Effects of Soil Pollution
1. Most of the heavy metals are toxic, for example, arsenate impregnated areas can often be recognized by the absence of vegetation. The most toxic metal are nickel, chromium and cadmium. Compounds of nickel, chromium and arsenate cause lung cancer. Several nickel compounds, including the volatile nickel tetracarbonyl, are carcinogenic. Lead tetra alkyls are extremely poisomous, affecting the central nervous system. Lead itself causes lead poising characterized by painful intestinal colic, failure of kidney functions, loss of function in peripheral nerves leading to tumours and paralysis.
2. Hazards caused by biomagnification of pesticides are of increasing concern. These pesticides enter food chain, attain concentration through biomagnification and destroy members of different trophic levels, and may pass from one ecosystem to the other.
3. Persistent pesticides become concentrated in higher links of foods. Recent declines in number of eagles, falcons hawks, gulls and brown pelicans are linked with unsuccessful reproduction. The predators accumulate DDE in their tissues from rodents and other organisms which they eat. DDE is correlated with disturbance in liver enzyme action and interference in calcium metabolism. Eggs are produced with little or no hard shell, are easily broken and do not hatch.
4. There is also a strong pressure of natural selection in insect population exposed to insecticides,which leads to the development of resistance, often by metabolizing the compounds in new ways, SO in lime, heavier dosages are required to produce the same effects or none. However the danger to the community increases with increased release of the toxic substance in the environment. The history of pesticides chemistry is, therefore of continuous struggle to keep one ‘jump ahead of the insect’. Dioxin will kill small animals but the major effect on human being are skin lesions, including a very unsightly and long-persisting acne, due to the blocking of the ducts of the sebaceous glands.
5. The PCBs, posses many of the unwelcome biological properties of organochlorine, Paricularly, long persistence, lipid solubility leading to concentrated food chains and toxic effects in animals. In accidently induced contamination it has been seen o cause malfunctioning intestinal system and the brain.A widespread concern arose for the human population, because the PCBs were secreted into milk and could be shown to be concentrated in human adipose tissue. A part mild neurological effects, there has been no immediate human toxicity.They are also potent inducers of hepatic mixed function oxidases.
6. Once radioactive materials reach the soil,they are accumulated by the producers, lichens for instance,are known to concentrate Caesium-13. When the green are fed upon by herbivores and subsequently pass through th food chan, biomagnification of radionuclides occurs showing distinct effects. The nuclide which is deposited on grass, is fed by cows, and appears in milk.
7. Dumping municipal wastes, garbage and improper sanitary conditions become breeding grounds of pathogenic organisms and their vectors. The soil becomes contaminated by various bacilli those causing dysentery, cholera, typhoid, paratyphoid and other. These are carried by vectors and the human population gets infected. When introduced into cropland, spores and cysts of various helminth parasites contaminate the food crops and enter the food chain.