Illinois, the No. 2 U.S. corn producer, has requested that the U.S. Food and Drug Administration (FDA) allow the state to let its grain handlers blend corn containing aflatoxin, a naturally-occurring toxic substance, with other grain to make animal feed.

The request comes less than a week after Iowa, the biggest U.S. corn state, received a similar FDA allowance.

Aflatoxin is the byproduct of a mold that tends to spread in corn during times of drought, which gripped the Corn Belt this summer.

The FDA generally forbids grain handlers from mixing corn containing aflatoxin with "clean" grain, but it has relaxed this policy during years of widespread aflatoxin problems upon the request of state officials.

In a letter to the FDA dated Monday, the Illinois Department of Agriculture said the state "has experienced one of the most severe droughts in recent history" and that initial results from a statewide survey show above-normal levels of aflatoxin in corn.

"As a result of the dry growing conditions, there is a general concern that this year's crop has experienced decreased yields, quality issues and the presence of potentially higher levels of aflatoxin than is normally experienced," the letter said.

Under FDA guidelines, certain types of animal feed can contain an aflatoxin concentration of up to 300 parts per billion (ppb). Human foods must contain less than 20 ppb, while the threshold for milk is even lower, at 0.5 ppb.

Last month, Iowa began requiring the state's dairy processors to test all milk received in the state for aflatoxin.

In Illinois, the state Department of Agriculture said initial results from a statewide sampling of the corn harvest showed that 18 of 223 samples contained 100 to 200 ppb of aflatoxin, and six samples contained more than 200 ppb.

Aflatoxin can cause liver disease and is considered carcinogenic.

Human exposure to high amounts of aflatoxin is rare. Aflatoxin contamination prompted a series of pet food and livestock food recalls last December, including products produced at Cargill's Lecompte, Louisiana, plant and Procter & Gamble Co's plant in Henderson, North Carolina.