Water-quality assessment of the eastern Iowa Basins: Selected pesticides and pesticide degradates in streams, 1996-98

Water-Resources Investigations Report 2003-4075
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Abstract

Water samples were collected in streams of the Eastern Iowa Basins study unit from 1996 to 1998 as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. More than 350 samples were collected to document the occurrence, distribution, and transport of pesticides and pesticide degradates. The Eastern Iowa Basins study unit encompasses about 50,500 square kilometers (19,500 square miles) in eastern Iowa and southern Minnesota and is drained by four major rivers—the Wapsipinicon, Cedar, Iowa, and Skunk—which flow into the Mississippi River at the eastern border of Iowa.

The most commonly detected pesticides— acetochlor, alachlor, atrazine, cyanazine, and metolachlor—were those most heavily used on crops during the study. Atrazine and metolachlor were detected in 100 percent, and acetochlor, alachlor and cyanazine were detected in more than 70 percent of all surface-water samples. Four pesticide degradates—metolachlor ethane sulfonic acid, alachlor ethane sulfonic acid, metolachlor oxanilic acid, and acetochlor ethane sulfonic acid were detected in more than 75 percent of the samples. Only one nonagricultural herbicide, prometon, was detected in more than 80 percent of the samples. Carbofuran, the most commonly detected insecticide, was found in 16 percent of all samples.

Mixtures of pesticide compounds commonly occurred in the samples. Five or more parent pesticide compounds were detected in 50 percent of the samples. Four or more pesticide degradates were detected in 68 percent and seven or more pesticide degradates were detected in 17 percent of the samples. Acetochlor, alachlor, atrazine, cyanazine, and metolachlor were generally present at low concentrations; median concentrations ranged from 0.01 to 0.22 microgram per liter. However, median concentrations for the pesticide degra-dates, 0.07 to 3.7 micrograms per liter, were larger than their parent compounds. Acetochlor, alachlor, atrazine, cyanazine, and metolachlor pesticide compounds were detected at an order of magnitude or higher in the late spring and summer than at other times of the year. Pesticide concentrations generally peak following application in May and June and decrease during the growing season. A small secondary peak of atrazine, acetochlor, alachlor, cyanazine, and metolachlor concentrations occurred in late winter at all sites. The seasonal patterns for the triazine (atrazine and cyanazine) degradates were similar to the parent compounds (increasing in the spring), but the triazine degra-dates often had higher median concentrations than their parent compounds in the fall and winter. The chloroacetanilide (acetochlor, alachlor, and metolachlor) degradates did not follow a strong seasonal pattern like their parent compounds. In general, the chloroacetanilide degradates had constant and higher median concentrations when compared to their parent compounds throughout the year. The median concentrations for the chloroacetanilide pesticide degradates were often an order of magnitude higher than their parent compounds.

Concentrations of pesticides varied by land-form region. Atrazine and cyanazine and their degradates were present in significantly greater concentrations in streams of the Southern Iowa Drift Plain than streams of either the Des Moines Lobe or the Iowan Surface.

Study Area

Table of Contents

Abstract
Introduction
     Purpose and scope
Description of the Eastern Iowa Basins
     Geomorphology
     Climate
     Streamflow
     Land Use
     Pesticide Use and Properties
Study Design and Methods of Study
     Sampling Site Selection
     Sampling Methods
     Analytical Methods
     Quality Assurance/Quality Control
     Data Analysis
          Statistical Analysis of Pesticide and Pesticide Degradates
          Ancillary Data
Pesticides and Pesticide Degradates in Streams
     Occurrence and Distribution
          Seasonal Variability
          Spatial Variability
Relevance of Pesticides in Streams
     Human Health
     Aquatic Life
Summary and Conclusions
References
Appendix

Publication type Report
Publication Subtype USGS Numbered Series
Title Water-quality assessment of the eastern Iowa Basins: Selected pesticides and pesticide degradates in streams, 1996-98
Series title Water-Resources Investigations Report
Series number 2003-4075
DOI 10.3133/wri034075
Year Published 2003
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Iowa Water Science Center
Description vi, 62 p.
Country United States
State Iowa, Minnesota
Other Geospatial eastern Iowa Basins
Online Only (Y/N) N
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details