Heavy metals (Cd, Pb, Cu, Zn) in mudfish and sediments from three hard-water dams of the Mooi River catchment, South Africa

Abstract

Fish tissue from Labeo capensis and sediment core samples from three dams in the Mooi River catchment area were collected and analysed for Cd and Pb by electro-thermal AAS, and for Cu and Zn by flame AAS. The highest Cd concentrations were found in the clay fractions in all three dams, with a range between 66.0 μg g^-1 and 107 μg g^-1. Lead concentrations below 34 μg g^-1 were found in all six sediment types from Klerkskraal Dam, while Potchefstroom Dam had the highest lead levels (range: 34 - 62 μg g^-1) for the six sediment fractions and also for all the fish tissue types (range: 38 - 79 μg g^-1). Lead alkyls from motorboat exhausts were probably responsible for the high lead concentrations in the sediment of Potchefstroom Dam and in the mudfish tissues. The mean zinc concentrations from five of the six fractions in Boskop Dam were significantly higher compared to the other dams, with a range between 25 μg g^-1 to 59 μg g^-1>. The combined six fractions were between five and 100 times lower in concentration when compared to the pelitic sediment samples from sediments at the Lebanon and West Driefontein mines in the Mooi River catchment. Copper concentrations in dam sediment from the six fractions for the three dams, ranging between 11 μg g^-1 to 36 μg g^-1, were higher when compared with copper levels worldwide. The kidneys, gills and liver had the highest levels of Cd, Pb and Cu respectively compared to other tissues from L. capensis, while the gills had the highest concentration of Zn. In conclusion, higher than normal metal concentrations were found in Boskop Dam sediments, which could be linked to gold mine operations inside the Mooi River catchment area. Lead, Cd, Cu and Zn concentrations in L. capensis tissues were much lower compared to reported data on South African fish, but on par with world levels. The percentage of uranium present in sediment samples (analysed by energy dispersive X-ray spectrometry) from the three dams was 9.0 % (SD 2.1%). In sediment it was found that cation exchange capacity measurements and the dolomitic hard water and high pH of the Mooi River water effectively \'detoxified\' Cd and Pb, forming insoluble complexation products buried in the sediment.


WaterSA Vol.30 (2) 2004: 211-218