90 Organic compounds in soils, sediments & sludges
The binary solvents used in this study were various mixtures of hexane: acetone;
hexane: dichloromethane isooctane: acetone, isooctane: dichloromethane, representing different classes of polarity. The recoveries of all pyrthroids and Mirex were
satisfactory over three solvent systems: hexane: acetone: hexaneidichloromethane and
isooctane: acetone, but results of isooctane: dichloromethane produced low recoveries. The average recovery increased with the extraction time, but the increase was
not statistically significant. A 30-min optimum extraction was deemed sufficient for
recovering pyrethroids from soil. After 30 minutes, extraction decreased owing to the
re-distribution of the analyte on the soil matrix.
Ali et al [267] also carried out studies on the determination of six pyrethroids in
soils. These were Permethrin, Cyfluthrin, Cypermethrin, λ-Cyhalothrin, Deltamethrin
and Fenvalerate and Mirex. These were determined in soils possessing a range of
organic content (1.15–2.46%). Solutions (in deionised water, pH 6.5–7.5) of the
samples were shaken using a mechanical shaker for 24 hours. The suspensions were
centrifuged and aliquots of clear supernatant were passed through a C-18 column (SPE
extraction). The eluates were concentrated to dryness before a volumetric standard
was added. The analytes were determined by gas chromatography with negative ion
chemical ionisation mass spectrometry either in SIR or SCN mode. Sorption isotherm
parameters (n and k) were calculated according to the Freundlich equation. The values
n are around unity. Permethrin and Cyfluthrin were the least sorbed pyrethroids, with
k values less than 2,Mirex and Fenvalerate the most. The effect of the pH on sorption was examined also (at pH values 2,4,6 and 9). Sorption behaviour on different
soils and silica was also examined. Desorption studies were conducted on the same
pyrethroid solutions. After sorption, the supernatant was replaced with similar volume
of deionised water. Desorption was achieved by removing all the supernatant from the
centrifuged samples and then replacing it with deionised water. This equilibration process was repeated five times. Each time the suspension was centrifuged, concentrated
and analysed using GC/MS analysis. The residual amount of pyrethroid on the soil
was calculated as the difference between the initial amount and the desorbed amount
(mass balance).
Jensen and others [266] studied the extraction and determination of the potato
glycoalalkaloid in L-solamine in soil.
Miscellaneous herbicides
New designs of pesticide formulations based on organoclays are receiving increasing
attention in reducing offsite movement of pesticides in the environment and in prolonging the efficacy of soil-applied pesticides. Celis et al [268] reported the results of
laboratory and field experiments conducted to evaluate the influence of the saturating cation, the sorbent: herbicide ratio and the type of preparation on the controlled
release properties of organoclay-based formulations of the herbicide hexazinone. Two
organoclays with different affinities for Hexazinone (hexadecyltrimethylammoniumexchanged Arizona montmorillonite, HDTMA-SA and phenyltrimethylammoniumexchanged Arizona montmorillonite, PTMA-SA), two herbicide loadings (10% and
20%) and three types of preparation were assayed. Laboratory experiments showed
that Hexazinone formulations based on HDTMA-SA displayed slow-release properties
in water, retarded herbicide leaching through soil columns, and maintained a herbicidal
The binary solvents used in this study were various mixtures of hexane: acetone;
hexane: dichloromethane isooctane: acetone, isooctane: dichloromethane, representing different classes of polarity. The recoveries of all pyrthroids and Mirex were
satisfactory over three solvent systems: hexane: acetone: hexaneidichloromethane and
isooctane: acetone, but results of isooctane: dichloromethane produced low recoveries. The average recovery increased with the extraction time, but the increase was
not statistically significant. A 30-min optimum extraction was deemed sufficient for
recovering pyrethroids from soil. After 30 minutes, extraction decreased owing to the
re-distribution of the analyte on the soil matrix.
Ali et al [267] also carried out studies on the determination of six pyrethroids in
soils. These were Permethrin, Cyfluthrin, Cypermethrin, λ-Cyhalothrin, Deltamethrin
and Fenvalerate and Mirex. These were determined in soils possessing a range of
organic content (1.15–2.46%). Solutions (in deionised water, pH 6.5–7.5) of the
samples were shaken using a mechanical shaker for 24 hours. The suspensions were
centrifuged and aliquots of clear supernatant were passed through a C-18 column (SPE
extraction). The eluates were concentrated to dryness before a volumetric standard
was added. The analytes were determined by gas chromatography with negative ion
chemical ionisation mass spectrometry either in SIR or SCN mode. Sorption isotherm
parameters (n and k) were calculated according to the Freundlich equation. The values
n are around unity. Permethrin and Cyfluthrin were the least sorbed pyrethroids, with
k values less than 2,Mirex and Fenvalerate the most. The effect of the pH on sorption was examined also (at pH values 2,4,6 and 9). Sorption behaviour on different
soils and silica was also examined. Desorption studies were conducted on the same
pyrethroid solutions. After sorption, the supernatant was replaced with similar volume
of deionised water. Desorption was achieved by removing all the supernatant from the
centrifuged samples and then replacing it with deionised water. This equilibration process was repeated five times. Each time the suspension was centrifuged, concentrated
and analysed using GC/MS analysis. The residual amount of pyrethroid on the soil
was calculated as the difference between the initial amount and the desorbed amount
(mass balance).
Jensen and others [266] studied the extraction and determination of the potato
glycoalalkaloid in L-solamine in soil.
Miscellaneous herbicides
New designs of pesticide formulations based on organoclays are receiving increasing
attention in reducing offsite movement of pesticides in the environment and in prolonging the efficacy of soil-applied pesticides. Celis et al [268] reported the results of
laboratory and field experiments conducted to evaluate the influence of the saturating cation, the sorbent: herbicide ratio and the type of preparation on the controlled
release properties of organoclay-based formulations of the herbicide hexazinone. Two
organoclays with different affinities for Hexazinone (hexadecyltrimethylammoniumexchanged Arizona montmorillonite, HDTMA-SA and phenyltrimethylammoniumexchanged Arizona montmorillonite, PTMA-SA), two herbicide loadings (10% and
20%) and three types of preparation were assayed. Laboratory experiments showed
that Hexazinone formulations based on HDTMA-SA displayed slow-release properties
in water, retarded herbicide leaching through soil columns, and maintained a herbicidal