SORPTION AND LEACHING OF SHORT-TERM-AGED PAHS IN EIGHT EUROPEAN SOILS

LINK TO PHYSICOCHEMICAL PROPERTIES AND LEACHING OF DISSOLVED ORGANIC CARBON

Abstract

Polycyclic aromatic hydrocarbons (PAH) are among the major contaminants in the terrestrial environment. In tools for ranking contaminated soils according to risks and cleanup measures, simple predictions of contaminant leaching rates and actual leaching concentrations need to be established preferably using simple sorption and leaching estimates based on easily measured soil characteristics. In this study, 24 hrs PAH sorption experiments were performed with the PAH pyrene and phenanthrene onto eight European soils, and sorption characteristics were compared with and related to soil characteristics. Also, the leaching of pyrene and dissolved organic carbon from the soils was investigated using a short multicolumn setup and a 30 mm h⁻¹ of water application rate. The soils were spiked with pyrene and aged between 7 and 180 days before leaching. Freundlich sorption coefficients, K_f, correlated well with the soil organic carbon contents, but the variability of K_oc values among soils indicated that sorption could not be predicted from soil organic carbon contents alone. However, sorption predictions based on organic matter content and one additional simple soil parameter (e.g., clay content, cation exchange capacity, or pH) would yield accurate predictions of K_f. The leaching of both pyrene and dissolved organic carbon (DOC) was characterized by a two-stage release behavior with high concentrations in the initial samples followed by sharp decrease to lower baseline concentrations. In all experiments, only 1.2% of the spiked pyrene mass had been leached after 200 mm of water had leached, pointing to a low release of PAHs with water. The similar release behavior of pyrene and DOC along with pyrene concentrations in the leachate above the maximum solubility suggests that pyrene was mobilized along with DOC. Relating the leached amounts of pyrene to the amounts of leached DOC and subtracting the initial flush of pyrene and DOC yields fairly identical curves for accumulated pyrene leaching as a function of accumulated DOC leaching. These findings seem useful for estimating DOC-facilitated PAH leaching at contaminated sites.