Polychlorinated biphenyls (PCBs) are persistent pollutants that have become an increased global concern. They are recognized to be among the most abundant of the chlorinated hydrocarbons in the ecosystem. The physical and chemical properties of PCBs are: low volatility, low water solubility, high lipophilicity, low electrical conductance, chemical inactivity and difficult redox reactivity (Chakrabarty, 1982). All of these properties contribute to the poor degradability of PCBs. In general, PCBs are considered to be highly persistent in natural environments such as soils and sediments (Quensen et al., 1988). The sediment acts as an important sink where the residence time of the PCBs increases. The biodegradation of PCBs is of primary importance to minimize their toxic effects on the biota (Furakawa et al., 1978). Factors affecting microbial degradation of PCBs in the environment are:

1. The physical and chemical nature of PCB components: degree of chlorination, position of chlorination, position of substituted chlorines on the biphenyl molecule, and water solubility and volatility.

2. Microbial aspects: occurrence and distribution of PCB degrading organisms, and their ability for PCB degradation.

3. Environmental factors: photolysis by sunlight, pH, temperature, oxygen, nutrition, and adsorption of PCBs by such various materials as soil, sediment, sludge, and biological matter (Chakrabarty, 1982).

The owner of the transformer plant consulted a group of keen Biology 447 students to find a plausible bioremediation process for the following situation:

In the Chesapeake Bay area, a transformer plant spilled thousands of gallons of high level PCB-contaminated oil. The spilled material contained over 80% PCB isomers (Aroclor). The owner proposes to cleanup the sediment with controlled bioremediation procedures. The sediment has over 30 000 ppm PCBs in the most contaminated areas and less than 50 ppm in the least contaminated ones. Levels of less than 1 ppm are required for safety in the river environment.

Before deciding on the most effective method, the group researched the contaminated site, investigated the necessary requirements for the bioremediation process, and evaluated its feasibility.

Information Requirements

Bioremedition is a managed or spontaneous biological process that can be used to detoxify contaminated soil and/or water (Cox & Major, 1992). Chemical, geological and microbiological factors influence bioremediation. Thus, in evaluating the requirements and feasibility of bioremediation, several factors must be first examined.

1. Characteristics of the Contaminants Involved:

In this particular study, over 80% PCB isomers (Aroclor) are identified. AroclorJ is a trade name given by the Monsanto Chemical Company to its commercial PCB products (Clark, Chian, Griffin, 1979). A variety of Aroclors exist and differ in the percentage of chlorine by weight. For instance, Aroclor 1260 contains 12 carbon atoms and is 60 percent by weight chlorine. The isomers can have different mechanisms or pathways in degradation. In general, monochlorobiphenyls are more easily degraded than di-,tri- and tetra-chlorobiphenyls (Clark et al., 1979). Furthermore, rates of degradation can vary for different isomers. Degradation rates depend on: the number of chlorines per molecule, the position of chlorine substitution as well as the availability of specific organisms and/or metabolic modes (Cookson, 1995).

2. Characteristics of Physiochemical Attributes of the Contaminated Area

The geochemistry of the Chesapeake Bay area such as pH, Eh / redox conditions, temperature, osmotic pressure, moisture content, and presence of nutrients / electron acceptors must first be analysed by our research team (Cox & Major, 1992). As well, the hydrogeological / geological conditions of the Chesapeake Bay area will be investigated in order to find the most effective bioremediation technique. This includes a thorough examination of: delineation of the saturated and unsaturated zones, estimation of the depth to the watertable, measurement of the hydraulic parameters K, gradient porosity and permeability, and measurement of the cation exchange capacity and the natural organic carbon content (Cox & Major, 1992).

