Tissue elemental status of the freshwater clam, Galatea paradoxa (Donacidae) from the Cross River, Nigeria

The soft tissue levels of six nutritional elements [Magnesium (Mg), Calcium (Ca), Iron (Fe), Copper (Cu), Zinc (Zn), Manganese (Mn)] and two toxic ele ments [Lead (Pb), Cadmium (Cd)], were determined in the freshwater clam, Ga latea paradoxa from the lower Cross River, Nigeria. The dominant element wa s Mg which accounted for 69.97% of total tissue elemental concentration. Th is was followed by Ca (12.97%), Fe (10.53%), Cu (7.19%), Zn (5.56%) and Mn (2.72%). Both Pb and Cd constituted < 1% of the total elemental content. Th e concentrations of Mg, Ca, Pb and Cd increased with clam age while those o f Fe and Mn decreased. Variations in the concentrations of Cu and Zn were a ge-independent Clams stored in demineralized water over a 5-day period exhibited a decline of tissue elemental contents. The toxic elements (Pb, Cd) were most heavil y lost on the first day and the majority of the essential nutritional eleme nts, between the second and third days. It is conjectured that the consumer can reduce the toxicological impacts of Pb and Cd by depuration over a min imum duration of one day. However, for optimum, consumer nutritional benefi t from the essential elements, depuration should not exceed two days.