South Florida Water Management District ambient pesticide monitoring network: 1992 to 2007.

The South Florida Water Management District has collected surface water and sediment samples for analysis of over 80 pesticides since 1992. Residues of atrazine and DDE-p,p(') are nearly ubiquitous throughout the sampling area. Surface water concentrations of atrazine at nine of 14 selected monitoring locations exhibited a downward trend and none of the detected concentrations exceeded established levels of concern. Seventy-five percent of the sampled locations had average sediment residues of DDE-p,p(') at levels that may impact sediment-dwelling organisms. Monitoring locations with the highest average DDE-p,p(') concentrations (based on detected values) and the highest percentage of pesticide detections did not exhibit consistent trends. Some locations exhibited increasing trends while trends at other locations showed a decrease in concentrations. Additionally, specific location concentrations for ethion, diazinon, and endosulfan documented periods of surface water quality exceedances. However, product label changes and grower education have substantially contributed to the reduced number of exceedances over time.