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The effects on newly fertilized eggs, embryos and larvae of zebrafish Danio rerio following exposure to sediment samples from the more heavily contaminated River Kö rsch, southern Germany, occurred earlier and were more prominent than in samples from the less contaminated Krähenbach. Dose-and time-related effects following exposure to Kö rsch sediment eluates and extracts included: (1) hatching failure and subsequent death of larvae exposed to undiluted aqueous sediment eluates and reduced hatching rates at sediment extract concentrations d0·0125%; (2) increased mortality after exposure to 25 and 50% dilutions of aqueous sediment eluates, and dilutions of d0·00625% sediment extracts; (3) reduction of heart beat frequency for 50% dilutions of sediment eluates and concentrations of d0·025% extracts; (4) increased frequency of heart and yolk sac oedema after exposure to d0·0125% sediment extracts. Since adverse effects of sediment extracts observed in zebrafish laboratory tests correlated with reproductive failure in natural populations of brown trout Salmo trutta f. fario in the severely polluted River Kö rsch, early life stages tests with zebrafish appear to be a suitable tool to assess the contamination rate of natural sediments.

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