The herbicide glyphosate was detected at least once in 66 of 70 U.S. streams and rivers located in a range of land-use settings, according to a recent study by the U.S. Geological Survey National Water Quality Program. Glyphosate is the active ingredient in the popular weed killer Roundup® and is the most widely used herbicide in the United States.
At half of the 70 stream sites studied, glyphosate was detected in at least 80% of the 14 to 24 samples collected at each site during 2015–18. The glyphosate breakdown product AMPA was detected even more frequently—in 80% of samples collected at 84% of the sites. Measured concentrations of glyphosate did not exceed human-health or aquatic-life benchmarks; these benchmarks are not available for AMPA.
The occurrence of glyphosate and AMPA in the streams increased with the amount of glyphosate used in the watershed for agriculture. Smaller watersheds or watersheds with developed land in arid areas had less breakdown of glyphosate into AMPA than larger watersheds or those with agriculture, indicating the more efficient transport of glyphosate to streams in small or arid watersheds.