Determination of phenylurea herbicides in natural waters at concentrations below 1 ng l(-1) using solid-phase extraction, derivatization, and solid-phase microextraction-gas chromatography-mass spectrometry.

A procedure is presented which allows the ultratrace level determination of phenylurea herbicides (PUHs) in natural waters. Samples were enriched by solid-phase extraction (SPE) on Carbopack B and alkylated with iodoethane and sodium hydride to yield thermostable products. After derivatization, the aqueous samples were extracted and injected by SPME. The use of iodoethane instead of iodomethane allowed the differentiation between parent compounds and the N-demethylated metabolites. Limits of detection were between 0.3 and 1.0 ng/l for the parent compounds. Standard deviations below 10% were achieved for samples containing more than 4 ng/l in very different matrices including Nanopure water, lake water, and waste water treatment plant (WWTP) effluent. Moreover, the para-hydroxylated metabolite of diuron could be quantified with the same procedure. The presence of further metabolites was assessed qualitatively. Chromatography was stable over a large number of measurements even with dirty samples from WWTP effluent. The precision and sensitivity of the developed analytical method allowed the investigation of the fate of PUHs in lakes, their degradation during drinking water treatment and their transport within the North Sea.

Quantification of dissolved natural organic matter (DOM) mediated phototransformation of phenylurea herbicides in lakes.

For many important classes of pesticides including phenylurea herbicides (PUHs) and triazines, photosensitized transformation may be the only relevant elimination process in surface waters. In this study, the dissolved organic matter (DOM) mediated phototransformation of PUHs has been investigated in laboratory and field experiments. The results indicate that, in surface waters, the photosensitized transformation of PUHs may be significant and occurs primarily by an initial one-electron oxidation most likely involving excited triplet states of DOM (3DOM*) constituents. Using isoproturon and diuron as model compounds, it is shown that for a given DOM, quantum yield factors determined in the laboratory at a few selected wavelengths can be used to quantify the overall DOM- mediated phototransformation of a given PUH under sunlight irradiation. Furthermore, it is demonstrated that this process can be modeled for a given surface water, by applying the program GCSOLAR and a simple algorithm for cloud cover for quantification of average daily light intensities. Finally, the model has been successfully applied to predict vertical concentration profiles of isoproturon and diuron in a small lake in Switzerland. To our knowledge, this is the first study in which DOM-mediated phototransformation of organic pollutants has been quantitatively validated in the field.