NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

U.S. Department of the Interior

U.S. Geological Survey

Pesticide Compounds in Streamwater in the

Delaware River Basin,

December 1998–August 2001 

Scientific Investigations Report 2004-5105 
NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

U.S. Department of the Interior

U.S. Geological Survey

Pesticide Compounds in Streamwater in the

Delaware River Basin,

December 1998–August 2001 

Scientific Investigations Report 2004-5105 
Pesticide Compounds in Streamwater 

in the Delaware River Basin, 

December 1998–August 2001

By R. Edward Hickman

U.S. Department of the Interior

U.S. Geological Survey

Prepared as part of the

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Scientific Investigations Report 2004-5105
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

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 iii

Foreword

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that helps enhance and protect the overall quality of life, and facilitates effective management of water, biological, energy, and mineral resources. (http://www.usgs.gov/). 

Information on the quality of the Nation’s water resources is of critical interest to the USGS 

because it is so integrally linked to the long-term availability of water that is clean and safe for 

drinking and recreation and that is suitable for industry, irrigation, and habitat for fish and wildlife. 

Escalating population growth and increasing demands for the multiple water uses make water 

availability, now measured in terms of quantity and quality, even more critical to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program to support 

national, regional, and local information needs and decisions related to water-quality management and policy. (http://water.usgs.gov/nawqa/). Shaped by and coordinated with ongoing efforts 

of other Federal, State, and local agencies, the NAWQA Program is designed to answer: What is 

the condition of our Nation’s streams and ground water? How are the 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. NAWQA results 

can contribute to informed decisions that result in practical and effective water-resource management and strategies that protect and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 

50 of the Nation’s most important river basins and aquifers, referred to as Study Units. 

(http://water.usgs.gov/nawqa/nawqamap.html). Collectively, these Study Units account for more 

than 60 percent of the overall water use and population served by public water supply, and are 

representative of the Nation’s major hydrologic landscapes, priority ecological resources, and 

agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and 

analysis. The assessments thereby build local knowledge about water-quality issues and trends 

in a particular stream or aquifer while providing an understanding of how and why water quality 

varies regionally and nationally. The consistent, multi-scale approach helps to determine if certain 

types of water-quality issues are isolated or pervasive, and allows direct comparisons of how 

human activities and natural processes affect water quality and ecological health in the Nation’s 

diverse geographic and environmental settings. Comprehensive assessments on pesticides, 

nutrients, volatile organic compounds, trace metals, and aquatic ecology are developed at the 

national scale through comparative analysis of the Study-Unit findings. 

(http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and relevant science so that the most recent and available knowledge about water resources can be 

applied in management and policy decisions. We hope this NAWQA publication will provide you 

the needed insights and information to meet your needs, and thereby foster increased awareness 

and involvement in the protection and restoration of our Nation’s waters. 
iv 

The NAWQA Program 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 a fully integrated understanding of watersheds and for cost-effective management, regulation, and conservation of our Nation’s water resources. The Program, therefore, depends extensively on the 

advice, cooperation, and information from other Federal, State, interstate, Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder groups. The assistance and suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water
 v

Contents

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

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

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Description of the Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Design and Methods of Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Streamwater Sampling Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Field Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Laboratory Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Quality Assurance/Quality Control Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Application Rates of Pesticides to Agricultural Land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Methods of Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Pesticide Compounds in Streamwater in the Delaware River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Summary of Detection Frequencies and Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Pesticide Compounds (Gas Chromatography) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Pesticide Degradation Products (High Performance Liquid Chromatography) . . . . . . . . . . . . . . . . . . . 17

Bias and Variability of Detection Frequencies and Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Pesticide Compounds (Gas Chromatography) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Pesticide Degradation Products (High Performance Liquid Chromatography) . . . . . . . . . . . . . . . . . . . 18

Relations Between Concentrations of Selected Pesticides and Indicators of Agricultural 

and Nonagricultural Uses of Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Variation in Concentrations of Selected Pesticides with Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Relations of Concentrations of Selected Pesticides to Streamwater Turbidity . . . . . . . . . . . . . . . . . . . . . . . . . 26

Comparison of Concentrations of Selected Degradation Products with Concentrations of 

Parent Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Deethylatrazine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Ethane Sulfonic Acid and Oxanilic Acid Degradation Products of Alachlor, 

Acetochlor, and Metolachlor at Two Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Comparison of Concentrations of Pesticide Compounds to Standards and Guidelines for 

the Protection of Human Health and Aquatic Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Human Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Aquatic Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
vi 

Figures

1–2. Maps showing—

1. Location of the Delaware River Basin, New York, Pennsylvania, New Jersey, 

and Delaware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2. Physiographic provinces and land use in the Delaware River Basin, 1992 . . . . . . . . . . . . . . . . . . . . .4

3. Graph showing crops with the largest areas of cultivation in the Delaware River Basin. . . . . . . . . . . . . .5

4–5. Maps showing—

4. Location of fixed streamwater sampling sites with drainage areas in the Delaware 

River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

5. Location of synoptic and fixed streamwater sampling sites in the Delaware 

River Basin, 1998–2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6–8. Graphs showing—

6. Frequences of detection of the pesticide compounds most often detected in 531 samples 

of streamwater by use of gas chromatography, Delaware River Basin, 

December 1998–August 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

7. Relation of frequency of detection to estimated annual application to agricultural land 

within the Delaware River Basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8. Relation of concentration of atrazine in streamwater to percentage of agricultural land 

in subbasins of the Delaware River Basin, May and June 2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

9. Map showing streamwater sampling sites and association of atrazine under base-flow 

conditions, and application rates, Delaware River Basin, May and June 1999–2001 . . . . . . . . . . . . . . . 22

10. Graph showing relation of concentrations of prometon in streamwater to the percentage 

of urban land in subbasins of the Delaware River Basin, May and June 2000. . . . . . . . . . . . . . . . . . . . . . 23

11. Map showing streamwater sampling sites and associated concentrations of prometon 

under base-flow conditions, and population density, Delaware River Basin, May and 

June 1999–2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

12–17. Graphs showing—

12. Concentrations of (A) atrazine, and (B) acetochlor in streamwater samples from 

fixed sites in the Delaware River Basin, December 1998–August 2001. . . . . . . . . . . . . . . . . . . . . . . 27

13. Concentrations of (A) prometon, and (B) diazinon in streamwater samples from 

fixed sites in the Delaware River Basin, December 1998–August 2001. . . . . . . . . . . . . . . . . . . . . . . 28

14. Relation of diazinon concentration to streamwater turbidity at streamwater sampling 

site 01464907, Little Neshaminy Creek near Neshaminy, Pa., April–October, 1999–2001 . . . . . . 29

15. Relation of concentrations of deethylatrazine to concentrations of atrazine in 

streamwater samples from the Delaware River Basin, 1998–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

16. Relation of frequency of detection of ethane sulfonic acid and oxanilic acid degradation 

products to the frequency of detection of metolachlor, alachlor, and acetochlor in 

68 streamwater samples from two sites in the Delaware River Basin, 1999–2000.. . . . . . . . . . . . 30

17. Concentrations of metolachlor and its degradation products at fixed site 01474500, 

Schuylkill River at Philadelphia, Pa., March 1999–August 2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
 vii

Tables

1. Description of fixed and synoptic streamwater sampling sites in the Delaware River Basin, 

December 1998–August 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

2. Pesticides and degradation products analyzed for in streamwater in the Delaware River Basin, 

December 1998–August 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Summary of the frequencies of detection and the concentrations of pesticide compounds 

detected in streamwater in the Delaware River Basin, December 1998–August 2001. . . . . . . . . . . . . . 15

4. Selected nationwide uses of pesticides detected most often in streamwater in the 

Delaware River Basin, December 1998–August 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5. Relations of concentrations of selected pesticides in streamwater to rate of application 

to agricultural land, and relations of concentrations of selected pesticides to percentage of 

agricultural land in subbasins of the Delaware River Basin, 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6. Relations of concentrations of selected pesticides in streamwater to population density, and 

relations of concentrations of selected pesticides to percentage of urban land in subbasins of 

the Delaware River Basin, 2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

7. Summary of relations of concentrations of selected pesticides to streamwater turbidity at fixed 

streamwater sampling sites in the Delaware River Basin, April–October, 1999–2001. . . . . . . . . . . . . . . 29

8. Selected standards and guidelines for the protection of the health of humans and aquatic life 

from pesticide compounds in streamwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
viii 

Conversion Factors

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (μg/L).

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Area

square mile (mi2) 2.590 square kilometer (km2)
Pesticide Compounds in Streamwater in the 

Delaware River Basin, December 1998–August 2001

By R. Edward Hickman

Abstract

During 1998–2001, 533 samples of streamwater at 94 sites 

were collected in the Delaware River Basin in Pennsylvania, 

New Jersey, New York, and Delaware as part of the U.S. Geological Survey National Water-Quality Assessment Program. 

Of these samples, 531 samples were analyzed for dissolved concentrations of 47 pesticide compounds (43 pesticides and 4 pesticide degradation products); 70 samples were analyzed for an 

additional 6 pesticide degradation products.

Of the 47 pesticide compounds analyzed for in 531 samples, 30 were detected. The most often detected compounds 

were atrazine (90.2 percent of samples), metolachlor (86.1 percent), deethylatrazine (82.5 percent), and simazine (78.9 percent). Atrazine, metolachlor, and simazine are pesticides; 

deethylatrazine is a degradation product of atrazine. 

Relations between concentrations of pesticides in samples 

from selected streamwater sites and characteristics of the subbasins draining to these sites were evaluated to determine 

whether agricultural uses or nonagricultural uses appeared to be 

the more important sources. Concentrations of atrazine, metolachlor, and pendimethalin appear to be attributable more to 

agricultural uses than to nonagricultural uses; concentrations of 

prometon, diazinon, chlorpyrifos, tebuthiuron, trifluralin, and 

carbaryl appear to be attributable more to nonagricultural uses.

In general, pesticide concentrations during the growing 

season (April–October) were greater than those during the nongrowing season (November–March). For atrazine, metolachlor, 

and acetochlor, the greatest concentrations generally occurred 

during May, June, and July.

Concentrations of pesticide compounds rarely (in only 7 

out of 531 samples) exceeded drinking-water standards or 

guidelines, indicating that, when considered individually, these 

compounds present little hazard to the health of the public 

through consumption of the streamwater. The combined effects 

of more than one pesticide compound in streamwater were not 

considered.

Diazinon appeared to be the pesticide compound most 

likely to adversely affect aquatic life in the streams of the Delaware River Basin; concentrations of diazinon exceeded guidelines (designed to protect aquatic life) in 19 samples, the most 

of any pesticide compound. Concentrations of as many as 5 

compounds exceeded guidelines in 29 of 531 samples.

Introduction

Pesticides have been detected in streams draining urban 

and agricultural areas throughout the Nation (Fuhrer and others, 

1999). Most pesticides are synthetic organic compounds 

designed to kill specific plants or insects on selected sites, such 

as agricultural land, lawns, golf courses, roadsides, or in or 

around buildings. Their presence in streamwater is the result of 

transport by ground-water discharge, surface runoff, or other 

processes from sites of application to streams. 

Pesticides in streams are of concern to water-resource 

managers and drinking-water suppliers because pesticides can 

adversely affect the health of the aquatic biota in the streams 

and(or) the health of humans who drink the streamwater. Fuhrer 

and others (1999) consider the presence of pesticides in streamwater to be a potential concern because of uncertainties in the 

methods used to assess the effects of pesticide concentrations 

on the health of aquatic biota and the health of humans and 

because these methods do not address all effects. For example, 

an assessment of the health effects of a pesticide does not usually include the health effects of its degradation products (compounds created from the breakdown of the pesticide). 

Pesticide concentrations in streamwater of the Delaware 

River Basin in Pennsylvania, New Jersey, New York, and Delaware were measured by the U.S. Geological Survey (USGS) at 

sites throughout the basin from December 1998 through August 

2001. These concentrations, as well as other measurements of 

water quality, have been published in DeLuca and others (2000, 

2001, and 2002). 

Samples of streamwater in the Delaware River Basin were 

collected as part of the USGS National Water-Quality Assessment (NAWQA) Program, a study of the quality of the Nation’s 

surface and ground water. The national goals of this program 

are to (1) describe current water-quality conditions of much of 

the Nation’s freshwater streams and aquifers (water-bearing 

sediments and rocks), (2) describe how water quality is changing over time, and (3) increase our understanding of the natural 

and human factors that affect water quality (Leahy and others, 

1990; Gilliom and others, 1995). The Delaware River Basin 

NAWQA Program also provides information to address local 

concerns, which include (1) the presence of pesticides in drinking-water supplies and recreational waters, and (2) relations 

between land use and nonpoint sources of contaminants 

(Fischer, 1999).
2 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Purpose and Scope

This report presents the results of analyses of 533 streamwater samples collected at 94 sites in the Delaware River Basin 

from December 1998 to August 2001 for selected pesticide 

compounds (pesticides and pesticide degradation products). Of 

these samples, 531 samples were analyzed for 43 pesticides and 

4 degradation products; these pesticides are those that have 

been, or are currently (2004), in common use throughout the 

Nation. In addition, 70 streamwater samples from 2 sites were 

analyzed for 6 other pesticide degradation products. 

Concentrations and frequencies of detection are summarized by pesticide compound. Bias and variability of detections 

and concentrations as indicated by quality-assurance/qualitycontrol (QA/QC) samples are presented. 

Factors that appear to affect the detection and concentration of selected pesticide compounds are discussed. The importance of nonagricultural uses and agricultural uses of pesticides 

as sources of pesticide compounds to streams was inferred from 

relations between concentrations and selected subbasin characteristics. Relations between (1) pesticide concentration and season and (2) concentration and streamwater turbidity are presented. Concentrations of selected pesticide degradation 

products are compared with concentrations of parent pesticides.

A measure of the hazard which pesticide compounds in 

streamwater appears to represent to human health and aquatic 

life is assessed. Concentrations of pesticide compounds are 

compared to standards and guidelines for drinking water and for 

the protection of aquatic life. 

Description of the Study Area

The study area of the Delaware River Basin NAWQA 

study unit is the Delaware River Basin other than that part of the 

basin in the central and southern parts of the State of Delaware 

(fig. 1). The basin includes 12,100 mi2 of the States of New 

York, Pennsylvania, New Jersey, and Delaware. 

Five physiographic provinces are represented in the study 

area (fig. 2). In the northern part of the basin, the rugged hills 

and broad ridges of the Appalachian Plateaus rise to an elevation of about 4,000 ft. The Valley and Ridge Province consists 

of a series of valleys and ridges, and the New England Province 

is one ridge. The Piedmont Province is characterized by a series 

of rolling hills and broad uplands. The Coastal Plain, the southernmost province, has the lowest elevation (generally less than 

200 ft above sea level) and is relatively flat as compared to the 

other provinces. Land elevation generally decreases from the 

Appalachian Plateaus in the north to the Coastal Plain in the 

south.

