Temporal variability of organic micropollutants in suspended particulate matter of the River Elbe at Hamburg and the River Mulde at Dessau, Germany.

Abstract

The compound classes of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and a number of chlorinated hydrocarbons (CHs) in the River Elbe and its tributary Mulde were investigated on the basis of monthly mixed samples of suspended particulate matter (SPM). Covering the period from September 1994 to August 1995, samples from the River Elbe were taken at Hamburg, those from the River Mulde at Dessau. The samples were extracted by supercritical fluid extraction (SFE). Analysis of all substance groups were performed by highperformance liquid chromatography (HPLC), followed by gas chromatography with mass spectrometric detection (GC/MSD). As a statistical approach for the interpretation of data, hierarchical cluster analysis of the individual compound classes were performed to determine differences or similarities between the sampling sites Hamburg and Dessau to find spatial and seasonal concentration patterns. These analysis showed that, with a high significance, the concentration patterns of n-alkanes, PAHs, and CHs were sampling site-specific in both the Elbe and Mulde throughout the entire sampling period. In all cases, clustering of mostly consecutive months indicated continuous, slow changes of input, which moreover showed a constancy with respect to annual cycles. Correlation analysis of pollutant loads with different hydrographic parameters showed a number of linear dependencies of the contaminants with temperature, SPM content, and water discharge. Annual fluxes of particle-bound pollutants were calculated for each sampling site, taking into account the average monthly SPM levels and the water discharge. The particle-bound pollutant loads for the River Elbe at Hamburg were estimated to 13.4 t/a n-alkanes, 4.1 t/a PAHs, and 175. 8 kg/a CHs. The pollutant loads for the River Mulde at Dessau amounted 0.55 t/a n-alkanes, 0.14 t/a PAHs, and 15.5 kg/a CHs during the monitoring period. The input of n-alkanes originated from different sources. The n-alkane pattern of samples of the River Elbe showed a predominance of odd-numbered compounds in the range of C-20 and C-30 originating from terrestrial plants and, depending on the season, high concentrations of C-15 and C-17 due to aquatic organisms. Only a small proportion of n-alkane input originated from petroleum sources. Samples from the River Mulde showed high amounts of the n-alkanes C-12 to C-15, indicating the input of light oil throughout the entire sampling period, constituting approximately 25% of the total n-alkane concentration. PAHs, which are considered combustion products, were widely distributed in all samples. Although the major inputs of PAHs were probably combustion sources and urban runoff, unusually high concentrations were found for some PAHs, which can be explained by point sources. A comparison of the standardized PAH patterns in samples from both stations clearly showed that higher fused ring systems, which mainly originate from combustion processes (four- to six-ring systems), had considerably higher relative concentrations in SPM from the Elbe than from the Mulde, where higher relative concentrations of the two- and three-ring systems were measured. This confirms findings that petroleum input was higher in the Mulde than in the Elbe. Concentrations of chlorinated hydrocarbons in SPM samples from the river Mulde had comparatively high levels. The largest differences were found for p,p'-DDT and its metabolites p,p'-DDD and p,p'-DDE. On average, concentrations of p,p'-DDT, p,p'-DDD, and p,p'-DDE in the Mulde were about 10, 15, and 25 times higher, respectively, than in the Elbe. Concentrations of HCB, which in the samples from Hamburg had the highest concentrations of all CHs, were found to be higher by about a factor of 3 in the Mulde River. The PCB levels in samples from the Mulde and Elbe were about equal, although there were differences in the pattern of PCB congeners.