More than 200 children were hospitalized this month after they were fed food tainted with lead in a kindergarten in northwest China, a food safety scandal that has set off a public uproar and raised questions about local officials’ ability to protect the health of children.

The police in Tianshui, a city in Gansu Province, have detained eight officials and employees of the privately owned kindergarten, including the principal and an investor. They found that school cooks used inedible pigments bought online to decorate buns and cakes that were served to the children, Chinese state media reported on Tuesday.

The head of the Tianshui police, Guo Qingxiang, said that an investigation showed that the school sought to use photos of the colorful food for marketing purposes, to try to increase enrollment, according to the state broadcaster CCTV. The food included sausage buns made to look like bright yellow corn on the cob and red date cakes with layers of teal and pink.

Security camera footage posted by state media taken from the school, Peixin Kindergarten, appeared to show kitchen workers adding bright yellow powdered pigments to a bowl of flour.

Investigators found that samples of the sausage buns and the red date cakes contained traces of lead that were more than 2,000 times higher than the national food safety standard of 0.5 milligrams per kilogram for any contaminant.

There also appeared to be skepticism over whether local officials were willing to confront the scandal. Reports of the poisoning first emerged on July 1, but some parents complained that local clinics in Tianshui did not properly test and diagnose their children, state media reported. That prompted some families to travel more than 200 miles east to the city of Xi’an to have their children tested and confirmed for lead poisoning.

By Monday, all 251 children at the school had been tested (though state media did not say where). Of them, 233 children were found to have abnormally high levels of lead in their blood, state media reported. Some remain hospitalized.

Investigators raided the school last Thursday and seized the school’s stock of powdered pigments.

Peixin Kindergarten received its school qualification certificate in June 2022 and began enrolling students in late August of that year, state media reported.

Food safety remains a sensitive subject in China. But conditions have improved from more than a decade ago, when scandals like milk powder contaminated with melamine and recycled cooking oil regularly made headlines.

Tianshui was the site of another lead poisoning incident in 2006 when more than 200 people were found to have high levels of the toxin in their blood. No official cause was ever announced, though a nearby lead and zinc smelter plant was accused of illegally releasing waste into the area.