U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007-1369

National Water-Quality Assessment Program

Pesticides in Air and Rainwater in the Midcontinental 

United States, 1995—Methods and Data

Pesticides in Air and Rainwater in 

the Midcontinental United States, 

1995—Methods and Data

By Michael S. Majewski, William T. Foreman, Richard H. Coupe, Donald A. 

Goolsby, and Frank W. Wiebe

National Water-Quality Assessment Program

Open-File Report 2007–1369

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

For product and ordering information:World Wide Web: http://www.usgs.gov/pubprod

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Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested reference:

Majewski, M.S., Foreman, W.T., Coupe, R.H., Goolsby, D.A., and Wiebe, F.W., 2008, Pesticides in air and rainwater in 

the midcontinental United States, 1995—Methods and data: U.S. Geological Survey Open–File Report 2007–1369, 

24 p. Available at http://pubs.water.usgs.gov/ofr/2007/1369
iii

FOREWORD

The U.S. Geological Survey (USGS) is committed to providing the Nation with credible scientific information that helps to enhance 

and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources 

(http://www.usgs.gov/). Information on the Nation’s water resources is critical to ensuring long-term availability of water that 

is safe for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife. Population growth and increasing 

demands for water make the availability of that water, now measured in terms of quantity and quality, even more essential to the 

long-term sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support national, regional, State, 

and local information needs and decisions related to water-quality management and policy (http://water.usgs.gov/nawqa). The 

NAWQA Program is designed to answer: What is the condition of our Nation’s streams and ground water? How are conditions 

changing over time? How do natural features and human activities affect the quality of streams and ground water, and where 

are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and 

aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. 

From 1991 to 2001, the NAWQA Program completed interdisciplinary assessments and established a baseline understanding 

of water-quality conditions in 51 of the Nation’s river basins and aquifers, referred to as Study Units (http://water.usgs.gov/

nawqa/studyu.html). 

Multiple national and regional assessments are ongoing in the second decade (2001–2012) of the NAWQA Program as 42 of the 

51 Study Units are reassessed. These assessments extend the findings in the Study Units by determining status and trends at 

sites that have been consistently monitored for more than a decade, and filling critical gaps in characterizing the quality of surface 

water and ground water. For example, increased emphasis has been placed on assessing the quality of source water and finished 

water associated with many of the Nation’s largest community water systems. During the second decade, NAWQA is addressing 

five national priority topics that build an understanding of how natural features and human activities affect water quality, and 

establish links between sources of contaminants, the transport of those contaminants through the hydrologic system, and the 

potential effects of contaminants on humans and aquatic ecosystems. Included are topics on the fate of agricultural chemicals, 

effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment 

on aquatic ecosystems, and transport of contaminants to public-supply wells. These topical studies are conducted in those Study 

Units most affected by these issues; they comprise a set of multi-Study-Unit designs for systematic national assessment. In addition, national syntheses of information on pesticides, volatile organic compounds (VOCs), nutrients, selected trace elements, and 

aquatic ecology are continuing. 

The USGS aims to disseminate credible, timely, and relevant science information to address practical and effective waterresource management and strategies that protect and restore water quality. We hope this NAWQA publication will provide you 

with insights and information to meet your needs, and will foster increased citizen awareness and involvement in the protection 

and restoration of our Nation’s waters. 

The USGS recognizes that a national assessment by a single program cannot address all water-resource issues of interest. 

External coordination at all levels is critical for cost-effective management, regulation, and conservation of our Nation’s water 

resources. The NAWQA Program, therefore, depends on advice and information from other agencies—Federal, State, regional, 

interstate, Tribal, and local—as well as nongovernmental organizations, industry, academia, and other stakeholder groups. Your 

assistance and suggestions are greatly appreciated.

 Robert M. Hirsch

Associate Director for Water
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v

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Background............................................................................................................................................1

Purpose and Objectives of Study and Report ..................................................................................2

Acknowledgments................................................................................................................................3

Site Selection, Description, Criteria, and Identification..........................................................................3

Mississippi Study Area ........................................................................................................................3

Urban Location—Jackson ........................................................................................................3

Agricultural Location—Rolling Fork ........................................................................................5

Iowa Study Area....................................................................................................................................5

Urban Location—Iowa City .......................................................................................................5

Agricultural Location—Cedar Rapids .....................................................................................6

Minnesota Study Area .........................................................................................................................6

Urban Location—Minneapolis .................................................................................................6

Agricultural Location—Princeton.............................................................................................7

Michigan Background Site .................................................................................................................8

Background Location—Eagle Harbor......................................................................................8

Sample Collection Methods.........................................................................................................................9

Field Sampling .......................................................................................................................................9

Air....................................................................................................................................................9

Rain...............................................................................................................................................10

Meteorological Data...........................................................................................................................11

Analytical Methods......................................................................................................................................12

Sample Preparation—Air..................................................................................................................12

Sample Cleanup .........................................................................................................................14

Polyurethane Foam Plug Reuse ..............................................................................................14

Sample Preparation—Rain ...............................................................................................................14

Sample Analysis..................................................................................................................................15

Method Analyte Reporting Levels....................................................................................................15

Field Data Results ........................................................................................................................................15

Air...........................................................................................................................................................15

Rain........................................................................................................................................................16

Quality Assurance Program.......................................................................................................................16

Quality Control for Air Samples ........................................................................................................16

Air Method Set Blanks..............................................................................................................16

Air Method Set Spikes ..............................................................................................................17

Polyurethane Foam Plug Collection Efficiency Spike Experiments...................................17

Polyurethane Foam Plug Collection Efficiency Estimation from Field Samples..............18
vi

Figures

Figure 1. Study area showing sampling locations. ................................................ 4

Photos

Photo 1. Urban sampling site at Jackson, Mississippi ............................................. 3

Photo 2. Agricultural sampling site at Rolling Fork, Mississippi ................................. 5

Photo 3. Urban sampling site at Iowa City, Iowa ................................................... 5

Photo 4A. Agricultural sampling site at Cedar Rapids, Iowa ....................................... 6

Photo 4B. Agricultural sampling site at Cedar Rapids, Iowa, alternate view ..................... 6

Photo 5. Urban sampling site at Minneapolis, Minnesota ....................................... 6

Photo 6. Agricultural sampling site at Princeton, Minnesota .................................... 7

Photo 7A. Background sampling site at Eagle Harbor, Michigan ................................. 8

Photo 7B. Background sampling site at Eagle Harbor, Michigan, alternate view ............... 8

Photo 8. Air sampler showing the glass-fiber filter holder and the polyurethane 

foam cartridge .............................................................................. 9

Photo 9. Modified automatic wet-deposition collector showing the refrigerated 

water-collection container ............................................................... 10

Surrogate Recoveries in Air Sample Components and Associated 

Quality Control Samples.......................................................................................................19

Quality Control for Rain Samples .....................................................................................................19

Field Equipment Water Blanks.................................................................................................19

Laboratory Water Blank and Spike Samples .......................................................................20

Laboratory Water Spike Recoveries.......................................................................................20

Surrogate Recoveries in Rainwater and Associated Quality Control Samples ..............20

Pesticide Stability in Rainwater Test......................................................................................20

References....................................................................................................................................................21

The following appendixes do not have page numbers because they are linked to Excel files: 

Appendix 1. Weekly meteorological summaries of air temperature, wind speed, and wind direction for 

Jackson, Mississippi.

Appendix 2. Weekly meteorological summaries of air temperature, wind speed, and wind direction 

for Rolling Fork, Mississippi.

Appendix 3. Weekly meteorological summaries of air temperature, relative humidity, wind speed, and 

wind direction for Iowa City and Cedar Rapids, Iowa.

Appendix 4. Weekly meteorological summaries of air temperature, relative humidity, wind speed, 

and wind direction for Minneapolis, Minnesota.

Appendix 5. Weekly meteorological summaries of air temperature, wind speed, and wind direction for 

Princeton, Minnesota.

Appendix 6. Weekly meteorological summaries of air temperature, relative humidity, wind speed, and 

wind direction for Eagle Harbor, Michigan.
vii

Tables

(The following tables do not have page numbers (except table 1) because they are linked to 

Excel files) 

Table 1. Analyte list, grouped by chemical class, and associated reporting levels for rainwater 

and air methods.............................................................................. 13

Table 2. Air sampling results for the Jackson, Mississippi, urban sampling site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 3. Air sampling results for the Rolling Fork, Mississippi, agricultural site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 4. Air sampling results for the Iowa City, Iowa, urban site including the number and 

percentage of analyte detections and mean and standard deviation for the surrogate 

quality assurance compounds.

Table 5. Air sampling results for the Cedar Rapids, Iowa, agricultural site including the number 

and percentage of analyte detections and mean and standard deviation for the 

surrogate quality assurance compounds.

Table 6. Air sampling results for the Minneapolis, Minnesota, urban site including the number 

and percentage of analyte detections and mean and standard deviation for the 

surrogate quality assurance compounds.

Table 7. Air sampling results for the Princeton, Minnesota, agricultural site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 8. Air sampling results for the Eagle Harbor, Michigan, background site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 9. Weekly field notes and laboratory comments for each of the urban, agricultural, and 

background air sampling sites.

Table 10. Rainwater sampling results for the Jackson, Mississippi, urban site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 11. Rainwater sampling results for the Rolling Fork, Mississippi, agricultural site 

including the number and percentage of analyte detections and mean and standard 

deviation for the surrogate quality assurance compounds.

Table 12. Rainwater sampling results for the Iowa City, Iowa, urban site including the number 

and percentage of analyte detections and mean and standard deviation for the 

surrogate quality assurance compounds.

Table 13. Rainwater sampling results for the Cedar Rapids, Iowa, agricultural site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 14. Rainwater sampling results for the Minneapolis, Minnesota, urban site including the 

number and percentage of analyte detections and mean and standard deviation for 

the surrogate quality assurance compounds.

Table 15. Rainwater sampling results for the Princeton, Minnesota, agricultural site including 

the number and percentage of analyte detections and mean and standard deviation 

for the surrogate quality assurance compounds.
viii

Table 16. Rainwater sampling results for the Eagle Harbor, Michigan, background site 

including the number and percentage of analyte detections and mean and standard 

deviation for the surrogate quality assurance compounds.

Table 17. Weekly field comments for each of the urban, agricultural, and background 

rainwater sampling sites.

Table 18. Pesticide detections and concentrations in field and laboratory air blank samples.

Table 19. Air sample analytical method laboratory spike percent recovery data and summary 

statistics.

Table 20. Recovery of pesticides from the spiked glass-fiber filter and the front and back 

polyurethane foam plugs for the three polyurethane foam collection efficiency 

experiments done at three different total air volumes in Sacramento, California.

Table 21. Summary of analyte breakthrough on polyurethane foam plugs for analytes detected 

in field air samples.

Table 22. Air analytical method summary statistics for surrogate compound percent recoveries 

from laboratory spike samples, field and laboratory set-blank samples, and from the 

glass-fiber filter and polyurethane foam plug components of field samples for the air 

method.

Table 23. Concentrations of pesticides detected in laboratory water-blank samples identified 

by sample preparation set number.

Table 24. Percent recovery of pesticides and pesticide degradates in 59 laboratory reagentwater spike samples coded by sample preparation set number.

Table 25. Percent recovery and statistical summaries for surrogate compounds in the 

laboratory reagent water blank samples, the laboratory reagent water spike 

samples, and the combined laboratory reagent water blank and spike samples.

Table 26. Summary statistics for surrogate compound recoveries from laboratory water blank 

and spike samples, field blank water samples, and rain samples.

