Chinese authorities have detained 38 people and seized over 30,000 tons of contaminated chicken feet, which are a popular dish in the country, Chinese news agency Xinhua reported on Tuesday.

The arrests followed raids on nine factories in the provinces of Jiangsu, Anhui, Henan and Guangdong, where police found that excess hydrogen peroxide was being added to the meat. The Chinese police are still searching for 11 suspects.

Hydrogen peroxide is widely used in manufacturing and various medical sectors, but the chemical can cause serious health problems if mixed with food.

The police operation uncovered and broke up 35 sales networks for the tainted chicken feet, often broiled or used in soups, valued at over 300 million yuan ($48.8 million), according to news agency Reuters.

China has recently been hit by widely publicized food scandals and earlier this month, U.S. ketchup producer H.J. Heinz apologized to Chinese consumers as it recalled infant cereal, which had been contaminated by excessive levels of lead.

In 2013, Xinhua reported that China had seized 20 tons of chicken feet, some of which had production dates on their packaging going back as far as 1967.

According to Reuters, China was the largest buyer of chicken feet from the U.S. last year.