Minnesota National Lakes Assessment Project: 

Pesticides in Minnesota Lakes 

This report is part of a series based on Minnesota’s 

participation in U.S. Environmental Protection Agency’s 

2007 National Lake Assessment 

October 2008

MAU-08-102
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture ii

Minnesota Department of Agriculture 

625 Robert Street North 

Saint Paul, MN 55155-4194 

http://www.mda.state.mn.us/index.htm 

651-201-6000 or 800-967-2474

TTY: 1-800-627-3529 -800-627-3529 

651-201-

Authors and Contributors 

Minnesota Department of Agriculture 

Pesticide and Fertilizer Management Division 

Monitoring and Assessment Unit 

Bill VanRyswyk 

Hydrologist

David Tollefson 

Hydrologist

ACKNOWLEDGEMENTS 

NLAP study coordination: Steve Heiskary, Minnesota Pollution Control Agency (MPCA) & 

Michael Duval, Minnesota Department of Natural Resources (MDNR) 

MPCA (Environmental Analysis and Outcomes) sampling team leaders: Jesse Anderson, 

Steve Heiskary, Matt Lindon, and Kelly O’Hara (emphasis on water quality and sediment 

sample collection) 

MPCA student interns – David Tollefson and Monica Brooks 

MDNR sampling team: Paul Eiler, Mark Henry, Andy Levar, Dale Lockwood and Jason 

Neuman (emphasis on near-shore assessment, plant identification and benthic collection) – 

Lake IBI sampling: Bobbi Chapman, Paul Eiler (plus another staff member from NE), Chris 

Foster, Chris Gelner, Melissa Lasch, Ryan Lisson, Jason Neuman, Ryan Ransom, Nissa 

Rudh, and Kimberly Strand. 

U.S. Forest Service (sampling assistance in Superior National Forest): Jason Butcher, Brent 

Flatten, and Ken Gebhardt (coordination) 

Report Review: Ron Struss and Heather Johnson (MDA) & Steve Heiskary and Angela 

Preimesberger (MPCA) 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture iii

Table of Contents Page

Abstract 1

Introduction 1

Background 1

Previous Investigations 3

Methods 6

 Sampling Protocol 6

 Chemical Analysis 7

Results 9

 Detected compounds and frequency of detection 9

 Rivers and lakes compared 10

 Persistence in lakes 11

 Land use 12

Conclusions 14

References 15
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture iv

List of Tables Page

Table 1 Acetochlor Registration Partnership monitoring results in lakes/reservoirs. 5

Table 2. Base neutral target analyte list. 8

Table 3. Chloroacetanilide degradates target analyte list. 9

Table 4. Concentration of pesticides detected in the Minnesota portion of the 2007 

National Lakes Assessment Project. 

10

Table 5. Concentration of pesticide degradates detected in the Minnesota portion of

the 2007 National Lakes Assessment Project. 

10

Table 6. Land use characteristics of each dominant land use group for lakesheds in 

NLAP study. 

12

List of Figures Page

Figure 1. Total corn herbicide use estimates in Minnesota, 1990- 2005 (MDA and 

NASS data). 

2

Figure 2. Average monthly pesticide concentration in precipitation samples from 

1998 through 2005 collected in southeastern Minnesota (MDA data). 

4

Figure 3. Lakes sampled for pesticides as part of the 2007 Minnesota portion 

of the National Lakes Assessment Project. 

7

Figure 4. Median concentration of atrazine in NLAP lakes compared 

with median atrazine concentration in rivers sampled in 2007 by 

pesticide monitoring region. 

11

Figure 5. Pesticide concentrations of replicate sampling of South and 

Pebble Lakes.

12

Figure 6. Average total pesticide and average atrazine + degradate concentration 

determined by the dominant land use in each lakeshed. 

12
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 1

Abstract

In 2007 the Minnesota Department of Agriculture (MDA) cooperated with the Minnesota 

Pollution Control Agency (MPCA) in a statewide assessment of pesticides in Minnesota 

lakes as part of the National Lakes Assessment Program (NLAP) coordinated by United 

States Environmental Protection Agency (USEPA). Fifty-three lakes were randomly 

selected and sampled by MPCA and USEPA staff from throughout the state. Samples 

were analyzed by the MDA laboratory for 37 commonly used agricultural pesticides and 

their degradates. Pesticides and/or degradates were detected in 91 percent of the samples 

collected. The corn herbicide atrazine was the most frequently detected compound. All 

pesticide detections were well below established water quality standards or USEPA 

reference values. Pesticide detections were widespread, including many non-agricultural 

areas of the state. Atmospheric deposition of pesticides is suspected as the primary 

transport mechanism in non-agricultural areas. 

