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Ecotoxicological information

Long-term toxicity to fish

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Description of key information

According to REACH Annex IX no testing is required if the results of the Chemical Safety Assessment (CSA) indicates no need to investigate further the effects of the substance on aquatic organisms. The CSA indicates no concern for fish. Furthermore, in accordance with REACH Annex XI, section 1.5 (Grouping of substances and read-across approach) the long-term toxicity test on fish does not need to be conducted as nitric acid will further dissociate into H+ ions (resulting in a pH decrease) and nitrate ions, and the endpoint can consequently be covered with a study done on sodium nitrate, which also dissociates into nitrate ions. 
There are reliable 30d growth rate and 32d embryo-larval tests with Sodium nitrate available from Adelman (2009).
In the 30d growth rate test the NOEC for juvenile Topeka shiner was 268 mg/L (growth rate) and the NOEC for Fathead minnow was 58 mg/L (mortality).
In the 32d embryo-larval test, the NOEC to Fathead minnow was 157 mg/L based on growth rate (no effect on embryo survival).
Based on these results, long-term effects to fish at environmentally relevant pH values are not expected to occur.

Key value for chemical safety assessment

Additional information

The endpoint 'long-term toxicity to fish' can be covered by a waiver, which is based on two arguments:

1. According to REACH Annex IX no testing is required if the results of the Chemical Safety Assessment (CSA) indicates no need to investigate further the effects of the substance on aquatic organisms. The CSA indicates no risks for the aquatic environment, so the aforementioned waiving argument is valid.

2. According to REACH Annex XI, the study can be waived when it can be covered by a structural analogue. In water, dinitrogen tetraoxide (EC 234-126-4) will decompose to nitrous acid and nitric acid, and the aquatic toxicity should be equal to the water concentrations of these substances due to the decomposition of the actual concentrations of dinitrogen tetroxide. (European Commission). Nitrous acid molecules then combine to produce nitric acid, nitric oxide and water. Since nitric oxide is a gas, it is assumed that only nitric acid is relevant for the aquatic toxicity. Nitric acid will further dissociate in the environment into its ions: H+ ions and nitrate ions. The H+ ions will cause a pH decrease, but in the aquatic environment the net pH decrease will be limited due to buffering. Regulatory aquatic ecotoxicity studies should be conducted at relevant environmental pH (i.e. pH 6 -9). At this pH, exposure to nitric acid comes down to exposure to nitrate ions. Therefore this endpoint can be covered by a study conducted on sodium nitrate, which also dissociates in the environment into its ions.

There are reliable 30d growth rate and 32d embryo-larval tests with Sodium nitrate available from Adelman (2009).

In the 30d growth rate test the NOEC for juvenile Topeka shiner was 268 mg/L (growth rate) and the NOEC for Fathead minnow was 58 mg/L (mortality).

In the 32d embryo-larval test, the NOEC to Fathead minnow was 157 mg/L based on growth rate (no effect on embryo survival).

Based on these results, long-term effects to fish at environmentally relevant pH values are not expected to occur.