Monsanto's Roundup herbicide may be dangerous to plants, animals, and humans.

From Alternet:

Dr. Don Huber did not seek fame when he quietly penned a confidential letter to Secretary of Agriculture Tom Vilsack in January of this year, warning Vilsack of preliminary evidence of a microscopic organism that appears in high concentrations in genetically modified Roundup Ready corn and soybeans and "appears to significantly impact the health of plants, animals and probably human beings." Huber, a retired Purdue University professor of plant pathology and U.S. Army colonel, requested the USDA's help in researching the matter and suggested Vilsack wait until the research was concluded before deregulating Roundup Ready alfalfa. But about a month after it was sent, the letter was leaked, soon becoming an internet phenomenon.

Huber was unavailable to respond to media inquiries in the weeks following the leak, and thus unable to defend himself when several colleagues from Purdue publicly claiming to refute his accusations about Monsanto's widely used herbicide Roundup (glyphosate) and Roundup Ready crops. When his letter was finally acknowledged by the mainstream media, it was with titles like "Scientists Question Claims in Biotech Letter," noting that the letter's popularity on the internet "has raised concern among scientists that the public will believe his unsupported claim is true."

Now, Huber has finally spoken out, both in a second letter, sent to "a wide number of individuals worldwide" to explain and back up his claims from his first letter, and in interviews. While his first letter described research that was not yet complete or published, his second letter cited much more evidence about glyphosate and genetically engineered crops based on studies that have already been published in peer-reviewed journals.

The basis of both letters and much of the research is the herbicide glyphosate. First commercialized in 1974, glyphosate is the most widely used herbicide in the world and has been for some time. Glyphosate has long been considered a relatively benign product, because it was thought to break down quickly in the environment and harm little other than the weeds it was supposed to kill.

According to the National Pesticide Information Center, glyphosate prevents plants from making a certain enzyme. Without the enzyme, they are unable to make three essential amino acids, and thus, unable to survive. Once applied, glyphosate either binds to soil particles (and is thus immobilized so it can no longer harm plants) or microorganisms break it down into ammonium and carbon dioxide. Very little glyphosate runs off into waterways. For these reasons, glyphosate has been thought of as more or less harmless: you spray the weeds, they die, the glyphosate goes away, and nothing else in the environment is harmed.

But Huber says this is not true. First of all, he points out, evidence began to emerge in the 1980s that "what glyphosate does is, essentially, give a plant AIDS." Just like AIDS, which cripples a human's immune system, glyphosate makes plants unable to mount a defense against pathogens in the soil. Without its defense mechanisms functioning, the plants succumb to pathogens in the soil and die. Furthermore, glyphosate has an impact on microorganisms in the soil, helping some and hurting others. This is potentially problematic for farmers, as the last thing one would want is a buildup of pathogens in the soil where they grow crops.