Table 27. Analytical method percent recoveries at days 0 and 5, and overall test recoveries for 

analytes spiked into rainwater and held for 5 days at ambient temperature.
ix

Abbreviations and Acronyms

(Clarification or additional information given in parentheses)

degrees/10 wind direction in degrees divided by 10

GC gas chromatography

GC/ECD gas chromatography/electron capture detection

GC/EIMS gas chromatography/electron-impact mass spectrometry

GC/MS gas chromatography/mass spectrometry

GC/MS-SIM gas chromatography/mass spectrometry–selective ion mode

GFF glass-fiber filter

IADN Integrated Atmospheric Deposition Network (U.S. and Canadian collaborative project)

ID identification

IDL instrument detection level

MDL method detection limit

MSEA Management Systems Evaluation Area (U.S. Dept. of Agriculture)

NAWQA National Water-Quality Assessment (USGS)

NADP National Atmospheric Deposition Program (Illinois Department of Natural Resources)

n.d no date

NTN National Trends Network

PUF polyurethane foam

QC quality control

RSD relative standard deviation

SPE solid-phase extraction

TSP total suspended particles

U.S. United States

Organizations

NOAA National Oceanic and Atmospheric Administration (NWS)

NWQL National Water Quality Laboratory (USGS)

NWS National Weather Service

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey
x

Units of Measurement

cm centimeter (0.3937 in.) 

d day

g gram (0.0353 ounce) 

h hour

in. inch (2.54 cm)

kg kilogram (2.205 pounds)

km kilometer (0.6214 miles)

L liter (0.264 gallons)

mL milliliter (10–3 liter)

m meter (3.28 feet)

m2 square meter

m3 cubic meter

mg milligram (10–3 gram)

min minute

mL milliliter (10–3 liter)

ng nanogram (10–9 gram)

yr year

μg microgram (10–6 gram)

μL microliter (10–6 liter)

μm micrometer (10–6 meter)

Notes

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32)/1.8

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation data were not recorded.

Concentrations of chemical constituents in rainwater are given in micrograms per liter (μg/L); 

in air, are given in nanograms per cubic meter (ng/m3); and in TSP, are given in micrograms per 

cubic meter (μg/m3).

NOTE TO USGS USERS: Use of liter (L) as a special name for cubic decimeter (dm3) is restricted 

to the measurement of liquids and gases. 
Abstract

Weekly composite high-volume air and wet-only 

deposition samples were collected from April through 

September 1995 at paired urban and agricultural areas in 

Mississippi, Iowa, and Minnesota, and at a background site 

in Michigan’s Upper Peninsula. This report describes the 

methods used to collect, analyze, and quality assure the 

samples, and presents the results of all chemical analyses 

and quality control procedures. Each sample was analyzed 

for 49 compounds, including several pesticides not examined 

in previous atmospheric studies. Eighty-five percent of the 

herbicides, 70 percent of the insecticides, and 100 percent of 

the transformation products that were targeted for analysis 

were detected in one or more samples at each paired site. 

Introduction

The atmosphere is an important, but often neglected, part 

of the hydrologic cycle with regard to investigating pesticide 

movement in the environment. The U.S. Geological Survey’s 

(USGS) Toxic Substances Hydrology program (Kolpin, 

2000) and the National Water-Quality Assessment (NAWQA) 

program (Gilliom and others, 1995; Larson and others, 

1999; Barbash and others, 1999) are providing a wealth of 

information on pesticide occurrence and trends in our nation’s 

surface and ground waters. For a more complete understanding 

of the environmental fate of pesticides, however, the 

atmospheric component must also be investigated.

Background

A wide variety of pesticides has been detected in the 

atmosphere throughout the world (Bidleman and others, 1990; 

Tatsukawa and others, 1990; Majewski and Capel, 1995; van 

Dijk and Guicherit, 1999, Waite and others, 2005). Pesticides 

become airborne through volatilization and wind erosion of 

particles both during and after the application process. Many 

are applied to agricultural fields by aircraft and some are 

sprayed directly into the atmosphere, in the attempts to control 

insects in orchards and mosquitoes and other pests in urban 

areas. Volatilization from treated areas is a continuous process 

and can be a major dissipative route for many pesticides 

(Seiber and Woodrow, 1995; Majewski, 1991; Glotfelty, 

1978). 

Once airborne, a pesticide will be distributed between the 

gas and particle phases by adsorptive or absorptive processes, 

or both (Pankow, 1994a, 1994b; Harner and Bidleman, 1998). 

This distribution can be estimated from the vapor pressure 

and octanol-air partition coefficient of the pesticide, and is 

influenced by the ambient air temperature, humidity, and the 

type and concentration of airborne particulate matter. The 

airborne pesticide can be carried by wind and deposited in 

unintended areas by dry deposition (gases, particles, and fog) 

and wet deposition (rain and snow). These deposited residues 

can revolatilize, reenter the atmosphere, and be transported 

and redeposited downwind repeatedly until they are 

transformed or they accumulate, usually in areas with cooler 

climates (Risebrough, 1990; Wania and Mackay, 1996). This 

same process also can occur for the products from abiotic or 

biotic transformations of pesticides. For persistent compounds, 

this deposition and revolatilization process can continue for 

decades. 

Pesticides in Air and Rainwater in the Midcontinental 

United States, 1995—Methods and Data

By Michael S. Majewski, William T. Foreman, Richard H. Coupe, Donald A. Goolsby, and Frank W. Wiebe
2 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

In 1995, more than 550 million kg of pesticides were 

used in the United States (U.S.) to control many different 

types of weeds, insects, and other pests in a wide variety 

of agricultural, commercial, and urban settings (Aspelin, 

1997; Aspelin and Grube, 1999). Seventy-seven percent of 

this amount was used in agriculture. The highest density of 

agricultural activity and harvested cropland in the U.S. is in 

the upper Midwest and along the lower Mississippi River. A 

wide variety of herbicides and insecticides are used on many 

of the diverse crops grown in this region. Pesticides are not 

only used in agriculture, however. The U.S. Environmental 

Protection Agency (USEPA) estimates that about one 

quarter of all conventional pesticides used in the U.S. are 

for nonagricultural purposes, primarily for home and garden 

uses (Whitmore and others, 1992). Pest control applications 

are also used in and around industrial, commercial, and 

governmental properties, parks, golf courses, and other 

public areas. Many of the same pesticides used in agriculture 

also are used in urban areas, but others are not and should 

not be detected in urban areas. Increased pesticide use has 

resulted in increased crop production, more visually appealing 

produce, insect-population-controlled living and work 

environments, and weed-free lawns. Concurrently, concerns 

about the potential adverse effects of pesticides and pesticide 

transformation products on the environment and human health 

have grown. 

To address the lack of information on pesticides and 

pesticide transformation products in the atmosphere, the 

USGS has conducted several studies to determine the 

occurrence, concentrations, and geographic distribution 

of pesticides in the atmosphere of the Midwestern U.S. 

During 1991–92, a study was conducted in 26 Midwestern 

and Northeastern states to determine the occurrence, spatial 

distribution, and deposition of several corn and soybean 

herbicides in precipitation (Goolsby and others, 1995; Goolsby 

and others, 1997). This study found detectable concentrations 

of herbicides in precipitation in all 26 states. Estimated 

deposition rates for atrazine and alachlor ranged from more 

than 240 mg/m2

/yr in some Corn Belt states to 12–63 mg/

m2

/yr on the Great Lakes to less than 10 mg/m2/yr in New 

England. In 1994, a brief study of pesticides in air along the 

Mississippi River from New Orleans, Louisiana, to Saint Paul, 

Minnesota, analyzed samples for 42 pesticides and 3 pesticide 

transformation products. Twenty-five compounds—15 

herbicides, 7 insecticides, and 3 transformation products—

were detected in concentrations ranging from 0.05 to 80 ng/m3

(Majewski and others, 1998). In 1995, the USGS conducted 

a detailed study of the atmospheric occurrence of pesticide 

compounds in atmospheric gases, particles, and rainwater at 

three locations in the Mississippi River Valley plus a reference 

site. Partial interpretations of the results from this study have 

been published by Majewski and others (2000), Foreman and 

others (2000), and Coupe and others (2000).

Purpose and Objectives of Study and Report

This study was designed to characterize the atmospheric 

occurrence, temporal, transport, and wet depositional patterns 

for a variety of pesticides used in the agricultural and urban 

environments of three geographically different regions of the 

Mississippi River Valley—Mississippi, Iowa, and Minnesota. 

Atmospheric monitoring in each geographic region consisted 

of paired monitoring sites, with one station located in an urban 

area and the other in an agricultural area. A background site 

in Michigan’s Upper Peninsula far from major metropolitan 

and agricultural areas was also included in the study. Samples 

from this site allowed for the investigation of long-range 

atmospheric transport and deposition into a more remote 

and pristine area. Scientists conducting the study collected 

air (both operationally defined gas and particle phases) and 

precipitation (rain) for 6 months, from April to September 

1995. Each sample was a weekly composite and was analyzed 

for a wide variety of currently used pesticides and several 

transformation products. 

The principal objectives of the study were to:

1. Document the occurrence and detection frequency 

of a wide variety of herbicides, insecticides, 

and selected transformation products in three 

atmospheric matrices (operationally defined gas and 

particle phases, and precipitation) over one growing 

season. 

2. Compare the types of pesticides detected at 

urban and agricultural environments in three 

geographically different areas of the Mississippi 

River Valley. 

3. Investigate the long-range transport potential for the 

targeted pesticides.

The objective of this report is to describe the 

methodology used to collect, analyze, and quality assure the 

samples, and presents the results of all chemical analyses and 

quality control results. 
Site Selection, Description, Criteria, and Identification 3

Acknowledgments

We thank Larry Shelton, USGS Hydrological Technician, 

for his valuable assistance in the initial instrument design 

modifications and set-up of the rain samplers, and with 

the air sampler calibration at each site. We also thank 

the USGS NAWQA personnel and others involved in the 

maintenance and service of the collectors, the sample 

processing and shipping, as well as in the installation and 

removal of the sampling equipment: Mississippi—Mike 

Manning; Iowa—Brenda Nations, Debra Sneck-Fahrer, Ron 

Kuzniar; Minnesota—Greg Stratton; Michigan—Dr. Martin 

Auer, Department of Civil and Environmental Engineering, 

Michigan Technical University, Houten, Michigan, and his 

graduate students James Pauer and Aron Cromwell. We also 

thank J.R. Drivas, Buddy Hyde, Scott McBride, and John C. 

McKenzie for their help in preparing the glass-fiber filters, Bill 

Battaglin and Mike Thurman for their thoughts, suggestions, 

and efforts in the initial planning and design of the study, 

and Mike McGinley, Galen Frahm, Jeff Coup, Steve Glodt, 

Mark Sandstrom, and Mike Schroeder for their analytical or 

technical support.

Site Selection, Description, Criteria, 

and Identification

Paired monitoring sites were established in agricultural 

and urban–suburban settings in each of three geographic areas 

within the Mississippi River Valley (fig. 1). These areas were 

(1) the delta region in west-central Mississippi, (2) eastcentral Iowa, and (3) the Minneapolis vicinity in east-central 

Minnesota. The urban–agricultural paired sites were chosen 

to be within 100 km of each other to allow comparison of 

pesticide occurrence in these different land-use environments. 

