Molecular Size as a Limiting Characteristic for Bioconcentration in Fish

The relationships between bioconcentration factor (BCF) and molecular weight (MW) using an experimental data set of 737 new and 441 existing chemicals monitored by the Japanese Chemical Substances Control Law (CSCL) were investigated. It was found that many substances with BCF greater than or equal to 1000 and Dmax greater than or equal to 1.5 nm had Deff < 0.95 nm, implying that cell penetration of a stick-shaped molecule with a base diameter < 0.95 nm was somewhat independent of the length of the longer axis. Results showed that low-density compounds, such as perfluorides, showed BCF values that seemed overly high when using MW as a determining factor. Deff was related to the size of cell membranes and was considered to be a better predictor than MW in discriminating between bioconcentrative and non-bioconcentrative substances.