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RATIONALE: The recent development of compound-specific online chlorine isotope analysis ((37) Cl-CSIA) methods has fostered dual chlorine-carbon isotope studies to gain better insights into sources and environmental transformation reactions of chlorinated ethenes (CEs). 1-point and 2-point calibration schemes are currently used to convert raw data to the international δ(37) ClSMOC scale, but a critical evaluation of best practices to arrive at reliable δ(37) ClSMOC signatures and enrichment factors was missing and is presented here. METHODS: Aqueous solutions of neat PCE and TCE and aqueous samples from a TCE biodegradation experiment with pure cultures of Desulfitobacterium hafniense Y51 were analysed for their chlorine isotope ratios using GC/qMS and GC/IRMS. The δ(37) ClSMOC values were obtained using 1-point and 2-point calibration schemes. Chlorine isotope enrichment factors, ɛCl , were calculated using both approaches and the corresponding bias of δ(37) ClSMOC values introduced by the different types of calibration was determined. RESULTS: Different calibration methods resulted in significant differences (up to 30%) in both δ(37) Cl signatures and ɛCl -values. CONCLUSIONS: Our results demonstrate that a 2-point calibration together with comprehensive information on reference materials is indispensable and should become standard practice for reliable (37) Cl-CSIA of organic compounds.

The present study investigates the oxidation of methyl tert-butyl ether (MTBE) by conventional ozonation and the advanced oxidation process (AOP) ozone/hydrogen peroxide under drinking water treatment conditions. The major degradation products identified were tert-butyl formate (TBF), tert-butyl alcohol (TBA), 2-methoxy-2-methyl propionaldehyde (MMP), acetone (AC), methyl acetate (MA), hydroxyisobutyraldehyde (HiBA), and formaldehyde (FA). The rate constants of the reaction of ozone and OH radicals with MTBE were found to be 0.14 and 1.9 x 10(9) M-1 s(-1), respectively. The rate constants for the same oxidation processes were also measured fort he degradation products TBF, MMP, MA, and HiBA (k(O3-TBF) = 0.78 M-1 S-1; k(OH-TBF) = 7.0 x 10(8) M-1 s(-1); k(O3-MMP) = 5 M-1 s(-1); k(OH-MMP) = 3 x 10(9) M-1 s(-1), k(O3-MA) = 0.09 M-1 s(-1), k(O3- HiBA) = 5 M-1 s(-1); k(OH-HiBA) = 3 x 10(9) M-1 s(-1)). Since all compounds reacted slowly with molecular ozone only the degradation pathway of MTBE with OH radicals as been determined, including the formation of primary degradation products. In experiments performed with several natural waters, the efficiency of MTBE elimination and the formation of bromate as disinfection byproduct have been measured. With a bromide level of 50 mug/L, only 35-50% of MTBE could be eliminated by the AOP O-3/ H2O2 without exceeding the current drinking water standard of bromate (10 mug/L). The transient concentrations of MTBE and its primary degradation products were modeled using a combination of kinetic parameters (degradation product distribution and rate constants) together with the ozone and OH radical concentration and were in good agreement with the experimental results.