Registration Dossier
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EC number: 234-126-4 | CAS number: 10544-72-6
Toxicity to aquatic algae and cyanobacteria
Administrative data
Link to relevant study record(s)
Description of key information
This information is read across from the Lead Registrants dossier for potassium nitrate (EC # 231-818-8).
The NOEC is 6.75 mmol N/L (i.e. 682 mg KNO3/L or 419 mg nitrate/L)
Key value for chemical safety assessment
Additional information
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 tetraoxide. (European Commission). Nitrous acid molecules then combine to produce nitric acid, nitric oxide and water.
The overall reaction can be written as follows:
3 N2O4 + 2 H2O = 4 HNO3 + 2 NO
This reaction is known to be rapid (Masteller & Berman), with Larkin having made calculations assuming an instantaneous rate of reaction between dinitrogen tetraoxide and water.
Since nitric oxide is a gas, it is assumed that only nitric acid is relevant for the aquatic toxicity.
It is therefore considered appropriate to read across to nitric acid (EC 231-714-2).
Nitric acid in water immediately dissociates into H+ ions and nitrate ions. The H+ ions will cause a significant pH decrease. As regulatory ecotoxicity studies should be conducted at environmentally relevant pH values (usually pH 6-9), the pH of the nitric acid test solutions should be adjusted. Consequently the pH effect is disregarded and the effects potentially caused by nitrate ions should be examined. Nitrate salts are all well soluble and in water immediately dissociate into nitrate ions and its counterions, similar to nitric acid. The counterions, sodium and potassium, are considered not significant in respect of ecotoxicological properties.
Therefore, this endpoint can be covered by a study conducted with potassium nitrate (Admiraal, 1970), which also dissociates in the environment into its ions. In this study, several marine benthic diatoms were exposed to potassium nitrate. The derived NOEC is 6.75 mmol N/L (i.e. 682 mg KNO3/L or 419 mg nitrate/L). References: 1. European Commission, ESIS (2000) IUCLID Dataset, Dinitrogen tetraoxide (CAS #10544-72-6) p.10 (CD-Rom edition). 2. Masteller, R.D. & Berman, L.D. (1964) Evaluation of the Mechanism of Corrosion in Capillaries, Status report #1, Oxidiser Diffusion Studies DRS S 11047, ME #531. U.S. Department of Defense.
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