Fate and Behavior of Toxic Organic Pollutants in Plant, Soil and Irradiated Sewage Sludge

Abstract

This study was conducted to determine the toxic organic pollutants, Polycyclic Aromatic Hydrocarbons (PAH) and Polychlorinated Biphenyls (PCB) in Navel orange fruits, soil, and sewage sludge. The fruits were collected from 20 years old trees grown at three different farms at El-Gabal El-Asfar. The three farms received sewage water for irrigation for different periods of time: 20, 50, 90 years. The control farm is located in Anshas area, which received canal water for irrigation. The soil samples were collected from the same locations as for the fruits. The raw sludge samples were colleted from the drying beds of El-Gabal El-Asfar farm, whereas the digested sludge samples were collected from the drying beds of El-Gabal El-Asfar Wastewater Treatment Plant. The results indicated that long-term irrigation with sewage water induced the accumulation of toxic organic pollutants (PAHs and PCBs) in the Navel orange fruits and soil. The accumulation of PAHs in the fruits is less than PCBs due to their lower water solubility and hence uptake by the plant roots. The same pollutants tend to accumulate more in the top soil layer (0-20 cm) and decrease with the soil depth. Gamma irradiation (dose = 6 kGy) of raw sludge showed degradation effect on several PAHs and PCBs congeners. However, the extend of the degradation vary between the different compounds. In the digested sludge the PAHs and PCBs concentrations stay more or less similar for irradiated and non-irradiated samples indicating the lower degradation effect of gamma irradiation on the digested sludge than on the raw sludge.