Batch adsorption and desorption kinetic experiments of fenitrothion on clay soil and sandy clay loam soil indicated that the equilibration time was approximately 30 hours. The kinetics of adsorption and desorption exhibited two distinct stages: a rapid process in the initial stages followed by a slow process. The pseudo-first-order model followed by the Elovich kinetic model fit the experimental adsorption and desorption data quite well, with high values of R2 and low values of ∆qe% and SSE. Accordingly, the pseudo-first-order model is most suitable for describing the adsorption and desorption kinetics of fenitrothion on clay soil and sandy clay soil. Pseudo-second-order model type-1 and type-2 models fit the experimental adsorption data; however, these models cannot be used to describe desorption kinetics. Moreover, the modified Freundlich model has limited applicability, and the intraparticle diffusion kinetic model cannot describe the kinetics of the adsorption and desorption of fenitrothion on clay and sandy clay loam soils.

Knowledge of pesticide adsorption characteristics is essential to predict their behavior in soil. The adsorption equilibrium isotherms of two insecticides chlorantraniliprole (CAP) and dinotefuran (DNF) on two common Egyptian soil types, clay loam and sandy loam were studied and modeled. To predict the adsorption isotherms and to determine the adsorption parameters, ten isotherm models: Langmuir (five linear forms), Freundlich, Temkin, Dubinin-Radushkevich, Elovick, Fowler-Guggenheim, Kiselev, Jovanoic, Harkins-Jura, and Halsey were applied on experimental data. The results revealed that the adsorption isotherm models fitted the data in the order of Halsey > Freundlich > Jovanoic > Langmuir isotherme. The models of Harkins-Jura, Elovich, Temkin, and Fowler-Guggenheim are not applicable to predict the adsorption isotherms of the tested insecticides. In order to determine the best-fit isotherm, the correlation coefficient (R2), comparing the experimental (exp) and calculated (cal) adsorption data, and a normalized standard deviation (Δg%) were used to evaluate the data. Therefore, the isotherm models Halsey and Freundlich could be used to predict the adsorption characteristics of CAP and DNF in the common Egyptian soil types, clay loam and sandy loam. Consequently, the mathematical models Halsey, Freundlich, and Jovanoic can describe the fate of CAP and DNF and can be used to control Egyptian soil contamination.

The leaching of two pesticides, cholantraniliprole (CAP) and bispyribac-sodium (BPS) in sandy clay loam soil (soil A) and sandy loam soil (soil B) were examined, by soil columns under laboratory conditions. In addition, the effect of adding 5% biochar and wheat straw to the soils on the leaching of CAP and BPS was studied. It is clear from the results that BPS is more leachable than CAP in all soil columns, and more leached to soil B. It was found that the addition of biochar and wheat straw has a significant effect on the movements of these pesticides and can be used to reduce the environmental impact. For CAP, 71 to 97% and 84 to 97% were recovered from the soil A columns and soil B columns, respectively, while for BPS, 94 to 99% were recovered from columns of soil A and soil B.

The effect of biochar, compost, peat and wheat straw at 1 and 5% on adsorption isotherm of chlorantraniliprole, dinotefuran, bispyribac-sodium, and metribuzin was studied in clay loam soil and sandy loam soil. Biochar, compost, peat and wheat straw (at a rate of 1 % in soil) improved the adsorption capacity of chlorantraniliprole and metribuzin in sandy loam soil. The sorption coefficients are higher for chlorantraniliprole and metribuzin whereas lower for dinotefuran and bispyribac-sodium in amended soil compared to unamended sandy loam soil. There is not a clear direct correlation between Freundlich parameters as well as Kd or Koc and type of organic amendment. The sorption of all tested pesticides on biochar was increased, whereas on compost was decreased. The order of pesticides sorption in soils and different organic amendments is generally inversely proportional to their aqueous solubilites. Adsorption of chlorantraniliprole increases on the sandy loam soil amendment at the rate of 1% in the following order: peat > compost > biochar > original soil. Also, the magnitude of adsorption on soil A amendment at the rate of 5% can be arranged for dinotefuran in the order; peat > biochar > compost > original soil and for bispyribac-sodium and metribuzin peat = wheat straw > biochar > original soil.

