Indiana University Assistant Professor Todd Royer said the study suggested pollen and other plant parts containing toxins from genetically engineered Bt corn are washing into streams near cornfields.

The researchers determined consumption of Bt corn byproducts produced increased mortality and reduced growth in caddisflies -- aquatic insects that are related to the pests targeted by the toxin in Bt corn.

Royer noted caddisflies are a food resource for higher organisms, such as fish and amphibians.

"If our goal is to have healthy, functioning ecosystems, we need to protect all the parts," said Royer. "Water resources are something we depend on greatly."

The study, which included Emma Rosi-Marshall of Loyola University, Jennifer Tank of the University of Notre Dame and Matt Whiles of Southern Illinois University, appears in the Proceedings of the National Academies of Sciences.