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Field Scale Bioremediation: Relationship of Parent Compound Disappearance to Humification, Mineralization, Leaching, Volatilization of Transformation Intermediates

Principal Investigators
R.C. Sims, Utah State University


Goal: The overall goal of this research effort is to provide new information concerning the distribution of polycyclic aromatic hydrocarbon (PAH) biotransformation products among humic materials associated with the solid fraction of soil and the water soluble extract (leachate) fraction, and the effect of environmental variables and amendments on humification and leaching.

Rationale: There is a lack of information concerning transformation intermediates regarding their reactions, measurement, and management in soil bioremediation systems. Specifically, the role of the humification process is currently unknown in prepared bed systems. Disappearance of compounds within soil treatment systems does not necessarily indicate mineralization or detoxification of toxic and hazardous compounds. The formation of intermediates and the fate of those intermediates with regard to association with the soil solid phase in the process of humification is an area where information is needed in order to fully assess the treatment effectiveness of soil bioremediation systems. Development of information addressing behavior of transformation intermediates with an emphasis on characterizing humification of target organic chemicals would increase our understanding of soil bioremediation processes with regard to protection of public health and the environment. Based on information developed in this project, techniques for management of the humification process may be identified and applied to soil bioremediation systems.

Approach: The approach in this project is to use samples of soil taken from field-scale bioremediation systems treating creosote- and creosote/PCP-contaminated soil. Soil samples have been taken from the Champion International Superfund site. The first activity involves identification of PAH and PCP transformation products that occur in soil systems and that can be extracted. The second activity involves chemical mass balance and toxicity determinations during treatment and development of instrumental approaches for evaluating humification. The approach is used to generate information concerning: (1) chemical bonding of PAHs and PCP/intermediates with the soil solid phase, humic and fulvic acid fractions, and with leachate; (2) effects of environmental variables (light, temperature, soil moisture) on the humification process; and (3) effects of amending soil with electron acceptors on humification, mineralization, and volatilization.

Status: PAH microbial intermediates that could be obtained commercially and that were selected for further analysis in wood preserving-contaminated soil included: (1) 1-hydroxy-2-naphthoic acid, (2) 2-carboxygenzaldehyde, (3) 2-hydroxy-3-naphthoic acid, (4) 2,3-dihydroxynaphthalene, and (5) 3,4-dihydroxybenzoic acid. These intermediates have been tentatively identified in field site soil by HPLC instrumentation. Microtox Toxicity(TM) assay results indicated that both phenanthrene and PCP exhibited higher toxicities than the intermediates. An evaluation of the fate of the intermediates was undertaken using mass balance microcosms containing field site soil. Results indicated up to 50% mineralization of 1H2NA and up to 20% mineralization of 2,3-DHN over a 30-day period, measured as CO2 evolution. Additional tests are currently underway to determine the significance of volatilization of intermediates from site soil. In order to evaluate apparent humification potential through clay mineral "trapping," changes in d-basal spacing in montmorillonite and illite clays were measured in the presence of low dielectric constant solvents using X-ray diffraction instrumentation. Initial chemical mass balance experiments have been performed for both pyrene and PCP. This project is in its first year.

Clients/Users: Information generated from this project will be useful for regulators and the wood preserving industry. The U.S. Environmental Protection Agency has expressed interest in this project. The U.S. Department of Defense is also interested in this project.

Key words: bioremediation, humification, mineralization, leaching, volatilization, intermediates.

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