PCBs are deposited primarily in soils and lake sediments (Chen et al., 1988). The sediment is mainly anaerobic with the top few centimetres being aerobic. Naturally occurring anaerobic microorganisms, such as Pseudomonas putidas and other Pseudomonas species are commonly found in this anaerobic environment. With the proper environmental conditions , these microorganisms are able to exist and biodegrade PCBs. The fate of PCBs is therefore dependent upon the specific geochemistry and environmental conditions most favourable for PCB biodegrading microorganisms.

3. Biochemical Biodegradation Processes

Both anaerobic and aerobic processes affect the biotransformation of PCBs. PCBs chlorinated with four or more chlorine atoms are resistant under aerobic conditions but are degraded under anaerobic conditions (Cookson, 1995). In turn, no single organism in a particular environment can be responsible for the degradation of multiple chlorinated PCBs.

Anaerobic Biodegradation processes

Reductive dechlorination is the major anaerobic process for removing chloride from biphenyl rings. As microorganisms dechlorinate PCBs, there is a significant loss of the more highly chlorinated congeners, with an increase in the amount of lower chlorinated products (Abramowicz, 1990). This process of breaking down highly chlorinated PCBs to lower chlorinated PCBs does not include the actual breakdown of the biphenyl ring (Abramowicz, 1990). Theoretically and under ideal circumstances, PCBs should be metabolized to carbon dioxide, water and chloride. Chloride must first be removed from the ring and the intermediates must be cleaved and oxidized (Boyle et al, 1992). Past studies have found that meta and para chlorines are selectively removed, while ortho-substituted PCBs are accumulated (Abramowicz, 1990).

The presence of electron acceptors affects reductive dechlorination. Electron acceptors may compete with the halogenated compound for reducing potential (Cookson, 1995). However, a deficiency of electron acceptors limits microbial growth in most anaerobic environments. Any microorganism that can use PCBs as terminal electron acceptors would have an advantage in anaerobic sediments (Quensen et al., 1988). Energy is obtained from the dechlorination step.

Some compounds, such as sulfate, have been found to inhibit dehalogenation of PCBs, while other compounds, such as carbon dioxide or nitrate have been found to increase PCB dechlorination (Cookson, 1995).

Laboratory Confirmation of Anaerobic Breakdown

A number of studies have found laboratory evidence confirming that PCBs are broken down by microorganisms in the process of anaerobic dechlorination (Boyle et al (1992), Van dort and Bedard (1991) and Quensen et al (1988)). Laboratory experiments most often use purified PCB-degrading bacteria acting on defined PCB congener mixtures in the absence of soil or sediment (Harkness et al., 1994). It was found that a PCB mixture from the Hudson River was converted from 85% tri- and tetra-chlorinated PCBs to 88% mono- and dichlorinated products. These lower chlorinated PCBs were of lower toxicity and were further degraded by aerobic bacteria. Meta and para chlorines were selectively removed in the laboratory. In another study, Chen et al (1988) reported a significant drop in the amount of PCB in Hudson River sediment when it was incubated with a mixed population of bacteria.

Environmental Evidence of Anaerobic Breakdown of PCBs

Studies have found that highly chlorinated PCBs are naturally biodegraded to lower chlorinated PCBs through the process of dehalogenation (Abramowicz, 1990). Chromatogram patterns have shown decreased levels of tri-, tetra- and pentachlorobiphenyls and increased levels of mono- and dichlorobiphenyls. Tiedje (1992) found that microorganisms selectively removed meta and para chlorines. Anaerobic biodegradation by sediment microorganisms has been proposed to account for the changes, since evaporation and aerobic biodegradation had no effect in an anaerobic environment. Thus, our research team will take advantage of this biodegradation process using naturally occurring microorganisms found in the anaerobic environment.

Aerobic Biodegradation Process

For aerobic biodegradation to occur, the PCB congeners must be limited to five or fewer chlorine atoms and two adjacent unsubstituted carbon atoms. It has been shown that higher chlorinated PCBs are only hydroxylated and not dehalogenated under aerobic conditions (Cookson, 1995). Thus, anaerobic must occur before aerobic biodegradation.

