Legal Agricultural Use Determination for Metolachlor/S-Metolachlor Degradate Detections in California
Abstract
Metolachlor, a preemergent herbicide, was registered in California in 1977. It is primarily used in the production of corn (human consumption and forage), beans (dry and succulent), cotton, and processing tomatoes. In 2000, S-metolachlor, a purified version of metolachlor, was registered. S-metolachlor currently accounts for 70% of the combined total metolachlor/Smetolachlor use. Metolachlor and S-metolachlor’s physical and chemical properties indicate that they are persistent and mobile. Persistent and mobile pesticides are placed on the California Department of Pesticide Regulation’s (DPR) Groundwater Protection List (GWPL) for future ground water monitoring, as required by Title 3 California Code of Regulations section 6800(b). DPR has currently analyzed 433 samples from 282 wells for the presence of metolachlor. While DPR has not detected either metolachlor or S-metolachlor in ground water, DPR has detected their ethanesulfonic and oxanilic acid degradates, MESA and MOXA, respectively. These residues range in concentrations from 0.05 to 20.2 parts per billion (ppb) in 62 wells. DPR’s monitoring results for metolachlor, MESA, and MOXA are consistent with detection patterns nationwide.
There have been eight groups of adjacent detections located in San Joaquin, Solano, and Stanislaus Counties. Metolachlor/S-metolachlor has been used in the vicinity of these adjacent detections. These detections are likely due to legal agricultural use of metolachlor/S-metolachlor.
DISCLAMIER: The mention of commercial products, their source, or use in connection with material reported herein is not to be constructed as an actual or implied endorsement of such product.