Occurrence and removal of pesticides in the drinking water treatment plant of Thessaloniki, northern Greece

Fifteen pesticides (lindane, trifluralin, alachlor, metolachlor, simazine, atrazine, diazinon, methyl parathion, parathion, chlorpyrifos, chlorothalonil, metribuzin, endosulfan I, endosulfan II, endosulfan sulfate) were the main target analytes at several stages of the newly established Drinking Water Treatment Plant (DWTP) of Thessaloniki, Northern Greece. The DWTP that is supplied with surface water from Aliakmon river has been designed to remove organic pollutants (including pesticides) with combined ozonation and activated carbon adsorption. Pesticide residue analysis took place at four sampling points along the process train: (a) the raw water inlet, (b) after pre-ozonation, flocculation/ coagulation/ clarification and sand filtration, (c) after ozonation, and (d) after filtration through granular activated carbon (GAC), disinfection and pH adjustment. A multi-residue analytical method using solid phase extraction disks (C18) and a dual gas chromatographic system, coupled with ECD and NPD detector, was employed. Results obtained during, a 24-months surveying period showed very low frequencies of detection and quantifiable concentrations of target pesticides in source river water. Moreover, removal of existing traces during the water treatment process was demonstrated.