TAICHUNG FIRM: Authorities are focused on tracing the source of the contaminated oil’s raw materials, the manufacturing process and quality control systems By Hsu Kuo-chen, Fang Wei-li and Jake Chung / Staff reporters, with staff writer The Taichung District Prosecutors' Office yesterday confirmed that it has launched an investigation after about 1,300 tonnes of soybean cooking oil produced by Taichung-based Central Union Oil Corp. were found to contain excessive levels of benzopyrene.The contaminated batch has been traced to at least 200 downstream businesses nationwide.The Food and Drug Administration (FDA) was notified by Central Union Oil on Tuesday last week that batch No. 315-1150404, manufactured in April, contained excessive levels of benzopyrene — a carcinogen — during internal te