Abstract
The exploration and production of petroleum resources create both opportunities and environmental challenges for sustainable development. In Kenya, the Government, along with private investors, has pursued oil and gas activities in the Anza, Mandera, Lamu, and Tertiary Rift Basins. Sixty-three petroleum exploration blocks were created through Gazette Notice No. 3344 on May 13, 2016, and later reduced to fifty through Gazette Notice No. 4832 on April 16, 2025. This study evaluated the impact of petroleum operations on soil quality at the Twiga 1 waste consolidation site in Turkana County (Block T7, previously 13T, Tertiary Rift Basin). It focused on concentrations of lead (Pb) and cadmium (Cd). A descriptive cross-sectional and experimental design was used. Soil samples were collected using the grid sampling method. A soil auger was used for soil sampling, and samples were transported to the laboratory in well-labeled aluminum containers. The samples were analyzed for heavy metals using an Atomic Absorption Spectrometer (AAS-7000, Shimadzu). The study objectives were to i) assess the levels of lead and cadmium in the soil at the Twiga 1 waste consolidation site, ii) determine the levels during the wet and dry season, and iii) compare the levels with established environmental standards. Heavy metal concentrations were found to be very low at all sites and in both seasons, remaining well below WHO and US EPA limits. In the wet season, mean concentrations (mg/kg) were: Pb (0.003–0.035) and Cd (0.000–0.003). During the dry season, slightly higher values were recorded than in the wet season: Pb (0.000–0.044) and Cd (0.000–0.004). Although the differences were small, they showed seasonal variation, with higher dry-season concentrations linked, limited leaching, moisture loss from evaporation, and dust deposition from the atmosphere. All concentrations were well below World health organization set limits (WHO) (Pb: 100 mg/kg; Cd: 1–3 mg/kg) and US EPA (Pb: 400 mg/kg; Cd: 70 mg/kg). The soils are therefore uncontaminated and safe for farming, living, and ecological purposes. Comparing p-values of heavy metal concentrations between wet and dry seasons (α = 0.05) supports the hypothesis that levels are higher in the dry season at the Twiga 1 waste consolidation site. Lead (0.001–0.055) shows significant differences, while cadmium (0.000–0.046) provides strong evidence for higher levels in the dry season. Heavy metal concentrations were significantly higher in the dry season compared to the wet season but remained below world health organization set limits (WHO) and US EPA limits. The increase in metal concentrations during the dry season highlights the impact of climate variability on soil chemistry. Although the soils at the Twiga 1 waste consolidation site are safe, ongoing monitoring is recommended to protect long-term soil health and environmental integrity around petroleum operations.
Keywords
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