Dichloro diphenyl trichloroethane
Dichlorodiphenyl trichloroethane (DDT) or more precisely 1,1,1-trichloro-2,2-bis(4-chlorophenyl)-ethane , with formula (ClC6H4)2CH(CCl3) is a compound main organochlorine of insecticides. It is colorless. It is very soluble in fats and in organic solvents, and practically insoluble in water. Its molecular weight is 354 g/mol.
Paul Hermann Müller was a Swiss chemist and winner of the 1948 Nobel Prize in Physiology or Medicine for his discovery of DDT as an insecticide used to control malaria, yellow fever, typhus, and many other infections caused by insect vectors..
In the 20th century it was used intensively as an insecticide but, after verifying that this compound accumulated in trophic chains and given the danger of contaminating food, its use was prohibited.
Getting
DDT was synthesized by the Austrian scientist Othmar Zeidler, during his doctoral thesis in Vienna (1874). It was rediscovered and produced in the laboratories of the Geigy Company in Switzerland. DDT can be easily synthesized from low-cost substances that are readily available. It is obtained by condensation of chloral, or trichloroacetaldehyde, with the formula CCl3CHO, with chlorobenzene, C6H5Cl, in excess. last, in the presence of aluminum chloride, AlCl3 or fuming sulfuric acid (oleum), H2S2O7, as a catalyst, thus obtaining the crude DDT, is purified by washing it with large amounts of water, causing the DDT to separate from the impurities together with the water, since like other chlorinated hydrocarbons, DDT is practically insoluble in water. We can also wash the crude DDT by neutralization with Na2CO3 after draining the spent acid.
Ban
In the best seller Silent Spring, from 1962, Rachel Carson exposed all the ecological dangers derived from the use of DDT, even claiming that all the birds in the world would end up disappearing if it continued to be used that insecticide. This obviously exaggerated concept led the United States Environmental Protection Agency (EPA) to ban DDT in 1972, following a political decision against the advice of EPA scientists.
DDT was excluded from the list of active substances authorized for use in plant protection products in 1969 under the Law, in many countries, for the protection of plants against pests and pests. The production, use and commercialization of all plant protection products containing DDT is currently prohibited. DDT is designated as a PIC chemical.
In Spain, plants and animals were selected to measure DDT concentrations in each of the links in the chain, and it was verified that at each trophic level the amount of mg/Kg of animals increased from one level to another.
Controversy
The same year as the ban, 1972, EPA-appointed administrative law judge Edmund Sweeney would conclude after seven months of hearings in his opinion report that:
"DDT is not a carcinogenic risk for man... the use of DDT under the regulations involved here does not have a spelling effect for freshwater fish, estuarian organisms, wild birds or other wildlife."
(Sweeney, EM. 1972. "Recommendations of the EPA Examiner, and findings concerning the DDT hearings", April 25, 1972 (40 CFR 164.32, 113 pages)
Despite this, EPA Administrator William Ruckelshaus dismissed the judge's opinion and banned virtually all uses of DDT as a "potential human carcinogen."
The controversy seemed to revive, perhaps due to a pressure campaign that on May 24, 2006 was denounced by EPA scientists in a letter that was later made public by an association of environmental officials PEER.
On September 15, 2006, the World Health Organization (WHO) announced that the insecticide will again be part of its program to eradicate malaria by fumigating inside residences and thus killing mosquitoes that transmit malaria. Scientific studies show that the use of DDT indoors associated with mosquito nets is effective in the prevention of malaria and does not present the dangers for wildlife and the ineffectiveness in the medium term that its indiscriminate use as a biocide does have in crops, etc..
However, the United Nations Environment Program (UNEP) proposed in May 2005 at the first meeting of the Stockholm Convention on Persistent Organic Pollutants the elimination of 12 compounds considered "pesticides and industrial chemical products substances that can kill people, damage the nervous and immune systems, cause cancer and reproductive disorders, as well as disturb the normal development of infants and children", among which is DDT, whose characteristics fall under the classification of: "highly toxic; they are stable and persistent and last for decades before degrading; they evaporate and travel long distances through air and water, and accumulate in the fatty tissue of humans and wildlife".
