Insecticide residues in soils

In the past twenty years increasing quantities of very stable insecticides have reached agricultural soils. Much of these residues comes from foliage sprays or dusts which miss their targets and fall onto the soil either close to the plants, or after drifting, especially as very fine mists from the low- volume sprays now in common use. It has been estimated that as much as 50 percent of the sprays applied to foliage may reach the soil in this way. Even some that is applied to foliage, reaches the soil when it is washed or blown off crops or when the plant remains are ploughed into the soil. The second main source of insecticide residues in soil is from the large quantities of insecticides applied directly to it to control soil-inhabiting pests, as sprays, dusts, or granules: these are cultivated into the soil or mixed and drilled with fertilizer as dressings.