EVALUATION AND HEALTH RISK ASSESSMENT QUANTIFICATION OF HEAVY METALS CONTAMINATION IN AGRICULTURAL SOIL ONNA RIVER BASIN DEVELOPMENT AUTHORITY

Heavy metals are environmental pollutants, most notably Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. When heavy metals accumulate to toxic levels in agricultural soils, these non-biodegradable elements adversely affect crop health and productivity. This study assessed the level of contamination and health risk of some heavy metals including Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in agricultural soil in Onna River Development Authority, Onna, Akwa Ibom State, Nigeria. Agricultural soils at 0 – 15 and 15 – 30 cm were collected at the study site and analysed using Atomic Absorption Spectrophotometer. The level of contaminations of heavy metals in agricultural soil were assessed by contamination indices including contamination factor (CF), degree of contamination (CD), pollution load index (PLI) and geo-accumulation index (I-geo). Risk assessment quantification were calculated including potential ecological risk index, health risk assessment, non-carcinogenic risk assessment and carcinogenic risk assessment. The concentration of metals occurrence showed that 0 – 15 cm depth was greater than 15 – 30 cm depth. Cu, Ni, Pb and Zn were below the World Health organization (WHO) target value of uncontaminated soil (WHO, 1996). Whereas Cd at 0 -15cm was above World Health organization (WHO) target value of uncontaminated soil. Cd called for concern in agricultural soil due to application of fertilizer NPK+ 12 12 17 2, manure (poultry drop) and herbicide as was reported by the farmer who according him have been planting in that field for than 7 years. Comparing between the CF values and the description of soil contamination. Cu, Pb, Zn and Ni measured at 0 – 15 and 15 – 30 cm depth revealed low environmental risk potential as CF values were less than one ( < 1). Whereas Cd presents moderate risk potential at 0 – 15 and 15 – 30 cm depth with 1< < 3. The results of geo-accumulation index (1-geo) revealed that all the heavy metals under consideration presents uncontaminated to moderately contamination as Igeo values less than one ( − < 1). This indicates that these heavy metals did not pose any threat of contamination (Table 3.1) at 0 – 15 and 15 – 30 cm sampling depth. Hazard index (HI), the summation of hazard quotients of individual metals which was calculated to estimate health risks associated with exposure to multiple metals. According to results, heavy metals posed no harmful effect to both adult and children health as HI < 1. Life cancer risk (LCR) calculated to determine the health risk for carcinogenic heavy metals in overall, were in the range of 1 × 10-6 – 1 × 10-4 which is widely considered acceptable for adult and children except for ingestion the overall for children is in the range 10-2 . For inhalation, the overall is in the range of 10-9 – 1010 which is regarded as negligible