Land use in the study area was determined from 1992 satellite imagery. Overall, the study area consists of 60 percent forested, 24 percent agricultural, 9 percent urban, and 7 percent 

other land uses, which includes water, bare rock, mines, 

orchards, grasslands, and wetlands (Fischer, 1999). 

Most of the population and urban land is in the southern 

part of the study area in the Piedmont and Coastal Plain Provinces (fig. 2). In 2000, about 85 percent of the 7 million inhabitants of the study area lived within these two provinces; most 

people lived in and around Philadelphia, Pa., the largest city in 

the study area. 

Most of the agricultural land is in the central and southern 

parts of the study area. About 80 percent of the agricultural land 

in the study area is within the Valley and Ridge, Piedmont, and 

Coastal Plain Provinces (fig. 2). Corn and soybeans are the 

crops with the largest areas of cultivation in the study area 

(fig. 3). 

Most of the forested land is in the central and northern 

parts of the study area. About 70 percent of the forested land in 

the study area is in the Appalachian Plateaus and Valley and 

Ridge Provinces (fig. 2). The Appalachian Plateaus Province is 

about 80 percent forested. 

The major rivers in the study area are the Delaware, 

Lehigh, and Schuylkill (fig. 1). The head of tide of the Delaware 

River is at Trenton, N.J.; that of the Schuylkill River is at Philadelphia. 

Reservoirs throughout the study area provide storage for 

water supply, recreation, and flood control. Some of the larger 

reservoirs are shown in figure 1. Streamflow in the rivers downstream from the reservoirs is affected by reservoir operation. 

Streamwater throughout the Delaware River Basin is used 

for public supply. Withdrawals for public water supply are 

made from reservoirs as well as from streams. The City of Philadelphia makes the largest municipal withdrawals for public 

water supply within the basin; withdrawals are made from the 

Delaware and Schuylkill Rivers. 

Streamwater also is transferred out of the Delaware River 

Basin for use elsewhere. The City of New York withdraws 

water from the Neversink, Pepacton, and Cannonsville Reservoirs (fig. 1). The New Jersey State Water Supply Authority 

withdraws water from the Delaware River near Trenton for use 

in eastern New Jersey. 

Design and Methods of Study

The design and methods of this study are common to all 

USGS NAWQA studies in order that results from one NAWQA 

study can be compared directly with results from another 

NAWQA study. A general discussion of the design of NAWQA 

studies can be found in Gilliom and others (1995). 
Design and Methods of Study 3

0 10 20 30 MILES

0 10 20 30 KILOMETERS

42°

41°

40°

39°

76° 75° 74°

NEW YORK

NEW JERSEY

P E N N S Y LVA N I A

MARYLAND

DELAWARE

Reading

Wilmington

Philadelphia

Trenton

Allentown

Pepacton

Reservoir

Cannonsville

Reservoir

Mongaup

System

Neversink

Reservoir

Nockamixon

Reservoir

Lake

Wallenpaupack

Delaware River

Lehigh

River

Schuylkill River

Blue Marsh

Reservoir

Delaware Estuary

Delaware River

Lake

Hopatcong

Merrill Creek

Reservoir

Francis E. Walter

Reservoir

Beltzville

Reservoir

Delaware River

Basin boundary

HEAD OF

TIDE

New York City

Pennsylvania

New York

Delaware

New Jersey

Maryland

STUDY UNIT

76°

80°

44°

38°

72°

Figure 1. Location of the Delaware River Basin, New York, Pennsylvania, New Jersey, and Delaware.
4 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

0 10 20 30 MILES

0 10 20 30 KILOMETERS

42°

41°

40°

39°

76° 75° 74°

NEW YORK

NEW JERSEY

P E N N S Y LVA N I A

MARYLAND

DELAWARE

APPALACHIAN

PLATEAUS

VALLEY AND

RIDGE NEW ENGLAND

PIEDMONT

COASTAL

PLAIN

EXPLANATION

Land use

Agricultural

Forested

Urban

Other

Delaware River

Basin boundary

Figure 2. Physiographic provinces and land use in the Delaware River Basin, 1992.
Design and Methods of Study 5

Streamwater Sampling Sites

Two types of streamwater sites were sampled, “fixed” and 

“synoptic”. Ten fixed sites were sampled throughout the year to 

provide detailed information about the variation of pesticide 

concentrations and loads during storms and base flow (between 

storms) (fig. 4; table 1). In general, fixed sites were sampled at 

least monthly and during some storms from December 1998 

through August 2001. For this report, base-flow conditions in 

smaller subbasins (17–66.5 mi2) generally were considered to 

exist after about a week of no precipitation; in the larger subbasins, base-flow conditions sometimes took 2 weeks or longer to 

develop. In this report, the term, ‘subbasin’, refers to the area 

draining to each streamwater sampling site. 

The following four fixed sites, known as “integrator” sites, 

were sampled to determine the water quality of the streams 

draining large subbasins with different land uses and geology 

(fig. 4; table 1): 01434000, Delaware River at Port Jervis, N.Y.; 

01454700, Lehigh River at Glendon, Pa.; 01463500 Delaware 

River at Trenton, N.J.; and 01474500, Schuylkill River at Philadelphia, Pa. The sizes of the subbasins range from 1,359 to 

6,780 mi2

.

The other six fixed sites, known as “indicator” sites, are on 

streams with small subbasins (17–66.5 mi2

) (fig. 4; table 1). 

These sites were sampled to relate streamwater quality to subbasin geology and land use. Of these, the following two are in 

subbasins considered to be predominantly urban: 01464907, 

Little Neshaminy Creek near Neshaminy, Pa.; and 01467150, 

Cooper River at Haddonfield, N.J. Land use was determined 

from satellite images captured during 1992; the subbasin of the 

site on the Little Neshaminy Creek had more agricultural land 

(32 percent of the subbasin) than urban land (26 percent) in 

1992. This subbasin was reclassified as urban after inspection of 

the subbasin by project personnel who found considerable 

recent urbanization, however. The following four sites are on 

subbasins considered to be predominantly agricultural: 

01451800, Jordan Creek near Schnecksville, Pa.; 01470779, 

Tulpehocken Creek near Bernville, Pa.; 01472157, French 

Creek near Phoenixville, Pa.; and 01477120, Raccoon Creek 

near Swedesboro, N.J.

Synoptic sites were sampled during base-flow conditions 

to better understand the areal variation in streamwater quality 

and relations between water quality and subbasin characteristics, such as land use and geology (fig. 5, table 1). At most of 

these sites, samples were collected during spring (mostly during 

May–June) and late summer (mostly during August–September) of 1999, 2000, or 2001. During 1999, 24 sites were sampled to identify the quality of surface water throughout the study 

area. During 2000, 40 sites were sampled during spring to relate 

water quality to urban and agricultural land use in the Piedmont 

and Valley and Ridge Provinces; only 30 sites in the Piedmont 

Province were sampled during late summer. During 2001, 23 

sites were sampled to determine relations between streamwater 

quality and land use in the Appalachian Plateaus. Three synoptic sites were sampled during spring and late summer of each 

year. 

Field Methods

Field methods used for streamwater sampling are 

described in Shelton (1994). A discharge-integrated sample was 

collected from the stream and split into subsamples, one of 

which was filtered through a 0.70-micron glass-fiber filter 

(Sandstrom, 1995). The filtrate was chilled with ice and transported to the laboratory for analysis for pesticide compounds. 

Sampling and field-processing equipment was cleaned prior to 

the collection of each sample.

Streamwater turbidity was measured with an YSI 6820 

model water-quality meter fitted with a nephelometric turbidimeter. The value of turbidity at the time each sample is collected usually is the median of multiple measurements across 

the stream width. 

012345

CROPLAND IN THE STUDY AREA, IN PERCENT

APPLES

PEACHES

SWEET CORN

BARLEY

OATS

WHEAT

ALFALFA HAY

SOYBEANS

PASTURE

CORN FOR GRAIN OR SILAGE

Figure 3. Crops with the largest areas of cultivation in the Delaware River Basin. 

(Data are from Gianessi and Marcelli, 2000.)
6 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

0 10 20 30 MILES

0 10 20 30 KILOMETERS

42°

41°

40°

39°

76° 75° 74°

NEW YORK

NEW JERSEY

P E N N S Y LVA N I A

MARYLAND

DELAWARE

6,780 square miles

Delaware River

at Trenton

3,070 square miles

Delaware River

at Port Jervis

1,886 square miles

Schuylkill River

Racoon Creek

26.9 square miles

French Creek

59.1 square miles

Tulpehocken Creek

66.5 square miles

Cooper River

17 square miles

Little Neshaminy Creek

26.8 square miles

1,359 square miles

Lehigh River

Jordan Creek

53 square miles

Delaware River

Basin boundary

Integrator site–Number

is drainage area

Indicator site–Number

is drainage area

Agricultural subbasin

Urban subbasin

EXPLANATION

Figure 4. Location of fixed streamwater sampling sites with drainage areas in the Delaware River Basin.
Design and Methods of Study 7

Table 1. Description of fixed and synoptic streamwater sampling sites in the Delaware River Basin, December 1998–August 2001.

[Locations of fixed sites are shown in figures 4 and 5; locations of synoptic sites are shown in figure 5]

Index 

number

Station 

number Station name

Subbbasin of site

Area, in 

square 

miles

Land use, in percent

Agricultural Urban Forested

Fixed sites

1 01434000 Delaware River at Port Jervis, N.Y. 3,070 11 1 84

2 01451800 Jordan Creek near Schnecksville, Pa. 53 66 1 33

3 01454700 Lehigh River at Glendon, Pa. 1,359 23 7 63

4 01463500 Delaware River at Trenton, N.J. 6,780 17 3 75

5 01464907 Little Neshaminy Creek at Valley Road near Neshaminy, Pa. 26.8 32 26 36

6 01467150 Cooper River at Haddenfield, N.J. 17 7 57 25

7 01470779 Tulpehocken Creek near Bernville, Pa. 66.5 82 4 13

8 01472157 French Creek near Phoenixville, Pa. 59.1 34 1 63

9 01474500 Schuylkill River at Philadelphia, Pa. 1,893 38 10 48

10 01477120 Raccoon Creek near Swedesboro, N.J. 26.9 64 4 27

Synoptic sites

11 01411500 Maurice River at Norma, N.J. 112 31 14 43

12 01420500 Beaver Kill at Cooks Falls, N.Y. 241 3 1 95

13 01423000 West Branch Delaware River at Walton, N.Y. 332 23 1 75

14 01425000 West Branch Delaware River At Stilesville, N.Y. 456 20 1 78

15 01427203 Equinunk Creek at Equinunk, Pa. 57.7 12 0 85

16 01427500 Callicoon Creek at Callicoon, N.Y. 110 24 1 73

17 01427702 Calkins Creek 1200 feet above mouth at Milanville, Pa. 43.9 22 0 77

18 01428750 West Branch Lackawaxen River near Aldenville, Pa. 40.6 24 0 74

19 01431250 Middle Creek at Hawley, Pa. 81.2 18 1 73

20 01431500 Lackawaxen River at Hawley, Pa. 290 19 1 75

21 01431600 Wallenpaupack Creek at East Sterling, Pa. 70.7 5 1 88

22 01432000 Wallenpaupack Creek at Wilsonville, Pa. 228 9 2 78

23 01432180 Halfway Brook at Barryville, N.Y. 28.3 1 1 92

24 01432512 Shohola Creek at Shohola, Pa. 84.7 1 1 87

25 01433510 Mongaup River at Mongaup, N.Y. 206 7 3 82

26 01435000 Neversink River near Claryville, N.Y. 66.6 0 0 99

27 01437500 Neversink River at Godeffroy, N. Y. 307 3 3 89

28 01438302 Vandermark Creek at mouth at Milford, Pa. 5.22 1 4 94

29 01438396 Sawkill Creek 2000 feet above mouth at Milford, Pa. 24.5 1 2 91

30 01438399 Shimers Brook at Millville Road near Montague, N.J. 6.97 7 6 76

31 01438712 Raymondskill Creek below Swale Brook near Silver Spring, Pa. 21.6 1 1 84

32 01438890 Dingmans Creek below Fulmer Falls near Dingmans Ferry, Pa. 13.1 0 4 82

33 01439400 Toms Creek at Egypt Mills, Pa. 9.34 1 1 96

34 01439500 Bush Kill at Shoemakers, Pa. 117 0 1 87

35 01439680 Little Bushkill Creek at Bushkill, Pa. 32.6 1 1 79
8 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Synoptic sites--Continued

36 01440000 Flat Brook near Flatbrookville, N.J. 64 7 1 88

37 01440304 Brodhead Creek near Mountainhome, Pa. 41.8 2 1 92

38 01442500 Brodhead Creek at Minisink Hills, Pa. 259 7 5 83

39 01442550 Marshalls Creek near Marshalls Creek, Pa. 10.6 1 0 93

40 01443500 Paulins Kill at Blairstown, N.J. 126 26 5 59

41 01447000 Delaware River at Northampton Street at Easton, Pa. 4,717 12 2 81

42 01447120 Lehigh River near Gouldsboro, Pa. 17.8 1 3 76

43 01447530 Tobyhanna Creek at Warnertown, Pa. 22.7 1 7 73

44 01449000 Lehigh River at Lehighton, Pa. 591 3 2 83

45 01450400 Lizard Creek at Ashfield, Pa. 46.5 32 0 67

46 01450455 Buckwha Creek at Little Gap, Pa. 42.5 32 1 66

47 01451110 Hokendauqua Creek near Northampton, Pa. 38.1 52 1 46

48 01451425 Little Lehigh Creek near East Texas, Pa. 51.2 68 8 23

49 01451624 Cedar Creek above Lake Muhlenberg at Allentown, Pa. 13.7 40 41 17

50 01452500 Monocacy Creek at Bethlehem, Pa. 44.5 67 10 19

51 01457400 Musconetcong River at Riegelsville, N.J. 156 22 9 60

52 01458920 Tinicum Creek near Smithtown, Pa. 24 20 1 77

53 01459500 Tohickon Creek near Pipersville, Pa. 97.4 32 4 59

54 01460880 Lockatong Creek at Raven Rock, N.J. 22.9 55 0 40

55 01461900 Alexauken Creek near Lambertville, N.J. 14.8 53 1 44

56 01462100 Pidcock Creek near New Hope, Pa. 12.1 37 0 61

57 01462800 Jacobs Creek at Somerset, N.J. 13.3 54 11 31

58 01462949 Buck Creek below Brock Creek at Yardley, Pa. 6.89 45 23 26

59 01463810 Shabakunk Creek near Lawrenceville, N.J. 11.7 14 62 16

60 01464500 Crosswicks Creek at Extonville, N.J. 81.5 36 7 44

61 01464710 Pine Run at Chalfont, Pa. 11.6 49 12 37

62 01465470 Mill Creek near Langhorne, Pa. 14.6 18 43 32

63 01465500 Neshaminy Creek near Langhorne, Pa. 210 39 20 37

64 01467000 North Branch Rancocas Creek at Pemberton, N.J. 118 4 8 63

65 01467040 Pennypack Creek at Paper Mill, Pa. 23.74 5 63 23

66 0146708450 Tacony Creek at Cheltenham, Pa. 9.45 0 67 26

67 01470500 Schuylkill River at Berne, Pa. 355 15 4 72

68 01470640 Ontelaunee Creek at Wanamakers, Pa. 26.8 54 1 44

69 01470744 Mill Creek at Dietricks Mill Bridge near Kutztown, Pa. 17.60 72 0 27

70 01470818 Little Northkill Creek near Bernville, Pa. 21.2 68 1 29

Table 1. Description of fixed and synoptic streamwater sampling sites in the Delaware River Basin, December 1998–August 2001.

