Environmental Analysis of Crude Oil-Contaminated Soils in Niger

This study examines the physicochemical properties of soils contaminated by crude oil in Niger, particularly at the Agadem site and along the pipeline corridor exposed to acts of sabotage. Grain size analyses show a predominance of sand (67–78%), accompanied by moderate proportions of silt (13–25%) and clay (8–10%), classifying these soils as silty sand to sandy silt. This texture, which is highly permeable and weakly adsorbent, promotes the infiltration and vertical migration of hydrocarbons. Chemically, the soils have variable organic matter (1.92–5.76%) and total nitrogen (0.12–0.32%) contents, while the high C/N ratio (9.10–10.57) indicates slow mineralisation. The levels of available phosphorus (2.50–17.20 mg/kg) and exchangeable potassium (0.01–0.04 ppm) reveal limited fertility, accentuated by a slightly acidic pH (5.11–5.25) and low conductivity (4–14 µS/cm). Total hydrocarbon (THC) levels, ranging from 3 to 10%, confirm significant pollution. The positive correlations between TPH and OM, N (r = 0.85–0.87) reflect an accumulation of poorly biodegradable carbon, while the association between C/N and TPH (r = 0.74) suggests a nutritional imbalance linked to microbial inhibition. Negative correlations with phosphorus and potassium (r = −0.30 and −0.19) indicate a decline in nutrient availability. Overall, the combination of sandy texture, acidity and low fertility makes these soils vulnerable, justifying remediation through phytoremediation and organic amendments.