DDE Remediation and Degradation - Reviews of Environmental Contamination and Toxicology - page 63

DDT, a large amount of DDE was generated (Pirnie et al. 2006). Eggen and
Majcherczyk (2006) used DDT contaminated and naturally aged sediments with
zero-valent iron at two different temperatures, 9°C and 22°C, under anoxic condi-
tions. Under these conditions, some degradation of DDE occurred in the initial
10- to 20-week incubation time at 22°C then remained constant up to 40 weeks,
whereas there was no transformation at 9°C. The difference in DDE degradation
between the microcosms with and without Fe° was not significant. Using acidic
rice paddy soil spiked with p , p '-DDT, Yao et al. (2006) reported that Fe° or Fe° +
Al 2 (SO 4 ) 3 exhibited an initial 25%-35% decrease in p , p '-DDE in the first week,
a return to the initial concentration after 2 wk, and, finally, a dramatic decrease in
the following 3 wk with the final concentration of p,p '-DDE at 60% of the original.
However, the effect of these adjuncts was complicated by the observation that
the control removed more extractable p , p '-DDE than the treated samples.
In contrast to the Fe ° systems, which can take days to weeks and leave residual
DDE, the complete removal of DDT within 10 min was observed for an acidified
aqueous system treated with palladium/magnesium (Mg°/Pd +4 ) particles under
ambient temperatures and pressures with no DDE residues detected (Engelmann et al.
2001). Palladized magnesium has also been used to dechlorinate more than 99%
extractable DDT from soil as well as 88% of DDE from a soil slurry made from 1 g
soil spiked with 50

g DDE and aged 30 d (Gautam and Suresh 2006). More com-
plex supported-catalyst systems have been developed involving Pd /C, Pt /C, or the
more inexpensive Raney-Ni catalyst (1:1 Ni/Al alloy) to degrade DDT and its
metabolites (Zinovyev et al. 2005). The complexity results from the two-phase
organic/aqueous liquid system, which requires a quartenary ammonium salt and
KOH to act as a promoter/carrier. When KOH and a quartenary ammonium salt are
present, DDE is rapidly dechlorinated and the ethylene double bond is reduced.
Another Pd/C catalyst system that can rapidly degrade DDE involves the addition
of triethylamine and hydrogen under ambient pressure and temperature. The
authors claim that this catalyst system is simple, effective, reliable, and inexpensive
(Monguchi et al. 2006).
Titanium dioxide has been used as a catalyst in the degradation of DDT, DDD,
and DDE by UV light in soil (Quan et al. 2005). The photodegradation rate
increased with an increase in pH and photon flux rate, but decreased with an
increase in humic acid content of the soil. It was hypothesized that the humic acid
either reduced the amount of light reaching the TiO 2 or that the humic acid
quenched the radicals responsible for oxidizing the contaminants. p , p '-DDE, p , p '-
DDD, and DDMU were all reported to be degradation products, but all compounds
were further degraded by TiO 2 and UV light. DDT can be degraded by UV light
without TiO 2 in aqueous system that contains a surfactant such as Brij 52; however,
DDE and DDD are the resulting products (Chu 1999). DDE was found to be
degraded in a 1:1 acetonitrile:water system with DDT, methylene green (photosen-
sitizer), and triethylamine (electron donor) under visible light, but it was not
degraded if the concentration of the methylene green fell below 10 −7 M (Lin and
Chang 2007). Overall, the abiotic methods have had varying degrees of success in
the remediation and degradation of DDE (Table 4).

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