Pathways to Natural Organochlorine Formation in Decaying Plant Material: A Novel Assay

Organochlorine compounds were long believed to be exclusively anthropogenic environmental toxins, but recent research has shown that such compounds occur naturally in soils. The processes leading to the formation of soil organochlorine are poorly understood but are believed to be associated with the decay of plant material. Fallen leaves undergo degradative processes that transform them into highly decomposed organic matter (soil humus), which contains high levels of organochlorine. Natural chlorination may occur via catalysis by the enzyme chloroperoxidase (CPO), which converts inorganic chloride to reactive chlorine (HOCl). It is possible that fungi and other organisms implicated in leaf litter decomposition produce HOCl to aid in the breakdown of plant material. Oxidized chlorine, released extracellularly, can react with organic matter to produce organochlorine by‐products. We measured the formation of organochlorine in senescent leaves exposed to enzyme extracts of leaf litter and soil humus using X‐ray absorption spectroscopy and mass spectrometry. Colorimetric UV‐Vis assays show substantial chlorinating activity in the enzyme extracts. These results link CPO‐like activity with the formation of organochlorine in the terrestrial environment, identifying a biological chlorination pathway associated with leaf litter decomposition.