Bioconcentration factors of heavy metals in tropical crab (carcinus sp) from River Aponwe, Ado-Ekiti, Nigeria

The bioconcentration factors (BCF) of heavy metals in the tissues of tropical crab (Carcinus sp) obtained from River Aponwe in Ado-Ekiti, Nigeria, were determined. Nine heavy metals (As, Cd, Cu, Hg, Mn, Ni, Pb, Se and Zn) were studied. Tissues from the chest region as well as from the appendages were collected and their bioconcentration factors separately determined. The bioconcentration factors obtained for the various heavy metals in the chest region and the appendages are respectively as follows: As (0.50, 0.40). Cd (3.75, 3.00); Cu (1.83, 1.71); Hg (0.83, 0.50); Mn (0.15, 0.14); Ni (0.11, 0.09), Pb (0.20, 0.19); Se (0.37, 0.38) and Zn (5.00, 4.89). Bioconcentration factors obtained for As, Hg, Mn, Ni, Pb and Se were all less than 1.00 implying no bio-accumulation. However, bioconcentration factors greater than 1.00 obtained for Cu, Cd and Zn evidently indicated that the metals were highly bio-accumulated and bio-magnified. Zn with the highest bioconcentration factors was the most bio-accumulated and bio-magnified of all the metals studied. There is a growing concern about the physiological and behavioural effects of environmental trace metals in human population. Toxicities of heavy metals at high levels of exposures are well known, but of a major concern is the possibility that continual exposure to relatively low levels of these metals through regular consumption of the crabs may entail adverse health effects.