Sustainability

Pollution caused by heavy metals

Heavy metals (cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, zinc, molybdenum, tin) are among the main soil pollutants. In fact they are widely spread, highly toxic and persistent, as they stay in the environment for a long time (through the food chain, for example). If these pollutants exceed determined quantities, they provoke damages to those organisms that absorb them. Why can heavy metals in the soil be harmful to living organisms? Usually the metal in the soil is absorbed by the plants and transported through their leaves and fruits. The leaves and fruits that contain the pollutants are eaten directly by the primary consumer (man or animal) that assimilates them in his organism. Pollutants can be absorbed also by eating the meat of an animal that was fed with heavy-metal polluted vegetables. Once they have been accumulated in the organism (man, animal or vegetable) in quantities that are higher than the normal quantity, they can produce serious damages and sometimes provoke the death of the organism. What has just been described is the method through which pollutants are transmitted inside the food chain: for this reason it is very important to have a high soil quality, in order not to have damaging substances in the food. Why can heavy metals be present in the soil? In nature, heavy metals are present in underground deposits (see the pages dedicated to this resource) and, without men’s action, they would very hardly manage to spread in the surrounding environment and particularly in the soil. At the moment, the main cause for their spreading is human activity. Heavy metals can be left in the environment or directly discharged by the industry only during some productive processes (for example they can be discharged by mining industries that extract them from the subsoil or by other industries that discharge fumes or polluted waste water), or by the consumer who uses products that contain them (for example paints, tyres, fuels, and others). These products, when they are used or if they are not correctly disposed of, discharge some heavy metals. Heavy metals, like other toxic elements, derive not just from industrial activities, but also from civil activities (they are contained, for example, in sewage waters). Is it possible to eliminate this type of pollution? The governments of many countries have been paying special attention to this type of pollution and, in the last few years, they have forced their factories to respect strict limits in the emission of heavy metals. They have also forced the factories to produce goods that do not contain heavy metals or contain very small quantities of them. The aim is to keep their presence in the environment below certain threshold levels, that are safe for men, animals and the vegetation.