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Environmental fate & pathways

Henry's Law constant

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Description of key information

In general, the volatility of dissolved constituents of pitch, coal tar, high-temp. (CTPht) from the water phase is very low. Benzo[a]pyrene (BaP) has been selected as marker substance in order to characterise the environmental fate of CTPht. Hence, an experimental value of Henry's Law Constant for BaP is used for the chemical safety assessment.

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):
at the temperature of:
20 °C

Additional information

The experimental HLC value for BaP is taken from the publication of de Maagd et al. (1998, see Reference). Reported value is 0.034 Pa*m³/mol.

In addition, a HLC value for CTPht is calculated for comparison using the water solubility (0.242 mg/L) and the vapour pressure (5.8*10-06 Pa) of CTPht at 20 °C. As there is no definite molecular weight for CTPht (UVCB), the molar mass of BaP (252.3) is used in the calculation.

H = VP / WS x MW = 5.8*10-6 Pa / 0.242 mg/L x 252.3 g/mol = 0.006 Pa*m³/mol


de Maagd P. G.-J., ten Hulscher D. Th.E.M., van den Heuvel H., Opperhuizen A., and Sijm D. T.H.M. (1998) Physicochemical Properties of Polycyclic Aromatic Hydrocarbons: Aqueous Solubilities, n-Octanol/Water Partition Coefficients, and Henry's Law Constants. Environmental Toxicology and Chemistry 17, 251-257