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DETERMINATION OF TRANSFORMATION RATES OF CHIRAL PESTICIDES AND PCBS IN SOIL AND SEDIMENT MICROCOSMS
Citation:
O'Niell, W. L., W J. Jones, A Whittemore, AND J Avants. DETERMINATION OF TRANSFORMATION RATES OF CHIRAL PESTICIDES AND PCBS IN SOIL AND SEDIMENT MICROCOSMS. Presented at 8th Federation of the European Chemical Societies Conference on Chemistry and the Environment: Chemistry for a Sustaining World, Athens, Greece, September 1-4, 2002.
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
Risk Based Corrective Action (RBCA) has gained widespread acceptance as a favorable approach to remediating contaminated sites. The use of RBCA methods often requires computer-based modeling to assess the fate and transport of hazardous contaminants in subsurface environments, and accurate modeling results require input of realistic transformation rates of the contaminants of concern. Unfortunately, relatively few microbial transformation rate studies have been conducted using natural soils or sediments, and have instead focused more on degradation of contaminants by pure microbial cultures. The purpose of our research was to compare degradation rates of selected pesticides and PCBs under different natural environmental conditions where the indigenous microbial population controlled degradation. Chiral contaminants were examined in this study to gain a better understanding of enantioselective transformation reactions. The microbial transformation rates and enantiomeric ratios of several chiral pollutants were determined in laboratory microcosms (25oC). Over 3,000 aerobic and anaerobic microcosms were prepared using agricultural soils from three different locations. The soil slurries were separately dosed with the following chiral pesticides: o, p'-DDT, o, p'-methoxychlor, cis-chlordane, trans-chlordane, heptachlor, heptachlor epoxide, and "-HCH. In addition, approximately 500 microcosms were prepared anaerobically with lake sediment and separately dosed with a polychlorinated biphenyl mixture (Arochlor 1260) and the chiral PCB congeners 2,2',3,4',5',6-hexachlorobiphenyl and 2,2',3,3',4,4',5,6-octachlorobiphenyl. In all studies, experimental treatments consisted of live (natural) slurries, live slurries dosed with an organic nutrient mixture, and autoclaved controls. The concentrations of the chiral pollutants in the experimental microcosms were analyzed over a 2 year period using enantioselective high-resolution GC/MS, and data were modeled to determine transformation rates. Enantiomer concentrations in transformed and unaltered (control) microcosms were compared to assess enantioselective transformation of the chiral chemicals. Appreciable losses of the parent compounds were observed in microcosms dosed with o, p'-DDT, o, p'-methoxychlor, trans-chlordane, heptachlor, "-HCH, and 2,2',3,4',5',6-hexachlorobiphenyl (Tables 1 and 2, and Figure 1). The addition of an organic nutrient mixture to the microcosms generally decreased transformation rates, and transformation was greater in microcosms incubated under anaerobic conditions. Transformation was insignificant in cis-chlordane, heptachlor epoxide, Arochlor 1260, and 2,2',3,3',4,4',5,6-octachlorobiphenyl dosed microcosms for most experimental treatments. Although statistically significant enantioselective transformation was not observed in most of the samples following approximately 2 years of incubation, differences in enantiomeric ratios were observed in selected samples dosed with 2,2',3,4',5',6-hexachlorobiphenyl and o, p'-DDT. The primary benefit of this study to other researchers will be the determination of realistic degradation rates that can be used in the mathematical simulation of the fate and transport of these hazardous compounds. Overall, these results can be used to protect human health and the environment by improving decision making for remedial actions. Additional research of this type may be directed toward determining the degradation rates of model compounds that can then be used to determine realistic transformation rates of other compounds with similar chemical structures.