EFFECTS OF XAD-8 FRACTIONS OF DISSOLVED ORGANIC-CARBON ON THE SORPTION AND BIOAVAILABILITY OF ORGANIC MICROPOLLUTANTS

The dissolved organic carbon (DOC) from a stream water near a peat deposit was fractionated into hydrophobic-acid (HbA), hydrophobic-neutral (HbN), and hydrophilic (Hl) subcomponents by XAD-8 chromatography. The capacity of these fractions and the total (unfractionated) water to bind hydrophobic organic contaminants was measured by equilibrium dialysis, and the effect of binding on contaminant bioavailability was measured in Daphnia magna. Model contaminants were the poly cyclic aromatic hydrocarbons, naphthalene (NPH) and benzo(a)pyrene (BaP), and the polychlorinated biphenyl, 2,2′,5,5′-tetrachlorobiphenyl (TCB). Both BaP and TCB exhibited high partition coefficients (Kp's) for binding to both the total DOC and the hydrophobic components of the DOC. BaP had a higher affinity for binding to the HbA fraction, while TCB (and 3 other PCB's had a higher affinity for the HbN fraction. The Kp's for binding to the Hl fraction were twofold to tenfold lower than for binding to the hydrophobic fractions. The less hydrophobic compound, NPH, had a much lower Kp, and little difference was seen between the fractions. The total water and the different DOC fractions reduced the uptake and accumulation of BaP and TCB by D. magna in proportion to the capacity of the DOC for binding the contaminants. Data were consistent with the hypothesis that a contaminant bound to DOC (total water or any of the fractions) is unavailable for uptake by biota. Uptake of NPH was not substantially affected by the DOC, consistent with its lower Kp. © 1990 Springer-Verlag New York Inc.