MP5 Agrochemicals and Pesticides
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(SMA-1117-819482) Input of dissolved and sediment-associated pesticides to the Yolo Bypass, California.

Smalling, K¹, Orlando, J¹, Kuivila, K¹, ¹ U.S. Geological Survey, Sacramento, CA, 95819

ABSTRACT- Current-use pesticides are transported into the Yolo Bypass, a leveed flood-control basin in northern California. The objective of this study was to compare the relative distribution of pesticides in waters and sediments transported from five source watersheds to the Bypass. Water and suspended sediments were collected during two high-flow runoff events (February 2004 and January 2005), while bed sediments were collected during the dry season in late September 2004. Dissolved pesticides were analyzed using solid-phase extraction and gas chromatography/mass spectrometry (GC/MS). Sediments were extracted using microwave-assisted extraction, cleaned with carbon and alumina followed by gel-permeation chromatography, and analyzed by GC/MS. The more hydrophilic pesticides (hexazinone, simazine and diazinon) were detected most frequently and at the highest concentrations in the water samples. Pesticides with high use and ranging in log K_oc from 2 to 5 were detected in the water and the sediments. Suspended sediments generally had more pesticides and higher concentrations, compared to bed sediments. Equilibrium partitioning between the water and the suspended sediments was modeled for six pesticides varying in K_oc values and application amounts. Two pesticides, metolachlor and oxyfluorfen, appeared to be in equilibrium between the water and the sediment. In contrast, the other four pesticides (molinate, thiobencarb, trifluralin, and pedimethalin) were not in equilibrium, with higher-than-predicted pesticide concentrations associated with the sediment. Although the current-use pesticides are hydrophilic, a significant percentage of the total amount of each pesticide is associated with the suspended sediments. Differentiating the partioning between the dissolved and sediment-bound fractions is important in understanding the fate and transport of current-use pesticides in the environment.

Key words: current-use pesticides, Yolo Bypass, sediment, water