Pharmaceutical firms are under investigation after claims of using "gutter oil," rather than the more expensive soy bean oil in antibiotic production.

"Gutter oil," is reprocessed kitchen waste dug up from restaurant drains.

Among the latest companies, Chinese officials are investigating are Qilu Pharmaceutical Co., Charoen Pokphand Group, and two Shenzhen-listed forage makers, Beijing Dabeinong Technology Group and Tangrenshen Group Co.

According to Chinese officials in 2010 and 2011 more than 30,000 tons of gutter oil was processed by Huikang Grease, which stood trial on August 30.

Qilu Pharmaceutical Co., along with Jiaozuo Joincare Biological Product Co., used gutter oil to develop colonies during the production of a variety of antibiotics, which violates Chinese laws that explicitly state drug makes must use cooking oil to develop colonies of chemical compounds.

In the last few years gutter oil has become an increasingly new scandal sweeping Chinese provinces. In 2008 approximately six infants died, while nearly half a million had become ill drinking infant formula contaminated with the chemical melamine.

In 2011, following a four-month police inquiry, police detained 32 individual's in an operation to prevent sale of gutter oil as cooking oil. Of the raids across 14 provinces, more than 100 tons of oil were seized.

Earlier this year state-run media published an article chronicling the authorities bust on underground workshops that used decomposing animal fat and organs to produce gutter oil. According to officials most of the oil was sold to oil companies for food production or used in making hotpot soups in restaurants.

The Chinese government has arranged for experts to assess the health risks of using gutter oil in the production of antibiotics.

The Chinese government is unsure of the health risks that may come along with consuming antibiotics made of gutter oil. The government plans to release an inquiry regarding its findings soon.