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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

Median lethal pH (48h) 4.4-4.7 for Ceriodaphnia dubia (US EPA guideline). This study shows that the pH rather than the anion (nitrate) is causing the toxic effects in daphnids. This is confirmed by two additional studies with sodium nitrate (24h EC50 8609 mg/L for Daphnia magna; similar to OECD TG 202) and potassium nitrate (48h EC50 490 mg/L for Daphnia magna; 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

In the Belanger and Cherry study (1990), the water flea Ceriodaphnia dubia was exposed to nitric acid pH-adjusted test solutions for 48 hours with test solution renewal at 24 hours. The 48-hour LC50 was determined after testing two pH ranges, 3.4-8.1 and 3.2-8.0. The grand probit 48-hour LC50 (combined analyses) was 4.6 pH standard units.

Similar to the other aquatic toxicity endpoints, it is shown that adverse effects due to nitric acid exposure are caused by the decreased pH and not by the nitrate anion. This finding is strengthened by the BASF (1983) and Dowden and Bennett (1965) studies which show high LC50 values in daphnids exposed to sodium nitrate (24h-LC50 = 8609 mg/L) or potassium nitrate (96h-EC50 = 900 mg/L).

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