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Dechlorination of polychlorinated biphenyl(PCB) congeners and
three commercial PCB mixtures Aroclor 1242, Aroclor 1254 and
Aroclor 1260 in anaerobic mixed cultures were studied with PCB
contaminated sediments from Er-Jen River located in Tainan
prefecture. The results showed the microorganisms from
sediments of Er-Jen River possessed ability to dechlorinate
234-CB, 345-CB and 2345-CB that containing three chlorine in
adjacent position and removed the middle one chlorine to produce
24-CB, 35-CB and 235-CB respectively. Mixed cultures enriching
with yeast extract, the lag phase for dechlorination was
shortened. The first transferred cultures showed their
dechlorination activity after 6 days of incubation, and
completely transformed 234-CB to 24-CB for 17 days.
Continuously feeding with 345-CB and 2345-CB to the
microorganisms precultured in 234-CB, both compounds were
immediately dechlorinated without significant lag time. The
results suggested that there might be a unique microbial system
in charge of the dechlorination of these PCB congeners.
In the study on dechlorination of Aroclors, Aroclor 1242, 1254
and 1260 were dechlorinated to the extent of 7.11%, 7.72% and
11.94%, respectively, at m-, p-position by mixed cultures which
acclimated with Aroclors for two months. Aroclors showed the
same dechlorination pattern in the cultures acclimated by the
different PCB congeners , and the 345-CB-acclimated cultures
gave the great dechlorination to the extent of 15.23% for m-, p-
Cl removal. Addition of surfactants to the culture medium
would shortenthe lag phase of Aroclor 1260 dechlorination, but
it seemed no influence to Aroclor 1242 dechlorination. The
anaerobic mixed cultures also transformed high concentration(50
mg/l and 100 mg/l) of Aroclor 1242 to 10.12% and 11.56% of m-,
p-Cl dechlorination in culture medium. Furthermore,
microorganisms collected from all sediments and soils showed
dechlorination activity to PCBs no matter how contaminated with
PCBs they had. It suggestedthat the PCBs dechlorinating
bacteria were widespread in Taiwan. Each of PCBs dechlorination
reactions with their physical and chemical properties including
heat of reaction (△H), related retention time (RRT) and charge
distribution were also examined. Selective dechlorination of
the indigenous microorganisms in Taiwan was according to the
thermodynamic favorable reaction. Actually, reactions with
more energy released to proceed dechlorination was selected by
microorganisms collected from low-PCB-contaminated sediments.
But those bacteria from badly contaminated evironments didn''t
follow the same rule, they simply selected the dechlorination
reactions which could get rid of the oringinal PCBs toxicity .
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