Each of the monitoring sites was also chosen to be within 

or near an existing USGS NAWQA study unit (Gilliom and 

others, 1995). Each sampling site was uniquely identified by 

latitude and longitude. In addition, a background monitoring 

site was established in northern Michigan near Lake Superior, 

far from major metropolitan and agricultural areas. The 

logistical requirements for each site were that they be easily 

accessible to USGS personnel, reasonably secure from public 

access, and have a 120-volt power source available to operate 

the samplers. 

To the extent possible, the sampling sites and the samplecollector placement followed the protocols recommended by 

the NADP/NTN (National Atmospheric Deposition Program/

National Trends Network) (Bigelow, 1984; Bigelow and 

Dossett, 1988). Briefly, these requirements state that the 

collector should be located in an area that: 

•	 typifies the region; 

•	 minimizes the impact of local point or area sources; 

•	 is at least 10 km from major industrial operations 

(including power plants, chemical plants, and large 

manufacturing facilities); and 

•	 is far enough removed from objects and structures 

surrounding the collector that would interfere with the 

sample collection (the 45° angle rule).

Because the NADP/NTN sampling system was developed 

to study atmospheric deposition at sites that are regionally 

representative of surrounding ecoregions, the guidelines 

pertaining to urban influences could not be strictly adhered 

to at the urban sites, and the 45° angle rule was not always 

attainable with respect to utility poles. Care was taken, 

however, to locate these sites to minimize impacts from local 

point or area sources. 

Mississippi Study Area

The USGS NAWQA study unit responsible for 

maintaining these sites and sample collection was the 

Mississippi Embayment Study Unit (Mallory, 1994), based in 

Pearl, Mississippi.

Urban Location—Jackson (site ID number 

321604090124050). 

This urban site is located near a residential neighborhood 

at the intersection of Interstate 55 and McDowell Road, in the 

southeast Jackson metropolitan area (population 202,062 in 

1996, U.S. Census Bureau, 1998) of Hinds County in central 

Mississippi (fig. 1). The samplers were located within the 

confines of a Highway Department construction facility, but 

no pesticide operations were staged from this facility. The 

air and precipitation samplers were installed on a wooden 

platform elevated about 1 m above the ground (photo 1). This 

site was representative of a suburban airshed and was several 

kilometers from the nearest agricultural field. 

Photo 1. Urban sampling site at Jackson, Mississippi.
4 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

Louisiana

Arkansas

Tennessee

Mississippi

Kentucky

Indiana Ohio Illinois

Missouri

Iowa

Michigan

Minnesota

Wisconsin

Study area

in the 

United States

Princeton

Minneapolis

Eagle Harbor

Cedar Rapids

Iowa City

Rolling 

Fork

Jackson

SAMPLING SITES

Urban

Agricultural

Background

NAWQA STUDY UNIT

EXPLANATION

Upper Mississippi River Basin

Eastern Iowa Basins

Mississippi Embayment

0 50 100 200 MILES

0 10050 200 KILOMETERS

Figure 1. Study area showing sampling locations.

Urban sites (Jackson, Mississippi; Iowa City, Iowa; and Minneapolis, Minnesota); agricultural sites (Rolling Fork, Mississippi; 

Cedar Rapids, Iowa; and Princeton, Minnesota); and background site (Eagle Harbor, Michigan).
Site Selection, Description, Criteria, and Identification 5

Agricultural Location—Rolling Fork (site ID 

number 325626090553650). 

This agricultural site is located in the center of a catfishaquaculture complex (photo 2) near the town of Rolling 

Fork in Sharkey County (population 6,833 in 1995, U.S. 

Census Bureau, 1995) in the Mississippi River Delta region 

of upper Mississippi (fig. 1). No pesticides were used within 

the aquaculture complex, but the complex is surrounded 

by intense agricultural activity including cotton, soybeans, 

pecan, corn, and some rice production. The nearest field was 

located about 0.5 km away. This site was representative of an 

agricultural airshed in this region of Mississippi even though 

the micrometeorology would be different from that in an 

actual crop field. This site was about 80 km northwest of the 

Jackson urban site.

Iowa Study Area

The NAWQA study unit responsible for maintaining 

these sites and sample collection was the Eastern Iowa Basins 

Study Unit (Kalkhoff, 1996), based in Iowa City, Iowa.

Urban Location—Iowa City (site ID number 

413937091314501). 

This urban site is located in downtown Iowa City 

(population 59,735 in 1996, U.S. Census Bureau, 1998) 

in Johnson County, Iowa (fig. 1) in east-central Iowa. The 

sampler was located on the roof of the Iowa City police station 

(photo 3) at 410 East Washington Street. The area immediately 

surrounding the site consists of a mixture of residential 

housing, small businesses, and light industry. Iowa City is 

situated in the heart of the Corn Belt, and is surrounded by 

intense corn production. The nearest agricultural fields were 

about 5 km to the west and about 4 km to the east.

Photo 2. Agricultural sampling site at Rolling Fork, 

Mississippi.

Photo 3. Urban sampling site at Iowa City, Iowa.
6 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

Agricultural Location—Cedar Rapids (site ID 

number 415236091423401). 

This agricultural site is located at the Cedar Rapids 

airport in Linn County (fig. 1) and situated about 16 km south 

of the city of Cedar Rapids (population 108,772 in 1996, U.S. 

Census Bureau, 1998). The samplers were placed in a grassy 

area, but were within about 15 m from a cornfield (photos 4A

and 4B). The area surrounding the sampling site, with the 

exception of the airport, was agricultural fields, mostly used 

for corn production. It is not known how much or what type 

of herbicides were used at the airport. This sampling site was 

about 34 km north of the Iowa City urban site.

Minnesota Study Area

The NAWQA study unit responsible for maintaining 

these sites and sample collection was the Upper Mississippi 

River Basin Study Unit (Stark and others, 1996) based in 

Mounds View, Minnesota.

Urban Location—Minneapolis (site ID number 

445557093173001). 

This urban site is located in a suburban area of the city 

of Minneapolis, (population 368,383 in 1990, U.S. Census 

Bureau, 1998) near Lake Harriet in Hennepin County (fig. 1). 

The population of the Minneapolis metropolitan area is 

approximately two million. The samplers were located within 

the confines of the Minneapolis Park and Recreation Board 

field office and storage area (photo 5), but no pesticide use 

or preparation activities were staged from this facility. The 

land use in the immediate area surrounding the site was 

mainly residential (94 percent) with some light commercial 

(4 percent). The Minneapolis metropolitan area is surrounded 

by agricultural areas that are intensively farmed with row 

crops. The nearest substantial agricultural fields were about 

30 km or more in all directions from this site. Other, related 

USGS atmospheric studies have been conducted at this site, 

including co-located samples collected in 1995 (Capel and 

others, 1998; Young, 1998; Ma, 2000) along with those 

described in this report.

Photo 4A. Agricultural sampling site at Cedar Rapids, Iowa.

Photo 4B. Agricultural sampling site at Cedar Rapids, Iowa, 

alternate view.

Photo 5. Urban sampling site at Minneapolis, Minnesota.
Site Selection, Description, Criteria, and Identification 7

Agricultural Location—Princeton (site ID number 

453136093365101).

This agricultural site is located about 5 km southwest 

of Princeton, Minnesota, (population 52,809 in 1995, U.S. 

Census Bureau, 1998) in Sherburne County (fig. 1). The 

samplers were located about 300 m west of a U.S. Department 

of Agriculture MSEA (Management Systems Evaluation Area) 

research field (photo 6) near observation well MC19 (see 

fig. 4 in Delin and others, 1994). Information on crop type 

and pesticide application activities on the MSEA fields was 

known. Agricultural activities to non-MSEA fields located 

across 136th Street to the east and across 305th Street south 

of the sampler, however, were unknown. Related atmospheric 

studies by the USGS have been conducted at this MSEA 

location (Capel and others, 1998). This site was about 80 km 

northwest of Minneapolis.

Photo 6. Agricultural sampling site at Princeton, Minnesota.
8 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

Michigan Background Site

There were no NAWQA study units in Michigan’s Upper 

Peninsula that could maintain this site or collect the samples. 

This site was managed by graduate students from Michigan 

Technical Institute in Houghton, Michigan.

Background Location—Eagle Harbor (site ID 

number 47274708808590)

Eagle Harbor is a summer resort town on the north 

shore of upper Michigan’s Keweenan Peninsula (fig. 1). This 

site was located near Eagle Harbor in Keweenaw County 

(population 1,953 in 1995, U.S. Census Bureau, 1995). The 

sampling site was located at the Integrated Atmospheric 

Deposition Network (IADN) sampling site (photos 7A and 

7B), 100 m from Lake Superior. IADN was established by 

the U.S. and Canadian governments for conducting air and 

precipitation monitoring in the Great Lakes Basin (Egar and 

Adamkus, 1990; Mills and Ullrich, 1998). 

Photo 7A. Background sampling site at Eagle Harbor, 

Michigan.

Photo 7B. Background sampling site at Eagle Harbor, 

Michigan, alternate view.
Sample Collection Methods 9

Sample Collection Methods

The techniques used for collecting both the air and 

the rain samples were based on established methodologies 

(Thrane and Mikalsen, 1981; U.S. Environmental Protection 

Agency, 1997; Bigelow and Dossett, 1988). Each sampling 

site consisted of a conventional high-volume air sampler to 

collect atmospheric particles and gas-phase pesticides, an 

automatic wet-dry precipitation collector to collect wet-only 

deposition, and a precipitation gage to record the total rainfall 

amount during the sampling period.

Field Sampling

Air

Air samples were collected using a modified high-volume 

air sampler (Anderson, Inc., Cleves, Ohio). The sampling 

train consisted of a stainless-steel filter holder connected to an 

18-cm-long aluminum cylindrical cartridge (the modification) 

that was connected to an electric blower motor (photo 8). 

The whole assembly was housed in an aluminum shelter. 

The top of the filter holder was covered with a fine-mesh, 

stainless-steel screen that held a 20.3 × 27.9 cm GFF (glassfiber filter, Whatman, Inc., number EPM2000). The GFF 

was used to collect airborne particles and was rated to have 

a 99.999 percent retention efficiency for sodium chloride 

particles having a mass median diameter of 0.6 μm at a 5 

cm/s face velocity (Whatman, n.d.). The aluminum cartridge 

held two 7.6-cm long by 8.6-cm diameter PUF (polyurethane 

foam) plugs positioned in series. The PUF was used to collect 

pesticides present in the gas phase. The blower motor pulled 

ambient air through the GFF and the PUF at a constant flow 

rate (ranging from 0.90 to 1.26 cubic meters of air per minute 

[m3

/min]) that was monitored and controlled by a mass flow 

controller. Most air samples were 7-d composites taken 

concurrently with the rain sample collection. Initially, the air 

samples were collected for a continuous 4-h period each day 

from 10 a.m. to 2 p.m. By mid-May, sampling times at all 

sites except Eagle Harbor were modified to sample for 5 min 

every hour, 24 h a day, for the 7-d period. The sample timing 

at Eagle Harbor was changed by mid-June. This change in the 

sampling procedure was made to include the diurnal variations 

in ambient concentrations and to provide a more representative 

air sample (Wallace and Hites, 1996). Typical week long air 

volumes for the 4 h/d sampling regime were about 2,000 m3

per sample. The 5-min/h sampling regime averaged about 850 

m3 per sample. 

Prior to use, the GFFs were precleaned by the USGS’s 

Quality of Water Service Unit in Ocala, Florida, by baking 

at 500 °C (degrees Celsius) for several hours. Each GFF was 

then desiccated overnight, preweighed to 0.1 mg, packaged in 

heat-treated aluminum foil, and sealed inside a plastic bag for 

storage and shipment. The cleaned GFFs were then shipped to 

each of the NAWQA study unit offices responsible for sample 

collection. All subsequent handling of the GFFs (and the PUF 

plugs) was performed using solvent-rinsed stainless-steel 

forceps. 

