Decontamination of Automobile Workshop Soils containing Heavy Metals and PAHs using Chelating Agents

Automobile repair workshops are major anthropological sources of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in Nigerian cities. The extent of contamination of soil from workshops in Ibadan city was evaluated by contamination or pollution index (C/P index) assessment. The C/P index assessment indicated that the soils were categorized from moderately contaminated to severely polluted class with Pb, Cd, Cr, Zn and Mn. The concentration of 16 PAHs in the soil samples ranging from 245±21 to 23400±25 μg/kg were far above the levels in the control samples. Washing of soil from different automobile repair workshops using ethtylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and ethanol was investigated. Since mixed contaminants are usually co-existing in the environment, additional experiments involving a combined solution were conducted to remove both PAHs and heavy metals. The results indicated that the removal efficiencies of the extractants were in the order 0.1M DTPA > 0.1M EDTA > 0.01M DTPA > 0.01M EDTA for the heavy metals removal. However, the combined extractants of EDTA and ethanol had much higher PAHs removal efficiency than ethanol alone. The use of mixed extractants was more effective for PAHs and had very little effect for the removal of heavy metals, especially zinc.