Effects of Toxic Materials

Abstract

Toxic materials considered here are largely the waste by-products of industrial activity or the residues of substances, such as pesticides, which have been manufactured for use in agriculture, horticulture or forestry. The nature and character of these poisons (toxicants) have changed over the years, as has the relative importance attached to them. Around the turn of the century and until quite recently, many poisons were associated with heavy industries and included ammonia, phenols, hydrocarbons, cyanide and tars from town-gas manufacture, coking plants, or heavy metals (for example, chromium, nickel, copper and cadmium in plating wastes). Reduction in the importance of coal as a source of energy and improvements in the treatment of effluents either by in-plant units or by discharge to sewer and combined treatment with domestic sewage has changed the significance of industrial effluents as a source of poisons. However, the recognition that diffuse sources of certain substances, notably pesticides and some heavy metals, which may be accumulated and concentrated in food chains, means that the emphasis on the short-term (acute) toxicity of poisons has given way to greater interest in their long-term (chronic) consequences.