Occurrence and spatial and temporal distribution of pesticide residues in groundwater of major corn-growing areas of Greece (1996-1997).

During 1996-1997, residues of selected pesticides were monitored, at 3-month intervals, in 80 wells, including both irrigation and drinking water wells, distributed among the main corn-growing areas (Pieria, Thessaloniki, Serres, Kavala, and Evros) of Greece. Pesticide residues were found in 48% of the wells; however, in most cases residues were very low ranging from LOQs (quantification limits of the analytical methods) to <0.1 microg/L, while in 11% (nine wells) pesticide residues higher than 0.1 microg/L were present. Most of the latter wells were found in Evros and specificallythe Ardas Valley. The frequency of occurrence, in descending order, was atrazine > DEA > alachlor = metolachlor; however, the order of descending concentrations was atrazine > metolachlor > DEA > alachlor. The occurrence and the spatial and temporal distribution patterns of pesticide residues indicate that at the present the situation of groundwater quality is favorable throughout the corn-growing areas of Greece with the exception of the Ardas Valley.