Where It Comes From
Forms when metolachlor/S‑metolachlor degrades; it moves easily with water and can persist longer than the original herbicide [1][2].
How You Are Exposed
Mainly through drinking water from private wells or public systems drawing from affected rivers or aquifers; exposure from food or air is expected to be low [1][2].
Why It Matters
Health studies on MOA are limited. EPA evaluates it using metolachlor data; high-dose animal studies of the parent show liver and blood effects, so EPA includes degradates like MOA when assessing drinking-water risk [1].
Who Is at Risk
People in agricultural regions, private well users, and infants or pregnant people (higher intake per body weight and greater sensitivity) [1].
How to Lower Your Exposure
If you use a private well, test for metolachlor and its degradates; consider reverse osmosis or activated carbon treatment certified for pesticide reduction; check your utility’s water report and follow label directions to reduce runoff if using herbicides [3][1].
References
- [1]U.S. EPA, Office of Pesticide Programs. S‑Metolachlor—Human Health Risk Assessment for Registration Review (2018).
- [2]U.S. Geological Survey (USGS). Occurrence and transport of metolachlor degradates (MOA, MESA) in surface and groundwater (multiple studies, e.g., Kolpin et al.).
- [3]U.S. EPA. Drinking Water Treatability Database: Metolachlor and related compounds.