Soil surface photolysis can be a significant dissipation pathway for agrochemicals under field conditions, although it is assumed that such degradation ceases once the agrochemical is transported away from the surface following rainfall/irrigation and subsequent drainage of soil pore water. However, as both downward and upward water movement occurs under field conditions, relatively mobile compounds may return to the surface, prolonging exposure to UV light and increasing the potential for degradation by photolysis. To test this hypothesis, a novel experimental system was used to quantify the contribution of photolysis to the overall dissipation of a new herbicide, bicyclopyrone, under conditions that mimicked field studies more closely than the standard laboratory test guidance. Soil cores were taken from three US field study sites and the surface treated with [14 C]-bicyclopyrone.

 

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