This work deals with the evolution of intermediates and ecotoxicity upon Fenton's oxidation of phenol in aqueous solution. The EC50 values of the intermediates identified in the oxidation pathway of phenol have been measured. Some of these compounds, mainly hydroquinone and p-benzoquinone, showed toxicity levels much higher than phenol itself. Depending on the operating conditions, these intermediates could be completely transformed into organic acids, mainly oxalic and formic. Ecotoxicity values substantially lower than those expected from the chemical composition were measured in the reaction samples. This is explained by a reduction of the concentration of aromatic intermediates when the pH was adjusted at 6-8 (according to what is required by the standard bioassay ISO 11348-3). Formation of complexes between hydroquinone and p-benzoquinone at increasing pH can remove from solution those highly toxic intermediates whose very low EC50 values give rise to a high ecotoxicity even at fairly low concentrations. This together with the enhanced decomposition of residual H202 at increasing pH represent important beneficial effects of the neutralization step following Fenton treatment which allow a complementary cleaning of the effluent.

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Priority organophosphorus pesticides in water samples were subjected to analysis by solid-phase extraction followed by liquid chromatography/high-flow pneumatically assisted electrospray mass spectrometry (LC/ESP-MS). The operational parameters of ESP optimized by use of an eluent flow rate of 0.3 mL/min and at a source temperature of 150 °C were as follows: drying gas flow rate, 250-300 L/h; ESP nebulizing gas flow, 5-20 L/h; ESP voltage, 2-3.5 kV; HV lens voltage, 0.2-1.0 kV; extraction voltage, 20-130 V; focus voltage, and the ion energy. Water samples (500 mL) were preconcentrated by use of either Empore disks of Cis and styrenedivinylbenzene or monofunctional Cis cartridges in an ASPEC XL system. No thermal degradation was observed for the organophosphorus pesticide triclorfon, which usually causes a problem under LC/MS using thermospray interface. The method detection limit was 0.01 fig/L for most of the organophosphorus pesticides used employing SIM of the [M + Na]+ ion.The analysis of organophosphorus pesticides in water samples is performed with either liquid-liquid extraction or solid-phase extraction (SPE) followed by gas chromatography (GC) with nitrogen-phosphorus or mass spectrometric detection.1-3 During the last few years, liquid chromatographic (LC) techniques have grown in this application field due to the possibility of determining thermally labile and polar compounds that are not GC amenable. Since several organophosphorus pesticides, e.g., dichlorvos and trichlorfon, do not exhibit a good chromophore under conventional LC/UV detection,1 2 the use of liquid chromatography /mass spectrometry (LC/MS) with a thermospray (TSP) interface has been employed.4-9 However, still difficulties arise for the determination of organophosphorus pesticides, as pointed in several LC/MS publications; e.g., this is the case for the organophosphorus pesticide

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