Nickel Accumulation byScenedesmusand Daphnia: Food-Chain Transport and Geochemical Implications

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Abstract
The accumulation of Ni in two levels of a simple aquatic food chain was determined as a function of the concentration of the free metal ion. in NTA-buffered media, Scenedesmus obliquus accumulated Ni to concentrations 30–300 times above ambient. At pNi (= −log Ni2+concentration) below 8, algal growth rate declined, cellular Ni quota increased, but no change in the relative size of labile and nonlabile Ni pools was detected. In the same media, Daphnia magna also concentrated Ni but only to levels slightly above ambient. Both short-term (72-h) and long-term (13-d) incubations with D. magna indicated that direct uptake from solution rather than uptake from ingested algae was the primary accumulation vector. There was no biomagnification from the algae to the zooplankton. Ingested particulate Ni was concentrated presumably in fecal matter, which normally sinks to the sediment.

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