Aerobic biodegradation follows a complex pathway beginning with the conversion of PCB to cis 2,3-dihydro-2,3-dihydroxybiphenyl. Different enzymes are utilized to get to the first product, benzoate, which is then converted to catechol. Further enzymes lead to $-ketoadipate, which is cleaved by thiolase to succinyl CoA and acetyl CoA. These two compounds then enter the tricarboxylic cycle (Boyle et al, 1992). Abramowicz (1990) summarizes the aerobic breakdown pathway as initial addition of oxygen at the 2,3-position by a dioxygenase enzyme, with subsequent dehydrogenation to the catechol followed by ring cleavage.

Evidence of Aerobic Breakdown of PCBs

Aerobic bacterial biodegradation of PCBs has been well characterized and studied extensively (cf. Abramowicz, 1990). Natural aerobic bacteria were isolated that could degrade PCBs in nearly all contaminated soils tested. It has been confirmed that the aerobic biodegradation of PCBs is limited to congeners with fewer than six chlorine atoms and two adjacent unsubstituted carbon atoms (cf. Cookson, 1995).

Proposed Bioremediation Process

By this stage, our research team will have identified and analysed the PCB contaminants as well as the environmental conditions. From our research, a common theme has emerged about PCB-contaminated sediment: anaerobic biodegradation followed by aerobic biodegradation is a recommended remediation process. Brown et al (1987) conclude that Aa two-step sequence of dechlorination in aquatic sediment followed by oxidative biodegradation in aerobic environments will eventually effect total PCB destruction@. In the present case, we will enhance the natural microbial populations found in the Chesapeake Bay area which are most effective in biodegrading PCBs. Microbial reductive dechlorination under anaerobic conditions has been extensively documented, and it has been found that Athe less chlorinated PCB congeners produced by anaerobic dechlorination are suitable substrates for oxidative degradation by a wide range of microorganisms@ (Harkness et al., 1994).

Therefore, it would seem that anaerobic biodegradation followed by aerobic biodegradation is complementary, and that this two-step process may degrade most common PCB mixtures (Abramowicz, 1990). The first stage of a 2-stage process would anaerobically remove the chlorine atoms, and the second stage would aerobically degrade the lesser chlorinated products from the first step. Prior to converting the sediment into an aerobic environment, we would ensure that the higher chlorinated biphenyls were degraded to lower chlorinated biphenyls.

Our Proposal and Necessary Conditions

Research has shown that PCBs do biodegrade in the environment, but at a very slow rate. It should be noted that no one yet has demonstrated a process that can accelerate PCB biodegradation to rates necessary to make such a process commercially viable. According to Ward (1996), there is no known successful in-situ bioremediation of a PCB-contaminated sediment. Therefore, we must base our proposal on previous laboratory work and field studies. It should be mentioned that our lab technicians would modify previous laboratory work by using the specific environmental conditions in our problem.

We will implement anaerobic in-situ biodegradation by promoting conditions for growth of the naturally occurring anaerobic microorganisms. A diverse group of organisms have been identified as participating in the degradation of PCBs (Table 1). It should be noted that various microbial strains have distinct congener preferences. For example, Alcaligenes eutrophus and Pseudomonas putida strains prefer congeners with substitutions at the 2,5 position, whereas Corynebacterium is capable of handling congeners substituted in both para positions (cf. Cookson, 1995). Figure 1 illustrates the proposed oxidation for PCBs by Alcaligenes species. The microorganism-specific nature of PCB degradative attack by Corynebacterium sp., Alcaligenes eutrophus and Pseudomonas putida is shown in Figure 2.

Table 1: PCB- Degradation Organisms

(Source: Cookman, 1995)

Pseudomonas putida

Pseudomonas cepacia

Pseudomonas testosteroni

Pseudomonas sp.

