title: Linear and non-linear relationships between bioconcentration and hydrophobicity: theoretical consideration.
abstract: A non-linear relationship (e.g. Gaussian-type) between measured bioconcentration factor (BCF) and octanol/water partition coefficient (K(OW)) was noted many years ago. Many studies have focused on the cause of the breakdown in the log BCF/log K(OW) curve for highly hydrophobic chemicals with log K(OW)>6. However, there has been little investigation on the theoretical background of this feature for highly hydrophilic chemicals. In this paper, the cause of linear and non-linear relationships between log BCF and log K(OW) has been investigated on the basis of the partitioning-based mechanism for classified non-ionic and ionisable compounds. For highly hydrophilic compounds, lipid tissue in fish is not the major storage site of chemicals. Uptake from other tissues/organs plays a much more important role than the lipid content, leading to a variation of measured log BCF around 0.5. For hydrophobic chemicals with 0.5<log K(OW)<6, hydrophobicity is the principal driving force of bioconcentration and log BCF increases with increasing log K(OW). The log BCF/log K(OW) curve breaks down for highly hydrophobic chemicals with log K(OW)>6. The main reason for this is attributed to the reduced bioavailability of chemicals in water. A linear solvation energy relationship shows that the bioconcentration increases with increasing molecular size by increasing the dispersion interactions between the chemical and lipid content. Bioconcentration decreases with increasing the basicity of hydrophobic compounds by increasing the H-bonding of chemicals with water. Principal component analysis shows that the octanol/water system is the closest system, but not an ideal surrogate, to describe the bioconcentration for hydrophobic compounds as compared with other solvent/water partition systems.
authors.affiliation: Key Laboratory for Wetland Ecology and Vegetation Restoration of National Environmental Protection, Department of Environmental Sciences, Northeast Normal University, Changchun, Jilin 130024, PR China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wen
authors.affiliation: Key Laboratory for Wetland Ecology and Vegetation Restoration of National Environmental Protection, Department of Environmental Sciences, Northeast Normal University, Changchun, Jilin 130024, PR China.
authors.forename: Jia
authors.initials: J
authors.lastname: He
authors.affiliation: Key Laboratory for Wetland Ecology and Vegetation Restoration of National Environmental Protection, Department of Environmental Sciences, Northeast Normal University, Changchun, Jilin 130024, PR China.
authors.forename: Xian
authors.initials: X
authors.lastname: Liu
authors.affiliation: Key Laboratory for Wetland Ecology and Vegetation Restoration of National Environmental Protection, Department of Environmental Sciences, Northeast Normal University, Changchun, Jilin 130024, PR China.
authors.forename: Jinjie
authors.initials: J
authors.lastname: Li
authors.affiliation: Key Laboratory for Wetland Ecology and Vegetation Restoration of National Environmental Protection, Department of Environmental Sciences, Northeast Normal University, Changchun, Jilin 130024, PR China. Electronic address: zhaoyh@nenu.edu.cn.
authors.forename: Yuanhui
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D020003:1-Octanol / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008962:Models, Theoretical; D012044:Regression Analysis; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D014874:Water Pollutants, Chemical; D014867:Water; D020003:1-Octanol