—Continued

[Locations of fixed sites are shown in figures 4 and 5; locations of synoptic sites are shown in figure 5]

Index 

number

Station 

number Station name

Subbbasin of site

Area, in 

square 

miles

Land use, in percent

Agricultural Urban Forested
Design and Methods of Study 9

Synoptic sites--Continued

71 01471520 Wyomissing Crreek at West Reading, Pa. 15.6 25 31 43

72 01471667 Hay Creek near Scarlets Mill, Pa. 18.7 23 0 74

73 01471980 Manatawny Creek near Pottstown, Pa. 85.5 41 2 56

74 01472000 Schuylkill River at Pottstown, Pa. 1,147 40 5 50

75 01472100 Pigeon Creek near Parker Ford, Pa. 14 46 3 51

76 014721884 Pickering Creek at Charlestown Road Bridge at Charlestown, Pa. 27.5 48 4 47

77 01472280 Macoby Creek at Green Lane, Pa. 17.4 42 2 55

78 01473000 Perkiomen Creek at Graterford, Pa. 279 42 5 51

79 01473470 Stony Creek at Steriger Street at Norristown, Pa. 20.4 30 37 31

80 01474000 Wissahickon Creek at mouth, Philadelphia, Pa. 64 11 43 40

81 01475430 Darby Creek at Foxcroft, Pa. 15.7 13 35 50

82 01475510 Darby Creek near Darby, Pa. 37.4 7 51 38

83 01475543 Cobbs Creek at East Lansdowne, Pa 12.5 0 71 21

84 01475845 Crum Creek at Goshen Road near Whitehorse, Pa. 12.5 20 17 60

85 01476470 Ridley Creek near Media, Pa. 27.3 29 11 59

86 01476950 West Branch Chester Creek near Chester Heights, Pa. 18 30 16 53

87 01478200 Middle Branch White Clay Creek near Landenberg, Pa. 12.7 68 4 27

88 01478650 White Clay Creek at Newark, Del. 69 54 6 38

89 01479800 East Branch Red Clay Creek near Five Point, Pa. 10.2 49 14 34

90 01480350 West Branch Brandywine Creek at Cedar Knoll, Pa. 24.3 64 1 33

91 01480665 East Branch Brandywine Creek near Dorlan, Pa. 33.4 52 1 46

92 01480775 Beaver Creek near Downingtown, Pa. 16.5 46 13 40

93 01480890 Valley Creek near Altor, Pa. 16 26 23 46

94 01481500 Brandywine Creek at Wilmington, Del. 314 44 8 45

Table 1. Description of fixed and synoptic streamwater sampling sites in the Delaware River Basin, December 1998–August 2001.

—Continued

[Locations of fixed sites are shown in figures 4 and 5; locations of synoptic sites are shown in figure 5]

Index 

number

Station 

number Station name

Subbbasin of site

Area, in 

square 

miles

Land use, in percent

Agricultural Urban Forested
10 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

0 10 20 30 MILES

0 10 20 30 KILOMETERS

42°

41°

40°

39°

76° 75° 74°

NEW YORK

NEW JERSEY

P E N N S Y LVA N I A

MARYLAND

DELAWARE

24

19 23

22

20

31 30

29

28

35 33

34 36

3 41

56

55

54

52

53

8

75

73

71

74

9

86

85

84 83

82

81 66

65 62

63

7

6

5 4

2

1

43

42

39

37

32

25

21

18 17

16

15

93 92

91

90

89 87

79

77

76

72

70

69

68

61 59 58

57

50

49

48

47

46 45

40

94

88

80

78

67

60

51

44

38

27

14

13

12

11

64

26

10

EXPLANATION

Site type. Number is index number

(listed in table 1)

Physiographic Province

Appalachian Plateaus

Valley and Ridge

New England

Piedmont

Coastal Plain

Fixed site

Delaware River

Basin boundary

Synoptic site sampled in

1999, 2000, and 2001

Synoptic site sampled in 1999

Synoptic site sampled in 2000

Synoptic site sampled in 2001

Figure 5. Location of synoptic and fixed streamwater sampling sites in the Delaware River Basin, 

1998–2001.
Design and Methods of Study 11

Laboratory Methods

Two laboratory methods were used to determine the concentration of pesticide compounds. All concentrations of pesticide compounds are dissolved.

Solid-phase extraction with gas chromatography/mass 

spectrometry (Zaugg and others, 1995) was used to determine 

concentrations of 47 pesticide compounds. The 43 pesticides 

and 4 degradation products (table 2) are referred to as “GC pesticide compounds” in this report. For each compound, the laboratory reported one of three types of concentrations: an uncensored value, a nondetected value, or an estimated value. 

Uncensored values indicate that the concentrations have been 

determined reliably at values greater than or equal to the laboratory reporting level (some laboratory reporting levels changed 

during the period of study). Nondetected values indicate that the 

compound was not detected at concentrations greater than, 

equal to, or less than the laboratory-reporting level. Estimated 

values indicate that the laboratory detected but could not reliably quantify the concentration of the compound; estimated values may be greater than, equal to, or less than the laboratory 

reporting level. All detected concentrations of the following 

five compounds could not be quantified reliably and were estimated: deethylatrazine, carbofuran, carbaryl, terbacil, and 

methyl azinphos.

High-performance liquid chromatography/mass spectrometry (Lee and others, 2001) was used to determine the concentrations of six additional pesticide degradation products 

(table 2). The ethane sulfonic acid (ESA) and oxanilic acid 

(OA) degradation products of acetochlor, alachlor, and metolachlor are referred to as “HPLC pesticide degradation products” in this report. The laboratory reported either nondetected 

values or uncensored values greater than or equal to 0.05 μg/L, 

the laboratory reporting level. 

Pesticide compounds detected by use of GC were determined in all but 2 samples collected at fixed and synoptic sites. 

Pesticide degradation products detected by use of HPLC were 

determined in samples collected at two fixed sites (01470779, 

Tulpehocken Creek near Bernville, Pa., and 01474500, 

Schuylkill River at Philadelphia, Pa.) from March 1999 to 

August 2000 (fig. 4, table 1).

Quality Assurance/Quality Control Methods

Samples for QA/QC (Quality Assurance/Quality Control) 

were collected and analyzed to determine the bias and variability of the frequency of detection of pesticide compounds as well 

as the bias and variability of the concentration. Bias is the systematic error inherent in a method and can be positive or negative (Mueller and others, 1997). Positive bias indicates that the 

reported concentrations, in general, are greater than the concentrations actually present in the streamwater; negative bias indicates that the reported concentrations are less than those actually present. Variability is the degree of random error in 

repeated measurements of the same quality (Mueller and others, 

1997). The smaller the variability, the more likely it is that 

repeated measurements of a pesticide compound in a streamwater sample will result in the same concentration value.

Field blanks were collected to determine whether reported 

concentrations of pesticide compounds were biased high 

because of sample contamination. Field blanks were created for 

selected streamwater samples by processing water free of pesticide compounds through the equipment used for sample collection, splitting, and filtration; the blank then was sent to the laboratory for analysis for pesticide compounds.

Replicates were collected to provide information on the 

variability of the detection and concentration of pesticide compounds. Replicates were created for selected samples by filtering a second subsample and sending it to the laboratory for analysis for pesticide compounds. 

The variability of the concentrations of pesticide compounds was determined by calculating the difference between 

concentrations in streamwater samples and concentrations in 

associated replicates by use of equation (1) given below. Nondetected concentrations were set to zero.

, (1)

Application Rates of Pesticides to Agricultural Land

Amounts of pesticides annually applied to agricultural 

land within the Delaware River Basin were determined from 

information in Gianessi and Marcelli (2000). For important 

crops in each county of the conterminous United States during 

1997, Gianessi and Marcelli provide estimates of the area of 

cultivation as well as estimates of the annual amounts of pesticides applied per unit area of cultivation. For most crops and 

counties, the area of cultivation is for commercial farms; a farm 

is any place from which $1,000 or more of agricultural products 

were produced and sold, or normally would have been sold, during 1997. For each of the pesticides most often detected in the 

Delaware River Basin, the amount annually applied to agricultural land within the Delaware River Basin was determined by 

use of the following equations:

where S = streamwater concentration, in micrograms 

per liter; 

R = replicate concentration, in micrograms per 

liter;

D = difference, in percent of mean concentration; 

and

Abs = absolute value of.

D = 100 × Abs S R [ ] ( ) – ⁄ ( ) ( ) S R + ⁄ 2
12 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Table 2. Pesticides and degradation products analyzed for in streamwater in the Delaware River Basin, December 1998–

August 2001.

[Pesticide compounds shown in bold type were not detected; GC, gas chromatography; HPLC, high performance liquid chromatography; H, herbicide; 

I, insecticide; DP, degradation product; ESA, ethane sulfonic acid; OA, oxanilic acid; common or trade names are from Ebbert and Embrey (2002) and 

Meister Publishing Company (2000); na, not available or not applicable] 

Pesticide compound

Type of compound 

(parent pesticide of 

degradation 

product)

Laboratory reporting level, in 

micrograms per liter Common or trade 

names

Chemical 

Abstract Services 

At beginning of registry number

study At end of study

GC Pesticide compounds

Acetochlor H 0.002 0.0041 Guardian 34256-82-1

Alachlor H .002 .0024 Lasso 15972-60-8

Atrazine H .001 .007 AAtrex 1912-24-9

Azinphos, methyl1 I .001 .05 Guthion 86-50-0

Benfluralin H .002 .01 Balan, Benefin 1861-40-1

Butylate H .0020 .0020 Sutan +, Genate Plus 2008-41-5

Carbaryl1 I .003 .041 Sevin, Savit 63-25-2

Carbofuran1 I .003 .02 Furadan 1563-66-2

Chlorpyrifos I .004 .005 Lorsban, Dursban 2921-88-2

Cyanazine H .004 .018 Bladex 21725-46-2

Dacthal H .002 .003 Dachtal, DCPA 1861-32-1

p,p’-DDE DP (DDT) .006 .0025 na 72-55-9

Deethylatrazine1 DP (atrazine) .002 .006 Desethyl atrazine 6190-65-4

Diazinon I .002 .005 Diazinon 333-41-5

Dieldrin I .001 .0048 Panoram D-31 60-57-1

2,6-Diethylaniline DP (alachlor) .0030 .0017 na 579-66-8

Disulfoton I .0170 .0210 Di-Syston 298-04-4

EPTC H .002 .002 Eptam, Eradicane 759-94-4

Ethalfluralin H .0040 .0090 Sonalan, Curbit EC 55283-68-6

Ethoprop I .0030 .0050 Ethoprophos, Mocap 13194-48-4

Fonofos I .0030 .0027 Dyfonate 944-22-9

alpha-HCH2 DP (lindane) .0020 .0046 na 319-84-6

Lindane I .004 .004 Lindane, gamma-HCH 58-89-9

Linuron H .002 .035 Lorox, Linex 330-55-2

Malathion I .005 .027 Malathion 121-75-5

Methyl parathion I .0060 .0060 Penncap-M 298-00-0

Metolachlor H .002 .013 Dual, Pennant 51218-45-2

Metribuzin H .004 .006 Lexone, Sencor 21087-64-9

Molinate H .0040 .0016 Ordram 2212-67-1

Napropamide H .003 .007 Devrinol 15299-99-7

Parathion I .0040 .0070 (several) 56-38-2

Pebulate H .0040 .0016 Tillam 1114-71-2

Pendimethalin H .004 .01 Prowl, Stomp 40487-42-1

Permethrin, cis I .0050 .0060 Ambush, Pounce 54774-45-7

Phorate I .0020 .0110 Thimet, Rampart 298-02-2
Design and Methods of Study 13

GC Pesticide compounds--Continued

Prometon H 0.018 0.015 Pramitol 1610-18-0

Propachlor H .007 .01 Ramrod 1918-16-7

Propanil H .004 .011 Stampede 709-98-8

Propargite I .0130 .0230 Comite, Omite 2312-35-8

Propyzamide H .003 .0041 Kerb 23950-58-5

Simazine H .005 .011 Aquazine, Princep 122-34-9

Tebuthiuron H .01 .016 Spike 34014-18-1

Terbacil1 H .007 .034 Sinbar 5902-51-2

Terbufos I .0130 .0170 Counter 13071-79-9

Thiobencarb H .0020 .0048 Bolero 28249-77-6

Triallate H .0010 .0023 Far-Go 2303-17-5

Trifluralin H .002 .009 Treflan, Trilin 1582-09-8

HPLC pesticide degradation products

Acetochlor ESA DP (acetochlor) .05 .05 na na

Acetochlor OA DP (acetochlor) .05 .05 na na

Alachlor ESA DP (alachlor) .05 .05 na na

Alachlor OA DP (alachlor) .05 .05 na na

Metolachlor ESA DP (metolachlor) .05 .05 na na

Metolachlor OA DP (metolachlor) .05 .05 na na

1

 All detected concentrations were estimated.

2

 Alpha-hexachlorocyclohexane.

Table 2. Pesticides and degradation products analyzed for in streamwater in the Delaware River Basin, December 1998–

August 2001.—Continued

[Pesticide compounds shown in bold type were not detected; GC, gas chromatography; HPLC, high performance liquid chromatography; H, herbicide; 

I, insecticide; DP, degradation product; ESA, ethane sulfonic acid; OA, oxanilic acid; common or trade names are from Ebbert and Embrey (2002) and 

Meister Publishing Company (2000); na, not available or not applicable] 

Pesticide compound

Type of compound 

(parent pesticide of 

degradation 

product)

Laboratory reporting level, in 

micrograms per liter Common or trade 

names

Chemical 

Abstract Services 

At beginning of registry number

study At end of study
14 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

, (2)

, (3)

The amount of each pesticide annually applied to the 

drainage basins of selected sites was calculated by use of the 

equation

, (4)

Methods of Data Analysis

The probability plot method (Helsel and Cohn, 1988) was 

used to determine the median concentration of each pesticide 

compound in all samples. Estimated values were treated as 

uncensored values. Medians less than the laboratory reporting 

level were displayed as nondetected.

