1 Department of Environmental Engineering, Technical University of Denmark2 Environmental Chemistry, Department of Environmental Engineering, Technical University of Denmark
The role of pH for the bioconcentration of ionizable organic compounds was investigated using measured bioconcentration factor (BCF) data of monovalent acids and bases collected from literature. Only studies where BCF was measured at more than one pH were considered. The measured BCF-values were highly correlated to the log D, external pH (except acids in fish) and pKa of the test substances. Existing regressions (Veith and Fu for fish and Briggs RCF for plant cells) with log D (apparent octanol-water partition coefficient) as input parameter were tested for their capability to predict BCF-values determined at different pH. As second tool, a dynamic cell model based on the Fick-Nernst-Planck equation was tested. For the BCF fish of monovalent acids and bases, the BCF regressions and the cell model performed similar. For the BCF of water plants and plant roots, the regression failed to predict the BCF for low log D values. The cell model had higher accuracy and precision for both acids and bases. The results indicate that for the BCF data in fish, lipophilic sorption of neutral molecule and ion are the dominating process. For the BCF in plant cells, the ion trap often led to an increase in accumulation. An ion trap is pH dependent and occurs when the molecule permeates the cell membrane in a neutral state but dissociates inside. For measurements of BCF-values of acids and bases it is recommended to use a low pH for acidic compounds and a high pH for alkaline compounds.
Acid; Base; Bioconcentration factor; Dissociation; Fish