The adsorption and desorption processes by solid materials are important in determining the movement and fate of pesticide compounds in aquatic systems. Chitin is one of the constituents of natural organic matter and may serve as a model organic phase for studying the pesticide adsorption-desorption in marine systems. The lindane adsorption-desorption to chitin has been studied as a function of chitin concentration (2.5 gl#x2212;1to 12.5 gl#x2212;1), temperature (5 to 45#xB0;C), pH (1.5 to 8) and salinity (15#x2030; to 36#x2030;). Both, Freundlich and linear isotherms for the adsorption and desorption processes were used to represent the experimental data. Two-site Langmuir isotherm can describe well the measured sorption isotherm. The adsorbent-concentration effect and the adsorption-desorption hysteresis show the existence of different classes of site with different accessibility. Thus, the adsorption-desorption reaction of lindane is the result of more than a single mechanism. An increase in temperature (#x394;H= #x2212;4.0 #xB1; 0.7 Kcal mol#x2212;1) and a decrease in salinity resulted in both lower lindane adsorption and in a more reversible process. An increase of pH resulted in lower adsorption partition coefficients.
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