Referring to the contamination that has prompted the recall of more than 100 brands of pet food, he said investigators are trying to determine whether Chinese producers purposely added melamine to their wheat gluten shipments to Menu Foods.
The Food and Drug Administration found melamine, a plastic component whose use is not approved in food, in pets that died. Investigators traced the melamine to wheat gluten, shipped from China, that is used to thicken pet food.
According to Durbin, investigators are examining whether Chinese manufacturers added nitrogen-rich melamine to wheat gluten in order to raise its nitrogen level. Nitrogen levels are measured to calculate the protein content, which determines the value of a shipment.
The FDA is sampling all imports of wheat gluten from China and the Netherlands, which also received shipments from China. The agency says it has found no evidence that the wheat gluten entered the human food supply.
A bag with the word "melamine" stenciled on the side was found Sunday in a shipment of rice protein concentrate, a second pet food ingredient that has been linked to the pet food scare.
Investigators want to visit Xuzhou Anying Biologic Technology Development Co. Ltd., the suspected wheat gluten producer, and Binzhou Futian Biology Technology Co. Ltd., which is thought to have made the rice protein, according to Durbin.
But FDA Commissioner Andrew C. von Eschenbach told the senator that investigators haven't been able to make the trip because they cannot get visas from the Chinese government. FDA officials did not respond to requests for comment.
Durbin and Democratic Rep. Rosa L. DeLauro of Connecticut wrote yesterday to China's ambassador to the United States, protesting the failure to respond to visa requests from the FDA on April 4 and 17 and urging cooperation in the investigation.
A man who answered the telephone at the Chinese embassy's press office refused to confirm that visas had not been granted. Xuzhou Anying, the manufacturing company, has denied making the tainted wheat gluten.
The developments come a month after Menu Foods, of Ontario, Canada, recalled 60 million cans of pet food following reports of kidney problems and deaths in dogs and cats.
The recall has since expanded to more Menu Foods products, as well as food made by other companies that found tainted wheat gluten in their brands.
On Tuesday, Natural Balance Pet Foods Inc. recalled Venison and Brown Rice canned and bagged dog foods and dog treats, and Venison and Green Pea dry cat food.
The company, based in Pacoima, Calif., said it acted after pet owners reported kidney failure in some dogs and one cat that ate its food.
Laboratory tests on the Natural Balance products indicated that they contained melamine. Natural Balance doesn't use wheat gluten, but recently began using rice protein concentrate, which the testing indicated had melamine.
The rice protein was distributed in the United States by Wilbur-Ellis Company. On Sunday, the San Francisco company found a bag with the word "melamine" stenciled on the side in a shipment of rice protein concentrate it had received from China.
The bag tested positive for melamine, and the company has sealed the rest of the shipment in a warehouse until it completes safety tests, Wilbur-Ellis said on its Web site.
Durbin met with the FDA officials after complaining about the agency's handling of the pet food scare. He and DeLauro plan to offer legislation that would require FDA to develop national inspection standards for pet food-making facilities, rather than relying on states.
The proposed measure would also strengthen penalties that FDA could impose on pet food makers who delay reporting safety problems, an accusation critics have levelled against Menu Foods.
Durbin, the Senate's second-ranking Democrat, said von Eschenbach should have already penalized Menu Foods for waiting three weeks to report its concerns.