school energy&environment

Changes in the food chain

Technological innovations applied to agriculture in the fight against crop-damaging parasites led to the use of large quantities of pesticides for long periods of time. These substances are toxic and their accumulation varied the balance of the biosphere, as they have harmful effects on organisms, man included. DDT is a substance that, when introduced into the environment, provoked damages to the ecosystem, creating a phenomenon of pesticide pollution at world level. Researches that studied the quantity of DDT that is present in the environment, confirmed its presence in fish all around the world, in Eskimo populations, animals that live in polar regions and mother’s milk. This passage of DDT through the different levels of the food chain is made possible by the fact that the molecule keeps unaltered, as it does not degrade easily. As a consequence, at each different level (from plants to insects, from insect-eating birds to predator mammals), the concentration of DDT in organisms increased by 10 times. That is to say that, is the mass of the organisms becomes a tenth, the concentration of the pesticide increases by ten times.
The damages caused by DDT on organisms are alarming: when the molecule reaches the sea, DDT slows algae photosynthetic activity, bird eggs get fragile and break easily during hatching because they lack calcium, the number of individuals is reduced and human organs and systems are damaged.
An altered ecosystem
In Borneo, the use of DDT caused the alteration of the ecosystem, directly affecting men. The wide use of DDT to kill malaria-carrying mosquitoes killed all insects, including those that are useful to men, like cockroaches. These insects are the main food for lizards, therefore the number of lizards dramatically dropped, as well as the number of felines that ate lizards. Felines also kept mice population under control. The reduction of felines lad to an increase in the number of mice, that in over-population conditions transmit dangerous diseases to man.
Borneo, after DDT disinfestations campaigns, was affected by infectious epidemics that caused more victims than malaria.