Keywords:

NLAP, Minnesota, Pesticides, Lakes, Atrazine, Degradates, Atmospheric Deposition 

Introduction

Minnesota is known as “The Land of 10,000 Lakes” and has a history and heritage linked 

to its abundant water resources. These valued natural resources are used and promoted 

by a vibrant tourism industry. Minnesota is also known as a major agricultural state, 

ranking fourth nationally in the production of corn and soybeans. Both water-based 

recreation and agriculture are key contributors to Minnesota’s economy. 

In recent years there has been an increase in corn acres planted in response to demand for 

corn-based ethanol (Hartwig, 2008). Along with this has come an associated increase in 

corn herbicide usage. In 2008, the first surface water impairment by a corn herbicide 

(acetochlor) in Minnesota was identified and placed on the 303(d) list of the state’s 

impaired waters maintained by the Minnesota Pollution Control Agency (MPCA). 

This study focused on the presence of pesticides, and their associated breakdown 

products, or degradates, in lakes across Minnesota. This survey of 53 randomly selected 

lakes was completed in conjunction with the United States Environmental Protection 

Agency’s (USEPA) National Lake Assessment Program (NLAP). The lakes were 

sampled by MPCA and USEPA staff during the summer of 2007. The Minnesota 

Department of Agriculture (MDA) provided laboratory analytical services and data 

analysis for the pesticide samples. 

Background 

The MDA has an extensive statewide water monitoring program designed to evaluate the 

impact of pesticides on surface and ground water throughout the state. The surface water 

portion of the program has historically focused on streams and rivers, specifically 

systems which drain agricultural areas of Minnesota. Streams and rivers have been the 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 2

focus of MDA pesticide monitoring efforts because they are generally regarded to be at 

greater risk than lakes from land-applied pesticides. Approximately 60 river and stream 

locations are sampled annually with varying levels of intensity. Lake pesticide sampling 

in Minnesota has been limited and is discussed in greater detail below. 

Corn herbicide use estimates in Minnesota from 1990 through 2005 are shown in Figure 

1. Figure 1 suggests an overall decline in pesticide usage on corn. With the increased 

use of the herbicide glyphosate on corn there has been a general decrease in use of 

historically popular corn herbicides such as atrazine and acetochlor. In addition to the 

general declining use of corn herbicides, there has been an expanded outreach and 

regulatory effort to educate Minnesota pesticide applicators on pesticide product label

requirements and voluntary Best Management Practices (BMPs) for water-quality 

protection.

Figure 1.Total corn herbicide use estimates in Minnesota, 1990-2005: Pounds of all 

herbicides and major active ingredients by year (MDA and United States 

Department of Agriculture - National Agriculture Statistics Service (USDA-NASS)).

Pounds of All Herbicides and Major Active Ingredients by Year

0

2

4

6

8

10

12

14

16

18

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2005

Pounds (millions)

All Corn

Herbicides 

Atrazine

Acetochlor

Alachlor

Metolachlor

s-Metolachlor

Glyphosate
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 3

Previous Investigations 

From 1992 through 1995 the MDA cooperated with the Minneapolis Park and Recreation 

Board, United States Geological Survey (USGS) and the Minnesota Grey Freshwater 

Institute in a study of Lake Harriet, an urban lake located in Minneapolis, Minnesota.

The purpose of the study was to evaluate the presence of 26 commonly used urban and 

agricultural pesticides in the watershed. The study found that between 25 percent and 91 

percent of lake samples collected from the epilimnion (upper 4 meters) contained 

detectable levels of atrazine (0.10 – 0.40 ug/L). Atrazine detections in samples collected 

from the hypolimnion were similar, ranging from 29 percent to 92 percent with 

concentrations ranging from 0.10 to 0.40 ug/L. During this period (1992 – 1995) no 

other agricultural, base-neutral pesticides were detected in Lake Harriet, however, several 

were detected in storm water runoff within the watershed. Rainfall analysis over the 

same period was conducted in the watershed and found alachlor, atrazine, cyanazine, and 

metolachlor present in 54 percent, 71 percent, 42 percent, and 46 percent of the samples 

respectively. Atmospheric deposition was identified as the primary source of agricultural 

pesticides in the urban area evaluated (Wotzka, 1998). 

