The potential use of the South African river crab, Potamonautes warreni, as a bioindicator species for heavy metal contamination

In 1995, preliminary water and sediment analyses of the river bed and burro w sediments from 9 locations along the Mooi River, NW Province, South Afric a had shown cadmium concentrations up to 0.009 mg l(-1) +/-0.003 and up to 0.33 and 0.89 weight % with scanning electron microscopy (SEM) and x-ray mi croanalysis. Samples of the adult river crab (Potamonautes warreni) were co llected from the Mooi River at Noordbrug (26 degrees 40'S/27 degrees 05'E), 1 km north of Potchefstroom Town, and exposed to 0.2 or 2.0 mg Cd2+ l(-1) in situ to determine tolerance, uptake and bioaccumulation of cadmium. Usin g flame atomic absorption spectroscopy (FAAS) the gills, haemolymph and dig estive gland of naturally exposed P. warreni showed wet mass values of 0.74 +/-0.27 mug Cd2+ g(-1), 0.007 +/-0.007 mug ml(-1) and 0.12 +/-0.09 mug g(- 1) respectively. The tolerance of crabs to aqueous Cd reached its limit (ET 50=42 hours) at 2.0 mg l(-1) aqueous Cd exposure. At an exposure to 0.2 mg Cd2+ l(-1) for 21 days, the greatest Cd (n=11; 9.99 +/-5.09 mug g(-1) wet m ass) and Cu concentrations (n=11; 17.90 +/-4.66 mug g(-1) wet mass) were as sociated with the gills, and to a lesser extent the digestive gland (n=11; 0.38 +/-0.20 mug g(-1) wet mass), whereas concentrations of Zn were variabl e in both organs. In the haemolymph Cd levels were relatively small (n=11; 0.012-0.006 mug ml(-1)) with exposure and time and Cu, Zn concentrations va ried. Changes in the uptake of Cd in P. warreni indicated that transport, s torage and possibly regulatory mechanisms are likely to operate in adult cr abs. The potential of P. warreni as a bioindicator species of pollution is also discussed.