Compound-specific stable chlorine isotope analysis : A versatile tool for investigating biochemical and geochemical processes of organochlorine substances

University dissertation from Stockholm : Institutionen för tillämpad miljövetenskap (ITM)

Abstract: Chlorinated organic compounds (OCls) from anthropogenic sources are generally considered to be a class of chemicals with high potential for ecotoxicity, including infamous substances such as polychlorinated biphenyls (PCB), dichloro-dibenzo-trichloroethane (DDT) and polychlorinated dibenzo-p-dioxins (PCDD). OCls are also produced naturally, sometimes at the same order of magnitude as anthropogenic compounds. The scope of this thesis was to develop and apply a method for isotope analysis of OCls, as a part of compound-specific chlorine isotope analysis (CSIA-?37Cl) of trace level compounds. Isotope analysis of chlorine was performed with sealed-tube combustion and thermal-ionization mass spectrometry (TIMS), in order to improve the analytical sensitivity by a factor 20 relative to conventional techniques. Chlorine isotope signatures of organochlorines (?37Cl-OCl) can be used for source apportionment in the natural vs. anthropogenic spectrum. CSIA-?37Cl was tested as a tool to resolve the origin of putatively natural PCDD found in ball clay from the Mississippi Embayment, USA. Combined with results from 14C analysis, the ?37Cl-PCDD was consistent with a natural abiotic formation of PCDD. Reactions involving the scission of a chemical bond to a molecular chlorine substituent will induce a shift in the ?37Cl-OCl of the remaining reactant. This concept was used to calculate the undegraded fraction of DDT in the Baltic marine environment (~7% DDT remaining) based on ?37Cl-OCl measurements of DDT harvested from seal blubber. Hence, it is suggested that CSIA-?37Cl may be very useful in studies of fate and origin of OCls in the environment, and that further applications of the technique are warranted.

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