Carcinogenic and non-carcinogenic risk assessment of heavy metal levels in soil and plants farmed around crude oil exploration areas of Edo State, Nigeria

Abstract

In this study, the heavy metals concentration levels in soil and plants farmed around crude oil-producing areas of Edo State, Nigeria was assessed. A total of thirty samples (fifteen each of soil and plant samples) were collected for heavy metals concentration using X-ray fluorescence spectrometer. The soil to pant transfer factor and hazard indices, which include carcinogenic and non-carcinogenic risk were determined. Geographical positioning system was used to record the coordinates of the sampling points. The mean heavy metal concentration in soil (plant) sample for Fe, Ni, Cu, Zn, Al, and Pb are 1.735473 mg/kg (1.593541 mg/kg), 0.003157 mg/kg (0.003888 mg/kg), 0.016773 mg/kg (0.024786 mg/kg), 0.014725 mg/kg (0.015556 mg/kg), 5.595267 mg/kg (2.406267 mg/kg), and 0.004201 mg/kg (0.004185 mg/kg), respectively. The result of soil to plant transfer factor for Fe, Ni, Cu, Zn, Al, and Pb are 1.059474, 1.599154, 5.532104, 1.187205, 0.450386, and 1.117902, respectively. The highest mean TF (5.532104) and a very high maximum TF (14.10619) of Cu indicate a strong potential for copper accumulation in plants. The result of mean hazard quotient for ingestion of Fe, Ni, Cu, Zn, Al, and Pb for child (adult) are 3.17E-05 (3.40E-06), 2.02E-06 (2.17E-07), 5.35E-06 (5.75E 07), 6.27E-07 (6.73E-08), 7.15E-05 (7.66E-06), and 1.49E-05 (1.92E-05), respectively. Result of mean hazard quotient for dermal of Ni, and Zn, for child (adult) are 7.07E-06 (7.57E-07), and 2.57E-06 (2.75E-07), respectively. Result of mean hazard quotient for Inhalation of Fe, Ni, Cu, Zn, Al, and Pb for child (adult) are all not significant for heavy metals consideration. The hazard index for ingestion, and dermal for child (adult) are 1.26E-04 (3.11E-05), and 9.63E-06 (1.03E-06), respectively. Aluminum has the highest HQ for ingestion for both children and adults, indicating a higher potential risk. This suggests that ingestion of aluminum from soil or other sources could be a significant concern. The HI values for both children and adults are less than 1, indicating that the overall risk is below the threshold of concern. The mean risk pathway and the maximum values are higher for children than for adults. This difference highlights the greater vulnerability of children to airborne contaminants and the necessity for stricter protective measures for this demographic.