Mobility and bioavailability of trace metals in sulfidic coastal sediments

High concentrations of Hg, Cd, Pb, Cu, and Zn were found in the euxinic sed iment of the inner archipelago of Stockholm. In the sulfide-rich sediment, they are precipitated as metal sulfides with low dissolving capacity and bi oavailability. In two experiments, the significance of acid-volatile sulfid e (AVS) and dissolved sulfides for mobility, bioavailability, and toxicity of metals were studied by oxygenation of intact sediment cores. Influence o f bioturbating deposit-feeding amphipods, that is, Monoporeia affinis, was examined on studied sediment processes. Results showed a low mobility of mo st metals except Cd and Zn. Bioturbation did not enhance mobility. Cd and Z n, released from the sediment, were not bioaccumulated in amphipods. In con trast, the less mobile metals Hg and Pb were bioaccumulated. A low toxicity of contaminated sediments, in terms of mortality and embryonic malformatio ns of amphipods, was recorded. Results indicate that Cd, Zn, and Cu are com paratively unavailable after oxygenation of the metal sulfides. Similar res ults were recorded in contaminated sediments differing in redox potential, AVS, dissolved sulfides, and organic contents, suggesting that other metal ligands, in addition to AVS. are important for metal bioavailability and to xicity in anoxic and suboxic environments.