Insecticides and herbicides in soils 93
acids on the degradation rate in natural waters was studied under laboratory conditions
(Suntest apparatus). The photodegradation rate of the studied herbicide in different
natural waters follows first-order kinetics with half-lives ranging from 12 to 29 h. The
presence of dissolved organic matter in the selected natural waters retarded the photo
process relative to distilled water. Laboratory experiment has showed that the presence
of humic acid inhibits the photolytic degradation of the herbicide. On the contrary,
it was found that the degradation kinetics of Trifluralin in soil is accelerated as the
percentage content of organic matter increases. Photodegradation of Trifluralin on the
absorbed phase (soils) gave depletion curves that can be well described by a first-order
equation with half-lives varying from 15 to 38 h depending on the composition of the
adsorbing media.
Wang et al [274] studied the degradation and metabolism of Imazapyr in soils
both under aerobic and anaerobic conditions. Lika and Tsiropoulos et al [275] studied
the behaviour of residues in soil after it has been treated with micro encapsulate and
emulsified formulations.
Simoes et al [310] described a fast and simple electroanalysed procedure for the
determination of Methylparathion in a solution extracted from a typical Brazilian
soil using square wave voltammetry and glassy carbon electrode. The effects of pH,
scan rate and surface poisoning were studied in order to establish the optimum conditions for the electroanalysis of Methylparathion. It was observed that the substances
commonly present in the soil solution modify the voltammograms, which improves
the current values and displaces the peak potential to a less negative value. This was
attributed to the more alkaline pH caused by dissolved organic matter, mineral colloids and other substances in the soil solution. The best response was obtained in
neutral or in slightly acidic solutions. In such conditions, the limits of detection were
0.32 mg L
−1 (1.21 × 10
−6 mol L
−1 ) in pure water and 0.36 mg L
−1 (1.37 × 10
−1 ) in the
soil extracted solution.
Inam et al [260] have described a polargraphic determination of Thifensulphuron
methyl herbicide in soil. The differential pulse polographic procedure was based on
a highly-sensitive peak formed due to the reduction of Thifensulfuron-methyl on a
dropping mercury electrode over the pH range 1.00–10.00 in Britton-Robinson buffer.
The polarographic reduction exhibits only a single peak in the pH range PH 3.0 and
pH ≤ 6.0 and pH = 10.0 located at potential values of −1.010, −1.350, and −1.610 V
(v. SCE), respectively. The single peak appeared as a maximum of pH 3.0 (−1.010 V)
was well resolved and was investigated for analytical use. This peak showed quantitative increments with the additions of standard Thifensulfuron-methyl solution under
the optimal conditions, and the cathodic peak current was linearity proportional to the
Thifensulfuron-methyl concentration in the range of 2 × 10
−7 –5 × 10
−5 M. The limit of
detection and limit of quantification were obtained as 1.05 × 10
−7 and 3.50 × 10
−7 M,
respectively, according to the relation k × SD/b (where k = 3 for limit of detection,
k = 10 for limit of quantification, SD is standard deviation of the blank, and b is the
slope of the calibration curve). The method was applied to pesticide formulation and
the average percentage recovery was in agreement with that obtained by the spectrophotometric comparison method, 97.82 and 102.6% respectively. The method was
extended to determination of Thifensulfuron-methyl in spiked soil showing a good
reproducibility and accuracy with a relative standard deviation of 4.55 and a relative
error of +2.80.
acids on the degradation rate in natural waters was studied under laboratory conditions
(Suntest apparatus). The photodegradation rate of the studied herbicide in different
natural waters follows first-order kinetics with half-lives ranging from 12 to 29 h. The
presence of dissolved organic matter in the selected natural waters retarded the photo
process relative to distilled water. Laboratory experiment has showed that the presence
of humic acid inhibits the photolytic degradation of the herbicide. On the contrary,
it was found that the degradation kinetics of Trifluralin in soil is accelerated as the
percentage content of organic matter increases. Photodegradation of Trifluralin on the
absorbed phase (soils) gave depletion curves that can be well described by a first-order
equation with half-lives varying from 15 to 38 h depending on the composition of the
adsorbing media.
Wang et al [274] studied the degradation and metabolism of Imazapyr in soils
both under aerobic and anaerobic conditions. Lika and Tsiropoulos et al [275] studied
the behaviour of residues in soil after it has been treated with micro encapsulate and
emulsified formulations.
Simoes et al [310] described a fast and simple electroanalysed procedure for the
determination of Methylparathion in a solution extracted from a typical Brazilian
soil using square wave voltammetry and glassy carbon electrode. The effects of pH,
scan rate and surface poisoning were studied in order to establish the optimum conditions for the electroanalysis of Methylparathion. It was observed that the substances
commonly present in the soil solution modify the voltammograms, which improves
the current values and displaces the peak potential to a less negative value. This was
attributed to the more alkaline pH caused by dissolved organic matter, mineral colloids and other substances in the soil solution. The best response was obtained in
neutral or in slightly acidic solutions. In such conditions, the limits of detection were
0.32 mg L
−1 (1.21 × 10
−6 mol L
−1 ) in pure water and 0.36 mg L
−1 (1.37 × 10
−1 ) in the
soil extracted solution.
Inam et al [260] have described a polargraphic determination of Thifensulphuron
methyl herbicide in soil. The differential pulse polographic procedure was based on
a highly-sensitive peak formed due to the reduction of Thifensulfuron-methyl on a
dropping mercury electrode over the pH range 1.00–10.00 in Britton-Robinson buffer.
The polarographic reduction exhibits only a single peak in the pH range PH 3.0 and
pH ≤ 6.0 and pH = 10.0 located at potential values of −1.010, −1.350, and −1.610 V
(v. SCE), respectively. The single peak appeared as a maximum of pH 3.0 (−1.010 V)
was well resolved and was investigated for analytical use. This peak showed quantitative increments with the additions of standard Thifensulfuron-methyl solution under
the optimal conditions, and the cathodic peak current was linearity proportional to the
Thifensulfuron-methyl concentration in the range of 2 × 10
−7 –5 × 10
−5 M. The limit of
detection and limit of quantification were obtained as 1.05 × 10
−7 and 3.50 × 10
−7 M,
respectively, according to the relation k × SD/b (where k = 3 for limit of detection,
k = 10 for limit of quantification, SD is standard deviation of the blank, and b is the
slope of the calibration curve). The method was applied to pesticide formulation and
the average percentage recovery was in agreement with that obtained by the spectrophotometric comparison method, 97.82 and 102.6% respectively. The method was
extended to determination of Thifensulfuron-methyl in spiked soil showing a good
reproducibility and accuracy with a relative standard deviation of 4.55 and a relative
error of +2.80.