Impact of sewage wastes on the heavy metal content of water, soil, plants and fish in Wadi Hanifah Stream

Disposal of sewage waste from the city of Al-Riyadh and adjacent areas is partially carried out through a flood channel known as Wadi Hanifah Stream. It is a permanent stream that flows from north (Badiah) to south (southeast of the city of Al-Hair) covering a distance of about 50 km. It carried only seasonal rainwater before the urbanization of the area. At present the main sources of water are sewage effluent, agricultural runoff, pumped shallow ground water from the city of Al-Riyadh and seasonal rainwater. Samples of water, soil, plants and fish were collected from different locations outside the boundaries of the city of Al-Riyadh. The water quality and the heavy metals (Ag, Ba, Cd, Co, Cr, Cu, Fe, Pb, Ni and Zn) in these samples were studied. The pH of the water was overall alkaline (average 7.38). The water appeared to be very hard (mean value 879 mg/l) with high levels of total dissolved solids (average 1601 mg/l). The levels of dissolved oxygen (DO), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) on the average were 4.50; 39.33 and 6.62 mg/l respectively. The amount of heavy metals in the water was lower than the amount in soil, plants and fish. The maximum concentration of heavy metals was found in the soil followed by plants and fish. Overall iron was found in the highest concentration, followed by barium, zinc, cobalt, copper, chromium and lead. Silver, cadmium and nickel showed the lowest concentrations. Highly positive correlation for various metals was observed between the water, soil, plants and fish. The results indicated that the heavy metal content of water, soil, plants and fish in the Wadi Hanifah Stream was within the acceptable limits and did not pose a high risk of accumulation at this stage. Based on the physical and chemical water quality parameters and heavy metal content of wastewater, it is concluded that it may be used for agricultural purposes.