The relative rates of desorption and mineralization for spiked concentrations of [ 14 C]phenanthrene and [ 14 C]chrysene preloaded on two previously contaminated soils (f oc , 0.029 and 0.0026) were investigated using static, slurry phase microcosms (V water /V soil ) 10). Desorption rates of [ 14 C]phenanthrene and [ 14 C]chrysene preloaded on the contaminated soils were much faster than observed mineralization rates, whereas the desorption rates of native polynuclear aromatic hydrocarbons (PAH) in the higher organic content contaminated soil were equal to or slower than mineralization rates. This suggests that the desorption of aged PAH may control their degradation and may explain the persistence of PAH even in soils containing a large and active community of PAH-degrading microorganisms. In addition, using 14 C-spiked PAH in contaminated soils to measure desorption and biodegradation rates may lead to misleading interpretations of the environmental fate of soilbound polynuclear aromatic hydrocarbons.

The influence of microbial activity on pyrene biodegradation and fate was assessed by quantifying the distribution of 14C-label and pyrene among soil organic matter fractions (SOM) in soils that contained varied microbial communities. A southern, hardwood forest soil was incubated with pyrene in aerated chambers for 9 months. Soil was incubated in three sets:  soil alone, soil augmented with a pyrene-degrading community, and soil inhibited with sodium azide (NaN3). After 9 months, pyrene mineralization was observed only in the degrader-amended soil set. Most of the pyrene and [14C]pyrene in the NaN3-amended soil set was recovered by solvent extraction (>75%). The [14C]pyrene extracted from the NaN3-amended soil set was mineralized by a microbial community shown to mineralize pyrene. Extractable pyrene from nonamended soil and degrader-amended soil sets decreased with time due to biodegradation. Extracted label from these soils was not mineralized to the same extent as NaN3-amended soil. Nonextractable label in humic/fulvic acid and humin fractions was greater in these soils than in the NaN3-amended soil set. Pyrene degradation products were detected in biologically active soils by HPLC. Over time, the extractability of pyrene and pyrene products in biologically active soils decreased to a greater extent than NaN3-amended soil.

sp. cells converted 1,1 ,l-trichloro-2,2-bis(/>chlorophenyl)ethane (DDT) to 1 ,l-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), l-chloro-2,2-bis(p-chlorophenyl)ethane (DDMS), 4,4'-dichlorobenzophenone (DBP), and several other products under anaerobic conditions. p-Chlorophenylacetic acid was formed when whole cells and oxygen were subsequently added, thereby demonstrating that enzymes of a single organism can convert DDT to ring-cleavage products. A strain of Arthrobacter grew on p-chlorophenylacetic acid, thus showing that action of two bacteria leads to extensive biodegradation of DDT. The Arthrobacter formed

The influence of inorganic and organic amendments on the mineralization of ethylene dibromide, p-nitrophenol, phenol, and toluene was examined in subsurface soil samples from a pristine aquifer near Lula, Okla. The responses indicate that the metabolic abilities and nutrient requirements of groundwater microorganisms vary substantially within an aquifer. In some samples, additions of inorganic nutrients resulted in a more rapid adaptation to the test substrate and a higher rate of metabolism, indicating that metabolism may have been limited by these nutrients. In other samples from the same aquifer layer, inorganic amendments had little or no influence on mineralization. In general, the addition of multiple inorganic nutrients resulted in a greater enhancement of degradation than did the addition of single substances. Additions of alternate carbon sources, such as glucose or amino acids, inhibited the mineralization of the xenobiotic substrates. This inhibition appears to be the result of the preferential utilization of the more easily degradable carbon amendments.

Abstract-The [a]pyrene added to the microcosms. Metabolite production and cellular incorporation usually accounted for less than 10% of the added [ 14 C]PAH. The fate of PAHs was usually not related to measurements of microbial community size, characteristics of the PAH (water solubility and K ow ), and many characteristics of soils (soil f oc and PAH concentration). The fraction of silt and clay in the soils for each soil-PAH combination, however, was negatively related to the extent of added [ 14 C]PAH mineralized and the amount solvent extractable from the soil, and positively related to the amount of [ 14 C]PAH remaining in soils after extraction.