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Short-term toxicity to fish

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Description of key information

LC50 = 6.82 mg/L 

Key value for chemical safety assessment

LC50 for freshwater fish:
6.82 mg/L

Additional information

The acute toxicity of 4-tert-butylcyclohexanol to fish was investigated in a study conducted by (96-0394-DKO). This non-GLP test was carried out as static dose-response test according to DIN 38412, part 15. Golden orfes (Leuciscus idus melanotus) were exposed for 48 h to the nominal test concentrations 13, 16 and 20 mg/L. No analytical verification of the test substance concentrations in the test media was performed. The test duration of 48 h is not in line with today's standards where a test duration of 96 h is recommended. Consequently, the resulting LC50 (48 h) value of 17 mg/L (nominal) is not sufficient for the fully evaluation of the acute toxicity of the test substance to fish.

Thus, short-time toxicity to fish is further investigated by QSAR-calculations. Therefore, a trend analysis on the basis of QSAR Toolbox 2.2.1.1120, Database version 2.1.8/1.0.0 for 4-tert-butylcyclohexanol is performed (2012). Taking into account a test duration of 96 h, the calculation resulted in an LC50-value of 7.42 mg/L for fathead minnows (Pimephales promelas). In a second QSAR-calculation on the basis of ECOSAR v1.00 the LC50 (96 h) for fish was determined to be 6.82 mg/L (2013-0036-DKB). The fish species is not further specified in this model.

To further support the available information on 4-tert-butylcyclohexanol, acute fish toxicity data obtained with the structural analogue L-menthol (CAS 2216-51-5) were considered. Both substances share a cyclohexanol ring, whereas 4-tert-butylcyclohexanol has one tert-butyl substituent and L-menthol has two substituents, a methyl and an isopropyl group. To demonstrate the similarity of the substances, the physical-chemical parameters are summarized in the following table.

Similarity of the physical-chemical properties of 4-tert-butylcyclohexanol and L-menthol

 

4-tert-Butylcyclohexanol

L-Menthol

(2-isopropyl-5-

methylcyclohexanol) 1)

CAS-No

98-52-2

2216-51-5

Molecular weight

156.27

156.27

Physical state at ambient temperature

solid

solid

Melting point (° C, 1013 hPa)

56 (cis form)
- 83 (trans form)

41 – 43 2)

Boiling point (° C, 1028.3 hPa)

218.6

218.94

Density

0.87 g/mL

0.89 g/cm3

Vapor pressure (at 25 °C)

6 Pa

6.37E-02 mm Hg
(8.49E+000 Pa)

Log Kow

3.32

3.38

Water solubility (mg/L)

264

434.5

1)      EPIsuite 4.10 calculation with CAS 2216-51-5

2)      http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB (search CAS 2216-51-5)

For menthol an acute flow-through test (no guideline mentioned) is conducted on fathead minnows (Pimephales promelas) and is summarized in a publication of Russom et al. (1996). The test resulted in an LC50-value of 18.9 mg/L (nominal) after 96 h.

Taking into account all available data for 4-tert-butylcyclohexanol (pTBCol) and its structural analogue menthol, the LC50-value of the test substance is expected to be above 1 mg/L. For the calculation of PNEC-values, the worst-case endpoint determined by using the ECOSAR v1.00 (LC50 (96 h) = 6.82 mg/L) will be used.