Where It Comes From
Forms as metolachlor breaks down in soil and water; it’s mobile and relatively persistent, so it can leach to groundwater and streams [1][2].
How You Are Exposed
Mainly by drinking contaminated well water or surface‑water–influenced tap water; much less from food. Workers can be exposed when mixing or applying herbicides [1][3].
Why It Matters
ESA is generally less acutely toxic than metolachlor, but human data are limited. EPA considers ESA when assessing drinking‑water risks, and its presence signals pesticide impacts on water sources [1][3].
Who Is at Risk
People using private wells in agricultural regions; infants and pregnant people; farmworkers and pesticide applicators; small water systems with limited treatment [2][3].
How to Lower Your Exposure
Test private wells for pesticide degradates; if found, use NSF‑certified activated carbon or reverse osmosis filters, or use another safe water source, and maintain filters properly [4]. Workers should follow label directions and wear protective gear to reduce contact and runoff [5].
References
- [1]U.S. EPA, Office of Pesticide Programs. S‑Metolachlor: Human Health Risk Assessment for Registration Review (includes ESA/OA degradates).
- [2]U.S. Geological Survey (USGS). Acetanilide (chloroacetanilide) herbicide degradates (including metolachlor ESA) are widespread in U.S. ground and surface waters.
- [3]U.S. EPA. Unregulated Contaminant Monitoring Rule (UCMR 2) – included acetanilide pesticide degradates such as metolachlor ESA; occurrence in public water systems.
- [4]CDC. A Guide to Drinking Water Treatment Technologies for Household Use.
- [5]U.S. EPA. Pesticide Worker Protection Standard and safety guidance for handlers/applicators.