Variation in half-life of penta-chlorodibenzofuran (PeCDF) blood level among Yusho patients
Introduction
Yusho (oil disease), is the name given to a food poisoning incident caused by rice bran oil contaminated with polychlorinated biphenyls (PCBs) that occurred in west Japan, particularly around northern Kyushu island, in 1968 (Yoshimura, 2003, Furue et al., 2005). At that time, PCBs were considered to be the causative agent because they were used as a heat conductor during the refining process of rice bran oil. Later studies have suggested that 2,3,4,7,8-penta-chlorodibenzofuran (PeCDF), one of the dioxins formed by heat denaturation of PCBs, may have also been a causative agent. Presently, the causative agents of Yusho are considered to be PCBs and their by-products (dioxins) (Imamura et al., 1977, Toyota et al., 1999, Yoshimura, 2003, Iida et al., 2003, Furue et al., 2005).
Advancement in techniques to measure dioxins including PeCDF has made it possible to determine the blood level of dioxins in regular blood samples. Thus the blood levels of dioxins have been measured since 2001 in Yusho patients who have medical check-ups (Todaka et al., 2003, Kanagawa and Imamura, 2005). Seven years have now passed since this began, enabling an estimation of the half-life of the dioxins in the blood of actual patients. This study aims to estimate the half-life of PeCDF based on the changes in PeCDF blood levels measured in more than 300 Yusho patients.
Section snippets
Subject data
The subjects were 326 patients who had the level of PeCDF in their blood measured three times or more during regular Yusho medical check-ups from 2001 to 2006. The technique for measuring PeCDF used in the medical checkups is described in Tokunaga et al. (2005). Thirty-eight patients underwent an annual check-up in all 6 years, 124 patients had five check-ups, 74 had four and 90 had three. Since this study aimed to calculate the half-life of PeCDF in each patient, all patients whose PeCDF
Average decay rate by blood PeCDF level
Table 1 shows the average decay rates and the standard deviation ranges by blood level. In the patient group with PeCDF levels of less than 20 pg g−1, the average decay rate was −0.0057 (estimated half-life: 176 years). In the 20–50 pg g−1 group, the average decay rate was 0.0083, which suggests that the concentration may be doubled in 120 years. These data show that blood PeCDF levels hardly decreased in the low level groups. On the other hand, all groups with 50 pg g−1 or more showed a decreasing
Discussion
Dioxins have been responsible for various human health hazards and damage, for instance Yusho in Japan, Yucheng in Taiwan (Hsu et al., 1985, Guo et al., 2004) and the incident in Seveso (Bertazzi et al., 1998, Pesatori et al., 2003). Once taken into the body, dioxins usually accumulate in fat because of their high affinity for fat. Many studies have investigated the half-life of dioxins in rat and human (Ryan et al., 1993, Geyer et al., 2002, Kerger et al., 2006, Leung et al., 2007). Geyer et
Acknowledgment
This study was supported by a Grant-in-Aid for scientific research from the Ministry of Health, Labour and Welfare, Japan (Research on Food Safety, H18-012).
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