Eight people have been detained in Gansu province after more than 200 children of a kindergarten were found to have abnormal levels of lead in their blood, local officials and police said on Tuesday.

The detained include the principal and investor of Peixin Kindergarten, a privately run institution based in Maiji district in the city of Tianshui, which was set up in 2022 and enrolls 251 children. Two other people accused in the incident have been released on bail pending trial, according to a joint investigation report.

On July 1, the market supervision administration and the public security bureau of Maiji received a report about the abnormal blood lead levels of some children enrolled in the kindergarten. The two departments immediately launched a probe, and a joint investigation team comprising officials from seven relevant departments was formed.

A total of 223 samples, including raw materials, cooked food and water, from Peixin Kindergarten and three preschools that have the same investor as Peixin were tested.

Two samples from Peixin — a tricolor red date sponge cake served for breakfast and corn roll with sausage served for dinner — failed to meet food safety standards, the joint investigation found. The breakfast and dinner samples had lead content of 1,052 milligrams per kilogram and 1,340 mg per kg, respectively, both far exceeding the national food safety standard limit of 0.5 mg per kg for food contaminants, the report said.

Public health experts said that elevated levels of lead in the blood could cause abdominal pain, anemia and hyperactivity. At higher concentrations, lead exposure could result in seizures, coma, or long-term neurological damage.

The joint investigation also revealed that the kindergarten's principal, surnamed Zhu, and its investor, surnamed Li, allowed kitchen staff to purchase brightly colored industrial pigments through online platforms and use them in preparation of food after dilution.

As of Monday, all 251 children were examined by doctors, and 233 of them were found to have abnormal blood lead levels. By Tuesday, 201 children were sent to hospitals for treatment.

Sun Chengye, chief expert of poison control at the Chinese Center for Disease Control and Prevention, said the National Health Commission sent experts to Tianshui on Friday to guide on-site handling of the incident.