comparison of zinc and chromium bioaccumulation in the internal organs of freshwater mussel anodonta cygnea (bivalvia: :union:idae)

nowadays, bivalves are used in monitoring levels of heavy metals in aquatic environments. the aim of this study was to investigate bioaccumulation of heavy metals zinc (zn) and chromium (cr) in the internal organs of anodonta cygnea. for this purpose, bivalve specimens were collected from semeskandeh region, sari, and then in laboratory, were exposed to 125 µg l-1 concentrations of each metal for 27 days. basal levels, accumulated amounts and δc/c0 of both metals in mantle, gill, hepatopancreas and foot of the mussel during study period were measured. zn basal levels in all studied organs were significantly (p < 0/01) higher than cr. there were no difference in zn basal levels between different organs, but for the case of cr, basal levels were different: gill > hepatopancreas ≈ foot > mantle. highest accumulation of both metals were observed in gill and hepatopancreas and minimum accumulation were belonged to the mantle. calculated ratios of δc/c0 for cr were significantly (p < 0/01) higher than zn in all studied organs: zn: hepatopancreas > foot > mantle > gill; cr: mantle > hepatopancreas ≈ foot > gill. based on our results, it can be said that a. cygnea, is a good species for biomonitoring zn and cr levels in aquatic ecosystems.