PHENANTHRENE BINDING AND SORPTION TO DISSOLVED AND TO MINERAL-ASSOCIATED HUMIC ACID YAEL LAOR 1 *, WALTER J. FARMER 2 , Y. AOCHI 2 and PETER F. STROM 3* M 1 Department of Environmental Science, Cook College, Rutgers University, New Brunswick, NJ 08903-0231, U.S.A., 2 Department of Soils and Environmental Science, University of California, Riverside, CA 92521, U.S.A. and 3 Department of Environmental Science and NJ Agricultural Experimental Station, Cook College, Rutgers University, New Brunswick, NJ 08903-0231, U.S.A. (First received July 1996; accepted in revised form September 1997) AbstractÐPhenanthrene, a three ring aromatic hydrocarbon, was used as a model substrate to dis- tinguish between binding and sorption to dissolved and to mineral-associated humic acid (HA), with an emphasis on its implication to bioavailability. Binding was analyzed by a ¯uorescence quenching tech- nique using Aldrich HA and HAs derived from compost, loamy and clay loamy soils. Measurements were made both in buered water and in a mineral medium to be used later in a bioavailability study. Sorption of phenanthrene to mineral-associated HA was analyzed in batch experiments. Mineral±HA complexes were prepared with goethite, hematite, and Ca 2+ - and Cu 2+ -montmorillonite. Interaction of HA with clay minerals was greater at low pH and was dependent on the mineral type. Sorption of phe- nanthrene to these complexes was substantially higher at lower pH and higher when the HA was associ- ated with montmorillonite rather than goethite or hematite. Binding coecients (K b(oc) ) obtained for dissolved HA were at least an order of magnitude higher than sorption coecients (K p(oc) ) obtained for mineral-associated HA. Both binding and sorption coecient values were substantially higher for Aldrich HA. This work emphasizes the need for a detailed sorption study before conducting well con- trolled bioavailability experiments. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐphenanthrene, PAH, sorption, binding, bioavailability, humic acid, dissolved humic sub- stances, organic contaminants. INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and have been identi®ed in a variety of soils, natural waters and wastewaters. Although they also occur naturally, high levels of PAHs are mainly attributed to anthropogenic sources such as oil spills, automobile exhaust and coal re®ning pro- cesses. Phenanthrene, a three ring PAH, may be found in relatively high concentrations in coal tar contaminated sites and in polluted aqueous environ- ments. While phenanthrene and its metabolites are not acutely toxic, carcinogenic or mutagenic, it has been used as a model substrate in many environ- mental studies. It has structural features found in other PAHs that do have carcinogenic properties, such as benzo[a]pyrene and benz[a]anthracene. Fate and transport of hydrophobic organic pollu- tants can be substantially in¯uenced by sorption processes. Sorption of hydrophobic pollutants to humic material that is associated with the soil or aquifer solid phase usually inhibits its transport. On the other hand, binding to dissolved humic material will facilitate desorption from the solid phase and thereby enhance pollutant transport (Rebhun et al., 1996). Both types of associations may aect the bioavailability of the associated pollutant and alter its fate. It has been shown that binding and sorption pro- cesses are aected by the nature of the humic material (Gauthier et al., 1987; Murphy et al., 1990; Herbert et al., 1993). Binding was also found to be dependent on the solution properties (Schlautman and Morgan, 1993) and yielded higher binding coecient values compared with sorption to solid phase humics (Murphy et al., 1990; Rav-Acha and Rebhun, 1992). These ®ndings implies also for aspects of bioavailability as it would be critical to characterize the type of humic material that is under investigation and to distinguish between dissolved and mineral-associated phases. The objective of this study was to determine binding coecients (K b(oc) ) and sorption coecients (K p(oc) ) values for the same HA sources. It also Wat. Res. Vol. 32, No. 6, pp. 1923±1931, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/98 $19.00 + 0.00 PII: S0043-1354(97)00405-3 *Author to whom all correspondence should be addressed [Current address: Faculty of Civil Engineering, Environmental and Water Resources Engineering, Technion Ð Israel Institute of Technology, Haifa 32000, Israel. Tel: +972-4-8293312, Fax: +972-4- 8228898, E-mail: laor@techunix.technion.ac.il]. 1923