In a related study, the MDA cooperated with the USGS in evaluating wet atmospheric 

deposition of pesticides in Minnesota between 1989 and 1994 (Capel, 1994). More than 

350 precipitation samples were collected at several sites across Minnesota during the 

study and all samples had detectable quantities of at least one pesticide. The most 

frequently detected compounds were alachlor, atrazine, cyanazine and metolachlor, all 

corn herbicides. Acetochlor was detected in precipitation in 1994, the first year of 

registration for use in Minnesota. Concentrations peaked following periods when the 

pesticides were applied and were highest in agricultural areas. 

Figure 2 contains precipitation monitoring data collected by MDA from 1998 through 

2005 in an agricultural area of southeastern Minnesota. The average monthly 

concentration for the four most frequently detected pesticides is presented. The figure 

shows strong seasonality in the relative concentration of these pesticides. This seasonal 

pattern corresponds to the herbicide’s primary application periods in Minnesota. 

These values are generally consistent with the findings of a USGS study that examined 

the atmospheric transport and deposition of commonly used herbicides in the “Corn Belt” 

of the United States (Starner, 1998). According to their report: 

“Herbicides can be transported into the atmosphere by volatilization and 

entrainment on dust particles and then dispersed by air currents for possible

re-deposition on watersheds at considerable distances from their application.” 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 4

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

April

May

June

July

August

September

October

November

(ug/L)

Acetochlor

Alachlor

Atrazine

Metolachlor

Figure 2. Average monthly pesticide concentration in precipitation samples 

collected from 1998 through 2005 in southeastern Minnesota (MDA data). 

The USGS study analyzed 6,230 rainfall samples collected from sites located throughout 

the Midwest and Northeast United States. Immunoassay results of 5,927 samples found 

that 30.1 percent of samples had triazines and/or acetanilides present. Atrazine was 

present in 30.2 percent and alachlor was present in 19.2 percent of the samples (n=2,085 

samples) screened by immunoassay and analyzed by gas chromatography/mass 

spectrometry (GC/MS) methods. These two compounds were detected most frequently. 

The concentrations of each pesticide measured in rainfall varied with climatic variability, 

but ultimately increased during periods of pesticide applications and were greatest in rain 

that fell during periods of low rainfall. Overall, rainfall-weighted average concentrations 

during the application period of mid-April through mid-July yielded concentrations of 

both atrazine and alachlor in rainfall of 0.2 to 0.4 ug/L. Higher concentrations of atrazine 

and alachlor were reported in areas of higher use (Iowa, Illinois, and Indiana) indicating a 

decrease in the amount of pesticides in the atmosphere as the distance from the source is 

increased (Starner, 1998). 

A 2000 study was conducted by the University of Maryland and USDA in the 

Chesapeake Bay area to examine atmospheric deposition of pesticides into the Choptank 

River. The study concluded that 3 percent to 20 percent of metolachor in the Choptank 

River was deposited via wet atmospheric deposition. In addition to metolachor, pesticide 

compounds including chlorothalonil, atrazine, simazine, endosulfan, and chlorpyrifos 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 5

were detected in both dry and wet deposition. The concentration of these chemicals, and 

their usage in the local area of this study, predicts atmospheric deposition is a significant 

source of agricultural pesticides in surface waters (Kuang, 2003). 

One of the largest studies of pesticides in lakes of the Corn Belt region of the United 

States was conducted by the Acetochlor Registration Partnership (ARP). In 1995 the 

ARP implemented a multi-year, multi-analyte monitoring program to satisfy the 

conditions of the USEPA registration of acetochlor. The ARP study sampled surface 

water bodies used as drinking water sources throughout the Midwest and included lakes 

and reservoirs in Illinois, Indiana, Iowa, Kansas, Nebraska, Missouri, Ohio, and 

Wisconsin. Table 1 is based on all 31 ARP sites that had raw (pre-treatment) water 

samples and were categorized as either lakes or reservoirs. Watershed sizes for these 31 

sites varied from 208 acres to more than 28 million acres. Land cover in these 

watersheds varied from 13 percent to 45 percent corn production (Acetochlor 

Registration Partnership, 2008). 

