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Environmental fate & pathways

Hydrolysis

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Description of key information

The test substance is unstable under alkaline conditions.

Key value for chemical safety assessment

Additional information

No experimental data according to accepted guidelines are available for this endpoint. In accordance with Regulation (EC) No 1907/2006, Annex VIII, 9.2.2.1., column 2 testing is not required since aminoiminomethanesulphinic acid (CAS No. 1758-73-2) is readily biodegradable. However, data from literature indicate that the substance is unstable under alkaline conditions. Miller et al. (1988) investigated the stability of aminoiminomethanesulphinic acid in buffer solutions at pH 7.4, pH 10 and pH 13-14 for 24 h. Urea and cyanamide were identified as primary degradation products. After 24 h 5% formation of urea was recorded at pH 7.4, whereas 35% formation of urea and 5% of cyanamide was measured at pH 10. At pH 13 85% formation of urea was found. Svarovsky et al. (2001) studied the kinetics and mechanism of decomposition of thioureas in alkaline solutions. The decomposition of thiourea dioxide is characterized by an induction period which is followed by the formation of dithionite (S2O4 2-) under aerobic conditions.The initial step of decomposition is the cleavage of the C-S bond to give an urea residue and the sulfoxylate ion, SO2-, which is the precursor to the formation of dithionite vial a rapid equilibrium. In aerobic environments the sulfoxylate ion can produce the highly tissue-damaging series of reactive oxygen species superoxide, peroxide, and hydroxyl radical. These species could be responsible for the inherent toxicities associated with thioureas.
An additional study which is available only as a short summary, indicated that an aqueous solution of aminoiminomethanesulphinic acid is unstable under aerobic conditions at 20 °C (OECD, 2002). 30% of the substance were degraded after 22 h.
All available data indicate that aminoiminomethanesulphinic acid is unstable under alkaline conditions leading to the formation of urea.