brought by other studies.

To conclude, depending on the studies, either no effect were observed up to the highest tested concentration, or indirect effects (e.g. food depletion, clustering between algal cells and nanoparticles) could be implied in the observed toxicity. In the absence of further data and knowing an extensive OECD testing program was ongoing on cerium dioxide nanoparticles (see the reference below*) , no PNEC was thus derived at the time being.

 

PNEC STP: the only data available on aquatic micro-organisms was obtained using an activated sludge respiration inhibition test. During this study, no toxicity was observed using a saturated solution of cerium dioxide nanoparticles; resulting in 3h-EC50 and 3h-NOEC of > 1000 mg/L and >= 1000 mg/L, respectively. In the absence of toxic effects and for the reasons explained above, it is thus not relevant to derive a PNEC STP.

 

PNEC sediment: no data are available on sediment-dwelling organisms. Furthermore, it is not possible to use the equilibrium partitioning theory to derive the PNEC sediment as not really adapted to inorganic substances. In addition, as a non-classified substance, nanometric cerium dioxide does not require an exposure assessment and a risk characterization. In the absence of risk characterization, no refinement is necessary, especially for the PNECs. As a result, there is no need to launch a test for the sedimentary compartment.

 

PNEC soil: two studies were found in the literature regarding impacts on soil organisms: one dealing with a nematode, another with plants. The first of them, scored as Klimisch 3, tested only one relatively low concentration and used a test species and a methodology not sufficiently close to the recognized guidelines to reliably conclude on toxicity to terrestrial macro-invertebrates. By contrast, the study on terrestrial plants was quoted as reliability 2 according to Klimisch. It provides 5d-EC50 superior to 2000 mg/L and 5d-NOEC superior or equal to 2000 mg/L on two species (Brassica napus and Triticum aestivum). As indicated in the Part E of ECHA guidance on information requirement and chemical safety assessment, it is not possible and not relevant to derive a PNEC based on these data showing no toxicity up to the highest tested concentration.

 

PNEC oral: based on the reliable literature data of Johnston et al. (2010), nanoparticulate cerium dioxide does not present any potential for bioaccumulation. As a result, there is no need to derive a PNEC oral.

 

* OECD (2008). List of manufactured nanomaterials and list of endpoints for phase one of the OECD testing program. Series on the safety of manufactured nanomaterials Number 6. Environment Directorate – Joint Meeting of the Chemicals Committee and the Working Party on Chemicals, Pesticides and Biotechnology. ENV/JM/MONO(2008)13/REV.

Conclusion on classification

Micrometric cerium dioxide

As an inorganic substance, cerium dioxide is not biodegradable. Based on the analogy made with soluble salts of cerium, cerium dioxide should not show any potential for bioaccumulation. Short-term tests performed on the three trophic levels (i.e. fish, daphnids, algae) does not reveal any acute toxicity. Furthermore, the long-term data on daphnids indicates that cerium dioxide presents no chronic adverse effects on this species. As a result, cerium dioxide is not classified regarding its environmental impacts, neither under the criteria of CLP, nor under those of DSD.

 

Nanometric cerium dioxide

As an inorganic substance, nanometric cerium dioxide is not biodegradable. Furthermore, a reliable literature data indicated it does not show any potential for bioaccumulation. While short-term tests performed on fish and daphnids did not reveal any acute toxicity, the algal study reported significant adverse effects of nanometric cerium dioxide, with the lowest 72h-EC50 ranging from 10 to 100 mg/L. As a result, nanometric cerium dioxide is harmful to algae. However, the NOEC obtained on the same algal species were superior to 1 mg/L. Furthermore, the 21d-NOEC deduced from the chronic test on daphnids were also superior to 1 mg/L. Concerning this last study, it is important to notice that the effects on survival and reproduction were probably due to food deprivation due to complexation of nutritive algal cells with nanoparticles. As a result, there is no clear evidence of chronic toxicity of nanometric cerium dioxide to daphnids. Taking into consideration these two chronic results on algae and daphnids with NOEC > 1 mg/L, and in accordance with criteria of CLP and DSD, nanometric cerium dioxide is not classified regarding its environmental impacts.