Waste cooking oil (hogwash oil) is oil extracted from leftovers. According to the calculation of relevant departments, all kinds of hotels in this city produce not less than 3000 tons of gutter oil every month. According to the regulations of relevant departments, the waste cooking oil can be recycled for environmental protection. One is processed into "butter", which is widely used for lubrication in mechanical equipment, and the other is used as a raw material for making candles or soap. However, in recent years, some unscrupulous traders have refined waste oil into "edible oil" for higher profits, which directly endangers people's health and food safety.

Waste oil is very harmful. According to scientific experiments, the rancidity and carbonyl value of waste cooking oil far exceed the national hygienic index of edible oil. The rancid oil will destroy several enzyme systems, such as cytochrome. High oxidation of oil will produce aflatoxin, which can lead to many cancers. Animals who eat rancid oil for a long time will lose weight and develop stunted. The highly toxic aflatoxin in gutter oil is 100 times more toxic than arsenic, and it is the strongest chemical carcinogen found so far. Experiments show that long-term low-dose use of aflatoxin can cause liver cancer in 100% animals, and cancer can also occur in other parts, such as gastric adenocarcinoma, renal cancer, rectal cancer and cancer in breast, ovary and small intestine.