Toxicity of Ground Water and Subsurface Sediment Samples Collected at a Site Contaminated with TCE Undergoing In Situ Methanotrophic Bioremediation

Ground water and subsurface sediment samples collected at a site contaminated with trichloroethylene (TCE) that was undergoing in situ bioremediation were tested for acute toxicity with a bacterial toxicity assay known as Microtox® (Carlsbad, CA). A representative sample of the ground water collected was tested for genotoxicity with the newly developed bacterial assay known as Mutatox® (Carlsbad, CA). Toxicity is an important endpoint of bioremediation, as the reduction of target compound does not ensure safety to human health and the environment. Often times a more toxic or harmful product will be formed during the breakdown of the target contaminant. Using toxicity as an endpoint of bioremediation will help detect and monitor potential hazards occurring during the bioremediation efforts. Acute toxicity appeared in only two ground water wells (out of 12). The toxicity in one of the wells (mht-7c) appeared only at one time point, while the toxicity in the other wells (mhc-lOc) persisted transiently for about six months. Both of these wells were located at the periphery of the treatment zone. All of the samples that exhibited toxicity had a very high pH (above 10). Genotoxicity was present in the ground water sampled from all of the wells. The compound causing the genotoxicity seemed to be present in the water in an active form as more samples came up positive when tested in the absence of S-9 (rat liver homogenate) than in the presence of S-9. Sediment samples were more toxic in the contaminated zone, depths greater than 100 feet (30.5 meters), than in the uncontaminated zone, depths less than 100 feet (30.5 meters). All of the toxic sediments that exhibited toxicity significantly above the control sediments were clay sediments. It was not possible to determine significant changes in the toxicity over time partially because of the wide confidence intervals of the data. Basically, no changes in toxicity in the sediment samples were seen during the course of the bioremediation.Master of Science in Public Healt