The PUF plugs were precleaned, prior to use, by initial 

extractions with water, rinsed with acetone to remove excess 

water, followed by sequential overnight extractions in a 

Soxhlet apparatus with pesticide-grade acetone followed 

by hexane. Residual solvent was drained from the extracted 

PUFs, and the plugs were dried in a vacuum oven. Individual 

plugs were stored and shipped in heat-treated, wide-mouth 

glass jars with Teflon-lined lids.

Photo 8. Air sampler showing the glass-fiber filter holder and the 

polyurethane foam cartridge.
10 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

At the field office prior to sampling, two clean PUF 

plugs were carefully placed into the aluminum cartridge using 

clean forceps. The plugs were designated as “front” (or “top”) 

and “back” (or “bottom”) depending on their position in the 

cartridge relative to the airflow direction through the cartridge. 

The ends of the cartridge were sealed using screw caps with 

solvent-rinsed silicone gaskets. The cartridge was then sealed 

in a large plastic bag for transport to the sampling site.

At the field site, the air sampler was assembled by 

attaching the PUF cartridge to the sampler blower motor, 

attaching the stainless-steel filter holder to the top of the PUF 

cartridge, followed by placing a clean GFF on the screen of 

the filter holder using forceps. The GFF was held in place 

with a solvent-rinsed gasket and a rigid aluminum frame that 

was secured to the filter holder assembly. At the end of each 

sampling period, the exposed GFF was carefully removed 

from the screen of the filter holder and placed back into the 

original aluminum foil. Any GFF fragments adhering to the 

filter holder screen and gasket were carefully removed with 

the forceps and placed onto the center of the GFF sample. 

Recovery of the entire filter matrix was required, because 

the weight of the collected particulate material was used to 

determine a total suspended particle concentration (TSP; see 

below). The loss of any filter fragments would result in a 

lower than actual TSP calculation. The GFF was gently folded 

in half and again into a quarter of its original size, with the air 

particles inside the filter. The GFF was then wrapped in the 

original aluminum foil and sealed in the original plastic bag. 

The used PUF cartridge was removed from the sampler and 

the ends sealed with the caps from the new PUF cartridge. The 

used PUF cartridge was than sealed in a plastic bag and stored, 

along with the GFF, in a cooler containing ice for transport to 

the field office. The new PUF cartridge and GFF were placed 

into the air sampler to begin the next sample. Basic sample 

collection information recorded for each air sample included 

the sampling period start and stop dates and times, elapsed run 

time from the blower motor counter, and the airflow rate.

Before each air sampler was used to collect an 

environmental sample, the airflow rate was calibrated 

according to the manufacturer specifications and set to about 

1.1 m3/min. The calibration on each sampler was rechecked 

in late June. The electric blower motors that pulled the air 

through the GFF and PUF plugs use graphite brushes to 

operate. These brushes wear down with use and needed to be 

replaced periodically. The air sampling unit was recalibrated 

and the airflow rate set to about 1 m3/min after the graphite 

brushes were replaced and seated properly, or if a new motor 

was installed.

Rain

Weekly wet-only precipitation samples were collected 

using a modified automatic wet-dry precipitation collector 

(Aerochem Metrics, Model 301, Bushnell, Florida). 

Modifications to the collector included replacing the plastic 

collection bucket with a 31-cm diameter, Teflon coated, 

metal funnel connected by corrugated Teflon tubing to a 9-L 

glass carboy inside a small refrigeration unit located beneath 

the deposition collector (photo 9). The tubing was held in 

place and the top of the carboy was covered with aluminum 

foil. Teflon sheeting also lined the rain sampler lid that 

automatically covered the funnel during dry periods. 

Before the first use, the funnel, connecting tubing, and 

carboy were thoroughly cleaned by washing with a 1 percent 

Liquinox detergent solution, followed by thorough sequential 

rinsing with tap water, distilled or deionized water, and 

organic-free water. Finally, each component was rinsed with 

pesticide-grade methanol and allowed to air dry. The carboy 

was then capped with a stopper covered with solvent-rinsed or 

heat-treated aluminum foil until used. 

Photo 9. Modified automatic wet-deposition collector showing 

the refrigerated water-collection container.
Sample Collection Methods 11

During a rainfall event, a rain sensor on the sampling unit 

activated a motor that moved the lid, exposing the collection 

funnel to precipitation. The collected rainwater was funneled 

into the carboy and refrigerated at 4 °C. Refrigeration was 

used to help minimize evaporative losses of the water and to 

reduce volatilization losses and biotic and abiotic degradation 

of the pesticides during the sample collection period.

The total amount (in cm) of rainwater accumulated 

during the sample collection period was obtained from a rain 

gauge (Belfort recording precipitation gage) at each site. 

The amount of rain that fell in a 1-week period ranged from 

zero to several centimeters. Most samples were a composite 

of precipitation events that occurred during a 1-week (7-d) 

period. If more than 1-L of rainwater was collected during 

a sampling period, the total volume was recorded and a 1-L 

subsample was taken for analysis as describe below. Large 

rain events in mid-April, 1995, resulted in shorter collection 

periods for several samples collected at Jackson and Rolling 

Fork, Mississippi. In two cases (April 12 and July 18 samples), 

the sample collection bottles filled to overflowing and the total 

sample volume was estimated. To ensure reasonable analytical 

results, at least 75 mL of rainfall were required as a minimum 

sample size. This volume of rainwater would be produced by 

a rainfall of about 0.1 cm (about 0.04 in.) being collected by 

the precipitation sampler. Sufficient rainwater was collected 

to provide 75 mL or greater volumes of water used for the 

analysis of all samples in this study with the exception of two 

weekly samples from Cedar Rapids (69 mL, July 11 and 62 

mL, August 1) and one weekly sample from Minneapolis (64 

mL, August 24). Typically, if less than 75 mL of rainwater 

was collected at the end of the 1-week sampling period, it was 

left in the container, and the sampling period was extended 

for another week. If at the end of the 2-week period, there 

still was not sufficient rainwater for an appropriate sample 

extraction, the liquid was discarded, and a clean carboy was 

placed into the refrigerator, and a new collection period began. 

Each glass container was marked to show the 75-mL, 350-mL, 

and 1-L fill volumes to help quickly make decisions about 

whether enough rainwater was collected to warrant processing 

the sample.

At the end of a sample collection period, the corrugated 

Teflon tubing attached to the funnel was shaken to dislodge 

and transfer any trapped rainwater into the collection carboy. 

The carboy was then removed from the refrigerator and 

capped with an aluminum-foil covered stopper. The carboy 

was placed into a cooler with ice and transported to the local 

field office for subsequent sample processing (see below). 

In preparation for the next sample, the Teflon-coated 

funnel and tubing were washed with the detergent solution, 

using a soft brush if necessary, followed by thorough 

sequential rinsing with tap water and distilled or deionized 

water, followed by a rinse with pesticide-grade methanol and 

allowed to air dry. This cleaning was done on-site in the field 

laboratory vehicle. A precleaned 9-L collection carboy was 

placed in the refrigerator, the tubing inserted into the carboy, 

and clean aluminum foil wrapped around the mouth of the 

carboy to secure the tubing in place.

Meteorological Data

Meteorological measurements (air temperature, relative 

humidity, wind speed, and wind direction) were not taken 

at the sampling sites with the exception of the Princeton, 

Minnesota, and the Eagle Harbor, Michigan, sites. Each of 

these two sites had fully instrumented weather stations near 

the sampling location that were operated as part of existing 

research operations in the immediate area. Meteorological 

information for the other sites was obtained from the nearest 

National Weather Service (NWS) site, usually located at the 

nearest airport. Often the closest meteorological site was 

several kilometers from the sampling site and consisted of 

hourly maximum and minimum air temperature and wind 

speed and direction. The rainfall amounts accumulated during 

the sampling period were recorded continuously at each 

site by the co-located recording rain gage. The units that 

the meteorological parameters were recorded in were often 

different from one site to the next.

Meteorological data for the Jackson and Rolling Fork 

sites were obtained from the National Climatic Data Center, 

Asheville, North Carolina. Daily maximum, minimum, and 

mean air temperature (°F) values, plus daily means of wind 

speed (mi/h), and wind direction (degrees) for Jackson were 

recorded at the Allen C. Thompson Air Field (site ID number 

321909005). Weekly mean, maximum, and minimum values 

of these data are listed in Appendix 1. Meteorological data for 

Rolling Fork was obtained from two sites: Rolling Fork and 

Greenville, Mississippi. The Rolling Fork site (site ID number 

325409053) recorded daily maximum, minimum, and mean 

air temperature (°F), and the Greenville Municipal Airport 

site (site ID number 3329090 04) recorded hourly wind 

speed (knots) and direction (degrees/10) from about noon to 

midnight each day. Weekly mean, maximum, and minimum 

values of these data are listed in Appendix 2. The same 

meteorological data were used for both the Iowa sites because 

the only available data for the area was from the Cedar Rapids 

International Airport (site ID number 415209142). Data for 

the Iowa and Minneapolis sites were obtained from the NWS’s 

National Oceanic and Atmospheric Administration (NOAA), 

Midwest Regional Climatic Center, Champaign, Illinois. These 

data consisted of hourly measurements of air temperature 

(°F), relative humidity ( percent), wind speed (mi/h), and 

wind direction (degree/10) and were measured at the Cedar 

Rapids International Airport and at the Minneapolis–St. Paul 

International Airport (site ID number 445209313). Weekly 

mean, maximum, and minimum values of these data for the 

Iowa sites are listed in Appendix 3, and in Appendix 4 for the 

Minneapolis site.
12 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

Both the Princeton and the Eagle Harbor sites had 

on-site meteorological stations operated and maintained by 

other organizations conducting research in the area. The 

University of Minnesota at Minneapolis operated the MSEA 

site at which the USGS–Princeton site was located and 

provided the meteorological data for the site. Weekly means 

of air temperature (°C) wind speed (m/s), and wind direction 

(degrees) are listed in Appendix 5. The University of Indiana 

at Bloomington operated the IADN site at which the USGS–

Eagle Harbor site was located and provided the meteorological 

data for the site. Weekly mean, maximum, and minimum 

values of air temperature (°C), relative humidity (percent), 

wind speed (m/s), and wind direction (degrees) are listed in 

Appendix 6.

Analytical Methods

The rain samples were analyzed using a USGS method 

designed for the determination of 44 primarily high-use 

pesticides and 5 pesticide degradates (table 1) in 1-L filtered 

water samples (Zaugg and others, 1995). The method was 

developed initially to support analysis of water samples 

collected by the USGS’s NAWQA program (Gilliom and 

others, 1995). Dissolved-phase analytes were extracted 

from water using an octadecyl (C-18) solid-phase extraction 

(SPE) column and determined by gas chromatography/

mass spectrometry (GC/MS). This study represents one of 

the first applications of this water method to rain samples. 

