Insecticides and herbicides in soils 91
efficacy similar to that of the currently available commercial Hexazinone formulation
(wettable powder). In contract, PTMA-SA formulations released the herbicide instantaneously and did not display slow-release properties. High organoclay-herbicide ratios
and the use of organic solvent made the interaction between HDTMA-SA and the herbicide more intimate and reduced the release rate of Hexazinone suggesting that a range
of release and leaching behaviours can be achieved by selecting the type of preparation and the herbicide loading in the formulations. A field experiment confirmed the
usefulness of HDTMA-SA formulations of Hexazinone to reduce herbicide leaching
while maintaining weed-control efficacy.
Wang et al [269] conducted a laboratory experiment to study the effects of two
different formulations (25% Arsenal SL and 5.0% Arsenal G) and doses (equivalent to
0.5 ug A.I. g
−1 ) soil on the persistence of Imazapyr in four soils of Zhejiang province,
south eastern China. Based on the first-order kinetic equation, the calculated half-lives
of Imazapyr in the range 22.0–35.7 days in four soils (30.9 days) and lowest (24.1
days). The highest mean half-lives were observed in Soil C (Coastal Saline Soil, pH
8.78) and Soil B (Yellow-Red Soil, pH 5.23) respectively. The persistence of Imazapyr
increased in the order soil C (pH 8.78) > soil A (Silt-Loamy Paddy Soil pH 7.86) > soil
D (Fluvio-Marine Yellow Loamy Soil, pH 7.06) > soil B pH 5.25), which demonstrated
that an increase in soil pH tended to lead to higher persistence of Imazapyr in soil.
The difference between the mean half-lives, corresponding to 0.5 and 1.0 ug A.I. g
−1
soil treatment for 25% Arsenal SL or for 5.0% Arsenal G, respectively, was not significant, which showed that the different initial application rates had little impact upon
degradation of Imazapyr. In contrast, a greater impact of the different formulation
type upon persistence of Imazapyr was observed. Higher persistence was observed
with the granular formulation (t 1/2 = 28.1d) compared with the liquid formulation
(t 1/2 = 26.2sd) for the lower dose, which was statistically significant, and an identical trend also existed in the higher dose. Three major metabolites were separated by
preparative TLC. On the basis of their spectral (IR, LC-MS and
1 H NMR), the structure
of each compound was deducted and their formation pathway was also discussed.
Artemisinin, a bioactive compound in Artemisia annua L.(sweet wormwood) is
used as active ingredient in drugs against malaria. Cultivation of A.annua in field
studies implies high amounts of Artemisinin produced and potential high losses to soil
with impact to vulnerable organisms in soil and leaching to the aquatic environment.
Jessing et al [270] developed a method of extraction of the Artemisinin in sandy,
clayey and humic soil samples by supercritical fluid extraction and determination by
HPLC. Optimal supercritical fluid extraction conditions were reached using ethanol
as modifier at a flow of 0.5 mL min
−1 and a total extraction time of 20 minutes.
The HPLC method had linearity up to greater than 535 mg kg
−1 for all types, limit of
detection was 13 µg kg
−1 soil and limit of quantification was 43 µg kg
−1 soil. Recovery
for soil samples spiked with Artemisinin one hour before extraction was determined
to be 70–80%. No matrix effect was observed. The method enabled quantification
of Artemisinin in three common soil types, and was applied for determination of
degradation kinetics of Artemisinin in spiked soils. Degradation kinetics consisted of
an initial fast degradation followed by a slower one Figure 3.10. The slower reaction
could be fitted by first-order kinetics resulting in rate constants of 0.05, 0.084 and
0.32 per day in sandy, clayey and humic soils respectively. Both the rate of the fast and
slow reaction appeared to increase with soil organic matter content. The relative long
efficacy similar to that of the currently available commercial Hexazinone formulation
(wettable powder). In contract, PTMA-SA formulations released the herbicide instantaneously and did not display slow-release properties. High organoclay-herbicide ratios
and the use of organic solvent made the interaction between HDTMA-SA and the herbicide more intimate and reduced the release rate of Hexazinone suggesting that a range
of release and leaching behaviours can be achieved by selecting the type of preparation and the herbicide loading in the formulations. A field experiment confirmed the
usefulness of HDTMA-SA formulations of Hexazinone to reduce herbicide leaching
while maintaining weed-control efficacy.
Wang et al [269] conducted a laboratory experiment to study the effects of two
different formulations (25% Arsenal SL and 5.0% Arsenal G) and doses (equivalent to
0.5 ug A.I. g
−1 ) soil on the persistence of Imazapyr in four soils of Zhejiang province,
south eastern China. Based on the first-order kinetic equation, the calculated half-lives
of Imazapyr in the range 22.0–35.7 days in four soils (30.9 days) and lowest (24.1
days). The highest mean half-lives were observed in Soil C (Coastal Saline Soil, pH
8.78) and Soil B (Yellow-Red Soil, pH 5.23) respectively. The persistence of Imazapyr
increased in the order soil C (pH 8.78) > soil A (Silt-Loamy Paddy Soil pH 7.86) > soil
D (Fluvio-Marine Yellow Loamy Soil, pH 7.06) > soil B pH 5.25), which demonstrated
that an increase in soil pH tended to lead to higher persistence of Imazapyr in soil.
The difference between the mean half-lives, corresponding to 0.5 and 1.0 ug A.I. g
−1
soil treatment for 25% Arsenal SL or for 5.0% Arsenal G, respectively, was not significant, which showed that the different initial application rates had little impact upon
degradation of Imazapyr. In contrast, a greater impact of the different formulation
type upon persistence of Imazapyr was observed. Higher persistence was observed
with the granular formulation (t 1/2 = 28.1d) compared with the liquid formulation
(t 1/2 = 26.2sd) for the lower dose, which was statistically significant, and an identical trend also existed in the higher dose. Three major metabolites were separated by
preparative TLC. On the basis of their spectral (IR, LC-MS and
1 H NMR), the structure
of each compound was deducted and their formation pathway was also discussed.
Artemisinin, a bioactive compound in Artemisia annua L.(sweet wormwood) is
used as active ingredient in drugs against malaria. Cultivation of A.annua in field
studies implies high amounts of Artemisinin produced and potential high losses to soil
with impact to vulnerable organisms in soil and leaching to the aquatic environment.
Jessing et al [270] developed a method of extraction of the Artemisinin in sandy,
clayey and humic soil samples by supercritical fluid extraction and determination by
HPLC. Optimal supercritical fluid extraction conditions were reached using ethanol
as modifier at a flow of 0.5 mL min
−1 and a total extraction time of 20 minutes.
The HPLC method had linearity up to greater than 535 mg kg
−1 for all types, limit of
detection was 13 µg kg
−1 soil and limit of quantification was 43 µg kg
−1 soil. Recovery
for soil samples spiked with Artemisinin one hour before extraction was determined
to be 70–80%. No matrix effect was observed. The method enabled quantification
of Artemisinin in three common soil types, and was applied for determination of
degradation kinetics of Artemisinin in spiked soils. Degradation kinetics consisted of
an initial fast degradation followed by a slower one Figure 3.10. The slower reaction
could be fitted by first-order kinetics resulting in rate constants of 0.05, 0.084 and
0.32 per day in sandy, clayey and humic soils respectively. Both the rate of the fast and
slow reaction appeared to increase with soil organic matter content. The relative long