Monitoring of organonitrogen pesticides in the Ebro river. Preliminary loadings estimates†

Abstract

Enzyme-linked immunosorbent assay (ELISA) and gas chromatography mass spectrometry (GC–MS) were applied in the annual monitoring of atrazine in the Ebro river and in the estuary at different salinity values. Alachlor, metolachlor, simazine and deethylatrazine were determined by GC–MS in the same river basin. The annual loads were calculated for all the herbicides determined from March 1995 to June 1996. Following monthly sampling, water samples were determined directly by ELISA and preconcentrated by solid-phase disk extraction (SPE) with C₁₈ Empore disks followed by GC–MS. Atrazine was found to be the herbicide exhibiting the highest concentration throughout the year, varying from 20 to 225 ng l^–1, the other herbicides were detected at lower concentrations reaching values of up to 150 ng l^–1. The salinity profile was performed in the Ebro delta waters from salinity levels of 0.5 to 8 g l^–1 using 13 sampling points. The atrazine profile indicated higher concentrations in the river water down to a few ng l^–1 at higher salinity levels (varying from 120 to 20 ng l^–1). Annual loads of organonitrogen herbicides were directly correlated with field application rates and stream discharge and the physicochemical properties of the herbicides.