Relating desorption and biodegradation of phenanthrene to SOM structure characterized by quantitative pyrolysis GC-MS

A set of four soils was extensively studied for composition, sorption/desorption, and biodegradation to investigate linkages among these three inter-related factors. Composition of soil organic matter (SOM) was quantitatively characterized using pyrolysis GC-MS; although CO2 dominated the total ion chromatogram for all soils, each soil produced a distinctively different pyrogram and 1.4-4.8% of the soil carbon was quantified as one of 205 pyrolysis marker compounds using external standards. Amorphous and free iron and aluminum contents were determined as potential indicators of the reactivity of the mineral phase, which may influence the configuration and accessibility of SOM domains within soil. We observed a statistically significant positive correlation between two-site model fast fraction f values derived from mineralization and desorption rate studies, which suggests that desorption limits biodegradation. However, no statistically significant correlation was observed between two-site model fast and slow rate constants (k(f), k(s)) for the two processes. No evidently strong correlations were found between functional parameters (organic carbon normalized distribution coefficient Koc, hyeteresis index HI, and two-site model parameters f, k(f), and k(S) for both desorption and biodegradation and maximum rate and extent of biodegradation) and SOM structural descriptors (pyrolysis results). Lack of strong correlations may suggest (i) that multiple SOM structures are collectively responsible for desorption resistance or (ii) that the pyrolysis GC-MS method used in this study was unable to identify relevant structures. In contrast, amorphous and free iron and aluminum contents showed statistically significant correlations with K(OC) and HI values, indicating the potential importance of underlying mineral phases in determining desorption and biodegradation rates.