The degradates that were targeted for analysis included 

2,6-dichloroaniline, formed from alachlor; 2-chloro-4-

isopropylamino-6-amino-s-triazine (CIAT), a potential 

degradation product of either atrazine or propazine; and 

4,4 ́-DDE (p,p ́-DDE), the primary aerobic microbial and 

photooxidative degradation product of the insecticide 

4,4 ́-DDT (Crosby and Moilanen, 1977). Neither DDT nor 

the anaerobic degradation product 4,4 ́-DDD were included 

as compounds in the rain or air method. The air method 

targeted the same 47 analytes determined in the rain method, 

plus dimethoate and 2-chloro-4-ethylamino-6-amino-striazine (CEAT), a potential degradation product of atrazine, 

cyanazine, simazine, and terbuthylazine (table 1). The custom 

air method was based, in part, on aspects of other highvolume air methods (Foreman and Bidleman, 1990; U.S. 

Environmental Protection Agency, 1997), and incorporated 

some extract preparation and the GC/MS analytical procedures 

of the water method to facilitate data interpretation. Portions 

of this air method previously were used for the determination 

of gas-phase pesticides in air samples collected along the 

Mississippi River (Majewski and others, 1998).

Sample Preparation—Air

The GFF and PUF plugs from the field samples were 

prepared and analyzed individually to facilitate interpretation 

of apparent gas–particle distributions of the detected 

pesticides. In addition, each of the two in-series PUF plugs 

was individually extracted and analyzed to monitor the field 

collection efficiency of the PUF for pesticides in the gas 

phase. 

Upon receipt at the NWQL (National Water Quality 

Laboratory), each sample component (one GFF wrapped in 

aluminum foil and sealed within a plastic storage bag, and 

two PUF plugs in separate glass jars) were stored at –10 °C 

until prepared for analysis. Storage times ranged from several 

days to up to 5 months. No storage stability experiments 

were conducted as a part of this study. Each air sample 

was prepared for analysis in batches that are identified by a 

“set number” in this document. Samples or components of 

samples from weeks 1 through 5 overlapped two or more sets. 

For weeks 6 through 24, all samples for a given week were 

contained within a discrete set. The set numbers are provided 

in many of the data tables to provide a cross reference link 

between the field-sample and the quality-control data.

Prior to extraction the foil wrapped GFF was removed 

from the storage bag, the foil partially opened, was then placed 

in a desiccator containing moisture-indicating drying agent 

for 24 h at room temperature. Following desiccation, the GFF 

was immediately weighed to 0.1 mg. The difference in this 

weight and the original GFF tare weight provided the mass of 

particles collected on the GFF, assuming the entire GFF matrix 

was recovered when removed from the sample holder. The 

TSP concentration (in micrograms per meter cube of air, μg/

m3

) was obtained by dividing the mass of particles collected 

by the volume of air sampled.

Next, each GFF was cut into approximately 6-cm- by 

2-cm-wide strips and placed into a 500-mL boiling flask 

containing extraction solvent (see below) for reflux extraction 

as used by Foreman and Bidleman (1990). Each PUF plug 

was inserted sideways into a Soxhlet extractor using solventcleaned, stainless-steel forceps. Each PUF plug was handled 

carefully to avoid tearing the foam, because most plugs were 

reused at least once (see below). To each sample component, 

100 μL of a methanol surrogate solution containing 

1 ng/μL each of 2

H10-diazinon (diazinon-d10), 2H6-αhexachlorocyclohexane (α-HCH-d6), and terbuthylazine was 

added. This addition was made to the top of the PUF plug or 

directly into the round bottom flask containing the GFF strips. 

Each component was then extracted with 300 mL of either 

a 1:1 by volume acetone:hexane solution (samples collected 

prior to May 16, 1995; sets 95.168 and lower) or a 36 percent 

ethyl acetate in hexane solution (May 16, 1995 and later 

samples; sets 95.177 and higher) for at least 16 h. Following 

extraction, clean, granular sodium sulfate was added to the 

extracts to remove any residual water. The extracts were 

then stored at either –10 °C or 4 °C between subsequent 

preparation steps, as necessary. 
Analytical Methods 13

Table 1. Analyte list, grouped by chemical class, and associated reporting levels for rainwater and air methods.

[m3, cubic meter; na, compound not included in water sample analysis; ng/m3, nanogram per cubic meter; PUF, polyurethane foam; μg/L. microgram per liter; 

—, reporting level not estimated because of poor PUF collection efficiency; >, greater than; ≥ , greater or equal to]

Herbicides

Reporting level

Insecticides

Reporting level

Air 

samples1

(ng/m3)

Rain 

samples2

(μg/L)

Air 

samples1

(ng/m3)

Rain 

samples2

(μg/L)

Chloroacetanilides Organophosphates

Acetochlor 0.012 0.002 Azinphos-methyl9 0.076 0.001

Alachlor 0.012 0.002 Chlorpyrifos 0.024 0.004

2,6-Diethylaniline3,4 — 0.003 Diazinon 0.012 0.002

Metolachlor 0.012 0.002 Dimethoate 0.047 na

Propachlor 0.041 0.007 Disulfoton9 0.100 0.017

Triazines Ethoprop5 0.003

Atrazine 0.006 0.001 Fonofos 0.018 0.003

CEAT6 0.018 na Malathion 0.058 0.005

CIAT7 0.012 0.002 Methyl parathion 0.035 0.006

Cyanazine 0.024 0.004 Parathion 0.024 0.004

Metribuzin 0.024 0.004 Phorate4 — 0.002

Prometon8 0.106 0.018 Terbufos4 — 0.013

Simazine 0.029 0.005 Carbamates

Dinitroanilines Carbaryl9 0.036 0.003

Benfluralin5 0.100 0.002 Carbofuran9 0.036 0.003

Ethalfluralin5 0.100 0.004 Organochlorines

Trifluralin5 0.100 0.002 α-HCH 0.012 0.002

Pendimethalin 0.024 0.004 γ-HCH (Lindane) 0.024 0.004

Thiocarbamates 4,4 ́-DDE10 0.035 0.006

Butylate4 — 0.002 Dieldrin 0.006 0.001

EPTC4 — 0.002 cis-Permethrin 0.029 0.005

Pebulate4 — 0.004 Fungicide

Triallate 0.012 0.001 Propargite I and II11 0.076 0.013

Thiobencarb 0.012 0.002

Miscellaneous

Dacthal 0.012 0.002

Linuron 0.012 0.002

Molinate4 — 0.004

Napropamide 0.018 0.003

Pronamide 0.018 0.003

Propanil 0.024 0.004

Tebuthiuron8 0.175 0.010

Terbacil9 0.082 0.007

1 Estimated for an air volume of 850 m3

. 

2

 Reporting levels for rain method are set at the method detection limit (MDL) values listed in table 9 of Zaugg and others (1995).

3

 An alachlor degradation product.

4

 Gas-phase compound poorly collected by two PUF plugs at air volumes used in this study. No reporting levels for air samples were calculated for these 

compounds.

5

 Typical PUF plug breakthrough >50 percent at ≥ 850 m3 air volume.

6

 CEAT, 2-chloro-4-ethylamino-6-amino-s-triazine, a transformation product of atrazine, cyanazine, simazine, and terbuthylazine.

7

 CIAT, 2-chloro-4-isopropylamino-6-amino-s-triazine, a transformation product of atrazine and propazine. CIAT concentrations in the rain method are all 

estimated because of low recovery of this compound during the solid-phase extraction step (Zaugg and others, 1995).

8

 Variably low recovery during extract preparation in the air method.

9

 Estimated quantitation in both rain and air methods because of thermal instability during gas chromatography (Zaugg and others, 1995).

10

 A DDT transformation product. DDT was not determined in the analytical methods used.

11

 Propargite consists of two isomeric forms that were incompletely resolved with the analytical conditions used.
14 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

The extracts were then reduced to 6 to 10 mL by 

distillation at 90 °C in a Kuderna-Danish apparatus fitted with 

a 10-mL receiver tube. This extract was further reduced to 8 

mL or less under a gentle stream of nitrogen gas, if needed. 

A 0.25-mL equivalent amount of granular sodium sulfate 

was added to the extracts to scavenge any residual water. The 

extracts were then mixed on a vortex mixer, and more sodium 

sulfate was added in similar aliquots as required to ensure 

that all residual water was scavenged from the extracts. The 

extracts were then reduced to 0.5 mL under a gentle stream of 

nitrogen gas.

Sample Cleanup

The samples from extraction set 95.118 (including 

selected sample components from week 1, April 5 and week 

2, April 12) initially were passed through a Pasteur pipette 

column containing about 0.75 g of powdered sodium sulfate 

and eluted with ethyl acetate to a final volume of 2 mL. This 

cleanup procedure, however, was inadequate in eliminating 

unwanted interferences, even after repeating. These extracts 

were again reduced to about 0.5 mL and introduced into an 

octadecylsilane (C18) solid-phase extraction (SPE) column 

(the same column type used to isolate the pesticides from the 

rainwater samples, see below). The pesticides were eluted 

from the C18 column with ethyl acetate to a final volume of 

4 mL. This C18 column cleanup step was also inadequate in 

removing sufficient amounts of co-extracted interferences 

from the PUF extracts, so a Florisil column cleanup procedure 

was employed for all subsequent samples in this study. 

Extracts from sets 95.122 (selected samples from weeks 

1 through 3) and above were passed through a Pasteur pipette 

column containing 0.75 g of Florisil (EMD Chemicals, Inc. 

number FX0284-1, fully activated at 150 °C for at least 

2 h) overlain with 1 cm of powdered sodium sulfate. The 

Florisil columns were prerinsed with at least 6 mL of ethyl 

acetate prior to introducing the 0.5-mL sample extracts to 

the columns. The pesticides were eluted from the column 

with ethyl acetate and collected into a test tube containing 

0.1 mL of a perdeuterated polycyclic aromatic hydrocarbon 

internal standard solution in toluene. The initial column 

elution volumes were 2 mL for extraction set 95.122. This 

was increased to 3 mL for sets 95.130 and 95.138 (selected 

samples from week 3 and all samples from weeks 4 and 5), to 

3.5 mL for sets 95.168 through 95.237 (weeks 6 to 13), and 

finally to 4 mL for all remainder sets (weeks 14 to 24). The 

ethyl acetate volumes were increased to ensure an adequate 

elution of all the pesticides from the Florisil column (see 

Quality Control—Air Samples section below). Any glass 

fibers in GFF extracts that were not removed during previous 

sample transfer steps were removed during sample cleanup.

Polyurethane Foam Plug Reuse

Limitations in the total number of PUF plugs available 

for this study required that the PUF plugs not torn or damaged 

during handling be reused. After the PUF sample was solvent 

extracted, the residual solvent was squeezed from it. Each PUF 

was then vacuum dried at 90 °C, then individually sealed in 

heat-treated glass jars. The recycled PUF plugs were used in at 

least one subsequent field sample collection, either as a field 

air sample or field air blank component.

Sample Preparation—Rain

The rainwater samples were prepared and analyzed 

according to the procedures detailed in Zaugg and others 

(1995) and Lindley and others (1996). For all sites except 

Eagle Harbor, Michigan, the rainwater samples were filtered, 

and the pesticides were isolated on a C18 SPE column at the 

field offices using an “on-site” processing procedure (Zaugg 

and others, 1995). Briefly, this processing procedure included 

swirling the rainwater sample in the 9-L carboy, then removing 

approximately 1 L (or less, if 1 L was unavailable) from the 

carboy and filtering it through a 0.7-μm pore size GFF into a 

1-L heat-treated, amber glass bottle (Sandstrom, 1995). The 

filtrate was fortified with methanol (volume equivalent to 

1 percent of the sample volume) and 100 μL of a surrogate 

solution containing 1 ng/μg each of diazinon-d10, α-HCH-d6, 

and terbuthylazine. The water was then passed through a 0.5-g 

C18 SPE column at about 25 mL/min. The excess water was 

removed from the cartridge by passing a small volume of 

air through it. The cartridge was then sealed in a plastic bag, 

packaged with ice, and shipped to NWQL. The Eagle Harbor 

water samples were sent to NWQL unfiltered. Both the GFF 

filtration and SPE isolation steps for these samples were 

performed at NWQL. 

