AbstractsChemistry

Inadvertent releases of nitroaromatic compounds (NACs) during the production of dyes, explosives, and pesticides have led to soil and groundwater contamination at a chemical production facility in New Jersey. Elevated carbon dioxide fluxes and depleted ¹⁴C content were observed in the contaminated area compared to a background area, indicating that anthropogenic organic contaminants were degrading under natural site conditions. Recent research at Colorado State University has shown that maintaining soil temperatures ~5°C above natural site conditions substantially increases rates of anaerobic petroleum hydrocarbon degradation. The overarching goal of this research is to determine whether thermal enhancement might increase attenuation rates of NACs under otherwise natural conditions at the contaminated site. Detailed depth-resolved site characterization was performed to elucidate current biogeochemical processes. While nitronaphthalene dominated the nonaqueous phase contamination at concentrations up to 47,500 mg/kg, major aqueous contaminants were the more water-soluble 1,3-dinitrobenzene (up to 216 mg/L), 2,4-dinitrotoluene (up to 163 mg/L), and 1,2-chloronitrobenzene (up to 91 mg/L). Comparison of organic carbon in detected contaminants with total organic carbon revealed that there were no other organic contaminants at relevant concentrations in the contaminated area, indicating that the increased CO₂ fluxes were due to mineralization of NACs under natural conditions. The presence of nitroaniline and chloroaniline throughout the entire depth of the shallow aquifer (~3-24 ft bgs) in aqueous samples suggested partial degradation of NACs through reduction of the nitro group, given there are no upstream sources for the anilines. For nitronaphthalene and nitrated toluenes, no degradations products were detected. Microbial diversity analysis revealed that the contaminated transmissive zone was dominated by Pseudomonas stutzeri, a facultative aerobe that has been shown to degrade a variety of monoaromatic compounds including chloronitrobenzene and chlorobenzene. At abundances of up to 83%, it appears likely that P. stutzeri plays a key role in the biodegradation of NACs at the site. The dominance of a nitrate-reducing microbial species, P. stutzeri, and depleted nitrate concentrations suggested that natural degradation processes at the site are limited by electron acceptor availability. Further degradation and mineralization of aniline intermediates, however, may require aerobic conditions. Thus, the aniline compounds may persist under natural conditions or irreversibly sorb to natural organic matter as long as sorption sites are available. To determine the effect of temperature on biodegradation rates, anaerobic microcosms containing homogenized site soil were held at temperatures between 10-30 °C for 350 days. Concentrations of the minor contaminants toluene, xylene, ethylbenzene, and chlorobenzene were significantly depleted. The extent of their degradation along with generated gas volumes suggested a temperature… Advisors/Committee Members: Blotevogel, Jens (advisor), De Long, Susan (advisor), Ronayne, Michael (committee member).