Unintentional anthropogenic thermal chlorination of carbon is known to be a contributor to global environmental pollution of organochlorine compounds. We found unexpected, serious chlorination of carbon promoted by a "sulfide" of copper. which has been generally thought of and studied as an inactive metal catalyst. Our quantitative and X-ray spectroscopic results show that a fraction of cupric sulfide indirectly promoted thermochemical solid-phase formation of a large quantity of organochlorine compounds such as polychlorinated dibenzo-p-dioxins, dibenzofurans. biphenyls, and benzenes that used inactive inorganic chloride as chlorine storage, which partly caused environmental pollution by organochlorine compounds. (C) 2011 Elsevier B.V. All rights reserved.