Spatial and temporal trends of paraquat, diquat, and difenzoquat contamination in water from marsh areas of the valencian community (Spain)

The levels and distribution of diquat, paraquat, and difenzoquat were determined by solid phase extraction (SPE) and high-performance liquid chromatography (HPLC) in water samples from irrigation channels, rivers, and lagoons taken during 1 year from three different marsh areas of the Valencian community. These areas are representative of the typical Mediterranean coastal ecosystems. All three compounds were detected. Diquat was found most frequently at all the sampling sites. Although the spatial distribution of diquat and paraquat showed a maximum concentration near the fields where they were originally applied, their location fluctuated due to irregular large spill and/or loading. The herbicide concentration tended to be highest during the summer (June, July, and August) because these are the months with the least rainfall and highest evaporation rates, when weeds grow best and pesticides are needed more often. The average concentration found for diquat was 0.09 &mgr;g/L, with a maximum of 3.10 &mgr;g/L. The average concentration for paraquat was 0.01 &mgr;g/L, with a maximum of 3.95 &mgr;g/L. Samples that were below the method detection limit are included in the mean calculation as zero. Difenzoquat was only detected in one sample at a concentration of 1.75 &mgr;g/L.