Comments on “Reductive dechlorination of organochlorine pesticides in soils from an abandoned manufacturing facility by zero-v

Recently, Cong et al. (2010) published a comprehensive study on the characterization of reductive properties of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethane (DDTs) using powdered metallic iron (Fe). Quantum chemical descriptors characterizing different molecular structures and physicochemical properties of the seven tested organochlorine pesticides (4 HCHs and 3 DDTs) were computed to discuss the major influential factors over their reductive dechlorination rates. A model was reported to be established, which correlates the reductive dechlorination properties of pollutants with their structural descriptors. As major result, the reductive dechlorination rate of tested organochlorine pesticides appears to be mainly limited by the rate of dissolution in the aqueous phase. It is evident that this conclusion is not specific to reduction by Fe but rather a simple solubility issue. The work of Cong et al. (2010) is a justified attempt to correlate the intrinsic properties of individual contaminants to their chemical reactivity in a aqueous systems. Accordingly, the authors are to be commended for having listed up to twenty two (22) structural and thermodynamic parameters which may influence the chemical reactivity of individual contaminants. Table 1 gives three structural [molecular weight (Mw) and average molecular polarizability (Polar), Van der waals volume of molecule (V)] and one thermodynamic parameters [formation free energy (ΔfG)] representative for discussing the reactivity. For instance, if Mw is the most determinant parameter for the reactivity then two classes of