Production at two factories has been halted after 21 children in a residential compound in east Shanghai suffered lead poisoning, local authorities said Wednesday.

“A total of 756 children in Kangqiao Town in the Pudong New Area were tested in hospital. Among them, 21 have been confirmed to have high levels of lead in their blood,” Bai Yun, head of the Public Health Administration of Pudong’s health department, told the Global Times. 

Ten of them with lead level counts of more than 250 micrograms per liter have been sent to Xinhua Hospital for treatment. Another 11 children whose lead levels were between 100 and 250 received outpatient treatment and were given medicine, Bai added.

“If lead is more than 100 micrograms, it may prevent intellectual development, especially in kids,” said Wang Wei, vice director of the pediatrics department at Ruijin Hospital.

Ju Chunfang, a senior official from Pudong’s Environmental Protection Department, said that Johnson Controls, an American battery manufacturer, is likely the source of the lead poisoning. The company used 20,060 tons in the past nine months.

Ma Tianjie, head of the pollution prevention department at Beijing office of Greenpeace, said that many previous lead poisoning cases were due to factories. 

“Food and water nearby are vulnerable to contamination, which could cause a long-term effect on human health,” he said. 

Lu Wenjun, who lives near the factories, claimed on a local Internet forum Sunday that lead in children’s blood was found to be too high when they were given annual physicals before school. He said he’s also worried about his pregnant wife. 

Costs of examinations are covered by residents now, however the town press officer said the local government will make their best efforts to help with treatments.

It usually takes the patients two to three phases of treatment to eliminate lead out from their body. 

Each phase lasts about one week. Since the procedure harms the kidneys, a week of rest is recommended.