|WILLIAMS, W MARTY|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 12/1/2007
Publication Date: 7/24/2008
Citation: Denton, D.L., Moore, M.T., Cooper, C.M., Wrysinski, J., Williams, W., Miller, J.L., Reece, K., Crane, D., Robins, P. 2008. Mitigation of Permethrin in Irrigation Runoff by Vegetated Agricultural Drainage Ditches in California. In: Gan, J., Spurlock, F., Hendley, P., and Weston, D. (Eds.) Synthetic Pyrethroids: Occurrence and Behavior in Aquatic Environments. American Chemical Society Symposium Series No. 991. pp. 415-425. 2008
Interpretive Summary: Irrigation runoff from California tomato fields carries pesticides, such as permethrin, to aquatic receiving systems. To help reduce the amount of pesticide transport, vegetated agricultural drainage ditches have been suggested as a best management practice on the edge-of-field. Three ditches were constructed along the edge of a tomato field in Yolo County, California. A simulated irrigation event containing water, sediment, and permethrin was conducted on each of the three ditches. Permethrin fate and transport was evaluated temporally and spatially in each ditch. Vegetated ditches were able to reduce initial pesticide concentrations by 50% in 22-169 m, while unvegetated ditches required 347 m to accomplish the same task. Plant sorption capabilities in agricultural drainage ditches are important components in improvement and design of economical and environmentally sound best management practices for agriculture.
Technical Abstract: As organophosphate use has decreased in California, a concomitant increase in their replacement insecticides (pyrethroids) has occurred. Although the probability of off-site movement of pyrethroids is less than its predecessors (organophosphates), transport of pyrethroids to aquatic receiving systems is still a potential threat. To mitigate possible harm, several in-field and edge-of-field management practices have been proposed, including conservation tillage, stiff grass hedges, riparian buffers, and constructed wetlands. By incorporating several individual components of these management practices, vegetated agricultural drainage ditches (VADD) have been proposed as a potential economical and environmentally efficient management practice to mitigate effects of pesticides in irrigation and storm runoff. A field trial was held in Yolo County, California, where three ditches (U-shaped vegetated; V-shaped vegetated; and V-shaped unvegetated) were constructed and amended for 8 h each with a mixture of permethrin and suspended sediment simulating an irrigation runoff event. Spatial and temporal collections of water, sediment, and plant samples were analyzed for cis and trans permethrin concentrations. Because the cis- isomer of permethrin is considered more toxic than the trans- isomer, only cis-permethrin results are reported herein. Cis-permethrin half-lives in water were similar between ditches ranging from 2.4-4.1 h. Half-distances (distance required to reduce initial pesticide concentration by 50%) among V-shaped vegetated and unvegetated ditches were substantial, indicating importance of vegetation in mitigation. Cis-permethrin half-distances ranged from 22 m (V-vegetated) to 347 m (V-unvegetated). These studies are being used to validate a computer simulation model that is being developed to design VADD for site-specific implementation. Utilizing features already present in the agricultural landscape, such as drainage ditches, will provide farmers with an economical alternative that still is protective of the receiving aquatic environment.