Occurrence of sulfonylurea, sulfonamide, imidazolinone, and other herbicides in rivers, reservoirs and ground water in the Midwestern United States, 1998

Sulfonylurea (SU), sulfonamide (SA), and imidazolinone (IMI) herbicides are relatively new classes of chemical compounds that function by inhibiting t he action of a plant enzyme, stopping plant growth, and eventually killing the plant. These compounds generally have low mammalian toxicity, but plant s demonstrate a wide range in sensitivity to SUs, SAs, and IMIs with over a 10 000-fold difference in observed toxicity levels for some compounds. SUs , SAs, and IMIs are applied either pre- or post-emergence to crops commonly at 1/50th or less of the rate of other herbicides. Little is known about t heir occurrence, fate, or transport in surface water or ground water in the USA. To obtain information on the occurrence of SU, SA, and IMI herbicides in the Midwestern United States, 212 water samples were collected from 75 surface-water and 25 ground-water sites in 1998. These samples were analyze d for 16 SU, SA and IMI herbicides by USGS Methods Research and Development Program staff using high-performance liquid chromatography/mass spectromet ry. Samples were also analyzed for 47 pesticides or pesticide degradation p roducts. At least one of the 16 SUs, SAs or IMIs was detected above the met hod reporting limit (MRL) of 0.01 mu g/l in 83% of 130 stream samples. Imaz ethapyr was detected most frequently (71% of samples) followed by flumetsul am (63% of samples) and nicosulfuron (52% of samples). The sum of SU, SA an d IMI concentrations exceeded 0.5 mu g/l in less than 10% of stream samples . Acetochlor, alachlor, atrazine, cyanazine and metolachlor were all detect ed in 90% or more of 129 stream samples. The sum of the concentration of th ese five herbicides exceeded 50 mu g/l in approximately 10% of stream sampl es. At least one SU, SA, or IMI herbicide was detected above the MRL in 24% of 25 ground-water samples and 86% of seven reservoir samples. (C) 2000 El sevier Science B.V. All rights reserved.