DichloroDiphenylT

1
DichloroDiphenylT
Alan Yanahan CPSC 270, 2009
richloroethane

• An Organochlorine

2
History

• First synthesized by Othmar Zeidler in 1874
• German graduate student in chemistry
• Interested in the compounds structure and was
  unaware of its insecticidal properties
• His creation was later put on a shelf and
  forgotten until

3
History

• its rediscovery in 1939 by Paul Müller
• Swiss entomologist working for J.R. Geigy AG in
  Basel, Switzerland
• Wanted a long-lasting pesticide for use against
  the clothes moth
• Awarded Nobel Prize
• in Medicine in 1948
• because of DDTs
• role in the control of
• insect vectored diseases

4
Medical Targets of DDT

• Anopheles mosquitoes transmit malaria
• Aedes mosquitoes transmit yellow fever

5
Medical Targets of DDT

• Oriental rat flea (Xenopsylla cheopis ) transmits
  plague
• Human body louse (Pediculus humanus) transmits
  epidemic typhus

6
DDT during WWII

• The United States sprayed DDT in military
  installations, ports, and transportation centers
  to control malaria
• Soldiers were dusted with DDT to control epidemic
  typhus

7
Agricultural Targets of DDT
Corn Earworm
Codling Moth
Colorado Potato Beetle
8
DDT Today

• All usage in United States ceased when
  Environmental Protection Agency banned DDT use on
  January 1st, 1973
• DDT deemed an environmental hazard
• Long residual life
• Biological magnification
• Particularly harmful to birds

9
DDT Today

• Still used in some developing countries in Africa
  and Asia to control malaria
• Sprayed sparingly on interior and exterior of
  walls to deter and kill mosquitoes

10
How Does DDT Work?
11
Mode of Action

• DDT is thought to interact with voltage-gated
  sodium channels that line the axon of nerve cells
• However, the mode of action is not entirely
  worked out

12
Mode of Action

• Under normal circumstances, axons carry messages
  from one nerve cell to another via electrical
  impulses (action potentials)
• This occurs as follows

13
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
This causes that region of the axon to repolarize
But during that time, the sodium ions have
migrated further down the axon
More potassium ions exit the axon
Voltage gated sodium channel opens when the nerve
cell receives a stimulus
Another voltage gated sodium channel opens
Na
Voltage gated potassium channel opens
Exterior of the axon is positively charged with
respect to the interior
Voltage gated sodium channel closes
Voltage gated sodium channel closes
Na
Voltage gated potassium channel closes
This causes a region of the axon to depolarize
Na
Na
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_



























































_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_





























K
Na
Na
K
K
Axons interior is negatively charged with
respect to the exterior
Voltage gated potassium channel opens
K
More sodium ions enter the axon to further
depolarize neighboring regions
This causes the neighboring region of the axon to
depolarize
Sodium ions (Na) enter the axon
Potassium ions (K) exit the axon
This region of the axon repolarizes
K
K
Voltage gated potassium channel closes
K
K
K
14
Mode of Action

• When DDT is present, it causes the voltage-gated
  sodium channel to remain open longer
• Spontaneous nerve impulses are generated
• Leads to muscle twitch, convulsion, and death
• Occurs as follows

15
Na
Na
Na
Na
Na
Na
Na
Na
Na
But during that time, the sodium ions have
migrated further down the axon and more sodium
ions have entered the axon
Na
DDT interacts with the voltage gated sodium
channel stabilizing it in the open state
while sodium ions continue leaking into the axon
to generate false action potentials
Na
Na
this region is depolarizing and repolarizing
This causes that region of the axon to repolarize
Voltage gated sodium channel opens when the nerve
cell receives a stimulus
Na
The exterior of the axon is positively charged
with respect to the interior
Na
This causes a region of the axon to depolarize
Na
Voltage gated potassium channel opens
Na
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_










































































_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_













































Na
K
Na
Na
Na
K
K
K
The axons interior is negatively charged with
respect to the exterior
Sodium ions (Na) enter the axon
Potassium ions (K) exit the axon
Voltage gated potassium channel closes
As this region is depolarizing and repolarizing
K
K
K
K
K
16
Sources

• Kreiger, Robert I. Handbook of Pesticide
  Toxicology 2nd Edition Agents. Smith, Andrew G.
  Chapter 60DDT and its Analogs. San Diego
  Academic Press, 2001.
• Silverthorn, Dee Unglaub. Human Physiology An
  Integrated Approach 4th Edition. San Francisco
  Pearson Education Inc., 2007.
• Ware W., George. Pesticides Theory and
  Application. New York W.H. Freeman and Company,
  1978.