The world is awash in glyphosate, the active ingredient in the herbicide Roundup, produced by Monsanto. It has now become the most heavily-used agricultural chemical in the history of the world. A study published Tuesday ... reveals that Americans have applied 1.8 million tons of glyphosate since its introduction in 1974. Worldwide, 9.4 million tons of the chemical have been sprayed onto fields. That's ... enough to spray nearly half a pound of Roundup on every cultivated acre of land in the world. And it's troubling, considering that in March 2015 the World Health Organization's International Agency for Research on Cancer unanimously determined that glyphosate is probably carcinogenic to humans. Research has also shown that glyphosate is an endocrine disruptor, meaning that it interferes with the proper functioning and production of hormones, in human cell lines. The mass-spraying of glyphosate has [also] led to the explosion of resistant weeds, which have evolved to survive despite being sprayed. Already, weeds resistant to the herbicide are found on half of all American farmers' fields. Glyphosate was once only used on a small-scale. However, in the 1990s, Monsanto began introducing genetically modified crops that were resistant to the herbicides, such as Roundup Ready corn and soybeans. Since then, its use has skyrocketed. At the same time, the U.S. Environmental Protection Agency has relaxed its rules. Fifty times more glyphosate is allowed on corn grain now than in 1996.