Registration Dossier
Registration Dossier
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EC number: 231-714-2 | CAS number: 7697-37-2
Toxicity to microorganisms
Administrative data
Link to relevant study record(s)
Description of key information
A waiver is proposed to cover this endpoint, and supporting evidence with a study on sodium nitrate (Schwarz, 2008) is provided. 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
Nitric acid in water will dissociate in nitrate anions and H+ ions, the latter causing a decrease of pH. However, pH levels in wastewater are typically adjusted in wastewater treatment plants to ensure a neutral discharge to the receiving water (e.g., pH between 6-9). Therefore, the microorganisms are essentially exposed to nitrate and not to nitric acid or to low pH values. The study therefore does not need to be performed, according to REACH Annex VIII column 2.
In addition, nitrogen is an essential nutrient for activated sludge systems, as it comprises part of the biomass in the activated sludge. Typical nitrate levels in domestic sewage are near zero; bacterial oxidation of the ammonia present in sewage produces nitrates. Where excessive ammonia levels are of concern, treatment plants are designed to incorporate a two-step nitrification-denitrification process: (1) ammonia is converted to nitrite and then nitrate, and (2) nitrate is reduced anoxically to NO, N2O, and N2 gases.
Furthermore, in accordance with REACH Annex XI, section 1.5 (Grouping of substances and read-across approach) the toxicity test on microorganisms does not need to be conducted as it can be covered with a study done on sodium nitrate, which also dissociates into nitrate ions. This study (Schwarz, 2008) showed a 3h-EC50 of >1000 mg/L.
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