Relationship between concentration of dissolved organic matter (DOM) and the effect of DOM on the bioconcentration of benzo[a]pyrene

Dissolved organic matter (DOM) from five different origins decreased the bi oconcentration of benzo[a]pyrene (BaP) in the nematode, Caenorhabditis eleg ans. The decrease became more pronounced with increasing concentrations of DOM, but the effect per mg l(-1) DOC was largest at low levels of DOM, indi cating the lack of a simple direct relationship between DOM concentration a nd the bioconcentration factor (BCF). We tested the hypothesis that the qua ntitative relationship between DOM concentration and BCF can be described b y a theoretically derived equation based on the assumption that only freely dissolved contaminants ape bioavailable (BCF = control BCF x 1/(1 + partit ion coefficient x DOM concentration)). This equation was used in non-linear regression procedures to fit curves to the experimental data. The resultin g regression curves for data from this study (correlation coefficients (r(2 )) ranging from 0.80 to 0.94), and for data from the literature (r(2) rangi ng from 0.62 to 1.00), showed that the model equation was able to correctly describe the relationship between DOM concentration and BCF. The slope of each curve resulted from the 'biologically determined' partition coefficien t (K-DOC) that had been estimated by the regression procedure. Thus, the da ta set for each DOM source was reduced to a single K-DOC value (range: 20 /- 4 x 10(4) to 49 +/- 6 x 10(4) l kg(-1) DOC (mean +/- S.E.), which allowe d to compare different types of DOM, regarding their ability to reduce the bioconcentration of BaP. A comparison of 6,,, values showed that there were clear differences between the effects of DOM from different sources. In su mmary, we conclude that distinct effects of DOM on the bioconcentration of contaminants can occur at environmentally representative concentrations of DOM, but only for combinations of very hydrophobic contaminants (e.g. BaP) and DOM with a high binding capacity. (C) 1999 Elsevier Science B.V. All ri ghts reserved.