Thesis (M. Eng. in Ocean Engineering)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references (leaves 97-103). / by Rachel H. Levine. / M.Eng.in Ocean Engineering

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This research is part of an effort to develop non-mammalian surrogate immunoessays with the earth worm Lumbricus terrestris to assess immunotoxic potential of xenobiotics to mammals. The objective was to determine if earthworm immunoessays, namely E- and S- rosette formation and phagocytosis, are sensitive to a known mammalian immunotoxin, the PCB Arclor 1254. Results are presented in terms of PCB exposure and tissue concentrations during uptake/depuration.

Polychlorinated biphenyls (PCBs) are a class of environmentally persistent halogenated organic compounds that were once used as stabilizers to improve the properties of a variety of materials such as lubricants, heat transfer fluids, paints, and caulking materials. PCBs are also capable of migration through processes such as spillage into soils, leaching into groundwater, and volatilization into the atmosphere. Although banned in 1979 over health concerns, PCBs persist in these materials to this day because they are resistant to biotic degradation and natural weathering processes. The wide variety of contaminated materials means that many existing treatment options cannot be used across all media. This research focuses on the adaptation of a reductive dehalogenation system for dechlorination of PCBs from machine oils, paints, sludges, and soils. The system utilizes magnesium, glacial acetic acid, and ethanol in order to remove the chlorine atoms from the biphenyl backbone, which is less toxic and can be broken down biotically. A treatment plan was devised for machine oil contaminated with PCBs, involving sorption of PCBs onto a column of super activated alumina followed by desorption into hexane and treatment of the hexane with magnesium and acidified ethanol to dechlorinate the PCBs. In a small-scale study, 98.5% of PCBs from an oil sample were sorbed to the column, and the PCBs that were subsequently desorbed were dechlorinated to below detectable levels within one day of magnesium and acidified ethanol treatment. Information from small-scale studies was used to design larger sorption columns intended for use at a field site. iv A field study was conducted to compare the effectiveness of two different treatment system pastes at removing PCBs from painted surfaces. These pastes were formulated with bulking and viscosity control agents in order to cling to vertical surfaces, and contained either acidified ethanol and magnesium (Activated Metal Treatment System, AMTS) or acidified ethanol only (Non-Metal Treatment System, NMTS). AMTS was capable of 64.8% average removal of PCBs from paint, while NMTS demonstrated 89.5% average removal but required a second step to dechlorinate the extracted PCBs. This system allows for treatment of surfaces without demolishing the structure. AMTS was also studied for in situ dechlorination of PCBs in soils, and NMTS enclosed in a polyethylene barrier was studied for extraction of PCBs from sludges. A two-step system was devised for the ex situ treatment of PCB-contaminated soils. Solvent extraction with ethanol or an ethanol/ethyl lactate cosolvent is followed by dechlorination using magnesium and glacial acetic acid. Studies included the optimization of extraction solvent, cosolvent ratio, cost, and reuse of magnesium or extraction solvent. Surface analysis of magnesium particles used in dechlorination showed a precipitate occluding part of the surface, which was thought to be a combination of magnesium ethoxide and magnesium hydroxide. This precipitate is thought to come from the reaction of magnesium ethoxide formed during the PCB dechlorination process with pore water extracted from the soil.

Polychlorinated biphenyls are a ubiquitous environmental contaminant that can be found today throughout the world in soils and sediments, lakes and rivers, and flora and fauna. PCBs have percolated throughout the food chain, so that almost every human being has a detectable amount of the contaminant within their blood stream. Existing remediation methods include incineration, dredging and landfilling, and microbial degradation, but all of these methods have drawbacks that limit their effectiveness as treatment options. Recently, the use of zero-valent metals as a means of reductive dechlorination has been explored. Using a combination of zero-valent magnesium and catalytic palladium, a successful bimetallic system capable of degrading PCBs has been created and optimized. Determining the mechanism for the reductive dechlorination has proven to be an arduous task, but experimental evidence has suggested three possible radical-type mechanisms for the use Mg/Pd specifically in methanol (as compared to aqueous systems). These possible mechanisms differ in the type of hydrogen species that replaces the chlorine atom on the PCB. Thermodynamic information has also aided in narrowing down which of the suggested pathways is most likely. It appears likely that the hydrogen involved in the dechlorination has the form of a "hydride-like" radical, which is a form of electron-rich atomic hydrogen. According to the literature, Pd catalysts create this species within the first few subsurface layers of the palladium in the presence of molecular hydrogen. Further work will be necessary to confirm that the "hydride-like" radical is actually the species involved in the dechlorination.