Kendall’s tau (Helsel and Hirsh, 1992) was used to identify 

relations among pesticide concentrations and streamflow, 

streamwater turbidity, land use, population density, or the rate 

of pesticide application to agricultural land. Relations were considered to be present at a 0.05 level of significance. Estimated 

values were assumed to be equivalent to uncensored values, and 

nondetected values were set to zero. 

LOWESS smoothed curves (described in Helsel and 

Hirsh, 1992) are shown in figures to provide a visual indication 

of some relations identified by Kendall’s tau. In some figures, 

nondetected concentrations are plotted at values of 0.001 μg/L. 

Pesticide Compounds in Streamwater in the 

Delaware River Basin

Summary of Detection Frequencies and 

Concentrations

A summary of the frequencies of detection for each pesticide compound in all streamwater samples is given in table 3. 

Maximum laboratory reporting levels and median and maximum concentrations also are shown. Compounds not detected 

are shown in bold in table 2.

Pesticide Compounds (Gas Chromatography)

A total of 531 samples were collected at 94 sites in the 

study area for analysis for these pesticide compounds. Of this 

total, 361 samples were collected at the 10 fixed sites under 

base-flow and stormflow conditions, and 170 were collected 

under base-flow conditions at synoptic sites.

At least one pesticide compound was detected in 95 percent of samples. The median number of compounds detected in 

a sample was 6, and the maximum number was 15. 

Of the 47 pesticide compounds analyzed for, 30 were 

detected (table 3). Fourteen pesticide compounds—10 herbicides, 3 insecticides, and 1 degradation product—were detected 

in 8 percent or more of samples (fig. 6). Atrazine, metolachlor, 

deethylatrazine, and simazine were the compounds most often 

detected. 

The variation of maximum laboratory reporting level 

(0.002 to 0.05 microgram per liter) does not appear to be the 

reason that these compounds were the most often detected. 

These compounds also were the most often detected of those 

with concentrations greater than or equal to 0.05 μg/L, the value

where Lj = total application of selected pesticide to agricultural land in county i

, in pounds;

Ci,j = area of crop i in county j to which pesticide is 

applied, in square miles; 

and

Pi,j = application rate for crop i in county j, in 

pounds per square mile.

where T = total amount of selected pesticide applied to 

study area, in pounds;

Bj = area of county j in Delaware River Basin, in 

square miles;

Cj = area of county j, in square miles; 

and

Lj = total annual application of selected pesticide 

to county j

, in pounds.

where A = amount of a selected pesticide annually 

applied to agricultural land in a selected 

drainage basin, in pounds per square mile;

Fj = area of drainage basin in county j, in square 

miles;

Cj = area of county j, in square miles;

Lj = total application of selected pesticide to 

county j

; 

and

D = area of drainage basin, in square miles.

Lj Ci j , ( ) Pi j , [ ] × ( )

crops

= ∑

T Bj Cj ( ) ⁄ Lj [ ] × ( )

counties

= ∑

A Fj Cj ( ) ⁄ × Lj [ ]

counties

= ∑ ⁄ D
Table 3. Summary of the frequencies of detection and the concentrations of pesticide compounds detected in streamwater in the Delaware River BAugust 2001.[GC, gas chromatography; HPLC, high performance liquid chromatography; H, herbicide; I, insecticide; DP, degradation product; sources of standards and guidelines are describethan; ESA, ethane sulfonic acid; OA, oxanilic acid; --, not available or not applicable]

Pesticide 

compound

Type of pesticide 

compound 

(parent pesticide 

of degradation 

product)

Frequency of detection, in 

percent of all samples Laboratory 

reporting 

level, in 

micrograms 

per liter 

(maximum 

during period 

of study)

Concentration, in 

micrograms per liter

Drinking-water standard or 

guideline 

Of all 

concentrations

Of 

concentrations 

greater than or 

equal to 

0.05 milligram 

per liter

Median Maximum

Value, in 

micrograms 

per liter

Number of 

samples in 

which 

concentration 

exceeded 

standard or 

guideline

GC pesticide compounds detected in 531 streamwater samples at all sites

Acetochlor H 9.8 0.9 0.0041 < 0.0041 0.36 -- -- Alachlor H 11.1 .4 .0024 < .0024 .074 2 0 Atrazine H 90.2 29.2 .007 .021 E 4.9 3 1 Azinphos, methyl1 I 1.5 0 .05 < .05 E .027 20 0 Benfluralin H 5.1 .2 .01 < .01 E .071 -- -- Carbaryl1 I 33 6.2 .041 < .041 E 2.4 700 0 Carbofuran1 I 1.5 .2 .02 < .02 E .11 40 0 Chlorpyrifos I 11.1 .2 .005 < .005 .051 20 0 Cyanazine H 9.6 1.1 .018 < .018 .48 1 0 Dacthal H 7.7 0 .003 < .003 .015 70 0 p,p’-DDE DP (DDT) 5.8 0 .006 < .006 E .004 1 0 Deethylatrazine1 DP (atrazine) 82.5 20 .006 .02 E .3 -- -- Diazinon I 34.6 5.9 .005 < .005 .47 .6 0 Dieldrin I 2.1 0 .0048 < .0048 .033 .02 5 EPTC H 1.7 0 .002 < .002 .016 -- -- Lindane I .9 0 .004 < .004 .015 0.2 0 Linuron H .6 .6 .035 < .035 .509 -- -- Malathion I 2.6 .2 .027 < .027 .055 100 0 Metolachlor H 86.1 15.4 .013 .013 1.3 100 0 Metribuzin H 1.7 .2 .006 < .006 .10 200 0 Napropamide H 1.7 0 0.007 < 0.007 0.014 -- -- 
GC pesticide compounds detected in 531 streamwater samples at all sites--Continued Pendimethalin H 10.9 0.9 .01 < .01 .12 -- -- 

Prometon H 58.8 4.7 .018 < .018 2.0 100 0 Pronamide H .8 0 .0041 < .0041 .015 50 0 Propachlor H .4 0 .01 < .01 E .0052 90 0 Propanil H .2 0 .011 < .011 .0088 -- -- Simazine H 78.9 9.2 .011 .011 9.4 4 1 Tebuthiuron H 20.3 0 .016 < .016 .039 500 0 Terbacil1 H 6.2 4.5 .034 < .034 E .19 90 0 Trifluralin H 12.1 0 .009 < .009 .011 5 0 

HPLC pesticide degradation products detected in 70 streamwater samples at two fixed sites Acetochlor ESA DP (acetochlor) 8.6 8.6 .05 <.05 .28 -- -- 

Acetochlor OA DP (acetochlor) 2.9 2.9 .05 <.05 .06 -- -- Alachlor ESA DP (alachlor) 80 80 .05 .145 1.05 -- -- Metolachlor ESA DP (metolachlor) 98.6 98.6 .05 .51 1.65 -- -- Metolachlor OA DP (metolachlor) 55.7 55.7 .05 .06 .37 -- -- 

1 All detected concentrations were estimated. Table 3. Summary of the frequencies of detection and the concentrations of pesticide compounds detected in streamwater in the Delaware River B

August 2001.—Continued [GC, gas chromatography; HPLC, high performance liquid chromatography; H, herbicide; I, insecticide; DP, degradation product; sources of standards and guidelines are describe

than; ESA, ethane sulfonic acid; OA, oxanilic acid; --, not available or not applicable] Pesticide compound Type of pesticide compound (parent pesticide of degradation product) Frequency of detection, in percent of all samples Laboratory reporting level, in micrograms per liter (maximum during period of study) Concentration, in micrograms per liter Drinking-water standard or guideline 

Of all concen- trations Of concentrations greater than or equal to 0.05 milligram per liter Median Maximum Value, in micrograms per liter Number of samples in which concentration exceeded standard or guideline 
Pesticide Compounds in Streamwater in the Delaware River Basin 17

of the greatest maximum laboratory reporting levels for 

detected compounds (table 3, fig. 6). Unless stated otherwise in 

this report, detection frequencies include all detected concentrations.

The pesticide compounds most frequently detected in 

streamwater samples from the Delaware River Basin (fig. 6; 

table 3) are among the compounds most frequently detected by 

other NAWQA studies in streamwater samples throughout the 

Nation and in the Northeast. These compounds were among the 

most frequently detected in samples from 50 streamwater sites 

nationwide (Larson and others, 1999). Atrazine, metolachlor, 

prometon, simazine, and deethylatrazine were the compounds 

most frequently detected in samples from 50 streams in New 

York and New Jersey (Reiser and O’Brien, 1999) and in samples from 46 streams of the Hudson River Basin (Wall and others, 1998). In streamwater of the Lower Susquehanna River 

Basin, atrazine and metolachlor were the most frequently 

detected herbicides, and diazinon and carbaryl were the most 

frequently detected insecticides (Lindsey and others, 1998). 

Pesticide Degradation Products (High Performance 

Liquid Chromatography) 

Of the 6 pesticide degradation products analyzed for in 70 

samples from 2 sites, 5 were detected (table 3); alachlor OA was 

the only compound not detected (table 2). At least one degradation product was detected in 69 of 70 samples; the median number of degradation products detected was 2 and the maximum 

number was 5. The most often detected degradation product 

was metolachlor ESA (98.6 percent of samples). 

ESA and OA degradation products of alachlor, acetochlor, 

or metolachlor have been detected in streams in the Midwest 

(Kalkhoff and others, 1998; Kalkhoff and others, 2003) and in 

New York State (Phillips and others, 1999). Most of these 

streams drain basins with agricultural land use.

Bias and Variability of Detection Frequencies and 

Concentrations

Bias and variability in reported concentrations of the pesticide compounds were determined from (1) examination of the 

results of analysis of QA/QC samples, (2) comparison of these 

results with results of analysis of streamwater samples, and 

(3) evaluation of results of analyses of QA/QC samples from 

previous NAWQA studies (Martin, 2002; Martin and others, 

1999). These previous studies may not represent current conditions because of changes in laboratory reporting procedures in 

1999 (Oblinger Childress and others, 1999) and annual reassessment of the laboratory reporting levels since then.

Pesticide Compounds (Gas Chromatography)

Evaluations of results of analysis of the 16 field blanks 

indicated that, of the 47 GC pesticide compounds, the analytical 

results of only p,p’-DDE were biased because of sample contamination. p,p’-DDE was the only pesticide compound 

detected in any of the 16 field blanks; it was detected in one 

blank. Comparison of the detection frequencies in streamwater 

samples and field blanks also supports this hypothesis; the 

0 20 40 60 80 100

CYANAZINE

ACETOCHLOR

PENDIMETHALIN

ALACHLOR

CHLORPYRIFOS

TRIFLURALIN

TEBUTHIURON

CARBARYL

DIAZINON

PROMETON

SIMAZINE

DEETHYLATRAZINE

METOLACHLOR

ATRAZINE

Herbicide concentration greater than or equal 

to 0.05 microgram per liter

Herbicide concentration detected at less than 

0.05 microgram per liter

Insecticide concentration greater than or equal 

to 0.05 microgram per liter

Insecticide concentration detected at less than 

0.05 microgram per liter

Degradation product concentration greater than 

or equal to 0.05 microgram per liter

Degradation product concentration detected at 

less than 0.05 microgram per liter

EXPLANATION

STREAMWATER SAMPLES IN WHICH A PESTICIDE

COMPOUND WAS DETECTED, IN PERCENT OF

ALL STREAMWATER SAMPLES

Figure 6. Frequences of detection of the pesticide compounds most often detected in 531 samples of streamwater by use of gas 

chromatography, Delaware River Basin, December 1998–August 2001. (Compounds were detected in at least 8 percent of samples.)
18 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

frequency of detection of p,p’-DDE in field blanks (6.3 percent) 

is close to the frequency of detection in all streamwater samples 

(5.8 percent), which would be expected if detections resulted 

because of sample contamination only. From an evaluation of 

results of analyses of field blanks and streamwater samples for 

pesticide compounds in previous NAWQA studies, Martin and 

others (1999) concluded that p,p’-DDE was one of the pesticide 

compounds for which contamination should be considered 

when interpreting its detection in streamwater samples.

The variability of detections and concentrations of GC 

pesticide compounds in streamwater samples was determined 

by comparing detections and concentrations in 14 replicate 

samples to corresponding values in the associated streamwater 

samples. For the purpose of this comparison, there were considered to be 658 pairs of concentrations (47 compounds in 14 

samples); each pair included one value from the replicate sample and one from the streamwater sample. 

For this study, the variability of analyte detection is 

defined as the ratio of the pairs of values with inconsistent 

results to the pairs of values with at least one detection. Inconsistent results were present for the pairs of values in which the 

analyte was detected in one value of the pair but not the other. 

The variability of detection was calculated to be 9.7 percent on the basis of the 10 pairs of values with inconsistent 

results and the 103 pairs of values with at least one detection. 

This result is an estimate of the overall variability of all the GC 

pesticide compounds detected. 

This variability of detections of pesticide compounds is 

within the range of corresponding values calculated from 

results reported by Martin (2002). Martin compared detections 

of compounds in environmental samples (both ground water 

and streamwater) collected by the NAWQA Program during 

1992–97 to detections in associated replicates; in some cases, 

there was more than one replicate for an environmental sample. 

Martin noted that (1) variability of detections of pesticide compounds was greatest when the compound concentration was 

small, and (2) variability decreased with increasing concentration. For samples/replicates with the smallest concentrations, a 

variability of 37 percent was calculated (for GC pesticide compounds in Martin, 2002, table 4). For samples with the largest 

concentrations, a variability of 0.7 percent was calculated (GC 

pesticide compounds in Martin, 2002, table 6). Martin attributed this variability of detection to variability of the laboratory 

method and to matrix interferences (or other processes) that 

result in false-negative errors. Matrix interference is the effect 

of the presence of compounds not being analyzed for on the 

results of the laboratory analysis.

An estimate of the variability of concentration of pesticide 

compounds was calculated as the median of the differences 

between concentrations in streamwater samples and concentrations in replicates by use of equation 1. Only the 103 pairs of 

values with at least one detected value were included. Nondetected values were set to zero.

By the definition described above, the variability of concentrations appears to be small; the median difference between 

concentrations in replicates and concentrations in streamwater 

samples was 4.5 percent of the mean concentration; 95 percent 

of the differences were within 36 percent. These results are a 

gross estimate of the variability of all concentrations of all 

detected analytes but most accurately reflect the variability of 

compounds most often detected (atrazine and metolachlor, for 

example).

