地沟油实际上是一个泛指的概念，是人们在生活中对于各类劣质油的通称。通俗地讲，地沟油可分为以下几类：一是狭义的地沟油，即将下水道中的油腻漂浮物或者将宾馆、酒楼的剩饭、剩菜(通称泔水)经过简单加工、提炼出的油;二是劣质猪肉、猪内脏、猪皮加工以及提炼后产出的油;三是用于油炸食品的油使用次数超过规定要求后，再被重复使用或往其中添加一些新油后重新使用的油。潲水油（俗称地沟油）对人体的危害极大，长期食用可能会引发癌症。由于销售地沟油存在不小的经济诱惑，仍有人铤而走险。据说国人每年要吃掉 200～300 万吨。据专家估计，国人每吃10顿饭中，可能会有1顿碰上地沟油。

媒体视角：Food safety is once again being put into the limelight following media reports last week that a "significant portion" of used cooking oil is being recycled and returned to people's dining tables across China.

Catering industry insiders and food safety experts say huge profits, inadequate supervision and the difficulty of disposing of used cooking oil are the main reasons that used oil is collected from kitchen waste and reused as cooking oil.

Huang Fenghong, deputy director of the Oil Crops Research Institute at the Chinese Academy of Agricultural Sciences, told the Global Times that, after seven years of field research, his research team has concluded that the use of recycled oil is rampant in some areas, especially where cash-strapped migrant workers and students are major diners.

Recycled cooking oil, dubbed "drainage oil," is refined from discarded kitchen waste and reused in the preparation of meals at restaurants and canteens.

"The use of drainage oil will put the public's health in peril because it may contain heavy metal, waste antibiotics or aflatoxins, a highly toxic substance that could cause cancer," he said.

Huang did not specify how much drainage oil China consumes each year, saying it is difficult to calculate the figure.

Earlier, He Dongping, a nutrition professor at central China's Wuhan Polytechnic University and a member of Huang's team, told the China Youth Daily on Thursday that people in China consume about 2 to 3 million tons of drainage oil a year.

"China consumes about 22.5 million tons of cooking oil annually, which means that one in 10 meals in the country may be cooked with illegal cooking oil," the newspaper quoted him as saying.

Although Huang said the media misinterpreted He's statements, which only suggested the total amount of China's recycled oil annually, the shocking report renewed concerns among authorities, experts and citizens over food safety in China.

In Wuhan, the capital of Hebei Province, the Food and Drug Bureau set up a hotline Saturday to process citizens' complaints about the use of drainage oil by restaurants or cafeterias.

A hotline worker who refused to be named told the Global Times Sunday that the line had been busy ever since it was opened. People called in to report what they said might be recycled oil at restaurants, or to report people allegedly involved in the illegal recycling business.

"Many recycling plants are based in the suburbs," Chen Debin, general manager of NZBM, a Beijing-based fast food chain with over 10 outlets in China, told the Global Times that recycling drainage oil for cooking meals is an open secret in the catering industry, and especially so for small restaurants, unlicensed restaurants, roadside food stands and in-house cafeterias.

Chen said that his restaurants don't practice oil recycling.

"They send workers to collect kitchen waste from restaurants. It is normal if they process it into pigwash or soup, but some illegal processors sell it to the black market as cooking oil," he said.

Handing over kitchen waste to private processors seems to be the only way to get rid of the waste, since the sanitation department has stopped.

--" Recycled cooking oil surfaces at tables ", 2010-3-22, Global Times