Cs. Helling et al., DDT DISSIPATION IN HAWAIIAN IN-SITU SOIL COLUMNS, Journal of environmental science and health. Part B. Pesticides, food contaminants, and agricultural wastes, 29(1), 1994, pp. 103-119
[C-14]DDT persistence and movement was monitored for 25 months after t
reatment of in-situ soil columns in Hawaii, USA. This was part of an i
nternational collaborative protocol coordinated by the International A
tomic Energy Agency and carried out at 13 tropical locations. DDT meta
bolite DDE, and herbicide tebuthiuron, were included in the Hawaiian t
est for comparison with DDT. Persistence based on overall loss of radi
oactivity was described by first-order and two-compartment models: hal
f-dissipation times were 53 and 25 weeks, respectively. The second mod
el represented more accurately the rapid loss of C-14 during the first
month after treatment. Time to 50% loss based on analysis of methanol
-extractable C-14 was 66-68 weeks (both models), or somewhat shorter (
40-53 weeks) when C-14 was measured in the final hexane solution befor
e gas chromatographic (GC) analysis. Direct GC analysis of that soluti
on gave 24 weeks (first-order) and 13 weeks (two-compartment) for DDT
alone, and 37 weeks and 27 weeks, respectively, for the sum of DDT + D
DE + DDD residues. After 10 months, further dissipation of either radi
oactivity or of DDT itself was very slow; the two-compartment model pr
edicted 90% loss of methanol-extractable C-14 in 11 years and of DDT,
in 3 years. Within 18 weeks post-DDT-treatment, metabolite DDE had rea
ched a stable concentration of ca. 7% of added DDT. No DDD accumulated
. Bound residue content was 10-15% by 2 years. [C-14]DDT and other rad
ioactivity moved below the 10-cm leaching column by 3-4 months. By 25
months, 3% of the originally applied C-14 occurred deeper than 10 cm,
or about 8% of the total C-14 then recovered. Little or no radioactivi
ty migrated below 17.5 cm. Rainfall at the site averaged ca. 2500 mm y
(-1). Tebuthiuron was less persistent than DDT; estimated half-life wa
s ca. 12 weeks and the herbicide was much more mobile.