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Organochlorine molecules are commonly observed in natural soils and in most cases have been attributed to pollution from manmade sources.
Natural organic matter, such as humic and fulvic acid, in the shallow subsurface is both universal and little understood. It has no fixed stoichiometry or structure, cannot be crystallized, and is famously difficult to characterize reproducibly. Professor Satish Myneni of Princeton University, together with co-workers at Lawrence Berkeley National Laboratory and the University of Puerto Rico used x-ray microscopy to provide the first in situ images of the macromolecules in various solutions and soils and showed that the molecules coil and relax depending on the composition of the solution and their proximity to a mineral surface.
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The new research uses synchrotron x-ray spectroscopy
to document changes in the chemical state of chlorine in humic materials. The position of the x-ray adsorption edge for chlorine is sensitive to the molecular environment of chlorine. The research confirms the startling conclusion, suspected before by others, that natural organochlorine compounds are common in soil and that there is a net transfer of chlorine from inorganic to organic forms with common weathering. Abundant catalytic peroxidase facilitates the chlorination of natural aromatic organics. These results add strong support to the hypothesis that chlorination of organic compounds in humic materials is widespread, and may explain the puzzling organochlorine concentrations found in otherwise unpolluted environments. Accurately understanding natural conditions is critical in identifying and taking action to correct man-made problems.
For additional details, see:
Myneni, S., et al., 1999, Imaging of humic substance macromolecular
structures in water and soils. Science, 286 (5443), pp 1335-7.
Myneni, S., 2002, Formation of stable chlorinated hydrocarbons in weathering plant
material. Science, 295 (5557): 1039-41
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