At least 31 residents in an east China county have been found to have elevated levels of lead in their blood after the metal was improperly disposed of by a local battery plant, officials said Monday.

Investigators from the environmental protection authority of eastern Zhejiang Province concluded that the lead poisoning incident in Deqing County was caused by Zhejiang Haijiu Battery Co., Ltd.'s "illegal disposal of industrial waste" and lax supervision by a local environment watchdog.

Three-hundred and seventeen villagers have taken blood tests in Deqing so far, according to a spokesman from the county government. Thirty-one of the villagers, including 11 children, were found to have excessive amounts of lead in their blood, and others are still awaiting their test results, the spokesman said.

Excessive amounts of lead in the blood can damage the digestive, nervous, and reproductive systems and cause stomachaches, anemia and convulsions.

The head of the battery plant is being questioned by the police and the plant's operations had been halted, according to the spokesman.

Authorities have ordered a thorough safety check for all 273 battery factories in Zhejiang.

Haijiu Battery Co., Ltd., founded in May, 2003, mainly produces lead-acid batteries for motorcycles. It has about 1,000 employees and an annual output of 9 million batteries.