A TALE OF THREE CHEMICALS
DDT, PCB, and DIOXIN

All three of the chemicals (DDT, PCBs, and Dioxin) have chemical similarities

They are all organochlorine compounds
(i.e., made up of the elements CARBON and CHLORINE)

They are persistent (i.e., they persist in the environment for several years)

They are non-polar (i.e., water-hating)

They bioaccumulate (i.e., they concentrate in the fat of organisms, and their concentration increases as one moves up the food chain)

They are causing a toxic effect at low concentrations

DDT at parts per million
Dioxins at parts per trillion

3963 miles = 20924640 feet = 251095680 inches
How much is a part per trillion?
one part per trillion of this is 0.0025 inches

They differ in the way they were released into the environment

DDT-Applied as a pesticide
PCBs- Industrial chemical
Dioxins-Were never manufactured

DDT

• Discovered as an insecticide in 1939
  • Used extensively in World War II
• Cheap, effective against many insects (broad spectrum), and persistent
• Decline of bird populations associated with DDE, a metabolite of DDT
  • DDE interferes with calcium transport, resulting in eggshell of poor quality
    • causing near extinction in several bird species
    • causing near extinction of alligators in Lake Apopka, Florida
  • Many bird populations have recovered, however, there are still populations which are effected by DDT
• Banning of DDT in the US in 1972 (most other industrial nations by 1980)
• Still used in developing nations

PCBs

Polychlorinated biphenyls

• Manufactured in the US from 1930-1977
  • Over 1 million tons made
• Wide spectrum of toxic effects
  • Chloracne, immune suppression, embryonic mortality, mutagenic
• Several cases of widespread poisoning
  • Yusho oil
  • Marine mammals
• Some PCB compounds have been reported to act in a manner similar to Dioxins

PCDDs and PCDFs

• Never "made"
• Generally industrial by-products created during the manufacture of other compounds.
  • Agent Orange
• Not produced, therefore it is not regulated
• Estimates of emissions do not match the amounts being measured; there must be other, unaccounted for sources
• One of the most toxic organochlorine compounds, however species sensitivities vary greatly
• Some PCDD, PCDF, and PCB congeners are very similar in structure and mode of toxic action
  • Toxic equivalence factors are a way to asses the total dioxin-like toxicity

Positive

Banning of DDT and the recovery of many bird populations
Elimination of the formation of dioxins in the bleaching of paper

Negative

Of the one million tons of PCBs made:

65% is still in use or in land fills
31% is in the environment
4% has been incinerated

Literally thousands of new compounds produced every year