Physicochemical Properties of Gosa Dumpsite Soil and Their Potential Influence on the Bioavailability and Retention of Polycyclic Aromatic Hydrocarbons (PAHs)

Abstract

This study investigated the physicochemical properties of soils within and around the Gosa dumpsite, Abuja, Nigeria, and evaluated their potential implications for the retention, mobility and bioavailability of polycyclic aromatic hydrocarbons (PAHs). Seventy-four soil samples were collected from the 0–20 cm depth, comprising 10 samples within the fenced dumpsite and 64 samples from four directional zones outside the dumpsite. The samples were analysed for pH, temperature, electrical conductivity (EC), cation exchange capacity (CEC), soil organic carbon (SOC), soil organic matter (SOM), and particle-size distribution. Soil pH ranged from 7.46 ± 0.05 to 8.25 ± 0.01, indicating neutral to moderately alkaline conditions, while temperature varied narrowly from 29.5 ± 0.01 to 29.7 ± 0.01 °C. EC ranged from 130 ± 1.15 to 494 ± 0.50 µS cm⁻¹, with the highest value recorded at SC, suggesting greater accumulation of soluble ionic constituents and possible influence of waste-derived leachate. SOC varied from 1.21 ± 0.13 to 2.02 ± 0.13%, while SOM ranged from 2.36 ± 0.23 to 4.00 ± 0.26%, with the highest concentrations observed at SC. CEC ranged from 16.54 ± 0.01 to 20.17 ± 0.01 [unit], indicating relatively moderate spatial variation in exchange capacity. The soils were predominantly sandy, with sand contents reaching 82.47% at SS and 83.00% at SW, whereas SE exhibited a comparatively high clay fraction of approximately 33.19%. The observed heterogeneity suggests that soil physicochemical properties may collectively influence the environmental behaviour of PAHs. Higher SOC and SOM at SC may favour the partitioning and retention of hydrophobic PAHs, potentially reducing their freely dissolved fraction while increasing persistence. Conversely, the predominantly sandy texture at SS and SW may favour infiltration and downward transport of weakly sorbed contaminants during rainfall. Overall, the findings demonstrate that site-specific variations in soil properties are important considerations when assessing the potential mobility, retention and bioavailability of PAHs at dumpsites. Direct measurement of PAH concentrations and bioavailable fractions is recommended to quantitatively establish these relationships.