Historical Deposition of Riverine Contamination on Terrestrial Floodplains as Revealed by Organic Indicators from an Industrial Point Source

Environmental compartments of riverine systems are polluted by organic contaminants in particular as a result of industrial activity. Sediments and soils of conjunct floodplains can act as archives for long-term anthropogenic pollution. While some chemicals are prevalent, several compounds show source specificity. Compounds closely related to industrial chemical processes comprise precursors, intermediates, and by- and side-products. To better understand the environmental fate of such contamination in aquatic systems, we examined historic sediments of the Mulde River, a riverine system adjacent to the former industrial area Bitterfeld-Wolfen, Germany. This industrial complex produced a variety of chemical compounds between 1950 and the late 1980s. Comparison with related, more recent soil samples from floodplains revealed the presence of these organic indicators (e.g., halogenated naphthalenes, tetrachlorothiophene, dichlorodiphenylsulfone, 1,1,1,2,2-pentachloroethylbenzene, chlorinated diphenylethers) in the uppermost soil layers even over 20 years after the general shutdown of industrial production. Concentrations of numerous non-source-specific pollutants such as DDT metabolites, chlorinated benzenes, and dinaphthyl sulfones were also elevated in most recent wetland soil layers. Generally, concentration profiles showed the highest concentration of compounds in the uppermost soil layer. With increasing soil depth, concentrations decreased. Therefore, the results suggest a continuous input of source and non-source specific contaminations over secondary pollution pathways. This long-term pollution of the environment poses a threat to the quality of riverine systems.