Pseudomonas aeruginosa

Acinetobacter odorans

Alcaligenes faecalis

Alcaligenes eutrophus

Alcaligenes denitrificans

Arthrobacter sp.

Corynebacterium sp.

The addition of biphenyl to the sediment to promote co-metabolism and increased rate of degradation will also be implemented. Past research has found that the addition of biphenyl as an analogue substrate has significant effects on the degradation of Aroclor 1242 (Figure 3) (Cookson, 1995). In general, biphenyl is known to induce PCB-degrading activity in selected bacterial forms. However, the addition of biphenyl is not the only significant factor in increasing the rate of degradation. It has been found that the addition of Acinetobacter with the biphenyl substrate reduces the adaptation period for the biodegradation of Aroclor 1242. A mixed culture will be used, again consisting of microorganisms that are indigenous to the environment. Alcaligenes eutrophus H850 can degrade a large variety of PCB congeners including many tetra-, penta- and some hexachlorobiphenyls and therefore should be a primary component of the mixture. However, Acinetobacter cannot dehalogenate any of the products that it forms from cometabolism (Cookson, 1995). Therefore, further degradation of these compounds must be carried out by other microorganisms.

It appears that the presence of sediment itself enhances PCB dechlorination, perhaps by providing some carbon or growth factor for the microorganisms (Cookson, 1995). This is an advantage which is naturally present that will increase the PCB biodegradation rate.

Once the higher chlorinated PCBs are biodegraded to lower chlorinated PCBs in the anaerobic sediment aerobic biodegradation will be implemented. We will add oxygen into the sediment to promote an aerobic environment. This is accomplished by adding hydrogen peroxide, which will then be broken down into oxygen and hydrogen. The sediment can be mixed using agitators such as high-mix turbines and low-mix rakes (Harkness et al, 1992). The actual technical process will be left up to our highly qualified bioremediation engineers.

Inorganic nutrients are also needed in correct proportions of the bacterial cells in order for maximal biodegradation to occur. Past studies have found that PCB losses ranged from 30 to 40 per cent over four weeks. PCB losses were highest among mono- and dichlorobiphenyl congener groups. However losses of higher congeners were also evident.

A similar method as the one described above was used in a 73 day field study and resulted in a statistically significant loss of PCB in the range of 38 to 55 per cent. The required goal of 1 ppm in the proposal is in all likelihood unfeasible. As a bioremediation research team we would not want to mislead our client into believing that such unattainable goals could be achieved. A more realistic goal is 10 ppm in the most contaminated regions (Cookson, 1995).

Possible Limitations of PCB Bioremediation:

1. Containment of PCB to the Chesapeake Bay area: PCBs entering the aquifer and PCBs leaving the estuary.

2. Measurement of PCBs: A decreasing concentration may occur due to movement and dispersion of PCBs, thus giving inaccurate measurements of PCB levels.

3. Hydrogeology: Inadequate mixing of PCBs and microorganisms can result in poor bioremediation.

4. Chlorine residue : There is a concern in the creation of halomethanes, a group of compounds that may be carcinogens, that can arise when chlorine reacts with organic matter (Prescott et al.,1993).

5. Nutrient and environmental requirements need to be maintained for successful degradation of PCBs. Monitoring the increase in biomass of microorganisms upon PCB degradation can be a useful indicator.

6. Stage two of the process (ie. changing the sediment from anaerobic to aerobic) will only work if the higher chlorinated biphenyls are degraded to the lower chlorinated biphenyls.

7. We recognize that the degradation rate of PCBs may be inhibited by the presence of oil. We would throughly investigate the relationship between oil and PCBs in lab work prior to implementing our remediation process.

