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Acute tests evaluating the toxicity of aminoiminomethanesulphinic acid (CAS No. 1758-73-2) to aquatic organisms from three different trophic levels are available. Aquatic algae turned out to be the most sensitive taxonomic group with an ErC50 (72 h) of 55.1 mg/L based on growth rate of Selenastrum capricornutum, whereas no toxicity was observed in fish up to a concentration of 100 mg/L after 96 h (nominal) and an EC50 (48 h) of 80.7 mg/L was derived for Daphnia magna. Long-term toxicity testing with aquatic invertebrates and algae are additionally available. A NOEC (21 d) of 2.13 mg/L was calculated based on reproduction of Daphnia magna and whereas a NOEC (72 h) of 17.1 mg/L resulted based on the growth rate of Selenastrum capricornutum. The test substance is known to be unstable under alkaline conditions (see IUCLID Section 5.1.2). Therefore, the available studies were performed either under semi-static or flow-through conditions in order to maintain the test concentrations at a constant level. Only the algae study was performed under static conditions. A decrease in test substance concentrations was measured reflecting the instability of the substance and the effect concentrations were based on the nominal concentrations.
An additional long-term study with fish was not considered to be additionally necessary since it did not turn out to be the most sensitive species based on the acute data. Moreover, the environmental exposure assessment for aminoiminomethanesulphinic acid according to Annex XI, Section 3 according to Regulation (EC) No 1907/2006 indicates no risk for the aquatic compartment (all RCR < 1; please refer to Chapter 9 and 10 of the Chemical Safety Report for detailed information). Thus, long-term testing with fish is not deemed necessary. Aminoiminomethanesulphinic acid did not cause inhibition of biodegradation in a study according to OECD 301C with mixed inoculum of activated sludge microorganisms, natural water from rivers and lakes and marine water including marine sediment. No inhibition of degradation was observed at the applied test concentration of 100 mg/L. A NOEC (28 d) of ≥ 100 mg/L was derived. The overall potential to cause inhibition of activated sludge microorganisms is low and significant inhibition of the subsequent degradation process in sewage treatment plants is not expected. The environmental exposure assessment for aminoiminomethanesulphinic acid according to Annex XI, Section 3 according to Regulation (EC) No 1907/2006 indicates no risk for STP microorganisms (all RCR < 1; please refer to Chapter 9 and 10 of the Chemical Safety Report for detailed information).