The MDA monitors rivers, lakes, and groundwater in agricultural and urban areas for the presence of pesticides.
Metribuzin and its degradates (metribuzin DA, metribuzin DADK, metribuzin DK) have been found by the MDA in both Minnesota’s groundwater and surface water. The U.S. Environmental Protection Agency (EPA) conducts a risk-benefit analysis when registering a new pesticide or an existing pesticide with new use. For metribuzin, the EPA determined that when used according to the label, metribuzin does not pose unacceptable risks to water resources.
Metribuzin water monitoring data are reviewed by the MDA for both the frequency and concentration at which metribuzin and its degradates are detected. Monitored concentrations are compared against risk-based guidelines or standards established by the EPA and the Minnesota Department of Health (MDH) (see table below). State statute and agency policy require the MDA to take action when pesticides are frequently detected or when detections occur at concentrations approaching or exceeding the guidelines or standards.
Minnesota water quality guidelines or standards for metribuzin
| Water Resource | Chemical | Reference Number | Basis for Number | Responsible Agency |
|---|---|---|---|---|
| Drinking water | Metribuzin | 10 µg/L | Chronic Health Based Guideline | MDH |
| Drinking water | Metribuzin DA | 10 µg/L | Chronic Health Based Guideline | MDH |
| Drinking water | Metribuzin DADK | 10 µg/L | Chronic Health Based Guideline | MDH |
| Drinking water | Metribuzin DK | 10 µg/L | Chronic Health Based Guideline | MDH |
| Surface Water | Metribuzin | 2,100 µg/L | Water Quality Benchmark | EPA |
| Surface Water | Metribuzin DA | -- | Water Quality Benchmark | EPA |
| Surface Water | Metribuzin DADK | -- | Water Quality Benchmark | EPA |
| Surface Water | Metribuzin DK | -- | Water Quality Benchmark | EPA |
Notes:
- μg/L stands for micrograms per liter; which in water is also equivalent to parts per billion (ppb).
- Chronic guidelines and standards provide protection from long-term exposure over a period of days (surface water) or years (drinking water).
- The EPA benchmark values for metribuzin is based specifically on protecting aquatic plants, but is also protective of other aquatic life, water recreation, and drinking water sources.
In groundwater, metribuzin or its degradates are seldom detected. When metribuzin or its degradates are detected, they are usually at concentrations below established standards.
In surface water, metribuzin and both of its degradates have been found. In general, metribuzin detections are low relative to the EPA benchmark value of 2,100 μg/L. Metribuzin degradates are found more frequently but at low levels relative to aquatic life or human health guidelines.
In response to the metribuzin detections, the Commissioner of Agriculture called for the development of voluntary Water Quality Management Practices (BMPs) in 2002. These voluntary BMPs help reduce the contamination of water resources. The MDA first published the voluntary BMPs in 2004, updated them in 2008, and revised them in 2010 and 2019.
For more information on the MDA’s water monitoring efforts, refer to the MDA’s Monitoring and Assessment Program and the annual water monitoring reports.