There are seven years of monitoring data available for the three parent compounds of 

acetochlor, atrazine and metolachlor (1995-2001). There are three years of monitoring 

data available for their degradates (1999-2001). Fourteen samples were collected each 

year, biweekly through the spring and summer months, and quarterly during the fall and 

winter. Results indicate that detection frequencies for these compounds ranged from 100 

percent for atrazine to 21 percent for acetochlor (Table 1). 

Table 1. Acetochlor Registration Partnership (ARP) monitoring results in lakes/reservoirs 

(raw water only, N=31 sites, 14 samples per year).

Analyte (years monitored) Limit of Detection (ug/L) Detection Frequency

Acetochlor (1995-2001) 0.03 21%

Atrazine (1995-2001) 0.03 100%

Metolachlor (1995-2001) 0.03 61%

Acetochlor-ESA (1999-2001) 0.2 32%

Acetochlor-OXA (1999-2001) 0.1 58%

Metolachlor-ESA (1999-2001) 0.2 70%

Metolachlor-OXA (1999-2001) 0.1 77%

In 2005 the Wisconsin Department of Agriculture, Trade and Consumer Protection 

completed a survey of atrazine in 53 lakes in agricultural areas of Wisconsin using 

immunoassay methods. Atrazine was detected in more than 90 percent of the lakes with 

concentrations ranging from non-detect (0.10 ug/L) to 0.40 ug/L. Concentrations were 

greater where agriculture represented greater than 75 percent of the surrounding land use 

(Allen, 2006). 

Methods

A total of 53 Minnesota lakes were sampled for pesticides. Of these 53 lakes, 41 were 

originally selected by the USEPA to be part of the National Lakes Assessment Program. 

An additional nine lakes were added by the MPCA to make it feasible to statistically 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 6

assess lakes statewide. Additional lakes were added by the USEPA as reference lakes. 

These lakes provided a greater basis for comparing lakes statewide, and nationally 

(Lindon, 2008). Two of the 53 lakes, South and Pebble, were sampled twice 

approximately one month apart. 

Figure 3 shows the lakes and their location within the MDA Pesticide Monitoring 

Regions (PMRs). The PMRs were developed to allow monitoring data to be compared 

for areas of similar agriculture, hydrology, geology, and soils. Although lake locations 

relative to PMRs were not part of the selection criteria, at least one lake was sampled in 

nine of the ten PMRs, as shown in Figure 3. No lakes from PMR 9 were sampled. This 

region is known as the “Driftless Area” because it was missed in the last glacial advance 

across Minnesota. PMR 9 generally represents a more mature geologic landscape with 

karst terrain where lakes are notably absent. 

Sampling Protocol 

Pesticide samples were collected at all of the lakes chosen for the NLAP study. A 

surface grab sample was taken from the pelagic (index) site of the lake. The pesticide 

samples were collected early in the sampling routine and taken off the bow of the boat 

facing upwind to minimize the possible contamination from equipment and samplers. 

The samples were chilled on the boat, transported on ice for the duration of the sampling 

trip, and refrigerated upon return. Samples had a 10-day holding time with 52 of 53 

samples analyzed within the holding time. The samples were transferred by MPCA staff 

to the MDA laboratory for analysis. 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 7

Figure 3. Lakes sampled for pesticides as part of the 2007 Minnesota portion of the 

National Lakes Assessment Project in cooperation with the MPCA and EPA. Map 

also presents the MDA Pesticide Management Regions (PMRs). 

Chemical Analysis 

All analyses of the pesticide samples were conducted at the MDA laboratory in St. Paul, 

Minnesota. Base neutral (BN) pesticide samples were prepared using automated solid 

phase extraction methods and analyzed with gas chromatography/mass spectrometry 

(GC/MS) with large volume injection. The chloroacetanilide degradate (CHL) samples 

were prepared using automated solid phase extraction methods and analyzed with liquid 

chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 8

Lake samples were analyzed for the standard BN target analyte pesticide list used for 

surface and groundwater sampling by the MDA. The BN list given in Table 2 includes 

many of the commonly used agricultural pesticides and their degradates. It does not 

include glyphosate which requires a different analytical method. In addition to the BN 

list, all samples were also analyzed for the chloroacetanilide degradates listed in Table 3. 

