Add another compound to the long list of agricultural pollutants in the nation's streams, rivers and waterways: the Bacillus thuringiensis or Bt toxin, a protein crystal known as Cry1Ab that kills caterpillars and other agricultural pests. A wide variety of crops, including 63 percent of the corn planted in the U.S. in 2009, have been genetically engineered to build the bacterial protein in their leaves and stems.

Those roots and stems are apparently washing into the waterways of the Midwest; 86 percent of 217 streams in Indiana surveyed by scientists contained such detritus. And, according to the results of that survey published online September 27 in Proceedings of the National Academy of Sciences, 23 percent of the streams had the Bt toxin floating in the water—six months after harvest.

All of the contaminated streams lay 500 meters or less from a corn field and, based on current maps of lands used for agriculture, the researchers estimate that 91 percent of waterways in the Midwest—Iowa, Illinois, Indiana—are within that distance from a corn field. The finding may also be the result of a practice known as "no-till" farming, in which the unused portions of the crop are left on the fields to minimize erosion, though the crop waste itself seems to end up in the adjacent streams.

Of course, these streams ultimately feed one of the great river systems of the planet—the Mississippi and Missouri river basin. Ultimately, those rivers terminate in the Gulf of Mexico, where runoff of agricultural fertilizers promotes algal blooms that end up creating vast "dead zones" of seawaters devoid of oxygen. In fact, the U.S. Geological Survey found that levels of such fertilizer runoff have remained the same or even increased since the 1990s in a recent analysis.

It remains unclear what impact the Bt toxin may be having in any of these aquatic ecosystems, if any. But it is clear now that the insecticides genetically engineered into plants—like their manufactured chemical counterparts—are capable of traveling with the rain from field to stream.

Image: Courtesy of Google Maps