Measurements to Characterize Biodegradation of Volatile Organic Compounds in Field Samples and Experiments
Oral Presentation
Prepared by M. Lorah1, I. Cozzarelli2
1 - U.S. Geological Survey, 5522 Research Park Dr, Baltimore, MD, 21228, United States
2 - U.S. Geological Survey, 431 National Center, Reston, VA, 20192, United States
Contact Information: [email protected]; 443-498-5601
ABSTRACT
Characterization of biodegradation processes in groundwater requires measurement of geochemical constituents, the contaminants and their expected metabolites, and other indicators of biogeochemical conditions and microbial activity such as volatile fatty acids (VFAs), pH, oxidation-reduction potential, and dissolved organic carbon. Microbial community data also assists with determining biogeochemical processes. Collection of samples is needed in small volumes and with minimal agitation or oxygen exposure to avoid mixing different geochemical zones and altering or losing chemical species. This presentation will discuss sample collection, preparation, and analytical techniques used for an investigation of biodegradation of chlorinated benzenes and benzene in a wetland. Results of field samples from groundwater and porewater sampling devices, in situ microcosms in the wetland sediment, and on-site bioreactor experiments will be presented.
Samples collected from piezometers by traditional pumping techniques and by various passive samplers, including passive diffusion bags, dialysis samplers, and peepers, sometimes showed large differences in concentrations that could affect interpretations of contaminant distribution and redox conditions. Results from field spectrophotometric analyses of redox constituents (such as sulfate and ferrous iron) and chloride generally agreed well with laboratory analyses by ion chromatograph or inductively coupled plasma mass spectrometer, although interferences from organic acids were sometimes problematic. Porewater samples collected at multiple depths and locations within a 2-foot diameter indicated that the spatial and lateral heterogeneity in the wetland groundwater chemistry can be greater than the differences observed between sampler types or analytical methods. In addition, in situ microcosms, bioreactor tests, and microbial community analyses showed that both anaerobic and aerobic degradation of the contaminants can occur in the wetland sediment, even where geochemical analyses indicated that anaerobic conditions were prevalent. This study highlights the importance of multiple lines of evidence in evaluating contaminant biodegradation, and the need for field tools for fine-scale delineation of groundwater chemistry.
Oral Presentation
Prepared by M. Lorah1, I. Cozzarelli2
1 - U.S. Geological Survey, 5522 Research Park Dr, Baltimore, MD, 21228, United States
2 - U.S. Geological Survey, 431 National Center, Reston, VA, 20192, United States
Contact Information: [email protected]; 443-498-5601
ABSTRACT
Characterization of biodegradation processes in groundwater requires measurement of geochemical constituents, the contaminants and their expected metabolites, and other indicators of biogeochemical conditions and microbial activity such as volatile fatty acids (VFAs), pH, oxidation-reduction potential, and dissolved organic carbon. Microbial community data also assists with determining biogeochemical processes. Collection of samples is needed in small volumes and with minimal agitation or oxygen exposure to avoid mixing different geochemical zones and altering or losing chemical species. This presentation will discuss sample collection, preparation, and analytical techniques used for an investigation of biodegradation of chlorinated benzenes and benzene in a wetland. Results of field samples from groundwater and porewater sampling devices, in situ microcosms in the wetland sediment, and on-site bioreactor experiments will be presented.
Samples collected from piezometers by traditional pumping techniques and by various passive samplers, including passive diffusion bags, dialysis samplers, and peepers, sometimes showed large differences in concentrations that could affect interpretations of contaminant distribution and redox conditions. Results from field spectrophotometric analyses of redox constituents (such as sulfate and ferrous iron) and chloride generally agreed well with laboratory analyses by ion chromatograph or inductively coupled plasma mass spectrometer, although interferences from organic acids were sometimes problematic. Porewater samples collected at multiple depths and locations within a 2-foot diameter indicated that the spatial and lateral heterogeneity in the wetland groundwater chemistry can be greater than the differences observed between sampler types or analytical methods. In addition, in situ microcosms, bioreactor tests, and microbial community analyses showed that both anaerobic and aerobic degradation of the contaminants can occur in the wetland sediment, even where geochemical analyses indicated that anaerobic conditions were prevalent. This study highlights the importance of multiple lines of evidence in evaluating contaminant biodegradation, and the need for field tools for fine-scale delineation of groundwater chemistry.