Procedures for Monitoring Progress

This is a step which is commonly overlooked yet plays a significant role in the success of the overall remediation process. Careful sampling and analysis must be taken in order for precise decisions and conclusions to be made. A mass balance approach is the most accurate method available yet as time increases and the plume involved increases the task at hand to gather data for the entire plume becomes tedious .(Cox and Major, 1992)

It is possible through linking several indirect pieces of evidence to achieve validation of progress without having to gather all of the plume=s data. A simple reduction in the target contaminant=s concentration, an increased microbial biomass in the impacted zones and/or a decreased toxicity of the contaminants to the microbial populations are all ways to indirectly measure microbial activity. (Cox and Major, 1992)

Several sampling techniques currently being used for obtaining PCB concentrations includes PCB immunoassay test kits and Environmental test kits. The EnviroGard PCB immunoassay kit involves adding extracts and washing away the remains until a concentration can be reached. Initially the test tubes are coated with PCB molecule binding antibodies and a sample is added whereby the PCBs form a complex with the antibodies. The extra material is washed away and another sample is added containing an enzyme that mimics the PCBs and binds to any remaining antibodies. After this next washing a colouring agent is introduced giving the concentration of PCBs in terms of a range. The categories given are <5, 5-10, 10-50, >50 ppm PCB. Such a test can be used for PCBs in food, soil, water and contaminated surfaces.(U.S. EPA, 1994)

Another sampling method is the Dexsil Clor-N-Soil PCB Screening kit and the Dexsil L2000 PCB/Chloride Analyzer. The Dexsil Clor-N-Soil kit dissociated the PCBs into free chloride ions using a sodium reagent. The ions react with mercuric ions to form a compound of mercuric chloride. This is then treated with diphenylcarbazone turning the compound purple. The greater the concentration of PCBs in the extract the lighter the colour purple. This value is given in terms of a regulatory number and whether the sample is above or below this number. The Dexsil L2000 PCB/Chloride Analyzer also dissociates the PCBs into ions but instead of forming a compound, a calibrated chloride-specific electrode is used to analyse the concentration. The accuracy is very good ranging from 2-2000 ppm PCB in solution. Both of these tests can be used for soil, sediment and transformer oils.(U.S. EPA, 1994)

Identification and measuring of the contaminants can also involve a more common approach including gas chromatography or galvimetric analyses and mass spectroscopy. Complex mixtures of compounds like oils that are composed of simple alkanes to complex aliphatic compounds need the proper chemical analyses to monitor such a wide range in chemicals. High resolution gas chromatography and mass spectroscopy provide this high degree of separation of gas-liquid chromatography and spectral resolution from the mass spectrometer needed for such complex mixtures. Lower costs for such systems and new regulations are making it more feasible for their use in laboratories. (Roques, Overton and Henry, 1994)

Bruker Instruments have developed a mobile environmental monitor that is a mass spectrometer designed to use retention time, molecular weight and fragment pattern to identify and measure organic pollutants in a variety of settings. An integrated gas chromatograph allows complex separation and further analysis to be done on location. Both volatile and semivolatile organic compounds in soil, sediment, water and sludge can be detected. (U.S. EPA, 1994)

A typical situational assay with the gas chromatograph consists of the following conditions: a gas chromatograph/mass spectrometer with a coiled glass column packed with silicon. Helium and sometimes nitrogen (Kimbara et. Al., 1988) used as the carrier gas with a flow rate of 20 ml/min and 50ml/min respectively. An increase in temperature from 140'C to 250'C at a rate of 8'C/min or 120'C to 250'C at a rate of 16'C/min (Kimbara et al., 1988) and methane used as the reagent gas (Boyle et al., 1992). The polychlorinated biphenyl metabolites typically obtained as trimethylsilyl derivatives.(Furukawa, Tomizuka and Kamibayashi, 1979) From here the identification and the concentration can be determined and the necessary conclusions made.

If problems arise that are more serious than originally thought making this bioremediation proposal too time consuming or unapplicable then we would suggest considering one or several of the following alternatives.

