CALCULATION OF BIOCONCENTRATION FACTORS OF PERSISTENT HYDROPHOBIC COMPOUNDS IN THE AIR/VEGETATION SYSTEM

A multi-compartment model based on equilibrium partitioning has been developed for predicting leaf/atmosphere partition coefficients (theoretical K-BA) of persistent hydrophobic organic compounds. The leaf was considered to consist of five major phases i.e. cuticular lipids, cellular lipids, protein, structural carbohydrate and water, with chemicals partitioned between these compartments and the vapour phase in the ambient atmosphere. The input data required for the model were the 1-octanol/water partition coefficient (K-OW) and Henry's Law constant (H) of the compound, together with the volume fractions of the individual phases in the leaf. The model was evaluated using laboratory-based experimentally determined partition coefficients (experimental K-BA) for a group of organic chemicals, mostly chlorohydrocarbons. The model was in relatively good agreement with the experimental values, and can take into account differences in leaf composition. Values for different plants can be successfully calculated since the results indicate that plant composition is the major influence on the partition coefficient of a compound.