Detections in Water

Maintaining Minnesota's water quality is a priority for the MDA. Through the MDA’s ambient water quality monitoring program, more than 150 pesticides and pesticide degradates are routinely monitored in surface water, groundwater, and private wells. The MDA designated chlorpyrifos as a “Surface Water Pesticide of Concern” in 2012 due to detections at concentrations of concern relative to Minnesota’s water quality standards. Chlorpyrifos has never been detected in groundwater or private wells by the MDA.
Two graphs illustrating 1. the number of chlorpyrifos detections (0 to less than 20) in rivers and streams from 2005-2019 and 2. monthly detections in rivers and streams from for 2005 to 2019. For more information please contact Raj Mann at


Impairments Due to Chlorpyrifos

If detections of chlorpyrifos occur at levels that exceed acute standards once or chronic standards twice within three years, the Minnesota Pollution Control Agency can list the water body as “impaired.”

There are currently 13 water bodies listed or proposed for listing as “impaired” for chlorpyrifos in Minnesota. For chlorpyrifos:

  • Chronic standard = 41 ng/L;
  • Maximum [acute] standard = 83 ng/L

Detections of chlorpyrifos in surface waters above Minnesota standards are a concern due to toxicity to aquatic organisms. Chlorpyrifos may enter water by several routes, including:

  • Spray drift or vapor drift
  • Runoff (primarily with eroded sediment)
  • Direct spray/overspray (i.e., misuse)

Chlorpyrifos Response Plan

In response to the chlorpyrifos surface water impairments, the MDA has created a Chlorpyrifos Response Plan. The information collected will also be used to gain a better understanding of the possible reasons chlorpyrifos is being detected in bodies of water (drift, overspray, runoff, erosion, etc.). In addition, the information collected as a result of the activities described in this plan will be used to determine if existing chlorpyrifos label requirements (setbacks and wind speed) are adequately protective of surface water.

The plan focuses on three areas to reduce the number of detections in Minnesota’s surface water bodies:

  • Education and Outreach
  • Inspections
  • Monitoring and Assessment

The MDA will focus its efforts in growing regions throughout the state where chlorpyrifos products are being used. Targeted efforts will also occur within the watersheds or rivers that have or may have impairments. Current education and outreach efforts are focused on educating applicators about setbacks which are legally required from surface waters.