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Abstract To determine the extent of pesticide buildup and their environmental contamination, the environmental half-lives of pesticides are examined. The influence of the factors affecting the half-lives of fipronil and thiamethoxam including soil type, sterilization, temperature, and time and their interactions was studied using experimental modeling design by Minitab software. Based on the dissipation kinetics data, fipronil concentrations reduced gradually over 60 days while thiamethoxam concentrations decreased strongly. Also, fipronil and thiamethoxam dissipated more rapidly in calcareous soil than in alluvial soil. Thiamethoxam, however, disappeared more rapidly than fipronil in all treatments. Incubation at 50 °C leads to rapid the pesticide degradation. For prediction of the dissipation rate, model 5 was found to be the best fit, Residue of insecticide (%) = 15.466 − 11.793 Pesticide − 1.579 Soil type + 0.566 Sterilization − 3.120 Temperature, R2 = 0.94 and s = 3.80. Also, the predicted DT50 values were calculated by a model, DT50 (day) = 20.20 − 0.30 Pesticide − 7.97 Soil Type + 0.07 Sterilization − 2.04 Temperature. The shortest experimental and predicted DT50 values were obtained from treatment of thiamethoxam at 50 °C in calcareous soil either sterilized (7.36 and 9.96 days) or non-sterilized (5.92 and 9.82 days), respectively. The experimental DT50 values of fipronil and thiamethoxam ranged from 5.92 to 59.95 days while, the modeled values ranged from 9.82 to 30.58 days. According to the contour plot and response surface plot, temperature and sterilization were the main factors affecting the half-lives of fipronil and thiamethoxam. The DT50 values of fipronil and thiamethoxam increased in alluvial soil and soil with low temperature. In general, there is a high agreement between the experimental results and the modeled results.

In this study, peat, compost and charcoal were added to reduce groundwater pollution with thiamethoxam by soil columns. Iodide has been used as a water tracer at a rate of 10 mL (0.1 M) for each soil column and that leached fast in all soil columns. The breakthrough curve of thiamethoxam was appeared from leachates of calcareous soil column and alluvial soil column with iodide. Accordingly it is considered thiamethoxam is highly mobile compound in tested soils. The addition of soil amendments reduced downward movement and significantly increased cumulative percentage of thiamethoxam from soil columns. After application; 85.21, 93.23, 98.12 and 97.84 % of applied thiamethoxam were recovered in leachates of alluvial soil, 5% peat-soil, 5% compost-soil and 5% charcoal-soil. While; 91.50, 99.30, 94.09 and 86.89 % from calcareous soil, 5% peat-soil, 5% compost-soil and 5% charcoal-soil columns. This is first study to assess, leaching of thiamethoxam and effect of soil amendments on leaching by soil columns. This information can be used to understand how alterations in agricultural practices and potential effects to groundwater.

In this study, peat, compost and charcoal were added to reduce groundwater pollution with thiamethoxam by soil columns. Iodide has been used as a water tracer at a rate of 10 mL (0.1 M) for each soil column and that leached fast in all soil columns. The breakthrough curve of thiamethoxam was appeared from leachates of calcareous soil column and alluvial soil column with iodide. Accordingly it is considered thiamethoxam is highly mobile compound in tested soils. The addition of soil amendments reduced downward movement and significantly increased cumulative percentage of thiamethoxam from soil columns. After application; 85.21, 93.23, 98.12 and 97.84 % of applied thiamethoxam were recovered in leachates of alluvial soil, 5% peat-soil, 5% compost-soil and 5% charcoal-soil. While; 91.50, 99.30, 94.09 and 86.89 % from calcareous soil, 5% peat-soil, 5% compost-soil and 5% charcoal-soil columns. This is first study to assess, leaching of thiamethoxam and effect of soil amendments on leaching by soil columns. This information can be used to understand how alterations in agricultural practices and potential effects to groundwater.

In this study, peat, compost and charcoal were added to reduce groundwater pollution with thiamethoxam by soil columns. Iodide has been used as a water tracer at a rate of 10 mL (0.1 M) for each soil column and that leached fast in all soil columns. The breakthrough curve of thiamethoxam was appeared from leachates of calcareous soil column and alluvial soil column with iodide. Accordingly it is considered thiamethoxam is highly mobile compound in tested soils. The addition of soil amendments reduced downward movement and significantly increased cumulative percentage of thiamethoxam from soil columns. After application; 85.21, 93.23, 98.12 and 97.84 % of applied thiamethoxam were recovered in leachates of alluvial soil, 5% peat-soil, 5% compost-soil and 5% charcoal-soil. While; 91.50, 99.30, 94.09 and 86.89 % from calcareous soil, 5% peat-soil, 5% compost-soil and 5% charcoal-soil columns. This is first study to assess, leaching of thiamethoxam and effect of soil amendments on leaching by soil columns. This information can be used to understand how alterations in agricultural practices and potential effects to groundwater.