Automobile exhausts are considered the main source of air pollution with heavy metals. Airborne pollutants are precipitated on soils surrounding highways causing serious ecological hazards. The current study aimed at evaluating levels of Pb, Ni, Co and Cd in surface (0-15 cm) and subsurface (15-40 cm) soils nearby Cairo-Alexandria agricultural highway, and their accumulation in plants grown thereon. Seven locations were sampled at interval distances 50 meters on both sides of the highway road near Toukh city (Qualubya Governorate). Cabbage and citrus plants were also sampled and separated into its parts. Results revealed that the investigated soils are contaminated with Pb, Ni and Cd. These contaminants were brought to the subsurface layers of the soil at relatively high concentrations. Total and DTPA-extractable contents of Pb and Ni in the top surface soil decreased with increasing the distance from the high way on both sides of the road. Moreover, concentrations of these metals in the cabbage parts were significantly correlated with their total and DTPA-extractable contents. However, Co and Cd in soils seemed to be not affected by the exhausts of the cars on the highway. Heavy metals decreased in cabbage parts as follows: root > stem > outer leaves > inner leaves > core. Calculated BAF values for Pb, Ni and Co were very low indicating that cabbage might be an excluder for these metals whereas, their transfer from roots to shoots (transfer factor, Ts) were high. Heavy metal concentrations in citrus decreased as leaves > flavedo > albedo > segments. Generally, concentrations of heavy metals in plants particularly Pb exceeded the permissible limits. |
