Octamethyltrisiloxane

Henry's Law constant

Link to relevant study record(s)

Reference

Endpoint:

Henry's law constant

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study was conducted according to an appropriate test method, but not in compliance with GLP.

Principles of method if other than guideline:

The Kaw, Kow and Koa of 14C-labelled L3 were simultaneously determined at room temperature. A custom-made glass apparatus was used for the test, which allowed for the establishment of octanol/air/water three-phase equilibrium. The concentrations of the test substance in the three phases were analysed by LSC and HPLC/RAM.

GLP compliance:

no

H:

1 620 000 Pa m³/mol

Temp.:

12 °C

H:

2 680 000 Pa m³/mol

Temp.:

20.8 °C

Equilibrium concentrations of the test substance in the test vessels were achieved after 20 hours. At 20.8 ± 0.4°C, partitioning coefficients were determined in a range of L3 concentrations in water (2.7 to 6.3 µg L-1) much lower than its solubility limit (34 µg L-1at 25°C). The measured values of log Kow the substance was 6.87 ± 0.24 (average ± standard deviation). The measured partitioning coefficients at three other temperatures (4.5 ± 0.2, 12.1± 0.0, and 35 ± 0.3°C) can be well described by the following equation: log Kow= 6.97 - 54.3/T r2= 0.02 (n = 4) The r2 was very small because the measured log Kow values were almost constant in the entire temperature range. This implies that the log Kow of L3 is not temperature dependent at the temperature range tested. The internal energy change for phase transfer in partition equilibria (delta U) for L3 (defined as 2.303 × Ideal gas constant × slope) was -1.0 KJ mol-1 for octanol/water partitioning.

Type	Partition coefficient	Temp.	pH	Remarks
log Pow	6.87	20.8 °C		log Kow = ± 0.24, Temp. = ± 0.4°C
		20.8 °C		log Koa = 3.79± 0.01, Temp. = ± 0.4°C
		20.8 °C		log Kaw = 3.04± 0.20, Temp. = ± 0.4°C

Conclusions:

An air-water partition coefficient (log Kaw) value of 3.04 at 20.8°C was determined in a reliable study conducted according to an appropriate test protocol. This is equivalent to a Henry's Law Constant of 2.68E+06 Pa m3 mol-1 at 20.8°C; 1.62E+06 Pa m3 mol at 12°C.

Description of key information

Log K_aw: 3.04 ± 0.20 at 20.8 ± 0.4°C

Henry's Law Constant: Calculated HLC for L3 at environmental temperature (12°C): 1.62 E+06 Pa m³mol^-1

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):

1 620 000

at the temperature of:

12 °C

Additional information

The transfer of a substance from the water phase to the gas phase can be estimated by means of the Henry’s Law Constant (HLC).

A log K_aw of 3.04 (K_aw = 1096) at 20.8°C was determined in a reliable study conducted according to generally accepted scientific principles.

This is equivalent to Henry's Law Constant (HLC) of 2680000 Pa m3 mol-1 at 20.8°C, 1620000 Pa m³ mol^-1 at 12°C.

(HLC = K_aw x RT)