Glyphosate Reconnaissance, 2002 Completed

Since the stream reconnaissance study conducted in 1998, several substantial changes in herbicide use occurred. The most significant was the rapid increase in the use of glyphosate that corresponded with the introduction of "Roundup Ready" crops to the market. Between 1997 and 2000, glyphosate use in 11 midwestern States more than tripled from 11.3 to 37.5 million pounds applied. Over this same time period the use acetochlor increased from 27.0 to 28.7 million pounds, the use of atrazine increased from 44.8 to 47.4 million pounds, the use of metolachlor decreased from 47.4 to 24.9 million pounds, the use of alachlor decreased from 8.0 to 4.0 million pounds, and the use of cyanazine decreased from 16.0 to 0.3 million pounds.

In 2002, water samples were collected during two post-herbicide-application runoff events and one harvest-season runoff event from sites on 51 midwestern streams. All samples were analyzed for glyphosate and 20 other herbicides, and AMPA and 27 other herbicide transformation products, using GC/MS or HPLC/MS at the USGS Organic Geochemistry Research Laboratory in Lawrence, Kansas. Glyphosate was detected at a concentration of 0.1 ug/L or greater in 38% of post-application runoff samples and 31% of harvest-season runoff samples. AMPA was detected at a concentration of 0.1 ug/L or greater in 68% of post-application runoff samples and 73% of harvest-season runoff samples. The concentrations of glyphosate or AMPA rarely exceeded 1 ug/L in any sample.