At NWQL, the rainwater extraction cartridges were 

prepared for analysis along with other water extraction 

cartridge samples that were submitted from other USGS 

studies. The samples were processed similar to the air 

samples, in batches identified by “set number.” Any residual 

water remaining in the cartridge was removed by briefly 

passing a gentle stream of dry nitrogen gas through it. The 

pesticides were eluted from each cartridge with 2 mL of ethyl 

acetate (substituted for the hexane–isopropanol elution solvent 

described in Zaugg and others, 1995 and Lindley and others, 

1996) into a test tube containing 0.1 mL of a toluene solution 

containing 1 ng/μL each of three perdeuterated polycyclic 

aromatic hydrocarbon internal standards. 
Field Data Results 15

Sample Analysis

Each air and rainwater extract was reduced in volume 

by evaporating it to about 150 μL using nitrogen gas and a 

Zymark TurboVap evaporator. They were then transferred into 

a 400-μL autosampler vial insert along with a 100-μL toluene 

rinse. Analysis was accomplished using gas chromatography/

electron-impact mass spectrometry (GC/EIMS) operated 

in the selected-ion-monitoring mode. Chromatographic 

conditions and a listing of quantitative and secondary ions 

monitored are detailed in Zaugg and others (1995) and 

Lindley and others (1996). Qualitative identification of an 

analyte in a sample required meeting both chromatographic 

and mass spectrometric criteria. The observed retention time 

of the gas chromatography (GC) peak for the quantitation 

ion for the analyte needed to be within ±6 seconds of the 

expected retention time. These times were computed relative 

to the internal standard, with expected retention times 

derived from injections of the calibrations. Mass-spectral 

verification for each analyte was accomplished by comparing 

the relative integrated abundance values of the three or four 

ions monitored with the relative integrated abundance values 

obtained from the calibration standards. The relative ratios 

of the monitored ions needed to be within 20 percent of 

the relative ratios of those obtained on injection of a 1-ng 

calibration standard in the absence of any obvious interference 

(Zaugg and others, 1995). Qualitative analysis using dualcolumn GC with electron capture detection (GC/ECD) 

(Foreman and others, 1995) was used to verify the presence 

of 4,4 ́-DDE in the Rolling Fork 12th week air sample, and 

dacthal in the Eagle Harbor 12th week air sample. 

Method Analyte Reporting Levels

The reporting levels for the water method used for the 

rainwater samples were set equivalent to the method detection 

limit (MDL) calculated by Zaugg and others (1995) and 

Lindley and others (1996) using the approach of the U.S. 

Environmental Protection Agency (1997). The reporting levels 

for all the analytes included in the air and rain methods are 

shown in table 1. An MDL determination was not performed 

for the air method. Reporting levels for the air method were 

estimated on the basis of reporting levels for the water method. 

These estimates were based on a typical 850-m3

 sample 

volume and were set with consideration for the recoveries 

from the air method laboratory-spike samples, the field PUF 

collection efficiency experiments, and interfering compounds 

observed in the samples and blanks. For seven compounds, 

the PUF collection efficiencies were so poor at the typical 

air volumes used in this study (see below) that reporting 

levels were not estimated. Reported concentrations for these 

seven analytes in field samples are, most likely, substantial 

underestimates of the true air concentration. 

The concentrations of four analytes—azinphos-methyl, 

carbaryl, carbofuran, and terbacil —if detected, were reported 

as an estimated value and qualified with an “E” code. These 

compounds were susceptible to thermal instability during 

GC/MS–SIM (selective ion mode) analysis that could result 

in a high or low bias during analyte quantitation (Zaugg and 

others, 1995). CIAT exhibited a reduced collection efficiency 

on the SPE column (42 percent mean recovery in laboratory 

water spike recovery results, see below), and its concentration 

was also qualified with an E code for the rainwater samples 

only. CIAT was well recovered in the air method and the E 

code qualification was not needed. Reported concentrations for 

those analytes detected in either the air or water samples that 

were at or below the reporting level for the method were also 

qualified with an E code. Tebuthiuron and prometon exhibited 

variably poor recoveries in the laboratory preparation of the air 

sample extracts and are coded with an “R.” 

Field Data Results

The pesticide concentration data for each site are 

presented in tables starting with the most southern site at 

Jackson, Mississippi, and ending with the most northern site 

at Eagle Harbor, Michigan. The air concentration units are 

in ng/m3, and the rainwater concentration units are in μg/L. 

The analytes in each table are sorted by type (herbicide or 

insecticide) and ordered by chemical class, as shown in 

table 1.

Air

Tables 2 through 8 (for access to tables 2 through 8, 

see list of Tables) show the GFF and PUF air concentration 

data for each sampling site. Each data table includes the 

start sampling date, the week number, the type of sample 

component (GFF, front PUF, back PUF), set number, total 

air sample volume (m3), total particle weight (g), TSP 

concentration (μg/m3), and analytical results (ng/m3) for each 

sample. At the bottom of each analyte column is the number 

of times and percent that the analyte was detected on a GFF 

and PUF during the study at that site. At the bottom of each 

of the surrogate compounds at the end of each table are the 

mean percent recovery and standard deviation for the number 

of samples analyzed. Table 9 (see at table_9.xls)lists the field 

and laboratory comments associated with each air sample 

component. 
16 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

Rain

Tables 10 through 16 (for access to tables 10 through 16, 

see list of Tables) show the rainwater concentration data for 

each sampling site. Each data table includes the start sampling 

date, set number, sample volume (mL), rainfall amount (cm), 

and analytical results (μg/L) for each sample. At the bottom of 

each analyte column is the number of times and percent that 

the analyte was detected during the study at that site. At the 

bottom of each of the surrogate compounds at the end of each 

table are the mean percent recovery and standard deviation for 

the number of samples analyzed. Table 17 (see at table_17.

xls) lists the field comments associated with each rainwater 

sample. 

Quality Assurance Program

A number of quality control (QC) activities were 

performed during this study to ensure the quality of the 

sampling and analytical methods. They were designed to 

monitor various aspects of the field sampling and analytical 

method performance for both the air and the rain samples, 

and included field blanks, laboratory blanks, equipment 

blanks, PUF collection efficiency spike experiments, field 

checks of the PUF trapping efficiency, and analyte storage 

stability in rainwater. The surrogate compounds diazinon-d10, 

α-HCH-d6, and terbuthylazine were added to all the samples 

(including the QC samples), as detailed above, to monitor 

sample-specific preparation and analytical efficiencies. Both 

the air and rain methods had QC procedures designed for the 

specific method and are discussed in detail below.

Quality Control for Air Samples

The sampling method used in this study to trap airborne 

pesticides is dependent on the capability of the GFF to trap 

the wide range of particulate matter that pesticides will sorb 

to, and the capability of the PUF to effectively sorb and retain 

the pesticides in the gas phase. The particle size range trapped 

by the GFF is based on the physical properties of the filter 

and is determined by the manufacturer. The capability of the 

PUF to trap and retain gas-phase pesticides is dependent on 

the physical and chemical properties of each pesticide and the 

PUF matrix that allow sorbtion to occur. Once sorbed to the 

PUF, each pesticide can also migrate through the PUF during 

the course of the sampling period. This migration is influenced 

by the physical and chemical properties of the pesticide as 

well as by environmental conditions such as the airflow rate 

through the PUF, the air temperature, and the atmospheric 

moisture content (Pankow, 1989; Bidleman, 1985). The PUF 

collection efficiencies for each pesticide and their migration 

potential were assessed in two ways. The first was with a spike 

experiment, and the second was by separate analyses of each 

PUF plug in almost all field samples as described below.

Sample-specific estimates of collection efficiencies 

for pesticides in the gas phase by the two PUF plugs were 

assessed by separate analysis of the front and back PUF plugs 

on nearly all field air samples. The presence of minimal 

amounts of an analyte on the back plug relative to the front 

plug suggested minimal penetration of the pesticide beyond 

the front plug and a complete collection of the gas phase by 

both plugs. The presence of an analyte in the back PUF at a 

concentration greater than in the front PUF, or its presence 

only in the back PUF, suggested that the collection efficiency 

for that compound was low, that the compound migrated 

through the PUF during the sampling period. In this situation, 

the total measured analyte concentration in the sample may 

represent a lower than actual air concentration. 

Air Method Set Blanks

One (or more) air method set-blank sample (air set blank) 

was processed with each set of field air samples. Most air set 

blanks were prepared using the field equipment air blanks 

submitted on a rotating basis from each of the seven sampling 

locations. These field air blanks were taken by briefly 

installing one GFF and two PUF plugs into the air sampler, 

then removing and placing them back into their original 

storage containers. The sampler was not turned on, and no 

air was pulled through the GFF and PUF plugs. The field air 

blanks used as air set blanks typically consisted of a GFF 

plus two PUF plugs, and were used to assess contamination 

derived from both the field handling and the laboratory 

analytical procedures. The GFF from the field air blank also 

was weighed to measure any blank contribution to the total 

suspended particle concentration determination. For five sets 

of samples, field blanks were not provided for use as the setblank sample. Therefore, a lab blank sample (consisting of 

only one PUF plug) was substituted for the field blank sample 

as the set blank. The PUF plugs used for the field blanks or 

laboratory blanks included reused, cleaned PUF from previous 

field samples in this study.
Quality Assurance Program 17

 Analyte concentrations in the air method set-blank 

samples were calculated assuming a typical air volume of 

850 m3 and are shown in table 18 (see at table_18.xls). Only 

6 of the 49 analytes were detected in any of the 21 field 

blanks. Dieldrin, EPTC, and tebuthiuron were each detected 

only once, whereas trifluralin and chlorpyrifos were detected 

three times, and diazinon was detected four times. CEAT 

was only detected once in a laboratory blank sample with a 

concentration near the instrument detection level (IDL). The 

GFF blanks were substantially cleaner than the PUF plug 

blanks in terms of the chromatographic baseline noise. For 

most analytes detected in field and laboratory blank samples, 

secondary ion responses were near the IDL, and one or more 

of the relative ion abundance ratios was not within 20 percent 

of the expected value. The procedure for classifying an analyte 

as “detected” in field samples was more conservative than 

that used for the blanks. An analyte was “detected” in an air 

sample component only if all the characteristic ions were 

present at sufficient intensity above the IDL and if the relative 

ion abundance ratios were correct so the analyte could be 

adequately distinguished from typical GFF or PUF plug blank 

noise.

Air Method Set Spikes

An air method laboratory spike sample (air-method 

spike) was processed with each set of field samples to monitor 

compound recoveries from the preparation of a sample through 

the analytical process. An air-method spike sample consisted 

of one clean (often reused) PUF plug that, after placing it into 

a Soxhlet extractor, was fortified with 100 μL of a methanol 

solution containing 1 ng/μL each of the 49 air method analytes 

listed in table 1.

For set numbers 95.177 and greater, either 3.5 or 4 mL 

(fraction F1) of the ethyl acetate elution solvent was collected 

from the florisil cleanup column. This F1 aliquot was used 

to quantitate the pesticide concentrations in the field and QC 

samples. For these sets, an additional 1-mL aliquot (fraction 

F2) of ethyl acetate was collected from the florisil column for 

the air-method spike samples. This F2 aliquot was analyzed 

separately from the F1 aliquot to assess the pesticide elution 

recovery from the Florisil column. 

