Degradation of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 72

S

P

O

C = O

H 3 CH 2 CO
H 3 CH 2 CO

O O

O

Cl

Cl C

CH 3

CH 3

S

P

OH

HO

HO

Dichlorvos (DDVP) : By microbial degradation, DDVP forms desmethyldichlorvos, which
on hydrolysis forms phosphate and carbon dioxide.
Methidathion : Microbial degradation is the dominating route for methidathion degrada-
tion in soil and water. The degradation occurs via isomerization, hydrolysis, and oxidation.

3.4.3 Organochlorine Pesticides

Microbial degradation of organochlorine pesticides occurs by Pseudomonas , Moraxella sp.,
Actinobacter , etc. Hydrolytic cleavage and dechlorination are the two major mechanisms of
microbial degradation.
Generally, methylated and halogenated aromatics are dissimilated via oxygenases. However,
nucleophile attack catalyzed by dehalogenases has also been reported. Bacteria transform aro-
matic compounds into dihydroxy derivatives, which serve as substrates for oxygenolytic cleavage
of the aromatic ring. Chlorophenoxy acids (2,4-D, 2,4,5-T, 2-methyl-4-chlorophenoxy acetic acid
(MCPA)) are degraded by bacteria such as Pseudomonas sp., Arthrobacter sp., Mycoplana sp., and
Flavobacterium . The degradation of 2,4-D occurs via cleavage of the ether linkage between oxy-
gen and the aliphatic side chain to form 2,4-dichlorophenol and glyoxalate. 2,4-Dichlorophenol
is degraded to succinic acid via ketoadipate. MCPA is also metabolized by Pseudomonas sp. and
Arthrobacter sp. through an oxidative cleavage. 2,4,5-T undergoes mineralization by Pseudomonas
cepacia to form 2,4,5-trichlorophenol, which is degraded to succinate derivative.

Cl C Cl

Cl

Cl C

Aerobic

Cl DDE

Cl Cl

C

Cl

Cl CH

DDT

H

Anaerobic

Cl C Cl

Cl

Cl CH

DDD