Malaria
Proponents of the use of DDT, including skeptical scientists, statisticians and environmentalists such as Bjørn Lomborg, argue that it is an effective method against malaria and is primarily responsible for the destruction of the Anopheles mosquito; they affirm that thanks to it malaria disappeared from Europe, where it was endemic in Greece or Italy. In Sri Lanka, malaria cases fell from 2,800,000 cases in 1948 to 17 in 1963; in India, from 100 million cases in 1935, the figure dropped to 300,000 in 1969. Bangladesh was declared a malaria-free zone. There is even a figure circulating that prohibition of DDT has caused 50 million deaths. They defend its suitability based on the effectiveness they attribute to it, along with the low cost of its application and the fact that it does not have patent problems. Precisely, some argue that the ultimate reasons for the ban are in the industry itself, which, after ending the DDT patents, wanted to impose new patented pesticides.
However, the environmental community and part of the scientific community doubt this benignity, and there is consensus to attribute harmful potential and in many cases carcinogenic to DDT. Being an issue in which economic interests and pressure groups intervene, the studies of both parties have not been conclusively and definitively accepted, although it is generally accepted that DDT is not an innocuous compound for the trophic chain. In any case, DDT began to be abandoned a decade before its prohibition due to the appearance of new insecticides according to some sources, and according to others, due to resistant strains of insects, for which reason its potential usefulness, if it had not been prohibited, is extremely doubtful, as has happened in India, where it has not been banned in all these years.
In Colombia, the presence of neurological and psychiatric symptoms associated with chronic exposure to DDT and other organochlorines has been documented in workers of the malaria control program. However, no effects were ever observed in factory workers of DDT whose exposure is much higher than that of the applicators.
Known hazards and risks to human health
WHO Classification: active ingredient: Class II-moderately hazardous. Formulations: if they are below 200 g/kg for solids and 500 g/L for liquids they are Class III, if they exceed it it is Class II.
Short-term toxicity: DDT primarily affects the peripheral and central nervous systems and the liver. It appears to be embryotoxic to mice (2.5 mg/kg/day). The NOEL is 0.25 mg/kg/day.
Chronic Toxicity: IARC concludes that DDT is a liver carcinogen that is not genotoxic to mice. The NOEL is 0.3 mg/kg/day; The tolerated daily intake of 0.02 mg/kg/day is proposed. There is no evidence of carcinogenicity to humans.
Being a substance with low solubility in water but with good solubility in fats, they tend to accumulate in adipose tissues and appear easily in the fats of breast milk.
Known hazards and risks to the environment
Adverse health effects in animals exposed to DDT include reproductive and developmental failure, possible effects on the immune system, and widespread deaths of wild birds after DDT spraying.
As with many organochlorine insecticides, the major target of acute DDT exposure is the nervous system. Long-term administration of DDT has resulted in hepatic, renal, and immune effects in animals. DDT prevents androgen from binding to its receptor, thereby blocking androgen from driving normal sexual development in male rats and leading to abnormalities.
In laboratory cultures of whole phytoplankton from the Caspian Sea to the Mediterranean, DDT at a concentration of 1 ppb reduced primary production by up to 50% a. Marine fish appeared to be very sensitive to DDT: their LC50 at 96 hours ranged from 0.4 to 0.89 micrograms/l for many teleosts. Bivalve molluscs, with their ability to concentrate organochlorine pesticides without being a hazard to them, have a 96 hour LC50 greater than 10 mg/l.
This pesticide affects birds of prey who are contaminated by incorporating it through the organisms they consume. It accumulates in the food chain and reaches raptors, normally top predators of the food chain, in large numbers. On the other hand, its insolubility in water means that it can be carried away by the wind or running water.
Long-range atmospheric transport of DDT in northern countries, including the Arctic, is well documented; DDT has been detected in Arctic air, soil, ice and snow, and at virtually all levels of the Arctic food chain. Many studies indicate that bottom sediments in lakes and rivers act as reservoirs for DDT and its metabolites.