Stability of isoproturon, bentazone, terbuthylazine and alachlor in natural groundwater, surface water and soil water samples stored under laboratory conditions.

The stability of isoproturon, bentazone, terbuthylazine and alachlor was investigated in groundwater (GrW), surface water (SuW) and soil water from the unsaturated zone (SoW). Samples fortified with a low spiking level (LSL) of about 0.3-0.5 microgram/L and a high spiking level (HSL) of about 0.9-1.3 micrograms/L were stored for 1, 2, 14 (GrW) and 30 days (SuW and SoW) at 4 degrees C in amber glass bottles without biological inhibition. The initial pesticide concentration played a significant role, the lowest concentrations being the least stable for all pesticides. Nevertheless, after 14 days of storage, no concentration had decreased significantly compared to day 0 values, except for bentazone LSL in the GrW and SuW. Significant losses of alachlor were observed only after 30 days. Terbuthylazine and isoproturon were stable for 30 days, except for a slight loss of terbuthylazine HSL in the SoW. The very poor recovery of bentazone from the SoW gave poor results for interpretation. Overall, the stability of the molecules was highest in the GrW and lowest in the SoW. For SoW, the variability of triplicate determinations at a given storage time was, in some cases, as great as the changes in mean concentrations observed over the total 30 day storage period.

Evaluation of ELISA microtiter plate-based assays for the direct determination of isoproturon in water samples and soil extracts.

Trials were carried out on the commercially available Millipore isoproturon ELISA microtiter plate tests and on laboratory assays developed by Hirst as part of a Joint European Union research project (BIOPTICAS). The lowest detectable dose (LDD) was determined as three times the standard deviation of the blanks. Depending on the calibration curves obtained on different days with different plates, the LDD varied from 0.020 to 0.064 microgram/L for the Millipore test and from 0.080 to 0.329 microgram/L for the Hirst test. The mean coefficients of variation within a single plate for triplicate determinations of standard solutions in the 0.05 to 0.5 microgram/L range were 5.5 and 3.6% for Millipore and Hirst respectively. Cross-reactivity was studied for mono- and di-demethylated isoproturon, chlortoluron, diuron and linuron. The highest cross-reactivity with both tests was that of mono-demethylated isoproturon (22% for Millipore, 4% for Hirst). This molecule was the only one to show significant cross-reactivity in the Hirst test, whereas in the Millipore test, the di-demethylated isoproturon also cross-reacted (4%). Natural water samples, 19 ground-, 53 lysimetric plate and 47 suction cup water samples, and 32 soil samples were also analysed with the ELISA tests. HPLC with a diode array detector was used as a validated control technique for the natural samples. For each water type, ELISA concentrations of both tests were significantly correlated with the HPLC values (r > or = 0.937; p < 0.001). For the soil extracts, the correlations were also significant (p < 0.001), but the scatter in the data was greater. Overall, the Millipore correlation coefficients were higher than those of Hirst.