A METHOD FOR PARTITIONING CADMIUM BIOACCUMULATED IN SMALL AQUATIC ORGANISMS

A series of laboratory experiments was conducted to evaluate bioaccumu lation and surface adsorption of aqueous cadmium (Cd) by sac-fry of th e African tilapia Oreochromis niloticus. In the first experiment, the design consisted of two cadmium treatments: 15 mu g Cd . L(-1) in dilu tion water and a Cd-ethylenediaminetetraacetic acid (Cd-EDTA) complex at 15 mu g . L(-1), and a water-only control. There were five replicat es per treatment and 40 fish per replicate. It was found that EDTA sig nificantly reduced the bioaccumulation of cadmium by tilapia sac-fry b y 34%. Based on these results, a second experiment was conducted to ev aluate four procedures: a no-rinse control; rinsing in EDTA; rinsing i n distilled water; and rinsing in 5% nitric acid, for removing surface -bound Cd from exposed sac-fry. In this experiment, 30 fish in each of five replicates were exposed to 15 mu g Cd . L(-1) for 72 h, processe d through the rinse procedures, and analysed for total Cd. The EDTA ri nse treatment significantly reduced (p < 0.05) Cd concentrations of th e exposed fish relative to those receiving no rinse. It was concluded that the EDTA rinse technique may be useful in studies evaluating the partitioning of surface-bound and accumulated cadmium in small aquatic organisms.