Ashley Watts
Aquatic Toxicology
Physical & Chemical Properties
• 1,1,1-trichloro-2,2-bis-(p-chlorophenyl) ethane
• Technical grade DDT
–
–
–
–
65–80% was the active ingredient, 4,4’-DDT
15–21% of the nearly inactive 2,4’-DDT
4% of 4,4’-DDD
1.5% of 1-(p-chlorophenyl)-2,2,2-trichloroethanol
• Degrades into 2,4’-DDE, and 2,4’-DDD 4,4’-DDE
Physical & Chemical Properties
Physical & Chemical Properties
Half-life
3-10
years
• Discovered in 1939
• U.S. used in WWII
– Control vectors of
malaria and typhus
• 1945 - Agricultural
pesticide for 30 years
– 1.3 billion pounds used
• 1959 – use declined
greatly
• 1974 – banned
DDT Timeline
Degradation Pathway
DDT
DDE
DDD
Environmental/Organismal Entry
• Introduced as a powder, emulsion, encapsulation
• Long term persistence in soil
– Dispersed via runoff
– Erosion
– Volatilization
• Solubility in lipids results in concentrated amounts in
aquatic organisms
• Biomagnification results in all levels of the food chain
being affected
Biomagnification
DDT and DDE are
readily stored
in fats of
vertebrates
Toxic Effects
• Insects
– Death
• Fish
– Reproductive effects
– Neurotoxin effects
• Birds
– Eggshell thinning
• Mammals
–
–
–
–
Localized liver and kidney damage
Neurotoxin effects
Teratogenic effects (mice)
Carcinogenic effects are likely
Molecular Interactions
• How it kills insects
– Na ion channels stay open, resulting in random neuron fire
and death “DDT Jitters”
– Those with a mutation or up-regulated CYP-450 genes are
resistant
• DDE mimics the action of estradiol causing a decline in
androgen synthesis in some vertebrates
• DDE inhibits the Ca2+ -ATPase or Ca2+-Mg2+ ATPase
activity in the eggshell gland
Biochemical Breakdown and Removal
• DDE and DDD formed
– In the presence of NADPH and NADH
– In anaerobic conditions
• Dechlorination is catalyzed enzymatically by
cytochrome P450
• DDT and DDE are further oxidized to form DDA
which is the major excreted product in
animals.
Detoxification
• Insects
– DDTase can render the compound
more water soluble. DDT -> DDE
• Mammals
– DDT is dehalogenated to DDD and
DDE is produced also in small
amounts
– DDD is produced and stored in
liver
– DDE found excreted in milk
• Fish
– DDT is highly resistant to
metabolism and very little is
excreted
References
• Agency for Toxic Substances & Disease Registry
http://www.atsdr.cdc.gov/toxprofiles/tp35-c4.pdf
• DDT Regulatory History: A Brief Survey (to 1975)
http://www.epa.gov/history/topics/ddt/02.htm
• Davies, T. Field, L., Usherwood, P., Williamson, M. 2007. DDT, Pyrethrins, Pyrethroids and Insect
Sodium Channels. Life, 59(3): 151 – 162.
• Lundholm, C. 1997. DDE-Induced Eggshell Thinning in Birds:Effects of p,p’-DDE on the Calcium and
Prostaglandin Metabolism of the Eggshell Gland. Comp. Biol. Physiol. Vol. 118C, No. 2, pp. 113128.
• Kitamura, S. Shimizu, Y., Shiraga, Y., Yoshida, M., Sugihara, K.,Ohta,S. 2002. Reductive Metabolism
ofp,p′-DDT ando,p′-DDT by Rat Liver Cytochrome P450. DMD,30.2.113.
• Low, W.Y. et al. Recognition and Detoxification of the Insecticide DDT by Drosophila melanogaster
Glutathione S-Transferase D1. J. Mol. Biol. (2010) 399, 358–366,
• Whiting, F. Et al. 1968. Detoxification of DDT by the Perfused Bovine Liver. Journal of Dairy
Science. 51.10, 1612-1615.
• Wang, X., Wang, W. Uptake, absorption efficiency and elimination of DDT in marine phytoplankton,
copepods and fish. Environmental Pollution 136 (2005) 453e464.
• Loomis &Thomas. Effects of Estrogens and Xenoestrogens on Androgen Production by Atlantic
Croaker Testes In Vitro: Evidence for a Nongenomic Action Mediated by an Estrogen Membrane
Receptor.. April 1, 2000 vol. 62 no. 4995-1004.