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The acute toxicity of n-isopropylhydroxylamine was examined in two species of fish, two aquatic invertebrate species, one algal species, and one additional microorganism species.


The fish studies consist of one acute study with the freshwater fish Rainbow trout (Onchorhynchus mykiss) and one with the marine fish Sheepshead minnow (Cyprinidon variegatus). Both tests were conducted according to OECD 203 guideline (Fish, Acute Toxicity Test). The freshwater Rainbow trout study determined the following: a 96-h EC50 of 465 mg/l and a 96-h NOEC of 360 mg/L, based on nominal concentrations. The marine Sheepshead minnow study was conducted as a limit test in order to reduce testing on vertebrates, with the limit dose set at the calculated LC50 value from the IPHA marine invertebrate (Acartia tonsa) test, which was 1.4 mg/L. Based on this, the 96-h LC50 was determined to be > 1.4 mg/L, the limit dose and the 96-h NOEC was 1.4 mg/L, based on nominal concentrations.


One freshwater invertebrate study and one marine invertebrate acute study were conducted. The freshwater invertebrate test with Daphnia magna (OECD 202 guideline) determined a 48-h EC50 of 201 mg/l and a 48-h NOEC of 77.8 mg/L, based on nominal concentrations. The marine invertebrate test with Acartia tonsa determined a 48-h LC50 of 1.4 mg/L and a 48-h NOEC was 0.56 mg/L, based on nominal concentrations. This study produced the most sensitive overall endpoint for aquatic species.


A single algal growth inhibition study was conducted with IPHA. The effects of IPHA on growth rate of the marine diatom Skeletonema costatum were evaluated over a 96-h time period. The key endpoint for this study is the 72-h ErC50, which is based on the growth rate endpoint. The 72-h ErC50 to Skeletonema costatum was determined to be 32 mg/L (95% confidence interval 29-34 mg/L. The NOErC for the growth rate endpoint was determined to be 23 mg/mg/L. However, these were expressed as nominal values so of limited relevance due to the fast hydrolysis. ErC50(24h) of 4.5 mg/L can be extrapolated from the whole dose-response curve and based on measured concentrations at 0h and 24h. Results after 24h are irrelevant since the hydrolysis of the test item allows a recovery of algae growth, and leads to impossibility to express EC50 in measured concentrations.


In the bacterial Cell Multiplication Inhibition Test, the 16-h EC10and EC50values were 40 mg/L and 130 mg/L, respectively.