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Compound-specific chlorine isotope analysis (CSIA–Cl) is promising as a novel and powerful method for monitoring in situ degradation of organochlorines in the environment and for source fingerprinting purposes. In order to apply CSIA–Cl in field studies of polychlorinated biphenyls (PCBs), the chlorine isotopic composition (δ37Cl) of individual PCB congeners in source materials must be known. In the present study, we determined δ37Cl of 18 congeners isolated from three widely produced technical mixtures. All congeners provided δ37Cl ranging between −1.9‰ and −3.5‰. Although the comparable products Aroclor 1242 (−2.0‰ to −2.5‰) and Clophen A30 (−1.9‰ to −3.0‰) were synthesized by different industries, they provided similar δ37Cl for the same type of congeners. On the contrary, the more chlorinated congeners present in Aroclor 1254 (−2.1 to −3.5‰) were more 37Cl depleted compared to Aroclor 1242 manufactured by the same company. Overall, δ37Cl of PCB congeners decreased by −0.26 ‰ for each additional chlorine atom. [Copyright &y& Elsevier]

Compound-specific chlorine-isotope analysis (CSIA-Cl) of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethene (p,p′-DDE) in blubber from Baltic Grey seal (Halichoerus grypus) was performed in order to investigate if a kinetic isotope effect (KIE) could be observed concomitant to environmental degradation of DDT. The δ37Cl of p,p′-DDT and p,p′-DDE were −0.69±0.21‰ and −2.98±0.57‰ (1σ, n =3), respectively. Both samples were enriched relative to the hypothesized initial isotope composition (−4.34‰), thus indicating a composite KIE associated with the degradation mechanisms pertaining to DDT. An isotope fractionation factor for degradation of dichloromethane, from the literature, was adapted and modified for use in the calculation of DDT degradation. A subsequent simplified Rayleigh distillation model of the DDT chlorine-isotope composition yielded an estimated fraction (f) of 7±2% of released DDT presently remaining as undegraded compound in the environment. The consistency between the result of the Rayleigh model (f ∼7%) and the use of the DDT/(DDT+DDE) ratio as a measure of DDT degradation (∼10% undegraded DDT) suggests that the KIE of DDT degradation may be significant, and that the novel approach of CSIA-Cl may be a valuable tool for degradation/persistence studies of lipophilic organochlorines in the environment. [Copyright &y& Elsevier]

Abstract: Chlorine isotope fractionation during preparative capillary gas chromatography (pcGC) was investigated using 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) as a model compound for semi-volatile organochlorine (OCl) molecules. Chlorine isotope analysis by thermal ionization mass spectrometry revealed no significant alteration of the chlorine isotope composition when the whole peaks were collected in pcGC (δ37Cl −3.2‰ versus −3.6‰ for the unprocessed DDT, ±0.5‰ SD). However, distinct isotope fractionations were measured for the front (δ37Cl −5.1‰) and tail (δ37Cl −1.8‰) segments of partially collected samples. Isolation of individual OCls by pcGC enables accurate off-line chlorine isotope analysis, and thus facilitates the investigation of naturally occurring OCls. [Copyright &y& Elsevier]

Improved sensitivity in the analysis of stable chlorine isotopes of organochlorines (δ37Cl-OCl) has been established using sealed tube combustion in conjunction with thermal ionization mass spectrometry (TIMS). TIMS of chlorine isotopes was performed on < 85 nmol of Cl with an achievable precision of < 0.25‰ for pure inorganic chloride samples and 0.46‰ for chloride liberated from organochlorines (OCls). This makes possible significant reductions in the overall sample size requirement, as compared to the techniques of gas source stable isotope ratio mass spectrometry (SIRMS). Yields in excess of 99% were demonstrated in the dechlorination of <0.14 μmol 1,1, l- trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and the overall yield, including purification of liberated chloride, was 86-97%. The accuracy of TIMS in the measurement of chlorine isotopes derived from OCls was con- finned by analysis of a DDT sample previously analyzed with SIRMS. Using the described method for TIMS, the DDT sample gave a bulk chlorine isotope ratio of δ37Cl -4.42 ± 0.46‰ (1σ). The reported value from SIRMS analysis is -4.34 ± 0.25‰ indicating the conformity of the two methods. [ABSTRACT FROM AUTHOR]