Long-term monitoring of pesticides and polar transformation products in ground water using automated on-line trace-enrichment and liquid chromatography with diode array detection

An automated system using on-line trace-enrichment, separation by liquid chromatography with a gradient elution and diode array detection is described for monitoring pesticides in ground water. Two systems were used for covering the wide range of polarities of the targeted pesticides: the first one consisted of a PLRP-S precolumn and a C-18 analytical column for moderately polar to non polar compounds and the second one, specially designed for the determination of polar pesticides and degradation products, consisted of a precolumn and analytical column both packed with porous graphitic carbon. The detection limits that can be reached by the two systems are in the low 0.1 mu g/l for the ground water samples of interest with the handling of 100-150 mi of water. An application is presented with the first objective of monitoring the quality of a ground water reservoir which comes from a small basin where the amount and nature of pesticides applied are known and where atrazine has been banned for the last five years and replaced by terbutylazine. The second objective was to have a better knowledge of the behaviour and persistence of pesticides from the results of a long-term survey of 18 months. Obviously, the water solubility is an important parameter for the leachability of pesticides. Although banned on this site for the last five years, atrazine and deethylatrazine are found at constant concentrations, 0.5 and 0.7 mu g/l respectively all the year round. The on-line system with the PGC precolumn and analytical column allowed to confirm the deethylatrazine concentration as well as the very low concentration (< 0.05 mu g/l) of both hydroxyatrazine and deisopropylatrazine. Although applied in replacement of atrazine, neither terbutylazine nor its major dealkylated metabolite were detected until now. Other more soluble compounds such as isoproturon or metamitron are detected during the period following their application.