4-tert-butylcyclohexanol

Short-term toxicity to fish

Description of key information

LC50 = 6.82 mg/L 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

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.