DDT got it's name
from an old and imprecise name DichloroDiphenylTrichloroethane
and was the insecticide to end all insecticides when
it came out. DDT is an organochlorine insecticide which was discovered
and first synthesised in 1874 by a chemist called Zeidler. Later another
scientist, Mueller, discovered DDT's insecticidal properties in 1939.
DDT is effective against many organisms, but its most spectacular success
has been in the control of the Anopheles mosquito, which transmits
malaria. Malaria has been the scourge of mankind for centuries. According
to the World health Organisation, malaria is still the chief cause of
human death in the world, aside from natural causes. The disease acquired
its name in ancient Rome ( L. mala, bad; aria, air), where
it was believed to be the result of bad air in the city. It is actually
caused by a parasite of the Plasmodium family which infects and
ruptures erythrocytes in the blood stream. The organism has a complex
life cycle requiring both vertebrate and invertebrate. Humans are infected
with the sporozoites of the organism which are injected into the bloodstream
by the bite of an infected mosquito. Although malaria may be treated,
the most effective way of controlling it is to eliminate the insect
vector which is essential for its transmission. DDT is especially effective
for this purpose, and malaria had essentially been eliminated from large
areas of the world through its use...signs are now that it is on the
increase again. It has been estimated that because of the efficacy of
DDT in checking malaria and other mosquito borne diseases (yellow fever,
encephalitis), more than 75 million deaths have been averted. A striking
example is Sri Lanka ( used to be Ceylon). In 1934 - 35, there were
1.5 million cases of malaria resulting in 80,000 deaths. After an intensive
mosquito-abatement program using DDT, malaria effectively dissappeared
and there were only 17 cases reported in 1963. When the use of DDT was
discontinued in Sri Lanka, malaria rebounded , and there were over 600,000
cases reported in 1968 and the first quarter of 1969
In spite of its obvious value in combatting diseases
like malaria, DDT has been abused. It is a "hard" inseciticide,
in that its residues accumulate in the environment. Although it is not
especially toxic to mammals ( The fatal human dose is 500 mg/kg of body
weight, about 35 grams for a 150lb person), it is concentrated by lower
organisms such as plankton and accumulates in the fatty tissues of fish
and birds. The toxicity of DDT was first noted in 1949 by the Fish and
Wildlife Service in America, and following abuse by crop sprayers, was
eventually withdrawn in 1972 by the then Environmental Protection Agency.
As animals on the lower end of the food chain are eaten
by those higher up, DDT becomes more and more concentrated the higher
you go. This continues until the primary predator is reached, who will
then receive the highest dose. DDT is highly persistent in the soil
and can last from 2 - 15 years, not too bad some people might say, but
when you look at the half-life in an aquatic environment, this can be
about 150 years, one half-life being that time to degrade by 50%. DDT
is highly acutely toxic to fish affecting membrane funtion and enzyme
systems. Atlantic salmon fry were found to be affected at concentrations
of 50 - 100 µg/L, suffering from balance problems and impaired
behavioural development. At the same time aquatic invertabrates and
amphibians are also affected allbeit to a very slighter extent.
It not only acts as a stomach poison but also as a contact
insecticide, and was remarkable for its high toxicity to insects at
low rates of application. DDT affects the nervouse system by interfering
with normal nerve impulses. DDT causes the nerve cells to repeatedly
generate an impulse, this accounts for the tremors seen in exposed animals.
DDT is moderately to slightly toxic to studied mammalian species via
the oral route. Reported oral LD50s range from 113 to 800 mg/kg in rats
(79,73); 150-300 mg/kg in mice (79); 300 mg/kg in guinea pigs; 400 mg/kg
in rabbits; 500-750 mg/kg in dogs and greater than 1,000 mg/kg in sheep
DDT may be slightly toxic to practically non-toxic to birds. Reported
dietary LD50s range from greater than 2,240 mg/kg in mallard, 841 mg/kg
in Japanese quail and 1,334 mg/kg in pheasant. In birds, exposure to
DDT occurs mainly through the food web through predation on aquatic
and/or terrestrial species having body burdens of DDT, such as fish,
earthworms and other birds. There has been much concern over chronic
exposure of bird species to DDT and effects on reproduction, especially
eggshell thinning and embryo deaths.
on Aquatic Species: DDT is very highly
toxic to many aquatic invertebrate species. Reported 96-hour LC50s in
various aquatic invertebrates (e.g., stoneflies, midges, crayfish, sow
bugs) range from 0.18 ug/L to 7.0 ug/L, and 48-hour LC50s are 4.7 ug/L
for daphnids and 15 ug/L for sea shrimp. Other reported 96-hour LC50s
for various aquatic invertebrate species are from 1.8 ug/L to 54 ug/L.
