Spatial and temporal variations in physicochemical properties and specific trace metals in soils of oil exploration and production host communities in Southern Nigeria

Abstract

The release of certain chemicals into the environment, especially into soil can pose significant and potentially dangerous threats to human health and ecosystems. This research investigates the spatial and temporal variations in the physicochemical characteristics and concentrations of selected heavy metals in soil. Composite soil samples, collected from a depth of 0–20 cm, were obtained from a consistent quadrant across five coastal wetland communities in Delta State. A total of 25 samples were gathered from some communities in Delta State. Heavy metal concentrations were determined using Atomic Absorption Spectroscopy (AAS), specifically the Solar 969 Unicam Series Model. The results revealed statistically significant differences (p<0.01) in several soil properties, including electrical conductivity (EC), organic carbon (OC), moisture content, available phosphorus (P), sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), cation exchange capacity (CEC), sand, silt, and clay content. However, soil pH and total nitrogen (N) did not show significant differences (p>0.05). The average concentrations of heavy metals and total hydrocarbon content (THC) in the coastal wetland soils were as follows: iron (Fe) at 217.741±130.42, chromium (Cr) at 5.997±6.33, cadmium (Cd) at 0.275±0.13, copper (Cu) at 4.732±3.00, zinc (Zn) at 34.729±33.37, manganese (Mn) at 23.298±19.19, lead (Pb) at 10.856±2.90, and THC at 17694.98±47114.37. The concentration order of these metals was: Fe > Zn > Mn > Pb > Cr > Cu > Cd. Cluster analysis indicated notable differences between the sampled locations, suggesting variations in soil physicochemical properties and heavy metal levels. The trend in soil property dissimilarity followed the sequence: Emevor > Kwale > Effurun > Olomoro > Sapele (control). Principal component analysis (PCA) extracted six components, explaining a total variance of 82.217% in the dataset. A strong, positive correlation was found between heavy metal concentrations and total petroleum hydrocarbons, implying a shared or related source of contamination. Deviations of these soil parameters from established guideline levels could lead to negative environmental and health impacts, limit the potential use of the soil, and compromise the ecological support systems crucial to the local people