Recoveries for laboratory air-method spike samples 

are shown in table 19 (see at table_19.xls). The recoveries 

for the F1 aliquot are reflective of compound recoveries 

from sample extraction through analysis for each set of 

field samples. Sample-specific preparation errors resulted 

in low analyte recoveries in set 95.243 air-method spike, 

and recoveries for this spike sample were omitted from the 

statistical summaries. Set 95.118 recoveries were obtained 

after three cleanup column steps (which included two sodium 

sulfate columns and one C18 SPE column). Although 

recoveries were acceptable for most analytes in set 95.118, 

these columns still were inadequate for eliminating unwanted 

interferences. Implementation of the Florisil column cleanup 

step removed additional, but not all, unwanted interference, 

especially in PUF extracts. Recoveries for most pesticides in 

F1 were acceptable (greater than 70 percent) using a 3.0-mL 

elution volume. Prometon and tebuthiuron, however, exhibited 

variably low recoveries. Increasing the F1 volume to 3.5 mL 

further improved the recoveries of all the analytes, although 

analysis of the F2 aliquots of the air-method spike sample still 

revealed low amounts (usually less than 10 percent of F1) of 

some pesticides. Increasing F1 to 4.0 mL seemed to provide 

acceptable recoveries for most compounds, with few analytes 

detected at low levels in F2. Prometon and tebuthiuron, 

however, continued to exhibit highly variable recoveries even 

at the 4.0-mL F1 volume. Partial loss of these two compounds 

appeared to be the result of irreversible sorption to highly 

active sites on the Florisil sorbent. Prometon occasionally 

exhibited a similar sorptive loss on the C18 SPE column used 

for isolating pesticides in the water method applied to the rain 

samples (see below). 

Mean laboratory method-spike recoveries exceed 65 

percent for all compounds except prometon and tebuthiuron. 

Thirty-one of the 49 air method analytes had mean recoveries 

of 90 percent or greater. Relative standard deviation of 

the mean recoveries ranged from 7 to 67 percent, with 29 

compounds at 20 percent or less. 

Polyurethane Foam Plug Collection Efficiency 

Spike Experiments

Three spike collection-efficiency experiments were 

performed to monitor the migration of pesticides through 

the two PUF plugs (front and back) and to estimate the total 

air sampling and analysis method recoveries. These tests 

were carried out by spiking a GFF with 80 μg of each of 

the air method pesticides and drawing ambient air through 

the GFF–PUF assembly at about 1 m3

/min under the 

following total sample volume/mean temperature conditions: 

310 m3/19.2 °C, 850 m3/23.3 °C, and 1,730 m3/24.0 °C. 

Pesticide concentrations were determined on the GFF and both 

PUF plugs from each test. The PUF collection efficiency for 

each test was calculated as the total amount of each analyte on 

both PUFs divided by the original spiked amount minus the 

concentration remaining on the GFF, times 100 (table 20 [see 

at table_20.xls]). The migration of each analyte from the front 

PUF into the back PUF was defined as “breakthrough” and 

calculated as the amount of each analyte recovered on the back 

PUF divided by the amount recovered on the front PUF, times 

100. 
18 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

High amounts (80 μg) of each method analyte were used 

in the PUF collection efficiency spike tests. This was done to 

ensure easy detection of the analytes and because the test was 

an elution and not a frontal (continuous gas-phase pesticide 

introduction) chromatography experiment (Bidleman, 1985). 

During the extraction set, each sample component was 

fortified with 100 μL of a surrogate solution containing 

1 ng/μg each of diazinon-d10, α-HCH-d6, and terbuthylazine. 

The high analyte-to-surrogate amounts resulted in an inability 

to adequately quantitate some surrogate recoveries because 

of interferences. These PUF plug collection efficiency tests 

were conducted using continuous air sampling over the sample 

period and not the 4 h/d or 5 min/h sampling schemes used to 

collect the week-long field air samples. It is not known how, or 

if, the 4 h/d or 5-min/h field-sampling scheme would change 

these PUF efficiency results.

The sampling and meteorological conditions and the 

pesticides recoveries from the spiked GFF and front and 

back PUF plugs for the three spike collection-efficiency 

experiments are shown in table 20 (see at table_20.xls). The 

total recoveries from all three components are also shown. 

Thirty of the 49 compounds tested had total recoveries of 

70 percent or greater at the 1,730-m3

 air volume. Fifteen of 

these analytes exhibited greater than 90 percent total recovery, 

indicating a quantitative collection by the sampler at the 

highest air-volume test. Cyanazine, tebuthiuron, azinphosmethyl, and cis- and trans-permethrin exhibited less than 

10-percent migration from the GFF to the front PUF plug, 

even at the highest (1,730 m3) air volume. This finding was 

not unexpected because most of these compounds have low 

liquid phase (or subcooled-liquid phase) vapor pressures 

(Majewski and Capel, 1995). Tebuthiuron, however, has a 

vapor pressure comparable to other analytes that exhibited 

greater migration to the PUF. This analyte was only observed 

in the 13 June (week 11) Iowa City air sample (see table 4 

[see at table_4.xls]) and was detected only on the PUF with 

a 123-percent breakthrough into the back plug (table 21 [(see 

at table_21.xls)]). Retention of tebuthiuron on the GFF in the 

spike experiment might be a result of strong adsorption of 

this pesticide to the GFF matrix (comparable to the apparent 

strong adsorption to active sites on the Florisil cleanup 

column). In fact, evidence of this partial strong adsorption 

to the GFF matrix in the spike experiment was indicated for 

most analytes, because small amounts of many, even volatile 

analytes (for example, 2,6-diethylaniline, butylate, pebulate, 

and EPTC) remained on the filter at all three test volumes. 

These four analytes also were observed on the GFF in low 

amounts in some field samples. Sometimes they were detected 

on the GFF only and not the PUF (see tables 2 through 8 [for 

access to tables 2 through 8, see list of Tables] and table 21 

[see at table_21.xls]). This further implicated binding of a 

small portion of the analyte to active sites on the GFF or to the 

particles collected on the GFF for a number of the analytes, 

even when most of the gas-phase component was poorly 

retained by the two PUF plugs.

Thirty-one analytes exhibited little or no breakthrough 

into the back PUF plug for all three test volumes. Although 

well recovered overall, several analytes (for example, 

propachlor and triallate) exhibited substantial breakthrough 

at the 1,730-m3 air volume sample. Benfluralin, ethalfluralin, 

trifluralin, and α-HCH exhibited substantial migration into 

the back PUF at the 850-m3 air volume, but total recoveries 

of each were in excess of 85 percent. Phorate was only well 

recovered at the 310-m3 air volume. Breakthrough was nearly 

90 percent for molinate at the 310-m3 air volume, and PUF 

appeared ineffective at collecting the more volatile pesticides 

2,6-diethylaniline, butylate, EPTC, and pebulate, because 

these compounds were poorly recovered at the 310-m3 air 

volume. Degradation losses during sampling were implicated 

for napropamide, terbacil, disulfoton, malathion, and 

propargite, because these compounds exhibited poor overall 

recoveries at one or more air volume, and there was little or no 

evidence of pesticide migration into the back PUF plug. These 

losses likely were a result of reaction of the pesticide with 

hydroxyl radical or other photochemical oxidants. Degradative 

losses might have occurred for some of the other poorly 

recovered analytes, as well. The reported concentrations in 

the field samples may substantially underestimate the true 

atmospheric concentration for those analytes that were poorly 

collected by the two PUF plugs at the 850 m3

 and greater air 

volumes typically used for collection of the air samples. 

Polyurethane Foam Plug Collection Efficiency 

Estimation from Field Samples

Sample-specific estimates of collection efficiencies 

for pesticides in the gas phase were assessed by separate 

analysis of the front and back PUF plugs on nearly all field 

air samples. Thirty-eight of the 49 analytes were detected in 

one or more of 148 air samples where front and back PUF 

plugs were individually analyzed (table 21 [see at table_21.

xls]). Fourteen of these 38 analytes were not detected in the 

back plug, and the maximum observed breakthrough did not 

exceed 17 percent for acetochlor, metolachlor, atrazine, CIAT, 

thiobencarb, chlorpyrifos, and methyl parathion (table 21 [see 

at table_21.xls]). These results indicate a complete gas-phase 

collection by the dual PUF-plug sorbent trap for these 21 

analytes. Minimal amounts, if any, of these 21 compounds 

were also detected on the back plug in the PUF collection 

efficiency spike tests (table 20 [(see at table_20.xls]). Most 

of the compounds that exhibited a moderate-to-high (100 

percent) breakthrough in the spike tests also exhibited a high 

breakthrough percentage in the field air samples. Propanil, 

fonofos and malathion exhibited breakthrough in few samples 

(<15 percent), but when breakthrough did occur, it sometimes 

exceeded 100 percent. Five compounds were detected only 

on the back PUF in at least one sample. This observation can 

occur for compounds that show considerable breakthrough 

at air volumes less than the sample volume, especially when 

the ambient air concentration decreased substantially during 
Quality Assurance Program 19

the week-long sampling period. Three of the most volatile 

pesticides—2,6-diethylaniline, pebulate, and EPTC—were 

detected on the filter, but not on the PUF plugs in one sample. 

This suggests apparent complete collection but, in fact, 

complete breakthrough likely occurred on the basis of PUF 

collection efficiency spike tests (table 20 [(see at table_20.

xls]). These results highlight the importance of conducting 

spike experiments to verify field observations.

Surrogate Recoveries in Air Sample 

Components and Associated Quality Control 

Samples

Individual recoveries of surrogate compounds are 

provided in table 18 (see at table_18.xls) for air method set 

blanks, in table 19 (see at table_19.xls) for air method setspike samples, and in tables 2–8 (for access to tables 2–8, see 

list of Tables) for the GFF and PUF plug components of field 

air samples. Surrogate recoveries indicated overall acceptable 

performance for the sample preparation and analysis steps for 

many samples. Some surrogate recoveries were uniformly low 

and reflective of sample preparation problems. 

Mean and standard deviation of surrogate recoveries 

for the air method set blank, set spikes, and the field sample 

GFFs and PUF plugs are shown in table 22 (see at table_22.

xls). The mean recoveries of diazinon-d10 were comparable in 

each of the four categories and ranged from 72 to 138 percent. 

The diazinon-d10 purity problem that resulted in high biased 

recoveries of this surrogate for some field-prepared rain 

samples (see below) was not a problem for the air method 

samples because the same diazinon-d10 source material was 

used to prepare both air method calibration and surrogate 

solutions. Recoveries of α-HCH-d6 and terbuthylazine in 

the field sample PUF plugs were higher and much more 

variable than observed in the air method laboratory set spikes, 

laboratory and field set blanks, and the GFF field sample 

components. This was due, in part, to one or more unidentified 

co-eluting compounds in the field PUF sample extracts that 

interfered with accurate quantification of the surrogates. As an 

indication of these interferences, high-biased recoveries or an 

interferent code are reported for the surrogate compounds in 

the data tables for field air samples. A conservative approach 

was used for reporting concentrations of target pesticides 

in field samples compared with the reporting of surrogate 

recoveries in these samples, as well as in the method setblank and set-spike samples, because of the interfering ions 

(noise) in PUF plug analyses. Concentrations for method 

analytes were reported only if the compound met detection 

(correct relative retention time and ion ratios) and quantitation 

(including no coeluting interferents with the quantified ion) 

criteria. If interferences occurred, target analytes were not 

reported as detected, and the reporting level was increased to 

a value above the concentration shown in table 1, if necessary. 