DDT is very highly toxic to fish species as well. Reported 96-hour LC50s
are less than 10 ug/L in rainbow trout (8.7 ug/L), northern pike (2.7
ug/L). DDT may be moderately toxic to some amphibian species and larval
stages are probably more susceptible than adults. In addition to acute
toxic effects, DDT may bioaccumulate significantly in fish and other
aquatic species, leading to long-term exposure. This occurs mainly through
uptake from sediment and water into aquatic flora and fauna, and also
fish. Fish uptake of DDT from the water will be size-dependent with
smaller fish taking up relatively more than larger fish. A half-time
for elimination of DDT from rainbow trout was estimated to be 160 days.
The reported bioconcentration factor for DDT is 1,000 to 1,000,000 in
various aquatic species, and bioaccumulation may occur in some species
at very low environmental concentrations. Bioaccumulation may also result
in exposure to species which prey on fish or other aquatic organisms
(e.g., birds of prey).
on Other Animals (Nontarget species): Earthworms
are not susceptible to acute effects of DDT and its metabolites at levels
higher than those likely to be found in the environment, but they may
serve as an exposure source to species that feed on them. DDT is non-toxic
to bees; the reported topical LD50 for DDT in honeybees is 27 ug/bee.
Laboratory studies indicate that bats may be affected by DDT released
from stored body fat during long migratory periods.
in Soil and Groundwater: DDT is very
highly persistent in the environment, with a reported half life of between
2-15 years and is immobile in most soils. Routes of loss and degradation
include runoff, volatilization, photolysis and biodegradation (aerobic
and anaerobic). These processes generally occur only very slowly. Breakdown
products in the soil environment are DDE and DDD, which are also highly
persistent and have similar chemical and physical properties. Due to
its extremely low solubility in water, DDT will be retained to a greater
degree by soils and soil fractions with higher proportions of soil organic
matter. It may accumulate in the top soil layer in situations where
heavy applications are (or were) made annually; e.g., for apples. Generally
DDT is tightly sorbed by soil organic matter, but it (along with its
metabolites) has been detected in many locations in soil and groundwater
where it may be available to organisms. This is probably due to its
high persistence; although it is immobile or only very slightly mobile,
over very long periods of time it may be able to eventually leach into
groundwater, especially in soils with little soil organic matter. Residues
at the surface of the soil are much more likely to be broken down or
otherwise dissipated than those below several inches.
of Chemical in Surface Water: DDT may reach
surface waters primarily by runoff, atmospheric transport, drift, or
by direct application (e.g. to control mosquito-borne malaria). The
reported half-life for DDT in the water environment is 56 days in lake
water and approximately 28 days in river water. The main pathways for
loss are volatilization, photodegradation, adsorption to water-borne
particulates and sedimentation. Aquatic organisms, as noted above, also
readily take up and store DDT and its metabolites. Field and laboratory
studies in the United Kingdom demonstrated that very little breakdown
of DDT occurred in estuary sediments over the course of 46 days. DDT
has been widely detected in ambient surface water sampling in the United
States at a median level of 1 ng/L (part per trillion).
of Chemical in Vegetation:
DDT does not appear to be taken up or stored by plants to a great extent.
It was not translocated into alfalfa or soybean plants, and only trace
amounts of DDT or its metabolites were observed in carrots, radishes
and turnips all grown in DDT-treated soils. Some accumulation was reported
in grain, maize and riceplants, but little translocation occured and
residues were located primarily in the roots.
The physical appearance of technical product p,pÕ-DDT is a waxy solid,
although in its pure form it consists of colorless crystals.
- Chemical Name:
1,1'-(2,2,2-trichloroethylidene)bis[4-chlorobenzene]; 1,1,1- trichloro-2,2-bis(4-chlorophenyl)
- CAS Number:
- Molecular Weight:
- Water Solubility:
< 1 mg/L @ 20°C
- Solubility in Other Solvents:
cyclohexanone v.s., dioxane v.s., benzene v.s., xylene v.s., trichloroethylene
v.s., dichloromethane v.s., acetone v.s., chloroform v.s., diethyl
ether v.s., ethanol s. and methanol s..
- Melting Point:
- Vapor Pressure:
0.025 mPa @ 25°C.
- Partition Coefficient:
- Adsorption Coefficient:
- World Health Organisation.
- USA Environmental Protection Agency.
- Oregon University.
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