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DIVISION S-2—SOIL CHEMISTRY

Sorption Strength of Persistent Organic Pollutants in Particle-size Fractions of Urban Soils

Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, Germany

* Corresponding author (martin.krauss{at}uni-bayreuth.de)

The bioavailability of persistent organic pollutants in soils depends on their sorption strength that may vary among different pools. We hypothesized that polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) had different soil organic C-water partition coefficients (K_OC) among particle-size fractions. We determined the concentrations of 20 PAHs and 12 PCBs in coarse-sand, fine-sand, silt, and clay fractions of 11 urban topsoils (0–5 cm). The K_OC values were determined using sequential extraction with methanol-water mixtures (35 and 65% methanol) at 60°C. The 20 PAHs concentrations ranged from 0.3 to 186 mg kg^-1, the 12 PCBs concentrations from 1.2 to 158 µg kg^-1. In most soils, the PAH concentrations decreased in the order, silt > clay fine sand > coarse sand, and those of the PCBs in the order, clay > silt fine sand > coarse sand. The distribution of PAHs among particle-size fractions was more heterogeneous than reported in the literature because the soils received PAH-contaminated wastes (ashes, slags, rubble) with varying texture. In all soils, the proportions of two- or three-ring PAHs decreased with decreasing particle size, indicating that the PAH mixture was increasingly altered. The K_OC values of the PAHs were three to 10 times higher than those of the PCBs with similar octanol-water partition coefficients (K_OW). The mean K_OC values of all individual PAHs were highest in silt. For all individual PCBs, mean K_OC values were highest in clay. The K_OC values of PAHs and PCBs varied up to a factor of 100 among the studied soils and particle-size fractions. Particle-size fractions with highest PAH and PCB concentrations also showed highest K_OC values indicating low bioavailability.

Abbreviations: ACE, acenaphthene • ACY, acenaphthylene • ANT, anthracene • BAA, benz(a)anthracene • BAP, benzo(a)pyrene • BBJK, benzo(b + j + k)fluoranthenes • BEP, benzo(e)pyrene • BGHI, benzo(ghi)perylene • CT, chrysene + triphenylene • DBAH, dibenz(a,h)anthracene • ECEC, effective cation-exchange capacity • f_c, methanol fraction • FLA, fluoranthene • FLU, fluorene • IND, indeno(1,2,3-cd)pyrene • K_OC, organic C-water partition coefficient • K_{OC, mix}, K_OC in methanol-water mixtures • K_OW, octanol-water partition coefficient • NP, naphthalene • PAH, polycyclic aromatic hydrocarbon • PCB, polychlorinated biphenyl • PER, perylene • PHE, phenanthrene • PYR, pyrene • SOC, soil organic C • SOM, soil organic matter • TSA, total molecular surface area • , deviation factor from ideal sorption in methanol-water systems • , difference of the interfacial free energies in the methanol-water system • H_des, enthalpy of desorption

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