ACCUMULATION OF NICKEL IN 3 FRESH-WATER CRAB POPULATIONS

An investigation was made into the nickel concentrations of the water and sediments of the Natalspruit and Bronkhorstspruit Rivers (Gauteng) and Nooitgedacht Dam (North West Province), as well as nickel concent rations in tissues of the freshwater crab Potamonautes warreni from th ese three water systems. Water nickel concentrations were relatively c onstant, while large fluctuations were detected in the sediment nickel concentrations. The highest water and sediment nickel concentrations were measured at the Natalspruit River. The highest mean tissue concen tration of nickel in P. warreni sampled from the three aquatic systems was detected in the carapace, indicating that this tissue might be us ed as a sink for nickel, for disposing of excessive amounts during the moult-cycle. No seasonal variation was detected. Sex also does not se em to be a variation factor in the bioaccumulation of nickel except in the mature gonads. P. warreni collected from the three different samp ling sites showed a general increase in tissue nickel concentrations w ith a decrease in size. Significant correlations were observed between the midgut gland nickel concentrations and the concentration of this metal in the water (r = 0,63) and sediment (r = 0,77), as well as betw een the muscle nickel concentration and the water and sediment nickel concentrations (r = 0,63 and r = 0,77, respectively). These phenomena, as well as the fact that Fl warreni is able to accumulate relatively high levels of nickel in various tissues, suggest that this freshwater crab is a potential indicator of nickel pollution in aquatic ecosyste ms.