DDE Remediation and Degradation - Reviews of Environmental Contamination and Toxicology - page 64

Table 4 The efficacies of selected abiotic treatments assessed in soil remediation studies and
their associated reductions in DDE

Percent reduction

Treatment of DDE (time) Conditions Reference

Deep plowing 14.2 (23 yr) No flooding Spencer et al. 1996

No amendments

Deep plowing and 69.6 (23 yr) 45 ton ha −1 manure Spencer et al. 1996

flooding
Shallow flooding 11.5 (42 d) 59% soil water Boul 1996

content

Photodegradation ~80 (12 hr) 1% TiO 2 on soil Quan et al. 2005

with UV light

Catalysis >99 (24 hr) Soil slurry Gautam and Suresh

Biosurfactant 2006

Pd/Mg catalyst

Catalysis ~60 (7 wk) Acidic rice paddy soil Yao et al. 2006

Fe ° catalyst

Catalysis ~70 (40 wk) Lake sediment at 22°C Eggen and

Fe ° catalyst Majcherczyk 2006

Summary

DDT and its metabolites, DDD and DDE, have been shown to be recalcitrant to
degradation. The parent compound, DDT, was used extensively worldwide starting
in 1939 and was banned in the United States in 1973. The daughter compound,
DDE, may result from aerobic degradation, abiotic dehydrochlorination, or photo-
chemical decomposition. DDE has also occurred as a contaminant in commercial-
grade DDT. The p , p '-DDE isomer is more biologically active than the o , p -DDE,
with a reported half-life of ~5.7 years. However, when DDT was repeatedly applied
to the soil, the DDE concentration may remain unchanged for more than 20 yr.
Remediation of DDE-contaminated soil and water may be done by several tech-
niques. Phytoremediation involves translocating DDT, DDD, and DDE from the
soil into the plant, although some aquatic species (duckweed > elodea > parrot
feather) can transform DDT into predominantly DDD with some DDE being
formed. Of all the plants that can uptake DDE, Cucurbita pepo has been the most
extensively studied, with translocation values approaching “hyperaccumulation”
levels. Soil moisture, temperature, and plant density have all been documented as
important factors in the uptake of DDE by Cucurbita pepo . Uptake may also be
influenced positively by amendments such as biosurfactants, mycorrhizal inocu-
lants, and low molecular weight organic acids (e.g., citric and oxalic acids).
DDE microbial degradation by dehalogenases, dioxygenases, and hydrolases
occurs under the proper conditions. Although several aerobic degradation
pathways have been proposed, none has been fully verified. Very few aerobic pure
cultures are capable of fully degrading DDE to CO 2 . Cometabolism of DDE by