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Taiwan, China

In May 1979, an unusual cluster of symptoms, characterized by chloracne and hyperpigmentation of the skin and nails, was reported in Taiwan (Hsu et al. 1985). By October 1979, PCBs and their heat-degraded products in samples of rice cooking oil were identified as the cause of the outbreak. In addition to PCBs, the contaminated oil contained an unusually high concentration of PCDFs, which can be more toxic than PCBs and could explain some of the reported effects (Schantz 1996). The resulting symptom complex, Yu-Cheng disease, was similar to that described in Yusho, Japan, ascribed to PCB-contaminated rice cooking oil. By the end of 1980, 1,843 cases had been reported in four central-Taiwan counties. Most were classified as mild (40.0%) or moderate (26.2%). Most of the affected population were between the ages of 11 and 20, and most were students or factory workers. It was estimated that PCB intake was 0.7-1.84 g, and the onset of clinical signs occurred 3-4 mo after exposure (Hsu et al. 1985).

Between 1979 and 1983, 39 babies with hyperpigmentation were born to exposed mothers. Their mortality rate was high; eight infants died of a variety of causes. The registry of Yu-Cheng, maintained by the Taiwanese Bureau of Disease Control, identified 128 surviving children born to 74 exposed women between June 1978 and March 1985. Over the next 2 decades, 1 8 of the children (born to 69 mothers) were followed to identify the cognitive-development effects of prenatal (transplacental) and postnatal (breast milk) exposure to PCBs (Hsu et al. 1985; Rogan et al. 1988; Yu et al. 1991). Exposure data were incomplete: Serum PCB concentrations were available from 61 of 69 exposed mothers (mean: 49.3 ppb; maximum: 456 ppb), serum concentrations were listed for 21 of 118 children (mean: 1 ppb; maximum: 77.8 ppb), and only fragmentary dietary data were available for the mothers. All of the exposed mothers in the study, however, had exposure-related symptoms at the time of enrollment. Control children were matched for neighborhood, age, sex, mother's age, educational level, and occupation of both parents. Testers were unaware of the child's exposure status (unless revealed by the parents' chloracne). Between the ages of 4 and 7 yr, there was a consistent, statistically significant, 5-point difference in the Chinese versions of the Stanford Binet test and Wechsler Intelligence Scale for Children, Revised (WISC-R) between exposed and control children. However, there was no relationship between either the mother's or the child's PCB serum concentration and developmental outcome. When the children's scores were arrayed by year of birth, there was some moderation in the effect among the 4- and 5-yr-olds born the longest after exposure. However, data from the 6- and 7-yr-olds indicated that children born up to 6 yr after the mothers' exposure and those born within 1 yr of exposure were equally affected (Chen et al. 1992).

The Japanese and Taiwanese studies demonstrate developmental delays and cognitive defects in young children prenatally exposed to PCBs and other products of heat-degraded PCBs. Because the studies were designed to assess thecontinue