Soil Fertility of Soils of Imo and Abia States as Influenced by Heavy Metal Concentrations

This study investigated the relationships between heavy metal concentrations (cadmium, chromium, lead, copper, and manganese) and soil fertility indices in crude oil-contaminated soils of Imo and Abia States, southeastern Nigeria. Ten soil profiles were sampled from oil-producing communities (four contaminated and one uncontaminated site per state), yielding 50 soil samples collected based on horizon differentiation. Heavy metal concentrations were determined using atomic absorption spectrophotometry following USEPA Method 3050B digestion. Principal Component Analysis, multiple regression models, and correlation analysis were employed to examine the relationships between fertility parameters and heavy metals. PCA revealed distinct state-specific patterns: Imo State exhibited orthogonal separation between fertility parameters (PC1, 41.84%) and heavy metals (PC2, 35.50%), while Abia State demonstrated a bipolar configuration (PC1, 55.89%) indicating integrated inverse relationships. Regression models showed strong predictive power (R² = 0.71–0.96), with state-specific variations in magnesium and pH effects. Correlation analysis established that cadmium and lead significantly depleted potassium, available phosphorus, and cation exchange capacity. Strong positive inter-correlations among Cd, Pb, and Cu (r = 0.586–0.770) indicated common anthropogenic sources. Heavy metal contamination affects soil fertility differently depending on local soil conditions. In Abia State, contaminants appear to be more extensively integrated into the soil, and soil fertility is more strongly suppressed, than in Imo State. Cadmium, lead, and copper pose the most significant threats to essential nutrient availability. These findings underscore the necessity for state-specific remediation strategies with particular attention to pH management, cation balance restoration, and integrated monitoring approaches for crude oil-impacted soils of the Niger Delta region