The method reporting limit (MRL) is the lowest concentration a given analytical method 

can reliably measure. 

Table 2. Base neutral target analyte list. 

Common Name Common Brand Name Type MRL 

(ug/L)

Acetochlor Harness, Surpass Herbicide 0.05 

Alachlor Bronco, Lasso Herbicide 0.05

Atrazine Aatrex, Atrazine Herbicide 0.05 

Boscalid Pristine Fungicide 0.30 

Chlorpyrifos Lorsban Insecticide 0.10 

Cyanazine Bladex Herbicide 0.20 

Deethyl atrazine Atrazine degradate Degradate 0.05 

Deisopropylatrazine Atrazine degradate Degradate 0.20 

Diazinon Diazinon Insecticide 0.12 

Dimethenamid Frontier, Outlook Herbicide 0.05 

Dimethoate Cygon Insecticide 0.22 

EPTC Eradicane Herbicide 0.23

Fonofos Dyfonate Insecticide 0.10 

Malathion Malathion 50 Insecticide 0.09 

Metolachlor Bicep, Dual Herbicide 0.07 

Metribuzin Boundry, Sencor Herbicide 0.10 

Metribuzin DA Metribuzin degradate Degradate 1.00 

Metribuzin DADK Metribuzin degradate Degradate 1.00 

Metribuzin DK Metribuzin degradate Degradate 1.00 

Methyl Parathion Penncap-M Insecticide 0.12 

Myclobutanil Laredo Fungicide 0.20 

Pendimethalin Prowl Herbicide 0.08 

Phorate Thimet Insecticide 0.12

Propiconazole Tilt Fungicide 0.20 

Tebucanazole Elite Fungicide 0.20 

Tebuprimiphos Aztec Fungicide 0.10 

Terbufos Counter Insecticide 0.19 

Tetraconazole Domark Fungicide 0.15 

Trifluralin Treflan Herbicide 0.17 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 9

Table 3. Chloroacetanilide degradates target analyte list. 

Compound Common Brand Name Type MRL 

(ug/L)

Acetochlor ESA Acetochlor degradate Degradate 0.07 

Acetochlor OXA Acetochlor degradate Degradate 0.07 

Alachlor ESA Alachlor degradate Degradate 0.07 

Alachlor OXA Alachlor degradate Degradate 0.07 

Dimethenamid ESA Dimethenamid degradate Degradate 0.07 

Dimethenamid OXA Dimethenamid degradate Degradate 0.07 

Metolachlor ESA Metolachlor degradate Degradate 0.07 

Metolachlor OXA Metolachlor degradate Degradate 0.07 

Results

Detected compounds and frequency of detection 

A total of four parent pesticide compounds were found in Minnesota lakes. Table 4 

indicates that the corn herbicides acetochlor, atrazine, dimethanamid and metolachlor 

were all detected at least once in the 53 lakes samples. 

Atrazine was detected at a much higher frequency (87 percent) and concentration as 

compared to the other compounds. Acetochlor, dimethanamid, and metolachlor had 

median concentrations that were at the non-detect level and maximum concentrations that 

were at or very near the method reporting limits (MRLs) identified in Table 2. The “P” 

in Tables 4 and 5 indicate the compounds were quantified as “present” by the laboratory 

but at insufficient levels to positively quantify. For statistical purposes, samples 

identified as “present” by the lab are assigned concentration of one half the MRL given in 

Table 2. 

The maximum concentration of atrazine detected (0.68 ug/L) was well below the chronic 

atrazine water quality standard for Minnesota waters of 10 ug/L. Detections of 

acetochlor and metolachlor were at or below their MRL (acetochlor 0.05 ug/L and 

metolachlor 0.07 ug/L) and were well below their respective water quality standards of 

3.6 ug/L for acetochlor and 23 ug/L for metolachlor. 

With the exception of atrazine, degradates were more frequently detected than were 

parent compounds (Table 5). This suggests that parent compounds were likely present in 

more of the lakes and had degraded prior to sampling. It is also possible that some of the 

degradates were transported to the lakes via runoff, groundwater or atmospheric 

deposition. The timing of the lake sampling (July-August) was completed well after the 

peak pesticide application period of late spring to early summer. This may have allowed 

for degradation of parent compounds applied in 2007 to be transported to lakes.

