Pesticide occurrence in selected South Florida canals and Biscayne Bay during high agricultural activity.

Climate and soil conditions in South Florida along with an extensive canal system facilitate movement of agricultural pesticides into surface waters. In a two-year study (2002-2004) of the currently used pesticides in South Florida, atrazine, endosulfan, metolachlor, chlorpyrifos, and chlorothalonil were the most frequently detected in the canals and in Biscayne Bay, with average concentrations of 16, 11, 9.0, 2.6, and 6.0 ng/L, respectively. Concentrations of atrazine and chlorpyrifos were highest near corn production. Chlorothalonil and endosulfan concentrations were highest near vegetable production, with no clear trend for metolachlor, which is used on multiple crops. Concentration data were used to calculate an aquatic life hazard potential for the planting period (November) versus the harvest period (March). This analysis indicated that a higher hazard potential occurs during harvest, primarily from the use of endosulfan. These data will also serve to document canal conditions prior to implementation of the Comprehensive Everglades Restoration Plan (CERP).