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

Microbial acclimation to, and mineralization of polycyclic aromatic hydrocarbons (PAHs), was studied using four uncontaminated soils (designated HS, HC, GP, MS) spiked with creosote and 14C‐phenanthrene. The effects of nutrient amendments (nitrogen and phosphorus), temperature (10°C and 22°C), and moisture content (50 or 85% of water‐holding capacity, WHC) on mineralization were monitored by measuring evolution of 14CO2 in microcosms. Acclimation and mineralization occurred more rapidly at 22°C than at 10°C and were enhanced by the P amendment, at 50% of WHC for GP soil and 85% of WHC for HC and MS soils. These conditions were applied to microcosms containing 1500 g soil and monitored for biodegradation of total petroleum hydrocarbons (TPHs) and PAHs using chemical analysis and six soil toxicity tests. Although 40% 14C was recovered as CO2 within 35–45 days in the smaller microcosms, analytical and toxicity test data indicated that bioremediation in the larger microcosms was not successful after 130 days. The soil depth and high moisture content may have restricted oxygen diffusion into the soil, which was not stirred during the experiment. Variations in toxicity and contaminant concentrations were observed but were considered a consequence of the sampling protocol and insufficient mixing during spiking, which may have produced pockets of “hot” soil. The mineralization experiment was useful for confirming that indigenous soil microorganisms could degrade PAHs, but was not indicative of the success of the bioremediation protocol on a larger scale. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 99–106, 2000