Significant levels of the world's most-used herbicide have been detected in air and water samples from two U.S. farm states, government scientists said on Wednesday, in groundbreaking research on the active ingredient in Monsanto Co's Roundup.

"It is out there in significant levels. It is out there consistently," said Paul Capel, environmental chemist and head of the agricultural chemicals team at the U.S. Geological Survey Office, part of the U.S. Department of Interior.

Capel said more tests were needed to determine how harmful the chemical, glyphosate, might be to people and animals.

The study comes on the heels of several others released recently that raise concerns about the rise of resitant "super weeds," and other unintended consequences of Roundup on soil and animals.

 Capel said glyphosate, the key ingredient in "Roundup" herbicide, was found in every stream sample examined in Mississippi in a two-year period and in most air samples taken. Tests were also done in Iowa.

"So people are exposed to it through inhalation," said Capel.

The research did not look at the impact of the glyphosate in the air and water; the purpose was purely to determine exposure.

More research is needed, Capel said, to analyze the implications.

It is difficult and costly to test for the presence of glyphosate, a popular herbicide used around the world to control weeds on farm fields, golf courses and in residential yards. As a result, little research has been done on the implications for waterways and the air, according to Capel.

"This study is one of the first to document the consistent occurrence of this chemical in streams, rain and air throughout the growing season," said Capel. "It is used so heavily and studied so little."

Capel said researchers looked at samples from Mississippi, a key agricultural area for corn, soybeans, cotton and rice. Many farmers of those crops use large quantities of glyphosate when growing to combat weeds. Researchers also took samples from areas in Iowa.

Monsanto Co. introduced glyphosate to the world in 1974 branded as Roundup, and has made billions of dollars over the years from Roundup herbicides as well as from the "Roundup Ready" corn, soybeans and cotton the company has genetically engineered to survive dousings of glyphosate.

Most of the corn, soybeans and cotton grown in the United States are part of the Roundup Ready system.

 The USGS said more than 88,0000 tons of glyphosate were used in the United States in 2007, up from 11,000 tons in 1992. The big increase in usage has spurred concerns on many fronts, most recently from farmers and environmentalists noting the rise of "super weeds" that are resistant to Roundup.

Fast-growing, glyphosate-resistant weeds are choking out crops in some areas, and some scientists say research shows harmful effects of glyphosate products on soil organisms, on plants, and on certain animals.

The Environmental Protection Agency is reviewing the registration for glyphosate and the data gathered by the U.S. Geological Survey has been submitted to the EPA, said Capel.

The EPA has set a deadline of 2015 for determining if glyphosate should continue to be sold or in some way limited. The EPA is working closely with regulators in Canada as they also assess the ongoing safety and effectiveness of the herbicide.

Monsanto spokeswoman Kelli Powers said the company was reviewing the study. The EPA had no immediate comment on the study.