The MDA monitors rivers, lakes and groundwater in agricultural and urban areas for the presence of pesticides. A description of the MDA's Monitoring and Assessment Program and copies of water monitoring reports are available.
Acetochlor and its degradates (breakdown products) have been found by the MDA in both Minnesota's surface water and groundwater. Finding acetochlor (the parent compound) in surface water and groundwater was not unexpected due to acetochlor's wide use and high solubility in water. When it was first registered for use by the Environmental Protection Agency (EPA), water resource impacts were anticipated from the water monitoring and computer modeling studies that were required by the EPA during the registration process. The EPA uses a risk-benefit analysis system in registering pesticides and it was determined that when used according to the label, acetochlor does not pose unacceptable risks to water resources.
Acetochlor water monitoring data are reviewed by the MDA for both the frequency and concentration at which acetochlor and its degradates are detected. Monitored concentrations are compared against risk-based guidelines or standards established by the Minnesota Pollution Control Agency (MPCA) and the Minnesota Department of Health (MDH) (Table 3). State statute and agency policy lead the MDA to take action when pesticides are frequently detected or when detections occur at concentrations approaching or exceeding these numbers.
|Water Resource||Chemical||Reference Number||Basis for Number||Responsible Agency|
|Drinking Water||Acetochlor parent||9 μg/L||Chronic Health Based Guideline||MDH|
|Drinking Water||Acetochlor ESA degradate||300 μg/L||Chronic Health Based Guideline||MDH|
|Drinking Water||Acetochlor OXA degradate||100 μg/L||Chronic Health Based Guideline||MDH|
|Surface Water||Acetochlor parent||3.6 μg/L||Chronic Water Quality Standard||MPCA|
|Surface Water||Acetochlor ESA degradate||9,900 μg/L||Water Quality Benchmark||EPA|
- 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 MPCA Chronic Water Quality Standard for acetochlor was adopted into rule in 2008.
- The MPCA Chronic Water Quality Standard for acetochlor has a time component; to violate the standard the average acetochlor concentration over a 4-day (96-hour) period needs to exceed 3.6 μg/L.
- The MPCA Chronic Water Quality Standard for acetochlor is based specifically on protecting aquatic plants, but is also protective of other aquatic life, water recreation, and drinking water sources.
Detection of the acetochlor parent compound in groundwater is rare, and when detected, is found at very low concentrations relative to the standard. Acetochlor degradates are found more frequently in groundwater, but not at concentrations that approach human health guidelines.
The MDA monitoring program has found both acetochlor and its degradates in surface water. Acetochlor has been found at concentrations that either approached or exceeded the water quality standards or guidelines at the time. Acetochlor degradates are found at low levels relative to aquatic life or human health guidelines.
Based on the frequency or concentration that acetochlor has been found in water from normal agricultural use, in 2002 the Minnesota Commissioner of Agriculture officially determined that voluntary Water Quality Best Management Practices (BMPs) for acetochlor are required. The voluntary BMPs were first published in 2004, updated in 2008 and revised in 2010. More details on the BMPs are in Water Quality Best Management Practices for Acetochlor.