The efficiency of different sorbents (bulk soil, sand, silt, clay and humic acid-HA) for chlorantraniliprole (CAP), dinotefuran (DNF), bispyribac-sodium (BPS), and metribuzin (MBZ) adsorption was described and compared. The adsorption of CAP, DNF, BPS and MBZ were significantly greater on clay and HA fractions than the bulk soils. Also, the tested pesticides sorption was greater on HA fraction compared to clay fraction except in the case of BPS. The mass unit of bulk soil adsorbed of CAP, DNF, BPS and MBZ approximately 15, 20, 10 and 5 % of the same of HA and 40, 60, 95 and 35 % of that of clay fraction, respectively. The actual amounts adsorbed on bulk soil ranged from (88.63 to 93.93 %) of the calculated amounts adsorbed on all soil components indicating high efficiency of the tested soils to adsorb tested pesticides. All adsorption data fitted well to the linear Freundlich equation. The adsorption of tested pesticides in soil and their different constituents is S-type according to 1/n (except some cases).

The effect of pH value at three levels (5, 7, and 9) and temperature at two levels (25 and 50ºC) on the sorption properties of chlorantraniliprole-CAP, dinotefuran-DNF, bispyribac-sodium-BPS, and metribuzin-MBZ were studied in calcareous soil. The sorption of CAP at pH 5 (38.2%) was significantly higher than that at pH 7 (32.4%) and 9 (28.4%), whereas the sorption of DNF at pH 5 was lower than that at pH 7. The adsorption of BPS at pH 9 was statistically significantly higher than that at pH 5 and pH 7. Regarding the herbicide MBZ adsorption percentages were 47.0, 61.1 and 57.1 % at pH 5, 7 and 9. The number of tested pesticides adsorbed by the soil was significantly influenced by the temperature. The adsorbed amount of CAP was decreased from 37% to 33% as the temperature was increased from 25˚C to 50 ˚C, while no significant differences of adsorbed DNF. Data showed that the adsorption of BPS and MBZ statistically decreases with temperature. The data from the adsorption behaviour of CAP, DNF, BPS, and MBZ in tested soil at different temperatures correspond well with the Freundlich isotherm. The negative ΔG˚ indicated that the adsorption of CAP, DNF, BPS, and MBZ were spontaneous at different temperatures. There was an increase in the entropy of the pesticide-soil systems as shown by the positive values of ΔS˚.

The behavior of bispyribac-sodium and metribuzin herbicides was investigated into alluvial soil. Effect of pH, temperature, and particle size of soil on the sorption process was studied. Sorption isotherms by bulk soil and its sand, silt, clay and humic acid (HA) fractions were quantified using the batch equilibration technique. The results showed that sorption of herbicides tested was significantly affected by temperature and was a spontaneous interfacial process into soil. Freundlich equation accurately predicted the sorption behavior of two herbicides. Thermodynamic parameters summarized that the negative values of the standard free energy changes (ΔG˚) were obtained therefore, the adsorption of tested pesticides in soil was spontaneous and small negative values indicate the sorption is physical in nature involving weak forces of attraction. The negative ΔH˚ value, indicating metribuzin and bispyribac-sodium interactions are exothermic processes and products are energetically stable with a high binding of compound to soil sites. There was an increase in the entropy of tested pesticides-soil systems as shown by positive values of ΔS˚. The highest adsorption in soil was at pH 5 for bispyribac-sodium and at pH 7 for metribuzin. The sorption of metribuzin and bispyribac-sodium were significantly greater on HA fraction followed by clay fraction than the bulk soil. The KF and Kd values increase with decreasing particle size particularly in the case of adsorption of metribuzin.

The dissipation and side-effect of metribuzin (MBZ) were studied with various factors; two soil types (clay loam and sandy loam), soil amendment (wheat straw and without amendment), two temperature levels (25 and 50°C), sterilization (sterilized and unsterilized soil) and time of incubation (15 and 30 days) and designed by Windows version of MINITAB software package to reduce the time and the cost as well as increased the precision. Determination of MBZ by HPLC with recoveries ranged from 50.85 to 108.09%. The MBZ residues were detected in all samples up to 60 days of storage, respectively with decline in their concentrations with the time of incubation. The clay loam soil showed higher dissipation than the sandy loam soil. The different factors in the present study confirmed that the wheat straw amendment, non-sterilization and incubation at 50°C caused higher dissipation of MBZ than without wheat straw, sterilization and incubation at 25°C. The dissipation was described mathematically by a first order equation with t0.5 was ranged from 9.62 to 16.82 days in clay loam soil and from 10.01 to 16.04 days in sandy loam soil. The side-effect of MBZ was tested on soil dehydrogenase activity that can be considered as an indicator of the biological activity and microbial degradation. The result proved that the enzyme activity was significantly decreased in all treatments compared with the controls at 1 and 3 days of incubation then it was gradually increased at 7, 10, 15 and 30 days of incubation. Treatments of wheat straw, non-sterilized and incubated at 25°C or 50°C showed the lowest enzyme inhibition among all treatments.