Case Study: Environmental History of DDT

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Case Study Environmental History of DDT

• Topic 3

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Concepts to learn

• History of DDT as an example of uncontrolled use
  of a chemical substance
• Physiological and biochemical mechanisms of DDT
  effects in birds
• The roles of public, government, science and
  industrial groups in environmental legislation
• Lessons for the future?

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DDT (p,p- dichloro-diphenyl-trichloroethane)

• First synthesized in 1874 by Zeidler, insecticide
  properties discovered only in 1938 by Müller and
  colleagues

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Benefits of DDT

• Highly specific neurotoxicity for insects and
  extremely low toxicity to humans and mammals
• Cheap synthesis (therefore available for use in
  developing countries)
• Highly persistent so that it continues to kill
  insects for months after application
• Used to virtually eliminate malaria, dengue fever
  and filariasis
• Estimated to have saved about 50 million human
  lives and to have prevented more than a 1,000
  million human illnesses

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Success of DDT in controlling malaria
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Glory years of DDT

• 1945-1960 used to control disease-carrying
  insects and agricultural pests
• 1948 Müller received Nobel Prize in Medicine for
  discovery of insecticide properties of DDT
• Discovery of other chlorinated insecticides
• Chlordane, mirex, dieldrine, lindane,
  methoxychlor, etc.
• Massive insect-controlling projects
• Gypsy moth (MA, 1954-1958), fire ants
• Increased DDT production
• 1953 38,000,000 pounds
• 1957 84,000,000 pounds
• 1959 125,000,000 pounds

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Silent Spring

• Published in 1962
• Written by Rachel Carson, a respected marine
  biologist
• An expose of the damage to the environment from
  indiscriminate use of chlorinated pesticides

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Silent Spring

• Over increasingly large areas of the United
  States spring now comes unheralded by the return
  of birds, and the early mornings are strangely
  silent where once they were filled with the
  beauty of bird song
• Rachael Carson (1962)
• Silent Spring

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Ecological effects of DDT

• Decline in populations of raptors associated with
  egg thinning in turn associated with DDT and DDE
  accumulation
• Average shell weight in peregrine falcon
• Pre-DDT (1900-1946) 3.8 g
• Post-DDT (1950-1967) 3.1 g
• Decrease in hatching success due to eggshell
  breakage (only thinning of 10 or more has
  reproductive consequences)
• Other chlorinated hydrocarbons (dieldrin, PCBs)
  may have contributed to the observed effects

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Experimental support for causality between DDT
exposure and shell thinning

• Ratcliffe (1970) close correlation between
  eggshell thickness and residue levels of DDT in
  14 species of birds including raptors and
  fish-eating birds
• Hickey and Anderson (1967) correlation between
  eggshell thickness and residue levels of DDT in
  Larus argentatus
• Johnston et al. (1996) 15 decrease in eggshell
  thickness in peregrine falcon breeding in
  Canadian Arctic due to DDt exposure
• Lundholm (1997) - laboratory exposure to DDT and
  DDE resulted in 19-26 decrease in eggshell
  thickness in ducks

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Different species have different sensitivity to
DDT

• Highly sensitive (30 or more thinning)
  peregrine falcon, brown pelican, some ducks,
  gulls
• Intermediately sensitive (5-15 thinning)
  Japanese quail, American kestrel
• Insensitive species (no thinning) domestic
  fowl, Bengalese finch

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Problems of DDT

• Persistency in organisms and the environment
  (biological half-life 8 years)
• Considerable environmental transport
• Lipid solubility
• Chemical resistance to biotransformation into
  water soluble compounds, which may be excreted
• Bioaccumulation

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Biotransformation of DDT
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Bioaccumulation of DDT and its derivatives
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Mechanisms of eggshell formation
From Bakst (1998) JEB
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Mechanisms of eggshell thinning
Blood
Mucosa
Lumen
H
H
HCO3-
CO32-
CO2H2O ? H2CO3 ? H HCO3-
CaCO3H
Ca2
Ca2
PhL ? AA ? PGE2
HCO3-
p,p-DDE
Cl-
Cl-
Cl-
Ca2
Ca2
Ca2
Ca2
K
K
Na
Na
Na
Na
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Other problems

• Technical DDT
• 80 p,p-DDT neurotoxic to insects, low
  toxicity to humans and mammals, no obvious
  estrogenic or carcinogenic effects
• 20 o, p-DDT estrogenic and possibly
  carcinogenic effects in mammals and birds

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Milestones towards the DDT ban (1972)

• Scientific Advisory Committee convened by the
  President
• Madison Conference (1965)
• Environmental Defense Fund (1967)
• Creation of EPA (1969)
• EPA bans DDT (1972)

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Impact of Silent Spring

• Call for a new attitude toward nature and
  recognition of the possibly destructive effects
  of humanitys action on the environment and
  associated responsibility
• Birth of the environmental movement in the USA

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DDT the end of story?

• The return of the sting

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Pre- and post-DDT ban distribution of malaria in
South America
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Africa

• The use of DDT in the 1940s and 1950s almost
  eliminated the mosquitoes that carry the parasite
  that causes malaria.
• Post-DDT ban Malaria rates in Africa are now
  higher than they are ever known to have been,
  except for Swaziland where DDT use was never
  stopped

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Pre- and post-DDT ban distribution of Aedes
aegypti
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Pre- and post-DDT ban distribution of hemorrhagic
fever
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Future for DDT?

• WHO, Greenpeace, and the World Wildlife Fund
  (WWF) met in December 2000 in Johannesburg and
  WWF and Greenpeace have suspended their arguments
  against the use of DDT in malarial areas,
  provided application is limited to indoor
  spraying, particularly on to wall surfaces, to
  protect people, minimizing environmental effects

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Take-home messages

• Write down three most important things you have
  learned from the environmental history of DDT
  application and ban.