Assessment of the levels of polycyclic aromatic hydrocarbons (PAHs) in soil and selected vegetable samples from challawa agricultural location in Kano State, Nigeria

This study aimed at measuring the concentrations of seventeen polycyclic aromatic hydrocarbons (PAHs) pollutants in soil and selected vegetables grown in Challawa agricultural area in Kano State, Nigeria. Representative soil samples were collected from ten plots and composited at each depth across three depths profiles (0–10 cm, 10–20 cm, and 20–30 cm). 20-gram portions of each of the five vegetables (onions, tomatoes, hot pepper, sweet pepper, and garden egg) were sampled and categorized into root, stem, and fruit parts. PAHs were extracted and cleaned-up using standard analytical methods, followed by instrumental analysis using a SHIMADZU GC-MS (GC-17A). The levels of PAHs in soil ranged from 2.00E-03 to 8.00E-03 mg/kg, with the highest concentration detected at the 0–10 cm depth. In the vegetable samples, PAH concentrations ranged between 4.00E-03 and 1.30E-02 mg/kg, with sweet pepper and hot pepper showing the highest levels. A comprehensive assessment revealed that PAH concentrations in vegetables exceeded those in soil. Diagnostic ratios identified both petrogenic and pyrogenic sources of PAHs pollution. The estimated daily dose of PAHs was highest (3.19E-08 mg/kg/day) for hot pepper, while the incremental lifetime cancer risk (ILCR) values ranged from 1.29E-07 to 1.79E-09, well below the threshold of 10E-06, implying negligible cancer risk. The mean effect range medium quotient values in soil were below 0.1, categorizing the Challawa agricultural area as a low-priority site for pollution control. These findings suggest that vegetables from the Challawa agricultural area are safe for human consumption. • Vegetables from Challawa have higher PAH levels than soil. • Sweet and hot pepper showed highest PAH levels, but safe to consume. • Onions show the highest estimated daily PAH dose, with negligible cancer risk. • Both petrogenic and pyrogenic sources contribute to PAH contamination.