Uptake and distribution of lead (Pb) and cadmium (Cd) in the freshwater crab, Potamonautes perlatus (Crustacea) in the Eerste River, South Africa

The uptake and distribution of lead (Pb) and cadmium (Cd) in the freshwater crab, Potamonautes perlatus in the Eerste River, South Africa were studied seasonally over two years by comparing concentrations in crabs, water and sediment in two localities, one upstream and one downstream from the town of Stellenbosch. Lead and cadmium concentrations in whole crabs of different size classes as well as concentrations in various organs and tissues were determined by atomic absorption spectrometry. Data on physical, chemical and bacteriological features are also presented. The mean Zn concentration in the sediment of the downstream locality (77.5 +/- 38.4 mug g(-1)) was significantly higher than in the less polluted upstream locality (44.7 +/- 32.8 mug g(-1)) whilst the manganese concentration of the sediment was significantly higher in the upstream locality. The gonads (mean Pb 23.4, range 0.1-125.0 mug g(-1); mean Cd 5.3, range 0.1-22.2 mug g(-1)) and carapace (mean Pb 23.4, range 0.7-327.6 mug g(-1); mean Cd 4.0, range 0.4-18.5 mug g(-1)) contained the highest concentrations of both metals irrespective of season or locality. For both Pb and Cd significant differences ( p < 0.05, Student's t-test) were found between the metal content of different organs. The gonads had the highest and the digestive glands the lowest concentrations of both heavy metals. Results indicated that anthropogenic activities did not influence sediment and water concentrations significantly. Smaller crabs accumulated more lead and cadmium than larger crabs with all crabs having significantly higher concentrations than both water and sediment. No significant differences in mean concentrations of lead and cadmium in whole crabs or organs were found between the two localities. Although body loads for both metals did not reflect prevailing environmental levels of these metals reliably, the crabs may still be used to monitor bioavailability over time.