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Polychlorinated biphenyls (PCBs) are toxic and persistent chemicals that have been largely dispersed into the environment. The biological and abiotic transformations of PCBs often generate hydroxylated derivatives, which have been detected in a variety of environmental samples, including animal tissues and feces, water, and sediments. Because of their toxicity and widespread dispersion in the environment, hydroxylated PCBs (OH-PCBs) are today increasingly considered as a new class of environmental contaminants. Although PCBs are known to be susceptible to microbial degradation under both aerobic and anaerobic conditions, bacterial degradation of OH-PCBs has received little attention. The overall objective of this study is therefore to evaluate the transformation of mono-hydroxylated PCBs by the well characterized aerobic PCB-degrading bacterium, Burkholderia xenovorans LB400. In order to achieve our overall objective, a series of model mono-hydroxylated PCBs have been selected and they are used to determine the toxicity of hydroxylated congeners toward the bacterium B. xenovorans LB400. The biodegradation kinetics and metabolic pathways of the selected OH-PCBs by B. xenovorans LB400 are then characterized using GC/MS. To understand further the molecular basis of the metabolism of OH-PCBs by B. xenovorans LB400, gene expression analyses are conducted using reverse-transcription real-time (quantitative) polymerase chain reaction (RT-qPCR) and microarray technology. More formally, the specific aims of the proposed research are stated as follows: (1) To evaluate the toxicity of selected mono-hydroxylated derivatives of lesser-chlorinated PCBs toward the bacterium B. xenovorans LB400. (2) To assess the degradation of the selected OH-PCBs by B. xenovorans LB400. (3) To gain further understanding of the molecular bases of the metabolism of the selected OH-PCBs by B. xenovorans LB400. Three hydroxylated derivatives of 4-chlorobiphenyl and 2,5-dichlorobiphenyl, including 2'-hydroxy-, 3'-hydroxy-, and 4'-hydroxy- congeners, were significantly transformed by Burkholderia xenovorans LB400 when the bacterium was growing on biphenyl (biphenyl pathway-inducing conditions). On the contrary, only 2'-OH-4-chlorobiphenyl and 2'-OH-2,5-dichlorobiphenyl were transformed by the bacterium growing on succinate (conditions non-inductive of the biphenyl pathway). Gene expression analyses showed that only exposure to 2'-OH-4-chlorobiphenyl and 2'-OH-2,5-dichlorobiphneyl resulted in induction of key genes of the biphenyl pathway, when cells grown on succinate. These observations suggest that 2'OH-PCBs were capable of inducing the genes of biphenyl pathway. These results provide the first evidence that bacteria are able to cometabolize PCB derivatives hydroxylated on the non-chlorinated ring. Genome-wide transcriptional analyses using microarrays showed that 134 genes were differentially expressed in cells exposed to biphenyl, 2,5-dichlorobiphenyl, and 2'-OH-2,5-dichlorobiphneyl as compared to non-exposed cells. A significant proportion of differentially expressed genes were simultaneously expressed or down regulated by exposure to the three target compounds i.e., biphenyl, 2,5-DCB, and 2'-OH-2,5-DCB, which suggests that these structurally similar compounds induce similar transcriptional response of B.xenovorans LB400. Results of this study may have important implications for the natural attenuation of PCBs and fate of OH-PCBs in the environment. The recalcitrance to biodegradation and the high toxicity of some OH-PCBs may provide a partial explanation for the persistence of PCBs in the environment. / Civil Engineering