DDE Remediation and Degradation - Reviews of Environmental Contamination and Toxicology - page 56

act as a carrier to facilitate the transport into subsurface soils despite the low aqueous
solubility (Ding and Wu 1997). Dispersion of DDE may occur through its adsorption
onto particulates, such as soil colloids, that are associated with the clay fraction that can
be eroded and carried to streams as runoff (Masters and Inman 2000). Another loss
mechanism is by volatilization from soil and water, with the trend being predicted by
Henry's law constant. The half-lives of p , p '- and o , p '-DDE from a model river that is
1m deep, flowing at 1m/sec, with a wind of 3m/sec, are 3.3 and 3.7d, respectively
(ATSDR 2002). It has also been reported, based upon laboratory study of the air-water
partitioning, that DDE will vaporize 10-20 times faster from seawater than from fresh-
water (Atlas et al. 1982). Soil-air exchanges of DDE can also occur, with one model
predicting that 200-600 kg p , p '-DDE is released from Alabama soil each year (Harner
et al. 2001). It has also been reported that p , p '-DDE comprised 66% of the total DDT
residuals in the atmosphere over a field that had been treated with DDT over a 7-yr
period then untreated for the next 2 yr; this suggests that volatilization by degradation
products can be a major pathway for loss by some organochorine insecticides in soil
(Cliath and Spencer 1972; Hussain et al. 1994).
In contrast, the half-life for reduction in atmospheric concentrations has been
measured in the Great Lakes area of the U.S. as ranging from 3.8 to 6.0 yr (Cortes
and Hites 2000), and with no decrease measured for p , p '-DDE in the Canadian
arctic (Hung et al. 2002), which indicates a temperature dependence. The half-life
of p , p '-DDE in soil treated one time has been given as 5.7 yr (Beyer and Krynitsky
1989); however, in soil that had repeated DDT applications, the amount of extract-
able p , p '-DDE had not appreciably changed in 20 yr (Boul et al. 1994). It was pre-
sumed that any DDE losses from the latter soil were compensated by further
transformation of p , p '-DDT. Therefore, to negate the toxicity and persistence of
DDE in soil that has been repeatedly treated, some form of remediation must take
place. Research into the remediation of DDE in soil and water has been done pre-
dominantly using (1) phytoremediation (phytoextraction), (2) aerobic biodegrada-
tion, (3) anaerobic biodegradation, and (4) abiotic degradation.
II Phytoremediation
Most of the literature on the phytoremediation of DDE focuses on the translocation of
DDT or DDE from soil or water into plants. Plant species that have been investigated
include rye, mustard, canola, vetch, pigeonpea, clover, peanut, white lupin, chicory,
squash, cucumber, pumpkin, zucchini, tall fescue, leek, duckweed, parrot feather, and
elodea (Gao et al. 2000; Gonzalez et al. 2003; Lunney et al. 2004; Suresh et al. 2005;
White 2002; White et al. 2005). For rye, vetch, pigeonpea, clover, and white lupin,
reductions or nonsignificant changes in p , p '-DDE uptake were observed when the
nutrient treatment was varied or when there was a change in the plant biomass. In
contrast, the amount of p , p '-DDE extracted from the soil doubled and was directly
correlated to the plant biomass for mustard, canola, and peanut (White et al. 2005).
The idea that fertilizer enhances phytoremediation appears to be highly species