The median difference (4.5 percent) is within the range of 

typical median differences reported by Martin (2002, table 8) 

when nondetected values were set to zero. Martin determined 

differences in concentrations of pesticides and degradation 

products in streamwater and replicate samples analyzed as part 

of previous NAWQA studies. 

Pesticide Degradation Products (High Performance 

Liquid Chromatography)

Bias because of sample contamination does not appear to 

be important. In the five blanks analyzed for the six degradation 

products, none were detected. 

Relations Between Concentrations of Selected 

Pesticides and Indicators of Agricultural and 

Nonagricultural Uses of Pesticides

Although pesticides traditionally have been associated 

with agricultural uses, many of the pesticides identified in the 

Delaware River Basin appear to have both agricultural and 

nonagricultural uses (table 4). A summary of nationwide uses is 

given in table 4, which could include uses not present in the 

study area. For this report, agricultural uses consist of the application of pesticides to agricultural land, and nonagricultural 

uses consist of the application of pesticides to buildings (including residences) and nonagricultural land such as lawns, roadways, and woodlands. 

The relation between frequency of detection in all streamwater samples and the estimated amount applied to agricultural 

land in the Delaware River Basin (fig. 7) indicates that agricultural uses could be important sources of some pesticides and 

nonagricultural uses could be important sources of others. Agricultural uses could be important sources of atrazine and metolachlor; these pesticides are applied most heavily to agricultural 

land and are detected most often in streamwater. Nonagricultural uses probably are important for prometon and tebuthiuron. 

Prometon has no agricultural uses, and the estimated application of tebuthiuron to agricultural land in the basin was zero. 

Other factors, such as how quickly a pesticide breaks down to 

its degradation products, also can determine the relation 

between the amount applied for agricultural uses and the frequency of detection in streamwater. 

Whether (1) agricultural uses appeared to be more important than nonagricultural uses or (2) nonagricultural uses 

appeared to be more important than agricultural uses was determined by identifying relations between pesticide concentrations 

at selected sites and characteristics of the subbasins associated 

with the sites. The pesticides included in this analysis were
Pesticide Compounds in Streamwater in the Delaware River Basin 19

Table 4. Selected nationwide uses of pesticides detected most often in streamwater in the Delaware River Basin, December 1998–

August 2001.

[Pesticides were detected in 8 percent or more of samples; H, herbicide; I, insecticide; --, uses not reported or found; USEPA, U.S. Environmental Protection 

Agency]

Pesticide Type of 

pesticide

Selected nationwide uses

Agricultural 

(Thelin and Gianessi, 2000) Nonagricultural

Acetochlor H Corn (USEPA, 2003a) --

Alachlor H Corn, soybeans, sweet corn -- (USEPA, 1998)

Atrazine H Corn, pasture, sweet corn Woodlands, lawns, parks, and golf courses (USEPA, 2002a)

Carbaryl I Alfalfa, corn, soybeans, apples Residential lawns and gardens, and pet care (USEPA, 2003b)

Chlorpyrifos I Corn, alfalfa, wheat, apples Structures (including residences), lawns, and ornamental 

plants; sales for most residential uses ended by end of 2001 

(USEPA, 2000)

Cyanazine (sales cancelled 

in 1999) (USEPA, undated)

H Corn, sweet corn --

Diazinon I Peaches, sweet corn, apples Structures, including residences, and lawns and gardens 

(USEPA, 2001)

Metolachlor H Corn, soybeans, sweet corn Lawns, rights-of-way, woodlands (USEPA, 1995)

Pendimethalin H Soybeans, corn Residential lawns and ornamental plants (USEPA, 1997)

Prometon H -- Roads, railways, fence lines (Capel and others, 1999) 

Simazine H Corn, alfalfa, apples, peaches Golf courses, lawns, industrial sites (Meister Publishing 

Company, 2000)

Tebuthiuron H Pasture Industrial sites, rights of way, roadways, and sidewalks 

(USEPA, 1994)

Trifluralin H Soybeans, alfalfa, wheat Residential uses (USEPA, 1996)

Figure 7. Relation of frequency of detection to estimated annual application to agricultural land within the Delaware River 

Basin. (Only pesticides detected in 8 percent or more of streamwater samples by use of gas chromatography are included.)

0 100,000 200,000 300,000 400,000 500,000

ESTIMATED ANNUAL APPLICATION TO AGRICULTURAL LAND, IN POUNDS

0

20

40

60

80

100

Metolachlor

Atrazine

Simazine

Prometon

Diazinon

Carbaryl

Tebuthiuron

Trifluralin

Chlorpyrifos

Pendimethalin

Alachlor

FREQUENCY OF DETECTION, IN PERCENT

Cyanazine Acetochlor

OF ALL SAMPLES
20 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

those detected in 8 percent or more of all samples. The concentrations included in this analysis were those collected under 

base-flow conditions at synoptic sites (1) in the Piedmont and 

the Valley and Ridge Provinces during May and June 2000 and 

(2) in the Piedmont Province during August and September 

2000. 

The following subbasin characteristics were assumed to be 

indicative of the relative amount of each pesticide used for agricultural purposes in a subbasin: (1) the rate of application to 

agricultural land in the subbasin (in pounds per year per square 

mile of subbasin) as estimated from information in Gianessi and 

Marcelli (2000) and (2) the percentage of the subbasin composed of agricultural land (table 1). Agricultural applications 

are considered to be important sources for those pesticides, the 

concentrations of which increased with increasing values of 

either characteristic. 

The concentrations of three pesticides (atrazine, metolachlor, and pendimethalin) increased with an increase in either 

the agricultural application rate or the percentage of subbasin 

composed of agricultural land (table 5); the relation of concentration to agricultural application rate showed nearly the same 

results as that to the percentage of subbasin composed of agricultural land. Relations in the spring were more likely to indicate an increase in concentrations with an increase in agricultural land than were relations in the late summer, possibly 

reflecting the application of pesticides in the spring. 

As an example, the relation between (1) atrazine concentrations in the spring and (2) the percentage of agricultural land 

in the subbasin is presented in figure 8. When all sites are considered, concentrations increase with increasing percentage of 

agricultural land in the subbasin. Concentrations measured in 

samples from sites on streams draining subbasins composed of 

little agricultural land (less than 20 percent) and a substantial 

amount of urban land (30 percent or more) do not appear to 

increase with increases in agricultural land, indicating that 

nonagricultural sources also may be important in predominantly 

urban subbasins.

From this analysis, agricultural uses appear to be more 

important sources of atrazine, metolachlor, and pendimethalin 

in streamwater than nonagricultural uses. The importance of 

agricultural uses tends to be supported by estimates of application rates to agricultural land; of the pesticides included in this 

analysis, atrazine, metolachlor, and pendimethalin are the most 

heavily applied to agricultural land (table 5). All three are used 

on corn and soybeans, major crops in the Delaware River Basin. 

Results for atrazine and metolachlor also agree with results 

from Larson and others (1999), who reported that atrazine and 

metolachlor were the pesticides most often detected in streamwater leaving agricultural basins throughout the Nation (Larson 

and others, 1999, fig. 14).

For atrazine, the areal variation in concentrations in 

streamwater throughout the Delaware River Basin also supports 

the importance of agricultural applications as appreciable 

sources to the streams. Most of the greatest concentrations during May to June during 1999, 2000, or 2001 were in samples 

from sites in counties with the largest estimated application per 

unit area of county (fig. 9). These concentrations were collected 

under base-flow conditions at sites with a subbasin less than or 

equal to 250 mi2

. 

0 20 40 60 80

AGRICULTURAL LAND, IN PERCENT

0.010

0.100

1.000

10.000

100.000

ATRAZINE, IN MICROGRAMS PER LITER

Smoothed curve, less than 30 percent urban land in subbasin

Smoothed curve, urban land greater than or equal to 30 percent of subbasin

Smoothed curve, all values

Uncensored concentration, less than 30 percent urban land in subbasin

Estimated concentration, less than 30 percent urban land in subbasin

Uncensored concentration, urban land greater than or equal to 30 percent of subbasin

Figure 8. Relation of concentration of atrazine in streamwater to percentage of agricultural land in subbasins of 

the Delaware River Basin, May and June 2000. (Streamwater samples were collected during base-flow conditions 

at synoptic sites.)
Table 5. Relations of concentrations of selected pesticides in streamwater to rate of application to agricultural land, and relations of concentrations 

percentage of agricultural land in subbasins of the Delaware River Basin, 2000.

[For pesticides in bold type, at least one relation indicated that concentrations increased with an increase in either rate of pesticide application to agricultural land or to in an incr

land in subbasin; Increased, pesticide concentrations increased with an increase in rate of application or percentage of agricultural land in subbasin; Decreased, pesticide concentr

in values of rate of application or percentage of agricultural land in subbasin; Not tested, relations were not evaluated; --, concentrations did not increase or decrease. Samples w

mont and Valley and Ridge Provinces during base-flow conditions. Relations were identified by use of Kendall’s tau at a 0.05 level of significance.]

Pesticide

Frequency of 

detection, in 

percent of all 

streamwater 

samples

Amount applied to 

agricultural land in the 

Delaware River Basin, 

in pounds per year

Concentrations in samples collected during 

May–June 2000 

(1 sample at each of 40 sites)

Concentrations in sam

August–Sep

(1 sample at e

Relations of 

concentrations to an 

increase in rate of 

pesticide application to 

agricultural land in 

subbasin

Relations of 

concentrations to an 

increase in percentage of 

agricultural land in 

subbasin

Relations of 

concentrations to an 

increase in rate of 

pesticide application to 

agricultural land in 

subbasin

Atrazine 90.2 350,000 Increased Increased -- Metolachlor 86.1 460,000 Increased Increased -- Simazine 78.9 36,000 -- -- -- Prometon 58.8 0 Not tested -- Not tested Diazinon 34.6 3,000 Decreased Decreased -- Carbaryl 33.0 13,000 Decreased Decreased -- Tebuthiuron 20.3 0 Not tested -- Not tested Trifluralin 12.0 3,000 -- Decreased -- Chlorpyrifos 11.1 46,000 -- -- -- Alachlor 11.1 85,000 -- -- -- Pendimethalin 10.9 170,000 Increased Increased -- Acetochlor 9.8 59,000 -- -- -- Cyanazine 9.6 47,000 -- -- -- 
22 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

0 10 20 30 MILES

0 10 20 30 KILOMETERS

42°

41°

40°

39°

76° 75° 74°

NEW YORK

NEW JERSEY

P E N N S Y LVA N I A

MARYLAND

DELAWARE

EXPLANATION

Streamwater sampling site and

associated concentration of atrazine,

in micrograms per liter

Application rate to agricultural land,

in pounds per year per square mile

of county

Less than or equal to 10

Greater than 10 and less

than or equal to 50

Greater than 50

Not detected

Less than or equal to 0.20

Greater than 0.20

Delaware River

Basin boundary

Figure 9. Streamwater sampling sites and association of atrazine under base-flow conditions, and 

application rates, Delaware River Basin, May and June 1999–2001.
Pesticide Compounds in Streamwater in the Delaware River Basin 23

The following subbasin characteristics were assumed to be 

representative of nonagricultural uses of pesticides: (1) the percentage of the subbasin composed of urban land and (2) the 

population density of the subbasin in 2000. Nonagricultural 

uses are considered to be important sources for those pesticides, 

the concentrations of which increased with increasing values of 

either characteristic. 

Concentrations of six pesticides increased with increasing 

values of either population density or the percentage of subbasin composed of urban land (table 6); relations between concentrations and population density showed nearly the same results 

as the relations between concentrations and the percentage of 

subbasin composed of urban land. An example of one relation 

is shown in figure 10. Relations for spring were different than 

relations for late summer. For example, concentrations for carbaryl and trifluralin in the spring increased with these basin 

characteristics, but concentrations in the late summer did not; 

on the other hand, concentrations of chlorpyrifos in the late 

summer increased with the basin characteristics, but concentrations in the spring did not. 

Relations between concentrations and subbasin characteristics indicate that nonagricultural uses appear to be more 

important than agricultural uses for prometon, diazinon, carbaryl, tebuthiuron, trifluralin, and chlorpyrifos (table 6). Of 

these six, prometon and tebuthiuron have no reported agricultural uses in the Delaware River Basin. Diazinon, carbaryl, trifluralin, and chlorpyrifos do have agricultural uses, but apparently, the nonagricultural uses require greater quantities of the 

pesticides than do agricultural uses. Results for diazinon, carbaryl, and chlorpyrifos agree with the results of Larson and others (1999) who report that these three pesticides were detected 

more often in streams that drain urban basins than in streams 

that drain agricultural basins throughout the Nation. 

The areal variation of prometon concentrations in streamwater throughout the Delaware River Basin also supports the 

importance of nonagricultural uses as sources to the streams. 

The greatest concentrations in streamwater samples during May 

to June occurred in areas with the largest population density 

(fig. 11). These samples were collected under base-flow conditions during May to June 1999, 2000, or 2001 at sites with a 

subbasin area less than or equal to 250 mi2. 

Relations between concentration of simazine and subbasin 

characteristics do not indicate that either agricultural uses or 

nonagricultural uses appear to be more important than the other. 

The high frequency of detection (78.9 percent of samples) indicates that both types of uses may have been important. Agricultural uses of simazine in the Delaware River Basin (table 5) are 

indicated in the information in Gianessi and Marcelli (2000). 

Information in Larson and others (1999), however, indicates 

that, in streams nationwide, nonagricultural uses may be greater 

than agricultural uses; simazine was detected more often in 

streams that drain urban basins than in streams that drain agricultural basins.

