Dataset for Pyrogenic Contamination and Carcinogenic Risk of Polycyclic Aromatic Hydrocarbons in Soils from Automobile Repair Workshops in Ilorin Metropolis, North-central Nigeria
Description
The lowest PAH concentration was Fluorene at 77.9 µg/kg in P2 (0–10 cm), while the highest was Indeno(1,2,3-cd)Pyrene at 171,509.7 µg/kg in P9 (0–10 cm). Low Molecular Weight (LMW) PAHs were poorly distributed and mostly below detection; Naphthalene, Acenaphthylene, and Acenaphthene were lowest, with Anthracene highest among LMW compounds. High Molecular Weight (HMW) PAHs were evenly distributed across almost all samples, reflecting accumulation over time. By ring number, PAH distribution followed 6 > 5 > 4 > 3 > 2 rings. Six-ring PAHs had the highest share (51.6%), five-ring 26.0%, four-ring 18.5%, and three-ring 3.4%; two-ring PAHs were below detection, likely due to volatilization during extraction. Using the Maliszewska-Kordybach (1996) classification (>1000 µg/kg heavily contaminated, 600–1000 contaminated, 200–600 weakly contaminated, <200 non-contaminated), the study area soils are heavily contaminated, ranging from P3 (10–20 cm, lowest) to P9 (0–10 cm, highest). Source identification Diagnostic ratios were used to trace PAH sources. LMW/HMW >1 indicates a petrogenic origin; <1 indicates pyrogenic (Wang et al., 1999). All samples had LMW/HMW <1 except P3 (10–20 cm), indicating a pyrogenic source. Phen/Ant >10, Ant/(Ant+Phen) <0.1, and IcdP/(IcdP+BghiP) <0.2 indicate petrogenic sources. In this study, Phen/Ant was <10 and Ant/(Ant+Phen) was >0.1, both indicating pyrogenic sources; IcdP/(IcdP+BghiP) was >0.2, also indicating a pyrogenic source. Sources for P6 (10–20 cm) and P8 (0–10 cm) could not be determined (ND) due to zero numerator/denominator values. Carcinogenic potency IARC identifies seven priority carcinogenic PAHs: benzo(a)anthracene, chrysene, benzo(ghi)perylene, benzo(a)pyrene, dibenzo(a,h)anthracene, indeno(1,2,3-cd)pyrene, and benzo(j+k+b)fluoranthene. Carcinogenic PAH concentration (PAHcarc) ranged from 294.9 µg/kg (P4, 0–10 cm, lowest) to 535,243.5 µg/kg (P9, 0–10 cm, highest). All sampled workshops showed a high carcinogenic burden relative to the total 17 PAHs, indicating potential long-term adverse health effects. Long-term carcinogenic risk was further assessed via total Benzo(a)Pyrene equivalence: Total BaPeq = Σ(Ci × TEFi), using toxic equivalency factors (TEF) from Nisbet and LaGoy (1992). Total BaPeq values ranged from 1481.3 to 222,750.7 µg/kg, indicating long-term carcinogenic health risk. The high carcinogenic potency of PAHcarc across sites confirms significant environmental and human health risk, and these data contribute a baseline for future pollution monitoring in the study area.
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Materials and methods used for data collection The instruments used to carry out the research include : Hand auger, Sieve shaker, set of sieve, weighing scale, measuring cylinder, Conical flasks, Beakers, Pasteur pipette, Retort stand, Sample bottles, Mortar and pestle, Cotton wool, Methylated spirit, Aluminum foil, Paper tape, Oven, Ultra-sonic machine (sonicator), Funnel, Filter paper, Gas Chromatography-Flame Ionization Detection. Reagents: Dichloromethane, Methanol, n-Hexane, Aluminum oxide (Alumina), Silica gel. For data collection, soil samples were collected from Automobile mechanic workshops around across Ilorin. 2 soil samples (0-10cm and 10-20cm) were collected from each sampling point, into foil paper to prevent contamination, using stainless steel hand auger. The samples were air dried for 10days in the laboratory free of dust and chemical fumes. Samples were pulverized, and 20g of each soil sample was measured into sample bottles. Extraction was done by the ultra-sonic machine (sonicator) using 40ml of Dichloromethane for 40minutes. The procedure was repeated three times, after which 40ml of Dichloromethane and Methanol in the ratio 1:1 was used for 40minutes thrice. The extracts were obtained and was kept in a clean dust-free laboratory for about 21days to enable vaporization of the solvents. The extracts were then fractionated into saturate and aromatic hydrocarbons using, activated aluminum oxide and silica gel. The column was packed with aluminum oxide at the bottom and silica gel at the top in the ratio 1:3. 25ml of n-Hexane was poured into the extract which was then introduced into the column to separate the saturate hydrocarbons into sample bottles, after which 25ml of n-Hexane and Dichloromethane in the ratio 2:3 was introduced to separate the aromatic hydrocarbons into sample bottles. The solvents in the extracts were made to dry, and taken to the laboratory for GC-FID analysis. The GC-FID analysis of the sample extract was carried out using a gas chromatograph Clarus 480 (Perkin Elmer, USA) equipped with a Flame Ionization Detector and an Elite-5 capillary column (30m×0.25mm×0.25im; PerkinElmer, USA). The detector and injector temperatures were 280℃ and 220℃ respectively. The carrier gas was helium (99.99%) at a flow rate of 0.5mL /min. The sample extracts were injected using the split mode. The concentration of the sample extract was calculated using the peak normalization method.