When compared with the results of the ARP study presented in Table 1, the detection 

frequencies in this study for acetochlor (2 percent vs. 21 percent) and metolachlor (4 

percent vs. 61 percent) are much lower. Atrazine detection frequency is also slightly 

lower (87 percent vs. 100 percent). Possible explanations for these differences include 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 10

the greater sampling frequency and the timing of the sampling in the ARP study as well 

as the fact that the ARP study targeted lakes and reservoirs in agricultural areas. It is also 

possible that concentration in lakes decreased due to lower application rates or other 

factors since the ARP study was conducted (1995-2001). 

The degradate detected at the greatest frequency was deethyl atrazine (Table 5) a 

breakdown product of atrazine. Other pesticide degradates were found less frequently 

but at higher concentrations. Currently there are no state or federal standards for 

pesticide degradates in surface waters; however, USEPA has available toxicity data and 

risk assessments for atrazine and other pesticide degradates that found water 

concentrations at or below reference values for the parent compound would be protective 

for human health (USEPA 2006a & 2006b). 

Table 4. Concentration of pesticides detected in the Minnesota portion of the 2007 

National Lakes Assessment Project. 

Acetochlor Atrazine Dimethenamid Metolachlor 

Median

(ug/L) nd* P** nd nd 

Maximum 

(ug/L) P 0.68 P P 

Detection

Frequency 2% 87% 4% 4% 

*nd indicates non-detect or the median concentrations were below the method reporting limit. 

** P indicates the compound was present but at a concentration below the method reporting limit 

(MRL) presented in table 3. 

Table 5. Concentration of pesticide degradates detected in the Minnesota portion of 

the 2007 National Lakes Assessment Project. 

Acetochlor

ESA

Acetochlor

OXA 

Alachlor

ESA

Deisopropyl

atrazine 

Desethly

atrazine 

Metolachlor 

ESA

Metolachlor 

OXA 

Median 

(ug/L) nd nd nd nd P nd nd 

Maximum 

(ug/L) 0.71 1.02 0.22 P 0.18 0.88 0.28 

Detection 

Frequency 16% 18% 16% 2% 64% 27% 7% 

Rivers and Lakes Compared 

The median concentration of atrazine, the most commonly found agricultural pesticide in 

the waters of Minnesota, was compared in lakes and rivers in the 10 Pesticide Monitoring 

Regions (PMRs). The concentration of atrazine in the monitored rivers generally tends to 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 11

be higher than the concentrations detected in lakes of the same PMR (Figure 4). PMRs 4 

and 8 had the largest comparable sample data sets and in both instances indicate higher 

median atrazine concentrations in the rivers.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

PMR 1 PMR 2 PMR 3 PMR 4 PMR 5 PMR 6 PMR 7 PMR 8 PMR 9 PMR 10

Concentration (ug/L)

Rivers Median

Lakes Median

28 3 10 0 4 0 29 1 61 22 16 1 12 1 21 63 8 03 45

number of 

samples

Figure 4. Median concentration of atrazine in NLAP lakes compared with median 

atrazine concentration in rivers sampled in 2007 by pesticide monitoring region. 

Persistence in Lakes 

The stability or persistence of pesticide parent compounds once they enter a lake system 

is not well understood. It is influenced by the conditions of the aquatic environment 

primarily temperature and sunlight, as well as the presence of microorganisms. Figure 5 

offers an insight into the persistence question by comparing samples collected from two 

lakes (South and Pebble) that were sampled twice as NLAP replicate visits. The two 

samples collected from Pebble Lake had identical concentrations of atrazine and 

deethylatrazine although they were collected on July 25th and August 22nd. These results 

suggest apparent stability of concentration over the course of approximately one month. 

The two samples from South Lake also had similar results for over the course of 

approximately one month with the same concentration of atrazine in both samples and 

similar, though slightly lower concentrations of acetochlor degradates were present in the 

second sample. Notably absent in South Lake is deethyl atrazine in both samples and 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 12

alachlor ESA in the second sample. Additional information including seasonal sampling 

would be required to provide further evaluation on the persistence of pesticides in lakes. 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

South Lake (7/23) South Lake (8/21) Pebble Lake (7/25) Pebble Lake (8/22)

Concentration [ug/L]

Acetochlor ESA

Acetochlor OXA

Alachlor ESA

Atrazine

Deethyl atrazine

Figure 5. Pesticide concentrations of replicate sampling of South and Pebble Lakes.

