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 w as investigated in groundwater (GrW), surface water (SuW) and soil wat er from the unsaturated zone (SoW). Samples fortified with a low spiki ng level (LSL) of about 0.3-0.5 mu g/L and a high spiking level (HSL) of about 0.9-1.3 mu g/L were stored for 1, 2, 14 (GrW) and 30 days (Su W and SoW) at 4 degrees C in amber glass bottles without biological in hibition. The initial pesticide concentration played a significant rol e, the lowest concentrations being the least stable for all pesticides . Nevertheless, after 14 days of storage, no concentration had decreas ed significantly compared to day 0 values, except for bentazone LSL in the GrW and SuW. Significant losses of alachlor were observed only af ter 30 days. Terbuthylazine and isoproturon were stable for 30 days, e xcept for a slight loss of terbuthylazine HSL in the SoW. The very poo r recovery of bentazone from the SoW gave poor results for interpretat ion. Overall, the stability of the molecules was highest in the GrW an d lowest in the SoW. For SoW, the variability of triplicate determinat ions at a given storage time was, in some cases, as great as the chang es in mean concentrations observed over the total 30 day storage perio d. (C) 1997 Elsevier Science Ltd.