Sediment water and octanol water equilibrium partitioning of volatile organic compounds:: Temperature dependence in the 25°C range

The sediment/water (K-d) and octanol/water (K-ow) equilibrium partitioning coefficients have been investigated for volatile chlorinated and monocylic aromatic hydrocarbons in the 2 to 25 degrees C temperature range. The equilibrium partitioning in closed systems (EPICS) method has been optimized to measure both equilibrium partitioning coefficients. Sediment/water equilibrium partitioning for a riverine sediment (organic carbon fraction 4.12%) proved to increase with increasing temperature, showing changes in enthalpy between 2.5 and 12.8 kJ.mol(-1) A statistical approach showed that for 5 our of 12 compounds investigated this temperature dependence is significant at alpha = 0.05. Next, the temperature dependence of the octanol/water equilibrium partitioning was investigated for 8 compounds. The octanol/water equilibrium partitioning coefficients increased with increasing temperature for all compounds, except for toluene. Changes in enthalpies of this process proved to be between -1.0 and 5.2 kJ.mol(-1) However, the temperature dependence of this process was statistically not significant (alpha = 0.05). The log K-d-log K-ow relationship showed correlation coefficients between 0.89 and 0.90 at 2.3, 6.2, 18.6 and 25.0 degrees C (n = 8). Slopes of the linear regression increased with increasing temperature. This was explained by the higher temperature dependence of sediment/water equilibrium partitioning process for compounds with higher K-d coefficients. (C) 1999 Elsevier Science Ltd. All rights reserved.