BEIJING (AP) -- Chinese officials have found large batches of milk powder laced with a deadly industrial chemical in at least three provinces that was apparently left over from a milk scandal in 2008 that killed six babies and sickened hundreds of thousands.
The discovery shows that toxic milk remains a danger in China despite a crackdown in which dozens of people were arrested and two -- a dairy farmer and a milk salesmen -- were executed for producing or selling toxic milk.
State media and food safety experts said the recently seized melamine-tainted powder was probably produced in or before 2008 and stockpiled instead of destroyed. China ordered tens of thousands of tainted milk products burned or buried after more than 300,000 children were sickened and at least six died from the contamination. But, crucially, the government did not carry out the destruction itself.
"It is crucial to account for the amount that was contaminated back in 2008 and make sure it is being destroyed or disposed of safely," said Dr. Peter Ben Embarek, a World Health Organization senior scientist on food safety based in Beijing. "As long as part of it is still not accounted for or destroyed properly we will unfortunately see these types of things happening again."
Tainted batches were also found earlier this year in Shanghai and the provinces of Shaanxi, Shandong, Liaoning and Hebei, prompting a 10-day emergency crackdown with inspection teams fanning out to 16 provinces.
Melamine is added to watered-down milk to make it appear rich in protein in quality tests that measure nitrogen, found in both melamine and protein. Health problems from the chemical include kidney stones and kidney damage.
The official Xinhua News Agency reported that the latest discovery occurred in June when authorities found 64 tons of raw materials for making milk powder and 12 tons of finished powder tainted with melamine at a factory in the far-western province of Qinghai. In a separate case, also in June, authorities seized about 1,000 packets of tainted milk powder in the northeastern province of Jilin, Xinhua said.
The owner and a production manager from Dongyuan Dairy Factory in Qinghai have been detained after tests showed some of their products had 500 times the legal limit for melamine, the report said.
The contamination was discovered because Dongyuan sent samples of the powder, which they had purchased from Hebei province, to a lab for testing so they could figure out how much to dilute it before selling it, Xinhua said, citing police.
Dongyuan had already sold some of the tainted goods to businesses in Jiangsu and Zhejiang provinces, it said.
In Zhejiang, about three tons of Dongyuan milk powder was used to make ice cream and other products, but most was still being processed and had not entered the market, Xinhua quoted a provincial food safety official as saying.
The Xinhua report didn't say whether there were any reports of people getting sick from the products.
The phone at the Dongyuan factory rang unanswered Friday and China's Administration of Quality Supervision Inspection and Quarantine did not immediately respond to a faxed request for comment.
Zhang Zhongjun, a representative for the U.N. Food and Agriculture Organization in Beijing, said the latest discoveries highlight China's ongoing struggle to step up food safety.
"We think the situation is improving but there are still some problems," Zhang said. He said many manufacturers are small-scale operations with little food safety awareness and numerous agencies handle enforcement, creating confusion that lets some offenders slip through the cracks.
Embarek, the WHO expert, said a food safety law passed last year has tough new standards for dairy and infant formula, but it will take time to train companies to implement them and regulators to enforce them.
"It will take years to put into practice, but the country is on the way to doing that," he said.
Associated Press researcher Zhao Liang contributed to this report.