Pharmaceutical firms in China have been told to check their suppliers after reports that some companies have used gutter oil to make antibiotics.
Gutter oil is reprocessed kitchen waste dredged from restaurant drains. The BBC reports it has been part of a series of recent food safety scandals in China.
In April, State media reported that officials had cracked down on underground workshops that used decomposing animal fat and organs to produce gutter oil.
Police said that most of the oil was sold to oil manufacturers for food production and making hotpot soup in restaurants.
In September last year, 32 people were arrested in an operation to prevent the sale of gutter oil as cooking oil.
More than 100 tonnes of oil produced by six underground factories were seized in raids across 14 provinces.
In 2008, at least six babies died and another 300,000 were ill after drinking infant formula tainted with the chemical melamine.
