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Long-term toxicity to fish

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Description of key information

Butyl 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxybenzenepropanoate (CAS 52449-44-2): NOEC: 0.36 mg/L (Goodband and Mullee, 2009)

Key value for chemical safety assessment

Additional information

Chronic toxicity to fish of Benzenepropanoic acid, 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxy-,C7 -9 branched alkyl esters (CAS 125643 -61 -0) is not investigated so far.

For the substance Butyl 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxybenzenepropanoate (CAS 52449 -44 -2) one experimental result is available and can be used as read-across possibility. The study assess the the effects of the substance on freshly hatched larvae of the fathead minnow (Pimpephales promelas) (Goodband and Mullee, 2009b).

The method followed that described in the OECD Guidelines for Testing of Chemicals (1992) No 210, "Fish, Early-Life Stage Toxicity Test”, US Code of Federal Regulations, Title 40, Part 797, Section 1600 and the US EPA Draft Ecological Effects Test Guideline OPPTS 850.1400.

The test material fell into the category of a ‘difficult substance’ as defined by the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (OECD 2000). Therefore a media preparation trial was conducted in order to determine the solubility of the test material under test conditions. The pre-study media preparation trial indicated that the use of a saturated solution method of preparation followed by filtration to remove the undissolved test material was the most appropriate method of preparation for the test material.Following a preliminary range-finding test, newly laid eggs were exposed to an aqueous solution of test material at time-weighted mean measured test concentrations of 0.11 and 0.36 mg/L for a period of 33 days at a temperature of approximately 25 ºC under semi-static test conditions. The test material solutions were prepared by stirring an excess (50 mg/L) of test material in dechlorinated tap water using a propeller stirrer at approximately 1500 rpm at a temperature of approximately 25 °C for 24 hours. After the stirring period any undissolved test material was removed by filtration to produce a saturated solution of the test material with a time-weighted mean measured concentration of 0.36 mg/L. This saturated solution was then further diluted as necessary, to provide the remaining test group. The test solutions were renewed daily.The number of mortalities or any sub-lethal effects of exposure in each test and control vessel were recorded daily until termination of the test (28 days post-hatch). At test termination the length and dry weight of the surviving fish were measured. Analysis of the freshly prepared saturated solution (equivalent to the highest test concentration) showed measured concentrations to range from 0.642 to 1.18 mg/L. This was more than the expected 0.10 mg/L based on the results from the Daphnia magna Reproduction study (Harlan Laboratories Ltd Project Number: 0525/0904). This variation in the concentration of the saturated solution was considered to be due to the low water solubility of the test material and slight variations in water quality characteristics of the test medium and in the preparation conditions despite every effort to ensure consistency of these conditions. In addition, this test was conducted at approximately 25 °C whereas the reproduction test was conducted at a temperature of approximately 21 °C. The slight increase in temperature may have resulted in increased dissolution of the test material in the test medium. Analysis of the freshly prepared 0.032 mg/L nominal test concentration showed measured concentrations to range from 0.195 to 0.336 mg/L. Analysis of the old media showed measured concentrations to range from less than the limit of quantitation to 0.114 mg/L for the nominal 0.032 mg/L test concentration and from 0.0176 to 0.328 mg/L for the nominal 0.10 mg/L test concentration. This decline was contrary to the stability analysis performed which showed the test material to be generally stable. However, stability analysis performed for the Daphnia magna Reproduction study (Harlan Laboratories Ltd Project Number: 0525/0904) indicated that the test material was unstable in the test medium. An explanation for the differences between the stability analyses from the two studies could not be ascertained from the data. However, given the results from the Daphnia magna Reproduction study, this study was conducted under a semi-static test regime using a daily media change as a precaution. Given this decline in measured concentration, and the variability of the saturated solution, it was considered justifiable to base the results on time-weighted mean measured concentrations only. The time-weighted mean measured concentrations were calculated to be 0.11 and 0.36 mg/L. Over the duration of the test there were no significant mortalities or sub-lethal effects of exposure resulting from the exposure of fathead minnow (Pimephales promelas) larvae to time-weighted mean measured test concentrations of 0.11 and 0.36 mg/L. The hatching rate ranged from 93 % to 97% and the survival rate ranged from 80 % to 97 %. Statistical analysis of the data showed no significant differences between the control and the time-weighted mean measured test concentrations in terms of fish length and dry weight, concluding that the No Observed Effect Concentration (NOEC) is 0.36 mg/L.