Effects of Cover Crops on the Movement and Fate of Soil-Applied (14C)-Fonofos in a Soil-Plant-Water Microcosm

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Abstract
The effects of com plants or a “lawn” of ryegrass on the movement and metabolism of soil-applied 14C-fonofos were studied in a microcosm which consisted of terrestrial and aquatic components. Artificial rain, applied to the fallow or plant covered soils, resulted in runoff that accumulated in aquaria containing lake bottom mud and aquatic organisms. The presence and the type of a cover crop had a considerable effect on the mobility and metabolism of soil-applied 14C-fonofos. The insecticide plus its metabolites were least persistent in systems with fallow soils and most persistent in those with ryegrass. Within the terrestrial soil, 14C-compounds moved downwards and also were trans located via the root systems into the leaves of com and ryegrass. Within the plant tops, 86% of the recovered benzene-soluble 14C-compounds were in the form of the detoxified methyl phenyl sulfone and 2% or less as fonofos. Due to rain, considerable runoff of soil and water had been deposited into all the aquaria, but the amounts of soil and 14C transported decreased drastically due to the presence and nature of cover crops. 14C-compounds transported were primarily associated with the runoff soil and most of these were later found in the soil-lake mud sediments. 14C-fonofos was the major constituent in soils and aquatic sediments, while the major metabolite recovered from both the terrestrial and aquatic portion of the microcosm was methyl phenyl sulfone, its amounts ranging from 13 to 92% of all benzene-soluble radiocarbon. Relatively small amounts of the insecticidal oxygen analogue of fonofos were recovered, the exception being in roots of corn and of ryegrass.

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