Police have busted 60 gutter oil producers across the country in the past three months, and the production and sale of the toxic cooking oil is now under control, the Ministry of Public Security said on Monday.

The ministry launched a nationwide campaign in August to crack down on the illegal production and sale of gutter oil, or oil made from old cooking oil and food waste. During the campaign, more than 120 cases had been cracked, over 700 suspects detained, and 60,000 tons of gutter oil seized.

The gutter-oil production network was spread across 28 provinces and municipalities, according to the statement issued by the ministry. The ministry said they also shut down some workshops that produced gutter oil under the guise of producing biological diesel oil.

Even still, the public should remain vigilant of some enterprises and persons, the ministry warned.

According to Chongqing police, some licensed cooking oil enterprises are also involved in the finishing processes and marketing of gutter oil.

Some wholesalers now blend gutter oil with qualified products to avoid being detected, while seeking exorbitant profits.

"Blending makes it more difficult to detect the workshops committing the crimes," a Chongqing police officer told the Beijing News.

Food safety has been a public concern in China following several scandals in recent years, including tainted infant formula and pork tainted with clenbuterol, a banned chemical that makes pork leaner, but is harmful to humans.

Wang Chengming, a professor at South China Agriculture University, said that up to 5 million tons of gutter oil is among the 22.5 million tons of total cooking oil consumed in China each year, Southern Metropolis Weekly reported last week.

The Ministry of Health issued a notice in October to solicit methods for identifying cooking oil made from restaurant leftovers.

To better break the illegal supply of gutter oil, the health ministry drafted national standard Tuesday, requiring all catering service providers sign contracts with kitchen waste dealers and obtain authorization certificates.

It was reported that people pay some restaurants and hotels thousands of yuan each year to get the swill from which gutter oil is extracted.

These restaurants and hotels would rather sell the swill than pay the waste disposal fee to the environment and sanitation department.

The public security ministry also listed 10 open gutter oil cases. The list mentions that Nanchang-based Jiangxi Huanyu Biological Diesel Oil Enterprise made more than 1,600 tons of the oil and sold it to cooking oil companies and wholesalers in Dongguan, South China's Guangdong Province, in deals worth 13 million yuan ($2 million).