Wednesday, November 15, 2006 - 8:45 AM

Distribution and Persistence of Selected Pesticides in Nursery Recycling Ponds.

Jianhang Lu, Univ of California, Riverside, Dept. of Environ. Science, 900 University Ave., Riverside, CA 92521, Laosheng Wu, Dept. of Env. Sciences, Univ. of California, Riverside, CA 92521, Julie Newman, Univ of California Cooperative Extension Ventura County, 669 County Square Dr, Suite 100, Ventura, CA 93003, Ben Faber, University of California, UC Cooperative Extension, 669 County Square Dr., Ste. 100, Ventura, CA 93003-5401, Donald J. Merhaut, Dept. of Botany and Plant Sci., Univ. of California-Riverside, 900 University Ave., Riverside, CA 92521, and Jianying Gan, 900 University Avenue, University of California-Riverside, University of California-Riverside, Dept. of Environmental Science, Riverside, CA 92521.

Recycling or collection ponds are often used in outdoor container nursery production to capture and recycle runoff waters, which often contain fertilizers and pesticides.  Knowledge of pesticide distribution and persistence in these ponds is critical for preventing phytotoxicity of pesticides during water reuse and to assess their impacts to the environment.  In this study, sorption and degradation of four commonly used pesticides diazinon, chlorpyrifos, chlorothalonil, and pendimethalin in waters and sediments from two nursery recycling ponds was investigated.  Results showed that diazinon and chlorothalonil were moderately sorbed (KOC  from 732 to 2448 mL/g) to the sediments, while chlorpyrifos and pendimethalin were strongly sorbed (KOC  > 7443 mL/g) to the sediments. The persistence of diazinon and chlorpyrifos was moderate in sediments (half-lives = 8 - 32 d, aerobic conditions), and appeared to be prolonged in recycling pond waters as compared to surface stream waters, possibly due to decreased contribution from biotic transformation. In contrast, chlorothalonil and pendimethalin were quickly degraded in sediments (half-lives < 2.8 d, aerobic conditions), and their degradation was further enhanced under anaerobic conditions (half-lives < 1.9 d).  The strong sorption of chlorpyrifos and pendimethalin by the sediments suggests that the practice of recycling nursery runoff would effectively retain these compounds in the recycling pond, minimizing their offsite movement. The prolonged persistence of diazinon and chlorpyrifos, however, implies that incidental spills, such as overflows caused by storm events, may contribute significant loads of such pesticides into down stream surface water bodies.