The world's worst polychlorinated biphenyl (PCB) contamination incident plagues male victims two decades later in their weakened ability to father boys. In 1979, 2,000 people in Yu-Cheng, Taiwan, were exposed to PCBs from contaminated cooking oil. Only 46% of children born to young men exposed in this oil disaster are male (compared to a world average of 51-52%), report a team of researchers from London and Taiwan in the 13 July 2002 issue of The Lancet. Women exposed in the same incident showed no abnormalities in the sex ratio of their offspring.
PCBs are synthetic organic chemicals used extensively for five decades to insulate electrical equipment. PCBs were used as a heat-transfer medium in processing the rice oil involved in the Yu-Cheng incident. PCBs accidentally leaked from a pipe into the oil, and polychlorinated dibenzofurans (PCDFs) were formed as a by-product during the oil processing as well as later during cooking.
PCBs were banned in the United States more than 25 years ago, but persist in the environment and accumulate in body fat. "Some PCBs are forever," says Walter Rogan, a senior epidemiologist at the NIEHS and a researcher in earlier Yu-Cheng studies. "They don't degrade or metabolize. They're very stable." PCB levels in Yu-Cheng victims remain about 20 times the U.S. average, according to Rogan, and their PCDF levels are 10,000 times the U.S. average.
The researchers don't understand how the chemicals alter sex ratios; they've had few exposed populations to study and are unable to replicate the phenomenon in animal models. But they suspect that PCBs somehow inhibit either sperm carrying the male Y chromosome or the XY-fertilized egg. Only men carry the sex-differentiating chromosome, which could explain why exposed women had children at normal sex ratios.
The researchers analyzed the sex of children born between 1979 and 1999 to 996 exposed mothers and 693 exposed fathers. (In a few couples, both parents had been exposed, but there were too few of these couples to be considered a study group.) For every exposed …