By Shawn Baskin
Table of Contents
Chemical Formulae and Structures
Chemical Properties
Sources and Routes of Entry
Concentrations in the Environment
Epidemics in Great Lakes attributed to Organochlorines
Chemical Formulae and Structures of DDT, DDE, DDD
DDT = C14H9Cl5 = 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane
DDE = C14H8Cl4 = 1,1-dichloro-2,2-bis(chlorophenyl)ethylene
DDD = C14H10Cl4 = 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane
Figure 1. The chemical structures of DDT, DDE, and DDD, respectively (from ATSDR).
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Synthesis of DDT
DDT is a white crystalline solid with no apparent odour or taste. It is a man-made organochlorine consisting of a
mixture of DichloroDiphenylTrichloroethane isomers. It is made by a reaction between chlorine gas and the double
benzene ring structure under optimal temperature and pressure conditions. When the two compounds are reacted, DDT
is formed easily because of the high reactivity of chlorine gas. DDE and DDD are also made in the same reaction and
often contaminate DDT, but are also both very toxic to living organisms.
Table 1. Chemical Properties of DDT.
Molecular Weight
Concentration in Gas Phase
Solubility in Water
Half-Life in Soil
Potential for Entry into Fresh Water
Aquatic Toxicity
Aquatic Persistence
Bioaccumulation Potential
355 g/mol
1.9 x 10-6 mg/L
Very Low (0.001-0.04 mg/L)
Approx. 2.8 yrs
Purpose, Uses of DDT
DDT was developed during the second World War to control a wide variety of insects. It was hailed as the "miracle
insecticide" and quickly became one of the most widely used pesticides in the world to control insects on agricultural
crops. It is also used to control insects that carry malaria, typhus, and other harmful diseases in third world countries.
The use of DDT was banned in the U.S.A. in 1972, although it is still being used in many underdeveloped countries.
Major Sources of DDT and its Route of Entry into Fresh Waters
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Figure 2. The Fate of DDT and Other Pesticides in the Environment.
The major source of DDT in water is agricultural run-off from fields that were once heavily sprayed with DDT for pest
control. Some DDT was also sprayed directly into lakes and streams through aerial spraying of crops. DDT binds very
strongly to soil particles and is very slow in reaching ground water, thus soil run-off is a key contributor to its
distribution to the aquatic environment. Industrial effluents and waste material from pesticide factories may also result
in DDT reaching aquatic environments. Some DDT evaporates from the soil and surface water into the air and some is
broken down by sunlight or by microorganisms in the soil or surface water. When DDT is broken down in soil, it
usually forms DDE or DDD. Levels of DDT in North America are due to contaminated sediments from lake bottoms
and tributaries due to runoff from sites of historical use, leaking landfill sites, illegal use of old stock, and long range
transportation through the atmosphere from countries still using DDT.
DDT builds up in plant tissues and in the fatty tissues of fish, birds, and animals. Most DDT enters the body through
ingestion of contaminated foods and sediments, but minute amounts may pass through the skin or lungs. DDT levels
increase in animals that are high on the food chain due to bioaccumulation.
Table 2. Ranges of Concentrations in Fresh Water, Sea Water, and Sediments
Lake Ontario Media (1989) (ppt or ng/kg)
Chemical Water
0.3-57 25000-218000 440000-1088000 40000
Herring Gull
63000-72000 620000-7700000 7700000-34000000
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Table 3. Threshold Levels for Toxicity of DDT
96 hr LC 50 for fish and other aquatic animals
Approximate Acute LD50
Lowest Chronic Value - Fish
Lowest Chronic Value - Daphnids
Lowest Chronic Value - Aquatic Plants
Lowest Test EC20 - Fish
Water Quality Guidelines (EPA)
1-30 ug/L
100 mg/kg
0.73 ug/L
0.016 ug/L
0.3 ug/L
0.35 ug/L
0.001 ug/L
Mechanism of Toxicity to Aquatic Animals
DDT is a hormone disrupter that mimics estrogen and binds to a cell's estrogen receptors, thus stimulating the
receptors and causing an imbalance in the normal levels and effects. It causes impaired reproduction in many species
of fish and other aquatic animals. DDT bioaccumulates in the fatty tissue of fish and other animals.
DDT can also affect the nervous system by altering action potentials through changes in the actions of the sodium
channels. It causes them to close very slowly and prolong each action potential sent in the nerve. This causes
excitation, spasms, and paralysis.
There is ongoing debate as to whether or not DDT is a carcinogen. Studies have been conducted on mice, humans, and
other animals, to determine the carcinogenicity of DDT. Large quantities of DDT have been fed to study animals
(including human volunteers), and no cancerous tumours have been found. Other studies have shown that DDT can
indeed cause tumours, especially in the liver. High levels of DDT and DDE have been found in some breast cancer
patients, but no conclusive evidence for a cause-effect relationship has been found. These contradictory findings fuel
the debate as to the role of DDT as a carcinogen.