0 20 40 60 80

URBAN LAND, IN PERCENT

0.001

0.010

0.100

CONCENTRATION OF PROMETON,

IN MICROGRAMS PER LITER

Smoothed curve

Uncensored concentration

Estimated concentration

Nondetected concentration, which 

is set to 0.001 microgram per liter

Figure 10. Relation of concentrations of prometon in streamwater to the percentage of urban land in subbasins of the Delaware River Basin, May and June 2000. (Concentrations were measured under base-flow 

conditions.)
Table 6. Relations of concentrations of selected pesticides in streamwater to population density, and relations of concentrations of selected pestici

land in subbasins of the Delaware River Basin, 2000. [For pesticides in bold type, at least one relation indicated that concentrations increased with an increase in either population density or percentage of urban land in subbasin; Inc

with an increase in population density or percentage of urban land in subbasin; Decreased, concentrations decreased with an increase in population density or percentage of urba

tions did not increase or decrease; Not tested, relations not evaluated. Samples were collected at sites in the Piedmont and Valley and Ridge Provinces during base-flow conditions

of Kendall’s tau at a 0.05 level of significance.] Pesticide Frequency of detection, in percent of all streamwater samples Amount applied to agricultural land in the Delaware River Basin, in pounds per year Concentrations in samples collected during May–June 2000 (1 sample at each of 40 sites) Concentrations in sam

August–Sept

(1 sample at ea

Relations of concentrations to an increase in population density in subbasin in 2000 Relations of concentrations to an increase in percentage of urban land in subbasin Relations of concentrations to an increase in population density in subbasin in 2000 

Atrazine 90.2 350,000 Decreased Decreased Decreased Metolachlor 86.1 460,000 Decreased Decreased -- Simazine 78.9 36,000 -- -- -- Prometon 58.8 0 Increased Increased Increased Diazinon 34.6 3,000 Increased Increased Increased Carbaryl 33.0 13,000 Increased Increased -- Tebuthiuron 20.3 0 -- Increased Increased Trifluralin 12.0 3,000 Increased Increased -- Chlorpyrifos 11.1 46,000 -- -- Increased Alachlor 11.1 85,000 -- -- -- Pendimethalin 10.9 170,000 -- -- -- Acetochlor 9.8 59,000 -- -- -- Cyanazine 9.6 47,000 -- -- -- 
Pesticide Compounds in Streamwater in the Delaware River Basin 25

0 10 20 30 MILES

0 10 20 30 KILOMETERS

42°

41°

40°

39°

76° 75° 74°

NEW YORK

NEW JERSEY

P E N N S Y LVA N I A

MARYLAND

DELAWARE

EXPLANATION

Streamwater sampling sites and

associated concentrations of

prometon, in micrograms per liter

Population density, in people per

square mile

Less than or equal to 100

Greater than 100 and less

than or equal to 1,000

Greater than 1,000

Not detected

Less than or equal to 0.015

Greater than 0.015

Delaware River

Basin boundary

Figure 11. Streamwater sampling sites and associated concentrations of prometon under baseflow conditions, and population density, Delaware River Basin, May and June 1999–2001.
26 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Relations between concentrations of alachlor, acetochlor, 

or cyanazine and subbasin characteristics do not indicate that 

either agricultural uses or nonagricultural uses appear to be 

more important than the other. Information in Larson and others 

(1999) indicates that, in streams nationwide, agricultural uses of 

alachlor and cyanazine were more important than nonagricultural uses; alachlor and cyanazine were among the pesticides 

most often detected in streams that drain agricultural basins. 

Acetochlor, which was not included in the analysis by Larson 

and others (1999), commonly is applied to corn (U.S. Environmental Protection Agency, 2003a). 

A reduction in the amount of use during the period of study 

could explain why the importance of agricultural uses was not 

indicated for cyanazine by relations between concentration and 

basin characteristics. Sales of cyanazine were cancelled at the 

end of 1999 (U.S. Environmental Protection Agency, undated). 

Results of this analysis indicate that pesticides used on 

agricultural land appear to be different from those used on urban 

land. One implication of these results is that, in agriculturalland-use areas being converted to urban land use, the types of 

pesticides detected in the streams likely will change. 

Variation in Concentrations of Selected Pesticides 

with Season

In general, pesticide concentrations during the growing 

season (April–October) were greater than those during the nongrowing season (November–March). This result was expected 

because pesticides generally are applied more often during the 

growing season. The differences in pesticide concentrations by 

season are shown in time-series plots (figs. 12 and 13) of concentrations of selected pesticides at the 10 fixed sites. 

For atrazine, metolachlor, and acetochlor, the greatest concentrations generally occurred during May, June, and July; concentrations of atrazine and acetochlor are shown in figure 12 as 

examples. This pattern is the same as that reported by Larson 

and others (1999) for concentrations of pesticides in streamwater leaving agricultural basins nationwide. Larson and others 

noted that this pattern usually has been attributed to pesticides 

applied in the spring and carried to streams by rainwater runoff 

soon after application. As previously discussed, atrazine and 

metolachlor in streamwater appear to be attributable more to 

agricultural uses than to nonagricultural uses. Although the 

same evaluation did not indicate that acetochlor in streamwater 

came from agricultural uses, the only known use found for acetochlor is on corn, which indicates that this pesticide was used 

predominantly for agricultural purposes. 

None of the pesticides that appear to be attributable more 

to nonagricultural uses than agricultural uses showed this pattern of greatest concentrations during May to July that is shown 

by atrazine, metolachlor, and acetochlor. This result could be 

attributable to the application of these pesticides (prometon, 

diazinon, carbaryl, tebuthiuron, trifluralin, and chlorpyrifos) 

throughout the growing season rather than just during the beginning.

Relations of Concentrations of Selected Pesticides to 

Streamwater Turbidity

Relations between concentrations of selected pesticides 

and streamwater turbidity were identified to determine whether 

concentrations in streams during stormflow conditions were 

greater than concentrations in streamwater during base-flow 

conditions. For this report, streamwater turbidity was used as an 

indicator of stormflow and base-flow conditions. The turbidity 

of the streamwater during stormflow conditions usually is 

greater than the turbidity during base flow because, during 

stormflow conditions, streamwater usually contains particulate 

material washed off the land surface and(or) resuspended from 

the streambed, and particulate material usually is not present 

during base-flow conditions. 

Relations of concentration to turbidity were identified by 

use of Kendall’s tau and data collected during the growing season at the 10 fixed sites. Only concentrations during the growing season were included because those concentrations tended 

to be greater than the concentrations during the non-growing 

season, and relations between concentrations and turbidity were 

more likely to be identified. An example of one relation is 

shown in figure 14.

Relations between concentrations of pesticides and 

streamwater turbidity are summarized by pesticide in table 7. 

For each pesticide, the number of sites at which concentrations 

increased with increases in turbidity is shown. No relation was 

determined for decreases in concentrations with increases in 

turbidity.

Metolachlor and diazinon were more likely than the other 

pesticides to be present in greater concentrations during stormflow than during base flow. Of the 10 fixed sites sampled, concentrations of metolachlor and diazinon increased with 

increases in turbidity at 8 and 6 sites, respectively (table 7). For 

the other pesticides tested, such relations were determined for 

no more than four sites.

These results indicate that, in general, large amounts of 

metolachlor and diazinon (in the dissolved form) were washed 

off the land surface during storms. One implication of these 

results is that any interpretation of concentrations of metolachlor and diazinon should consider whether the concentrations were measured during stormflow or base flow. 
Pesticide Compounds in Streamwater in the Delaware River Basin 27

Nondetected concentration

Concentration less than or equal to 0.0041 microgram per liter

Concentration greater than 0.0041 microgram per liter and less than or equal to 0.02 microgram per liter

Concentration greater than 0.02 microgram per liter and less than 0.1 microgram per liter

01470779

01451800

01477120

01474500

01472157

01464907

01454700

01463500

01434000

01467150

EXPLANATION

Nondetected concentration

Concentration less than or equal to 0.007 microgram per liter

Concentration greater than 0.007 microgram per liter and less than or equal to 0.12 microgram per liter

Concentration greater than 0.12 microgram per liter and less than 2.0 micrograms per liter

EXPLANATION

01470779

01451800

01477120

01474500

01472157

01464907

01454700

01463500

01434000

01467150

ON FMAMJ J ASO

(A) Atrazine

(B) Acetochlor

Growing season Non-growing season

FIXED STREAMWATER

SAMPLING SITES

FIXED STREAMWATER

SAMPLING SITES

DJ N FMAMJ J ASO DJ N FMAMJ J AS D J

1998 1999 2000 2001

ON FMAMJ J ASO DJ N FMAMJ J ASO DJ N FMAMJ J AS D J

1998 1999 2000 2001

Figure 12. Concentrations of (A) atrazine, and (B) acetochlor in streamwater samples from fixed sites 

in the Delaware River Basin, December 1998–August 2001. (Sites, indicated by station number, are listed 

in order, from bottom to top, of decreasing percentage of basin composed of agricultural land. Names of 

sites are listed in table 1. Vertical lines are at May 1 and July 31.)
28 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

01467150

01464907

01474500

01454700

01477120

01470779

01463500

01472157

01434000

01451800

(A) Prometon

(B) Diazinon

01467150

01464907

01474500

01454700

01477120

01470779

01463500

01472157

01434000

01451800

FIXED STREAMWATER

SAMPLING SITES

FIXED STREAMWATER

SAMPLING SITES

ON FMAMJ J ASO D J N FMAMJ J ASO DJ N FMAMJ J AS D J

1998 1999 2000 2001

ON FMAMJ J ASO D J N FMAMJ J ASO DJ N FMAMJ J AS D J

1998 1999 2000 2001

Nondetected concentration

Concentration less than or equal to 0.005 microgram per liter

Concentration greater than 0.005 microgram per liter and less than or equal to 0.06 microgram per liter

Concentration greater than 0.06 microgram per liter and less than 0.5 microgram per liter

EXPLANATION

Nondetected concentration

Concentration less than or equal to 0.018 microgram per liter

Concentration greater than 0.018 microgram per liter and less than or equal to 0.06 microgram per liter

Concentration greater than 0.06 microgram per liter and less than 2.0 micrograms per liter

EXPLANATION

Growing season Non-growing season

Figure 13. Concentrations of (A) prometon, and (B) diazinon in streamwater samples from fixed sites in 

the Delaware River Basin, December 1998–August 2001. (Sites, indicated by station number, are listed in 

order, from bottom to top, of decreasing percentage of basin composed of urban land. Names of sites 

are listed in table 1. Vertical lines are at May 1 and July 31.)
Pesticide Compounds in Streamwater in the Delaware River Basin 29

Comparison of Concentrations of Selected 

Degradation Products with Concentrations of Parent 

Pesticides

Deethylatrazine

Deethylatrazine, which was detected in 82.5 percent of 

samples, was most frequently detected GC pesticide degradation product and the third most frequently detected GC pesticide 

compound (table 3, fig. 6). Deethylatrazine has been detected 

commonly in streams nationwide, and is the fifth most often 

detected pesticide compound in 50 streams (Larson and others, 

1999). The high frequency of detection of deethylatrazine is 

likely related to the presence of atrazine, its parent pesticide, in 

streamwater; atrazine was the pesticide most often detected in 

this study and in the study by Larson and others (1999). 

The concentration of deethylatrazine generally increased 

with the concentration of atrazine in the samples (fig. 15). This 

correlation appears to indicate that the greater the amount of 

atrazine in the streamwater, the greater the amount of atrazine 

that has degraded to deethylatrazine. Only samples with 

detected concentrations of deethylatrazine or atrazine were 

included in this analysis.

The relation between concentrations of deethylatrazine 

and atrazine is dependent upon the time of the year in which the 

sample was collected (fig. 15). For a given atrazine concentration, the corresponding concentration of deethylatrazine in samples collected during May to July was less than the deethylatrazine concentration in samples collected during August to April. 

Table 7. Summary of relations of concentrations of selected 

pesticides to streamwater turbidity at fixed streamwater sampling 

sites in the Delaware River Basin, April–October, 1999–2001.

[For pesticides in bold type, concentrations increased with increases in streamwater turbidity at six or more sites; these pesticides were detected in 8 percent 

or more of all samples. For each fixed site, the number of samples included in 

the analysis ranged from 13 to 33. Relations were identified by use of Kendall’s tau and have a 0.05 level of significance. No relation showed decreasing 

concentration with increasing streamwater turbidity.]

Pesticide

Frequency of 

detection, in 

percent of all 

samples

Number of fixed sites with 

relations showing increasing 

concentration with increases 

in streamwater turbidity

Atrazine 90.2 3

Metolachlor 86.1 8

Simazine 78.9 1

Prometon 58.8 1

Diazinon 34.6 6

Carbaryl 33.0 2

Tebuthiuron 20.3 1

Trifluralin 12.1 2

Chlorpyrifos 11.1 4

Alachlor 11.1 2

Pendimethalin 10.9 4

Acetochlor 9.8 2

Cyanazine 9.6 3

1 10 100 1,000

STREAMWATER TURBIDITY, IN NEPHELOMETRIC TURBIDITY UNITS

0.001

0.010

0.100

1.00

10.0

CONCENTRATION OF DIAZINON,

IN MICROGRAMS PER LITER

Smoothed curve

Uncensored concentration

Estimated concentration

Nondetected concentration, value set to laboratory reporting level

Figure 14. Relation of diazinon concentration to streamwater turbidity at streamwater 

sampling site 01464907, Little Neshaminy Creek near Neshaminy, Pa., April–October, 

1999–2001.
30 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

This difference may be attributable to the time of application of 

atrazine to agricultural land. The atrazine concentrations in 

streamwater during May to July were greater than during other 

months (fig. 12), suggesting application just prior to or during 

this period. If so, atrazine in streamwater during May to July did 

not have as much time to decay to deethylatrazine as did atrazine in streamwater during the remaining months of the year.

Ethane Sulfonic Acid and Oxanilic Acid Degradation 

Products of Alachlor, Acetochlor, and Metolachlor at 

Two Sites

The frequencies of detection of the ESA and OA degradation products as a function of the frequencies of detection of the 

parent pesticides are shown in figure 16. A common reporting 

level of 0.05 μg/L was used to compare the frequencies of detection because the laboratory reporting level for the degradation 

products (0.05 μg/L) was greater than the laboratory reporting 

levels for the parent pesticides (table 3). Samples were considered to contain detected degradation products if the concentration of either the ESA or OA degradation product equaled or 

exceeded 0.05 μg/L in the 68 samples analyzed for both degradation products and parent pesticides. 

The ESA or OA degradation products of alachlor, acetochlor, and metolachlor were detected at concentrations 

greater than or equal to 0.05 μg/L more often than were the parent pesticides (fig. 16). The degradation products of alachlor 

and metolachlor were detected in at least 60 percent of samples, 

and the parent pesticides were detected in less than 30 percent. 

The concentrations of either the ESA or OA degradation 

product usually exceeded the concentrations of the parent pesticide (for example, see figure 17). In addition, concentrations 

of the ESA degradation products of metolachlor and alachlor 

usually exceeded the concentrations of the respective OA degradation product (for example, see figure 17). Similar results 

have been shown by studies of pesticide degradation products 

in streams in Iowa (Kalkhoff and other, 1998); Illinois, Iowa, 

and Minnesota (Kalkhoff and others, 2003); and New York 

(Phillips and others, 1999).

0.001 0.010 0.100 1.0 10.0

ATRAZINE, IN MICROGRAMS PER LITER 

0.001

0.010

0.100

1.0

10.0

DEETHYLATRAZINE, IN MICROGRAMS

PER LITER 

Smoothed curve, August-April

Smoothed curve, May-July

Line of equal value

Detected concentration of deethylatrazine, May-July

Detected concentration of deethylatrazine, August-April

Nondetected concentration of deethylatrazine, May-July

Nondetected concentration of deethylatrazine, August-April

EXPLANATION

0 20 40 60 80 100

0

20

40

60

80

100

FREQUENCY OF DETECTION OF

ETHANE SULFONIC ACID AND

OXANILIC ACID DEGRADATION

PRODUCTS, IN PERCENT

FREQUENCY OF DETECTION OF

PARENT PESTICIDES, IN PERCENT

LINE OF EQUAL VALUE

Metolachlor at 01470779 Tulpehocken Creek

Metolachlor at 01474500 Schuylkill River

Alachlor at 01470779 Tulpehocken Creek

Alachlor at 01474500 Schuylkill River 

Acetochlor at 01470779 Tulpehocken Creek

Acetochlor at 01474500 Schuylkill River

EXPLANATION

Figure 15. Relation of concentrations of deethylatrazine 

to concentrations of atrazine in streamwater samples from 

the Delaware River Basin, 1998–2001. (Only samples with 

detected concentrations of deethylatrazine or atrazine 

were included. All nondetected concentrations were set 

to 0.001 microgram per liter.)

