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Physical & Chemical properties

Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
according to guideline
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
GLP compliance:
no
Type of method:
other: calculation method by boiling point (modified Watson correlation)
Temp.:
25 °C
Vapour pressure:
342 Pa
Conclusions:
The estimated vapour pressure of the UVCBS test substance was calculated using the procedure outlined in OECD Test Guideline 104: Vapour Pressure. The value was calculated using the highest temperature recorded in the boiling point study before the material foamed and decomposed. The calculated vapour pressure for the test substance is 342 Pa at 25°C. The vapour pressures of individual constituents of the test substance were obtained from MPBPWINTM ver. 1.43 (U.S. EPA) or from the literature. The most abundant constituents of the test substance (phospholipids, triglycerides and free fatty acids) are expected to have vapour pressures of less than or equal to E-4 Pa. The more minor constituents of the test substance (glycerol, acetic acid, water) are more volatile and the expected vapour pressures range from E-2 to approximately 3000 Pa. Water is expected to be the most volatile constituent of the mixture.
Executive summary:

The test substance is a substance of unknown or variable composition, chemical reaction products or biological materials (UVCBS) that has no assignable molecular weight. Due to its very complex nature, direct measurement of vapour pressure is not technically feasible. The OECD test guideline 104 (Vapour Pressure) outlines a calculation method for vapour pressure based on the boiling point of the substance. For a complex mixture, this calculation should result in the vapour pressure for the lowest boiling constituent of the mixture. A boiling point study was conducted with the test substance with mixed results. The material foamed and appeared to decompose at approximately 160°C. However, this value was used as the boiling point for the purposes of calculation of the vapour pressure, assuming that this would be a worst-case measurement for volatility. The calculated vapour pressure for the test substance is 342 Pa at 25°C. The vapour pressures of individual constituents of the test substance were obtained from MPBPWINTM ver. 1.43 (U.S. EPA) or from the literature. The most abundant constituents of the test substance (phospholipids, triglycerides and free fatty acids) are expected to have vapour pressures of less than or equal to E-4 Pa. The more minor constituents of the test substance (glycerol, acetic acid, water) are more volatile and the expected vapour pressures range from E-2 to approximately 3000 Pa. Water is expected to be the most volatile constituent of the mixture.

Description of key information

Calculated

342 Pa

Value used for CSA: 1.87E-04 Pa (oleic acid)

Key value for chemical safety assessment

Additional information

The vapour pressure for the physical-chemical properties endpoint was calculated using the value from the boiling point measurement, as described in OECD Test Guideline 104.  Decomposition was noted in the boiling point experiment so this is not a true boiling point.  Further, the boiling point and vapour pressure are both representative of the most volatile component in the substance as tested, which is probably water (accounting for at least 1% of the total weight) or other minor water-soluble minor constituents.  For the purposes of risk assessment, the more appropriate value for vapour pressure is the most volatile major constituent of the substance, which is oleic acid (a free fatty acid). The vapour pressure of oleic acid is 1.87E-04 Pa (obtained from the Experimental database of MPVPBPWIN v. 1.43).