Carsten K. Schmidt

Kinetics and Mechanisms of N-Nitrosodimethylamine Formation upon Ozonation of N,N-Dimethylsulfamide-Containing Waters: Bromide Catalysis

N,N-Dimethylsulfamide (DMS), a newly identified, ubiquitous degradation product of the fungicide tolylfluanide, has been shown to be a N-nitrosodimethylamine (NDMA) precursor during ozonation. In this study, batch ozonation experiments in ultrapure buffered water, surface water, and tap water were performed to determine the kinetics and elucidate the mechanism of NDMA formation from DMS. It was found that at circumneutral pH, DMS reacts slowly with ozone (k approximately 20 M(-1) s(-1)) and moderately with hydroxyl radicals (k=1.5x10(9) M(-1)s(-1)). The reaction of DMS with these oxidants does not lead to NDMA. NDMA was only formed if bromide was present during ozonation of DMS-containing waters. Bromide is oxidized to hypobromous acid (HOBr) by ozone which then reacts with the primary amine of DMS to form a Br-DMS species. The rate limiting step of the formation of Br-DMS is the formation of HOBr. The reaction to form Br-DMS has an apparent second order rate constant at pH 8 of >3x10(4) M(-1)s(-1). The Br-DMS is transformed by ozone to NDMA and nitrate (k>or=5000 M(-1) s(-1)), with yields of 54% and 39%, respectively, based on the primary amine nitrogen of DMS. These reactions release bromide, making bromide a catalyst. NDMA is also formed during ozonation of DMS in the presence of hypochlorous acid (20-30% yield). The last step of NDMA formation is an intramolecular rearrangement with sulfur dioxide extrusion. On the basis of the mechanistic and kinetic information, it was possible to model NDMA formation in DMS-containing Lake Zurich water.

Trace-level analysis of phosphonates in environmental waters by ion chromatography and inductively coupled plasma mass spectrometry

A novel analytical method for the trace-level determination of the organic phosphonates 1-hydroxyethane(1,1-diphosphonic acid) (HEDP), nitrilotris(methylene phosphonic acid) (NTMP), ethylenediaminetetra(methylene phosphonic acid) (EDTMP), hexamethylenediaminetetra(methylene phosphonic acid) (HDTMP) and diethylenetriaminepenta(methylene phosphonic acid) (DTPMP) in natural waters is described. Key-elements of the novel method are the destruction of the various metal complexes which are present in natural water samples by a strong cation exchange resin, the subsequent 50-fold pre-concentration of the analytes by a weak anion exchanger and their final determination by ion chromatography and inductively coupled plasma mass spectrometry. Addition of the complexing agent diethylenetriaminepentaacetic acid (DTPA) to the eluent of the anion exchanger leads to a significant improvement of the chromatographic performance for all phosphonates, but especially for EDTMP. Detection of the phosphorous species in ICP-MS is done via the molecular ion 47PO+ which exhibits high sensitivity and which is only marginally affected by interferences. Validation of the method gives excellent performance parameters with recoveries close to 100%, limits of detection below 0.1 µg/L for each individual target compound and standard deviations for replicate analyses below 10%. Application of the novel method to environmental samples shows that trace amounts of HEDP and DTPMP may be found in river waters affected by discharges of municipal or industrial wastewater treatment plants.