Investigation on the relationship between bioconcentration factor and distribution coefficient based on class-based compounds: The factors that affect bioconcentration

• Nonlinear BCF models have been developed for ionic and nonionic chemicals.
• Most highly hydrophobic compounds still exhibit very high bioconcentration potential.
• Transformation of esters, three-membered rings and hydroxyphenols can lead to BCF bias.
• Long chain and large polycyclic compounds have low BCF because of physical barrier.
• Polychlorobiphenyls have higher BCF than expected because of kinetic methods.

Bioconcentration factor (BCF) is one of the most important parameters in the assessment of the potential hazard of new compounds in aquatic ecosystems. However, the factors that influence the estimation of BCFs for a large variety of chemicals have not been systemically investigated in the literature. In this paper, a large BCF data set containing 1088 nonionic and ionic organic compounds was used to study the relationship between BCF and molecular descriptors and influencing factors. Step-by-step analysis on the class-based compounds showed that nonlinear Gaussian and Sigmoid equations could well describe relationships between log BCF and distribution coefficient for the compounds over a wide range of structures and chloro or/and bromo substituted aromatics, respectively. The quality of fit from the nonlinear models is better than the BCFBAF method from the Epi Suite program for the class-based compounds. Systemic prediction deviations have been observed for some types of compounds. The reasons for systemic deviations for these compounds can be attributed to the difference in bioconcentration mechanism for hydrophilic compounds, transformation for hydroxyphenols and three-membered rings, physical barrier for long chain and large polycyclic compounds, difference in determining methods of BCF (kinetic and steady-state), bioavailability for highly hydrophobic compounds and accuracy of BCF measurements for compounds with extremely high or low BCFs. These factors are important and should be considered in any reliable bioconcentration prediction.