Adsorption of Insecticide Residues — Importance in Environmental Sampling and Analysis

Insecticides can become incorporated in the water of streams and lakes in several ways, such as spray drift or spillage, industrial or municipal waste, or from wind and water erosion of contaminated soil particles with adsorbed chemical residues. It would be impossible to document the amounts involved in spray drift and spillage, but by measuring soil insecticide residues we can examine the potential for contamination of water systems by erosion of soils. In Figure 1 are shown the insecticide residues found in organic soil of the Holland Marsh, an important vegetable growing area north of Toronto, Ontario, during a 4 year study (Miles et al, 1978). These data are average ppm in the soil of 13 farms, and the levels are very significant, with DDT averaging about 29 ppm. Some individual farm soils had as high as 60 ppm DDT and 25 ppm ethion. There appeared to have been little degradation of the DDT in these organic soils. A few percent had converted to DDE, but p,pf-DDT comprised 76% of the total DDT and o,p’-DDT 15% — very similar to the analysis of technical DDT (Schecter et al, 1945). We initiated studies of water and sediment in the area of the vegetable marsh in an attempt to determine the contribution of these contaminated farm soils to environmental pollution.