PCBs AND ASSOCIATED AROMATICS 875
et al.;^8 Humphrey;^10 Unger et al.^11 ). However, the health
effects in occupationally exposed workers are typically com-
plicated by such factors as incomplete exposure information,
job turnover and low chemical specificity.
The most prominent and consistent health effect associ-
ated with exposure to PCBs are chloracne and dermatitis.
These effects usually clear up quickly and, if they were the
only effects, would reduce the need for concern. It is beyond
the scope of this paper to investigate all the health effects
associated with PCBs but there is little doubt that PCBs
are compounds of concern. The concentration at which this
occurs is much higher than that of many other classes of
chlorinated aromatic compounds. The risk associated with
exposure to PCBs can be separated into a consideration of
the biological activity of PCB isomers contained in the PCB
mixture and the biological activity and probability of forma-
tion of degradation products and oxidation products.Estimates of the dosage of toxic compounds received by
victims of the Yusho and Yu-Cheng poisonings were somewhat
dependent upon the chemical specificity of the analytical meth-
ods used. There is no doubt that the PCB involved had under
gone partial oxidation and consequently, the overall toxicity of
the fluid was the combined effect of compounds of concern.
In 1970 Vos et al.^12 showed a correlation between the
toxic effects of European PCBs and the concentration levels
of PCDFs. The relative concentrations of the PCDF isomers
present in Yusho oil and in two samples of other used heat
exchanger PCBs (Kanechlor KC400 and Mitsubishi-Monsanto
T1248) were found to be strikingly similar. This fact under-
scores the work of Kunita et al.^6 who have concluded that not
only are PCDFs orders of magnitude more toxic than PCBs
but claimed also that there is a synergistic action between
them. The evidence suggests that PCDFs were a major caus-
ative agent in the Yusho and Yu-Cheng incidents.FIGURE 17 The dioxin-like isomers of PCBs.C016_003_r03.indd 875C016_003_r03.indd 875 11/18/2005 1:12:30 PM11/18/2005 1:12:30 PM