The uptake and distribution of selected heavy metals in the freshwater crab, Potamonautes perlatus (Milne Edwards), in the Eerste River, Western Cape

[摘要] A number of studies on the general physico-chemical character of the Eerste River, WesternCape, had previously been done, but the problem of heavy metal pollution had, by 1993, notbeen addressed. A study was therefore undertaken from 1993-1995 in order to investigate theseaspects. Since several researchers have shown that freshwater crabs accumulate certain heavymetals in their bodies and may therefore be used as monitors of environmental heavy metalpollution, the present study concentrated mainly on metal concentrations (Mn, Zn, Cu, Pb andCd) in the local freshwater crab species, Potamonautes perlatus, and its possible use asbiomonitor in the Eerste River.Two localities in the Eerste River were chosen,. in order to make comparisons, namely arelatively uncontaminated site in the Assegaaibosch Nature Reserve, Jonkershoek, and a visiblypolluted site downstream from Stellenbosch, behind Stellenbosch Farmers' Winery (SFW).Crabs, water and sediment samples were collected seasonally at both localities, and metalconcentrations thereof determined by atomic absorption spectrophotometry.The results showed that the Eerste River down to the SFW locality is still relatively unpollutedin terms of heavy metals. It was, however, clear that runoff from the Stellenbosch municipal,industrial and agricultural areas do have an influence on other physico-chemical features of theriver. The concentrations of heavy metals in whole crabs, tissues and carapace showed that Znconcentration was well regulated in P. perlatus from both localities, Mn and Cu wereaccumulated in individuals from SFW, and Pb and Cd accumulated in both populations.Compartmentalization of heavy metals was shown to occur in P. perlatus: the carapace wasfound to be the most important storage site for Mn, Zn and Pb, the carapace and gonads equallyimportant for Cd storage, and the digestive gland the most important site for Cu storage.Whereas gender was shown, generally, to be of little importance in heavy metal uptake in P.perlatus, crab body size and seasonality were both shown to influence heavy metal uptake tosome extent. However, only summer peaks in whole crab, carapace and tissue manganeseconcentrations were shown to correlate with peaks in environmental Mn concentrations.It was concluded that P. perlatus would possibly only be a Suitable monitor of environmentalMn, Pb and Cd pollution, although there is no guarantee that the crab body would accuratelyreflect environmental concentrations. It was also ascertained that, since a study of the spermultrastructure of P. perlatus showed a significantly larger number of abnormal spermatozoa inmale crabs from ,SFW, and since these observed differences could possibly be related to heavymetal exposure, the sperm of this species might be a more reliable indicator of heavy metalpollution. It was finally concluded that more intensive research need to be undertaken on variousaspects, especially the use of the spermatozoon as indicator of environmental heavy metalpollution, and that the results of the present study could serve as a basis for future studies.

[发布机构] Stellenbosch University