Compounds Elbe specific marker

Beside the components described above several compounds could be identified that seemed to be indicative of the contribution of the Elbe river to the pollution of the sediments in the German Bight (Tab. 3). The use of these compounds as potential Elbe-specific markers is, however, limited because of the limited information about the organic matter derived from other rivers also discharging into the German Bight. 

Two classes of substances are appropriate as Elbe-specific marker compounds (i) common compounds only detected in high amounts at the locations close to the Elbe river (A,B), and (ii) compounds with specific molecular structures that are not ubiquitous contaminants or have been described formerly as contaminants of the Elbe river. 

To a minor degree degradation products of the pesticide DDT might be useful Elbe-specific marker compounds, because of the longer period of DDT application in the catchment area of the Elbe river in contrast to the Weser and Ems rivers and the high concentration of DDD and DDE found in water as well as suspended particulate matter of the Elbe river (Goetz et al., 1994, lit). The para-substituted isomer of DDE could be detected only in sediment samples mainly influenced by the Elbe river (sites A,B,C), whereas 4,4 -DDD occurred additonally at sites D, E and F, but not at site G that is influenced by the Weser river. 

Also, an isomeric mixture of alkylsulfonic acid phenylesters, the individual contaminants tetrabutyl tin and l,2,3,6,7,8-hexahydro-l,l,6,6-tetramethyl-4-isopropyl-as-indacene as well as degradated compounds of DDT could be attributed to the group of Elbe-specific marker compounds. 

Fig. 1 Concentration and spatial distribution of selected Elbe specific marker compounds in sediments of the German Bight (all data are given in pg/kg dry matter and normalized to TOC). All abbreviations of the substances are explained in Tab. 2. The dotted lines indicate the main flow circle of the water body according to Ducrotoy et al. (2000).

Bis(4-chlorophenyl)-l,l,l-trichlorethane (DDT) and related substances were also detected in the North Sea sediments and were previously characterized as abundant compounds in the Elbe river system. They are only of minor use as marker substances because of their widespread occurrence in the aquatic environment (Schwarzbauer et al. 2000). However, DDT was applied in the Elbe river catchment area for a longer period of time than in regions affecting the Ems and Weser rivers. Hence, elevated concentrations were recently detected in Elbe river water and sediments (e.g., Goetz et al. 1994, Dannenberger and Lerz 1998, Ricking et al. 2003, Schulze et al. 2003) and, consequently, the application of DDT metabolites as Elbe specific marker compounds has to be reevaluated by quantitative analyses. 

Selected contaminants were quantified in seven sediment samples of the German Bight. The compounds analysed include substances formerly proposed as Elbe specific marker compounds and contaminants reflecting a diffuse contribution to the pollution of North Sea sediments. For the evaluation of the proposed Elbe marker compounds the quantitative and spatial distribution was investigated and discussed as the most important criterion to define their source specifity. 

Detailed analyses of the organic matter are necessary to identify such specific marker compounds, but only a few investigations have been carried out on organic contaminants in coastal water and sediments of the North Sea. Previous detailed analyses of lipophilic and low molecular compounds in Elbe river water have indicated a high abundance of river-specific organic substances (Franke et al., 1995 Theobald et al., 1995). 

All identified Elbe-specific substances are only potential molecular markers at present, because marker compounds reflecting the input of the Weser and the Ems river to the sediments of the German Bight are not known. 

Potential marker compounds indicating the contribution of the Elbe river are mainly chlorinated aromatic contaminants. Specifically, these markers include tetra- to hexachlorobenzenes, mono- to... 

For the evaluation of these proposed Elbe marker compounds the quantitative and spatial distribution was investigated. These data provide an important criterion to define their source specifity. 

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