Tainted oil Officials give food warningRecycled cooking oil, sometimes tainted with bleach, is on sale at many open markets, an expert has warned. Many consumers are tricked into buying the oils through packaging which often resemble well-known brands. However, some of the oil is recycled material and has been treated with bleach to make it look more attractive to consumers, according to Udon Thani medical official Worawit Kittiwongsunthorn. “Used cooking oil contains cancer-causing substances,” he said at a food and health conference in Nonthaburi on July 25.