The U.S. military offered an official apology to South Koreans today for dumping formaldehyde, a toxic chemical and suspected carcinogen, into the Han River, a main source of drinking water for Seoul’s 12 million citizens. The apology came after some 250 South Koreans held an anti-America protest in Seoul on Saturday, pelting an effigy of a U.S. soldier with eggs and demanding that President Clinton apologize for the pollution, which was dumped into the river in February from a U.S. military base.