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Short-term toxicity to fish

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Description of key information

Key Study Result: Measured 96h LC50 of 23.9 mg/L (based on initial measured concentrations)

Key value for chemical safety assessment

LC50 for freshwater fish:
23.9 mg/L

Additional information

A valid study is available for 2,6-dimethylheptan-2-ol. The acute toxicity to zebra fish was determined in a static system over an exposure period of 96 hours at nominal test concentrations of 4.64, 10.0, 21.5, 46.4 and 100mg/L (Munk, 1995). No results related to the analytically determined values were calculated since no test item was detected at the end of the study. This was considered to be probably due to the long time period of storage pending analysis. The stability of the test substance over the study period was proved by reanalysis. Based on the nominal concentrations the median lethal concentration LC50 (96h) was reported as >21.5 and < 46.4 mg/L. These concentrations are respectively the nominal concentrations at which 0% mortality and 100% mortality was observed. According to OECD Guideline 203 where the data obtained are inadequate for the use of standard methods of calculating the LC50, the highest concentration causing no mortality and the lowest concentration producing 100 per cent mortality should be used as an approximation for the LC50 (this being considered the geometric mean of these two concentrations). Thus a recalculation made by the registrant gives an LC50 of 31.6 mg/L based on nominal concentrations. The analytically detected concentrations at 1 hour were reported as 3.9, 8.0, 15.2, 37.7 and 87 mg/L for respectively nominal concentrations of 4.64, 10, 21.5, 46.4, 100 mg/L. Assuming that these analytically determined concentrations would represent the initial measured concentrations, the registrant calculated the LC50 to be 23.9 mg/L based on initial measured concentrations (i.e. geometric mean of 15.2 mg/L and 37.7 mg/L).

A QSAR prediction was also undertaken on 2,6-dimethylheptan-2-ol using iSafeRat® holistic HA-QSAR v1.3, which can reliably predict the aquatic toxicity for chemicals classified as Mode Of Action 1 substances (non-polar narcotics). The predicted value of 25.34 mg/L is extremely close to the experimentally measured value of 23.9 mg/L (based on initial measured concentrations). This supports the use of the recalculated measured value of 23.9 mg/L as the key value for chemical safety assessment. It also provides strong supporting evidence that Dimetol is a MOA1 substance and that the aquatic toxicity for other endpoints, such as daphnia and algae, can be reliably predicted with the iSafeRat® holistic HA-QSAR.