Alternative Remedial Methods

1. A combination of dredging, dewatering and disposal has been used to clean up PCB=s from a lake bottom. The process involves hydraulic dredging within a protective barrier of silt-screens using a suction dredger with an auger head specially designed to reduce the spread of the sediment material. Trial dredging should be carried out first for several reasons: it provides an idea of how much material is resuspended and what PCB levels can be built up inside the screen; it allows for preliminary assessment of the consequences of dredging without a protective screen; it affords the opportunity to calculate the residual amounts that may need to be post-dredged. When the sediments are pumped up they must be diluted with water. Therefore, once removed they must be dewatered either mechanically, by natural drainage, or a combination of the two. The dewatering process produces material with a dry solid percentage sufficient to render the product solid enough for handling. This product can then be transported to a landfill site positioned such that the lowest level is above sea level and the highest water level in the bay. The landfill site should be built up with sealing and covering layers to minimize the infiltration of precipitation so that the throughflow of water acting as a transport medium will be small. The most highly contaminated material should be situated in a special are of the site that is readily accessible should there be an economical way of destroying the PCBs. The entire landfill site should then be covered with at least one metre of uncontaminated material from the site. Note that leakage has been estimated to be small, especially compared to the leakage from the spill into the bay water. (Gullbring & Hammar, 1993).

2. A method has been proposed involving a procedure in which the bottom of the bay housing the contaminant of PCBs and oil is covered with uncontaminated material. In comparison to the first method, the chief advantage to this method is that a landfill site would not be required. However disadvantages are numerous: there is a lack of experience in its use; the oil and PCB pollutants will remain in the water; there are uncertainties as to whether or not an effective layer of material could be laid down since sediments can be quite porous; any currents will certainly affect (disrupt) the added layer; the bay will become shallower; there are uncertainties regarding the costs; if this method fails, suction-dredging will be made even more difficult. (Gullbring & Hammar, 1993).

3. The use of non-toxic supercritical solvents for the extraction of PCBs from waters has shown great promise. The contaminated sediments must be pumped up from the bottom and then treated. A solvent gas such as carbon dioxide, at high pressure and moderate temperature is put in contact with the contaminated sediment. A methanol cosolvent has been shown to enhance the ability of the carbon dioxide to extract the PCBs. Manipulation of temperature and pressure, even to small extents, change the solvent density and consequently its ability to solubilize the PCBs. This can be very useful. The process creates a tractable waste quantity that may be further treated by one of several means including combustion and biological degradation. (Dooley et. al., 1990)

4. Two fairly recent remedial procedures developed are known as the Resin-in-pulp (RIP) and carbon-in-pulp (CIP) technologies. They are based on the resin ion exchange and resin or carbon adsorption of contaminants from a sediment-slurry mixture. Incoming material is screened, oversized material crushed, and the two components combined. The leached solids are then passed to cyclones for further separation of coarse and fine material. The coarse material is washed free of the contaminant, with the wash liquors being sent to the contaminant recovery section. The fine component is sent to the RIP or CIP contactor where either ion exchange resins or activated carbon removes the contaminants. The resins and carbons are recycled during the extraction stage. The concentrated contaminant produced by the RIP or CIP contactor is sent to the recovery section where contaminants are recovered from both wash and eluate solutions by precipitation. The solid contaminant can then be transported away for further treatment or storage. Note that polluted sediments must first be brought up from the bottom. (U.S. Environmental Protection Agency, 1994)

5. Several patented thermal desorption processes have been developed to remove PCB contaminants. Contaminated sediments must first be dredged up from the bottom. Organic contaminants are removed as a condensed liquid. This liquid may then be incinerated or used as supplemental fuel. Chemical oxidation and reactions are discouraged by conserving an inert environment and low treatment temperatures. In the patented technology X*TRAX , a rotary dryer volatilizes water and organic contaminants from the polluted sediment into an inert carrier gas stream. The processed solids are cooled with water and then compacted. (U.S. Environmental Protection Agency, 1994)

