No abstract

It is generally accepted that the bioavailability of metals in sediments is influenced by the presence of acid volatile sulfides (AVS). The pore water hypothesis predicts that, if the molar concentration of simultaneously extracted metals (SEM) in a sediment is smaller than the molar concentration of AVS, the free metal ion activity in the pore water is very small and that consequently no metal toxicity in short-term toxicity tests is observed. In this study we examined (1) if this concept can be extended to predict the absence of chronic Ni toxicity to the oligochaete deposit-feeding worm Lumbriculus variegatus and (2) It has been demonstrated that the simultaneously extracted metals -acid volatile sulfide (SEM-AVS) method is an effective tool in predicting the absence of metal toxicity in sediments in short-term toxicity tests when [SEM-AVS] < 0 (Di Toro et al., 1990;Di Toro et al., 1992;Casas and Crecelius, 1994;Pesch et al., 1995;Hansen et al., 1996).The underlying principle is that except for pyrite, all other iron and manganese mono sulfides that may be present in sediments have higher solubility products than other metal sulfides. Thus, Fe and Mn can be displaced by other divalent metals (Cu, Cd, Ni, Pb, Zn) on a mole-to-mole basis. Because these metal sulfides exhibit very low solubility, sediments with an excess of reactive sulfide will exhibit very low dissolved metal concentrations in pore waters and will not cause toxicity .Sediments with excess SEM do not always exhibit toxicity to invertebrate sediment organisms. Organic matter can bind non-sulfide bound trace metals, thus preventing them to enter the dissolved phase . Based on this, [SEM-AVS]/f OC has been proposed as a measure of bioavailable metal (Di Toro et al., 2005;. In a recently proposed biotic ligand model for sediments, it has been shown that [SEM-AVS]/f OC determines the free metal activity in the pore water (Di Toro et al., 2005). If this value is greater than a critical threshold, sediments are predicted to be toxic.The [SEM-AVS]/f OC concept assumes that there is no metal toxicity caused by transformations of the sulfide and organic matter bound metal in the gut of sedimentingesting organisms or via exposure to contaminated food (Meyer et al., 2005 (Lee B.G., Griscom S.B. et al., 2000). However, they also note that generic relationships between metal bioaccumulation and toxicity are not well understood. Animal species differ in their abilities to detoxify bioaccumulated metals (e.g. via metallothionein or granule induction) or develop tolerance (Adams et al., 2000;. An increase in bioaccumulation may be a sign of active metal uptake and not toxicity in the case of metal deficiency (Muyssen and Janssen, 2002;Bossuyt and Janssen, 2003). Thus, bioaccumulated metals may not always reflect toxic effects (McGeer et al., 2003).To our knowledge, the applicability of the SEM-AVS concept to predict the absence of chronic, sub-lethal toxicity of nickel to a benthic organism exposed in single-species laboratory toxicity tests has not been demon...