The DDT or, in other words, diclorodifeniltricloroetano is an organic compound that belongs to the organ-chlorinated, in the past largely used as an insecticide and, following to its proven toxicity, it is dismissed in a lot of countries.
The molecule of the DDT was synthesized in laboratory in the 1874 by the German chemist O. Zeidler that, though, did not identify its possible applications; only in the 1939 the Swiss biochemical Paul Herman Müller, successively conferred of the Nobel Prize (1948) already verified its neurotoxic action against mosquitoes, tsetse flies, Fleas and louses. The DDT was quickly adopted in an agrarian ambit for the treatment of the soil and the sowings, and in campaign of medical prevention, above all for the eradication of the malaria fever, transmitted by the Anopheles mosquito, but also of the typhoid fever, yellow fever, elephantiasis and other diseases conducted by endemic insects in the tropical areas. In the end of the Fifties of the XX century it became the more used insecticide all over the world and it allowed the improvement of the agrarian productivity of some farming and reduces the mortality connected to the malaria fever.
At the beginning of the Sixties showed suspicious circumstances about the toxicity of the compound towards the human being and the ecosystems. Through the whispers that had the biggest sounding was the one that the American zoologist Rachel Carson, now considered as the pioneer of the ecologist movement that in 1962, with her book Silent Spring, exposed between the other the heavy consequences about the food chains of the insecticide. This work prompted eager controversies that contributed to start studied projects on the effects of the DDT and other compounds.
EFFECTS OF THE DDT
DDT and brown pelican
Between the 1950 and the 1970 the populations of the brown pelican, Pelecanus occidentalis, seabird of the Atlantic and Pacific seacoast, were been strikingly reduced for the ingestion of contaminated fish and residuals of DDT and other pesticides. For the phenomenon called biological amplification, the concentration of chemical compounds increase passing from a level of the food chain to the upper one. For this reason, if the concentration of the DDT did not result lethal for the fishes, at the contrary provoked damages in the pelicans that fed of those; particularly, provoked abnormalities in the eggshells, and for this reason the broods did not come to an end. After the banishment of the DDT in the 1972, was registered a slow increase of the population of these birds.
The dangerousness of the DDT, that was considered carcinogen, is connected to its chemical structure; because it is a hydrocarbon, it is not soluble in water but in the greases; it does not degrade easily and perdure in the ground for a very long time. The result is that it tends to concentrate more and more at every passage of the food chain, this phenomenon is known as biological amplification or bio-accumulation. The researches pointed out that the residuals of DDT were present in the majority of the foods between the Fifties and the Seventies of the twentieth century, for the intense sprayings affected on the intensive agrarian farming; they showed furthermore the concentration of the DDT in the human fatty tissue.
ECOLOGY OF THE FISH-HAWK
The population of the fish-hawk, breed for the most part monogamist, can be resident of migrant; the first one multiply in the wintry months, the other in the beginning of the spring. The female lays 3-4 eggs at the interval of a couple of days one from the other. The eggs hatched in the same sequence of the deposition and are hatched for about six weeks; the offspring is incapable and must be fed by the adults. After the first month, the offspring reach the 75% of the growth; after two weeks they take the first flight, leaving forever the nest; they reach the sexual maturity at about 3-5 years. The fish-hawk can live up to 13-18 years and it is considered very useful from an ecological point of view for the survey of the DDT levels and other chemical compounds in the aquatic environment, to which it is particularly sensible because it engages the top of the food chain.
It was observed that in some breeds of animals the DDT has got an action as that of the hormones, causing some endocrine disequilibrium. Besides, it was found that the strong reduction of the populations of some breeds of birds connected to the aquatic environment was caused by the high fragility of the eggshell, that was provoked by the DDT present into the fish that birds feed; between the breeds hit by the bald eagle (Haliaëtus leucocephalus), the fish-hawk (Pandion haliaetus), the brown pelican (Pelecanus occidentalis). Some breeds of insects, besides, developed during the time a resistance against the insecticide that will thwart its employment or will become necessary a major ration.
A RISK ALREADY PRESENT
The DDT was dismissed in the 1972 by the United States and the majority of the industrial countries. However it is already used in a lot of Third World Countries, above all because it is more inexpensive than other pesticides with a more recent formulation. In these countries the studies have highlighted the presence of remains of DDT in the mother’s milk, with a risk for the children breast-fed; furthermore, the exporting of agrarian products supplied with the pesticide to the Western countries establishes the reintroduction also in the countries where it has been formally forbidden.
A recent research of the Innsbruck University has realized that the DDT evaporates above Africa and India, countries where it is strongly used, and it remains freely circulating in the atmosphere of the areas with a hot climate, while it throw down headlong the areas with a cold temperature; the consequences of this phenomenon is the presence of the pesticide in the polar waters (it was also found in the seals and the penguins) and even in the alpine tarns at an height superior to 2500m. for this reason, a lot of people retains desirable the extension of the ban about the DDT all over the planet; other, at the contrary, already consider legitimate the use of the DDT in some countries because the exigency of defeating the malaria, as a responsible of millions of victims, should be stronger than the preoccupations for possible carcinogen effects at a long term.