6. Sediment washing is another potential candidate for use in the clean-up of PCBs. Again this method is ex situ. The polluted sediment is first screened to remove any coarse rock material and debris. Water and chemicals including surfactants, acids, bases and chelants are then added to produce a slurry. The slurry is then fed into an attrition scrubbing machine in which mechanical and fluid shear stress remove contaminated silts ad clays from the more granular components. This produces several fractions including a coarse clean fraction, a fine fraction enriched with pollutant PCBs and ready for further treatment, destruction or regulated treatment, and process wash water. The washwater can be treated by flocculation and/or sedimentation and then reused. (U.S. Environmental Protection Agency, 1994)

7. An ex situ method has been developed in which the hazardous waste (PCBs) is mixed with cement, water and one of 18 patented reagents known commercially as AChloranan@. Treatment occurs in batches and begins by adding Chloranan and water to a blending unit. The waste is then added and the constituents are mixed together. After a 12-hour period, the treated material hardens into a concrete-like mass with massive compressive strengths. Advantages to this method are that it can be carried out under water (in situ), and that it is effective for materials containing a high concentration of oil. (U.S. Environmental Protection Agency, 1994)

8. Microorganisms other than bacteria have been reported to aerobically degrade PCBs. The filamentous fungus Aspergillus niger has been found to degrade the lower chlorinated PCBs. The white-rot-fungus Phanerochaete chrysosporium has also been employed to degrade low concentrations of PCBs. It uses the same enzymes as those used in lignin degradation to attack PCBs via the production of hydroxy radicals. Furthermore, it is capable of completely degrading highly chlorinated PCBs. (Abramowicz, 1990)

The two fungi Pleurotus ostreatus and Trametes versicolor are also able to degrade PCBs aerobically when mixed and incubated with wood chips. An isooctane trap was used to contain potentially volatile substances such as highly toxic chlorinated dioxins or furans, however none were detected. Optimal degradation was achieved by incubation of white-rot-fungus in direct contact with wood chips. The white-rot-fungus was observed to degrade a wide range of isomers from tri to pentachlorobiphenyls. (Zeddel, Majcherczyk & Huttermann, 1991)

Pretreatment possibility

Another alternative which can also be applied as a pretreatment method is the use of synthetic surfactants. Since PCBs are strongly sorbed to the soils, only about fifty percent of the total contaminant is available to degradation. Synthetic surfactants such as alcohol ethoxylate can enhance the removal of PCBs by soil-washing methods. If the micelles can adsorb the hydrophobic PCBs into the hydrophobic interior there is an increased solubility of the PCBs. This enhancement of their transport through the soil varies greatly with the type of soil present.

Biosurfactants can also be used where microorganisms have biosurfactant-producing capabilities. In this case there is an increased mobility into the cell and localized effects where the bacterial coat creates an enhanced microbial habitat (Morris & Pritchard, 1993). Implementation of such a pretreatment could in fact shorten the time required for bioremediation, for more highly chlorinated PCBs will be converted to lower chlorinated congeners and speed up the clean-up process.

Costs as per discussion with Dr. Owen Ward

Initial Consultation: based on an hourly rate and degree of complexity of problem

Sampling costs: $5 sample

Labour costs: 2 to 2.5 times the hourly wage of the labourer(s)

Pretreatment steps: depends on treatment(s) used; very expensive; overall saves money by decreasing time required for bioremediation

Treatment per tonne: $100 and up depending on degree of chlorination

Equipment: varies according to technology used

Follow-up Consultation: based on an hourly rate and the progress achieved

Due to a lack of detail in combination with the number of assumptions that must be made in remediating this problem, an overall dollar value cannot be provided. An estimate for remediation of low chlorination contaminant spills is in the range of $20,000 while a highly chlorinated contaminated site may cost up to several million dollars to be cleaned up. The time required to remediate a PCB spill is again dependent upon degree of chlorination and the amount of contaminant spilled.

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