Figure 16. Relation of frequency of detection of 

ethane sulfonic acid and oxanilic acid degradation 

products to the frequency of detection of metolachlor, alachlor, and acetochlor in 68 streamwater 

samples from two sites in the Delaware River Basin, 

1999–2000. (Only concentrations greater than or 

equal to 0.05 microgram per liter are considered to be 

detected.)
Pesticide Compounds in Streamwater in the Delaware River Basin 31

Comparison of Concentrations of Pesticide 

Compounds to Standards and Guidelines for the 

Protection of Human Health and Aquatic Life

In this section, some of the deleterious effects of pesticide 

compounds in water on human health and aquatic life are 

assessed. Some effects not addressed in this analysis are mentioned. 

Standards and guidelines included in this analysis are values accepted by the U.S. Environmental Protection Agency 

(USEPA), the Canadian Council of Ministers of the Environment (CCME), or the International Joint Commission United 

States and Canada (IJC) (table 8). Standards are enforced 

legally, and guidelines are advisory.

Human Health

Potential effects of pesticide compounds on human health 

through consumption of streamwater were assessed by comparing concentrations of pesticide compounds to drinking-water 

standards and guidelines accepted by the USEPA (table 8). For 

each pesticide compound, the value of the maximum contaminant level (MCL), if available, was used. An MCL, the maximum permissible level of a contaminant in water that is delivered to any user of a public water system, is a legally enforced 

standard. An MCL is set as close to the maximum contaminant 

level goal as feasible, using the best available analytical and 

treatment technologies and taking cost into consideration; the 

maximum contaminant level goal is the level at which no 

known or anticipated adverse effect to health occurs and which 

allows an adequate margin of safety. 

If there was no value for the MCL for a specified compound, the smaller of either of the following two guidelines was 

used: the lifetime health advisory (HAL) or the risk-specific 

dose at 10-5 cancer risk (RSD5). The HAL is the concentration 

of a chemical in drinking water that is not expected to cause any 

adverse noncarcinogenic effects for a lifetime of exposure. The 

RSD5 is the concentration of a chemical in drinking water that 

corresponds to an excess estimated lifetime cancer risk of 1 in 

100,000.

Of the 35 pesticide compounds detected, drinking-water 

standards or guidelines are available for 21 (table 8). A summary of concentrations and standards or guidelines is provided 

in table 3. 

Out of 531 samples analyzed for GC pesticide compounds, 

only 7 samples contained concentrations of at least one compound that exceeded its drinking-water standard or guideline 

(table 3). These samples were collected under base-flow conditions at synoptic sites during spring and late summer 2000.

Atrazine, simazine, and dieldrin were the only pesticide 

compounds for which at least one concentration exceeded the 

drinking-water standard or guideline (table 3). Dieldrin 

exceeded the guideline in five samples from the following sites: 

0146708450, Tacony Creek at Cheltenham, Pa.; 01475510, 

Darby Creek near Darby, Pa.; and 01475543, Cobbs Creek at 

East Lansdowne, Pa. Atrazine exceeded the standard in one 

sample from 01478200, Middle Branch White Clay Creek near 

Landenberg, Pa., and simazine exceeded the standard in one 

sample from site 01472100, Pigeon Creek near Parker Ford, Pa. 

0.0

0.5

1.0

1.5

CONCENTRATION, IN MICROGRAMS PER LITER

Uncensored concentration of metolachlor

Uncensored concentration of metolachlor ethane sulfonic acid

Uncensored concentration of metolachlor oxanilic acid

Nondetected concentration of metolachlor oxanilic acid

1999 2000

MAMJ J AS MAMJ J A ONDJ F

Figure 17. Concentrations of metolachlor and its degradation products at fixed site 01474500, 

Schuylkill River at Philadelphia, Pa., March 1999–August 2000.
32 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Table 8. Selected standards and guidelines for the protection of the health of humans and aquatic life from pesticide compounds in 

streamwater.

[μg/L, micrograms per liter; --, not available or applicable; MCL, maximum contaminant level; USEPA, U.S. Environmental Protection Agency; HAL, lifetime health advisory; RSD5, risk specific dose at 10-5 cancer risk; CAN, Canadian water-quality guideline for the protection of freshwater aquatic life; CANinterim, interim value for Canadian water-quality guideline for the protection of freshwater aquatic life; USEPA CCC, chronic water-quality criterion for protection of freshwater aquatic organisms; GRL, Great Lakes water-quality objective for protection of aquatic life; IJC, International Joint Commission United 

States and Canada; CCME, Canadian Council of Ministers of the Environment; HPLC, high performance liquid chromatography; GC, gas chromatography; 

ESA, ethane sulfonic acid; OA, oxanilic acid]

Pesticide 

compound

Selected standards and guidelines

Drinking water Aquatic life

Value, 

in μg/L Type Reference Value, in μg/L Type Reference

GC pesticide compounds

Acetochlor -- -- -- -- -- --

Alachlor 2 MCL USEPA (2002b) -- -- --

Atrazine 3 MCL USEPA (2002b) 1.8 CAN CCME (2002a,b)

Azinphos, methyl -- -- -- .01 USEPA CCC USEPA (2002c)

Benfluralin -- -- -- -- -- --

Carbaryl 700 HAL USEPA (2002b) .2 CAN CCME (2002a,b)

Carbofuran 40 MCL USEPA (2002b) 1.8 CAN CCME (2002a,b)

Chlorpyrifos 20 HAL USEPA (2002b) .041 USEPA CCC USEPA (2002c)

Cyanazine 1 HAL USEPA (2002b) 2 CAN - interim CCME (2002a,b)

Dacthal 70 HAL USEPA (2002b) -- -- --

p,p’-DDE 1 RSD5 USEPA (2003c) 1 .001

1

 Total DDT.

USEPA CCC USEPA (2002c)

Deethylatrazine -- -- -- -- -- --

Diazinon .6 HAL USEPA (2002b) .08 GRL IJC (1978)

Dieldrin .02 RSD5 USEPA (2002b) .056 USEPA CCC USEPA (2002c)

EPTC -- -- -- -- -- -

Lindane .2 MCL USEPA (2002b) .01 CAN CCME (2002a, b)

Linuron -- -- -- 7 CAN CCME (2002a, b)

Malathion 100 HAL USEPA (2002b) .1 USEPA CCC USEPA (2002c)

Metolachlor 100 HAL USEPA (2002b) 7.8 CAN-interim CCME (2002a, b)

Metribuzin 200 HAL USEPA (2002b) 1 CAN-interim CCME (2002a, b)

Napropamide -- -- -- -- -- --

Pendimethalin -- -- -- -- -- --

Prometon 100 HAL USEPA (2002b) -- -- --

Pronamide 50 HAL USEPA (2002b) -- -- --

Propachlor 90 HAL USEPA (2002b) -- -- --

Propanil -- -- -- -- -- --

Simazine 4 MCL USEPA (2002b) 10 CAN CCME (2002a, b)

Tebuthiuron 500 HAL USEPA (2002b) 1.6 CAN-interim CCME (2002a, b)

Terbacil 90 HAL USEPA (2002b) -- -- --

Trifluralin 5 HAL USEPA (2002b) .2 CAN CCME (2002a, b)

HPLC pesticide degradation products

Acetochlor ESA -- -- -- -- -- --

Acetochlor OA -- -- -- -- -- --

Alachlor ESA -- -- -- -- -- --

Metolachlor ESA -- -- -- -- -- --

Metolachlor OA -- -- -- -- -- --
Summary and Conclusions 33

Concentrations of atrazine, dieldrin, and simazine in other 

streams outside of the Delaware River Basin have exceeded 

drinking-water standards or guidelines. Out of 50 streams 

throughout the Nation, atrazine, dieldrin, and simazine 

exceeded standards or guidelines in samples from 16, 4, and 6 

streams, respectively (Larson and others, 1999). 

The comparison described here shows there is little hazard 

to humans through the consumption of streamwater with 

reported pesticide concentrations. The apparent hazard probably is less than that presented in this analysis because processes 

used to treat streamwater for drinking probably reduce the concentrations of pesticide compounds in drinking water. 

Other effects were not addressed by this analysis. These 

include (1) the effects of the 14 pesticide compounds without 

drinking-water standards or guidelines (tables 3 and 8), (2) the 

combined effects of more than one compound, and (3) the 

effects of compounds on the human endocrine system. The 

human endocrine system is a set of glands that produce hormones which help guide development, growth, reproduction, 

and behavior. A description of endocrine systems in animals, 

including humans, is given in Encyclopedia Britannica, Inc. 

(1997).

Aquatic Life

Effects of pesticide compounds on aquatic plants and animals living in the streams were assessed by comparing concentrations to guidelines for streamwater concentrations designed 

to protect aquatic life. Three types of guidelines to protect the 

plants and animals in streams were used in this analysis 

(table 8). If available, the chronic water-quality criterion (CCC) 

was used (U.S. Environmental Protection Agency, 2002b). The 

CCC is an estimate of the highest concentration of material in 

surface water to which an aquatic community can be exposed 

indefinitely without resulting in an unacceptable effect.

If no CCC was available, the Canadian water-quality 

guideline for the protection of freshwater aquatic life (CAN) 

was used (Canadian Council of Ministers of the Environment, 

2002a, 2002b) (table 8). Values of CAN, intended to protect all 

forms of aquatic life during all stages of the aquatic life cycle, 

are not to be exceeded at any time. Some values of CAN are 

interim and have had less rigorous data requirements than final 

values.

For diazinon, the value of the Great Lakes water-quality 

objective (International Joint Commission United States and 

Canada, 1978) was used in this analysis (table 8). This value 

represents the minimum level of water quality desired in the 

boundary waters of the Great Lakes System. Values for the 

chronic water-quality criteria or the Canadian water-quality 

guideline were not available for diazinon. 

A summary of pesticide concentrations and aquatic-life 

guidelines is presented in table 3. Guidelines were not available 

for 18 of the 35 detected pesticides and degradation products.

Of the 531 samples analyzed for GC pesticide compounds, 

29 samples contained concentrations of one or more compounds that clearly exceeded the aquatic-life guidelines 

(table 3). A least one concentration of the following pesticide 

compounds exceeded guidelines: diazinon (19 samples), carbaryl (7 samples), lindane (2 samples), atrazine (2 samples), and 

chlorpyrifos (1 sample). 

Concentrations of atrazine, chlorpyrifos, diazinon, and lindane reported in other streams throughout the Nation have 

exceeded aquatic-life guidelines (Larson and others, 1999). 

Guidelines for carbaryl were not part of the analysis by Larson 

and others.

Diazinon appears to be the pesticide most likely to have 

adversely affected aquatic life in the streams of the Delaware 

River Basin; diazinon exceeded the guideline in more samples 

(19) than did the other pesticide compounds (table 3). Of these 

19 samples, 15 were collected at the following three fixed sites: 

01464907, Neshaminy Creek at Valley Road near Neshaminy, 

Pa.; 01467150, Cooper River at Haddenfield, N.J.; and 

01477120, Raccoon Creek near Swedesboro, N.J.

Concentrations of p,p’-DDE and methyl azinphos also 

may have exceeded their guidelines in 30 and 6 samples, 

respectively, but the results of this analysis are less clear than 

for the other 5 pesticides discussed above. For p,p’-DDE and 

methyl azinphos, all concentrations and the guidelines were less 

than the maximum laboratory reporting level (table 3). As a 

result, there is greater uncertainty in the results for these two 

pesticides than in the results for the other pesticides that have 

guidelines and concentrations in streamwater greater than the 

laboratory reporting level. 

The following effects on aquatic life were not addressed by 

this analysis: (1) the effects of the 18 pesticide compounds for 

which there are no guidelines, (2) the additive (or synergistic) 

effects of more than one pesticide compound, (3) the seasonal 

variation in concentration, and (4) some types of effects, such 

as endocrine disruption. A recent study (Hayes and others, 

2002) reports that endocrine disruption in frogs occurred when 

they were exposed to water containing atrazine at concentrations less than the Canadian water-quality guideline of 1.8 μg/L.

Summary and Conclusions

During December 1998 to August 2001, 533 samples of 

streamwater were collected in the Delaware River Basin as part 

of the USGS National Water-Quality Assessment Program. 

Most samples were collected monthly at 10 fixed sites; additional samples were collected under base-flow conditions at 84 

sites during spring and late summer 1999, 2000, or 2001. Of 

these samples, 531 samples were analyzed for dissolved concentrations of 47 pesticide compounds (43 pesticides and 4 pesticide degradation products); 70 selected samples at two sites 

were analyzed for six additional pesticide degradation products. 

The most often detected compounds were atrazine 

(90.2 percent of samples), metolachlor (86.1 percent), deethylatrazine (82.5 percent), and simazine (78.9 percent). Atrazine, 

metolachlor, and simazine are pesticides; deethylatrazine is a 

degradation product of atrazine.
34 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Of the 6 pesticide degradation products analyzed for in 70 

samples at 2 sites, 5 were detected. The most often detected was 

metolachlor ESA, a degradation product of metolachlor 

(98.6 percent of samples).

Quality-assurance / quality-control samples provided 

information on the bias and variability of concentrations of pesticide compounds. Results of analysis of field blanks indicated 

that, with the exception of p,p’-DDE, concentrations of all pesticide compounds analyzed for probably were not biased as a 

result of sample contamination. An evaluation of concentrations of pesticide compounds in replicates and streamwater 

samples indicated that the variability of pesticide concentrations most often detected is small; the median difference 

between concentrations in streamwater samples and replicates 

was 4.5 percent.

The concentrations of atrazine, metolachlor, and pendimethalin appear to be attributable more to agricultural uses of 

these pesticides than to nonagricultural uses. Concentrations of 

these pesticides in selected samples from sites in the Piedmont 

and Valley and Ridge Provinces increased with an increase in 

either the percentage of subbasin composed of agricultural land 

or the estimated rate of application of these pesticides to agricultural land in the drainage basin. These samples were collected under base-flow conditions during May and June or 

August and September 2000. These three pesticides are those 

most heavily applied to agricultural land in the study area; all 

are applied to corn and (or) soybeans, major crops in the study 

area. 

