Toxic Substances Hydrology Program
Glyphosate Herbicide Found in Many Midwestern Streams, Antibiotics Not Common
Researchers with the U.S. Geological Survey (USGS) recently investigated 51 streams in nine Midwestern States to determine the presence of a wide range of herbicides, their degradation byproducts and antibiotics. Herbicides were detected in most water samples, which were collected to coincide with runoff events following herbicide application, but antibiotics were detected in only 1 percent of the samples.
USGS scientists have conducted periodic studies of herbicide occurrence in midwestern streams since 1989 to measure changes in pesticide levels in water resources caused by changing pesticide use and the introduction of new pesticides. Recently, the USGS developed new methods to measure low-levels of glyphosate and antibiotics in environmental waters. The 2002 study is the first to look for the broad-spectrum herbicide glyphosate, its primary degradation product aminomethylphosphonic acid (AMPA), as well as antibiotics during runoff events in Midwestern streams.
What is Glyphosate?
Glyphosate (tradenames include Roundup@, Touchdown@, Rodeo@, and others) is an organic solid of odorless white crystals. It is a non-selective herbicide used on many food and non-food crops as well as non-crop areas such as roadsides. When applied at lower rates, it serves as a plant growth regulator. The most common uses include control of broadleaf weeds and grasses in: hay/pasture, soybeans, field corn; ornamentals, lawns, turf, forest plantings, greenhouses, rights-of-way. Glyphosate is currently the world's best selling herbicide, used in more than 90 countries and on more than 150 crops. Glyphosate use in agriculture has tripled since 1997, largely due to the increasing popularity of Roundup Ready® crops (including corn and soybeans), which have been genetically modified to tolerate glyphosate. The U.S. Environmental Protection Agency has set a drinking water Maximum Contaminant Level (MCL) of 700 micrograms per liter for glyphosate.
What was found?
A total of 154 water samples were collected during the 2002 study in nine Midwestern States. Glyphosate was detected in 36 percent of the samples, while its degradation product, aminomethylphosphonic acid (AMPA) was detected in 69 percent of the samples. The highest measured concentration of glyphosate was 8.7 micrograms per liter, well below the MCL (700 micrograms per liter). The highest AMPA concentration was 3.6 micrograms per liter (there is no MCL for AMPA). Other herbicides were detected at low levels, below health standards, in most samples. Atrazine was detected at or above the 3 microgram per liter MCL in 30% of the samples. Atrazine concentrations were generally lower, however, than those found in previous USGS studies conducted in the 1990s.
Median concentrations (µg/L) detected for each runoff period are:
The antibiotics, measured to determine if they also would attain peak concentrations during spring runoff events following pesticide application, were detected in only 1 percent of water samples. Of the 37 antibiotics tested, only sulfamethoxazole was detected in 2 samples.
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