Mechanochemical degradation of γ-hexachlorocyclohexane by a planetary ball mill in the presence of CaO

Although the use of the insecticide gamma-hexachlorocyclohexane (HCH) is now prohibited in many countries because of its hazardousness, stockpiles of gamma-HCH still exist. In this study, we subjected gamma-HCH to mechanochemical (MC) treatment with a planetary ball mill in the presence of CaO to investigate the feasibility of using this method for the treatment of gamma-HCH stockpiles. We confirmed the degradation of gamma-HCH and investigated the degradation mechanism. The major intermediates were identified to be 1,3,4,5,6-penta-chlorocyclohexene (gamma-PCCH) and chlorobenzenes (CBzs). Analysis of the steric structure of gamma-HCH and identification of the degradation intermediates suggested that successive dehydrochlorination led to the formation of trichlorobenzenes. Products of further degradation (dichlorobenzenes, monochlorobenzene, and benzene) were also detected. Surprisingly, methane and ethane were also detected, which suggests cleavage of the C C bonds of the cyclohexane ring and hydrogenation. All of the chlorine atoms in the gamma-HCH could be transformed into inorganic chloride compounds by the MC treatment with CaO. Our results indicate that gamma-HCH can be completely dechlorinated by MC treatment. (C) 2011 Elsevier Ltd. All rights reserved.