1,1,1-Trichloro-2,2-bis-(4'-chlorophenyl)ethane (DDT), the first chlorinated organic insecticide, is a widely distributed and persistent xenobiotic contaminant in the environment. DDT is not metabolized very rapidly by animals; instead, it is deposited and stored in the fatty tissues. The biological half-life of DDT is about eight years; that is, it takes about eight years for an animal to metabolize half of the amount it assimilates. If ingestion continues at a steady rate, DDT builds up within the animal over time. Despite being banned in the United States, DDT continues to be widely used in many developing nations.This page shows only its anaerobic pathway. The aerobic degradation of DDT is documented elsewhere in the EAWAG-BBD.
The steps labeled A, D, E and F are mutiple steps whose intermediates are not identified yet. Step E and its successor steps degrade DDM aerobically. The steps labeled B and C may be non-enzymatic reactions (Wedemeyer G Applied Microbiology (1967) 15: 569-574; Matsumura F and Benezet H (1978) Microbial Degradation of Insecticides in Pesticide Microbiology (Ttill IR and Wright SRL) New York: Academic Press P640).
The following is a text-format DDT pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (20K) format.
1,1,1-Trichloro-2,2- 1,1,1-Trichloro-2,2-
bis(4'-chlorophenyl)ethane bis(4'-chlorophenyl)ethane
(DDT) (DDT)
Synechococcus sp. Klebsiella pneumoniae subsp.
Proteus vulgaris |
| |
| |
| | DDT dehydrochlorinase
V A |
| |
| |
V V
1,1-Dichloro-2,2- 1,1-Dichloro-2,2-
bis(4'-chlorophenyl)ethane bis(4'-chlorophenyl)ethylene
(DDD) (DDE)
| from the |
DDD dehydro- | +---- Aerobic Pathway |
chlorinase | | |
| | V
| | to the
V V Aerobic Pathway
1-Chloro-2,2-
bis(4'-chlorophenyl)-
ethylene (DDMU)
|
| DDMS
| dehydrogenase
|
V
1-Chloro-2,2-
bis(4'-Chlorophenyl)- ---------------------------------------------+
ethane (DDMS) |
| |
| |
| DDMS dehalogenase DDMS |
| dehydrochlorinase |
| DDNU |
V hydratase V
2,2-bis(4'-Chlorophenyl)- <---------------------------- unsym-bis(4'-Chlorophenyl)-
ethanol (DDOH) ethylene (DDNU)
|
|
V F
|
|
V D
bis(4'-Chlorophenyl)acetate ---------------------------> 4,4'-Dichlorobenzophenone
(DDA) (DBP)
|
|
| DDA decarboxylase
|
|
V
bis(4'-Chlorophenyl)methane
(DDM)
|
|
V E
|
|
V
4-Chlorophenylacetate
|
|
|
|
V
to the
L-Tyrosine Pathway
Page Author(s): Jingfeng Feng and Michael Turnbull
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