Two studies by the U.S. Geological Survey found glyphosate is commonly present in rain and rivers in agricultural areas in the Mississippi River watershed.
USGS Chemist Paul Capel says the weed killer was in streams in Iowa and Mississippi, particularly during the growing season. It was also detected in the air.
"It was generally was thought not to enter the atmosphere so what was there was probably from spray drift or wind erosion of the soil particles," Capel said. "So its presence in the air was surprising and then its continual constant presence in the streams was also somewhat surprising from what we first expected."
U.S. use of the herbicide has soared from 11,000 tons a year as of 1992 to 88,000 tons as of the time of the study beginning in 2007.
Capel says the concentrations found in the streams were higher than other herbicides, however he says the concentrations of glyphosate were still low. Capel says because of the chemical's known low level of toxicity the concentrations do not present a direct, acute threat to human health or the environment.
"The question still remains is what is the long-term effect of these low levels in the environment," Capel said. "Are there other subtle effects that are non-direct toxicity, and that I think is the question that is still open."
Health and environmental advocacy groups say the studies combined with others that have reported toxic effects from glyphosate on human cells and on animals raise concern. Environmental Working Group President Ken Cook says he's written Monsanto President and CEO Hugh Grant asking whether the company anticipated such widespread contamination and calling on the company to make public any air and water tests it's conducted for glyphosate. Bill Freese, a science policy analyst for the Center for Food Safety says some sort of stewardship plans for glyphosate use should be looked at.