Pesticidal Proteins (Bt) From GM Corn Plants Are Now Common In Midwest Streams


Short-lived, non-biting, adult lake fly - Chironomus plumosus.
Image credit:Wikipedia

Common sense tells us that, following corn harvest, fragments of corn cobs, leaves, stalks, silk, and pollen may be blown by the wind or carried across the land surface by runoff. Corn plant residues will end up in the sediments of streams lakes and reservoirs. Scientists call the result detritus. The rest of us call it 'muck.' It follows that if most of the corn being grown is genetically modified ("GM") to contain toxic levels of Bt pesticide, as is currently the case throughout the corn belt, Bt residues are 'in the muck' - so to speak.

Are Bt pesticide residues in river muck of sufficient concentration to be toxic? Based on recent stream sampling done in Indiana, the exposure to pesticides of aquatic organisms could indeed be high - potentially impacting several of the thousands of chironomidae (aquatic insect) species found in North American streams ponds and lakes.From Proceedings of the National Academies of the Sciences, here is the full abstract of Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape

Widespread planting of maize throughout the agricultural Midwest may result in detritus entering adjacent stream ecosystems, and 63% of the 2009 US maize crop was genetically modified to express insecticidal Cry proteins derived from Bacillus thuringiensis. Six months after harvest, we conducted a synoptic survey of 217 stream sites in Indiana to determine the extent of maize detritus and presence of Cry1Ab protein in the stream network. We found that 86% of stream sites contained maize leaves, cobs, husks, and/or stalks in the active stream channel. We also detected Cry1Ab protein in stream-channel maize at 13% of sites and in the water column at 23% of sites. We found that 82% of stream sites were adjacent to maize fields, and Geographical Information Systems analyses indicated that 100% of sites containing Cry1Ab-positive detritus in the active stream channel had maize planted within 500 m during the previous crop year. Maize detritus likely enters streams throughout the Corn Belt; using US Department of Agriculture land cover data, we estimate that 91% of the 256,446 km of streams/rivers in Iowa, Illinois, and Indiana are located within 500 m of a maize field. Maize detritus is common in low-gradient stream channels in northwestern Indiana, and Cry1Ab proteins persist in maize leaves and can be measured in the water column even 6 mo after harvest. Hence, maize detritus, and associated Cry1Ab proteins, are widely distributed and persistent in the headwater streams of a Corn Belt landscape.

If you need pictures to be convinced of the movement of plant materials, have a look at a post I wrote back in August.
Bt is toxic to the chironomidae. This includes mosquitoes, midges, "lake flies," and thousands of other species (some of which have not been well described in the literature).

What we can say is that many of the exposed aquatic organisms, especially the muck dwelling larval forms, are important food for fish. Lake Sturgeon, for example, feed extensively upon lake fly larvae, sp. Chironomus plumosis, (adult form is pictured above).

Important update:
I have a hunch based on comments that not too many of our readers have a detailed understanding of watershed dynamics. Here are a few points that may help with understanding the eco-risk on a watershed scale.


  • Muck exists at depth in places where stream turbulence is low, such as in deep pools or at the downstream end of a sand/gravel bar. In lakes and ponds it accumulates off the lee shore or amidst dense stands of aquatic plants or at great depth.

  • Oxygen is very low in muck - dissolved oxygen is found only a few mm deep in summer and a few cm deep in winter - and hence biodegradation rates fo muck are very slow, which is why muck accumulates!

  • The larval forms of insects which evolved to live on the surface layers of muck play a key roll of mixing and assisting with oxidative degradation.

  • Bt corn has only been a predominant type in the corn belt since the late 1990's and later in some areas. It is a recent situation where large acreages are near stream courses.

  • Paradoxically, the stream insect life forms which are of concern could have already been extirpated in some areas, depending upon exactly how much Bt they had been exposed to.


Additional posts on GM corn
Monsanto "Seedless" Corn Sold To South African Farmers :
While Bill Gates Wants Africa to Embrace Industrial GM Food,

Tags: Corporate Responsibility | Great Lakes