Substandard pollution control equipment at the Hui County Non-Ferrous Metal Smelting Plant has been identified as the source of the lead poisoning, which can lead to severe mental retardation in children, earlier reports said.

The plant was shut last month.

Up to 1,400 people living in two villages near the plant have had their blood tested for excessive lead content, with many still awaiting test results, Xinhua said.

Since the scandal broke late last month, locals have repeatedly insisted that up to 2,000 people could have been poisoned by the plant that has operated for nearly 11 years.

The plant has spewed black smoke since it was opened, with ash and grit constantly covering crop lands surrounding the two villages, they said.

Environmental officials announced on Sunday that the plant's waste disposal system did not meet national standards and that the factory failed to undergo a mandated environmental assessment after an upgrade in 2004.

After 25 years of robust economic growth, the Chinese government has vowed to pay more attention to environmental protection as the nation's cities are some of the most polluted in the world.

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