1,2,4-Trichlorobenzene (1,2,4-TCB) is a colorless liquid with pleasant odor. Its solubility in water is moderate. 1,2,4-TCB has various uses in industry such as a carrier to apply dyes to polyester materials, a heat transfer medium, a degreaser and a lubricant. It also functions as a termite pesticide and an aquatic herbicide. About 93% of 1,2,4-TCB entering the environment through industrial discharges eventually evaporates into atmosphere, about 2.6% and 2.4% leave in terrestrial soil and aquatic sediments respectively, the rest end up in water. 1,2,4-TCB has been found to bioaccumulate in fish tissues. It has high acute toxicity to plants and aquatic life, its chronic toxic effects to aquatic life are also high.
The complete microbial mineralization of 1,2,4-TCB as a sole carbon and energy source under aerobic conditions has been observed. The proposed pathway shows that at first 1,2,4-TCB is biodegraded to the corresponding chlorinated catechol by means of dioxygenase and dehydrogenase system, and then channeled into the tricarboxylic acid pathway through ortho cleavage (van der Meer et al., 1991). Under anaerobic conditions, some methanogenic microbial consortia are capable of reductively dechlorinating 1,2,4-TCB to chlorobenzene via 1,4-dichlorobenzene (Middeldorp PJM, De Wolf J, Zehnder AJB, Schraa G Applied and Environmental Microbiology (1997) 63: 1225-1229). The aerobic 1,4-Dichlorobenzene Pathway is documented elsewhere in the UMBBD.
The following is a text-format 1,2,4-trichlorobenzene 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 (16k) format.
from the 1,2,3,4,5,6-Hexachloro cyclohexane Pathway | | | | 1,2,4-Trichlorobenzene <-------+ +------> 1,2,4-Trichlorobenzene Burkholderia sp. P51, PS12 methanogenic microbial consortium | | | | | chlorobenzene dioxygenase | 1,2,4-trichlorobenzene | | reductive dehalogenase | | v v from the 3,4,6-Trichloro-cis- 1,4-Dichlorobenzene <------- 1,4-Dichlorobenzene 1,2-dihydroxycyclohexa-3,5-diene | Pathway | | | cis-1,2-dihydrobenzene | 1,4-dichlorobenzene | 1,2-diol dehydrogenase | reductive dehalogenase | | | v v Chlorobenzene 3,4,6-Trichlorocatechol | | | | | | catechol 1,2-dioxygenase | | | | v v to the 2,3,5-Trichloromuconate Chlorobenzene Pathway | | | chloromuconate cycloisomerase | | v 2,5-Dichloro- carboxymethylenebut-2-en-4-olide | | | dienelactone hydrolase | | v 2,5-Dichloro-4-oxohex-2-enedioate | | | maleylacetate reductase | | v 2-Chloro-3-oxoadipate | | | 2-chloro- | 3-oxoadipate | hydrolase | | v Succinate + Chloroacetate | | | | | | | | | | v v Intermediary to the Metabolism(KEGG) 1,2-Dichloroethane Pathway
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