Assessment of the levels of polycyclic aromatic hydrocarbons (PAHs) from effluents of petroleum tank farms at Calabar jetty

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants of significant environmental and public health concern due to their toxicity, carcinogenicity, and resistance to degradation. This study assessed the occurrence, concentration, and possible sources of PAHs in soils collected from effluent channels of petroleum tank farms at Calabar Jetty, Cross River State, Nigeria. Soil samples were collected from six sampling locations associated with two petroleum storage facilities and analyzed for the sixteen United States Environmental Protection Agency (USEPA) priority PAHs. Extraction was carried out using Soxhlet extraction followed by clean-up and fractionation procedures, while identification and quantification were performed using an Agilent 7890A Gas Chromatography-Mass Spectrometry (GC-MS) system. The results showed that 11 out of the 16 priority PAHs were detected in the soil samples. Total PAH concentrations (∑PAHs) ranged from 8.0 × 10⁴ ng/kg to 9.4 × 10⁵ ng/kg dry weight, with a mean concentration of 4.23 × 10⁵ ng/kg dry weight. Sample 1O recorded the highest total PAH concentration (9.4 × 10⁵ ng/kg), while sample 6H exhibited the lowest concentration (8.0 × 10⁴ ng/kg). Among the detected compounds, indeno(1,2,3-cd)pyrene recorded the highest individual concentration (5.4 × 10⁵ ng/kg), followed by benzo(b)fluoranthene (1.6 × 10⁵ ng/kg) and benzo(a)pyrene (1.5 × 10⁵ ng/kg). Phenanthrene and benzo(b)fluoranthene were detected in all samples, indicating widespread contamination across the study area. The soils were generally neutral to slightly alkaline, with pH values ranging from 7.05 ± 0.01 to 7.79 ± 0.05, while organic matter content ranged from 11.19 ± 0.04% to 42.45 ± 0.19%. Diagnostic ratios including fluoranthene/pyrene (Fl/Pyr), fluoranthene/(fluoranthene + pyrene) [Fl/(Fl + Pyr)], and indeno(1,2,3-cd)pyrene/(indeno(1,2,3-cd)pyrene + benzo(ghi)perylene) [IcdP/(IcdP + BghiP)] indicated mixed PAH sources comprising petrogenic inputs, petroleum spills, liquid fossil fuel combustion, and biomass combustion from grass, wood, and coal. The detected concentrations exceeded several international environmental guideline values, suggesting significant ecological and human health risks. The study highlights the need for continuous environmental monitoring, improved effluent management practices, and implementation of effective pollution control measures to safeguard the Calabar Jetty ecosystem and surrounding communities.