Kathleen Hall, Ph.D., Minnesota Department of Agriculture, Research scientist, reviewed by Tana Haugen-Brown, UMN Pesticide Safety and Environmental Education Extension educator, Sally Raymond, UMN Pesticide Safety and Environmental Education Extension educator, and Jolene Warnke, UMN Pesticide Safety and Environmental Education Extension educator
Monitoring is crucial for assessing and protecting water quality. Each year starting in May, Minnesota Department of Agriculture (MDA) staff and their collaborators head out to rivers and streams across the state to begin collecting water samples. These samples are then sent to the MDA's lab, where analysts test the water for 185 pesticide chemicals, including a variety of herbicides, fungicides, and insecticides, as well as their breakdown products (also known as degradates). The results from these monitoring efforts provide valuable information that the MDA uses to evaluate the impacts of routine pesticide use on Minnesota's water resources, including impacts on aquatic life, and help guide pesticide management decisions.
In 2024, the MDA collected more than 1,000 samples from 56 rivers and streams across Minnesota (Figure 1). Results from the 2024 monitoring season were recently published in the MDA's 2024 Water Quality Monitoring Report. The MDA is also working to incorporate the 2024 data into its new interactive monitoring maps (Pesticide Water Quality Monitoring StoryMaps).
Monitoring is crucial for assessing and protecting water quality. Each year starting in May, Minnesota Department of Agriculture (MDA) staff and their collaborators head out to rivers and streams across the state to begin collecting water samples. These samples are then sent to the MDA's lab, where analysts test the water for 185 pesticide chemicals, including a variety of herbicides, fungicides, and insecticides, as well as their breakdown products (also known as degradates). The results from these monitoring efforts provide valuable information that the MDA uses to evaluate the impacts of routine pesticide use on Minnesota's water resources, including impacts on aquatic life, and help guide pesticide management decisions.
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| Figure 1. MDA river and stream pesticide monitoring sites in Minnesota, 2024. |
In 2024, the MDA collected more than 1,000 samples from 56 rivers and streams across Minnesota (Figure 1). Results from the 2024 monitoring season were recently published in the MDA's 2024 Water Quality Monitoring Report. The MDA is also working to incorporate the 2024 data into its new interactive monitoring maps (Pesticide Water Quality Monitoring StoryMaps).
Overview of 2024 results
In 2024, 81 of the 185 pesticide chemicals analyzed were detected in at least one sample. The most frequently detected chemicals were hydroxyatrazine (a degradate of the herbicide atrazine [Aatrex, Acuron, Callisto Xtra]1), the herbicide metolachlor (Matador, Dual II Magnum) and its degradates (metolachlor OXA and metolachlor ESA), and the herbicide 2,4-D (Enlist One, Enlist Duo, Unison) (Table 1). While multiple pesticides are detected in rivers and streams in Minnesota, the majority of detections are below levels of concern for aquatic life.
Table 1. Pesticide chemicals detected most frequently by the MDA in rivers and streams in 2024. Between 385 and 608 samples were analyzed for each chemical. See the Water Quality Monitoring Report for method reporting limits and additional details.
When a chemical is detected, it is important to consider the level or concentration that is present in the sample. The MDA Lab can detect chemicals at very low concentrations in water, but a detection alone does not necessarily indicate a risk to human health or the environment. To evaluate concentration data and identify potential risks, the MDA compares detected concentrations to “reference values.” Reference values can be water quality standards, benchmarks, or other guidance values established by state and/or federal agencies. For surface water, the MDA typically uses reference values that are based on toxicity to aquatic life.
In 2024, eight pesticides were detected above their applicable reference values in rivers and streams. Two neonicotinoid insecticides, clothianidin and imidacloprid, were responsible for 90% of the detections over a reference value (232 out of 258 detections). The other pesticides detected above reference values were acetochlor (13 samples), pyroxasulfone (5 samples), bifenthrin (2 samples), tebupirimfos (1 sample), atrazine (2 samples), and chlorpyrifos (3 samples).
Watch for Part 2, with details on pesticide monitoring in Minnesota’s groundwater, next week!
1 Use of trade names is for educational purposes only. No endorsement is implied and no discrimination is intended.
Table 1. Pesticide chemicals detected most frequently by the MDA in rivers and streams in 2024. Between 385 and 608 samples were analyzed for each chemical. See the Water Quality Monitoring Report for method reporting limits and additional details.
| Chemical | Detection frequency percent (%) |
|---|---|
| Hydroxyatrazine | 95 |
| Metolachlor OXA | 92 |
| Metolachlor ESA | 91 |
| 2,4-D | 88 |
| Metolachlor | 83 |
| Clothianidin | 80 |
| Acetochlor ESA | 79 |
| Atrazine | 78 |
| Acetochlor OXA | 74 |
| Dimethenamid ESA | 74 |
When a chemical is detected, it is important to consider the level or concentration that is present in the sample. The MDA Lab can detect chemicals at very low concentrations in water, but a detection alone does not necessarily indicate a risk to human health or the environment. To evaluate concentration data and identify potential risks, the MDA compares detected concentrations to “reference values.” Reference values can be water quality standards, benchmarks, or other guidance values established by state and/or federal agencies. For surface water, the MDA typically uses reference values that are based on toxicity to aquatic life.
In 2024, eight pesticides were detected above their applicable reference values in rivers and streams. Two neonicotinoid insecticides, clothianidin and imidacloprid, were responsible for 90% of the detections over a reference value (232 out of 258 detections). The other pesticides detected above reference values were acetochlor (13 samples), pyroxasulfone (5 samples), bifenthrin (2 samples), tebupirimfos (1 sample), atrazine (2 samples), and chlorpyrifos (3 samples).
Watch for Part 2, with details on pesticide monitoring in Minnesota’s groundwater, next week!
How to Help Protect Water Quality
Follow MDA’s water quality BMPs
The MDA works closely with University of Minnesota Extension to develop and promote pesticide-specific best management practices (BMPs). Both generic and pesticide-specific water quality BMPs are available on the MDA’s Pesticide BMPs webpage. BMPs were developed to target agricultural use of pesticides as well as non-agricultural use (e.g., application to turfgrass).Get certified
The Minnesota Agricultural Water Quality Certification Program is a voluntary program that allows farmers and agricultural landowners to take the lead in implementing conservation practices to protect water. Visit the MDA’s Minnesota Agricultural Water Quality Certification Program webpage to learn more.1 Use of trade names is for educational purposes only. No endorsement is implied and no discrimination is intended.
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