Effect of detergents and inorganic salts in water on the persistence and movement of insecticides in soils.

Abstract

The vertical movement and persistence of aldrin and parathion in agricultural loam soils were investigated under leaching and nonleaching conditions. The effect of the detergents ABS (alkyl benzene sulfonate) and LAS (linear alkyl benzene sulfonate) and sodium chloride in water, or of a complete plant nutrient solution, on the movement of the insecticides in the soil also was studied. The water, after its percolation through insecticide-treated soil and through lower insecticide-free soil layers, was analyzed for insecticidal residues. Quartz sand of no sorptive capacity and minimal microbiological activity was used as a control. The effects of the sorptive capacities of a loam soil became evident. After its percolation through loam soil, water that had been treated at a rate of 2 lb per 6-inch acre did not contain measurable amounts of aldrin but contained small amounts of parathion. The amount of parathion in percolated water was a function of the concentration of the insecticide in the soil. Detergents, having increased the persistence of parathion in soil, indirectly increased the amount of parathion within the percolated water. Aldrin moved within soils in the absence of percolated water, while parathion moved to a lesser extent. After the percolation of water or water + LAS through insecticide-treated (20 lb per 6-inch acre) soil and through lower untreated soil layers, small amounts of aldrin (0.1 to 0.2 ppb) and parathion (0.2 to 0.8 ppb) were found in the water samples. These amounts were far below the water solubility of these insecticides and the water was not toxic to mosquito larvae. The presence of salts prevented the appearance of aldrin residues in the percolated water and reduced the amount of parathion residues. It appears unlikely that water in deeper soil strata could be contaminated with insecticidal residues from the upper agricultural soil layers.