Environmental Engineering Reference
In-Depth Information
H
H
Cl
Cl
Cl
H
Cl
Cl
Cl
Cl
Cl
Cl
DDE
DDMU
DDNU
1,1-dichloro-
2,2-bis(p-chlorophenyl)ethylene
2,2-bis(p-chlorophenyl)ethylene
1-chloro-
2,2-bis(p-chlorophenyl)ethylene
H
H
H
OH
O
OH
H
H
H
H
H
Cl
Cl
Cl
Cl
Cl
Cl
DDA
2,2-bis(p-chlorophenyl) acetic acid
DDOH
2,2-bis(p-chlorophenyl)ethanol
DDNS
2,2-bis(p-chlorophenyl)ethane
Ring Dechlorination
OH
O
H
H
H
Cl
Cl
Cl
Cl
Cl
Cl
DCB
DBH
DDM
2,2-bis(p-chlorophenyl) methane
2,2-dichlorobenzophenone
2,2-bis(p-chlorophenyl)hydrol
Ring Opening
Fig. 2
Proposed degradation pathways for anaerobic degradation of DDE.
Reprinted from
Chemosphere, Vol. 62, T. Eggen and A. Majcherczyk, Effects of zero-valent iron and temperature
on the transformation of DDT and its metabolites in lake sediment, 1116-1125, with kind permission
from Elsevier, 2006.
Laboratory experiments have demonstrated that the conversion of DDE to
DDMU has occurred under methanogenic and sulfidogenic conditions, although the
presence of sulfate and low temperatures did lower the rate of degradation (Quensen
et al. 1998, 2001). The biotransformation of DDE in anoxic sediments has been
confirmed to occur in at least one other site (Huang et al. 2001). Batch reactor
experiments using alternating aerobic and anaerobic conditions found very little
DDE degradation after 105 d (Strompl and Thiele 1997). However, a batch reactor
using a mixed culture with surfactants, Triton X-114 or Brij 35, in conjunction with
reducing agents, Na
2
S or cysteine HCl, did reduce DDE concentration, although not
as much as DDT or DDD was degraded. It was assumed that the greater degradation
was caused by the surfactant solubilizing the DDE, making it more bioavailable. The
lower amount of DDE degradation than that observed for DDT and DDD was
assumed to be because DDE binds more strongly to the soil particles (You et al.
1996). It should be noted that in anaerobic microcosm experiments with cellulose
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