Monitoring biodegradation of creosote in soils using radiolabels, toxicitytests, and chemical analysis

Microbial acclimation to, and mineralization of polycyclic aromatic hydroca rbons (PAHs), was studied using four uncontaminated soils (designated HS, H C, GP, MS) spiked with creosote and C-14-phenanthrene. The effects of nutri ent amendments (nitrogen and phosphorus), temperature (10 degrees C and 22 degrees C), and moisture content (50 or 85% of water-holding capacity, WHC) on mineralization were monitored by measuring evolution of (CO2)-C-14 in m icrocosms. Acclimation and mineralization occurred more rapidly at 22 degre es C than at 10 degrees C and were enhanced by the P amendment, at 50% of W HC for GP soil and 85% of WHC for HC and MS soils. These conditions were ap plied to microcosms containing 1500 g soil and monitored for biodegradation of total petroleum hydrocarbons (TPHs) and PAHs using chemical analysis an d six soil toxicity tests. Although 40% C-14 was recovered as CO2 within 35 -45 days in the smaller microcosms, analytical and toxicity test data indic ated that bioremediation in the larger microcosms was not successful after 130 days. The soil depth and high moisture content may have restricted oxyg en diffusion into the soil, which was not stirred during the experiment. Va riations in toxicity and contaminant concentrations were observed but were considered a consequence of the sampling protocol and insufficient mixing d uring spiking, which may have produced pockets of "hot" soil. The mineraliz ation experiment was useful for confirming that indigenous soil microorgani sms could degrade PAHs, but was not indicative of the success of the biorem ediation protocol on a larger scale. (C) 2000 by John Wiley & Sons, Inc.