Cerium tetranitrate

Short-term toxicity to fish

Description of key information

The study performed on the analogue cerium ammonium nitrate reported a 96-h LC50 of 0.14 mg dissolved Ce/L (corresponding to 0.39 mg Ce(NO3)4/L), suggesting that Ce(NO3)4 is very toxic to fish. 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.14 mg/L

Additional information

No reliable data have been identified for cerium tetranitrate. Therefore, read across is performed from a key study for cerium ammonium nitrate, another tetravalent cerium compound (Hefner, 2014a).

Cerium ammonium nitrate had acute toxic effects on juvenile rainbow trout (Oncorhynchus mykiss) in a semi-static study performed according to OECD guideline 203 (Hefner, 2014a). The 96-hour LC50 was determined to be 0.14 mg/L for dissolved cerium with 95% confidence limits of 0.11 and 0.17 mg/L (corresponding to 0.53 mg/L of cerium ammonium nitrate with 95% confidence limits of 0.42 and 0.66 mg/L or, when expressed as cerium tetranitrate, the 96-h LC50 would be 0.39 mg/L). Based on these results cerium ammonium nitrate, as well as cerium tetranitrate, are considered to be very toxic to fish.

Because of the discrepancy of this result with that for aquatic invertebrates (no adverse effects observed up to and including the limit nominal test dose of 100 mg cerium ammonium nitrate or cerium tetranitrate/L), it was investigated whether or not there might have been a confounding effect of ammonia. Nominally, 6.58 mg/L ammonia have been added to the test medium at the 100 mg/L cerium ammonium nitrate loading rate. At an average pH of 6.2 and temperature of 13.5°C, this corresponds to about 0.002 to 0.003 mg unionized ammonia/L (i.e., the toxic form, calculations performed using several tools, e.g., Unionized Ammonia Calculator v1.2, after original by Dr. Landon Ross, Florida Department of Environmental Protection). Studies on acute unionized ammonia toxicity to rainbow trout report the following levels of toxicity:

- 96-h LC50 of 0.16-1.1 mg/L for 1-d-old fry up to 4-y-o adults - fry were most sensitive (Thurston RV, Russo RC, 1983. Acute toxicity of ammonia to rainbow trout. Transactions of the American Fisheries Society 112, 696-704).

- 96-h LC50 of 0.15 mg/L for rainbow trout (USGS).

Therefore, it is highly unlikely that ammonia would have contributed to the observed effects in the test performed by Hefner (2014a)

as the concentration in unionized ammonium present in this study (i.e. 0.002 to 0.003 mg/L) were well below the LC50 above reported.

The remarkable difference in observed effects between the test with fish and the tests with aquatic invertebrates may therefore be ascribed to a difference in sensitivity of the test organisms and/or a difference in exposure. Dissolved cerium concentrations in the undiluted filtrate were between 0.00259 and 0.00338 mg Ce/L and between 0.028 and 0.068 mg Ce/L in the tests with aquatic invertebrates with cerium ammonium nitrate (Hefner, 2014d) and cerium tetranitrate (Hefner, 2014b), respectively, whereas in the acute fish test with cerium ammonium nitrate the undiluted filtrate yielded dissolved cerium concentrations between 0.322 and 0.566 mg/L (during the second 48-h renewal period)).

It can be assumed that the observed toxicity in the acute fish test with cerium ammonium nitrate was due to bioavailable cerium (Ce+3) and that any Ce+4 present during the test (not appearing in dissolved state according to the Pourbaix diagram, see environmental fate section) did not contribute to the observed toxicity. This is confirmed by the fact that a similar test (same test organism, test medium, test conditions) with cerium trinitrate (a trivalent cerium compound) yielded almost exactly the same 96-h LC50 value, more specifically 0.13 mg Ce/L (Peither, 2011). Consequently, it can be stated that a prerequisite for observing adverse effects after adding a tetravalent cerium compound to the test medium is that under the prevailing conditions sufficient bioavailable cerium (Ce+3) can be formed in the test medium. For fish, dissolved cerium concentrations in the test with cerium ammonium nitrate were clearly high enough to cause toxicity. This however does not seem to be the case in the tests with cerium ammonium nitrate and cerium tetranitrate with aquatic invertebrates, although pH was kept deliberately low (pH 6.0) to maximise dissolved cerium levels in the test medium (see further).

References not included in this dossier:

- Hefner N, 2014d. Cerium ammonium nitrate: Acute toxicity to Daphnia magna in a 48-hour immobilization test. Harlan Laboratories Ltd., Zelgliweg 1, 4452 Itingen, Switzerland. Report no. D60755. Owner company: Treibacher Industrie AG.

- Peither A, 2011. Acute toxicity of cerium nitrate 99.5 cristallisé to rainbow trout (Oncorhynchus mykiss) in a 96-hour test. Harlan Laboratories Ltd., Zelgliweg 1, 4452 Itingen, Switzerland. Report no. C21560. Owner company: Rhodia.