Residents of Harbin, capital of northern China's Heilongjiang Province, escaped it when the 80-kilometer-long toxic slick drifted across the river's half-frozen waters. Songhua. Polluting substances, mainly benzene and nitrobenzene, carcinogenic and dangerous even in small doses, which, Saturday, November 26, should no longer be present in this area, because carried by the current towards the Amur River and the Russian city of Khabarovsk.