Land Use

An interesting characteristic of the data collected in this study is the presence of atrazine 

in lakes that are located long distances (greater then 100 miles) from areas of intensive 

row crop agricultural activity. Previous studies (Capel, 1997, Starner, 1998 and Goolsby, 

1993) have indicated that pesticides can be transported in the atmosphere long distances. 

Capel also suggested that there are local and regional influences on pesticide 

concentrations in precipitation. 

In an effort to evaluate the effects of local land use, agricultural pesticide concentrations 

were compared between lakes with similar lakeshed land use characteristics. The lakes 

were placed into land use groups that are categorized by their dominate land use: urban, 

forest/water, or cultivated agriculture. The breakdown in average land use within these 

three main groups is presented in Table 6. 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 13

Table 6. Land use percentage of each dominant land use groups for the lakesheds in 

NLAP study. 

Total pesticide concentrations were summarized for the detected parent and degradate 

compounds and then placed into the dominant land use group of the lakeshed from which 

they were collected. Figure 6 presents the average total pesticide and average atrazine 

concentration values for each dominant land use groups. 

0.59

0.08 0.08

0.11

0.08

0.05

0.00

0.10

0.20

0.30

0.40

0.50

0.60

Cultivated Agriculture (n = 22) Urban (n = 2) Forest and Water (n = 25)

Land Use Group

Concentration (ug/L)

Total Pesticides

Atrazine + Atrazine Degs

Figure 6. Average total pesticide (parent + degradate) and average atrazine 

concentration determined by the dominant land use in each lakeshed.

Agricultural 

Lakesheds

Forest and Water 

Lakesheds

Urban

Lakesheds

Mean Range Mean Range Mean Range 

Developed (%) 8 3-14 4 0-13 72 61-87 

Cultivated Agriculture (%) 56 32-86 7 0-33 3 2-3 

Pasture and Open (%) 5 0-23 1 0-8 2 1-2 

Forest (%) 12 2-28 54 12-84 11 3-18 

Water and Wetland (%) 19 5-33 33 14-61 12 5-18 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 14

Lakes within lakesheds dominated by cultivated agriculture had substantially higher total 

pesticide concentrations than lakes within lakesheds dominated by urban and forest/water 

land use. This is generally consistent with the findings of a Wisconsin lake study that 

found increased concentrations of atrazine in lakes with greater than 75 percent row crop 

agricultural in the lakeshed (Allen, 2006).

Urban and forest/water dominated lakesheds had very similar concentrations of total 

pesticides. It is possible that the concentration averages presented for urban and 

forest/water land use groups are indicative of concentrations that might be expected as a 

result of atmospheric transport and deposition (Figure 6). 

Conclusions

Atrazine was detected in 87 percent of the 53 sampled lakes in Minnesota 

including lakes far from areas of assumed atrazine application. 

A pesticide or a pesticide degradate was detected in 91 percent of the samples 

collected from Minnesota lakes. 

In general, the ranges of concentrations detected as well as the frequency of 

detection were similar or lower when compared with other studies of lakes and 

reservoirs in the Midwest. 

Concentrations of all detected pesticides were well below the Minnesota aquatic 

life standards and other reference values used by the Minnesota Department of 

Agriculture.

The concentration of atrazine was higher in samples collected from rivers then 

those measured in lakes located in the same Pesticide Monitoring Region (PMR). 

Lakes in lakesheds with row crop agriculture as a dominant land use had higher 

concentrations of total pesticides. This may be the result of direct runoff from 

adjacent lands or from greater atmospheric deposition due to closer proximity to 

areas of application.

Atmospheric deposition is suspected as the primary method of transport in lakes 

where pesticides, primarily atrazine, are detected far from areas of application. 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 15

References: 

2007 Water Quality Monitoring Report. Rep.No. Monitoring and Assessment Unit, 

Minnesota Department of Agriculture. St. Paul, MN, 2008. 

Monitoring and Assessment for Agricultural Chemicals in the Environment. Aug. 2008. 

Minnesota Department of Agriculture. 2 Sept. 2008 

<http://www.mda.state.mn.us/news/publications/chemfert/2007watqualmonrpt.pdf>. 

Acetochlor Registration Partnership (ARP) Data. Gustafson, David I.. 23 Sept. 2008. 

<http://www.arpinfo.com>.

