A study of streams in Indiana found that the insecticidal proteins produced by genetically modified corn ended up in 23% of tested waterways in amounts above detectible limits.
Corn genetically-modified to produce a mild insecticide has a gene added from a soil bacteria called bacillus thuringiensis. It is widely planted in the United States, making up 85% of the 2009 corn U.S. crop. The insecticidal protein the corn produces, used to ward off the European corn borer, is Cry1Ab.
In a paper published this week in the Proceedings of the National Academy of Sciences, researchers at the University of Notre Dame and Loyola University tested 217 streams, ditches and drains near corn fields and found 50 of them had levels of Cry1Ab above six nanograms per liter. It is unknown if levels that low are dangerous to invertebrates living in the water, but they were detectable.
The protein enters waterways through runoff and when corn leaves, stalks, and plant parts are washed into stream channels. To minimize soil erosion it’s become common in corn fields to leave discarded corn leaves, husks, stalks and cobs in the fields, a practice called ‘no-till’ agriculture. The researchers found this corn material in 86% of streams tested.
The study was conducted six months after crop harvest, which indicates that the proteins in the corn byproducts can persist in the landscape.
Bt is allowed to be used as a biological alternative to pesticides in organic agriculture.
By Elizabeth Weise