DDE Remediation and Degradation - Reviews of Environmental Contamination and Toxicology - page 60

Although the proposed pathway for DDE appears to be fairly complete, there
are very few reports of isolated bacterial or fungal cultures that can fully degrade
it to CO 2 (Table 3). The pure aerobic cultures of Pseudomonas acidovorans ,
Alicaligenes eutrophus , and Terrabacter sp. that could degrade DDE came from
liquid cultures that used the cometabolism of biphenyl to obtain the enzymes
required (Aislabie et al. 1999; Hay and Focht 1998; Nadeau et al. 1998). Biphenyl-
grown cells induced the production of biphenyl dioxygenase that catalyzed the
degradation of DDE through meta-fission of the phenyl rings. However, not all
cultures that are capable of producing biphenyl dioxygenase are capable of
degrading DDE. The use of structural analogues to DDE, such as 4,4'-dichlorobi-
phenyl and 1,1-dichloroethylene, led Megharaj et al. (1997) to conclude that the
recalcitrance of DDE to degradation by monooxygenase and biphenyl 2,3-dioxy-
genase enzymes produced by Rhodococcus globerulus , Psuedomonas fluorescens ,
Mycobacterium vaccae , and Methylosinus trichosporium may be the result of the
1,1-diphenylethenyl structure, rather than the extent of chlorination found in DDE.
Other factors that may inhibit DDT and DDE degradation include metal content,
such as elevated copper (Gaw et al. 2003) and arsenic (Van Zweiten et al. 2003)
in the soil. The elevated arsenic levels resulted from its use in cattle-dipping vats
as a tickicide. Arsenic was later replaced by DDT (Van Zweiten et al. 2003). The
elevated copper levels found in orchard soils probably resulted from its use as a
fungicide (Gaw et al. 2003).
Extracellular lignolytic enzymes produced by white rot fungi, Phanerochaete
chrysosporium and Pleurotus pulmonarius , have been shown to be effective in
degrading DDE (Bumpus et al. 1993; Gong et al. 2006). The Phanerochaete
chrysosporium required nitrogen-limited cultures to effectively degrade DDT
and DDE (Bumpus et al. 1993); however, Pleurotus pulmonarius, which secretes
lignolytic enzymes under nitrogen-rich or -deficient conditions, degraded 78%
of 10 mg DDE /kg soil within 5 wks (Gong et al. 2006). Wood-rotting basid-
omycetes are not the only type of fungi capable of degrading DDE. Genetically
improved strains of Fusarium solani have been developed by parasexual hybrid-
ization from native fungi that slowly metabolize DDT, DDD, and DDE in soil
(Mitra et al. 2001). Degradation by lignase enzymes from fungi can be inhibited
by metal chelates such as EDTA and tetramethylethylenediamine (Aislabie et al.
1997).

IV Anaerobic Degradation and Remediation

Flooding soil can lead to anaerobic conditions, which have been shown, in
some cases, to inhibit mineralization of DDT and DDE (Boul 1996; Xu et al.
1994). Until 1998, there was no convincing evidence to support reductive
dechlorination of DDE (Quensen et al. 1998, 2001). The proposed reductive
dechlorination pathway (Fig. 2) from DDE leads to DDMU (1-chloro-2,2-bis
(p-chlorophenol)ethene).