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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

Median lethal pH (96h) 3-3.5 for Lepomis macrochirus (no guideline followed).
Median lethal pH (96h) ca. 3.7 for Oncorhynchus mykiss (no guideline followed).
The available studies show that the pH rather than the anion (nitrate) is causing the toxic effects in fish. This is confirmed by variou studies with sodium nitrate: LC50 (96h) > 1000 mg/L to fish (no guideline followed). The read-across rationale can be found in the category approach document attached in Section 13 of IUCLID and is fully incorporated in the CSR.

Key value for chemical safety assessment

Additional information

Both K2 studies focus on the pH effects caused by nitric acid. Different pH levels have been tested in bluegill sunfish and rainbow trout.

The pH induced by nitric acid which caused 50% mortality was ca. 3.7 in rainbow trout and between 3.0 and 3.25 in bluegill sunfish.

No mortality was observed at pH 3.5 or above in bluegil sunfish after 96h exposure.

No mortality was observed at pH 4.0 in rainbow trout after 96h exposure, although 50% had died after 7 days of exposure.

The studies show that a pH caused by adding nitric acid roughly between pH 3 (or lower) and 4 is critical for fish. Furthermore, the Swift study shows that the nitrate ion alone (used as control) is not causing any mortality in fish. Also the studies from Westin (1974), Adelman et al. (2009), Trama (1954) and Wallen et al. (1957) conducted with sodium nitrate in marine and freshwater fish showed no effects (LC50 ≥ 1000 mg nitrate/L). It can thus be concluded that it is the low pH which is causing the toxic effects.

As regulatory ecotoxicity tests need to be conducted at pH 6-9, nitric acid will not cause adverse effects to fish when in this pH range.