Insecticides and herbicides in soils 101
The practical limit of determination for these herbicides is between 0.01 and
0.05 µg g
−1 depending on the background response from the soil extract.
Gambrell et al [278] have discussed the recovery of DDT, Kepone and Permethrin
added to soil suspensions incubated under controlled redox potential and pH conditions to determine the effect of time on the levels of the insecticides and their
degradation products. Samples were analysed by gas chromatography, pH and redox
potential affected the persistence of pesticides to different degrees. The recovery of
DDT was affected by redox potential but not by pH.
The stability of Kepone (chlorodecone) was not affected by pH or redox potential
while Permethrin stability was affected by both parameters.
Kavetski et al [279] developed a method for the simultaneous determination of
pesticides in soil. A combination of thin layer chromatography and gas chromatography was used. The pesticides examined were 4,4
DDT, 4,4
DDD, 4,4
DDE, 2,4
DDT
γGHCG, αGHCG, Metaphos, Phosphamidon, Phozalone, Atrazine, Prometryne,
Simazine and 2,4 dichlorophenoxy acetic acid. Detection limits were in the range
0.5–5 µg kg
−1 .
Acid herbicides such as 2,4 dichlorophenoxy acetic acid, 2,4,5-trichlorophenoxy
acetic acid, 3,6-dichlorpicolinic acid and other types of herbicides such as Dicamba,
Dichloroprop, Picloram, Fenoprop, 2,3,6-TBA, Bromoxynil and Ioxynil are widely
used in agriculture and are often formulated as mixtures. They may also be mixed in
the spray tank or used in sequence, so it is likely that residues of more than one of
these compounds may be present in the soil.
Many methods have been reported for the extraction of these compounds from
soil. Khan et al [280] use acidified acetone followed by methylation with diazomethane
for the simultaneous determination of 2,4-D, Dicamba and Mecoprop residues. Abbot
et al [281] developed a method for MCPA, MCPB, 2,4-D, Dichloroprop, and 2,4,-T in
which dilute sulphuric acid and diethyl ether were used for extraction. Byast et al [47]
have shown that diethyl ether-chloroform-acetic acid is a suitable extraction extrant
for 2,4,5-T, 2,4,-D, Dichloroprop and Dicamba et al [703] and saturated calcium
hydroxide solution is efficient for Picloram [282] and 3,6-dichloropicolinic acid [283].
All of the methods discussed above use liquid-liquid partition for clean-up. However, Smith and Hayden et al [284] and Johnson et al [285] have shown that the
macroreticular resin XAD-2 is an efficient absorber of 2,4-D.
After extraction and clean-up the acid and hydroxybenzonitrile herbicides are
either too polar or insufficiently volatile to be determined directly by gas-liquid chromatography, and a suitable derivative must therefore be prepared. Among the methods
reported at the preparation of methyl esters using diazomethane [280, 285–287] or
boron trichloridemethanol reagent [288] or iodomethane with alkali metal carbonate catalysis under anhydrous conditions [289]. Other esters have been prepared by
reaction of herbicide acids with the appropriate alcohol [290, 291]. Some workers
have prepared esters with enhanced electron-capturing properties to improve detection limits, such as straight-chain halogenated esters [292] or strongly halogenated
aromatic esters such as pentafluorobenzyl [293–297]. Various silyl esters have also
been prepared [298, 299].
Each of these methods has some disadvantage. Diazomethane is toxic, carcinogenic
and explosive. Boron trichloride-methanol will not alkylate hydroxybenzonitriles. The
silyl derivatives tend to condense in the electron-capture detector and decrease its
The practical limit of determination for these herbicides is between 0.01 and
0.05 µg g
−1 depending on the background response from the soil extract.
Gambrell et al [278] have discussed the recovery of DDT, Kepone and Permethrin
added to soil suspensions incubated under controlled redox potential and pH conditions to determine the effect of time on the levels of the insecticides and their
degradation products. Samples were analysed by gas chromatography, pH and redox
potential affected the persistence of pesticides to different degrees. The recovery of
DDT was affected by redox potential but not by pH.
The stability of Kepone (chlorodecone) was not affected by pH or redox potential
while Permethrin stability was affected by both parameters.
Kavetski et al [279] developed a method for the simultaneous determination of
pesticides in soil. A combination of thin layer chromatography and gas chromatography was used. The pesticides examined were 4,4
DDT, 4,4
DDD, 4,4
DDE, 2,4
DDT
γGHCG, αGHCG, Metaphos, Phosphamidon, Phozalone, Atrazine, Prometryne,
Simazine and 2,4 dichlorophenoxy acetic acid. Detection limits were in the range
0.5–5 µg kg
−1 .
Acid herbicides such as 2,4 dichlorophenoxy acetic acid, 2,4,5-trichlorophenoxy
acetic acid, 3,6-dichlorpicolinic acid and other types of herbicides such as Dicamba,
Dichloroprop, Picloram, Fenoprop, 2,3,6-TBA, Bromoxynil and Ioxynil are widely
used in agriculture and are often formulated as mixtures. They may also be mixed in
the spray tank or used in sequence, so it is likely that residues of more than one of
these compounds may be present in the soil.
Many methods have been reported for the extraction of these compounds from
soil. Khan et al [280] use acidified acetone followed by methylation with diazomethane
for the simultaneous determination of 2,4-D, Dicamba and Mecoprop residues. Abbot
et al [281] developed a method for MCPA, MCPB, 2,4-D, Dichloroprop, and 2,4,-T in
which dilute sulphuric acid and diethyl ether were used for extraction. Byast et al [47]
have shown that diethyl ether-chloroform-acetic acid is a suitable extraction extrant
for 2,4,5-T, 2,4,-D, Dichloroprop and Dicamba et al [703] and saturated calcium
hydroxide solution is efficient for Picloram [282] and 3,6-dichloropicolinic acid [283].
All of the methods discussed above use liquid-liquid partition for clean-up. However, Smith and Hayden et al [284] and Johnson et al [285] have shown that the
macroreticular resin XAD-2 is an efficient absorber of 2,4-D.
After extraction and clean-up the acid and hydroxybenzonitrile herbicides are
either too polar or insufficiently volatile to be determined directly by gas-liquid chromatography, and a suitable derivative must therefore be prepared. Among the methods
reported at the preparation of methyl esters using diazomethane [280, 285–287] or
boron trichloridemethanol reagent [288] or iodomethane with alkali metal carbonate catalysis under anhydrous conditions [289]. Other esters have been prepared by
reaction of herbicide acids with the appropriate alcohol [290, 291]. Some workers
have prepared esters with enhanced electron-capturing properties to improve detection limits, such as straight-chain halogenated esters [292] or strongly halogenated
aromatic esters such as pentafluorobenzyl [293–297]. Various silyl esters have also
been prepared [298, 299].
Each of these methods has some disadvantage. Diazomethane is toxic, carcinogenic
and explosive. Boron trichloride-methanol will not alkylate hydroxybenzonitriles. The
silyl derivatives tend to condense in the electron-capture detector and decrease its