2,4-D and Related Compounds 
MCPA [4-Chloro-2-methylphenoxyacetic acid] 
Arthrobacter sp. and flavobacterium peregrinum degraded MCPA to 
4-Chloro-2-methylphenol, The flavobacterium further oxidized the phenol 
to release all chloride (48, 133, 894). Aspergillus niger van Tiegh also 
metabolized MCPA to 4-chloro-2-methyl-5—-hydroxyphenoxyacetic acid (439, 
440). 
In other studies, a gram-negative soil bacterium metabolized MCPA 
to 5-chloro-o-cresol, a compound believed to be 6-hydroxy-—MCPA and a— 
methyl-y-carboxymethylene-A -butenolide. A pathway for microbi¢l 
degradation was suggested (529). 
Ultraviolet (3407 to 3888 Angstroms) activated MCPA (1137). 
Enzymes from an arthrobacter species catalyzed the removal of the side 
chain with formation of 2-methyl-4-chlorophenol [5-—chloro-o-cresol] (I) 
(1679). 
QH 

(I) butenolide 
MCPB [4-(4-Chloro-2-methylphenoxy) butyric acid] 
Degradation of compounds related to 2,4-D has also been studied 
(1460). MCPB gave rise to MCPA when fed to dairy cows (65, 66, 67). 
Aspergillus niger and Nocardia opaca degraded MCPB to MCPA and 
4-( 4-chloro-2-methylphenoxy)-3-hydroxybutyric acid (441, 1468, 1469). 
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