US biotech company ProdiGene is facing federal investigations into two incidents in which the company accidentally contaminated crops in Nebraska and Iowa.

ProdiGene has been criticised for its failure to keep separate its plant-produced pharmaceuticals from crops destined for the US food supply.

On Wednesday this week, the US Department of Agriculture (USDA) quarantined 500,000 bushels of soybeans in Nebraska on concerns that a small amount of ProdiGene bio-corn may have been mixed with the soybean harvest. The soybeans, which are valued at US$2.7m, had been growing in a field where ProdiGene bio-corn had previously been grown.

A similar incident occurred in Iowa in September. The USDA said on Thursday that in that incident ProdiGene had been ordered to destroy 155 acres of crop.

Food companies have now urged the USDA and the Food and Drug Administration (FDA) to stop biotech firms using food crops to make proteins and compounds for pharmaceuticals. It is feared by some environmental groups that humans could suffer allergic reactions and other health problems if the biotech crops, which have not been approved for human consumption, are ingested.

The National Food Processors Association said the federal government should halt plantings of gene-altered crops for pharmaceuticals until it imposes tougher regulations to prevent future incidents.

The Grocery Manufacturers of America, whose members include major food makers such as General Mills, Kellogg and Del Monte, said it was “deeply concerned” about the ProdiGene incidents.

"We strongly urge the biotech industry to direct its substantial research capabilities into investigating the use of nonfood crops for the development of pharmaceuticals," Karil Kochenderfer, the group's environment director, was reported as saying by Reuters.

The USDA and FDA are now trying to decide whether or not ProdiGene has violated any federal regulation. If the company is found to have contravened regulations, it could face fines of $500,000 for each violation.