In addition, although not registered for use as an agrochemical 

in the U.S., terbuthylazine is used as an algicide, microbicide, 

and microbistats in industrial water-cooling systems as well 

as in residential and commercial ornamental ponds, fountains, 

and aquaria (U.S. Environmental Protection Agency, 1995). 

This added environmental concentration produced an 

undesirable positive bias in terbuthylazine surrogate recoveries 

for some field samples and diminished its effectiveness as 

a reliable surrogate. As noted above, a more conservative 

approach was used for classifying target pesticides as 

“detected” in the field samples than was used in establishing 

surrogate recoveries in the air method set-blank and set-spike 

samples because of the noise in PUF plug analyses.

Quality Control for Rain Samples

The rain sampling method used in this study composited 

the collected rainfall during 7-d periods in a refrigerated glass 

container. Laboratory QC procedures (water-blank and waterspike samples) were routinely done. In addition, several field 

QC studies were done and included taking field equipment 

blanks and a pesticide stability in a rainwater test.

Field Equipment Water Blanks

During the 6-month study, one field equipment 

water-blank sample was collected at each sampling site to 

assess the extent of combined field and laboratory-derived 

contamination. The field equipment water-blank sample 

consisted of pouring 3 L of pesticide-residue grade water 

(Mallinckrodt-Baker) into a clean, 9-L glass carboy, then 

pouring it into the cleaned sampler collection funnel and 

Teflon tubing and collecting the water in another clean glass 

carboy. A 1-L aliquot of this water was then processed in the 

same manner as the rainwater samples. No target analytes 

were detected in any of the seven field blanks with the 

exception of atrazine (0.002 μg/L) in the Jackson, Mississippi, 

blank (collected 28 April 95; set 1942), and metolachlor 

(0.003 μg/L) and propanil (0.011 μg/L) in the Rolling Fork, 

Mississippi, (16 May 95; set 2042) field-blank sample.
20 Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data

Laboratory Water Blank and Spike Samples 

Laboratory reagent-water blank (laboratory water blank) 

and spike (laboratory water spike) samples were processed 

with each set of rain samples that were analyzed. The 

laboratory water blanks were used to monitor for laboratoryderived contamination, whereas laboratory water spikes 

were used to monitor matrix extraction efficiency of the 

target pesticides. These QC water samples were processed 

identically as the regular rainwater samples described above, 

but they were not filtered (comparable to the whole-water 

samples submitted from Eagle Harbor). The laboratory 

water blank and water spike samples were included in the 

laboratory sample preparation procedure beginning with the 

surrogate fortification step just prior to the SPE isolation step. 

The laboratory water blanks and water spikes were prepared 

using approximately 1 L of pesticide-free reagent water. Each 

laboratory water spike was fortified with 100 μL of a methanol 

solution containing 1 ng/μL each of the method analytes.

Table 23 (see at table_23.xls) shows the analytes detected 

in eight laboratory water blanks (coded by set number). No 

analytes were detected at less than the reporting level listed 

in table 1 in any of the other 52 laboratory water blanks 

processed with the rain samples. Only 9 of 47 water-method 

analytes were detected in the blanks. All detections were near 

or below the reporting level. Six analytes were detected only 

once, with five of them occurring in set 2058 laboratory water 

blank. The most commonly detected analyte was 4,4 ́-DDE 

in three blanks. The compound 4, 4 ́-DDE, however, was not 

detected in any rain sample.

Laboratory Water Spike Recoveries

Recoveries of analytes in laboratory water spikes from 

59 sets of samples are shown in table 24 (see at table_24.

xls). Mean recoveries were greater than 85 percent for most 

analytes and were generally excellent. Mean recoveries were 

comparable to, or somewhat greater than, those observed by 

Zaugg and others (1995) and Lindley and others (1996), but 

variability (as indicated by percent relative standard deviation 

[RSD] of the mean) in the recoveries were somewhat greater 

than previously reported by these authors for a number of 

analytes. Prometon had substantially lower mean recovery 

and greater variability than previously reported. Prometon 

appears to exhibit partial irreversible sorption to the SPE 

column when sample conductivity is low (as occurs in reagent 

water used to prepare laboratory water spikes). Disulfoton 

and, especially, linuron had higher than expected variability in 

their recoveries. Disulfoton is reportedly unstable in solution 

(Munch and Frebis, 1992), and linuron may be susceptible 

to variable thermal instability during GC/MS analysis. Both 

cis-permethrin and 4,4 ́-DDE had mean recoveries near 60 

percent, and recoveries in this range or lower were expected 

because these two analytes have the lowest water solubilities 

and highest octanol-water partition coefficients of any method 

analytes (Mackay and others, 1997). Loss of these analytes by 

sorption to surfaces such as the glass-fiber filter matrix during 

filtration, glass bottle walls and tubing during SPE steps, and 

to particles or dissolved organic matter in the rain samples, are 

likely to have contributed to their reduced recoveries.

Surrogate Recoveries in Rainwater and 

Associated Quality Control Samples

Recovery data and statistical summaries of surrogate 

compounds in laboratory water blanks and spike samples 

are shown in table 25 (see at table_25.xls). Most surrogate 

recoveries exceeded 80 percent and no sample preparation 

problems were evident for any field rain samples that were 

based on the surrogate recoveries. Table 26 (see at table_26.

xls) shows the statistical summaries of the surrogate recoveries 

for (1) all laboratory water blanks and spike samples 

combined, (2) rain samples from six sites where surrogate 

compounds were fortified into the water and the water was 

processed through the SPE column by field staff, and (3) rain 

samples from Eagle Harbor where surrogate fortification 

and SPE steps were performed at NWQL. Mean recoveries 

of the three surrogates exceeded 90 percent in each of these 

categories. Mean recovery for diazinon-d10 in the fieldprepared rain samples (136 percent) were higher than mean 

recoveries observed for laboratory water blank and spike 

samples and for the Eagle Harbor rain samples. The high 

bias in the field-prepared rain samples was attributed to a 

purity problem encountered with a diazinon-d10 standard 

used to prepare surrogate and calibration standards by NWQL 

during part of 1995. Issues regarding the use of terbuthylazine 

as a surrogate were addressed in the air method surrogate 

recoveries section above.

Pesticide Stability in Rainwater Test

The stability of each pesticide targeted for analysis 

in rainwater during the week-long collection periods was 

tested by spiking 3 L of excess, unfiltered rainwater from the 

20–27 June (week 14) Iowa City sample to a concentration of 

0.17 μg/L for each analyte (acetochlor was not added). After a 

thorough mixing, 1 L of the spiked rainwater was immediately 

filtered through a 0.7-μm GFF. The surrogate compounds 

were added next, and the sample was processed through a C18 

SPE column. The excess water was removed from the SPE 

column and it was stored at 4 °C until extracted. This sample 

provided the initial, day-zero (30 June 1995) recovery. The 

remaining spiked rainwater sample was then stoppered and 

allowed to sit on a laboratory bench, at ambient temperature 

(about 23 °C), but protected from direct sunlight, for 5 d. After 

5 d, another 1 L of the spiked water sample was processed in 

the same manner as the day zero rainwater sample, and both 

SPE columns were sent to NWQL for extraction and analysis. 

This matrix spike experiment was done at only one location 

to minimize the possibility of contamination of samples and 

equipment with the spike material. The matrix spike recoveries 
References 21

for each compound were corrected for ambient concentrations 

of the pesticide in the rainwater, if present. The results for this 

test are listed in table 27 (see at table_27.xls).

This stability study did not mimic the exact storage 

conditions of the field samples. Instead, ambient indoor 

temperatures (about 23 °C) were used in an attempt to 

simulate a more extreme, worst case, storage condition than an 

actual sample might encounter when stored 7 d at 4 °C in the 

field. No statistical comparison of recoveries for this holding 

time experiment was possible because the experiment was 

not replicated. The results of this test, however, do provide 

an indication of the storage stability for the target analytes 

and revealed that degradation during the 5-d holding period 

at ambient temperature was not a problem for most analytes 

(table 27 (see at table_27.xls)). Thirty-five compounds had 

overall test recoveries (defined as [day 5 recovery/day 0 

recovery] × 100) above 70 percent, and no obvious losses 

of these compounds was observed over the 5-d experiment. 

Five analytes—benfluralin, butylate, ethalfluralin, terbufos, 

and trifluralin—exhibited recoveries at day 5 that were 

below the range of expected recoveries on the basis of 

method performance data collected using laboratory reagent 

spike samples (table 24 [see at table_24.xls]). These results 

indicated a possible loss for these analytes during the 5-d 

experiment. 

Five other compounds—diazinon, disulfoton, phorate, 

4,4 ́-DDE, and terbufos—exhibited recoveries below the level 

of expected method performance at both day 0 and day 5. 

Although the recoveries for these compounds were unusually 

low at day 0, they showed a definite loss in concentration 

during the 5-d experiment. The low recovery for 4,4 ́-DDE is 

indicative of sorption to the glass carboy and other surfaces 

(such as suspended particles), as well as to the GFF during 

the filtration step, and likely not a result of degradation. 

Other analytes, like cis-permethrin and trifluralin, which 

have low water solubilities (Mackay and others, 1997), 

might also be susceptible to sorptive losses. A complete 

mass balance assessment for the pesticides was not possible 

because no attempt was made to recover pesticides sorbed 

to these sample-processing components. For several of the 

organophosphorus pesticides, losses during sample filtration 

might have accounted for some of the reduced recoveries. 

Reactive degradation processes, however, probably accounted 

for most of the losses for these pesticides. Indeed, Zaugg and 

others (1995) observed that of all 47 water method analytes, 

diazinon, phorate, and terbufos exhibited the most rapid 

degradation times in storage stability tests on SPE columns.

The average recoveries for all the analytes in the 

laboratory reagent-water (set) spike samples (table 24 [see 

at table_24.xls]) exceed 75 percent except for 4,4 ́-DDE (63 

percent) and cis-permethrin (60 percent). Losses attributable 

to the GFF filtration step, however, were not accounted for 

in the laboratory set-spike recoveries because these QC 

samples were not filtered through a GFF. The surrogate 

compounds were added to day 0 and day 5 aliquots of the 

spiked rainwater sample immediately after the GFF filtration 

step, and recoveries for the unfiltered α-HCH-d6 surrogate 

were comparable to day 0 and 5 recoveries for filtered α-HCH 

analyte in the spiked rainwater test. This indicates that no 

sorptive losses to the GFF occurred for α-HCH. Diazion-d10 

surrogate recoveries were much greater than observed for the 

unlabelled diazinon. A direct comparison of recoveries for 

these diazinon analogs is complicated by the apparent highbias recoveries observed for diazinon-d10 because of standard 

purity issues, as mentioned above. 

Acetochlor was not included in the spike solution, but it 

was present at a substantial concentration in the rainwater used 

in the experiment. The overall test recovery for acetochlor 

(82 percent) was estimated from the difference in the actual 

concentrations in rainwater at day 0 (0.028 μg/L) and day 5 

(0.023 μg/L). Although acetochlor was not tested, Goolsby 

and others (1995) found no sorption, degradation, or other 

losses for alachlor, atrazine, cyanazine, or metolachlor in 

spiked rain samples stored outdoors or indoors at ambient 

temperatures for up 3 weeks. 

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Michael S. Majewski and others—Pesticides in Air and Rainwater in the Midcontinental United States, 1995—Methods and Data— 

Open-File Report 2007-1369

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