Adsorption behavior of RH‐5992 insecticide onto sandy and clay loam forest soils |
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Authors: | KMS Sundaram |
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Institution: | Natural Resources Canada, Canadian Forest Service , Forest Pest Management Institute , 1219 Queen Street East, P.O. Box 490, Sault Ste. Marie, Ontario, Canada , P6A 5M7 |
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Abstract: | Abstract Adsorption‐desorption behavior of RH‐5992 Mimic®, N'‐t‐butyl‐N'‐(3,5‐dimethylbenzoyl)‐N‐(4‐ethylbenzoyl) hydrazine] in sandy and clay loam forest soils was studied using the batch equilibrium method. Adsorption was higher in the clay loam soil than in the sandy loam, and increased linearly with RH‐5992 concentration, but decreased with increasing pH and temperature. The adsorption data fit better to the Freundlich, than to the Langmuir equation. The KD (linear adsorption constant) and KF (Freundlich constant) were similar for each soil at 5, 15 and 25°C and decreased with increase of temperature, indicating that the enthalpy of adsorption was negative. The exponent of the Freundlich equation was close to unity for both soils at all three temperatures. The low Ea (energy of activation) indicated a diffusion‐controlled process during the initial stages of adsorption. The desorption isotherm differed from that of adsorption, and the linear desorption constant, KD(d), was ca 25 times higher than the KD, indicating that adsorption of RH‐5992 was not readily reversible. Evaluation of thermo‐dynamic parameters confirmed the presence of strong bonds between the solute and soil. These findings suggest that RH‐5992 has a limited potential for downward mobility leading to groundwater contamination. |
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Keywords: | Adsorption desorption isotherms Freundlich and Langmuir equations RH‐5992 forest soils sandy and clay loam soils |
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