By waste gases

Open-Hearth Process Method of steelmaking in which pig iron and scrap in a hearth are alternately heated by waste gases and then by incoming air and fuel gas also known as the Siemens-Martin process. 

Source of dioxins in nearly 50 affected farms were old bakery products, which were dried by waste gases from contaminated fuel. Food and feed raw materials imported from developing countries may also be hazardous materials. In 2007, the Rapid Alert System for Food and Feed (RASFF) pointed out a high concentration of PCDD/PCDF (exceeding normal quantities by up to 1000 times) in guar gum found by control laboratories in Switzerland. The source of contamination was impurities in low-quality biocidal product... 

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