Short-term and chronic exposure of the zebra mussel ( Dreissena polymorpha) to acridine: effects and metabolism

Abstract

To study the potential effects of the relative hydrophilic nitrogen containing polycyclic aromatic hydrocarbons (NPAH) in the aquatic environment, zebra mussels ( Dreissena polymorpha) were exposed to the model compound acridine (benzo[ b]quinoline). In a short-term experiment, the filtration rate of the mussels (1.5–2.0 cm) was measured after 48 h of exposure to different acridine concentrations in the water. In a chronic experiment (10 weeks), filtration rate was measured after 48 h and subsequently once a week, while mortality was monitored daily. Every other day, water and toxicant were renewed and mussels were fed algae ( Scenedesmus acuminatus; 20 000 cells ml −1). Filtration rates were calculated from the decrease in algal concentration. After 48 h of exposure, a clear dose-response relationship was observed for filtration rate, from which the concentration reducing filtration to 50% of that of the controls (EC 50) was calculated to be 0.96 mg acridine 1 −1. During chronic exposure, adverse effects on filtration rate were comparable to those after 48 h, but at the highest acridine concentrations tested, mortality increased rapidly. However, after 4 weeks mortality ceased, coinciding with the disappearance of acridine from the water, in spite of the 48 h water and toxicant renewal. Meanwhile, a metabolite appeared on the HPLC chromatograms, identified as 9(10H)-acridone. The metabolism of acridine seems to have been induced or enhanced, leading to lower toxicant concentrations and diminishing effects on the mussels. There were indications that the mussels, periphyton and bacteria (growing on the walls of the aquaria and on the mussels) all contributed to the breakdown of acridine. Information on transformation of NPAHs in aquatic communities and on the toxicity of metabolites is essential for assessing the ecological risk of these compounds.