ASSOCIATION OF LINEAR ALKYLBENZENESULFONATES WITH DISSOLVED HUMIC SUBSTANCES AND ITS EFFECT ON BIOAVAILABILITY

The association of C-10-, C-12- and C-14-linear alkylbenzenesulfonates (LAS) with natural and specimen-grade dissolved humic substances (DHS ) was measured with fluorescence quenching and with ultracentrifugatio n techniques. Good agreement was obtained with both of the analytical methods, suggesting that fluorescence quenching could be used to measu re aqueous-phase partition coefficients. LAS-DHS partition coefficient s increased with increasing length of the alkyl chain, Partition coeff icients for the sorption of LAS to alkylammonium surfactant-coated, ph yllosilicate clays also increased with increasing length of the alkyl chain in the LAS molecules. Taken together, these data indicate the si gnificance of nonpolar forces in LAS-organic matter interactions. Toxi city studies examined the effects of DHS on the bioavailability to the fathead minnow, Pimephales promelas. Changes in the uptake and toxici ty of LAS resulting from the addition of DHS were used to calculate aq ueous-phase LAS-DHS partition coefficients. Good agreement was found b etween the partition coefficients calculated from the response of the test organism and those obtained with fluorescence and ultracentrifuga tion measurements. The toxicity studies suggest that the association o f LAS with DHS can play a significant role in reducing the biologicall y available fraction of LAS in surface waters.