Particle processing by Mytilus edulis: effects on bioavailability of metals

Mytilus edulis were maintained in laboratory flow-through systems and fed estuarine permanently suspended particulate matter (PSPM), of particle diameters from < 3 to 40 mu m. The concentrations of Fe, Mn, Zn, and Cu in the PSPM, and in the faeces and pseudofaeces produced by the mussels, were determined by atomic absorption spectrometry, following digestion in 1 M HCl. The particulate organic carbon (POC) contents of the PSPM, faeces and pseudofaeces were also determined and used to estimate sorting efficiencies and absorption efficiencies. The concentrations of Fe, Zn, Mn and Cu in the pseudofaeces were often significantly higher than in the PSPM, indicating that mussels had rejected particles enriched in these metals. This finding was not observed in all experiments even when sorting efficiencies were high. The Cu concentrations of the faeces were always significantly lower than the PSPM, reflecting a net loss of Cu from particles in the mussel gut. The amount of Cu released during ingestion was positively related (r(2) = 0.50) to the HCl-extractable concentration of Cu, indicating that variations in the amount of bioavailable Cu in the PSPM may have occurred. The net amount of Cu released during ingestion was also strongly inversely related (r(2) = 0.96) to the POC ingestion rate of the mussels. Alterations in the digestive physiology of mussels (e.g. increases in the proportion of food sent to the digestive gland and increases in gut passage time) compensate for low organic digestion rates in mussels. These alterations may increase the net release of particulate Cu and hence the bioavailability of the metal to the organism. It was not possible to quantify how much released Cu was assimilated by the mussel but the net loss of Cu:carbon from the particles was high in comparison with mussel tissue Cu concentrations. indicating that the released Cu is either not assimilated or is assimilated and quickly excreted. (C) 1998 Elsevier Science B.V.