Allen, Paula. "Volunteer Monitoring of Atrazine in Wisconsin Lakes." Lake Tides. Vol. 

31. 2006. 12. Wisconsin Lakes Partnership. 23 Sept. 2008 

<www.uwsp.edu/cnr/uwexlakes>.

Capel, Paul D., Ma Lin, and Paul J. Wotzka. Wet Atmospheric Deposition of Pesticides 

in Minnesota, 1989-94. Rep.No. 97-4026. Water Resources Investigation Report. U.S. 

Geological Survery. USGS Water Science Center, Minnesota. 29 July 2008 

<http://mn.water.usgs.gov/pubs/atmospheric/atmospheric.html>.l, . "Wet Atmospheric 

Deposition of Pesticides in Minnesota. pt. 2008

Goolsby, D.A., Thurman, E.M., Pomes, M.L., and Battaglin, W.A., 1993, Occurrence, 

deposition, and long range transport of herbicides in precipitation in the midwestern and 

northeastern United States, in Selected Papers on Agricultural Chemicals in Water 

Resources of the Midcontinental United States: U.S. Geological Survey Open-File Report 

93-418, p. 75-89.

Hartwig, Douglas A., and Don Lofthus, comps. Minnesota Agriculture Statistics 2008. St. 

Paul, Minnesota. Minnesota Agriculture Statistics 2008. USDA-National Agriculture 

Statistics Service. 6 Oct. 2008 

<http://www.nass.usda.gov/statistics_by_state/minnesota/publications/annual_statistical_

bulletin/agstatbk2008/agstat08.htm>. 

Kuang, Zhihua, Laura L. McConnell, Alba Torrents, Donald Meritt, and Stephanie 

Tobash. "Atmospheric Deposition of Pesticides to an Agricultural Watershed." Journal of 

Environmental Quality 32 (2003): 1611-622. 

Lindon, Matt, and Steve Heiskary. Minnesota National Lakes Assessment Program: 

Microcystin Concentrations in Minnesota Lakes. St. Paul: Minnesota Pollution Control 

Agency, 2008. 23 July 2008 <http://www.pca.state.mn.us/publications/wq-nlap1-00.pdf>. 

"Minnesota's Impaired Waters and TMDLs." Minnesota Pollution Control Agency. 14 

July 2008. 6 Oct. 2008 <http://www.pca.state.mn.us/water/tmdl/tmdl-303dlist.html>. 
______________________________________________________________________________________ 

Pesticides in MN Lakes 10/2008 Minnesota Department of Agriculture 16

Scribner, E.A., Thurman, E.M., Goolsby, D.A., Meyer, M.T., Battaglin, W.A., and 

Kolpin, D.W., 2005, Summary of significant results from studies of triazine herbicides 

and their degradation products in surface water, ground water, and precipitation in the 

Midwestern United States during the 1990s: U.S. Geological Survey Scientific 

Investigations Report 2005–5094, 27 p. 

Starner, John K., Donald A. Goolsby, and E. T. Thurman. Herbicides in Rainfall Across 

the Midwestern and Northeastern United States, 1990-91. Issue brief No. 181-97. U.S. 

Department of the Interior, U.S. Geological Survey. 1998. U.S. Geological Survery. June 

1998. 25 Sept. 2008 <http://ks.water.usgs.gov/pubs/fact-sheets/fs.181-97.html#hdr0>. 

USEPA. 2006a. Report of the Food Quality Protection Act (FQPA) Tolerance 

Reassessment Program and Risk Management Decision (TRED) for acetochlor. Office of 

Pesticide Programs. March 2006. 

<http://www.epa.gov/oppsrrd1/reregistration/REDs/acetochlor_tred.pdf> 

USEPA. 2006b. Decision Documents for Atrazine. April 6, 2006. Office of Pesticide 

Programs. 

<http://www.epa.gov/oppsrrd1/REDs/atrazine_combined_docs.pdf> 

USEPA. 2007. Survey of the Nation's Lakes. Field Operations Manual. EPA 841-B-07-

004. U.S. Environmental Protection Agency, Washington, DC. 

Wotzka, P.J., Capel, P.D., Ma, L., and Lee, J.T., 1998. Pesticide Transport and Cycling 

in the Lake Harriet Watershed, Minneapolis, Minnesota. Special Session Proceedings of 

the Sixteenth Annual North American Lake Management Society International 

Symposium.