Gary Yang
								4/8/98
								Pd. 5

Dichlorodiphenyl-trichloroacetic acid (DDT)


	During the days of World War II (1939 to be precise), a Swiss
scientist named Paul Muller was experimenting with
dichlorodiphenyl-trichloroacetic acid (DDT) when he discovered its various
insecticidal uses.  This discovery was important because DDT was u sed
extensively for the control of insects and insect-transferred diseases for
the American troops during World War II.  After the war ended, the public
also demanded this new miracle chemical that killed off pests with no
apparent harm to humans.  In fac t, the DDT discovery was so critical
that, because of his research and findings dealing with DDT, Muller won a
Nobel Prize in 1948. 

	The use of DDT reached its height in 1970 when 385.9 million lb.
(175 million kg) were manufactured globally.  The largest amount of DDT
used in the United States during one year was 79.4 million lb. (36 million
kg) in 1959, but the largest annual produc tion was 198.5 million lb. (90
million kg) in 1964 because of the export market.  However, during the
1970s, various scientists, in particular the author and biologist Rachel
Carson, discovered the negative ecological effects of DDT.  Because of
this, mos t industrialized countries banned the use of DDT in the early
1970s.  However, it was and still is being used in many under-developed
countries, mostly because of its cost and effectiveness.  The evolution of
pests in resisting DDT is lowering its effecti veness, however, and the
future of DDT seems to be rather grim. 

	DDT was used widely across the United States, and later the world. 
It was used to kill insect pests of crops in agriculture, forestry, and to
control various diseases (i.e.: malaria, which is spread by mosquitoes). 
This is because, as a pest control su bstance, DDT is usually fairly
effective.  To expand on the use of DDT, its effectiveness in controlling
malaria was and is an important feature of it. 

	Malaria is a disease caused by the protozoan Plasmodium and is
transmitted by mosquitoes.  It used to be a major problem in various
tropical areas around the world, and it affected more then 5% of the
world's population every year during the 1950s.  An outbreak in the 1930s
in Sri Lanka affected half of the population and killed off 80,000 people. 
Around two to five million children died of malaria each year during the
1960s.  One way to reduce the amount of people who are infected by this
disease is to kill off the mosquitoes that spread it.  To do this, DDT is
applied to the aquatic breeding areas or the walls and ceilings of houses
in order to get the DDT onto the insects' bodies, where is can then
proceed to kill off the pest.  DDT was used for so l ong because it can
even be spread on a person's body in order to kill off any ticks or louses
a person might have.

	The use of DDT to control malaria had tangible results.  India,
which had 100 million cases of malaria and 0.75 million deaths per year
between 1933 and 1935 had only 0.15 million cases and 1,500 deaths in
1966, mostly because of the use of DDT.  Sri Lan ka, which had 2.9 million
cases of malaria in 1934 and 2.8 million in 1946, had only 17 cases in
1963.  However, despite (or possibly because of) the massive purge of
mosquitoes which DDT has allowed, the development of insecticide resistant
breeds has re cently increased the number of cases and deaths. 

	DDT, being the first widespread pesticide which was ever used, has
brought about a number of different opinions in its time.  Winston
Churchill praised the substance during World War II as miraculous, which
it may have seemed at the time.  However, with further research into its
effects, the public opinion of it changed.  The major turning point in the
public opinion of DDT came with the publishing of the book "Silent
Spring," by Rachel Carson.  In her book, Carson referred to a dead world
where the over -use of pesticides has killed off all of the wildlife,
leaving a barren land.  The horrible image brought about by this book led
most countries to ban the use of DDT, which still carries on to this day. 

	There are several chemical properties of DDT that make it such a
good pesticide but also make it a deadly substance to other forms of
wildlife.  DDT is harder to destroy then most other substances as it is
not easily degraded by microorganisms, sunlight, or heat.  And then, even
when it is decomposed, its primary breakdown product is DDE, which is
produced by enzymatic metabolism in organisms or by inorganic
de-chlorinating reactions in alkine environments.  Both DDT and DDE are
long-lasting substances t hat stay in the environment for years.  DDT is
also insoluble in water, while being highly soluble in fats and oils
(lipids).  In nature, the highest concentrations of lipids are in the
tissues of living organisms.  Because of this, the DDT is left in the
environment until consumed by animals, where it dissolves into the
animal's tissues.  The property of biomagnitivity takes affect here, which
means that the animals higher up in the food chain accumulate more and
more of the DDT in their bodies, which ev entually kills them.  This is
also called food-web accumulation because of the amount of accumulation at
the top of the food-web. 

	DDT occurs in very small concentrations in water and air.  Because
of organic matter in the soil, the ground tends to absorb more DDT.  As
for organisms, plants have a larger concentration then soil, but,
following the food-web, herbivores have more than plants and predators
have more than herbivores.  An example of this occurred in the ecosystem
surrounding Lake Kariba in Zimbabwe.  Despite being banned for use in
agriculture, DDT is still used there to control mosquitoes and flies.  At
one point, the c oncentration of DDT in the lake water was less then 0.002
ppb, but the amount in the lake bottom was 0.4 ppm, a significantly larger
number.  The algae contained 2.5 ppm and a filter-feeding mussel contained
10 ppm.  Herbivorous fish had 2 ppm in contrast to a bottom-feeding fish
which contained 6 ppm.  The tigerfish and a cormorant, which both feed on
small fish, contained 5 ppm and 10 ppm respectively.  The Mile crocodile,
the animal at the top of the food-chain, contained 34 ppm.  As is evident,
the am ount of DDT increased as the food-chain rose higher. 

	Unfortunately, DDT is globally distributed.  This occurs because
the pesticide, after being sprayed, immediately has potential for drifting
away in the wind.  After contact with the desired surface, the chemicals
can also evaporate, leach into the ground water, get washed away by the
rain, of get directly brushed onto nearby animals.  This all serves to
shift DDT away from its intended area of focus and allows it to reach out
and kill wildlife beyond its intended targets.  Even in Antarctica, where
DDT ha s never been used before, DDT concentrations of 5 ppm occur in the
southern polar skua (whereas findings show less than 1 ppm in birds which
reside lower in the food web like the penguins).  However, the main areas
of effect are still around the exposure area.  Up to 158 ppm of DDT was
found in the fat of seals off of the coast of California in the late
1960s.  The seals in the Baltic Sea had up to 150 ppm, and the ones in
Canada had as much as 35 ppm.  The Canadian porpoises also had an amazing
large 520 ppm.

	Beyond marine life, many people are also concerned with the
effects of DDT on predatory birds.  As much as 356 ppm (this may seem
surprising, but the average is only around 12 ppm) occurred in bald eagles
from the US, and up to 360 ppm in western grebes and 131 ppm in herring
gulls.  The most surprising number is in the white-tailed eagles in the
Baltic Sea, which have been found with as much as 36,000 ppm of DDT in fat
and with eggs with up to 1,900 ppm DDT. 

	DDT damages in a variety of ways.  It kills birds by its toxicity. 
However, this is not all that it does.  DDT also affects the birds
reproduction habits.  It has been demonstrated to decrease the clutch
size, cause thinner egg shells, kill off embryos, and change parental
behavior.  This all contributes to the death of the species, which is a
critical point when discussing endangered species like the bald eagle.

	The current project dealing with DDT is to clean up the residue
left from the past and to decrease its use by third-world countries.  The
benefits involved with DDT don't seem to balance out the risks, and so
better ways of controlling pests are being de veloped.  As of right now,
the public has the task of remaining informed on the substance and its
effects and role in the world's history.