acid were converted by f-oxidation to products with an even number of 
carbons (Levey and Lewis, 1947; Webley et al., 1955, 1957, 1958; Gutenmann 
et al., 1964a, c). A second mechanism involved cleavage of the ether linkage 
(Canny and Markus, 1960; MacRae et al., 1963a b, 1964; Audus, 1964; 
Bocks et al., 1964). 
Evidence has been obtained that 2,4-D is dissimi lated by a variety 
of microorganisms (Reid, 1960; Alexander and Aleem, 1961) through 2,4- 
dichlorophenol and 4-chlorocatechol and that MCPA is dissimilated through 
4-chloro-2-cresol (Audus, 1952b). MCPB was degraded by the bacteria 
Nocardia opaca via crotonic and B-hydroxy acid to 2,4-D (Webley et al., 
1957, 1958). A product from the degradation of 2,4-D by bacteria of the 
genus Pseudomonas has been identified as B-chloromuconic acid. A second 
species of Pseudomonas gave rise to a-chloromuconic acid (Fernley and Evans, 
1959). Pure cultures of a Nocardia species and an Achromobacter strain 
of bacteria rapidly degraded 2,4-D and the presence of 2,4-dichlorophenol, 
chlorohydroquinone, a monochlorophenol, an unchlorinated phenol, and three 
other unidentified compounds have been demonstrated (Newman and Thomas, 
1950; Audus, 1951; Bell, 1957, 1960; Steenson and Walker, 1957, 1958; 
Faulkner and Woodcock, 1961; Taylor and Wain, 1962). The main product of 
2,4-D metabolism by the mold Aspergillus niger van Tiegh was 2,4-dichloro- 
5-hydroxyphenoxyacetic acid. By means of infrared and mixed melting points, 
a second metabolite was identified as the 2,5-dichloro-4-hydroxyphenoxy- 
acetic acid - the first time such a rearrangement was reported (Faulkner 
and Woodcock, 1964, 1965). Another unidentified acid, not the 3- or 6- 
hydroxyacid, was also found. Under similar conditions, MCPA gave rise to 
64 
