| Summary: | The performance of the microbiologically-based tool kit employed in this study was critically evaluated for its ability to monitor the progress of hydrocarbon bioremediation. Different hydrocarbon remedial strategies (nutrient amendment, turning and inoculation) were applied to real hydrocarbon contaminated soil and the treatment effects monitored over a period of 60 days. The overall results of the tool kit evaluation showed that hydrocarbon biodegradation was clearly nutrient limited. The combination of turning and nutrient treatments were demonstrated to be more effective in increasing the rate of hydrocarbon biodegradation (as well as mediating a reduction in soil toxicity) than any single treatment. Although the chemical analysis methods demonstrated a significant reduction in hydrocarbon concentrations in the non-nutrient amended biopile microcosms, the biosensor assessment showed an increase in soil toxicity. Hence, an evaluation of hydrocarbon bioremediation based on analytical methods alone is not always indicative of a reduction in soil toxicity. The tool kit was further applied to biopile microcosms to identify constraints to hydrocarbon bioremediation. Soil matric potential was selected as a potential constraint to hydrocarbon bioremediation because of the great importance worldwide of this environmental control. Four different matric potentials (corresponding to a range of 20%, 40%, 60% and 80% soil water holding capacity) were assessed over a period of 40 days. The overall results from the use of the tool kit showed a strong positive correlation between the rate of hydrocarbon biodegradation and an increase in the soil matric potential tested. The increase in the rate of hydrocarbon biodegradation was also associated with a significant reduction in soil toxicity. Soil matrix was chosen as another potential constraint controlling the rate of hydrocarbon biodegradation. Bioremediation was greatest in the intermediate textured sandy loam (Insch soil). The slowest bioremediation rates were associated with the fine textured clay loam (Cruden Bay). Intermediate rates of biodegradation were associated with the coarse textured loamy sand (Boyndie soil). The chemical analysis showed a significant reduction in the overall hydrocarbon concentrations in the Cruden Bay soil (CB), but the toxicity biosensor assessment showed an increase in soil toxicity. Therefore, an assessment of hydrocarbon bioremediation based on chemical methods alone is not a sound approach, as hydrocarbon reduction does not always correlate with a decline in soil toxicity. The employment of the microbiologically-based tool kit to evaluate and monitor the performance of hydrocarbon bioremediation, complementing standard chemical methods, offers a powerful new approach as chemical monitoring alone does not provide an adequate assessment of the process of hydrocarbon bioremediation.
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