Research was conducted to examine the effects of various fractions of cosolvent solutions on dechlorination of toxaphene by zero-valent iron (Fe-0). Experimental results showed that toxaphene degradation in solution was found to be the result of dechlorination at the Fe-0 surface. The rate of toxaphene dechlorination was also found to reduce with the increase of cosolvent in solution, as the cosolvent presence caused a reduction in toxaphene adsorption to Fe-0 surfaces. Toxaphene sorption to Fe-0 was found to correspond to a Freundlich nonlinear sorption equation and indicated that the linearity of this isotherm in the presence of cosolvent was related to the saturation of solution, which was the ratio of aqueous concentration to the solubility (C-a/S-c,). When C-a/S-c > 0.2, the sorption isotherm was almost linear and the concept of cosolvency power can be applied mathematically to describe this process. A mathematical model detailing the sorption and dechlorination of toxaphene by Fe-0 was developed, and showed that experimental data agreed with the theoretically derived data. Overall, results indicated that dechlorination of complex chlorinated substances, such as toxaphene, by Fe-0 can be greatly dependent upon adsorption to the iron surface. (C) 2008 Elsevier B.V. All rights reserved.