China's top environment watchdog has started to set a specific standard for evaluating the impact of lead pollution on human's health, in the wake of a major lead poisoning case in the northwest region.

The State Environmental Protection Administration (SEPA) has dispatched a five-member team of investigators and will base the new standard on their inspection results, said an official with SEPA on Tuesday.

The poisoning case swept Xinsi and Muba villages in Huixian County in northwest China's Gansu Province, with the number of victims up to 368 by last Friday.

Health experts are now carrying out a general check among all residents in the region identified with lead pollution by SEPA investigators.

Earlier tests showed that the lead content in the blood of four of the poisoned children was three and half times higher than the normal level. One hundred and forty-nine children had been hospitalized with lead poisoning.

Three of the adult patients showed levels three times great than the normal level.

The smelter blamed for the pollution has been shut down. Mining and smelting of lead and zinc ores are the major source for lead pollution, which also exists in some areas in Liaoning, Hubei, Guizhou and Anhui provinces.

Lead is a major pollutant threatening children's health. A survey by the World Health Organization showed that 10.45 percent of the 17,000 children aged between 0 to 6 in China's 15 cities were found being lead-poisoned to various degrees in 2004.