During the last two decades, a decline in fish catch as well as a decrease in the abundance of many species was reported for the upper Danube River, Germany. A pilot investigation in 2002 and a more comprehensive study in 2004/05 was undertaken in order to elucidate the cause of the fish decline. These studies demonstrated a relatively high ecotoxicological hazard potential of Danube River sediments. Consequently, a further investigation on the exposure scenario of fish to sediment-borne pollutants was realised in the present study.
Main known moderately and strongly lipohilic sediment-borne pollutants are polycyclic aromatic hydrocarbons, polychlorinated biphenyls and polychlorinated dibenzo-p-dioxins and dibenzofurans. These substances may act harmfully on an organism’s health status and are known to elicit their adverse effect via the aryl hydrocarbon receptor (AhR) in the cell. In order to investigate the potential Ah receptor-mediated toxicity of sediment-borne compounds to fish, the measurement of the enzyme activity of 7-ethoxyresorufin-O-deethylase (EROD) was used as a biomarker. The chosen biomarker is known to reflect the levels of harmful substances as above-mentioned in the organism and the environment. Therefore, the recently described gill EROD-assay was developed further for sediment toxicity investigation in the three-spined stickleback (Gasterosteus aculeatus L.) in combination with the measurement of EROD-induction in the liver.
The results showed that the determination of EROD in gill filaments of the stickleback in combination with EROD-measurement in the liver is a suitable tool in vertebrate-based sediment toxicity assessment. The high EROD-inducing potency of the sediment indicates that a high concentration of sediment-borne Ah receptor agonists is a possible factor contributing to the fish decline in the upper Danube River. An observed sex-dependent pattern of the in vivo EROD-induction provides a first link between in vitro data and field observations.