Effects of humic substances on the bioconcentration of polycyclic aromatichydrocarbons: Correlations with spectroscopic and chemical properties of humic substances

The presence of dissolved humic substances (HS, fulvic and humic acids) gen erally reduces the uptake of hydrophobic organic compounds into aquatic org anisms. The extent of this effect depends both on the concentration and on the origin of the HS. The aim of this study was to investigate the role of qualitative differences between HS from different origins. The effects of s even different HS on the bioconcentration of pyrene and benzo[a]pyrene (BaP ) in the nematode Caenorhabditis elegans were related to the spectroscopic and chemical properties of the HS. The effect of each humic material on the bioconcentration of pyrene or BaP was quantified as a "biologically determ ined" partition coefficient K-DOC. We observed significant linear relations hips between K-DOC and the atomic H/C ratio, the specific absorptivity at 2 54 nm, the content of aromatic carbons (as determined by C-13 nuclear magne tic resonance spectroscopy, the copper-complexing capacity, the content of phenolic OH groups, and the molecular weight of the HS. There was no discer nible relationship of K-DOC with the atomic (N + O)/C ratio, an indicator o f the polarity of HS. Taken together, our results show that the variability in the effects of HS from different origins could be related to variations in bulk properties of the HS. Parameters describing the aromaticity of the humic materials seemed to be most useful for estimating effects of HS on t he bioconcentration of pyrene and BaP.