PCBs AND ASSOCIATED AROMATICS 877
but structure/activity relationships do not predict that they
should be particularly toxic. Nevertheless, cyclization to a
phenyl substituted dibenzofuran possibly could yield a toxic
product. The likelihood of the cyclization reaction provides
a measure for the concern to be accorded the presence of
ether precursors.
Polychlorinated naphthalenes (PCNs) have been char-
acterized in commercial PCBs and probably resulted from
the presence of naphthalene as an impurity in the biphenyl
raw material used for the manufacturing process. Typical
concentrations in PCB fluids are less than 600 ppm. Results
obtained by Kimbrough^16 and Goldstein,^14 indicated that it is
unlikely that PCNs would add significantly to the toxicity of
PCBs at the concentration levels typically observed in com-
mercial mixtures, although the stereochemical requirement
of planarity to include enzyme activity is fulfilled.
Polychlorinated biphenylenes (PCPs), because of their
structure, are expected to be as toxic as the correspond-
ingly substituted PCDDs. According to Poland and Glover,^17
2,3,6,7-tetrachlorobiphenylene is approximately as potent
as 2,3,7,8-TCDD. PCPs have been found to result from
the reductive conditions which occur in the early stages
of askarel transformer fires and are therefore compounds
of concern (Smith et al.;^18 Rappe et al.;^19 Williams et al.^20 )
(Figure 18).
Polychlorinated pyrenes (PCPYs) and polychlorinated
chrysenes (PCCYs) have been identified as components
of the soot from an askarel transformer fire (Rappe et al.^21
Williams et al.^20 ). The toxicities of these classes of com-
pounds have not been determined but their concentrations
are so low that they probably do not add significantly to the
overall toxicity of the degraded PCB.THE PERCEPTION OF PCB HEALTH EFFECTS:
THE YUSHO AND YU-CHENG POISONINGSAs was mentioned above, a large part of what is currently
known about the effects of human exposure to PCBs is
derived from two incidents of poisoning which occurred in
Japan in 1968 and in Taiwan in 1978. Both episodes involved
the contamination of rice oil used for cooking purposes, both
involved approximately the same number of people and both
involved the same total dose of PCBs (Table 14).
The poisoning in Japan in 1968 became the subject of
a special issue of the journal Fukuoka Acta Medica in June1969.^27 Many of the papers which have been written on vari-
ous aspects of the poisonings have been published in series
and there are now over 200 of them. Most of these papers are
in Japanese with English abstracts but there have also been
reviews written in English. 27 – 37
About 325 patients with acneiform eruptions had been
treated in northern Japan between the summer of 1968 and
January 1969. The apparent cause of the poisoning was traced
to the consumption of a particular brand of rice bran oil.
By May 1970 the total number of cases had risen to
1,291. The common symptoms included acneiform erup-
tions, hyperpigmentation of the skin, nails and mucous
membranes, swelling of the upper eyelids, and hyperemia of
the conjunctivae.
PCB concentration in the rice oil varied with the pro-
duction batch. The highest concentration was found to be
3,000 ppm PCB in oil shipped on February 5, 1968 and only
traces were found in oils produced after February 19, 1968.
The oil was consumed between March and October 1968
and the first known clinical examination of a Yusho patient
occurred on June 7, 1968. The onset of Yusho symptoms
occurred in the majority of patients in June, July and August
of 1968. The total quantity of contaminated rice oil ingested
by patients as well as the dose rate of ingestion of PCBs has
been estimated by several workers (T. Yoshimura et al.^38 )
(Table 15).
A typical quantity of oil consumed was 800–1200 mL con-
taining about 2g of PCB. For victims who had ingested more
than 720 mL of oil the attack rate of Yusho symptoms was
100%. The PCB content of Yusho oil was about 1,000 ppm
PCB as Kanechlor 400 (J. Nagayama et al.^39 ). Clinical features
of Yusho poisoning are listed below in Table 16.
Undegraded Kanechlor 400 has been found to contain
about 18 ppm PCDFs while the Yusho oil contained 5 ppm
PCDFs and 1,000 ppm PCBs. In addition, polychlorinated
quaterphenyls, PCQs, were found in the oil at concentrations
similar to the PCBs. The presence of these compounds ini-
tially caused the estimates of PCB contamination to be stated
at the 2000–3000 ppm PCB level. Table (14) shows the con-
centrations of PCDFs and PCBs in samples of Yusho oil.
The presence of PCDFs in the Kanechlor 400 mixture
is of great concern because if PCBs are not the major toxic
constituents of the mixture then either the ingested rice oil
contained contaminated PCBs or degraded PCBs. Several
authors have investigated the presence of PCDFs and other
toxic contaminants in commercial products prior to use.
Table 14 indicates the PCDF concentration in a number of
different rice oil products compared with the analysis of a
sample of the type used in the heat exchanger. Table 13 indi-
cates the levels of PCDFs in different Aroclors as well as
German and Japanese products. The data do not support the
hypothesis that the PCDFs were present in the Kanechlor
400 as manufactured because of their high relative concen-
trations in Yusho oils. Instead, chemical degradation of the
PCBs must have occurred, albeit in extremely low yield, to
produce degradation products of concern at concentrations
of concern. The production of PCDFs is markedly affected
by factors such as temperature, time, the presence of oxygen
and catalytic metals such as copper or iron. Miyata and
Kashimoto^41 have demonstrated that steel acts as an effec-
tive catalyst when Kanechlor 400 is heated to 360°C for 20
days. The effect of different catalysts is shown in Table 15
(Table 17).
It would be unusual to find a commercial PCB in an
application which would involve such high temperatures
unless the system was faulting in some way. The kinetics of
chemical reactions, as a rule of thumb, increase by a factor of
2 for every 10°C rise in temperature. In other words, the quan-
tity of PCDFs produced in twenty days at 350°C would be
expected to be about half the amount formed at 360°C underC016_003_r03.indd 877C016_003_r03.indd 877 11/18/2005 1:12:32 PM11/18/2005 1:12:32 PM