880 PCBs AND ASSOCIATED AROMATICS
TABLE 18
The relative ratios of toxic contaminants in Yusho and Yu-Cheng oils are constantConcentrations in Oil (ppm)Type of oil PCBs PCQs PCDFs PCDF : PCBYu Cheng:
Chen et al. (1984) 74 40 0.27 1:274
Kunita et al. (1984) 44 17 0.14 1:314
Masuda et al. (1982) 80 135 0.09 1:888
Yusho:
Kunjita et al. (1984) 430 630 3.8 1:113
Nagayama et al. (1976) 1,000 — 5 1:200
Masuda et al. (1982) 900 800 2 1:400P.H.-S Chen et al.^49TABLE 19
The most likely blood PCB level in Yu-Cheng victims
was in the range 51–100 ppbBlood level (ppb) Number Percent 10 29 5
11–50 143 23
51–100 272 44
101–150 91 15
151–200 28 5
201–300 24 4
301–400 17 3
401–500 4 1
500 5 1Cull and Dobbs^44 analysed two service aged PCB
transformers but did not find an unusually high
concentration of PCDFs.A similar incident to the Yusho poisoning occurred in
Taiwan in 1978–1979 and is now known as the “YuCheng”
incident. There are many coincidental similarities between
the two poisonings. Approximately 2,000 victims were
identified in the Yu-Cheng incident compared with a total
of about 1,800 Yusho victims. The sources of poisoning, the
toxic constituents and their health effects are very similar.
The source of the toxic constituents in the Yu-Cheng
incident was derived from Kanechlor 400 and 500 used in
a heat exchanger for the production of rice oil. The concen-
tration of polychlorinated aromatic hydrocarbons in the oil
was lower in Yu-Cheng than in Yusho but because the rate
of ingestion was higher in Yu-Cheng the total doses were
approximately the same. The amount of PCBs ingested by
victims in the two incidents was about 0.8 to 1.8 g.
Table 14 shows the distribution of toxic constituents con-
tained in the Yusho and Yu-Cheng oils and from the ratios ofPCBs: PCDFs it is possible to calculate the minimum effec-
tive dose of PCDFs about 1 mg. The blood PCB levels found
in Yu-Cheng victims measured within the first year of expo-
sure range between 3 and 1,156 ppb although 44% of the
cases had 51–100 ppb in their blood as shown in Table 19.
The relative rates of elimination of PCBS, PCQs and
PCDFs from the blood has been established to be PCQ
PCDF PCB although the differences between them are
small^.^6 The prominent clinical features of Yu-Cheng have
been correlated with exposure to Yu-Cheng oil as well as
to estimates of intake and blood levels of PCBs. Features
include pigmentation of the skin, gingiva and nails, chlor-
acne, meibomian gland enlargement, and eye discharge.
Subjective complaints against Yu-Cheng patients include
increased eye discharge, edema of eyelids, vision distur-
bances, general malaise, numbness of joints, headache and
dizziness, pain in joints and muscles and other less frequently
occurring ailments.
Several investigators have concluded that PCDFs were
the primary causative agents in both Yusho and Yu-Cheng
poisonings. Toxicity studies with PCQ mixtures similar to
those in Yusho oil suggest that PCQs are less toxic in rats
and cynomolgus monkeys than either PCBs or PCDFs.^6
A blood concentration of 40 ppb in Yu-Cheng vic-
tims was found to be a level above which severe skin and
ocular effects became frequent. This is in contrast with
the blood levels of PCB exposed populations who have as
much as 300 ppb in their blood without there being evi-
dence of severe health effects. This observation points to
the relative effect of other constituents in the Yusho and
Yu-Cheng oils as well as the possibility of PCB isomer
differences. For example, highly toxic PCB isomers such
as 3,3’,4,4’-tetraCB are 2,3,3’,4,4’,5-hexa-CB were more
prominent in the tissues of Yusho and Yu-Cheng victims
than are normally found in samples of Kanechlor 400. 52,53
Blood levels of PCBs in Yusho and Yu-Cheng victims re-
tuned to background levels over a period of about 7 years
but the signs and symptoms of Yusho have persisted for over
25 years. The above data suggest that even though the ratioC016_003_r03.indd 880C016_003_r03.indd 880 11/18/2005 1:12:32 PM11/18/2005 1:12:32 PM