TRANSPORT MECHANISM IN SOILt METABOLISM AND MOVEMENT OF INSECTICIDES FROM SOILS iNTO WATER AND CROP PLANTS

The persistence, movement and metabolism of insecticides in soils are affected by various environmental conditions. Field data are presented, showing that phorate—after granular band application—moved in both horizontal and vertical directions. Phorate sulphone was the major metabolite recovered. The metabolism and persistence of this insecticide was also affected by its mode of application. Utilizing a soil—plant—water ecosystem, it was demonstrated that the percolation of water through this system did not affect the movement of [14C]-phorate through loam soils, but did so with soils of lesser or no sorptive capacity. Water percolated through agricultural soils contained phorate metabolites (phorate sulphoxide and phorate suiphone), while corn greens grown in this system contained in addition phoratoxon sulphoxide and phoratoxon sulphone. With [14C]-Dyfonate it was shown that the insecticide did not move to an appreciable extent through an agricultural loam soil and its transport with water through soils was, to a large extent, a function of the soil type. Detergents, having increased the persistence of parathion in soil, indirectly increased the amount of parathion within the percolated water. The presence of salts prevented the appearance of aldrin residues in percolated water and reduced the amount of parathion residues. Movement of insecticides from soils into plants was shown to be dependent on energy supply systems of root cells, soil nutrients and soil insecticide concentrations. iNSECTICIDE PERSISTENCE The persistence and metabolism of an insecticide in soils is a function of the chemical nature of the pesticide itself and of a whole variety of environmental factors1. Attempts have been repeatedly made to define persistence, yet no clear-cut, definition could be obtained. This was the result of the dependence of the persistence of a pesticide on the multitude of environmental factors. However, after the application of several insecticides at the same rate, at the same time, in the same way and to the same soil type in Madison, Wisconsin, strict comparisons about the relative persistence of various insecticides could be made and expressed as percentage of the applied dose t To illustrate various principles and points in this presentation, data were used that primarily had been obtained through research in our own laboratory at the University of Wisconsin. This was done for sake of convenience only, although many scientists at various institutions are conducting excellent research in this particular field of interest.