Concentrations of prometon, diazinon, chlorpyrifos, 

tebuthiuron, trifluralin, and carbaryl in samples appear to be 

attributable more to nonagricultural uses of these pesticides 

than to agricultural uses. Concentrations of these pesticides in 

selected samples at sites in the Piedmont and Valley and Ridge 

Provinces increased with an increase in either the fraction of 

subbasin composed of urban land or the population density in 

the subbasin. These samples were collected under base-flow 

conditions either during May and June or August and September 2000. 

The relative importance of either agricultural uses or nonagricultural uses was not indicated by relations between concentrations and basin characteristics for simazine, alachlor, acetochlor, or cyanazine. Of these pesticides, simazine was one of 

the most often detected (78.9 percent of samples).

In general, pesticide concentrations during the growing 

season (April–October) were greater than those during the nongrowing season (November–March). This result was expected 

because pesticides generally are applied more often during the 

growing season. For atrazine, metolachlor, and acetochlor, the 

greatest concentrations generally occurred during May, June, 

and July. This pattern has been attributed to pesticides applied 

in the spring and carried to streams by rainwater runoff soon 

after application.

Metolachlor and diazinon were more likely than the other 

pesticides to show greater concentrations during stormflow than 

during periods of base flow. This conclusion is based on relations between pesticide concentrations and streamwater turbidity; the turbidity of streamwater during stormflow conditions 

generally is greater than the turbidity of streamwater under 

base-flow conditions. Concentrations of metolachlor and diazinon increased with increasing turbidity at 8 and 6 sites, respectively, of the 10 fixed sites sampled. 

Deethylatrazine was the pesticide degradation product 

most often detected (82.5 percent of samples) in samples collected at all sites. Concentrations of deethylatrazine increased 

with an increase in concentrations of atrazine, its parent pesticide. 

In samples collected at two sites, concentrations of the 

ethane sulfonic acid (ESA) or oxanilic acid (OA) degradation 

products of metolachlor and alachlor usually exceeded concentrations of the parent pesticides. For each of these two pesticides, concentrations of the ESA degradation product usually 

exceeded concentrations of the OA degradation product. 

A comparison of concentrations of pesticide compounds to 

drinking-water standards or guidelines indicate little hazard to 

humans through the consumption of streamwater with reported 

pesticide concentrations; concentrations of atrazine, dieldrin, or 

simazine exceeded standards or guidelines in only 7 of 531 samples. Not all adverse affects on human health were considered 

in this analysis, however. 

Diazinon appears to be the pesticide compound most likely 

to have adversely affected aquatic life in the streams of the Delaware River Basin; concentrations of diazinon exceeded the 

guideline (designed to protect aquatic life) in 19 samples, the 

most of any pesticide compound. Concentrations of as many as 

5 compounds exceeded guidelines in 29 of the 531 samples. Not 

all adverse effects of pesticides on aquatic life were considered 

in this analysis.

References Cited

Canadian Council of Ministers of the Environment, 2002a, 

Canadian water quality guidelines for the protection of 

aquatic life: Summary table. Updated, in Canadian environmental quality guidelines, 1999: Canadian Council of Ministers of the Environment, accessed August 5, 2003, at 

URL http://www.ccme.ca/assets/pdf/e5_002.pdf

Canadian Council of Ministers of the Environment, 2002b, 

Canadian Environmental Quality Guidelines, Summary 

Table, 2002: Canadian Council of Ministers of the Environment, accessed August 1, 2003, at URL http://www.ccme.ca/

assets/pdf/e1_06.pdf

Capel, P.D., Spexet, A.H., and Larson, S.J., 1999, Occurrence 

and behavior of the herbicide prometon in the hydrologic system: Environmental Science and Technology, v. 33, no. 5, 

p. 674–680.

DeLuca, M.J., Hoppe, H.L., Doyle, H.A., and Gray, B.J, 2002, 

Water resources data for New Jersey-water year 2001, 

volume 3. Water-quality data: U.S. Geological Survey 

Water-Data Report NJ-01-3, 580 p.
References Cited 35

DeLuca, M.J., Mattes, G.L., and Burns, H.L., 2001, Water 

resources data for New Jersey-water year 2000, volume 3. 

Water-quality data: U.S. Geological Survey Water-Data 

Report NJ-00-3, 618 p.

DeLuca, M.J., Romanok, K.M., Riskin, M.L., Mattis, G.L., 

Thomas, A.M., and Gray, B.J., 2000, Water resources data 

for New Jersey-water year 1999, volume 3. Water-quality 

data: U.S. Geological Survey Water-Data Report NJ-99-3, 

517 p.

Ebbert, J.C., and Embrey, S.S., 2002, Pesticides in surface 

water of the Yakima River Basin, Washington, 1999–2000, 

their occurrence and an assessment of factors affecting concentrations and loads: U.S. Geological Survey WaterResources Investigations Report 01-4211, 49 p.

Encyclopedia Britannica, Inc., 1997, Endocrine systems in The 

New Encyclopedia Britannica: Chicago, Encyclopedia Britannica, Inc., v. 18, p. 287–331.

Fischer, J.M., 1999, National Water-Quality Assessment Program, Delaware River Basin: U.S. Geological Survey Fact 

Sheet FS-056-99, 6 p. 

Fuhrer, G. J., and others, 1999, The quality of our Nation’s 

waters, nutrients and pesticides: U.S. Geological Survey 

Circular 1225, 82 p.

Gianessi, L.P, and Marcelli, M.B., 2000, Pesticide use in U.S. 

crop production, 1997, national summary report, November 

2000: Washington, D.C., National Center for Food and Agricultural Policy, sections 1.0–11.0. 

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design of 

the National Water-Quality Assessment Program: Occurrence and distribution of water-quality conditions: U.S. Geological Survey Circular 1112, 33 p.

Hayes, T.B., and others, 2002, Hermaphroditic demasculinized 

frogs after exposure to the herbicide atrazine at low ecologically relevant doses: Proceedings of the National Academy 

of Sciences of the United States, accessed on December 6, 

2002, at URL http://www.pnas.org/cgi/doi/10.1073/

pnas.082121499

Helsel, D.R., and Cohn, T.A., 1988, Estimation of descriptive 

statistics for multiply censored water quality data: Water 

Resources Research, v. 24, p. 1997–2004. 

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: Amsterdam, Elsevier Science Publishers 

B.V., Studies in Environmental Science, v. 49, 522 p. 

International Joint Commission United States and Canada, 

1978, Great Lakes Water Quality Agreement of 1978, as 

amended by Protocol signed November 18, 1987, Annex I, 

Specific objectives: International Joint Commission United 

States and Canada, accessed on August 5, 2003 at 

URL http://www.ijc.org/agree/quality.html#ann1

Kalkhoff, S.J., Kolpin, D.W., Thurman, E.M., Ferrer, I., and 

Barcelo, D., 1998, Degradation of chloroacetanilide herbicides—the prevalence of sulfonic and oxanilic acid metabolites in Iowa groundwaters and surface waters: Environmental Science & Technology, v. 32, no. 11, p. 1738–1740. 

Kalkhoff, S.J., Lee, K.E., Porter, S.D., Terrio, P.J., and Thurman, E.M., 2003, Herbicides and herbicide degradation products in upper Midwest agricultural streams during August 

base-flow conditions: Journal of Environmental Quality, 

v. 32, p. 1025–1035.

Larson, S.J, Gilliom, R.J, and Capel, P.D., 1999, Pesticides in 

streams of the United States, initial results from the National 

Water-Quality Assessment Program: U.S. Geological Survey 

Water-Resources Investigations Report 98-4222, 92 p.

Leahy, P.P., Rosenshein, J.S., and Knopman, D.S., 1990, 

Implementation plan for the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 

90-174, 10 p.

Lee, E.A., Kish, J.L., Zimmerman, L.R., and Thurman, E.M., 

2001, Methods of analysis by the U.S. Geological Survey 

Organic Geochemistry Research Group—Update and additions to the determination of chloroacetanilide herbicide degradation compounds in water using high-performance liquid 

chromatography/mass spectrometry: U.S. Geological Survey 

Open-File Report 01-10, 17 p.

Lindsey, B.D., Breen, K.J., Bilger, M.D., Brightbill, R.A., 

1998, Water quality in the Lower Susquehanna River Basin, 

Pennsylvania and Maryland, 1992–95: U.S. Geological 

Survey Circular 1168, 38 p. 

Martin, J.D., Gilliom, R.J., and Schertz, T.J., 1999, Summary 

and evaluation of pesticides in field blanks collected for the 

National Water-Quality Assessment Program, 1992-95: U.S. 

Geological Survey Open-File Report 98-412, 102 p. 

Martin, J.D., 2002, Variability of pesticide detections and concentrations in field replicate water samples collected for the 

National Water-Quality assessment Program, 1992–1997: 

U.S. Geological Survey Water-Resources Investigations 

Report 01-4178, 84 p.

Meister Publishing Company, 2000, Farm chemicals handbook 

2000: Willoughby, Ohio, Meister Publishing Company, 

v. 86, p. A1 to F24.

Mueller, D.K., Martin, J.D., and Lopes, T.J., 1997, Qualitycontrol design for surface-water sampling in the National 

Water-Quality Assessment Program: U.S. Geological Survey 

Open-File Report 97-223, 17 p.

Oblinger Childress, C.J., Foreman, W.T., Connor, B.F., and 

Maloney, T.J., 1999, New reporting procedures based on 

long-term method detection levels and some considerations 

for interpretations of water-quality data provided by the 

U.S. Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 99-193, 19 p.

Phillips, P.J., Wall, G.R., Thurman, E.M., Eckhardt, D.A., and 

Vanhoesen, J., 1999, Metolachlor and its metabolites, in tile 

drain and stream runoff in the Canajoharies Creek watershed: 

Environmental Science and Technology, v. 33, no. 20, 

p. 3531–3537. 

Reiser, R.G., and O’Brien, A.K., 1999, Pesticides in streams in 

New Jersey and Long Island, New York, and relation to land 

use: U.S. Geological Survey Water-Resources Investigations 

Report 98-4261, 12 p.
36 Pesticide Compounds in Streamwater in the Delaware River Basin, December 1998–August 2001

Sandstrom, M.W., 1995, Filtration of water-sediment samples 

for determination of organic compounds: U.S. Geological 

Survey Water-Resources Investigations Report 95-4105, 

13 p.

Shelton, L.R., 1994, Field guide for collecting and processing 

stream-water samples for the National Water-Quality 

Assessment Program: U.S. Geological Survey Open-File 

Report 94-455, 42 p.

Thelin, G.P., and Gianessi, L.P., 2000, Method for estimating 

pesticide use for county areas of the conterminous United 

States: U.S. Geological Survey Open-File Report 00-250, 

62 p.

U.S. Environmental Protection Agency, (undated), Cyanazine 

pesticide voluntarily canceled and uses phased out: Office of 

Pesticide Programs, International Pesticide Notice, accessed 

November 2, 2001 at URL http://www.epa.gov/oppfead1/

17b/cyanazin.htm

U.S. Environmental Protection Agency, 2003a, Acetochlor: 

Office of Pesticide Programs, accessed on September 25, 

2003, at URL http://www.epa.gov/oppefed1/aceto/index.htm

U.S. Environmental Protection Agency, 2003b, Carbaryl 

interim reregistration eligibility decision facts, accessed on 

September 25, 2003, at URL http://www.epa.gov/oppsrrd1/

REDs/factsheets/carbaryl_factsheet.pdf

U.S. Environmental Protection Agency, 2003c, Integrated Risk 

Information System (IRIS) database: U.S. Environmental 

Protection Agency, Office of Research and Development, 

National Center for Environmental Assessment, accessed on 

August 7, 2003, at URL http://www.epa.gov/iris

U.S. Environmental Protection Agency, 2002a, Overview of 

atrazine risk assessment, accessed September 25, 2003, at 

URL http://www.epa.gov/oppsrrd1/reregistration/atrazine/

srrd_overview_may02.pdf 

U.S. Environmental Protection Agency, 2002b, 2002 Edition of 

the Drinking Water Standards and Health Advisories: U.S. 

Environmental Protection Agency, Office of Water, EPA822-R-02-038, Summer 2002, accessed January 16, 2003, at 

URLs http://www.epa.gov/ost/drinking/standards/ and 

http://www.epa.gov/waterscience/drinking/standards/

dwstandards.pdf

U.S. Environmental Protection Agency, 2001, Diazinon revised 

risk assessment and agreement with registrants, accessed on 

September 25, 2003, at URL http://www.epa.gov/oppsrrd1/

op/diazinon/agreement.pdf 

U.S. Environmental Protection Agency, 2000, Chlorpyrifos 

revised risk assessment and risk mitigation measures: http://

www.epa.gov/pesticides/op/chlorpyrifos/consumerqs.htm

(accessed on September 25, 2003). 

U.S. Environmental Protection Agency, 1998, Reregistration 

eligibility decision facts, alachlor: EPA-738-F-98-018, 

accessed September 25, 2003, at URL http://www.epa.gov/

oppsrrd1/REDs/factsheets/0063fact.pdf 

U.S. Environmental Protection Agency, 1997, Reregistration 

eligibility decision facts, pendimethalin: EPA-738-F-97-007, 

9 p., accessed on September 25, 2003, at URL http://

www.epa.gov/oppsrrd1/REDs/factsheets/0187fact.pdf 

U.S. Environmental Protection Agency, 1996, Reregistration 

eligibility decision facts, trifluralin: EPA-738-F-95-007, 

accessed on September 25, 2003, at URL http://

www.epa.gov/oppsrrd1/REDs/factsheets/0179fact.pdf

U.S. Environmental Protection Agency, 1995, Reregistration 

eligibility decision facts, metolachlor: EPA-738-F-95-007, 

accessed on September 25, 2003, at URL http://

www.epa.gov/oppsrrd1/REDs/factsheets/0001fact.pdf 

U.S. Environmental Protection Agency, 1994, Reregistration 

eligibility decision facts, tebuthiuron: EPA-738-F-94-006, 

accessed on September 25, 2003, at URL http://

www.epa.gov/oppsrrd1/REDs/factsheets/0054fact.pdf 

Wall, G.R., Riva-Murray, K., and Phillips, P.J., 1998, Water 

quality in the Hudson River Basin, New York and adjacent 

states, 1992–95: U.S. Geological Survey Circular 1165, 32 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—determination 

of pesticides in water by C-18 solid-phase extraction and capillary-column gas chromatography/mass spectrometry with 

selected-ion monitoring: U.S. Geological Survey Open-File 

Report 95-181, 49 p.
For additional information write to:

District Chief

U.S. Geological Survey

New Jersey District

Mountain View Office Park

810 Bear Tavern Road

West Trenton, NJ 08628

or access the New Jersey District web site at: 

http://nj.usgs.gov