Four bioassays were selected to examine sediment-elutriates of three flowing waters in the Saarland (South-West Germany). The aims of this study were the determination of the most sensitive bioassay for a sediment assessment within routine screening procedures and the comparison of a recently developed long-term bacterial assay with other commonly used and standardized bioassays.
Sediment samples were elutriated with water and also with dimethyl sulphoxide in order to extract organic compounds. An expected accumulation of toxicants in the sediments was checked by additional examination of surface water at respective sampling sites, applying bioassays as well as chemical analysis methods.
Whereas the sensitivity of the Daphnia magna assay was relatively low, the Scenedesmus subspicatus chlorophyll fluorescence test denoted the presence of high loads of nutrients at all sites. The results obtained using the Vibrio fischeri short-term bioassay suggested that an ecotoxicological risk can be excluded.
The long-term luminescent bacteria assay is a further development of the short-term V. fischeri-assay. Prolonging the test duration from 30 min to 24 h should track down subacute toxicities, thus leading to a greater degree of sensitivity. However, the prolongation caused severe problems in respect of an accurate interpretation of the results. The long-term assay is not suited for routine deployment without major improvements.
The extractable content of metals, pesticides, polychlorinated biphenyls and chlorinated hydrocarbons remained below their threshold values by several orders of magnitude.
The use of dimethyl sulphoxide as solvent caused a decrease of bioluminescence in both bacterial assays. The inhibition was caused by toxic metabolic products of dimethyl sulphoxide formed by autochthonous bacteria from the sediment samples during the elutriation procedure. Thus, the use of dimethyl sulphoxide is not recommended for examinations of environmental samples when applying a luminescent bacteria assay.