Bioaccumulation of heavy metals in thionic fluvisols by a marine polychaete:: The role of metal sulfides

Bioavailable heavy metals have been widely studied in recent years because of their toxicity to natural ecosystems. Despite the number of studies tarried out, relatively little is known about the metal fraction that is biologically available. In this study, we analyzed seasonal concentrations of acid-volatile sulfide (AVS) as well as heavy metals associated with the reactive (soluble in 1 M HCI) and pyrite (soluble in HNO3) fractions of the soils of three salt marshes in the ria of Ortigueira (NW Iberian Peninsula). Heavy metal concentrations in polychaete worms (Nereis diversicolor) collected from each salt marsh were also determined and compared with metal contents in the different fractions of the soil. We did not find a relationship between the concentration of total metal or metal incorporated into the reactive fraction in the soil and the tissue-metal concentration in N. diversicolor. The results appear to indicate that this species preferentially accumulates metals associated with reduced forms of sulfur (pyrite and presumably AVS). Oxidation of these metal sulfides would lead to release of Cu and Ni into interstitial water and they would then be readily available to be taken up by these organisms, either by absorption through the body surface or across the digestive tract.