The effects of dissolved organic carbon on the behaviour of PCBs in fresh water

The hypothesis was tested that the binding of three polychlorinated biphenyl (PCB) congeners to natural (i.e. open water column) levels of dissolved organic carbon (DOC) would be equal to that measured using humic acid (HA) and interstitial DOC. However, the partition coefficients calculated on the basis of DOC (K$sb{rm DOC}$) measured in several lakes and streams in Ontario were 1- to 2-orders of magnitude lower than those that have been measured for other hydrophobic organic compounds (having similar octanol-water partition coefficients), when HA or DOC extracted from interstitial water are used. K$sb{rm DOC}$ values were too low to be ascertained for PCB 3 and averaged 3.04 $pm$ 3.17 $times$ 10$sp3$ mL/g C for PCB 52 and 5.29 $pm$ 4.16 $times$ 10$sp4$ mL/g C for PCB 153. In a second set of experiments, K$sb{rm DOC}$ values for PCB 153 averaged 3.57 $pm$ 2.16 $times$ 10$sp4$ mL/g C.;Neither the K$sb{rm DOC}$ values for PCB 52 and PCB 153 nor the ratio of the bound concentration of PCB 153 to the free concentration of PCB 153 (C$sb{rm B}$/C$sb{rm F}$) were significantly correlated with most chemical and physical properties of the lakewaters. However, for PCB 153 colour was significantly correlated with and explained more of the variability in C$sb{rm B}$/C$sb{rm F}$ than did the DOC concentration. These results indicate that only a small fraction of the DOC in lakes is involved in PCB binding and that this fraction may be associated with the colour-producing components of the DOC.;For PCB 52 and PCB 153, a model was derived relating the fraction of bound PCB to the octanol-water partition coefficient. For the congener PCB 153, a significant relationship was developed which predicted the ratio of the bound concentration of PCB 153 to the free concentration of PCB 153 from the colour and sulphate concentration of the water.;In another series of laboratory experiments, the hypothesis was tested that the uptake of PCB 153 by Daphnia magna in the presence of natural DOC would be less than the uptake in the absence of DOC. Uptake rate constants (K$sb{rm u}$) averaged 1.71 $pm$ 0.52 and 1.26 $pm$ 0.46 mL/mg ww/h in two sets of experiments. However, the K$sb{rm u}$ values were similar in the DOC-free simulated lakewater versus lake and streamwater having DOC concentrations which had been increased two- and ten times over ambient levels. Whereas K$sb{rm u}$ values were inversely correlated with the wet weight of the Daphnia the condition (lipid content) of the animals may have contributed to variability in the results.;PCB concentrations (sum of 19 congeners) measured in the plankton and sediments of 9 lakes in Ontario ranged between 1.6 and 9.8 ng/g ww and 6.0 and 35.2 ng/g dw, respectively and were unrelated to both the DOC concentration in the lake and other chemical properties of the lakewater. These results support the hypothesis that the binding of PCBs to natural DOC is unimportant in these lakes.