Abstract
The objective of this study is to assess the heavy metals pollution and microbial contamination in water, sediments and fish of Lake Manzala and study the direct and indirect effect for disposal of waste water, industrial and agricultural drainage water into the lake on the environmental situation. Samples were collected from four different sites in the lake and one site in the drain. The selected sites are exposed to direct and indirect industrial, municipal waste water and agricultural drainage disposals. A site near the connection between the lake and the sea was chosen as a possible unpolluted site to compare. Three water samples and one sediment sample were collected monthly from each site for thirteen months. Fish samples (Oreochromis niloticus) were collected randomly for eight months from different sites of the lake. Water salinity and pH values were measured to each site. Water, sediment and fish samples were analyzed for the concentration of five major heavy metals (Mn, Cd, Zn, Pb and Cu), and two groups of bacteria (Total viable bacteria TVB - faecal coliform bacteria FCB). Results show that all the water and sediment samples were collected from five sites contain different concentration of the five tested heavy metals. The highly polluted site with Zn, Pb, Cu in sediment was found in the drain as a result of the industrial disposal. The highly polluted site with Zn and Cu in water and Cd in sediment was found in site near the industrial area as a result of direct disposal of factories nearby. Although the site near the connection between the sea and the lake was assumed to be the purest site, It was found contained a maximum concentration of Pb in water. It is possibly due to the disposal from a new natural gas factories located near this area. All the five sites were contaminated with high rate of TVB and FCB in water which is an indicator of untreated waste water which spilled directly or indirectly to the lake. The most alarming result was found when analyzing fish; all the fish samples were contaminated on surface and internally with very high amounts of TVB and FCB at gill and intestine. Fish samples also had high concentrations of analyzed heavy metals at their flesh. The mean calculated value of Pb was high up to 38 times than the allowed permissible concentration. This confirms that lake fish is highly polluted and dangerous for human health.