Ecotoxicological Studies. 6. The first comparative study between Lake Qarun and Wadi El-Rayan wetland (Egypt), with respect to contamination of their major components

Abstract

Water, sediment and fish samples collected from Lake Qarun and Wadi El-Rayan lakes (Egypt) were subjected to different analyses in order to compare contamination levels in these ecosystems. The waters showed similar ionic characteristics, but those from Lake Qarun contained total dissolved salts (TDS) ranging from ca. 4.0 to 35.0 g/l with an average of 19.0 g/l which was much higher than those recorded for the first and the second lakes of Wadi El-Rayan (e.g. 1.6 and 4.7 g/l, respectively). The bacterial count was also greater in the water and sediment from Lake Qarun. Heavy metals (e.g. iron, manganese, zinc, nickel, copper, cobalt, chromium, lead, cadmium, tin) and pesticide residues (e.g. HCB, lindane, aldrin, some DDT analogues, malathion, pirimiphos-methyl) were detected in the major components of Lake Qarun. Some of these contaminants were also detected in different samples from Wadi El-Rayan, but at lower concentrations. The toxicity bioassay of Wadi El-Rayan water against Daphnia magna neonates and Culex pipiens larvae resulted in negligible mortality values. Lake Qarun water induced 8.0–100.0 and 3.0–100.0% mortality, respectively against the tested organisms. The overall results of this study revealed that Lake Qarun components were more polluted than those of Wadi El-Rayan lakes, and the second lake of this wetland was more contaminated than the first. Therefore, solutions have to be found; otherwise this virgin wetland will face pollution problems similar to those of Lake Qarun.