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Herbicide runoff along highways. 1. Field observations
Xinjiang Huang1, Theresa Pedersen, Michael Fischer
1Department of Civil and Environmental Engineering, University of California-Davis, One Shields Avenue, Davis, California 95616, USA.
Environmental Science & Technology
|July 21, 2004
Summary
Highway herbicide runoff, including oryzalin and glyphosate, can impact water quality. Herbicide solubility and storm timing significantly influence seasonal loss to surface water.
Area of Science:
- Environmental Chemistry
- Ecotoxicology
- Hydrology
Background:
- Herbicides are routinely applied to control vegetation along highways.
- Proximity of surface water to highways raises concerns about herbicide contamination.
Purpose of the Study:
- To assess the risk of herbicide runoff from highways to surface water quality.
- To investigate the behavior of various herbicides with different physicochemical properties in runoff.
Main Methods:
- Field study conducted over three rainy seasons at two northern California sites.
- Monitoring of five herbicides (oryzalin, isoxaben, diuron, glyphosate, clopyralid) in runoff after application.
- Collection of 24 samples per storm for detailed temporal analysis and calculation of flow-weighted event mean concentrations.
Main Results:
- Least soluble herbicides (isoxaben, oryzalin) persisted in runoff longer than more soluble ones (diuron, clopyralid).
- Glyphosate mobilization was low, but its metabolite aminomethylphosphonic acid was frequently detected.
- A first-order model effectively described herbicide decline in soil and runoff; runoff coefficients exceeded soil coefficients.
Conclusions:
- Herbicide loss to surface runoff is influenced by solubility, runoff volume, and crucially, the timing and intensity of the first storm post-application.
- Minimizing highway herbicide runoff requires considering compound mobility and application timing.