Significant losses of alachlor were observed only after 30 days. 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. The initial pesticide concentration played a significant role, the lowest concentrations being the least stable for all pesticides. Samples fortified with a low spiking level (LSL) of about 0.3-0.5 μg/L and a high spiking level (HSL) of about 0.9-1.3 μg/L were stored for 1, 2, 14 (GrW) and 30 days (SuW and SoW) at 4☌ in amber glass bottles without biological inhibition. The stability of isoproturon, bentazone, terbuthylazine and alachlor was investigated in groundwater (GrW), surface water (SuW) and soil water from the unsaturated zone (SoW). Over the course of four rainfall events comprising 353 mm, only 3% of the atrazine and 1% of the isoproturon applied to the core was recovered in drainage water. Nonequilibrium became more pronounced with depth on both occasions. After herbicide application, solution concentrations ranged from 1–26% and 1–34% of those predicted for atrazine and isoproturon respectively at equilibrium in the core top soil whilst twenty-one months later they ranged from 1–3% for both herbicides. This change was due to differences in water flow regimes resulting from changes in the structure of the cultivated horizon between rainfall events. Following application, herbicide losses were mainly from gravity drainage samplers at 0.55 m whilst 21 months later losses were mainly from samplers at 0.175 m.

Leaching of recently applied atrazine and isoproturon (2.475 kg/ha) through a large (1.1 m × 0.8 m in diameter), heavily cracked core of clay soil is compared with leaching of their aged residues twenty-one months later.

Cracked by R.K. Belford