New – Adoption of Water Quality Best Management Practices for Chlorothalonil
On April 6, 2026 the MDA adopted water quality best management practices (BMPs) for the use of chlorothalonil (Minnesota State Register / Minnesota.gov, Volume 50, Number 40).
In response to concerning levels of 4-hydroxychlorothalonil, a degradate of chlorothalonil, in groundwater samples, the MDA has developed these BMPs to aid growers and applicators in preventing and minimizing the contamination of Minnesota’s groundwater.
The MDA published draft BMPs for chlorothalonil and opened a 30-day public comment period on the proposed BMPs in September 2025 (50 SR 307). A total of two comments were received. No substantial edits were made to the BMPs based on comments received.
Comments Received on Draft Best Management Practices for Chlorothalonil (March 2026)
Water Quality Best Management Practices for Chlorothalonil (April 2026)
Chlorothalonil
| Pesticide Type | Fungicide (Group M05) |
|---|---|
| Chemical Class | organochlorine |
| Common Trade Names (No endorsement is implied in the referencing of trade names) | Bravo®, Daconil®, Echo®, Initiate® |
| Registration Status | EPA: Registered since 1966 MN: Registered |
| Structure |  |
Chlorothalonil is a broad-spectrum contact fungicide. It is widely used on potato and numerous other crops in Minnesota to protect against fungal and oomycete diseases such as late blight and downy mildew. It is commonly used on turf and ornamentals including golf course turf and sod production for control of dollar spot and snow molds. Additionally, chlorothalonil is used in paints and surface treatments as a mildewcide. From 2015-2024, between 300,000 and 500,000 pounds of chlorothalonil were sold in Minnesota annually (MDA Pesticide Sales Database).
Mode of Action
Chlorothalonil is classified by the Fungicide Resistance Action Committee (FRAC) as Group M05 (FRAC Code List 2024). It has multiple sites of action and causes inactivation of cell sulfhydryl enzymes that disrupts metabolic processes in fungi cells. Multi-site fungicides in Group M have a low risk of resistance development and to help mitigate resistance concerns, are often tank mixed or alternated with single site fungicides that have medium to high risk for resistance development.
Movement and Breakdown in the Environment
Chlorothalonil enters the environment directly through its labeled uses and has the potential to move offsite via runoff, spray drift, and atmospheric transport. Chlorothalonil is relatively insoluble in water (less than 1 mg/L), binds tightly to soil (average Koc = 3,113 mL/goc), and is considered slightly to hardly mobile in soil. Volatilization is not expected to be a major route of dissipation from either soil or water (Henry’s Law Constant = 2.6 x 10-7 atm-m3/mol).
Chlorothalonil breaks down or degrades in the environment through multiple pathways including soil and aquatic metabolism, hydrolysis, and photolysis. Soil metabolism half-lives of 2-58 days and 2-22 days have been reported under aerobic and anaerobic conditions, respectively. In aquatic environments, chlorothalonil rapidly breaks down under both aerobic and anaerobic conditions (half-lives <1 week). It is stable to hydrolysis under acidic conditions and is moderately susceptible to hydrolysis under neutral to basic conditions (half-life: 4-64 days). Degradation via photolysis can occur in clear, shallow water with environmentally relevant half-lives of 0.4 (pH 7) and 23 days (pH 5). Based on reported terrestrial field dissipation half-lives of less than 23 days, chlorothalonil is considered moderately persistent in the environment.
The main route of dissipation for chlorothalonil is transformation to the major degradate 4-hydroxychlorothalonil (SDS-3701) through soil metabolism. 4-Hydroxychlorothalonil is more mobile and persistent than chlorothalonil.
For more information on the movement and breakdown of chlorothalonil see the Environmental Protection Agency’s (EPA’s) Chlorothalonil: Drinking Water Assessment for Registration Review (2020) and the EPA’s Chlorothalonil: Draft Ecological Risk Assessment for Registration Review (2020).
Detection in Minnesota Waters
The MDA monitors groundwater and surface water throughout Minnesota for over 180 pesticide-related chemicals. Since the MDA began monitoring for chlorothalonil in 2001, detections have been limited, with less than 5 detections in either groundwater or surface water.
In 2020, the MDA began monitoring for 4-hydroxychlorothalonil, a major degradate of chlorothalonil. From 2020 through 2024, 4-hydroxychlorothalonil has been detected in approximately 10% of groundwater samples (n=1,113), and all detections have been in the central sands region of Minnesota. 4-Hydroxychlorothalonil has been detected in groundwater at concentrations above the Minnesota Department of Health (MDH) chronic health-based guidance value of 2 µg/L (MDH Human Health-Based Water Guidance Table). In 2024, there were 9 detections of 4-hydroxychlorothalonil above the health-based guidance value in groundwater, with a maximum concentration of 16.3 µg/L. From 2020 through 2024, there have been a total of 47 detections of 4-hydroxychlorothalonil over the health-based guidance value in groundwater.
The MDA has also detected 4-hydroxychlorothalonil in private drinking water wells. In 2023, 4-hydroxychlorothalonil was detected in 6 of the 19 private wells tested, and it was detected in 4 of 26 private wells tested in 2024. In 2024, the maximum concentration detected in private drinking water wells was 5.84 µg/L, which exceeded the 2 µg/L health-based guidance value. Two additional samples had concentrations between 50% and 100% of the health-based guidance value.
In 2024, 4-hydroxychlorothalonil was detected in < 1% of surface water samples (n=385) and the maximum concentration was 0.886 µg/L, well below the surface water reference value of 4,600 µg/L. For more information related to water monitoring results in Minnesota see Water Monitoring Reports and Resources.
Chlorothalonil and Non-target Organisms
The EPA classifies chlorothalonil as practically non-toxic to birds and small mammals on an acute oral basis and practically non-toxic to honey bees on an acute contact exposure basis. It is, however, classified as very highly toxic to fish and aquatic invertebrates on an acute exposure basis.
On an acute oral basis, the 4-hydroxychlorothalonil degradate is more toxic to birds and mammals than chlorothalonil, but it is significantly less toxic than chlorothalonil to aquatic taxa. For more information on non-target impacts of chlorothalonil and its degradates see the EPA’s Chlorothalonil: Draft Ecological Risk Assessment for Registration Review (2020).
Chlorothalonil and Human Health
Based on animal studies, impacts from exposure to chlorothalonil may be seen in the gastrointestinal, liver, and kidney systems in the body, which may increase the risk of certain kinds of cancer. The EPA classifies chlorothalonil as “likely to be carcinogenic to humans. No potential acute dietary risks of concern were identified but chronic dietary risks of concern were identified for chlorothalonil. In all instances where potential risks of concern were identified, drinking water exposure from groundwater contamination was the major source of exposure. A review of the existing toxicity database revealed that the 4-hydroxychlorothalonil metabolite appears to be much more acutely toxic than chlorothalonil. For more information on human health see the EPA’s Chlorothalonil Proposed Interim Registration Review Decision Case # 0097 (2023).
UPDATE: May 2026
