Pesticide concentrations in Louros River and their fluxes into the marine environment

Seasonal variations and riverine input of pesticide residues to the coastal zone were determined in Louros River for the period of 1995 and 1996. The sampling sites for the determination of fluxes were located at the main river flow and its estuary at the boundary between freshwater and the brackish zone. Solid-phase extraction (SPE) disks followed by gas chromatographic techniques (GC with MSD and FTD) were used for the monitoring of various pesticides and metabolites in river waters from the sources to the estuary. The inputs of the five major herbicides, atrazine, simazine, alachlor, metolachlor and desethyl-atrazine (DEA) to the Louros River are mainly from tributaries and the agricultural area draining to the river estuary. The highest concentrations of these pesticides occured in May and June seasons, just after their application. The seasonal variation studies showed a continuous presence of triazines, alachlor and metolachlor, which were detected in the dissolved phase throughout the year at 0.02-0.27 mu g/L, whereas the other pesticides exhibited a sporadic occurence related to agricultural and irrigation practices. Atrazine and its degradation product DEA are the most abundant herbicides discharged into Amvrakikos Gulf, followed by metolachlor, simazine and alachlor. Their annual mean flux was estimated as 122.7 g/day for atrazine, 127.5 g/day for DEA, 49.1 g/day for metolachlor, 43.9 g/day for simazine and 11.2 g/day for alachlor.