Wildlife are harmfully affected by concentrations of DDT in the food chain. Marine birds, alligators, and turtles
produce eggs that have shells too thin for survival of the young. Male reproductive ability and behavioural changes are
also noticed and gender switching is very common. DDE inhibits the binding of androgens in male animals and
hinders male sexual maturity. Liver enzyme levels can also be negatively affected by DDT and its breakdown
products. The table below outlines many of the effects on wildlife thought to be attributed to DDT in the environment.
Table 4. Epidemics in Great Lakes Species Attributed to Organochlorines Like
Lake Trout
Population failure, embryonic mortality, biochemical changes.
Decreased head circumference, decreased birth weight, impaired psychomotor
Human Infants
development, impaired cognitive development
Nervous system damage, linked to breast cancer, decrease in liver enzyme levels,
Human Adults
harmful effects on reproduction, rashes and irritation
Population decline, failure to nest, adult sterility, embryonic and hatching mortality,
Bald Eagle
eggshell thinning, wasting syndrome
Population decline, eggshell thinning, reproductive effects, biochemical changes,
Double-Crested Cormorant
birth defects
Black-Crowned Night Heron Population decline, eggshell thinning, birth defects, biochemical changes
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Common Tern
Ring-Billed Gull
Caspian Tern
Snapping Turtle
Forsters Tern
Beluga Whale
Embryonic mortality, wasting syndrome, birth defects, feminization of male chicks,
liver enlargement, biochemical changes, behavioural changes
Eggshell thinning, embryonic mortality, birth defects, biochemical changes,
reproductive effects
Birth defects, die-offs, female-female pairing
Reproductive failure, birth defects, alternations in recruitment
Birth defects, failure to hatch
Embryonic mortality, birth defects, infant wasting syndrome, nocturnal abandonment
of eggs, biochemical changes
Immunosuppression, tumours, reproductive failure
Population decline, reproductive failure, wasting syndrome in offspring
Population decline
Recent Studies Concerning Environmental Toxicity to Fish
A recent study of DDT levels in the Great Lakes showed a decrease in the levels of DDT in both fish and in birds over
the last two decades. Lake Michigan lake trout showed a decline in the concentration of DDT in their tissues as early
as the 1970s. The total concentration of DDT in lake trout in Lake Michigan dropped from 19.19 to 1.39 ug/g in the
period from 1970 to 1990 (See Figure 2). Each of the other Great Lakes showed similar trends, although no significant
decline has been seen since the early to mid 1980s, except in Lake Huron. Smelt and salmon DDT levels have shown
similar declines. Lake Ontario consistently has had the highest levels of DDT in fish and levels in the United States
have been higher compared to those in Canada. This study also looked at the levels of DDT in the eggs of fish eating
birds and found the same trends in DDT decline to be true, with the thickness and health of the shells and eggs
increasing with lower DDT levels.
DDT is still found in the Great Lakes originating from lake bottom sediments, contaminated tributary sediments,
runoff from sites of previous use, leaking landfill sites, illegal use of old stocks, and transport in the atmosphere from
countries still using DDT.
Cleanup of DDT in the Environment
Many scientists have said that DDT is so stable that it may never be completely eliminated from the environment.
However, a new method of DDT cleanup is being explored using supercritical CO2. Under extreme pressure and
temperature, CO2 is capable of acting as a solvent to dissolve DDT, and may be used to clear DDT from contaminated
soils. The cost of this process, however, may hinder it from ever being used to its full potential.
Agency for Toxic Substances and Disease Registry (ATSDR) - Public Health Statement
Britt, R. Decaffeinated DDT: Common process may decontaminate soil
Cotnoir, A.E. DDT: The Controversy
Hellawell, J.M. (1988). Toxic substances in rivers and streams. Env. Poll. 50: 61-85.
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McDonald, D.G. Toxicology of Aquatic Environments: Class Notes for Biology 4S03 at McMaster University,
Hamilton, Ontario, Canada, 1996. (A5,A7,A11,A31,B47,C10)
Organochlorine Pesticides
Resource Book for Biology 4S03 at McMaster University, Hamilton, Ontario, Canada
Smolen, M. Endocrine Disruption: Emerging Threats
The State of Toxic Contaminants in the Great Lakes
Suter, G.W. II. (1996). Toxicological benchmarks for screening contaminants of potential concern for effects on
freshwater biota. Env. Tox. and Chem. 15. 1232-1241.
Webster, T. et al. DDT.
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