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Environmental fate & pathways

Henry's Law constant

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Description of key information

Henry's law constant (H): 31500 Pa m^3/mol (HENRYWIN v3.20, EPISUITE v1.00)

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):
31 500
at the temperature of:
25 °C

Additional information

According to Appendix R.7.1-4 “Henry’s law constant and evaporation rate” from the Guidance on Information Requirements and Chemical Safety Assessment Chapter R.7a: Endpoint Specific Guidance,Henry’s law constant is one of the most important factors in determining the environmental fate of chemicals. This physical law states that the mass of gas dissolved by a given volume of solvent is proportional to the pressure of the gas with which it is in equilibrium. The relative constant quantifies the partitioning of chemicals between the aqueous phase and the gas phase such as rivers, lakes and seas with respect to the atmosphere (gas phase). Indeed, this constant is a fundamental input for fugacity models that estimate the multimedia partitioning of chemicals (Mackay, 1991).

CTFE is a volatile gas at ambient conditions with a boiling point in the range of -26.2°C (The Beilstein database. Reference: Miller - 1951 ) to -26.8°C (The Beilstein database. Reference: Henne - 1948) and in case of accidental emission is released only to air compartment, as indicated by the EQC Fugacity III Model (v.2.02, The Canadian Centre for Environmental Modelling and Chemistry, May 2003).

Hence, due to the gaseous nature of the substance and its partition to the atmosphere, as well as the consequent difficulty to appropriately test CTFE and provide meaningful results, no experimental data are reported for Henry’s Law constant. However, in order to evaluate this constant for CTFE, despite the fact that it is expected to rapidly partition to the atmosphere compartment, the result of the HENRYWIN model (v.3.20, EPI Suite v 4.0) is afterwards discussed. The Guidance on Information Requirements and Chemical Safety Assessment Chapter R.7a: Endpoint Specific Guidance, Appendix R.7.1-4 indicates that substances with a Henry's Law constant of around 1 hPa m3/mole rapidly volatilize from water.

On the basis of a Henry’s Law constant of 31,500 Pa m3/mol (HENRYWIN v3.20, EPI Suite v4.0), a boiling point ranging from -26.2°C (The Beilstein database. Reference: Miller - 1951 ) to -26.8°C (The Beilstein database. Reference: Henne - 1948) the high vapour pressure of 612 kPa at 25°C (ISCS No. 0685, NIOSH) and a moderate water solubility (the water solubility value of 380 mg/L has been evaluated in a closed system with the atmosphere saturated of CTFE hence it represents an overestimation of the actual water solubility of CTFE in the natural system) CTFE is expected to primarily and rapidly partition to the atmosphere.