associated with the structure of PCB components. Thus, 

 results from laboratory assays indicate that different PCB 

 congeners are subject to different degrees of microbial attack 

 and that each strain is capable of transforming a different 

 spectrum of congeners ( Kohler et ai . 1 988 ). 



Because the World Ocean can be regarded as a reservoir of 

 anthropogenic compounds, the assessment of PCB 

 transformation in the marine environment is important. Our 

 investigations of PCB microbial transformation under natural 

 marine conditions were conducted during the Third Joint 

 US-USSR Bering & Chukchi Seas Expedition. This work 

 assesses biodegradation potential of PCB " s by isolated bacterial 

 strains and natural marine bacterioplankton communities. 



Materials & Methods 



Experimental assessment of marine microflora 

 biodegradation potential of PCB's was made on board the 

 research vessel Akademik Korolev in July-August 1988. 

 Overall, 12 assays (Table 1) were conducted in the eastern, 

 northern, and southern parts of the Bering Sea, including the 

 Gulf of Anadyr, the Chirikov basin, and the southern Chukchi 

 Sea. 



TABLE 1 



Characteristics of the regions of sampling when conducting 

 experiments (see Frontispiece for location of Stations). 



Sea. Sampling Stations Experiment Water Salinity 

 Region Number Temperature (%) 



°C 



Niskin bottles (5-10 1) sterilized with 96° ethanol were 

 used to collect samples from the upper ().5-m surface layer. 

 Subsamples (200 ml) were drained into .500 ml dark glass 

 bottles. These bottles were washed thoroughly, rinsed with 

 acetone and hexane, and sterilized with dry heat at 200°C for 



2 hours. For assay control, seawater from the same samples 

 were sterilized by autoclaving at 1 atm (1.01 x 10^ Pa) for 30 

 minutes. 



Gas-liquidchromatography (Tuistra&Traag, 1983; Kohler 

 et ai. 1988) was used to determine background PCB 

 concentrations in 200-ml samples, which were always below 

 detection. To determine the most probable number (MPN) of 

 saprophytic (SB) and PCB-transforming (PCBB) bacteria, a 

 dilution method was used (Tsyban et al., 1988). 



To determine the MPN of SB, a broth based on seawater 

 from the various regions was used as the culture medium (see 

 Subchapter 4.3). The medium was distributed into test tubes 

 and sterilized by autoclaving. After inoculation, PCB solution 

 was added into each test tube. 



Considering the distribution of PCB in the Bering Sea 

 conducted in 1984 (Izrael & Tsyban, 1990), experiments were 

 based on the use of PCB Aroclor 1 232 mixture, a composition 

 similar to the PCB mixture found in the region. Each experiment 

 was conducted with two series of test bottles: the first series 

 with PCB concentration of 100 ng/1 and the second series of 

 lOng/1. Each test was duplicated. 



Polychlorinated biphenyls solution in ethanol was added 

 to control and test bottles and thoroughly shaken for 1-2 min 

 and then incubated in the dark to prevent photochemical 

 processes. The experiment was incubated under //; situ 

 conditions (range 2-10°C) over the period of investigations. 



At 1,3,5, 10, 14, and 21 days, water (1 ml ) was taken from 

 each test and control bottle to determine the MPN of SB and 

 PCBB. Concentrated H,S04 ( 1 ml ) was added into each bottle 

 to stop microbial metabolism. The amount of PCB remaining 

 was determined by gas-liquid chromatography. 



Results and Discussion 



From the Aroclor 1232 experiment. 1 9 out of 70 congeners 

 were transformed and those (Table 2) became the focus of the 

 study. 



In the East Polygon in the Bering Sea, the percentage of 

 individual Aroclor 1232 consumption, with an initial 

 concentration of 100 ng/1, varied from 7% for 

 hexachlorobiphenyls (Table 2) to 95-100% for 

 dichlorobiphenyls (Figs. 1,2). Trichlorobiphenyls were also 

 transformed, ranging from 64 to 90%. Degradation of 

 pentachlorobiphenyls varied little, ranging 36-44% (Fig. 1, 

 Table 3). Fortetrachlorobiphenyls, this group of Aroclor 1232 

 congeners can be divided into those that were readily labile 

 over the 10-21 days, a biotransformation rate of 49-58% of the 

 initial content, and those that were relatively stable, a rate of 

 10-18% of the initial content. 



Similar observations were revealed with an initial PCB 

 concentration of 10 ng/1. Transformation of congeners, however, 

 was more rapid, especially during the first 3 days (Table 3). 



Figure 1 a shows the change in number of saprophytic and 

 PCB-transforming microorganisms with an initial PCB 

 concentration of 100 ng/1. After the first day. the MPN of the 

 bacteria did not increase over the initial numbers, but bacterial 

 break down of PCB's continued. For dichlorobiphenyls, 40to 

 52% of these congeners (nos. 5,8, 15; Fig. lb) were transformed 



96 



