878 PCBs AND ASSOCIATED AROMATICS
TABLE 14
The most highly PCB contaminated Yusho oils also contained the highest
relative concentrations of PCDFsSamplePCB Concentration
(ppm)PCDF Concentration
(ppm)PCDF:PCB
ratioKanechlor 400 1,000,000 33 1:30,000
Kanemi-1 154 2.2 1:70
Kanemi-2 0.9 0.0021 1:492
Kanemi-3 1,029 5.3 1:194
Kanemi-4 1,025 4.9 1:209
Kanemi-5 1,023 5.4 1:189
Kanemi-6 2.7 0.0031 1:871
Kanemi-7 2.7 0.0021 1:1,286From reference 40: Miyata, H., T. Kashimoto and N. Kunita; “Detection and
determination of polychlorodibenzofurans in normal human tissues and Kanemi
rice oils caused Kanemi Yusho”; J. Food Hyg. Soc. Japan; 18 , 260 (1977).TABLE 15
The total concentration of PCDFs increase by a factor of up to 6.4 in the presence of catalystsTemperature 0° Duration (days) CatalystTotal PCDFs
(mg/kg PCBs)Total TCDFs
(mg/kg PCBs)
Ambient 0 none 33 26.2
360 20 none 65 52.1
360 20 steel 77 32.7
360 20 water 212.1 152.4
360 20 steel water 72.1 46.6Miyata H. and T. Kashimoto.^4similar conditions. Only a very small fraction of the PCDFs
produced at 360°C would be expected to be formed at 250°C.
The presence of PCDFs in heat exchanger fluids operated in
the range 200°−270°C was investigated by Miyata and his
results are shown in Table (16). The PCDF concentration in
the fluids increased by a factor of up to 15.5.
Nagayama et al.^42 have confirmed the hypothesis that
PCDFs as well as PCQs are produced in the degradation
process within heat exchangers. They found that the concen-
tration of PCDFs increased by as much as 40 to 50 times the
original level i.e., up to about 740 ppm PCDF by heating the
PCB mixture to 300°C for 7 weeks followed by heating to
350°C for 4 weeks in the presence of iron.
The concentration of PCDFs in service aged transformer
askarels has been shown to occur by Chittim et al.^43 It was
found that a correlation existed between the concentration of
tetrachlorodibenzofurans (T 4 CDFs) and the length of time
the fluid had been in service. The small number of samples
tested was insufficient to obtain a definite correlation between
TCDF concentration and transformer load. While the results
indicated that transformer load is probably a major factor in
the formation of PCDFs, the effects of discharging or arcing
appeared to be negligible.It has been observed that some PCB products were
manufactured with trace PCDF contamination caused by the
presence of dibenzofuran in the biphenyl starting material
(see Table 12). Fortunately, North American starting materi-
als seem to have been purer than those available in Japan
and very small amounts of PCDFs are found in undergraded
US PCB products. An alternative route of formation might
be derived from the use of sodium hydroxide to remove
traces of HCl produced during the PCB synthesis. Miyata
and Kashimoto^41 found that in the presence of catalytic
metals, such as copper and iron found in heat exchangers
and transformers, there is up to a 15.5 fold increase in the
PCDF concentration in a temperature range of 180 to 270°C
(Tables 18 and 19).
Brown et al.^45 have also investigated the levels of bioac-
tive PCDF congeners in PCB dielectric fluids obtained from
capacitors and transformers. Both service aged and unused
equipment was investigated and no indication was found of a
higher level of PCDFs caused by PCB degradation. None of
the equipment had malfunctioned and failed due to overheat-
ing but had all either never been used, or had been operated
for a documented period of up to 30 years. The distinction
between operating and failed units was not made, nor wasC016_003_r03.indd 878C016_003_r03.indd 878 11/18/2005 1:12:32 PM11/18/2005 1:12:32 PM