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Description of key information

KEY STUDY (KEY_401_1991_HRC_90339D/LZA 38/AC), LD50 female rat (= most sensitive sex): 1635 mg/kg bw
KEY STUDY (KEY_Met-Hb_1978_BASF_11.07.78 (dd)), LD50 male and female cat (= most sensitive species): >25 and <200 mg/kg bw
NON-KEY STUDY (NON KEY_401_1973_Consultox Lab Ltd_CL 73:91:889), LD50 female rat: ca. 2500 mg/kg bw
NON-KEY STUDY (NON KEY_401_1978_BASF_11.07.78 (dd)): LD50 rat: ca. 5500 mg/kg bw

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Dose descriptor:
1 635 mg/kg bw

Additional information

Testing for acute oral toxicity following OECD standard or company methods revealed LD50 values from 1635 to 5500 mg/kg bw. for the rat and >25, <200 mg/kg bw. for cat. An LD50 of 1635 mg/kg bw.was identified to be the most sensitive and most reliable value for the rat (1st key study). But although Acetoacetanilide congeners are suspected to form methaemoglobin no definite indications for MetHb formation were observed in this study. In the 2nd key study LD50 for the cat was found to be >25, <200 mg/kg bw. The findings in this study indicate that lethality is caused by methaemoglobin formation. With respect to MetHb forming substances cats are known to react with higher sensitivity than humans. Based on that the acute toxic point estimated relevant for humans is considered to be above 300 and not higher than 2000 mg/kg bw. Findings of the non-key studies are not inconsistend with this conclusion.

Justification for classification or non-classification

The oral LD 50 in rat is 1635 mg/kg bw and (derived from acute oral toxicity data in cat) the acute toxic point estimated relevant for humans is above 300 and not higher than 2000 mg/kg bw. These values meet criteria for classification according to 67/548/EEC (2.2 DSD-DPD) or REGULATION (EC) No 1272/2008 (2.1 GHS).

Based on this findings formation of methemoglobin in humans is suspected and systemic availability for all three exposure routs is not unlikely. Therefore classification as R20/21/22 or Cat 4, H302/H312/332 irrespective of the routes tested is warranted.